Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session D25: Flow Control: Aerodynamics |
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Chair: Ari Glezer, Georgia Institute of Technology Room: 31A |
Sunday, November 18, 2012 2:15PM - 2:28PM |
D25.00001: Rotorcraft Fuselage Flow Control Using Plasma Streamwise Vortex Generators Dustin Coleman, Flint Thomas Active flow control, in the form of dielectric barrier discharge (DBD) plasma actuators, is applied to a NASA ROBIN-mod7 generic rotorcraft fuselage model. The model is considered in what would be a typical cruise position \emph{i.e.} a nose down position at $\alpha = -5^{\circ}$. This configuration gives rise to a massive 3-D flow separation over the aft ramp section of the fuselage, characterized by two counter-rotating, streamwise vortices. The control objective is to minimize these concentrated vortices by means of flush fuselage-mounted plasma streamwise vortex generators (PSVGs), and consequently, reduce the form drag of the vehicle. Experiments were conducted at freestream Mach and Reynolds numbers of $M_{\infty} = 0.12$ and Re$_{L} = 2.65$ million, respectively. Aerodynamic loads under both natural and controlled conditions were acquired through use of an ATI Mini40 6-component force sensor. The pressure field on the ramp section was monitored by a 128 count static pressure array. Likewise, the flow field was captured by time-resolved PIV wake surveys. Results are compared with previous studies that utilized active flow control by way of pulsed jets or combustion actuators. [Preview Abstract] |
Sunday, November 18, 2012 2:28PM - 2:41PM |
D25.00002: Numerical simulations of a vertical tail of a commercial aircraft with active flow control Michel Rasquin, Jeffrey Martin, Kenneth Jansen A series of numerical simulations of a realistic vertical tail of a commercial aircraft, with a tapered swept stabilizer and a rudder, is considered in this work with application of flow control. Flow control is known to have the capacity to augment the streamwise momentum near the rudder suction peak where separation is typically observed to limit rudder effectiveness for high deflection angles. Specifically, we use Delayed Detached Eddy Simulations (DDES) to study the interaction of a cross flow with an array of 24 synthetic jets for a 0$^{\circ}$ angle of attack, a 30$^{\circ}$ deflection angle and a Reynolds number of 7x10$^{5}$. We concentrate our analysis on the influence of the spacing between successive active jets in the spanwise direction. Indeed, our current simulations suggest that doubling the number of active jets at a lower Reynolds number improves the lateral force while opposite effect is observed at the considered Reynolds number when using the same size jets. These simulations offer insight into the fundamental physics of the flow structures in the vicinity of the synthetic jets by accurately resolving the complete synthetic jet pathway and the vorticity plume where the jet structures interact with each other and with the primary flow. [Preview Abstract] |
Sunday, November 18, 2012 2:41PM - 2:54PM |
D25.00003: Lift enhancement with extremum seeking control for a low-aspect-ratio wing Kunihiko Taira, Clarence Rowley, Tim Colonius We introduce active flow control around a low-aspect-ratio flat-plate wing at post-stall angles of attack for lift enhancement. The separated flow is numerically examined with the immersed boundary projection method and the actuator is modeled as periodic momentum injection. It is emphasized that the present control technique does not suppress separation but benefits from the formation of the leading-edge vortices to take place closer to the suction side of the wing. This positions the low-pressure cores of the leading-edge vortices directly above the wing to provide added lift. For a certain range of actuation frequency, the wake is found to lock onto a periodic state that provides lift enhancement. To seek this high-lift state, we design a feedback controller with the extremum-seeking algorithm to determine the optimal actuation frequency. We discuss the design methodology and explain how the dynamics of the wake vortices is modified to yield added lift. [Preview Abstract] |
Sunday, November 18, 2012 2:54PM - 3:07PM |
D25.00004: Aerodynamic Control of a Pitching Airfoil using Distributed Active Bleed John Kearney, Ari Glezer Aero-effected flight control using distributed active bleed driven by pressure differences across lifting surface and regulated by integrated louver actuators is investigated in wind tunnel experiments. The interaction between unsteady bleed and the cross flows alters the apparent aerodynamic shape of the lifting surface by regulating the accumulation and shedding of vorticity concentrations, and consequently the distributions of forces and moments. The present experiments are conducted using a 2-D dynamically-pitching VR-7 airfoil model from pre- to post-stall angles of attack. The effects of leading edge bleed at high angles of attack on the formation and evolution of the dynamic stall vorticity concentrations are investigated at high reduced frequencies (k $>$ 0.1) using PIV phase-locked to the airfoil's motion. The time-dependent bleed enables broad-range variation in lift and pitching moment with significant extension of the stall margin. In particular, bleed actuation reduces the extent of ``negative damping'' or pitching moment instability with minimal lift penalty. [Preview Abstract] |
Sunday, November 18, 2012 3:07PM - 3:20PM |
D25.00005: Transitory Control of Separation over a Pitching Airfoil using Spatially-Compact Pulsed Actuation George T.K. Woo, Ari Glezer The dynamics of controlled three-dimensional attachment of transitory stall over a pitching 2-D airfoil is investigated in wind tunnel experiments using spanwise-compact (0.12S) pulsed actuation on time scales that are an order of magnitude shorter than the characteristic convective time scale. Actuation is effected using a surface-integrated pulsed, combustion-based fluidic actuators. The flow field above the airfoil and in its near wake is computed from multiple high-resolution PIV images in multiple cross stream planes that are obtained phase-locked to the actuation, and allow for tracking of vorticity concentrations. Transitory attachment spreads towards the outboard, unactuated flow domains and far exceeds the width of the actuator. The actuation results in the formation of 3-D vortical structures that are advected and shed into the near wake and induce spanwise variations in the sectional circulation. It is shown that coupling of the pulsed actuation to the airfoil's motion enhances the control authority of 3-D unsteady separation, can significantly mitigate the effects of dynamic stall and improve the unsteady aerodynamic lift and pitching moment. [Preview Abstract] |
Sunday, November 18, 2012 3:20PM - 3:33PM |
D25.00006: ABSTRACT WITHDRAWN |
Sunday, November 18, 2012 3:33PM - 3:46PM |
D25.00007: Feedback control of a pitching and plunging airfoil via direct numerical simulation Scott Dawson, Steven Brunton, Clarence Rowley Feedback control is implemented in direct numerical simulations at a Reynolds number of 100 to allow a two-dimensional flat plate airfoil to track desired lift profiles using pitching and plunging motions. Robust controllers are designed using both classical models (Theodorsen) and empirical reduced-order models identified from direct numerical simulations. We investigate the capabilities of a variety of controllers for plunging motion and for pitching about different pitch axis locations. Effective control is achieved across a wide range of angles of attack, despite strongly nonlinear flow physics. The forces caused by rapid airfoil motion may be utilized to achieve high lift coefficients for short periods of time. It is also possible to track periodic lift profiles with average lift coefficients that are significantly greater than those achieved by a steady airfoil. The enhanced lift that arises at certain frequencies appears to be caused by favorable interaction of wake vortices. The ability of the controllers to reject gust disturbances and attenuate sensor noise is also investigated, which is relevant for the implementation of such controllers in an experimental setting. [Preview Abstract] |
Sunday, November 18, 2012 3:46PM - 3:59PM |
D25.00008: The Transient Aerodynamic Forces Effected by Trailing Edge Active Flow Control Dan Brzozowski, John Culp, Ari Glezer The transient aerodynamic forces effected by trailing edge flow control are investigated in wind tunnel experiments using a 2-DOF traverse which enables application of time-dependent external torque and forces by servo motors. The global aerodynamic forces and moments are regulated by controlling vorticity generation and accumulation near the surface using hybrid synthetic jet actuators. The time-histories of surface pressure and aerodynamic lift and pitching moment immediately following the application of flow control are measured using simultaneous pressure, force and velocity measurements that are taken phase-locked to the commanded actuation waveform. Circulation time history that is estimated from a PIV wake survey shows that the entire flow over the airfoil readjusts within about $1.5 T_{\mathrm{CONV}}$, which is about two orders of magnitude shorter than the characteristic time associated with the controlled maneuver of the wind tunnel model. This illustrates that flow-control actuation can be typically effected on time scales that are commensurate with the flow's convective time scale, and that the maneuver response is primarily limited by the inertia of the platform. [Preview Abstract] |
Sunday, November 18, 2012 3:59PM - 4:12PM |
D25.00009: Parametric Investigation of Nanosecond Pulse Driven Dielectric Barrier Discharge Plasma Actuators for Aerodynamic Flow Control Robert Dawson, Jesse Little Nanosecond pulse driven dielectric barrier discharge plasma actuators are studied experimentally in quiescent atmosphere. Per unit length peak energy and instantaneous peak power are calculated using simultaneous voltage and current measurements. Electrical characteristics are evaluated as a function of peak voltage, pulse frequency, discharge length and dielectric thickness. Schlieren imaging of compression waves is used to provide a relative measure of discharge energy that is coupled to the near surface gas as heat for the same parameters. Characteristics of the DBD load have a substantial effect on voltage and current traces which are reflected in the peak energy and peak power. Both peak energy and compression wave strength depend primarily on dielectric thickness and secondarily on actuator length although this is not universal in the case of energy necessitating examination of alternative calculation strategies. Peak power is mainly dependent on actuator length which is inconsistent with schlieren data as expected. Higher pulse frequency produces higher pulse energy, but is primarily attributed to heating of the actuator and power supply components. This effect is mainly observed for short actuators. Pulse energy increases as peak voltage to the power 3.5. This behavior is similar to observations of energy and thrust for ac-DBD plasma actuators suggesting that aspects of lumped-element circuit models may be applicable for optimizing ns-DBD performance. [Preview Abstract] |
Sunday, November 18, 2012 4:12PM - 4:25PM |
D25.00010: On least-order flow decompositions for aerodynamics and aeroacoustics Michael Schlegel, Bernd R. Noack, Peter Jordan A generalisation of proper orthogonal decomposition (POD) for optimal flow resolution of linearly related observables is presented, as proposed in the identically named publication of Schlegel, Noack, Jordan, Dillmann, Groeschel, Schroeder, Wei, Freund, Lehmann and Tadmor (Journal of Fluid Mechanics 2012, vol. 697, pp. 367--398). This Galerkin expansion, termed ``observable inferred decomposition'' (OID), addresses a need in aerodynamic and aeroacoustic applications by identifying the modes contributing most to these observables. Thus, OID constitutes a building block for physical understanding, least-biased conditional sampling, state estimation and control design. From a continuum of OID versions, two variants are tailored for purposes of observer and control design, respectively. Three aerodynamic and aeroacoustic observables are studied: (1) lift and drag fluctuation of a two-dimensional cylinder wake flow, (2) aeroacoustic density fluctuations measured by a sensor array and emitted from a two-dimensional compressible mixing layer, and (3) aeroacoustic pressure monitored by a sensor array and emitted from a three-dimensional compressible jet. The most ``drag-related,'' ``lift-related'' and ``loud'' structures are distilled and interpreted in terms of known physical processes. [Preview Abstract] |
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