Browse Topic: Turbulence

Items (297)

Statistical Analysis of Data Acquired from Propagating Flames in Gasoline Engines Using a Multiple Ion Probe

2024-32-003504/18/2025

Multiple-ion-probe method consists of multiple ion probes placed on the combustion chamber wall, where each individual ion probe detects flame contact and records the time of contact. From the recorded data, it is also possible to indirectly visualize the inside of the combustion chamber, for example, as a motion animation of moving flame front. In this study, a thirty-two ion probes were used to record flames propagating in a two-stroke gasoline engine. The experiment recorded the combustion state in the engine for about 3 seconds under full load at about 6500 rpm, and about 300 cycles were recorded in one experiment. Twelve experiments were conducted under the same experimental conditions, and a total of 4,164 cycles of signal data were obtained in the twelve experiments. Two types of analysis were performed on this data: statistical analysis and machine learning analysis using a linear regression model. Statistical analysis calculated the average flame detection time and standard

Yatsufusa, Tomoaki, Okahira, Takehiro, Nagashige, Kohei

AI-Trained Vehicles Can Adjust to Extreme Turbulence on the Fly

TBMG-5212512/01/2024

In nature, flying animals sense coming changes in their surroundings, including the onset of sudden turbulence, and quickly adjust to stay safe. Engineers who design aircraft would like to give their vehicles the same ability to predict incoming disturbances and respond appropriately. Indeed, disasters such as the fatal Singapore Airlines flight this past May in which more than 100 passengers were injured after the plane encountered severe turbulence, could be avoided if aircraft had such automatic sensing and prediction capabilities combined with mechanisms to stabilize the vehicle.

Identification and Analysis of Aerodynamic Sound Sources on the External Surface of an SUV

2025-01-003305/05/2023

Currently, effective methods for analyzing the aerodynamic sound sources of Sport Utility Vehicles (SUVs) are still under development, and the relationship between sound sources and flow dynamics is not yet fully understood. This study presents a method for identifying multi-frequency sound dipole sources within the near-wall flow field by analyzing the relationship between unsteady flow field properties and dipole sources, thereby addressing the complex characteristics of aerodynamic sound sources on vehicle surfaces. Wind tunnel tests, along with full-scale (1:1) Large Eddy Simulation (LES) were conducted on a real SUV. The identification method was applied to analyze the location and magnitude of sound sources near the vehicle's surface. The results, validated using Acoustic Perturbation Equations (APE), indicated that the dipole sources are primarily distributed around the windward side of the front wheels, the side of the front headlights, the A pillar-rearview mirror-front side

Experimental Investigation into Modulated Aeroacoustic Cabin Noise arising from Unsteady Flow Conditions

2025-01-002905/05/2023

The unsteady wind conditions experienced by a vehicle whilst driving on the road are different to those typically experienced in the steady-flow wind tunnel development environment, due to turbulence in the natural wind, moving through the unsteady wakes of other road vehicles and travelling through the stationary wakes generated by roadside obstacles. This paper presents the use of experimental approach using an SUV-shaped vehicle to assess the effect of unsteady wind on the modulated noise performance, commonly used to evaluate unsteady wind noise characteristics. The approach is extended to assess the pressure distribution on the front side glass of the vehicle, caused by the aerodynamic interactions of the turbulent inflow, to provide insight into the noise generation mechanisms and differences in behaviour between the two environments. The vehicle response to unsteady wind conditions was assessed using two approaches: a dynamic upstream unsteady flow the using active side wind

Jamaluddin, Nur Syafiqah, Oettle, Nicholas, Staron, Domenic

An Effective Design of Micro Tesla Valve as a Passive Mixer in Microfluidics Channels

2022-26-117805/26/2022

Mixing fluids is one of the major challenges in microfluidics. Normally, the mixing process is done by diffusion rather than turbulence, which makes it very slow due to low Reynolds number (Re) flow in the range of 0.1 to1. Owing to this behaviour, ineffective mixing occurs when two miscible liquids are mixed purely by diffusion which requires longer striation lengths and therefore longer microfluidic channels along with lengthy mixing time. Homogeneous mixing of solute and solvent is important for providing consistent chemical and biological reactions in µTAS.In this study, we develop a passive mixer that provides efficient mixing using micro tesla valves which allows the flow of liquids in the forward and reverse directions to analyse the formed vortices, turbulent intense areas, Reynolds number, and pressure using Ansys fluent workbench. An optimum design has been arrived by varying the number of cells from 1 to 5 in series and realization is done by excimer laser micromachining.

Singh, Deepak, Sankar PhD, Ravi

An Estimation of the Effect of Turbulence from the Natural Wind and Traffic on the Cycle-Averaged-Drag Coefficient.

2022-01-107603/29/2022

A drag coefficient, which is representative of the drag of a car undergoing a particular drive cycle, known as the cycle-averaged-drag coefficient, has been previously developed. It was derived for different drive cycles using mean values for the natural wind. It assumed terrain dependent wind velocities based on the Weibull function, equi-probable wind direction and shear effects. It did not, however, include any effects of turbulence in the natural wind. Some recent research using active vanes in the wind tunnel to generate turbulence has suggested that the effect on drag can be evaluated from the quasi steady wind inputs. On this basis the effect of natural wind turbulence on the aerodynamic drag of a typical car has been obtained as a function of car velocity and both wind velocity and direction. For a particular combination of car and wind velocity the additional effects of turbulence are very sensitive to the wind angle and on the shape of the drag curve with yaw angle. The wind

Howell, Jeff, Passmore, Martin

Multiphase Flow Simulation of the Oil Splashing During the Actuated Stage of an Innovative Axle Dry Braking System

2021-01-123809/21/2021

This paper proposes the CFD simulation of the oil splashing within the discs’ chamber of a novel concept for axle dry braking system in off-highway vehicles. The system completely removes the lubricating oil from the discs’ chamber during the not-engaged configuration of the friction plates and it quickly restore it at the beginning of the braking stage when the discs’ cooling becomes crucial, thus ensuring a significant reduction of the power losses. The CFD analysis of the real component is performed to predict the efficiency of the system in terms of both the time needed to replenish the discs’ chamber when brake is actuated and the hydraulic torque exerted by the splashing of the oil. The entire three-dimensional geometry of the domain is accurately discretized and the multi-phase flow nature is addressed by means of the volume of fluid approach. Moreover, the two equation realizable k-epsilon model is adopted to describe the turbulent characteristic of the flow under actual

Muzzioli, Gabriele, Milani, Massimo, Rinaldi, Pier Paolo, Stefani, Matteo, Storchi, Gabriele, Montorsi, Luca

Spatial Correlation of Turbulent Flow Pressure Fluctuations Downstream of an Obstruction

2021-01-104908/31/2021

The structural excitation by turbulent flow pressure fluctuations continues to be an important part of vehicle NVH analysis and design. Much of the analytical work on turbulent flow has been limited to flow over smooth, flat surfaces. Measurements and CFD analyses show a significantly different pressure spectrum for flows over an obstruction. The coupling of the turbulent pressure excitation to the structural vibration and transmitted sound depends on the spatial matching between the source and response fields. This paper develops an analytical model for the spatial correlation of turbulent flow pressure fluctuations downstream of an obstruction. Such a model is useful in the early design stage of a vehicle and is compatible with SEA models of the fluid structure interaction.

DeJong, Richard, Tubergen, Renard, Willson, Abigail

Performance Evaluation of Eastman’s Saflex® E Series Acoustic Interlayer

2021-01-105408/31/2021

In 2020, Eastman launched a new acoustic PVB interlayer for automotive laminated glass. This interlayer not only helps to protect driver and passengers from injuries during impact but also provides enhanced acoustic comfort in the car. This newly developed interlayer offers substantially improved acoustic performance in the high-frequency range that is typically associated with wind noise at higher vehicle speeds. To demonstrate the in-vehicle performance, finite element simulations have been carried out using wind noise as the principal source of excitation. The results confirm previously published data that the acoustic contribution overwhelms the turbulent part, having a larger contribution to the ultimate acoustical pressure level. The acoustic insulation calculated is in excellent agreement with the static sound transmission loss data as measured according to the ISO or ASTM norm. In cases where both the windscreen and front-side windows have a laminated structure, a large

D'Haene, Pol, Van de Vyver, Stijn, Poulos, Athanasios, Robin, Xavier

A Priori Analysis of Acoustic Source Terms from Large-Eddy Simulation in Turbulent Pipe Flow

2020-01-151806/03/2020

The absence of combustion engine noise pushes increasingly attention to the sound generation from other, even much weaker, sources in the acoustic design of electric vehicles. The present work focusses on the numerical computation of flow induced noise, typically emerging in components of flow guiding devices in electro-mobile applications. The method of Large-Eddy Simulation (LES) represents a powerful technique for capturing most part of the turbulent fluctuating motion, which qualifies this approach as a highly reliable candidate for providing a sufficiently accurate level of description of the flow induced generation of sound. Considering the generic test configuration of turbulent pipe flow, the present study investigates in particular the scope and the limits of incompressible Large-Eddy Simulation in predicting the evolution of turbulent sound sources to be supplied as source terms into acoustic analogies, which have been proposed for the computation of the acoustic pressure

Tieber, Johannes, Steiner, Helfried

Simulation of Transient On-Road Conditions in a Closed Test Section Wind Tunnel Using a Wing System with Active Flaps

2020-01-068804/14/2020

Typical automotive research in wind tunnels is conducted under idealized, stationary, low turbulence flow conditions. This does not necessarily reflect the actual situation in traffic. Thus, there is a considerable interest to simulate the actual flow conditions. Because of this, a system for the simulation of the turbulence intensity I, the integral linear scale L and the transient angle of incidence β measured in full-scale tests in the inflow of a test vehicle was developed and installed in a closed-loop, closed test section wind tunnel. The system consists of four airfoils with movable flaps and is installed in the beginning of the test section. Time-series of the flow velocity vector are measured in the empty test section to analyze the system’s envelope in terms of the turbulence intensity and the integral length scales. It is shown that the length scales in spanwise and in driving (streamwise) direction can be varied from 0.15 m to 7.9 m and from 0.15 m to 2.5 m, respectively

Wilhelmi, Henning, Jessing, Christoph, Bell, James, Heine, Daniela, Wagner, Andreas, Wiedemann, Jochen, Wagner, Claus

Uncertainty Quantification of Motorcycle Racing Upstream Flow Conditions

2020-01-066704/14/2020

The upstream flow conditions in front of any vehicle are the first barrier a vehicle must overcome beside the acceleration itself. Both together, the vehicle speed and the upstream flow conditions, result in the oncoming wind vector experienced by the moving vehicle. The aim of the present work is to show a new approach to consider the chaotic and random behavior of surrounding flow conditions and their influence on driving performance. Special interest was put on a description of the flow conditions with respect to well know turbulent flow field parameters like the turbulence length scale or the turbulence intensity. Depending on where the flow conditions are measured, stationary in the earth reference frame, or on a moving vehicle, it is quite difficult to get a robust description of the previously mentioned flow field parameters. These parameters are used together with the Reynolds number to predict the aerodynamic behavior by correlation functions or maps. A lot of aerodynamic

Feichtinger, Christoph Simon, Fischer, Peter

Transport Method Boosts Capacity of Heat Exchangers

TBMG-3572312/01/2019

Turbulent heat exchange is a method of heat transport widely used in heating, ventilation, and air conditioning (HVAC) systems. Adding a readily available organic solvent to common water-based turbulent heat exchange systems can boost their capacity to move heat by 500%. Other methods for increasing heat flux — nanoparticle additives or other techniques — have achieved about 50% improvement.

Recovering Color Images from Scattered Light

TBMG-3547811/01/2019

Engineers at Duke University have developed a method for extracting a color image from a single exposure of light scattered through a mostly opaque material. The technique has applications in a wide range of fields from healthcare to astronomy.

Lattice Boltzmann Simulations of Flow Over an Iced Airfoil

2019-01-194506/10/2019

This paper presents an aerodynamic degradation study of an iced airfoil, using the Lattice Boltzmann approach with the commercial software PowerFLOW. Three-dimensional numerical simulations were performed with an extruded constant section of the GLC-305 airfoil with a leading-edge double-horn ice shape using periodic boundary conditions. The freestream Reynolds number, based on the chord, is 3.5 million and the Mach number is 0.12. An extensive comparison of the main flow features with experimental data is performed, including aerodynamic coefficients, pressure coefficient distributions, velocity and turbulence contours along with its profiles at several positions, and stagnation streamlines. The drag coefficient agrees well with experiments, in spite of a small shift. Two different wind tunnel measurements, using different measurement techniques, were compared to the CFD results, which mostly stayed in between the experimental data. Velocity and turbulence intensity contours as well

Ihi, Rafael, Ribeiro, Andre, Santos, Luis, Silva, Daniel

Equivalent Sand Grain Roughness Correlation for Aircraft Ice Shape Predictions

2019-01-197806/10/2019

Many uncertainties in an in-flight ice shape prediction are related to convection heat transfer coefficient, which in turn depends on the flow, turbulence and laminar/turbulent transition models. The height of ice roughness element used to calculate the Equivalent Sand Grain Roughness height (ESGR) is a very important input of the turbulence model as it strongly influences the shape of the accreted ice. Unfortunately, for in-flight icing, the ESGR is unknown and generally calculated using semi-empirical models or empirical correlations based on a particular ice shape prediction code. Each ice shape prediction code is unique due to the models and correlations used and the numerical implementation. Ice roughness correlations do not have the same effect in each ice shape prediction code. A new approach to calculate the ESGR correlation taking into consideration the particularities of the ice shape prediction code is developed, calibrated and validated. This new approach derives a

An Assessment of LEWICE Roughness and Convection Enhancement Models

2019-01-197706/10/2019

During aircraft design and certification, in-flight ice accretions are simulated using ice prediction codes. LEWICE, the ice accretion prediction code developed by NASA, employs a time-stepping procedure coupled with a thermodynamic model to calculate the location, size and shape of an ice accretion. LEWICE has been extensively validated for a wide range of icing conditions. However, continuing improvements to LEWICE predictive capabilities require better understandings of 1) the fundamental physics of turbulent flow generated by ice accretion roughness during an icing event and 2) the mechanisms responsible for convective enhancement of real ice accretion roughness. Recent experiments in the Icing Research Tunnel (IRT) at NASA Glenn Research Center have enabled significant insights into the nature of ice accretion roughness spatial and temporal variations. Other recent investigations have employed scans from the IRT to generate scaled test surfaces to investigate convection

Shannon, Timothy, McClain, Stephen T.

Structural Vibration of an Elastically Supported Plate due to Excitation of a Turbulent Boundary Layer

2019-01-147006/05/2019

High-Reynolds number turbulent boundary layers are an important source for inducing structural vibration. Small geometric features of a structure can generate significant turbulence that result in structural vibration. In this work we develop a new method to couple a high-fidelity fluid solver with a dynamic hybrid analytical-numerical formulation for the structure. The fluid solver uses the Large-Eddy Simulation closure for the unresolved turbulence. Specifically, a local and dynamic one-equation eddy viscosity model is employed. The fluid pressure fluctuation on the structure is mapped to the dynamic structural model. The plate where the flow excitation is applied is considered as part of a larger structure. A hybrid approach based on the Component Mode Synthesis (CMS) is used for developing the new hybrid formulation. The dynamic behavior of the plate which is excited by the flow is modeled using finite elements. However, the rest of the surrounding structure is modeled using finite

Diaz, Jonmarcos, Maki, Kevin, Vlahopoulos, Nickolas

Turbulent Pressure Spectra for Separated Flow Conditions

2019-01-147506/05/2019

The magnitude of the turbulent pressure spectrum in fluid flow over an obstruction is usually much larger than in attached flow over a smooth surface. External features on a vehicle, such as windshield wipers, side mirrors and pillars which cause flow separation, are a major source of wind noise. The modeling of the pressure spectrum in separated flow is important for designing quiet vehicles. In this study wind tunnel tests have been performed with different shaped obstructions to measure and correlate the surface pressure spectra with flow parameters such as the pressure coefficient and separation size. The model by Chase for attached turbulent boundary layer pressures is generalized to apply to separated flow conditions.

DeJong, Richard, DeVries, Kurtis

Automated 6DOF Model Generation and Actuator Sizing within AFSIM

2019-01-133603/19/2019

The Air Force Research Laboratory has interest in automatically generating the extensive aerodynamic databases essential for six degree of freedom (6DOF) models and the use of 6DOF models for design. To be most useful, automation must include all aspects of producing the database including meshing, control surface deflections, running the CFD solution, and storage of the results. This effort applies newly-developed software to produce the desired results. Firstly, AFRL software called Computational Aircraft Prototype Syntheses (CAPS) allows automated meshing using the Advancing Front Local Reconnection (AFLR) software from Mississippi State University1 and automated control surface deflection using Engineering Sketch Pad (ESP) software from MIT/Syracuse. CAPS includes the ability to run the NASA CFD code FUN3D and interpret the FUN3D results via an Application Interface Module (AIM). This may sound like a complicated process. However, it is quite simple using a python interface to CAPS

Allison, Darcy, Shimmin, Kyle, Schley, William, Bryson, Dean

Effects of Reynolds and Mach Numbers in Large Eddy Simulation of Supersonic Round Jets

TBMG-3393703/01/2019

Rockets/landers arrive on the Moon with supersonic speed and impact lunar regolith. There is no reliable software to computationally simulate in an effective way the supersonic plumes escaping from these rockets/devices. A Large Eddy Simulation (LES) model and hybrid WENO (weighted essentially non-oscillatory) scheme numerical method were developed to address this problem.

LES Analysis on Cycle-to-Cycle Variation of Combustion Process in a DISI Engine

2019-01-000601/15/2019

Combustion cycle-to-cycle variation (CCV) of Spark-Ignition (SI) engines can be influenced by the cyclic variations in charge motion, trapped mass and mixture composition inside the cylinder. A high CCV leads to misfire or knock, limiting the engine’s operating regime. To understand the mechanism of the effect of flow field and mixture compositions on CCV, the present numerical work was performed in a single cylinder Direct Injection Spark-Ignition (DISI) engine. A large eddy simulation (LES) approach coupled with the G-equation combustion model was developed to capture the CCV by accurately resolving the turbulent flow field spatially and temporally. Further, the ignition process was modeled by sourcing energy during the breakdown and arc phases with a line-shape ignition model which could move with the local flow. Detailed chemistry was solved both inside and outside the flame front. A compact 48-species 152-reactions primary reference fuel (PRF) reduced mechanism was used. By

Chen, Ceyuan, Ameen, Muhsin M, Wei, Haiqiao, Iyer, Claudia, Ting, Foochern, Vanderwege, Brad, Som, Sibendu

A Cycle-to-Cycle Variation Extraction Method for Flow Field Analysis in SI IC Engines Based on Turbulence Scales

2019-01-004201/15/2019

To adhere to stringent environmental regulations, SI (spark ignition) engines are required to achieve higher thermal efficiency. In recent years, EGR (exhaust gas recirculation) systems and lean-burn operation has been recognized as key technologies. Under such operating conditions, reducing CCV (cycle-to-cycle variation) in combustion is critical to the enhancement of overall engine performance. Flow-field CCV is one of the considerable factors affecting combustion in engines. Conventionally, in research on flow fields in SI engines, the ensemble average is used to separate the measured velocity field into a mean component and a fluctuation component, the latter of which contains a CCV component and a turbulent component. To extract the CCV of the flow field, previous studies employed spatial filter, temporal filter, and POD (proper orthogonal decomposition) methods. Those studies used a constant- separation filter size for the whole crank angle, although the turbulence scales change

Matsuda, Masayoshi, Yokomori, Takeshi, Minamoto, Yuki, Shimura, Masayasu, Tanahashi, Mamoru, Iida, Norimasa

Enhanced X-Ray Imaging Determines Molecular Structure

TBMG-3358501/01/2019

For more than 100 years, X-rays have been used in crystallography to determine the structure of molecules. At the heart of the method are the principles of diffraction and superposition, to which all waves are subject. Light waves consisting of photons are deflected by the atoms in the crystal and overlap — like water waves generated by obstacles in a slowly flowing stream. If a sufficient number of these photons can be measured with a detector, a characteristic diffraction pattern or wave pattern is obtained from which the atomic structure of the crystal can be derived. This requires that photons are scattered coherently, meaning that there is a clear phase relationship between incident and reflected photons. This corresponds to water waves that are deflected from the obstacles without vortexes or turbulences. If photon scattering is incoherent, the fixed phase relationship between the scattered photons disperses, making it impossible to determine the arrangement of the atoms — just

Effect of Fuel Injection Timing on the Mixture Preparation in a Small Gasoline Direct-Injection Engine

2018-32-001410/30/2018

Gasoline direct-injection (GDI) engines have evolved as a solution to meet the current demands of the automotive industry. Benefits of a GDI engine include good fuel economy, good transient response, and low cold start emissions. However, they suffer from problems, like combustion instability, misfire, and impingement of fuel on in-cylinder surfaces. Therefore, to highlight the influence of fuel injection timing on in-cylinder flow, turbulence, mixture distribution and wall impingement, a computational study is conducted on a small-bore GDI engine. Results showed that air motion inside the engine cylinder is influenced by direct-injection of fuel, with considerable variation in turbulent kinetic energy at the time of injection. Due to charge cooling effect, mixture density and trapped mass were increased by about 10.8% and 9.5%, respectively. A significant drop in mean in-cylinder temperature (about 100 °C) was observed with direct-injection of fuel as compared to the case without

Jose, Jubin, Parsi, Anil, Shridhara, Shrinidhi, Mittal, Mayank, Ramesh, A

A Numerical Study on Correlation of Chemiluminescent Species and Heat Release Distributions Using Large Eddy Simulation

2018-32-006610/30/2018

A mixed timescale subgrid model of a large eddy simulation was used to simulate the turbulence regime in diesel engine combustion. The combustion model used the direct integration approach with a diesel oil surrogate mechanism (developed at Chalmers University of Technology and consisting of 70 species and 309 reactions). Additional reactions for the generation and consumption of OH*, CO2*, and CH* species were added from recent kinetic studies. Collisional quenching and spontaneous emission resulted in de-excitation of the excited state radical. A phenomenological soot formation model (developed at Waseda University) was combined with the LES code. The following important steps were considered in the soot model: particle inception where naphthalene grows irreversibly to form soot, surface growth with the addition of C2H2, surface oxidation (induced by OH radicals and O2 attack), and particle coagulation. Using the aforementioned numerical approach, we investigated the correlation of

Zhou, Beini, Adachi, Takayuki, Kusaka, Jin, Aizawa, Tetsuya

Highly Efficient Civil Aviation, Now via Operations - AAR and Challenges

2018-01-192510/30/2018

Global civil aviation growth at 5+% yearly poses extreme environmental challenges. Advances have appeared gradually through improved aerodynamic shapes, using carbon fibres, and enhanced engines; however, as these technologies mature, direct efficiency advances require increasing effort. Often Passenger convenience is forgotten e.g. the long-range air traffic has developed on hub-spoke basis implying extra feeder flights, transit passenger inconveniences, capacity issues. Efficiency metrics emphasize “Why, How & What”, with an understanding of the range sensitivities, operational concepts and performance goals via the important “X-factor”. For given range, current aircraft are “greener” than previous generations. Medium range aircraft s are always greener than those for short or long ranges. However, currently, the major trend is for the latter: twin-aisle A350, A380, B787, B777X (10+% payload, 40+% fuel to MTOW). Shorter range single-aisle aircraft are “feeders” or newer derivatives

Effects of In-Cylinder Flow and Stratified Mixture on HCCI Combustion in High Load

2018-32-001610/30/2018

The purpose of this paper is to find a way to extend the high load limit of homogeneous charge compression ignition (HCCI) combustion. This paper presents the effect of in-cylinder flow and stratified mixture on HCCI combustion by experiments and three-dimensional computer fluid dynamics coupled with a detailed chemical reaction calculation. The first study was conducted using a rapid compression and expansion machine (RCEM) equipped with a flow generation plate to create in-cylinder turbulent flow and with a control unit of in-cylinder wall temperature to create in-cylinder temperature distribution. The study assesses the effect of the turbulent flow and the temperature distribution on HCCI combustion. In the second study, the numerical simulation of HCCI combustion was conducted using large eddy simulation coupled with a detailed chemical reaction calculation. The study analyzes the interaction between in-cylinder turbulent flow and mixture distribution and HCCI combustion. The

Yoshimura, Kei, Watanabe, Shogo, Ogawa, Kazuya, Kuboyama, Tatsuya, Moriyoshi, Yasuo

Compressible Brake Fluid Turbulent Flow Simulation and Experimental Verification on Brake Bleeding Performance Improvements of an EPB Caliper

2018-01-187610/05/2018

Brake bleeding is the process of removing air bubbles present on hydraulic brake systems from the master cylinder to the calipers of a vehicle, including the brake pipes and hoses. This is very important procedure affecting on brake performance, but still has been a key issue in automobile industry for last decades because reaching best bleeding performance has a limit that there is always remaining air in brake system. In this paper, it is reported on numerical and experimental investigations into the topic of bleeding performance improvements. Compressible brake fluid turbulent flow simulation with two-phase mixture model was performed to investigate the details of the bleeding performance drop during its cycles. The rig test of the hollow cylinder was carried out in order to secure the brake consumption amount curve whose results were used for the criterion of the parametric simulations using Tait equation to estimate the property of the brake fluid with the bulk modulus of 19,535

The Nozzle Flows and Atomization Characteristics of the Two-Component Surrogate Fuel of Diesel from Indirect Coal Liquefaction at Engine Conditions

2018-01-169109/10/2018

Recently, all world countries facing the stringent emission regulations have been encouraged to explore the clean fuel. The diesel from indirect coal liquefaction (DICL) has been verified that can reduce the soot and NOx emissions of compression-ignition engine. However, the atomization characteristics of DICL are rarely studied. The aim of this work is to numerically analyze the inner nozzle flow and the atomization characteristics of the DICL and compare the global and local flow characteristics of the DICL with the NO.2 diesel (D2) at engine conditions. A surrogate fuel of the DICL (a mixture of 72.4% n-dodecane and 27.6% methylcyclohexane by mass) was built according to its components to simulate the atomization characteristics of the DICL under the high-temperature and high-pressure environment (non-reacting) by the Large Eddy Simulation (LES). The simulation results show that the DICL is more likely to form cavitation compared with D2, and the turbulence level at the orifice exit

Huang, Zhong, Zhang, Wenzheng, Xia, Jin, Ju, Dehao, Han, Dong, Lu, Xing-Cai

A Heat Transfer Model for Low Temperature Combustion Engines

2018-01-166209/10/2018

Low Temperature Combustion is a technology that enables achieving both a higher efficiency and simultaneously lower emissions of NOx and particulate matter. It is a noun for combustion regimes that operate with a lean air-fuel mixture and where the combustion occurs at a low temperature, such as Homogeneous Charge Compression Ignition and Partially Premixed Combustion. In this work a new model is proposed to predict the instantaneous heat flux in engines with Low Temperature Combustion. In-cylinder heat flux measurements were used to construct this model. The new model addresses two shortcomings of the existing heat transfer models already present during motored operation: the phasing of the instantaneous heat flux and the overprediction of the heat flux during the expansion phase. This was achieved by implementing the in-cylinder turbulence in the heat transfer model. The heat transfer during the combustion was taken into account by using the turbulence generated in the burned zone

Broekaert, Stijn, De Paepe, Michel, Verhelst, Sebastian

Comparing Large Eddy Simulation of a Reacting Fuel Spray with Measured Quantitative Flame Parameters

2018-01-172009/10/2018

In order to reduce engine out CO2 emissions, it is a main subject to find new alternative fuels from renewable sources. For identifying the specification of an optimized fuel for engine combustion, it is essential to understand the details of combustion and pollutant formation. For obtaining a better understanding of the flame behavior, dynamic structure large eddy simulations are a method of choice. In the investigation presented in this paper, an n-heptane spray flame is simulated under engine relevant conditions starting at a pressure of 50 bar and a temperature of 800 K. Measurements are conducted at a high-pressure vessel with the same conditions. Liquid penetration length is measured with Mie-Scatterlight, gaseous penetration length with Shadowgraphy and lift-off length as well as ignition delay with OH*-Radiation. In addition to these global high-speed measurement techniques, detailed spectroscopic laser measurements are conducted at the n-heptane flame. Spontaneous Raman

Ottenwaelder, Tamara, Pischinger, Stefan

Development of Chemistry-Based Laminar Flame Speed Correlation for Part-Load SI Conditions and Validation in a GDI Research Engine

04/03/2018

The detailed study of part-load conditions is essential to characterize engine-out emissions in key operating conditions. The relevance of part-load operations is further emphasized by the recent regulations such as the new WLTP standard. Combustion development at part-load operations depends on a complex interplay between moderate turbulence levels (low engine speed and tumble ratio), low in-cylinder pressure and temperature, and stoichiometric-to-lean mixture quality (to maximize fuel efficiency). From a modelling standpoint, the reduced turbulence intensity compared to full-load operations complicates the interaction between different sub-models (e.g., reconsideration of the flamelet hypothesis adopted by common combustion models). In this article, the authors focus on chemistry-based simulations for laminar flame speed of gasoline surrogates at conditions typical of part-load operations. The analysis is an extension of a previous study focused on full-load operations. The

Del Pecchia, Marco, Breda, Sebastiano, D'Adamo, Alessandro, Fontanesi, Stefano, Irimescu, Adrian, Merola, Simona

The Effect of Inlet Turbulence Specifications on the RANS CFD Predictions of a NASCAR Gen-6 Racecar

2018-01-073604/03/2018

Turbulence modeling and the specific boundary conditions are among the two major simulation physics setup variables that affect the prediction veracity of a CFD simulation. The existing literature is rich with studies investigating the effect of the inlet boundary conditions on the predictability of a CFD simulation, and it is recognized that the turbulence characteristics of the freestream flow, viz. the turbulence intensity and length scale, can impact the simulation results significantly, even with the same turbulence model. However, none of these studies encompasses the significance of these two boundary specifications on the CFD analysis of a realistic racecar model. Against this backdrop, the purpose of this study is to systematically investigate the effect of different freestream turbulence specifications on the CFD predictions of the aerodynamic characteristics of a latest generation NASCAR Cup racecar model. Finite volume CFD simulations are carried out with: (a) five

Fu, Chen, Uddin, Mesbah, Selent, Christian

Refinement of a 0D Turbulence Model to Predict Tumble and Turbulent Intensity in SI Engines. Part I: 3D Analyses

2018-01-085004/03/2018

Recently, a growing interest in the development of more accurate phenomenological turbulence models is observed, since this is a key pre-requisite to properly describe the burn rate in quasi-dimensional combustion models. The latter are increasingly utilized to predict engine performance in very different operating conditions, also including unconventional valve control strategies, such as EIVC or LIVC. Therefore, a reliable phenomenological turbulence model should be able to physically relate the actuated valve strategy to turbulence level during the engine cycle, with particular care in the angular phase when the combustion takes place. Similarly, the capability to sense the effects of engine architecture and intake geometry would improve the turbulence model reliability. 3D-CFD codes are recognized to be able to accurately forecast the evolution of the in-cylinder turbulence field, taking into account both geometrical features (compression ratio, bore-to-stroke ratio, intake runner

Bozza, Fabio, De Bellis, Vincenzo, Berni, Fabio, D'Adamo, Alessandro, Maresca, Luigi

An Experimental Study of the Impact of Underbody Roughness on the Instantaneous Wake Flow Topology behind a Truck Geometry

2018-01-071404/03/2018

The turbulent wake behind a truck is responsible for a considerable proportion of the total aerodynamic drag. There is evidence to suggest that the underbody flow affects the wake topology, although this interaction is not well understood. Typical truck trailer underbodies are geometrically very complex and have a range of bluff bodies - such as the wheel and axle assembly, structural beams or the secondary fuel tank for refrigerated trucks - attached. These components block the underbody flow and erode its momentum. However, most of the previous studies of the wake flow have used models with clean underbodies. It is thus uncertain whether the wake shapes found by these studies accurately represent the wake topology behind a real truck with a detailed underbody. The aim of this study is therefore to investigate whether aerodynamic studies working with simplistic underbodies may observe a different wake pattern to those studies that correctly replicate the aerodynamic effects of a

Vallina Garcia, Isabel, Babinsky, Holger

Simplifications Applied to Simulation of Turbulence Induced by a Side View Mirror of a Full-Scale Truck Using DES

2018-01-070804/03/2018

In this paper, the turbulent flow induced by a production side-view mirror assembled on a full-scale production truck is simulated using a compressible k-ω SST detached eddy simulation (DES) approach -- the improved delayed DES (IDDES). The truck configuration consists of a compartment and a trailer. Due to the large size and geometric complexity of the configuration, some simplifications are applied to the simulation. A purpose of this work is to investigate whether the simplifications are suitable to obtain the reasonable properties of the flow near the side-view mirror. Another objective is to study the aerodynamic performances of the mirror. The configuration is simplified regarding two treatments. The first treatment is to retain the key exterior components of the truck body while removing the small gaps and structures. Furthermore, the trailer is shaped in an apex-truncated square pyramid. This simplification is proposed based on the assumption that the downstream flow near the

Yao, Huadong, Chroneer, Zenitha, Davidson, Lars

Scale-Resolving Simulation of an ‘On-Road’ Overtaking Maneuver Involving Model Vehicles

2018-01-070604/03/2018

Aerodynamic properties of a BMW car model taking over a truck model are studied computationally by applying the scale-resolving PANS (Partially-averaged Navier-Stokes) approach. Both vehicles represent down-scaled (1:2.5), geometrically-similar models of realistic vehicle configurations for which on-road measurements have been performed by Schrefl (2008). The operating conditions of the modelled ‘on-road’ overtaking maneuver are determined by applying the dynamic similarity concept in terms of Reynolds number consistency. The simulated vehicle configuration constitutes of a non-moving truck model and a car model moving against the air flow, the velocity of which corresponds to the car velocity. The presently modelled ‘on-road’ overtaking maneuver is designed by reference to the complementary ‘quasi stationary’ event investigated experimentally in full-scale wind tunnel of the BMW Group in Munich/Ascheim by fixing the truck model at eight discrete positions relative to the car model

Jakirlic, Suad, Kutej, Lukas, Basara, Branislav, Tropea, Cameron

The Effect of In-Cylinder Temperature on the Ignition Initiation Location of a Pre-Chamber Generated Hot Turbulent Jet

2018-01-018404/03/2018

Ignition location is one of the important factors that affect the thermal efficiency, exhaust emissions and knock sensitivity in premixed-charge ignition engines. However, the ignition initiation locations of pre-chamber generated turbulent jet ignition, which is a promising ignition enhancement method, are not clearly understood due to the complex physics behind it. Motivated by this, the ignition initiation location of a transient turbulent jet in a constant volume combustor is analyzed by the use of computational fluid dynamics (CFD) simulations. In the CFD simulations of this work, commercial codes KIVA-3 V release 2 and an in-house-developed chemical solver with a detailed mechanism for H2/air mixtures are used. Comparisons are performed between simulated and experimental ignition initiation locations, and they agree well with one another. A detailed parametric study of the influence of in-cylinder temperature on the ignition initiation location is also performed. As the

Wang, Nana, Liu, Jinxiang, Chang, Wayne, Lee, Chia-Fon

A Quasi-Dimensional Charge Motion and Turbulence Model for Diesel Engines with a Fully Variable Valve Train

2018-01-016504/03/2018

With the increasingly strict emission regulations and economic demands, variable valve trains are gaining in importance in Diesel engines. A valve control strategy has a great impact on the in-cylinder charge motions, turbulence level, thus also on the combustion and emission formation. In order to predict in-cylinder charge motions and turbulence properties for a working process calculation, a zero−/quasi-dimensional flow model is developed for the Diesel engines with a fully variable valve train. For the purpose of better understanding the in-cylinder flow phenomena, detailed 3D CFD simulations of intake and compression strokes are performed at different operating conditions with various piston configurations. In the course of model development, global in-cylinder charge motions are assigned to idealized flow fields. Among them, swirl flow is characterized by an engine swirl number that is determined by both developments of the swirl angular momentum and the moment of inertia. The

Yang, Qirui, Grill, Michael, Bargende, Michael

Choice of Tuning Parameters on 3D IC Engine Simulations Using G-Equation

2018-01-018304/03/2018

3D CFD spark-ignition IC engine simulations are extremely complex for the regular user. Truly-predictive CFD simulations for the turbulent flame combustion that solve fully coupled transport/chemistry equations may require large computational capabilities unavailable to regular CFD users. A solution is to use a simpler phenomenological model such as the G-equation that decouples transport/chemistry result. Such simulation can still provide acceptable and faster results at the expense of predictive capabilities. While the G-equation is well understood within the experienced modeling community, the goal of this paper is to document some of them for a novice or less experienced CFD user who may not be aware that phenomenological models of turbulent flame combustion usually require heavy tuning and calibration from the user to mimic experimental observations. This study used ANSYS® Forte, Version 17.2, and the built-in G-equation model, to investigate two tuning constants that influence

Liu, Jinlong, Szybist, James, Dumitrescu, Cosmin

Effects of Rear Slant Angles on the Flow Characteristics of the Ahmed Body by IDDES Simulations

2018-01-072004/03/2018

The present study aims to investigate the effects of the several rear slant angles, φ = 25°, 30°, 32°, 33° and 35°, on the wake characteristics downstream of the Ahmed body because the angle of the rear window plays an important role in the flow characteristics. This work presents numerical simulations using ISIS-CFD flow solver which is developed by Centrale Nantes and CNRS. The turbulence model used is an hybrid RANS-LES model: the Improved Delayed Detached Eddy Simulation (IDDES). Detailed discussions of the flow features are provided using time-averaged streamlines, vorticity contours, turbulent kinetic energy contours and an iso-surface of l2. Drag and lift coefficients are also presented. In the symmetry plane, three critical flow points, which correspond to foci of separation and saddle point in the wake of the Ahmed body, and the focus of separation over the slanted surface are presented. When the slant angle increases, these critical points move near the Ahmed body before

Guilmineau, Emmanuel

Assessment of Two Premixed LES Combustion Models in an Engine-Like Geometry

2018-01-017604/03/2018

Large Eddy Simulation (LES) of premixed turbulent combustion in a confined cylinder setup at engine relevant conditions has been carried out for three different initial turbulence intensities, mimicking different flame propagation regimes. Direct Numerical Simulation (DNS) of the setup under investigation provides the reference data to be compared against. The DNS fields have been filtered on the LES grid and are used as initial conditions for the LES at onset of combustion, guaranteeing a direct comparability of the single realizations between the modeled and reference data. Two different combustion models, the G-Equation and CMC-premixed (Conditional Moment Closure) are compared with respect to their predictive capabilities as well as their usability and computational cost. While the G-Equation is a widely adopted approach for industrial applications and usually relies on a tunable turbulent flame speed closure, the novel LES-CMC comes as a tuning parameter free model. Both modeling

Koch, Jann, Geringer, Stefan, Farrace, Daniele, Pandurangi, Sushant, Bolla, Michele, Wright, Yuri M., Jafargholi, Mahmoud, Frouzakis, Christos, Boulouchos, Konstantinos

Modeling Ignition and Combustion in Spark-Ignition Engines Based on Swept-Volume Method

2018-01-018804/03/2018

A swept-volume method of calculating the volume swept by the flame during each time step is developed and used to improve the calculation of fuel reaction rates. The improved reaction rates have been applied to the ignition model and coupled with the level set G-equation combustion model. In the ignition model, a single initial kernel is formed after which the kernel is convected by the gas flow and its growth rate is determined by the flame speed and thermal expansion due to the energy transfer from the electrical circuit. The predicted ignition kernel size was compared with the available experimental data and good agreements were achieved. Once the ignition kernel reaches a size when the fully turbulent flame is developed, the G-equation model is switched on to track the mean turbulent flame front propagation. Moreover, the models were also applied to a homogeneous propane-fueled TCC3 engine and compared with the model whose reaction rate calculations are not based on the swept

Zhu, Guangfei, Pattabiraman, Krishna, Perini, Federico, Rutland, Christopher

ECN Spray G Injector: Assessment of Numerical Modeling Accuracy

2018-01-030604/03/2018

Gasoline Direct Injection (GDI) is a leading technology for Spark Ignition (SI) engines: control of the injection process is a key to design the engine properly. The aim of this paper is a numerical investigation of the gasoline injection and the resulting development of plumes from an 8-hole Spray G injector into a quiescent chamber. A LES approach has been used to represent with high accuracy the mixing process between the injected fuel and the surrounding mixture. A Lagrangian approach is employed to model the liquid spray. The fuel, considered as a surrogate of gasoline, is the iso-octane which is injected into the high-pressure vessel filled with nitrogen. The numerical results have been compared against experimental data realized in the optical chamber. To reveal the geometry of plumes two different imaging techniques have been used in a quasi-simultaneous mode: Mie-scattering for the liquid phase and schlieren for the gaseous one. Different operating conditions, in terms of

Allocca, Luigi, Bartolucci, Lorenzo, Cordiner, Stefano, Lazzaro, Maurizio, Montanaro, Alessandro, Mulone, Vincenzo, Rocco, Vittorio

Investigation of Increase in Aerodynamic Drag Caused by a Passing Vehicle

2018-01-071904/03/2018

On-road turbulences caused by sources such as atmospheric wind and other vehicles influence the flow field and increases the drag in a vehicle. In this study, we focused on a scenario involving a passing vehicle and investigated its effect on the physical mechanism of the drag increase in order to establish a technique for reducing this drag. Firstly, we conducted on-road measurements of two sedan-type vehicles passed by a truck. Their aerodynamic drag estimated from the base pressure measurements showed different increment when passed by the truck. This result raised the possibility of reducing the drag increase by a modification of the local geometry. Then, we conducted wind tunnel measurements of a simplified one-fifth scale vehicle model in quasi-steady state, in order to understand the flow mechanism of the drag increase systematically. Two main factors of the drag increase, namely the pressure distribution and the change in the wind direction generated by the passing vehicle

Shimizu, Keigo, Nakashima, Takuji, Hiraoka, Takenori, Nakamura, Yusuke, Nouzawa, Takahide

Evaluation of an Open-grill Vehicle Aerodynamics Simulation Method Considering Dirty CAD Geometries

2018-01-073304/03/2018

In open-grille vehicle aerodynamics simulation using computational fluid dynamics, in addition to basic flow characteristics, such as turbulent flow with a Reynolds number of several million on the bluff body, it is important to accurately estimate the cooling air flow introduced from the front opening. It is therefore necessary to reproduce the detailed geometry of the entire vehicle including the engine bay as precisely as possible. However, there is a problem of generating a good-quality calculation grid with a small workload. It usually takes several days to a week for the pretreatment process to make the geometry data ‘clean’ or ‘watertight’. The authors proposed a computational method for complex geometries with a hierarchical Cartesian grid and a topology-independent immersed boundary method with dummy cells that discretize the geometry on a cell-by-cell basis and can set an imaginary point arbitrarily. It is possible to avoid problems of ‘dirty’ computer-aided-design data, such

Onishi, Keiji, Ando, Yasunori, Nakasato, Kosuke, Tsubokura, Makoto

Impact of Grid Density on the LES Analysis of Flow CCV: Application to the TCC-III Engine under Motored Conditions

2018-01-020304/03/2018

Large-eddy simulation (LES) applications for internal combustion engine (ICE) flows are constantly growing due to the increase of computing resources and the availability of suitable CFD codes, methods and practices. The LES superior capability for modeling spatial and temporal evolution of turbulent flow structures with reference to RANS makes it a promising tool for describing, and possibly motivating, ICE cycle-to-cycle variability (CCV) and cycle-resolved events such as knock and misfire. Despite the growing interest towards LES in the academic community, applications to ICE flows are still limited. One of the reasons for such discrepancy is the uncertainty in the estimation of the LES computational cost. This in turn is mainly dependent on grid density, the CFD domain extent, the time step size and the overall number of cycles to be run. Grid density is directly linked to the possibility of reducing modeling assumptions for sub-grid scales. The extent of the computational domain

Ko, Insuk, Min, Kyoungdoug, Fontanesi, Stefano, Rulli, Federico, Ha, Taehun, Choi, Hoimyung

Investigation of Interior Noise from Generic Side- View Mirror Using Incompressible and Compressible Solvers of DES and LES

2018-01-073504/03/2018

Exterior turbulent flow is an important source of automobile cabin interior noise. The turbulent flow impacts the windows of the cabins to excite the structural vibration that emits the interior noise. Meanwhile, the exterior noise generated from the turbulent flow can also cause the window vibration and generate the interior noise. Side-view mirrors mounted upstream of the windows are one of the predominant body parts inducing the turbulent flow. In this paper, we investigate the interior noise caused by a generic side-view mirror. The interior noise propagates in a cuboid cavity with a rectangular glass window. The exterior flow and the exterior noise are computed using advanced CFD methods: compressible large eddy simulation, compressible detached eddy simulation (DES), incompressible DES, and incompressible DES coupled with an acoustic wave model. The last method is used to simulate the hydrodynamic and acoustic pressure separately. The pressure fluctuations of the flow and noise

Yao, Huadong, Davidson, Lars, Chroneer, Zenitha

Stereoscopic Imaging in Hypersonic Boundary Layers Using Planar Laser-Induced Fluorescence

TBMG-2814501/01/2018

Stereoscopic time-resolved visualization of three-dimensional structures in a hypersonic flow was performed for the first time in NASA Langley Research Center’s 31-inch Mach 10 Air Tunnel. Nitric oxide (NO) was seeded into hypersonic boundary layer flows that were designed to transition from laminar to turbulent. A laser excitation and multiple-camera imaging scheme was used to obtain raw images containing three-dimensional spatial information. The images were processed in a computer visualization environment to provide stereoscopic image pairs that could be viewed several ways, including using the cross-eyed viewing method, with the aid of a stereoscope, as animated image pairs (i.e. wiggle stereoscopy), or as anaglyph images through conventional red/blue 3D glasses.

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