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 R25: Flow Control: General II |
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Chair: Hamid Johari, California State University at Northridge Room: 31A |
Tuesday, November 20, 2012 1:00PM - 1:13PM |
R25.00001: Robustness of Input Shaping for Liquid Sloshing Suppression in a Horizontally Accelerating Container Dongjoo Kim, Seong-Wook Hong, Kyoungjin Kim Input shaping has been recently shown to be effective in reducing liquid sloshing, which occurs when a partially filled container experiences acceleration for fast positioning control. However, its robustness to the change of system parameters needs to be further understood because input shaping is an open-loop control without feedback sensing. Therefore, the objective of this study is to investigate the robustness of input shaping as a means of suppressing liquid sloshing in a horizontally accelerating container numerically and experimentally. In the case of numerical simulation, the governing equations for unsteady two-phase fluid motions are solved rather than using the simple and common pendulum model for free surface motion. In this study, three different input shapers (ZV, ZVD, convolved ZV shapers) are considered and their sensitivity to system frequency variation is examined for various container accelerations. The control efficiency of input shapers is evaluated in terms of the amplitude of transient peak and residual oscillations of liquid sloshing. Detailed information including dynamic behaviors of free surface will be provided in the final presentation. [Preview Abstract] |
Tuesday, November 20, 2012 1:13PM - 1:26PM |
R25.00002: Estimation of the Concentration from a Gaseous Moving Source Using Collaborating Sensing Aerial Vehicles Tatiana Egorova, Michael A. Demetriou, Nikolaos A. Gatsonis This work considers the estimation of the concentration field caused by a moving gaseous source. A model-based estimation scheme incorporates the vehicle dynamics in the estimation scheme in order to arrive at a guidance control law that is dictated by the performance of the estimator. The model-based estimation scheme provides on-line estimates of the concentration field and of the proximity of the moving source. The process state estimate is realized through the use of multiple sensing aerial vehicles (SAVs) that have collaborating capabilities. Each SAV implements its own model-based estimator using its own sensor measurements and shares its estimate with the remaining SAVs. The advantage of the collaborating scheme is the faster convergence of the process state estimate. Computational results demonstrate the advantage of the SAV collaboration in estimating the process state and the proximity of the moving source. [Preview Abstract] |
Tuesday, November 20, 2012 1:26PM - 1:39PM |
R25.00003: Cavitation on Hydrofoils with Leading Edge Protuberances Derrick Custodio, Charles Henoch, Hamid Johari The effects of spanwise-uniform sinusoidal leading edge protuberances on the flow characteristics and forces of finite-span hydrofoils under vaporous cavitation conditions were examined experimentally over angles of attack ranging from -9\r{ } $\le $ \textit{$\alpha $} $\le $ 27\r{ }. Two planforms were studied, rectangular and swept, at a Reynolds number of $\approx $ 720,000. Two protuberance wavelengths, \textit{$\lambda $} = 0.25$c$ and 0.50$c$, and three amplitudes, $A$ = 0.025$c$, 0.05$c$, and 0.12$c$, were examined as they resemble the humpback whale flipper morphology. All hydrofoils retain a mean NACA 63$_{4}$-021 profile. The forces and moments were measured at a freestream velocity of 7.2 m/s, and high-speed digital photography was used to capture flow field images at several angles of attack. The cavitation number corresponding to incipient leading edge cavitation was also calculated. As far as forces and cavitation number are concerned, results show that the baseline hydrofoil tends to have nearly equal or improved performance over the modified hydrofoils at most angles of attack tested. Flow images reveal that it is possible that the extent of sheet and tip vortex cavitation can be reduced with the introduction of leading edge protuberances. The forces and cavitation characteristics will be presented. [Preview Abstract] |
Tuesday, November 20, 2012 1:39PM - 1:52PM |
R25.00004: An improved algorithm for balanced proper orthogonal decomposition using analytic tails Jonathan Tu, Clarence Rowley Balanced proper orthogonal decomposition (BPOD) can be used in flow control applications to identify coherent structures of interest and to form reduced-order models. Doing so involves simulating impulse responses of the direct and adjoint systems, in order to compute factorizations of the empirical Gramians. We present a new variant of the BPOD algorithm that simultaneously reduces its computational cost and increases its accuracy. Dynamic mode decomposition (DMD) is used to identify the slow eigenvectors that dominate the long-time behavior of the impulse responses, and the contribution of these eigenvectors to the empirical Gramians is then accounted for analytically. This procedure greatly reduces the error inherent in truncating the impulse responses after a finite time. We demonstrate the effectiveness of this algorithm by applying it to the flow past a two-dimensional cylinder, at a Reynolds number of 100. Reduced-order models are computed for the restriction of the wake dynamics to the stable subspace. Models generated using the analytic tail method yield the same accuracy as those computed using traditional BPOD, with a 70\% reduction in computation time. [Preview Abstract] |
Tuesday, November 20, 2012 1:52PM - 2:05PM |
R25.00005: Large-Eddy Simulations of Plasma Control for Separated Supersonic Flow Nicholas Bisek, Jonathan Poggie The Navier-Stokes equations were solved using a high-fidelity time-implicit numerical scheme and an implicit large-eddy simulation approach to investigate plasma-based flow control for supersonic flow over a compression ramp. The configuration includes a flat-plate region to develop an equilibrium turbulent boundary-layer at Mach 2.25, which was validated against a set of experimental measurements. The fully turbulent boundary-layer flow traveled over a $24^\circ$ ramp and produced an unsteady shock-induced separation. A control strategy to suppress the separation through a magnetically-driven gliding-arc actuator was explored. The size, strength, and placement of the actuator were developed based on recent experiments. Three control scenarios were examined: steady control, pulsing with a 50\% duty cycle, and Joule heating. The results show the control mechanism reduced the time-mean separation length for all three situations. The case without pulsing and Joule heating was the most effective, with a reduction in the separation length by more than 75\%. The controller was also found to significantly reduce the low-frequency content of the turbulent kinetic energy spectra within the separated region and reduce the total kinetic energy downstream of reattachment. [Preview Abstract] |
Tuesday, November 20, 2012 2:05PM - 2:18PM |
R25.00006: Control of Shock-Induced Boundary Layer Separation by using Pulsed Plasma Jets Benton R. Greene, Noel T. Clemens, Daniel Micka Shock-induced turbulent boundary layer separation can have many detrimental effects in supersonic flow including flow instability, fatigue of structural panels, and unstart in supersonic inlets. Pulsed plasma jets (or ``spark jets''), which are characterized by high bandwidth and the ability to direct momentum into the flow, are one promising method of reducing shock-induced separation. The current study is focused on investigating the efficacy of plasma jets to reduce the separated flow induced by a compression ramp in a Mach 3 flow. Three different 3-jet actuator configurations are tested: 20$^{\circ}$ pitched, 45$^{\circ}$ pitched, and 22$^{\circ}$ pitched and 45$^{\circ}$ skewed. The jets are pulsed at frequencies between 2 kHz and 4 kHz with duty cycles between 5 and 15\%. The shock wave is generated using a 20$^{\circ}$ compression ramp, and the location of the shock-induced separation is visualized using surface oil streak visualization as well as particle image velocimetry. The results of the study show that of the three configurations, the plasma jets pitched at 20$^{\circ}$ from the streamwise direction cause the greatest reduction in separation, and when pulsed at a frequency of 3.2 kHz and 12\% duty cycle can reduce the size of the separation region by up to 40\%. [Preview Abstract] |
Tuesday, November 20, 2012 2:18PM - 2:31PM |
R25.00007: 4D-Var identification of POD Reduced-Order Models Laurent Cordier, Gilles Tissot, Bernd R. Noack A reduced-order modelling (ROM) strategy is crucial to achieve model-based control in a wide class of flow configurations. In turbulence, ROMs are mostly derived by Galerkin projection of first principles equations onto the proper orthogonal decomposition (POD) modes. These POD ROMs are known to be relatively fragile when used for control design. In this communication, a four-dimensional variational assimilation approach (4D-Var) is used to identify the coefficients of the POD ROM. Essentially, data assimilation combines imperfect observations, a background solution and the underlying dynamical principles governing the system under observation to determine an optimal estimation of the true state of the system. The methodology will be illustrated for a cylinder wake flow on two datasets of increasing dynamical complexity: i) a DNS at $Re=200$, and ii) PIV measurements at about $Re=40000$. [Preview Abstract] |
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