Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session S23: Flow Control VII |
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Chair: Michael Amitay, Rensselaer Polytechnic Institute Room: 326 |
Tuesday, November 22, 2011 3:05PM - 3:18PM |
S23.00001: Synthetic Jets Flow Control on a vertical stabilizer Nicholas Rathay, Matthew Boucher, Michael Amitay The vertical stabilizer on most commercial transport aircraft is much larger than required for stability and control. The tail is significantly oversized in order to maintain controllability in the event of asymmetric engine failure and meet flying qualities requirements related to dynamic motion. Using aerodynamic flow control techniques, it may be possible to reduce the size of the tail while maintaining similar control authority during inclement flight conditions. Reducing the size of the tail decreases the weight and the drag of the airplane, which results in considerable savings in fuel costs. In this work, it is shown that synthetic jet (zero-net-mass-flux) actuators are capable of reattaching the separated flow on the rudder and augmenting the performance of the stabilizer. Experiments were conducted in an open-return wind tunnel on a 1/25th scale model of a vertical stabilizer and a partial fuselage section. The surface pressure, aerodynamic loads and data acquired with a Stereo PIV system were used to investigate the effectiveness of this technology as well as provide a more detailed analysis of the flowfield and showed that the synthetic jets are capable of augmenting the side-force by up to 20{\%}. [Preview Abstract] |
Tuesday, November 22, 2011 3:18PM - 3:31PM |
S23.00002: Interactions of a Propeller with a Circumferentially-Varying Flow John Farnsworth, Michael Amitay, David Beal, Stehpen Huyer The interactions of a circumferentially varying stator cascade and a downstream fixed pitch propeller were investigated experimentally in a water tunnel using the Stereoscopic PIV technique. A cyclic distribution of the stators' deflections resulted in non-axisymmetric distributions of the flow field downstream of the stator array. The stator distribution alone produced a significant side force that increased linearly with stator pitch amplitude. When a propeller was incorporated downstream from the cyclic cascade the side force from the stator cascade was reduced, but a small normal force and pitching moment were created. The generation of these secondary forces and moments can be related to the redistribution of the tangential flow from the cyclic cascade into the axial direction by the retreating and advancing blade states of the fixed pitch propeller. The Q criterion was utilized with measurements phase-locked to the propeller frequency to visualize the interactions of the vortical structures in the wake of the combined stator-propeller system. [Preview Abstract] |
Tuesday, November 22, 2011 3:31PM - 3:44PM |
S23.00003: On the Introduction of Unsteady Streaks into a Blasius Boundary Layer Using Dynamically Actuated Roughness Kyle Bade, Ahmed Naguib, Philippe Lavoie Observations of the spatio-temporal growth of streamwise elongated streaks emanating from a cylindrical roughness element undergoing dynamic actuation into/out of a Blasius boundary layer are presented. Hot-wire measurements provide 2D maps of the disturbance velocity of these streaks. Modal decomposition methods are performed on these maps to evaluate the nature of the temporal growth of the streaks. For this analysis, various roughness element actuation heights, velocities, and accelerations are examined in order to identify the ``dynamic-roughness'' actuation parameters range for which transiently growing streaks can be produced while avoiding the introduction of T-S wave packets and/or non-linearly-growing disturbances. The establishment of such streaks with 5-10{\%} disturbance magnitude will provide the basis for an experimental platform, and help develop efficient models for feedback bypass transition control in an ongoing study in collaboration with Princeton University. [Preview Abstract] |
Tuesday, November 22, 2011 3:44PM - 3:57PM |
S23.00004: Active Control of Vortex Induced Vibrations of a Tethered Sphere in a Uniform Air Flow Rene van Hout, David Greenblatt, Amit Zvi Katz VIV of two heavy tethered spheres ($D$ = 40 mm, $m^{\ast }$ = $m_{sphere}$/\textit{$\rho $}$_{f}V_{sphere}$ = 21 and 67, $L^{\ast }=L/D$ = 2.50) were studied in a wind tunnel under uniform free stream velocities up to $U^{\ast }=U$/$f_{n}D$ = 15.9, with and without acoustic control. Control was achieved using two speakers mounted on either side of the spheres and driven in-phase at $f $= 35Hz ($f^{\ast }$ = 22.3). In the non-controlled case, the bifurcation map of transverse sphere oscillation amplitude, $A_{y}$, showed stationary motion as well as periodic and non-stationary oscillations with increasing $U^{\ast }$. For $m^{\ast }$ = 21, $A_y^{\max } $ was about twice as large as for $m^{\ast }$ = 67. Acoustic control dampened $A_y^{\max } $ in the periodic region ($m^{\ast }$ = 67) and increased $A_y^{\max } $ in the non-stationary region for both spheres. Sphere boundary layer dynamics in the three different bifurcation regions were studied using time resolved PIV with a horizontal laser sheet positioned at the center of the sphere. The field of view was 55x55 mm$^{2}$ containing one quarter of the sphere. Results will be presented on the vortex dynamics near the sphere's surface with and without acoustic control. [Preview Abstract] |
Tuesday, November 22, 2011 3:57PM - 4:10PM |
S23.00005: Aero-Effected Flight Control Using Distributed Active Bleed John M. Kearney, Ari Glezer The aerodynamic effects of large-area air bleed that is driven through surface openings in a lifting airfoil by pressure differences are investigated in wind tunnel experiments. The bleed is actively regulated by arrays of addressable integrated louvers, and the time-dependent interactions between the bleed and cross flows alter the apparent aerodynamic shape of the lifting surface, and, consequently, the distributions of aerodynamic forces and moments. The 2-D Clark-Y wind tunnel model is oscillating in pitch, and the dynamic changes in the time-dependent forces and moment are measured over a wide range of angles of attack from pre- to post-stall using integrated load cells. Induced changes in surface vorticity concentrations are measured using PIV with emphasis on the effects of leading edge bleed at high angles of attack on the evolution of the dynamic stall vorticity concentrations. [Preview Abstract] |
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