Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session A30: Aerodynamics: Flow Control |
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Chair: Godfrey Mungal, Santa Clara University Room: 2016 |
Sunday, November 23, 2014 8:00AM - 8:13AM |
A30.00001: On the Efficiency of Fluidic Oscillators for Aerofoil Performance Recovery Dima Sarkorov, Avraham Seifert The paper describes a recent experiment in which the Suction and Oscillatory blowing (SaOB) actuator was used to control the flow on a thick, turbulent, trailing edge separating aerofoil. The Reynolds number range is 0.5 to 1.5 million. The experiment deals with performance recovery of a thick aerofoil in laminar and turbulent flow conditions. Performance was significantly degraded due to premature boundary layer separation. An array of 12 SaOB actuators was used to effectively restore lift and reduce drag. Overall system efficiency was increased in both turbulent and laminar flow conditions. The AFC outlets, located at 20{\%} chord location were shown to supplement or even being capable of replacing a slat. [Preview Abstract] |
Sunday, November 23, 2014 8:13AM - 8:26AM |
A30.00002: Nearfield Flow Topology of a Rounded Wingtip Subject to Circulation Control Adam Edstrand, Louis Cattafesta Trailing vortices are an adverse byproduct of lift causing induced drag, accounting for 40\% of the total drag on aircraft, and impose a wake hazard on trailing aircraft (Spalart 1998). The metric used to quantify the wake hazard is the average maximum swirl velocity measured in a velocity snapshot. Circulation control uses tangential blowing along a rounded surface, causing the flow to wrap around the surface. This control methodology is extended to a NACA 0012 wingtip by blowing tangentially over a rounded wingtip to control the circulation of the trailing vortex. Stereo particle image velocimetry measurements are acquired along the chord and downstream of the wingtip to characterize the effects of circulation control on vortex formation and evolution. Compared to the baseline case, the vortex core develops along the upper surface of the airfoil further upstream. This upstream development causes more rapid spatial growth of the vortex, resulting with a larger, less intense vortex than the baseline case. However, the circulation, five chords downstream of the leading edge, increases rather than decreases. This increase implies that favorable control of the circulation does not occur. However, there is a 30\% reduction in the wake hazard metric due to the increased vortex size. [Preview Abstract] |
Sunday, November 23, 2014 8:26AM - 8:39AM |
A30.00003: DBD Control of a Turbulent Shear Layer downstream of a Backward Facing Step Jean Paul Bonnet, Patricia Sujar-Garrido, Nicolas Benard, Eric Moreau An open loop control of a turbulent free shear layer downstream of a backward-facing-step at Re 3x10$^{4}$ is performed via a single Dielectric Barrier Discharge (DBD). Several actuation locations are tested, the best result being observed at the hinge of the step. Nanosecond DBD have been tested with no efficiency on the location of the reattachment location. By using AC DBD, a linear evolution of the reattachment is observed. Optimization of frequency, duty cycle and voltage amplitude is performed. An optimal frequency is observed and it is shown that the plasma discharge is able to manipulate the first stages of the formation of the free shear layer and consequently to modify the flow dynamics of the entire flow, with a regularization of the vortex shedding frequency. [Preview Abstract] |
Sunday, November 23, 2014 8:39AM - 8:52AM |
A30.00004: ABSTRACT WITHDRAWN |
Sunday, November 23, 2014 8:52AM - 9:05AM |
A30.00005: The effect of large aspect ratio wing yaw on active separation control Philipp Tewes, Lutz Taubert, Israel Wygnanski The applicability of the boundary layer independence principle to turbulent boundary layers developing on infinitely yawed wings, suggested that active separation control might be carried out differently to the two presumably independent developing boundary layers. At low incidence or flap deflection the control of the spanwise component of the flow is effective provided the aggregate number of actuators is small. In this case the actuator jets provide jet-curtains that virtually eliminate the spanwise flow component of the flow in their vicinity. At higher incidence or flap deflection, the focus of the active separation control has to shift to the chordwise component that has to overcome a high adverse pressure gradient. The idea was proven experimentally on a flapped wing based on a NACA 0012 airfoil that could be swept back and forward while being suspended from a ceiling of a wind tunnel connected to a six-component balance. The experiments were carried out at Reynolds numbers varying between 300,000 and 500,000. [Preview Abstract] |
Sunday, November 23, 2014 9:05AM - 9:18AM |
A30.00006: Experimental measurements on a single sweeping jet Damian Hirsch, Emilio Graff, Morteza Gharib ``Sweeping jets'' proved their effectiveness as Active Flow Control (AFC) actuators in improving the performance of vertical tails of generic and full-scale models. To gain further knowledge about the fundamental flow physics, the jets were investigated experimentally. The influence of a single jet on its surroundings was studied, especially the entrainment region. The results were compared to previous experiments to study the difference between a single isolated jet and multiple jets mounted on a vertical tail. [Preview Abstract] |
Sunday, November 23, 2014 9:18AM - 9:31AM |
A30.00007: The role of the vorticity field on the increase of drag forces during impulsive deployment of a rectangular flow actuator inside TBL Amir Elzawawy, Yiannis Andreopoulos An experimental Time Resolved PIV data is used to evaluate the significant role of the vorticity field on aerodynamic forces during an impulsive deployment of a 100x100 mm2 flow actuator. In this experiment, the flow actuator is placed inside TBL flow, while it is suddenly deployed, $\omega =$ 17 rad/s, against the incoming TBL flow with free stream air velocity of 3.7 m/s. The experiments data has shown a significant increase of drag forces during the impulsive deployment compared with the drag of those stationary actuator cases. In this work, a further analysis is carried out using vorticity moments-based relations of forces of finite bodies exerted by incompressible fluid flows (Wu et al. 2006). These formulations, which shown to be suitable for use with TR-PIV data, are used here to identify the role of the generated vorticity field on the increase of the drag. Only three terms out of the seven terms showed significant contribution to the drag forces enhancement. Two of those were dependent on the vorticity field; the first term represents volume integral of rate of change of the first moment of the vorticity. The second term, which showed a negative contribution to the increase of drag, was the volume integral of the Lamb force. The third term represents the inertia effects at the accelerating boundaries. This identification of the role of each term can provide a basic understanding to the role of the vorticity field and may help in flow actuator design process to obtain enhanced aerodynamics forces with impulsive motion. [Preview Abstract] |
Sunday, November 23, 2014 9:31AM - 9:44AM |
A30.00008: Fluidic Control of Flexible Structures Embedded in a Turbulent Boundary Layer Ori Friedland, Victor Troshin, Avi Seifert We investigate experimentally the flow around a flexible rectangular thin plate positioned normal to the wind direction and embedded in a thick turbulent boundary layer. The purpose of the study is to reduce the plate oscillations caused by unsteady wind loads. Two methods were tested. First, by mechanical Piezo-electric actuators attached to the plate. Second, by three mass-less Piezo-electric fluidic actuators. The two methods were applied with similar closed-loop control principles: Strain Gauge (SG) sensors captured the plate oscillations and a simple phase-lag and gain was used to attenuate the oscillations. The results show a 20-30{\%} reduction of the plate oscillations by mechanical control and a 30{\%}-40{\%} attenuation of the plate oscillation, compared to the uncontrolled case, using fluidic actuators positioned around the free-end flow separation points. The fluidic control was found to be superior to the mechanical control for the current application and conditions. We Hypothesize flow physics mechanism that link the unsteady pressures created on the plate by actuation to its oscillations. [Preview Abstract] |
Sunday, November 23, 2014 9:44AM - 9:57AM |
A30.00009: Hybrid flow control of a transport truck side-mirror using AC-DBD plasma actuated guide vane Theodoros Michelis, Marios Kotsonis A wind-tunnel study is conducted towards hybrid flow control of a full-scale transport truck side-mirror $(Re=4\times 10^5)$. The mirror is mounted on a structure that models the truck cabin. PIV measurements are performed at a range of velocities from 15 to 25m/s and from leeward to windward angles of $-5^\circ$ to $+5^\circ$. A slim guide vane of 6cm chord is employed along the span of the hub of the mirror for redirecting high momentum flow towards the wake region. Separation from the leading edge of the guide vane is reduced or eliminated by means of AC-DBD plasma actuator, operating at voltage of 35kV peak-to-peak and frequency of 200Hz. Time-averaged velocity fields are obtained at the centre of the mirror for three scenarios: a) reference case lacking any control elements; b) guide vane only and c) combination of the guide vane and the AC-DBD. The comparison of cases demonstrates that at 25m/s windward conditions $(-5^\circ)$ the guide vane is capable of increasing momentum (+20\%) in the wake of the mirror with additional improvement when plasma actuation is applied (+21\%). In contrast, at leeward conditions $(+5^\circ)$, the guide vane reduces momentum (-20\%), though with actuation an increase is observed (+5\%). Total recovered momentum is 25\%. [Preview Abstract] |
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