Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session D16: Aerodynamics: Control |
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Chair: Samik Bhattacharya, Queen's University Room: 204 |
Sunday, November 22, 2015 2:10PM - 2:23PM |
D16.00001: The effect of acceleration on the growth and shedding of laminar separation bubbles Samik Bhattacharya, David Rival It has been observed that when a laminar boundary layer separates, the shear layer undergoes transition to turbulence and subsequently reattaches to form a laminar separation bubble (LSB). In this work, a SD7003 airfoil, held at an angle of attack of 8 degree, is towed with different acceleration profiles starting from rest. The separation region is then analyzed with time-resolved, planar PIV at short convective times during the initial acceleration phase. The aim of this work is to characterize the variation in size and shedding frequency of the laminar separation bubble with increasing acceleration. We show that the formation and shedding process in the LSB depends on the rate of vorticity-containing mass transported by the separated shear layer. Consequently, any changes in the structure of the shear layer affect the formation of the LSB downstream. Finally, attempts are also made to characterize the shedding frequency of the bubble with increasing acceleration. Here the unsteadiness of the LSB is found to be closely linked to the degree of boundary-layer acceleration on the airfoil surface. [Preview Abstract] |
Sunday, November 22, 2015 2:23PM - 2:36PM |
D16.00002: A new plasma-driven pulsed jet actuator for flow control Jean-Paul Bonnet, Gwenael Acher, Anton Lebedev, Nicolas Benard, Eric Moreau Active flow control requires actuators with enough authority and high frequency response. Synthetic jets can have high frequency response but are rather limited in terms of authority providing the exit velocity is limited. Pressurized (flowing) jets have a very high potential in terms of authority particularly for high velocity flow control purposes. However, for most purposes, high frequency modulation (of order of several kHz) is required in order to excite most unstable modes and to operate in closed mode. Rapid mechanical valves are limited in terms of frequency (up to typically a few hundred of Hz). We develop a new generation of plasma-driven pulsation of flowing jet. The principle is to increase the temperature at the sonic throat through a plasma discharge located at the throat. The flow rate being proportional to the square root of the temperature for a perfect gas, for the same settling chamber pressure, the actuator flow rate can be varied. The frequency is then no limited by any mechanical constraint. A demonstrator has been tested with a 1mm sonic throat. The electric discharge is created by a 10 kV voltage applied between the anode and the throat acting as the cathode. Within these conditions, a 30{\%} modulation of the flow rate can be obtained. [Preview Abstract] |
Sunday, November 22, 2015 2:36PM - 2:49PM |
D16.00003: Large-Eddy Simulations of Plasma Flow Control on a GOE735 Wind Turbine Airfoil Alexander Czulak, Jennifer Franck Active flow control using plasma actuation was studied for the GOE735 airfoil and compared to non-actuated baseline cases using numerical simulations. This investigation considers two-dimensional simulations at a Reynolds number of 1,000 using direct numerical simulation (DNS) as well as three-dimensional simulations at a Reynolds number of 50,000 and 100,000 using large-eddy simulation (LES). Plasma actuation is applied in terms of a source term within the boundary layer close to the airfoil surface. Angles of attack of 0$^{\circ}$, 5$^{\circ}$ and 15$^{\circ}$ were considered, and control is shown to be effective at increasing the lift coefficient, decreasing the drag coefficient and reducing the root mean squared deviation of both lift and drag. An analysis of the flow physics reveals that the actuated cases delay the point of separation, reduce the wake width and diminish the size and strength of the shed vortices. For this particular airfoil, there are significant differences in Reynolds number in terms of the baseline flow, control effectiveness and performance factors such as lift and drag. [Preview Abstract] |
Sunday, November 22, 2015 2:49PM - 3:02PM |
D16.00004: Effects of actuation waveform shape on the performance of pitching and heaving panels Daniel Floryan, Tyler Van Buren, Clarence W. Rowley, Alexander J. Smits Experiments on panels pitching and heaving in a water channel are reported. The panels are rigid, of rectangular planform shape, and the flow is nominally two-dimensional. Through the use of Jacobi elliptic functions, we are able to actuate the panels in non-sinusoidal and asymmetric motions; we investigate how such motions affect the propulsive performance of the panels. Direct force measurements are taken using a six component force/torque sensor, and certain cases are supplemented with two-dimensional particle image velocimetry (PIV) taken at the mid-span of the panel; efficiency measurements are also reported. [Preview Abstract] |
Sunday, November 22, 2015 3:02PM - 3:15PM |
D16.00005: Experimental Study of the Effects of Blade Treatments on the Tip Vortex Characteristics. Vera Klimchenko The current study investigates the effects of blade tip treatments on the characteristics of a wind turbine blade tip vortex. Three blade tip shapes including a blunt edge, leading edge comb, and a winglet were designed and tested in a low speed wind tunnel. The rotor with a blunt edge was considered to be a baseline case corresponding to an untreated blade tip. The leading-edge comb rotor was designed with leading edge tubercles extending from the tip of the blade inward, 6 percent of rotor diameter. The winglet located at the tip of the winglet rotor had a cant angle of 45 degrees. The wind turbine operated at a tip speed ratio of 5 and a tip Reynolds number of 14,000. The tip treatments were intended to weaken the tip vortices by encouraging dissipation (leading edge comb) or promoting the formation of weaker vortices (winglet). Time-resolved and phase-averaged PIV was used to measure the velocity field behind the rotor. The time-averaged velocity field was subtracted from the phase-averaged velocity field to isolate the time-varying components of the flow. The vorticity of the phase-averaged time-varying field was calculated, and the tip vortices were identified using a vortex identification method. Vortex characteristics such as core radius and vortex strength were calculated and compared for the three rotors. The analysis of the vorticity showed that the winglet rotor had weaker tip vortices with a larger core radius, while the serrated tip rotor had strong tip vortices with the same core radius as the baseline case. [Preview Abstract] |
Sunday, November 22, 2015 3:15PM - 3:28PM |
D16.00006: Adjoint-based optimal control of an airfoil in gusting flows Jeesoon Choi, Tim Colonius In this study, we apply optimal control to an airfoil in gusting flow to investigate the possibility of extracting energy. The gradients~of an objective function are obtained via the adjoint method and used to minimize the cost. The immersed boundary~projection method~is used for our forward solver, and the~relevant~adjoint equations are derived by the discrete-then-differentiate approach. Translational~gusts are generated by a body force in the computational domain upstream to the body, and the method finds the optimal angles of the airfoil that exploits~the greatest amount of energy. The influence of a vortex traversing an airfoil is also investigated and optimized to reduce the fluctuating lift. [Preview Abstract] |
Sunday, November 22, 2015 3:28PM - 3:41PM |
D16.00007: Aerodynamics of ski jumping flight and its control: I. Experiments Daehan Jung, Kyeongtae Bang, Heesu Kim, Eunhye Ahn, Haecheon Choi In a ski jumping competition, it is essential to analyze the effect of various posture parameters of a ski jumper to achieve a longer flight distance. For this purpose, we construct a model of a ski jumper by using three-dimensional surface data obtained by scanning a ski jumper’s body (Mr. Chil-Ku Kang, member of the Korean national team). An experiment on this model is conducted in a wind tunnel. We consider four posture parameters (forward leaning angle, ski opening angle, ski rolling angle, and ski spacing) and measure the drag and lift forces for various flight postures at various angles of attack ($\alpha$ = 0$^{\circ}$ - 40$^{\circ}$) and Reynolds numbers (Re = 5.4 $\times$ 10$^{5}$ - 1.6 $\times$ 10$^{6}$) based on the length of the jump ski. Then, we derive optimum values of posture parameters for maximum lift-to-drag ratio using a response surface method. We also conduct a full-scale wind tunnel experiment with members of the Korean national team and confirm the results obtained from the experiment on the model. [Preview Abstract] |
Sunday, November 22, 2015 3:41PM - 3:54PM |
D16.00008: Aerodynamics of ski jumping flight and its control: II. Simulations Jungil Lee, Hansol Lee, Woojin Kim, Haecheon Choi In a ski jumping competition, it is essential to analyze the effect of various posture parameters of a ski jumper to achieve a longer flight distance. For this purpose, we conduct a large eddy simulation (LES) of turbulent flow past a model ski jumper which is obtained by 3D scanning a ski jumper's body (Mr. Chil-Ku Kang, member of the Korean national team). The angle of attack of the jump ski is 30$^{\circ}$ and the Reynolds number based on the length of the jump ski is 540,000. The flow statistics including the drag and lift coefficients in flight are in good agreements with our own experimental data. We investigate the flow characteristics such as the flow separation and three-dimensional vortical structures and their effects on the drag and lift. In addition to LES, we construct a simple geometric model of a ski jumper where each part of the ski jumper is modeled as a canonical bluff body such as the sphere, cylinder and flat plate, to find its optimal posture. The results from this approach will be compared with those by LES and discussed. [Preview Abstract] |
Sunday, November 22, 2015 3:54PM - 4:07PM |
D16.00009: Parametric Study of Synthetic-Jet-Based Flow Control on a Vertical Tail Model Marianne Monastero, Annika Lindstrom, Michael Beyar, Michael Amitay Separation control over the rudder of the vertical tail of a commercial airplane using synthetic-jet-based flow control can lead to a reduction in tail size, with an associated decrease in drag and increase in fuel savings. A parametric, experimental study was undertaken using an array of finite span synthetic jets to investigate the sensitivity of the enhanced vertical tail side force to jet parameters, such as jet spanwise spacing and jet momentum coefficient. A generic wind tunnel model was designed and fabricated to fundamentally study the effects of the jet parameters at varying rudder deflection and model sideslip angles. Wind tunnel results obtained from pressure measurements and tuft flow visualization in the Rensselaer Polytechnic Subsonic Wind Tunnel show a decrease in separation severity and increase in model performance in comparison to the baseline, non-actuated case. The sensitivity to various parameters will be presented. [Preview Abstract] |
Sunday, November 22, 2015 4:07PM - 4:20PM |
D16.00010: Numerical Investigation of Bending-Body Projectile Aerodynamics for Maneuver Control Eric Youn, Sidra Silton Precision munitions are an active area of research for the U.S. Army. Canard-control actuators have historically been the primary mechanism used to maneuver fin-stabilized, gun-launched munitions. Canards are small, fin-like control surfaces mounted at the forward section of the munition to provide the pitching moment necessary to rotate the body in the freestream flow. The additional lift force due to the rotated body and the canards then alters the flight path toward the intended target. As velocity and maneuverability requirements continue to increase, investigation of other maneuver mechanisms becomes necessary. One option for a projectile with a large length-to-diameter ratio (L/D) is a bending-body design, which imparts a curvature to the projectile body along its axis. This investigation uses full Navier-Stokes computational fluid dynamics simulations to evaluate the effectiveness of an 8-degree bent nose tip on an 8-degree bent forward section of an L/D$=$10 projectile. The aerodynamic control effectiveness of the bending-body concept is compared to that of a standard L/D$=$10 straight-body projectile as well as that of the same projectile with traditional canards. All simulations were performed at supersonic velocities between Mach 2--4. [Preview Abstract] |
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