Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session FM: Aerodynamics |
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Chair: David Williams, Illinois Institute of Technology Room: Hilton Chicago PDR 1 |
Monday, November 21, 2005 8:00AM - 8:13AM |
FM.00001: Control of Flow Structure and Topology on a Delta Wing of Low Sweep Angle via Trailing-Edge Blowing Mehmet Yavuz, Donald Rockwell The near-surface flow structure and topology are characterized on a low swept delta wing, which is subjected to trailing-edge blowing. A technique of high-image-density particle image velocimetry is employed to determine the topological critical points adjacent to the surface and in the near-wake of the wing, in relation to the dimensionless magnitude of the blowing coefficient. These topological features are, in turn, interpreted in conjunction with patterns of surface-normal vorticity and near-surface velocity fluctuations, which provide an indication of buffet loading. Even though the jet blowing is at the trailing-edge, it has a remarkable, global influence on the surface patterns located well upstream; at high angle-of-attack, it leads to eradication of large-scale, three-dimensional separation in the vicinity of the apex. Further investigation of the effect of trailing-edge blowing involves topological patterns in crossflow planes above the surface of the wing, which relate the structure of the leading-edge vortices to the existence of three-dimensional surface separation, as well as other features along the wing surface. [Preview Abstract] |
Monday, November 21, 2005 8:13AM - 8:26AM |
FM.00002: Plasma Flow Control Optimized Airfoil Vladimir Voikov, Thomas Corke, Chuan He, Benjamin Mertz, Mehul Patel Recent advances in flow control research have demonstrated that plasma actuators can be efficient in different aerodynamic applications, particularly in providing flight control without conventional moving surfaces. The concept involves the use of a laminar airfoil design that employs a separation ramp at the trailing edge that can be manipulated by a plasma actuator to control lift, similar to trailing-edge flaps. The advantages are lower drag by a combination of the laminar flow design, and elimination of parasitic drag associated with wing-flap junctions. This work involves numerical simulations and experiments on a HSNLF(1)-0213 airfoil. The numerical results are obtained using an unsteady, compressible Navier-Stokes simulation that includes a model for the plasma actuators. The experiments are performed on a 2-D airfoil section that is mounted on a lift-drag force balance. The results demonstrate lift enhancement produced by the plasma actuator that is comparable to a plane flap. They also reveal an optimum actuator unsteady frequency that scales with the length of the separated region and local velocity, and is associated with the generation of a train of spanwise vortices. Other scaling including the effect of Reynolds number is presented. [Preview Abstract] |
Monday, November 21, 2005 8:26AM - 8:39AM |
FM.00003: Wing Warping, Roll Control and Aerodynamic Optimization of Inflatable Wings Andrew Simpson, Suzanne Smith, Jamey Jacob The research presents work on aerodynamic control by warping inflatable wings. Inflatable wings are deformable by their nature. Mechanical manipulation of the wing's shape has been demonstrated to alter the performance and control the vehicle in flight by deforming the trailing edge of the wing near the wing tip. Predicting and correlating the forces required in deforming the wings to a particular shape and the deformation generated for a given internal pressure were conducted through the use of photogrammetry. This research focuses on optimizing the roll moments and aerodynamic performance of the vehicle, given the current level of wing warping ability. Predictions from lifting line theory applied to wing shape changes are presented. Comparisons from the experimental results are made with lifting line analysis for wings with arbitrary twist and the solutions are used to determine rolling moment and optimum L/D. Results from flight tests will also be presented. [Preview Abstract] |
Monday, November 21, 2005 8:39AM - 8:52AM |
FM.00004: Toward an Autonomous Micro-Air Vehicle Wing Tamanika Martin, Antoine Guitton, Mark Glauser, Ryan Schmit The purpose of the current research is to develop a Micro-Air Vehicle wing that actively responds to wind gusts. As a first step in this approach, it is necessary to estimate the flow conditions in the immediate vicinity of the wing. Previous estimation procedures have included the use of low dimensional tools such as the POD, LSE, and the Complementary techniques. The heart of Complementary technique lies in its ability to use dynamic strain measurements from the wing to estimate the velocity flow field, and having demonstrated this ability, we now use piezoelectric actuators to actively change the structural dynamics of the wing. When comparing the strain spectrum from the MAV wing between measurements made both with and without piezoelectric actuation, we find that we are able to change the strain spectrum in such a way to suggest that we can obtain significant control authority of the structural dynamics of the wing. Although the fore mentioned control authority was established in an open loop sense, we aim toward the development of a closed feedback control loop, wherein the MAV Wing will be able to autonomously change its shape when encountering wind gusts. [Preview Abstract] |
Monday, November 21, 2005 8:52AM - 9:05AM |
FM.00005: Generalizing the Kutta-Joukowski theorem to multiple aerofoils: an analytical approach Darren Crowdy A basic result of inviscid fluid dynamics is the Kutta-Joukowski theorem giving a formula for the lift on a single aerofoil, of arbitrary shape, in a steady streaming flow. What is the generalized result for multiple aerofoils? In the latter case, interference effects between aerofoils render the problem non-trivial both physically and mathematically. The respective lift forces are now delicate functions of the geometry of the aerofoil components and their global spatial configuration. Despite this complication, it turns out that the complex potential for uniform flow past multiple aerofoils, with circulation, can be found in analytical form. This talk will describe a new analytical approach to such problems which generalizes, to the case of an arbitrary finite number of aerofoils, the classical result for biplane (i.e. two) aerofoils due to Lagally (1929). Numerous examples will be given. [Preview Abstract] |
Monday, November 21, 2005 9:05AM - 9:18AM |
FM.00006: Dynamic Lift of Airfoils Stephan Barth, Thomas Bohlen, Rene Grueneberger, Joachim Peinke We present initial wind tunnel measurements which investigate the dynamic stall effect as it is caused by fluctuations of the wind direction in turbulent wind. In order to quantify this effect, the lift of an FX79-W-151A airfoil is determined by the integral of pressure distribution at the wind tunnel walls while rotating the airfoil with defined angular velocity. The rotation speed is varied by numeric control. The pressure measurement is performed by two sets of 40 pressure sensors. The temporal resolution is in the range of msec. For stochastic analysis the experiment is repeated several hundred times. In contrast to static lift values, there is an increase (overshoot) of lift before flow separation on the suction side occurs. The lift magnitude depends on the rate of change of the airfoil's angle of attack. This knowledge is relevant for the estimation of extreme mechanical loads for wind turbine blades. [Preview Abstract] |
Monday, November 21, 2005 9:18AM - 9:31AM |
FM.00007: Classification of Airfoils by Abnormal Behavior of Lift Curves at Low Reynolds Number Sutthiphong Srigrarom, Chi-Seng Lee, Di-Bao Wang, Fei-Bin Hsiao, Yen-Hock Lim Flow phenomena at low Reynolds number in the region of 104$\sim $105 are more complicated than those occurring at high Reynolds number. They present unfavorable aerodynamics characteristics and, they are poorly understood. This paper tries to classify airfoils according to the type of pattern showed by its corresponding lift coefficient (Cl) curve. Preliminary study of over 45 published airfoils data reveals that the shape of Cl curve is strongly related to the combination of airfoil's maximum thickness (t/c), camber, and the shape of the trailing edge. It was also observed that increasing the camber and leading edge radius would result in the transition of lift behavior from one trend to another. We determine the reasons contributing to the abnormal behaviors of the lift curves for various airfoils by investigating their flow line plots using a computational fluid dynamics (CFD) program and find common physical parameters between airfoils that may lead to the display of similar undesired characteristics in their lift curves. Results indicated that the formation of a long trailing edge separation bubble would induce a drastic drop in the lift coefficient due to the collapse of the suction peak and the formation of a short leading edge separation bubble would lead to a sudden jump in the lift coefficient. The trailing edge angle also played a significant role in determining the lift characteristics of an airfoil. [Preview Abstract] |
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