Browse Topic: Wind tunnel tests
The paper presents a general framework for building an aeromechanic model in FLIGHTLAB, suitable for high fidelity, pilot-in-the-loop simulator. The focus is on aerodynamic modeling of AW609 tiltrotor in Airplane Mode flight regime. The framework can be extended to helicopter and conversion modes with additional considerations for rotors-airframe aerodynamic interference. It can also be adapted to different tiltrotor geometries, with some adjustments depending on their peculiarities. The model uses Blade Element Theory loads evaluation of lifting surfaces, corrected with tabulated distributed loads to tune FLIGHTLAB predictions against high-fidelity aerodynamic references. Bluff bodies are modeled using force and moment tabulated data. Verification was conducted against reference data in wind tunnel mode and against flight data in trim analysis. The proposed method allowed to match lift distribution on slender bodies, as well as lift and drag integral loads, with aerodynamic references
This paper presents the results of an ongoing correlation study performed using three different comprehensive rotorcraft codes and data obtained from the Advanced Testbed for TILtrotor Aeroelastics (ATTILA) tiltrotor whirl flutter wind tunnel test campaign. The ATTILA testbed consists of a 1:5 scale semi-span wing with a powered, tip-mounted proprotor reflecting the proprietary design of the Next Generation Civil TiltRotor (NGCTR). Experimental dynamic characterization of the testbed has revealed non-negligible structural nonlinearities. Post-test efforts have focused on refining the damping trends extracted from the test data, and correlating the experimental results with numerical predictions. The objective of this paper is to assess the modelling fidelity required and afforded by modern comprehensive aeromechanics codes to predict tiltrotor whirl flutter instability given an industry-representative design that exhibits structural nonlinearities. Baseline numerical flutter models
This study presents computational analyses of coaxial rotor hub flows and validation against experimental data obtained from the fifth Rotor Hub Flow Prediction Workshop. Experiments were conducted in a 12-inch diameter water tunnel at Pennsylvania State Applied Research Laboratory, employing tomographic particle-image velocimetry (Tomo-PIV) and precise hub drag measurements. Three CFD codes (UMD Mercury, CREATETM-AV Helios, and OVERFLOW) utilizing hybrid Reynolds-Averaged Navier-Stokes (RANS) / Large Eddy Simulation (LES) modeling based on Spalart–Allmaras turbulence model, were applied to replicate and analyze hub flows. Counter-rotating coaxial rotor hubs under free-air condition was simulated as the simplest case and the hub drags are compared between the three CFD codes. The full water tunnel configuration, consisting of two hubs, a fairing, and shafts, was also simulated and compared to experimental results, with a focus on hub drag, wake velocity fields, and turbulence
The NASA Revolutionary Vertical Lift Technology project aims to support and guide the development of vertical flight vehicles for the benefit of the U.S. rotorcraft community and to increase the quality of life of the public. As part of this effort, the Multirotor Test Bed (MTB) – designed and built by NASA – has been tested twice at the U.S. Army 7- by 10-Foot Wind Tunnel at NASA Ames Research Center in 2019 (MTB1) and 2022 (MTB2). This study utilizes MTB2 experimental data for sensitivity studies on rotor aerodynamic performance of a quadrotor configuration using two mid-fidelity tools, the Comprehensive Hierarchical Aeromechanics Rotorcraft Model (CHARM) as well as Blade Element Theory based disk modeling in the OVERFLOW CFD solver. Additionally, this study leverages analyzing computational rotor performance predictions with experimental data to help identify future test configurations for the upcoming MTB3 test in the National Full-Scale Aerodynamics Complex 40- by 80-Foot Wind
Wind tunnel tests and comprehensive rotorcraft analysis were carried out on a slowed main rotor full-wing lift and thrust-compounded helicopter with a trailing propeller to investigate the effects of rotor and wing configuration on performance, blade structural loads, and hub vibratory loads. Experiments were conducted at advance ratios up to 0.7, incorporating three full-wing configurations with symmetric and asymmetric incidence angles and three different rotor shaft tilt angles. Propulsive thrust was measured by a trailing pusher propeller with its own balance system. The wind tunnel test data was used to validate the University of Maryland Advanced Rotorcraft Code (UMARC). Results showed that the maximum lift-to-drag ratio is achieved using either of the symmetric or asymmetric full-wing lift-compound configurations with high lift offloading and aft shaft tilt. Both blade structural loads and hub vibratory loads are significantly reduced when rotor lift is offloaded to the wings
This paper presents an overview of the results from the second wind-tunnel test of the TiltRotor Aeroelastic Stability Testbed (TRAST). The objective of this test was to obtain experimental data for understanding the effects of tiltrotor parameters on whirl flutter and analysis-validation data for the prediction of whirl flutter across a range of system configurations. Frequency and damping were measured at multiple rotor speeds for pitch-flap-coupling angles ranging from -0°to -30°. In addition, measurements were made for changes in blade stiffness, air density and wing-pylon connection stiffness. The paper also presents the results from supporting measurements that may aid analysis validation, such as wing-only damping, rotor frequencies and non-spinning modal frequencies.
Generalized Predictive Control (GPC) is an advanced form of an adaptive control algorithm that uses experimentally acquired data to determine the input-output relationship of complex systems through a process called system identification. GPC has historically been employed for stability augmentation and vibration reduction of dynamically-scaled tiltrotor aircraft wind-tunnel models since the complex nature of these dynamic systems does not lend itself well to traditional control approaches. The present research expands upon previous analytical and experimental work with wind-tunnel experiments that utilize improved GPC techniques. These techniques improved controller robustness such that a working controller was stable across a multitude of model configurations and wind-tunnel conditions and successfully suppressed vibration and vehicle flutter. Advanced GPC (AGPC) enables self-adaptation of a traditional GPC control law. AGPC was also investigated during the present research but was
A wind tunnel investigation to characterise the aerodynamic performance and aeroelastic response of a tiltrotor blade set operating in propeller mode is presented. A custom blade set was instrumented with fully bridged axial strain gauges to monitor the flap bending and torsional strain at several radial locations. Propeller thrust and torque measurements were acquired using a custom six component Rotating Shaft Balance. Measurements of blade tip deflection were obtained via stereoscopic Digital Image Correlation. Testing was performed at a range of rotational frequencies, blade pitch angles and advance ratios to assess the blade aerodynamic performance and aeroelastic response in both attached and stalled operating conditions. Strain measurements were shown to identify stall and blade eigenmode frequencies, where flap bending bridges show a more reliable capture of stalled flow than torsional bridges. Furthermore, blade tip deflection measurements were shown to reduce with increased
This study characterizes the dynamics of a novel lag-pitch-coupled underactuated rotor design that can be incorporated into rotary-wing unmanned aerial vehicles (UAVs) to provide pitch and roll control with effectiveness comparable to that of a conventional swashplate albeit with significantly lower mechanical complexity and weight. The concept integrates a single lag hinge tilted at a 45-degree angle located at the center of the rotor hub with independent flap hinges for each of the two blades. This idea relies on the ability to cyclically vary the angular velocity of the rotor in a 1/rev fashion via motor torque modulation, which induces a cyclic lag resulting in a cyclic pitch variation due to the tilted lag hinge (lag-pitch coupling) and causes the tip path plane (TPP) to tilt in a desired direction for pitch and roll control. To understand this concept, simulations using the Rotorcraft Comprehensive Analysis System (RCAS) were performed to capture the 1/rev response in lag, pitch
A 1/5th scale powered coaxial rotor and propeller system has been developed and tested in the National Full Scale Aerodynamic Complex (NFAC) 40x80 ft Wind Tunnel. Test conditions include airspeeds in excess of 250 kts, the highest recorded for a rotor in edgewise flight at the NFAC. The system was studied in four configurations: a powered coaxial rotor, a powered coaxial rotor with a propeller wake rake, a powered coaxial rotor with a powered propeller, and a bare hub rotor with a propeller wake rake. The high-quality data from the test included propeller, fuselage and main-rotor performance; aerodynamic-interactions between the rotors, fuselage, empennage, and propeller; acoustics and handling-qualities attributes. These results have been used to validate physics-based rotorcraft modeling tools and enhance the quality of full-scale X2 Technology® aircraft designs. Innovative solutions to test measurement challenges included rotor shaft strain gages, balance thermal control systems
The Rotor Blown Wing (RBW) is a tailsitter Vertical Takeoff and Landing (VTOL) Unmanned Aerial System (UAS) configuration that leverages cutting-edge autonomous flight controls through Sikorsky's MATRIX™ technology to create a highly capable, efficient, and scalable technology platform. By combining the benefits of fixed- and rotary-wing aircraft, the RBW configuration eliminates the need for traditional UAS launch and recovery infrastructure. This paper describes the RBW-5 prototype, a 100-pound, dual 5-foot diameter proprotor demonstrator, and discusses the comprehensive evaluation of its design and operability through a combination of flight tests, wind tunnel experiments, and computational fluid dynamics (CFD) simulations. The results demonstrate the maturity of the UAS and highlights key accomplishments of the RBW-5 program, including successful autonomous takeoff and landing and transitions between hover and forward flight, the extraction of critical "blown-physics" underlying
With recent advancements in the field of Advanced Air Mobility (AAM), including Electric Vertical Takeoff and Landing (eVTOL), Remotely Piloted Aircraft Systems (RPAS), and Unmanned Aerial System (UAS), it is beneficial to understand the impact of complex flow features on operations in urban and shipboard environments. Testing methods for studying these impacts, including simulated environments such as wind-tunnel flows and engineered equivalence tests, will need to be adapted to prepare for when the vehicles of interest are too large for the available testing facilities, and to permit low-cost alternatives for industry and government. This work demonstrates a development process that can be used to ensure the complex-flow-environment phenomena can be studied. First, this work illustrates the development of downdraft and turbulence flow types in a wind tunnel setting, and assesses the response of an M600 RPAS to these flows. Then, the same parameters are compared for a Mission Task
Generating multiple high-quality sets of rotor performance data is necessary to validate Vertical Take-Off and Landing (VTOL) aircraft performance prediction codes across a broad range of vehicle configurations. Many aircraft companies are actively pursuing multirotor vehicle configurations, which has created a need for validation data for multirotor systems. The NASA Multirotor Test Bed was designed to accommodate a broad range of reconfigurable multirotor systems and to measure rotor performance and loads in a wind tunnel environment. This paper presents results from the second wind tunnel entry of the test bed, which was completed in August 2022. This wind tunnel test focused on a quadrotor configuration, with variations in rotor placement, blade number, and rotor phasing, across a range of wind tunnel test conditions. This paper describes the test methods and provides and discusses a sample of the quasi-steady and dynamic loads data that were collected during the test program.
This paper discusses the development of a quantitatively-accurate non-linear hybrid flight dynamics model of a hover-capable Air-Launched Tailsitter Unmanned Aerial System (ALUAS) in order to 1) understand its dynamics during complicated maneuvers, and 2) provide a high-fidelity framework to develop novel control laws. Wind tunnel tests were conducted on a 1:1 scale model of the full aircraft to measure the airloads, which were used in the simulation as a lookup table. Flight tests of the ALUAS were performed in hover, transition, and cruise to collect a large amount of unique state measurements by providing large excitations to induce highly transient motion. The flight dynamics predictions using Rotorcraft Comprehensive Analysis System (RCAS) software were then compared with experimental flight test data. To correct any discrepancies in the RCAS physics-based predictions, a correction was learned from the experimental measurements, making use of the large amount of collected flight
This paper describes the design, development, and testing of a full-scale eVTOL propulsor optimized for quiet and efficient operation. To design the propulsor, a design tool was developed for predicting the aerodynamic and acoustic performance of eVTOL propellers and rotors. The design tool consists of an aerodynamic prediction code, AMP (Aerodynamic Modeling of Propulsor), and an acoustics prediction code, OpenCOPTER, coupled with an acoustics propogator, PSU-WOPWOP, which can receive inputs from either an acoustic solver or high-fidelity CFD. The tool was used to design a coaxial eVTOL propulsor, and both subscale and full-scale blades were manufactured. The aerodynamic and acoustic performance of the subscale propulsor was tested in hover and edgewise flight in an anechoic wind tunnel. A custom test stand was developed and used to measure the aerodynamic and acoustic performance of the 8-ft diameter full-scale propeller in hover. The experimental results were used to validate the
The UH-60A slowed rotor test campaign carried out at the 40- by 80-Foot Wind Tunnel at the U.S. Air Force's National Full-Scale Aerodynamics Complex (NFAC) provided valuable information of a classical helicopter rotor blades operating at very high advance ratios. This paper aims to show the correlation of the RCAS and HOST comprehensive analysis (CA) tools with respect to several experimental campaign cases. Particularly the influence of the rotor aerodynamic performance as a function of the advance ratio and the collective angle is studied. The influence of the shank drag modeling is observed and its importance to obtain accurate results is highlighted. The RCAS and HOST simulations are capable of reproducing the rotor performance trends observed in the test campaign. Furthermore, the correlation of RCAS and HOST with respect to the measured rotor loads data is studied for the advance rations of 0.4, 0.5 and 0.7 at iso-thrust coefficient conditions. The aerodynamic loads and the
This study investigates Reynolds number effects on rotor wake vortex development using a hyperbaric rotor facility capable of pressurizing air up to 100 bar. Background-oriented schlieren (BOS) and hot-wire anemometry (HWA) were applied to characterize vortex trajectories, core growth, and circumferential velocity distribution. BOS measurements revealed consistent blade-to-blade trajectory deviations and vortex pairing across all operating conditions, despite that the investigated three-bladed rotor was milled from a single piece of aluminum, ensuring precise manufacturing and a highly symmetric geometry. A statistical scheme was developed to analyze the radial structure of fluctuating tip vortices, which traverse the pointwise fiber-film sensor in a fixed position. With increasing vortex Reynolds number, the tip vortices are more compact with a reduction in core growth. The circulation in the vortices grows with the vortex radial coordinate, and converges at a radial position
Turbulence conditions at hospital heliports in the built environment are routinely assessed at the design stage through experimental, physical testing in boundary layer wind tunnels. Wind tunnel testing is the gold standard to evaluate wind conditions on and around buildings where human safety is of the upmost concern. Numerical techniques, such as computation fluid dynamics (CFD) are continuously improving and may offer a viable alternative to wind tunnel testing in some cases. Within the CFD toolbox, there are several techniques to simulate a flow field in an urban or suburban context. These techniques have advantages and disadvantages in terms of ease of use, efficiency, costs, level of fidelity, and reliability. This paper compares high-fidelity CFD tools to wind tunnel testing for two vertiport case studies in different urban settings with different wind climates. The results of this research inform the selection of the right tool to support vertiport design and operations and to
Preparation for Powered Flight (PPF) is a critical phase for Dragonfly, the National Aeronautics and Space Administration (NASA) mission to Saturn’s moon Titan. During PPF the descending Lander is lowered below the Backshell and uses its rotors to remove or “despin” any residual yaw motion of the vehicle. A 1/2-scale model of the Dragonfly PPF configuration was tested in the National Full-Scale Aerodynamics Complex (NFAC) 80 by 120-foot wind tunnel to measure aerodynamic loads and surface pressures on the Lander and Backshell. The results were used to improve understanding of the complex aerodynamic interactions and provide validation data for the Computational Fluid Dynamics (CFD) simulations used to develop the aerodynamic databases for full-scale, Titan conditions. Configurations tested in the wind tunnel included Lander-alone-no-rotors (L), Lander-alone-with-rotors (LR), and Lander-with-Rotors-and-Backshell (LRB). Both LR and LRB configurations were tested at multiple descent
Current paper summarizes a correlation study of two flow solvers (CREATETE-AV Helios and Simcenter STAR-CCM+), routinely used at Sikorsky, with multiple model-scale wind-tunnel tests. The Helios modeling approach was aiming for a high-fidelity accurate simulation, whereas the STAR-CCM+ modeling approach was aiming for a fast turn-around time with reasonable solution accuracy with a relatively coarse mesh and simplifications. The two solvers generally agreed well with the test data within reasonable accuracy and captured the airloads and flowfield trends. The calculations presented herein show the impact of the turbulence model on component loads, the aerodynamic interactions among components, and the effect of transition modeling on rotor performance. The Reynolds-Averaged Navier-Stokes CFD model generally delayed separation and resulted in lower drag. By modeling the airframe supporting structure in CFD simulations, an improvement on correlation for inflow on the propeller plane was
The subject of this paper is the conceptual development of two new configurations for HEMS Operations as a new fleet concept for the European theater. Previous studies showed an increase of the required flight range for an emergency patient transport. But in conjunction with an average share of less than 30% of the flights actually with the patient. In the most rescue missions an emergency physician is transported to the scene, the patients further transport is conducted on-road by an ambulance. Considering an improved flight performance, the first DLR design study revealed a growth of the maximum take-off mass of the primary rescue helicopter of 32%. That makes the rescue helicopter inefficient for the transport of only the emergency physician. Consequently, if an ambulance is already at the scene, an emergency doctor shuttle is the sensible approach. The requirements for such a configuration are developed from a feasibility study lead by the ADAC Air Rescue (ADAC Luftrettung
An extensive test campaign was conducted at the National Full-Scale Aerodynamics Complex 40- by- 80-Foot wind tunnel to acquire performance, loads, and acoustics measurements of the Joby Aviation propeller across a variety of operating conditions. The dataset provided validation of the design methodology as well as verification of computational tools. The Vold-Kalman filter was used to extract the shaft-coherent propeller noise in hover to obtain the residual noise, representing the broadband noise. This data verified broadband noise tip speed scaling laws as well as a low-order empirical model for overall sound pressure level. The OVERFLOW/PSU-WOPWOP method was used to simulate the propeller in pure edgewise flight and shown to accurately predict propeller performance. The low-frequency acoustics were predicted well but the solver underpredicted frequencies above 300 Hz, possibly due to the inability to capture the turbulent component of the blade-wake and blade-vortex interaction
Large eddy simulations (LES) of the Joby Aviation S4 propeller at the NFAC tunnel are performed with a GPUaccelerated low-Mach (Helmholtz) solver, and compared with experimental data provided by Joby at two flow conditions of hover and pure edgewise flow of 10 m/s. Accurate prediction of the laminar-turbulent transition was seen to be critical to the prediction of the noise sources for hover condition, with additional prominent noise sources found to be near the trailing edge and tip of the propeller. The dominant edgewise noise sources were seen to be from the dynamic outboard flow separation and reattachment from advancing to retreating side of the blade azimuth as well as the convective amplification of the acoustic waves from the 10 m/s flow. The far-field noise at the target set of microphone locations are predicted using the frequency-domain Ffowcs Williams-Hawking (FW-H) formulation. The A-weighted 1/3rd octave band results showed a good prediction of the noise compared with the
This paper investigates the amplitude-dependent characteristics of the TiltRotor Aeroelastic Stability Testbed. The recovery rate, MultiProny, and Stockwell transform methods are employed to measure nonlinear effects in the system, overcoming the limitations of conventional methods like logarithmic decrement, moving-block analysis, and Prony series that assume linear (amplitude-independent) behavior. The proposed methods reveal amplitude-dependent trends that conventional methods obfuscate, providing deeper insights into tiltrotor dynamics. A comprehensive study of ground vibration and wind tunnel test data highlights reduced local damping and frequency at larger response amplitudes for various blade materials, rotor speeds, and pitch-flap coupling parameters. This study offers novel analysis capabilities to support design and advances the understanding of tiltrotor nonlinear dynamics.
To validate simulation work towards the design of the Dragonfly rotorcraft lander, a process of extracting a modal model from impact test data is described in this paper. Through a curve-fitting process using Siemens Testlab software, modal frequencies, damping, and mode shapes are extracted and mass-normalized to be imported as a modal model into the Rotorcraft Comprehensive Analysis System (RCAS) to represent the dynamics of the underlying structure more accurately. Wind tunnel conditions were simulated to compare to hub loads measured during wind tunnel testing. An initial comparison of RCAS with VVPM inflow and RCAS coupled with HELIOS show similar hub loads but also show the importance of modeling the rotational degrees of freedom of the structure properly. Additional modeling comparisons between modeling the hubs and the load cell locations further illustrate that by capturing rotational mode shapes based on test data, in-plane hub loads are predicted more accurately.
This paper details the development of a tailsitter unmanned aerial system (UAS) that has the potential to be airlaunched in the near future. By simultaneously integrating air-launch capability with both rotary-wing vertical flight and fixed-wing horizontal flight, the vehicle can be rapidly deployed, perform hovering flight, and achieve high-speed and efficient cruising flight. The aircraft prototype has a mass of 1 kg (2.2 lbs) with wings that can fold to allow the aircraft to fit inside a 6-inch launch tube. A coaxial propeller with vectored thrust is used for control in vertical flight, and a unique avian-inspired wing-folding mechanism is used for stowing and deploying the wings. The aerodynamic design was characterized through a series of wind tunnel experiments, propeller tests, and flight dynamics simulations. High-fidelity simulations of vehicle dynamics validated its air-launch capability and flight tests performed with the prototype demonstrated the ability of the aircraft to
A joint experimental-computational research campaign is underway to develop physical understanding and a validation-quality database for a model-scale tractor propeller-wing system. Separate load measurements on the wing and propeller accompany wing surface pressure distributions and flow field measurements via stereoscopic particle image velocimetry (SPIV) at discrete wing spanwise locations for a range of static propeller tilt angles. The physical wind tunnel test is modeled using a high-fidelity computational approach (Helios). Computational simulations aid in assessing the influence of the wind tunnel facility effects and test support structure wake interference, as well as in reducing uncertainties in the physical experiments for use in computational validation. The behavior of the induced thrust and lift at a zero-degree wing angle of attack in the axial flow regime (cruise configuration) is correlated with flow field measurements, showing distinct differences between upwash and
The flow behavior of the two-blade MERIT rotor in hover, focusing on both pre-stall and stall regimes, is investigated through a comprehensive numerical-experimental approach. The study leverages unsteady RANS simulations to compute rotor thrust and power polars and validates them against experimental measurements. Valuable insights are provided into the capabilities of unsteady RANS methods and modern turbulence models for predicting rotor performance across these critical operating conditions. Furthermore, the numerical model incorporates blade deformations by implementing the experimentally measured flap and torsion displacements. A more realistic depiction of the rotor's aerodynamics is provided accounting for the structural deformations of the blades under aerodynamic loads. Highfidelity simulations closely predict the experiments in pre-stall conditions while discrepancies are present when the flow exhibits extended stalled regions. Blade deformations demonstrated to have only a
A 4.75-ft diameter dynamically scaled advanced hingeless hub swept-tip tiltrotor was tested up to unprecedented speeds of 200 knots. This paper describes its design, wind tunnel test, data, and comprehensive analysis predictions. The data consists of beam, chord, and torsion mode damping of the wing-pylon at a loosely Froude scaled RPM of 1050 extracted via the moving-block method. Three systematic parametric variations are studied; hingeless versus gimballed, hingeless versus gimbal-locked, and straight versus swept tip blades. In house comprehensive analysis, UMARC-II, was used to predict the data. The key conclusions were that the hingeless hub increases stability in the chord mode to more than twice that of a gimballed hub. The stability of the torsion mode increased when the hingeless hub was equipped with swept tip blades. The chord damping is slightly higher than the gimbal-locked hub. The beam mode remains unaffected. Comprehensive analysis is able to predict the beam mode but
The present study describes the computational methodology adopted to evaluate the aerodynamic characteristics of a shrouded tail rotor. The dependence of the aerodynamic characteristics of a shrouded rotor on the shroud geometry and flight condition deeply affects the accuracy in estimating the thrust sharing of the antitorque system. Experimental testing and numerical investigations have been carried out in the past to characterize the shrouded tail rotor performance and the influence of the variation of the characteristic geometrical parameters. In this study, a modified Virtual Blade Model (VBM) approach has been exploited to model the structure of the flow field produced by the AW09 shrouded tail rotor operating in hover. The proposed modified VBM was tested on the isolated configuration along with the canonical model implementation. By correlation with experimental and numerical data, the introduced modification translated into modeling improvements both in terms of accuracy and
A blade-tip-propeller driven rotor consists of small electric motors and propellers attached to the rotor blade tip to spin the main rotor. This study address a propeller driven shortcoming that was identified in previous research: a high required power to spin the main rotor. To investigate this, a series of wind tunnel and hover stand test campaigns were conducted to experimentally characterize the 6 ft diameter propeller driven rotor performance. A streamlined tip nacelle was designed to house the blade tip motor, and featured an embedded load cell to measure the tip propeller's aerodynamic forces and moments. A propeller aerodynamic model was developed from propeller hover tests and then validated through wind tunnel testing of the propeller in axial flow. Next, the interactional aerodynamics between the stationary rotor blade and tip mounted propeller were investigated through wind tunnel testing. These tests were performed between 0 and 12 degrees wing angle of attack, and at
Heavy class attack helicopter development program aims to develop a new generation assault helicopter with high weapon capacity and modern combat technologies. Design requirements lead to a complicated aerodynamic shape. Wind tunnel tests gain importance for validation of aerodynamic design decisions and methodologies. A short test campaign is planned in a high Reynolds number environment which is achieved through pressurization. Generation of aerodynamic characteristics, effect of under-wing stores, effectivity of tail surfaces and main rotor hub interactions construct the base of test plan. Tests are conducted under varying pressure and airspeed combinations starting from 1.1 Bar 100 m/s to 3 Bar 85 m/s. Test results are compared with CFD simulations as a part of validation studies. Reynolds Averaged Navier-Stokes Simulations provide satisfactory results. Improved results are obtained with high fidelity turbulence model, wall modeled very large eddy simulations.
Mid-fidelity computational techniques have long been sought after in the engineering community to expedite the generation of high-quality engineering data. As digital engineering gains prominence, the demand for faster computational methods continues to grow. Within the rotorcraft community, actuator line and immersed boundary methods play a crucial role as mid-fidelity tools for modeling full helicopters. This study investigates the efficacy of mid-fidelity immersed boundary and actuator line methods using the HPCMP CREATETM-AV Helios ROAM model in predicting the fuselage download of the ROBIN wind tunnel model. Predictions from these methods are compared against both high-fidelity computations and available wind tunnel data. The study also examines the impact of combining mid-fidelity and high-fidelity elements on the results and the time required for solution. The findings indicate that employing mid-fidelity rotor and fuselage models yields sufficiently accurate trends in fuselage
This paper presents the preliminary results of the recent whirl flutter wind tunnel test campaign performed within the Advanced Testbed for TILtrotor Aeroelastics (ATTILA) project. The Froude-scale ATTILA testbed consists of a semi-span wing with powered tip-mounted proprotor reflecting the proprietary design of the Next Generation Civil TiltRotor (NGCTR). An overview of the ATTILA testbed, wind tunnel test procedures, team organisation and preliminary flutter results are presented. In line with pre-entry dynamic characterization tests, the wind-on test activities in the DNW Large Low-speed Facility (LLF) revealed notable force-dependent nonlinearity in the modal characteristics of, particularly, the wing torsion mode. Further dimensionality was added by early observations that damping in the rotor gimbal degree of freedom, attributed to stiction in the blade pitch mechanism, had the potential to substantially contribute to the damping of the fundamental wing-pylon modes. Nevertheless
A system identification study was conducted on a quadrotor unmanned aerial system (UAS) that was free-flying inside the test section of the Naval Surface Warfare Center Carderock Division's Subsonic Wind Tunnel. Motion capture cameras installed in the wind tunnel provided position feedback information to the aircraft in real time, enabling autonomous flights. Longitudinal, lateral, heave, and yaw axis frequency sweeps were conducted at airspeeds up to 20 knots, in 5 knot increments. The extracted flight dynamics model showed excellent agreement in both the time and frequency domains across all airspeeds. Variation in the aircraft's stability derivatives, power usage, and trim information with airspeed was determined. This paper documents the test procedures, challenges with flying aircraft inside the wind tunnel, the controller model, and the system identification results. This free-flight wind tunnel testing methodology has wide applicability to assist with UAS flight control
This paper investigates the interactional aerodynamics and acoustics of three pusher propeller configurations from the Aerodynamic and Acoustic Rotorprop Test (AART), which were tested in the National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Foot Wind Tunnel at NASA Ames Research Center. The three CFD simulation models − isolated propeller, full-wing/propeller, and half-wing/propeller − are simulated using the multi-disciplinary rotorcraft simulation tool CREATE™-AV Helios. Unlike the previous work in which the acoustics were simulated using PSU-WOPWOP, in the current work, acoustic prediction is carried out using NASA's acoustic prediction software AARON/ANOPP2. No significant difference is found between the two acoustic solvers for all configurations. The current isolated propeller and full-wing/propeller simulations, which include the nacelle behind the propeller and the actual hub from the experiment, are compared with the previous simulations that had a notional hub and
The CH-53K® King Stallion™ is the most advanced heavy lift helicopter developed by Sikorsky, a Lockheed Martin Company, to address the requirements of the United States Marine Corps. The aircraft was designed to support missions with a maximum design gross weight of 88,000 lbs and can carry external loads up to 36,000 lb. Performance flight tests for the CH-53K® have been completed as part of its System Design and Development (SDD) phase. Tethered hover and level forward flight performance measurements have been acquired that are used as a basis for Naval Air Training and Operating Procedures Standardization (NATOPS) flight manual performance charts. They were also used in the Key Performance Parameter (KPP) verification analysis, demonstrating that the CH-53K® exceeds its KPP for mission effectiveness. In addition to overview descriptions of the performance flight test program, the test results are herein compared with predictions from aircraft performance modeling tools that were
A two-phase wind tunnel test was conducted to evaluate aerodynamic performance on a 1/5th scale model of the Sikorsky/Boeing X2™ technology representative aircraft for Future Vertical Lift (FVL). The test program provided valuable aerodynamic data for two important elements of the design: the faired coaxial hub system and the main inlet flow leading to the engine interface. Studies from previous X2™ technology aircraft have shown that hubs, pylons and sail fairings have strong interactions, and if well integrated can lead to low drag aircraft designs. Rotorcraft main inlets generally have aggressive turns; therefore, this inlet design was investigated for distortion and total pressure loss. Accuracy of modeling these aerodynamic interactions using Computational Fluid Dynamics (CFD) and other forms of computational aerodynamic assessment requires supporting empirical testing for validation. The two wind tunnel facilities used in Phase 1 and 2 offered different and unique advantages
The tiltrotor whirl flutter stability of a gimballed hub and a hingeless hub are investigated using multibody dynamics simulations. A semi-span wind tunnel tiltrotor model are developed using the multibody dynamics code: Dymore. CAMRAD II predictions are used to correlate the Dymore predictions of the baseline tiltrotor characteristics. The rotor structural frequencies of the gimballed tiltrotor and the hingeless tiltrotor are compared between Dymore and CAMRAD II predictions with good agreements. CAMRAD II model of the baseline TRAST gimballed tiltrotor is used for correlating the whirl flutter stability with that of the Dymore model. Overall good agreements are shown for both the frequencies and damping ratios of all three wing modes. The effects of key design variables, such as blade stiffness, rotor RPM, and ƍ3 on tiltrotor whirl flutter stability of both hubs are studied.
High-fidelity simulations are used to enhance the understanding of the sensitivity of propeller-wing interactions across a spectrum of conditions, focusing on both aerodynamics and aeroacoustics. The aerodynamics is analyzed using high-fidelity computational fluid dynamics, while the acoustics is assessed through the application of impermeable Ffowcs Williams and Hawkings surfaces. Initial assessments concentrate on the influence of simulation parameters on both convergence and accuracy of numerical results. It is determined that reducing the wake grid spacing from 10% of the reference chord length to 7.5% offers no notable improvement to acoustic predictions. Moreover, comparisons between acoustic predictions employing the SST turbulence model and the SA model, with and without transition modeling, reveals differences that are minor in comparison to the prediction errors observed against experimental data. Then, the sensitivities of both aerodynamic and aeroacoustic responses are
ABSTRACT A proof of concept test to measure the unsteady boundary layer transition locations on the lower surface of a Machscaled rotor in forward flight was performed during the Summer of 2017 in the NASA Langley 14- by 22-Foot Subsonic Tunnel. The transition locations were measured using high-speed infrared thermography with a rotating mirror assembly that could be remotely actuated to acquire data at several rotor azimuths. Data were acquired for eight unique rotor flight conditions for a range of advance ratios (μ=0:10 : 0:38), thrust coefficients (CT/α =0:04 : 0:12) and rotor shaft angles (αs = -6 deg : 0 deg). This paper presents the transition locations as a function of azimuth and radius for an advance ratio of, μ, of 0.30, and thrust coefficent, CT/α, of 0.08. At this condition, the lower surface is fully laminar on the retreating side and mostly turbulent on the advancing side except near the tip. The tip airfoils were greater than 60 percent laminar on the lower surface
ABSTRACT Interactional aerodynamic interactions between various rotorcraft components can make a large contribution to steady and unsteady loads, performance, and vibration. Wind tunnel results from a powered model test have been analyzed to identify trends in the unsteady aerodynamic pressures on the horizontal stabilizer. Flow velocity measurements were also made behind the fuselage, rotor hub, and blades. Velocity components in all three directions were separated into time-averaged, periodic, and broadband components to identify factors contributing to unsteady tail loads and provide validation data for analysis. Computational Fluid Dynamics (CFD) has been applied to four configurations of the wind tunnel model. The calculated steady rotor and fuselage forces and the unsteady tail pressures have been compared to experiment. CFD has also been applied to a flight test configuration and the results compared to measured stabilizer accelerations. When all relevant components are included
ABSTRACT Slowing down the rotor RPM is a viable method to alleviate the compressibility effect at the advancing side of a rotor in forward flight, which is proved effective in raising the cruise speed limitation of a compound helicopter. A series of wind tunnel tests were conducted in the Glenn L. Martin Wind Tunnel, and some basic understandings were gained on the high advance ratio aerodynamic phenomena, such as thrust reversal and dynamic stall in reverse flow region. In one of the wind tunnel tests, the rotor blades were instrumented with pressure sensors and strain gauges at 30% radius, and enough pressure data was acquired to calculate the integrated sectional airloads. Further, the experimental results of rotor performance, control angles, blade airloads and structural loads were correlated with the predictions of comprehensive analysis as well as CFD/CSD coupled analysis. Furthermore, the paper focuses on the comparison between experimental surface pressure and airload data and
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