Browse Topic: Kinematics

Items (320)
This paper explores novel airfoils for rotorcraft applications using a gradient-free, multi-objective genetic algorithm with 2D URANS simulations. The study considers dynamic kinematics at a Reynolds number of 5×105 and a mean Mach number of 0.35. Two optimization scenarios are analyzed: 1) pre-stall kinematics (0° ≤α ≤10°) and 2) dynamic stall kinematics (0° ≤ α ≤ 20°). The paper compares two objective functions: f1, based on the cycle averaged lift, and ˜ f1, which modifies f1 by penalizing hysteresis in the lift coefficient. The effects of uniform vs. fluctuating freestream velocity and reduced frequency on optimal airfoils are also discussed. The proposed optimization approach has resulted in novel airfoil shapes that are characterized by a drooped nose, with a convex surface on the aft upper surface similar to a reflex camber in pre-stall kinematics and less unsteadiness in the air loads for the optimized airfoils under the dynamic stall kinematics.
Badrya, Camli
Dynamic stall continues to be a limiting factor for rotorcraft performance in forward flight. The complex flow physics, resulting from blade kinematics, aeroelastic deformations, and blade-vortex interactions, makes this problem challenging. The availability of results from recent high-fidelity coupled computational aerodynamics-structural dynamics simulations provides an opportunity to gain new insights into the physics of dynamic stall on rotor blades in realistic operating conditions. Recent research efforts have also resulted in the identification of a leading-edge suction parameter (LESP), whose critical value has been shown to correlate with the flow events leading to dynamic stall. Critical LESP is largely independent of motion parameters, and is dependent mostly on the airfoil shape, Reynolds number, and Mach number. In this work, LESP variation along the blades of a UH-60A rotor in forward flight is extracted from high-fidelity computational results. The objective is to
Lee, Yi TsungGopalarathnam, AshokJain, RohitYeh, Chi-An
This SAE Information Report provides definitions and discussions of key terms concerning driver drowsiness and fatigue, and basic information on measuring drowsiness and fatigue. It also includes information and concepts for driver drowsiness as they relate to the safe operation of a vehicle. The key driver drowsiness and fatigue causal factors include the following: (1) sleep quality and quantity, (2) time of day, (3) time awake, (4) time on task (modulated by characteristics of the driving task), (5) task-related fatigue (variations of arousal levels related to task underload and overload), and (6) combinations of these factors. Medical conditions, medication, alcohol, or drugs exacerbate drowsiness; however, the discussion in this report is limited to fatigue concepts. This report has two primary outputs: (1) definitions and discussions of key terms concerning driver drowsiness and fatigue, and (2) basic information on measuring drowsiness and fatigue and its effects on the safe
Driver Metrics, Performance, Behaviors and States Committee
A deep-learning powered single-strained electronic skin sensor can capture human motion from a distance. The single strain sensor placed on the wrist decodes complex five-finger motions in real time with a virtual 3D hand that mirrors the original motions. The deep neural network boosted by rapid situation learning (RSL) ensures stable operation regardless of its position on the surface of the skin.
ABSTRACT The investigation presented in this paper is part of the project VARI-SPEED which aims to invent a speed variable drivetrain for different rotorcraft configurations. A kinematic and a mass analysis of compound split transmissions (CS) variations and a rotorcraft drivetrain simulation model to analyze the dynamic behavior during rotor speed change were performed. All solutions have the same power flow in the variator path but different fixed carrier transmission ratios of the planetary gears, which lead to a difference in mass. CS can be used as two speed transmissions and as continuous variable transmissions (CVT). As a two speed transmission less torque and friction energy is induced in the clutches than in a double clutch transmission, but CVT enable a smooth transition with no friction losses. CS offer the opportunity to vary rotor speed which decreases the overall power demand and lead to a more ecologically efficient rotorcraft aviation.
Amri, HannsHartenthaler, KatharinaWeigand, Michael
ABSTRACT This paper focuses on systematic time-averaged thrust and power measurements to characterize the effect of rotor geometry on the performance of a cycloidal rotor operating at Reynolds numbers between 100,000 and 300,000. A cycloidal rotor is a revolutionary horizontal-axis propulsion device that has proven to benefit from increased maneuverability and aerodynamic efficiency at micro air vehicle (MAV) scales. The current study aims to investigate cycloidal rotor performance at significantly larger UAV-scales. Towards this, experiments were conducted for a range of rotational speeds across different blade pitch amplitudes for rotor configurations with varying airfoils, blade spans, chord-by-radius ratios, and number of blades. The study found that the optimal pitch amplitude for symmetric pitch kinematics was highly dependent on the configuration due to changes in rotor inflow and flow curvature effects. An airfoil thickness as high as 25% of chord was capable of efficiently
Kellen, AdamBenedict, Moble
ABSTRACT This study provides the first in-depth analysis of the formation, strength, and convection of cycloidal rotor tip vortices. The blade force and PIV-based tip-vortex measurements were conducted for different blade aspect ratios and pitch kinematics in water at a chord Reynolds number of 18,000. Two phase-locked PIV configurations were utilized to investigate the flow field induced by the cyclorotor blade: (1) a laboratory-fixed field of view to enable investigation of vortex development at increasing vortex ages, and (2) a blade-fixed field of view to investigate the early development of the wingtip vortex at fixed 2° vortex age for varying azimuthal locations. The instantaneous blade force measurements on the cycloidal rotor showed a decrease in lift coefficient with decreasing blade aspect ratio. This is due to the higher peak swirl velocity of the tip vortex produced by the low AR blade, thereby resulting in higher induced downwash along the blade span. The aspect ratio of
McElreath, JamesBenedict, MobleTichenor, Nathan
ABSTRACT This paper describes the development of a biomimetic robotic hummingbird that utilizes biologically inspired wing kinematic modulation strategies for active stability and control. By tilting the flapping planes, varying the relative wing flapping amplitude, and shifting the mean position of the flapping stroke, the robotic hummingbird is able to modulate the magnitude, direction, and location of the lift vector of each of the wings in the same way that hummingbirds do to maneuver and stabilize themselves. In addition to the control strategies, biologically inspired, flexible, aeroelastically tailored wings were developed for use on the vehicle. Flight tests were conducted in which the vehicle was flown in a controlled hover using combinations of control techniques to quantify the effectiveness of each in stabilizing the vehicle. In the present study, emphasis was placed on pitch control, where two different control strategies were investigated, which were (1) pure tilting of
Coleman, DavidBenedict, Moble
Motion sickness in road vehicles may become an increasingly important problem as automation transforms drivers into passengers. Motion sickness could be mitigated through control of the vehicle motion dynamics, design of the interior environment, and other interventions. However, a lack of a definitive etiology of motion sickness challenges the design of automated vehicles (AVs) to address motion sickness susceptibility effectively. Few motion sickness studies have been conducted in naturalistic road-vehicle environments; instead, most research has been performed in driving simulators or on motion platforms that produce prescribed motion profiles. To address this gap, a vehicle-based experimental platform using a midsize sedan was developed to quantify motion sickness in road vehicles. A scripted, continuous drive consisting of a series of frequent 90-degree turns, braking, and lane changes were conducted on a closed track. The route was selected to be representative of naturalistic
Jones, Monica Lynn HaumannSienko, KathleenEbert-Hamilton, SheilaKinnaird, CatherineMiller, CarlLin, BrianPark, Byoung-KeonSullivan, JohnReed, MatthewSayer, James
ABSTRACT This paper provides a fundamental understanding of the unsteady aerodynamic phenomena on a cycloidal rotor blade operating at ultra-low Reynolds numbers (Re∼18,000) by utilizing a combination of experimental (force and flowfield measurements) and computational (CFD) studies. For the first time ever, the instantaneous blade fluid dynamic forces on a rotating cyclorotor blade were measured, which, along with PIV-based flowfield measurements revealed the key fluid dynamic mechanisms acting on the blade. A 2D CFD analysis of the cycloidal rotor was developed and systematically validated using both force and flowfield measurements. Studies were performed with both static and dynamic blade pitching. Direct comparison of the static and dynamic pitch experimental results helped isolate the unsteady phenomena (such as dynamic stall, unsteady virtual camber, etc.) from the steady effects. The dynamic blade force coefficients were almost double the static ones clearly indicating the role
Walther, CarolynLakshminarayan, VinodColeman, DavidBenedict, Moble
Items per page:
1 – 50 of 320