Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session L09: Aerodynamics: Flow Control |
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Chair: Elias Balaras, George Washington University Room: 213 |
Monday, November 25, 2019 1:45PM - 1:58PM |
L09.00001: Control of the Aerodynamic Loads on a 3-D Wing using Distributed Active Bleed M.E. Desalvo, D. Heathcote, M. Smith, A. Glezer The aerodynamic loads on a 3-D wing with a trailing-edge flap are controlled in wind tunnel experiments using active distributed bleed of ambient air that is driven through arrays of surface openings by the inherent pressure differences between the pressure and suction surfaces and regulated by integrated lateral louvers. Interaction between the bleed and the local cross flow over the surface induces large-scale changes in the global flow field which lead to direct modification of the aerodynamic loads and thereby can augment conventional electromechanical control surfaces without changing angle of attack or flap deflection. The present investigations focus on unsteady aerodynamic effects associated with temporal modulation of the bleed through different spanwise segments of the wing over a range of angles of attack and flap deflections. Stereo PIV measurements of the wake acquired phase-locked to the actuation in a streamwise- normal plane downstream of the model show the temporal effects of bleed on distributions of streamwise vorticity (including the tip vortex) and on the spanwise loading of the wing. [Preview Abstract] |
Monday, November 25, 2019 1:58PM - 2:11PM |
L09.00002: A numerical study on the delay of airfoil stall by traveling wave surface morphing Amir Akbarzadeh, Iman Borazjani Surface morphing is found to be an energy efficient active flow control technique. While these morphings are, typically, in the form of a simple vibration or a standing wave, a traveling wave morphing might to be more effective because traveling wave oscillations are thought to reattach the flow over aquatic swimmers and bluff bodies. Large eddy simulations (LES) of flow over a low Reynolds number (Re$=$50,000) airfoil at stall angle, which has a oscillatory suction side, are performed to investigate the effect of the morphing function, i.e., backward traveling waves, standing waves, and forward traveling waves, on reducing flow separation. In addition, the effects of frequency and amplitude of the wave are investigated. It has been observed that backward traveling waves can be more effective than other types of oscillations, including forward traveling waves and standing waves. [Preview Abstract] |
Monday, November 25, 2019 2:11PM - 2:24PM |
L09.00003: Characterizing Prescribed Surface Morphing for Aerodynamic Flows: Mechanistic Insights for Control Kevin Triner, Andres Goza Robust and efficient flow control is key to improving the maneuverability and disturbance rejection of micro- and unmanned aerial vehicles. Previous and current actuation strategies to achieve this aim include zero-net mass flux (synthetic), plasma, and combustion actuators. We investigate an alternative actuation framework in which prescribed deformations are imposed along the suction surface of the airfoil. This prescribed surface morphing, which is a variant of the actuation methodology suggested by Jones \textit{et al.} (2016), is designed to take the form of a traveling wave. This actuation strategy is promising because it has the ability to affect flow over the entire suction surface of the airfoil, and is not limited to specific streamwise locations. We use high-fidelity nonlinear simulations to quantify the effect of the surface morphing wave speed, frequency, and wave length on the aerodynamic performance of a 2D airfoil. The effect of morphing parameters is characterized in terms of the relationship between morphing kinematics, flow structures, and aerodynamic forces. These relationships are then used to synthesize surface morphing behavior that is beneficial to aerodynamic performance. [Preview Abstract] |
Monday, November 25, 2019 2:24PM - 2:37PM |
L09.00004: Transitory, Bi-Directional Control of the Aerodynamic Loads on an Airfoil in an Attached Flow Yuehan Tan, A. Glezer, R. Patterson, P. Friedmann The aerodynamic loads on a VR-12 airfoil are regulated bi-directionally to enable mitigation of structural vibrations when the base flow is fully-attached by using pulsed fluidic control upstream of the trailing edge. Actuation is effected using independently controlled high aspect ratio bi-stable, fluidically-switched actuation jets on the pressure and suction surfaces at nominally 0.88c. The transitory actuation temporally manipulates the circulation around the airfoil and its Kutta condition yielding changes in the aerodynamic loads. For example, it is shown that time-invariant actuation on the pressure and suction surfaces can lead to respective lift increments ΔCL of up to +0.73 and -0.65 with relatively low drag penalty. The transitory characteristics of the aerodynamic loads to pulsed actuation are investigated with specific emphasis on the initial response following the onset of the actuation along with corresponding unsteady vortex shedding near the trailing edge using phase-locked particle image velocimetry. Supported by [Preview Abstract] |
Monday, November 25, 2019 2:37PM - 2:50PM |
L09.00005: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 2:50PM - 3:03PM |
L09.00006: Manipulation of Streamwise Vortices by Air Injection on Trapezoidal Vane-Type Vortex Generators. Giovanni Nino, Lucas Weber, Robert Breidenthal This work investigated the feasibility of manipulating a streamwise vortex position by injecting pressurized air through the leading edge of a trapezoidal vortex generator (VG). The VGs were tested on a miniature wind tunnel.~ A pressure sensor was mounted on a two-dimensional traverse to gather dynamic pressure cross sections downstream of the vortex generator. From these pressure profiles, the vortex position was measured to determine the influence of the air injection. Supplied air pressure was varied as well as the location of the injection at three different positions along the leading edge. In addition, vortex generators with small round holes as injection ports as well as rectangular slots were investigated. Experimental results showed that injection at different VG leading-edge positions were able to displace the vortex in a controllable way. [Preview Abstract] |
Monday, November 25, 2019 3:03PM - 3:16PM |
L09.00007: Passive drag reduction on a sphere using polyhedral designs Nikolaos Beraltis, Kyle Squires, Elias Balaras It is established today that dimples are efficient in accelerating the drag crisis on a sphere reducing the drag coefficient at much lower Reynolds numbers when compared to a smooth sphere. Recently we reported Direct Numerical Simulations (DNS) demonstrating that the large difference in the minimum drag coefficient between a dimpled and smooth sphere in the post-critical regime comes from the dimples themselves as the flow separates and reattaches inside them. In this talk we propose a new class of geometries based on polyhedral designs resembling a faceted sphere. Wind tunnel testing and DNS demonstrate drag reduction by as much as $15\%$ compared to a typical dimpled sphere, without affecting the critical Reynolds number marking transition to the post-critical regime. We utilize the experiments establish the behavior of the drag coefficient as a function of the Reynolds number for different geometries and then use DNS for selected cases to obtain a detailed understanding of the flow physics. We will show important differences in the evolution of the boundary layers between a polyhedral and dimpled sphere as well as their wakes that reveal the underlying mechanism for the reduction in the drag coefficient. [Preview Abstract] |
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