Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session EJ: Flow Control III |
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Chair: Thomas Bewley, University of California, San Diego Room: Long Beach Convention Center 201A |
Sunday, November 21, 2010 4:10PM - 4:23PM |
EJ.00001: A proportional-integral-differential control of flow over a circular cylinder Donggun Son, Seung Jeon, Haecheon Choi In the present study, we apply a proportional(P)-integral(I)- differential(D) feedback control to flow over a circular cylinder for suppression of vortex shedding in the wake. The transverse velocity at a centerline location in the wake is measured and used for the feedback control. The sensing location is varied from $1d$ to $4d$ from the center of the cylinder. The actuation (blowing/suction) is provided to the flow at the upper and lower slots on the cylinder surface near the separation point based on the P, PI or PD control. Given each sensing location, the optimal proportional gain in the sense of minimizing the sensing velocity fluctuations is obtained for the P control. The additions of I and D controls to the P control certainly increase the control performance and broaden the effective sensing location. The P, PI and PD controls significantly reduce the velocity fluctuations at sensing locations and attenuate vortex shedding in the wake, resulting in the reductions in the mean drag and lift fluctuations. [Preview Abstract] |
Sunday, November 21, 2010 4:23PM - 4:36PM |
EJ.00002: Active control of vortex induced vibrations for flow past a circular cylinder M. Sridhar, B.S.V. Patnaik The flow past rigid bodies which are flexibly mounted would experience vortex induced oscillations. The phenomenon of eddy shedding is responsible for the asymmetric force distribution on the cylinder. In a variety of natural and technological applications, these vortex induced oscillations may cause resonance and structural failure [1]. Controlling vortex shedding by active annihilation of the wake vortices is of interest in flow control studies [2]. An active closed loop feedback control algorithm is designed and implemented for controlling the flow induced oscillations in the circular cylinder. Admissible acting functions are incorporated in the form of rotating control cylinders. The control algorithm is designed and integrated along with the equations for mass,momentum transport. The state of the flow is reported through multiple sensors and the quantum of actuations is performed by the controllers as dictated by the control algorithm. Present simulations are carried out at low Reynolds number, 100 and 200, and the complete suppression of self-excited oscillations is observed.\\[4pt] [1] Williamson C.H.K. and Govardhan R., Ann. Rev. Fluid Mech., \textbf{36}, 413-455, (2004). \\[0pt] [2] Muddada S. and Patnaik B.S.V., Eur. J. Mech. B - Fluids, \textbf{29}, 93 - 104 ,(2010). [Preview Abstract] |
Sunday, November 21, 2010 4:36PM - 4:49PM |
EJ.00003: The Hydrodynamic Cart-Pole: Experiments in Machine Learning and Control of Fluid-Body Interactions John W. Roberts, Jacob Steinhardt, Saverio Spagnolie, Russ Tedrake Unsteady fluid-body interactions at intermediate Reynolds numbers exhibit a great deal of dynamical complexity, as well as a great deal of structure. Abundant evidence from nature demonstrates that this structure can be exploited to achieve high performance at dynamical tasks. In this talk we present experimental work on a simple fluid-body system, a hydrodynamic analogue to the well- studied ``cart-pole'' system. Examples include balancing an immersed wing robustly at a passively unstable equilibrium, as well as more fundamentally nonlinear tasks such as moving the system from a passively stable to a passively unstable but controller-stabilized equilibrium. Our approach demonstrates the effectiveness of machine learning control and linear optimal control techniques for providing high-performance controllers in this challenging domain. The generality and transferability of the techniques to other systems will also be discussed. [Preview Abstract] |
Sunday, November 21, 2010 4:49PM - 5:02PM |
EJ.00004: Shape Optimization of Micro-Magnetic Locomotors Eric Keaveny, Shawn Walker, Michael Shelley Locomotion at the micro-scale is important in biology and in industrial applications such as targeted drug delivery and micro-fluidics. We present results on the optimal shape of a rigid body locomoting in 3-D Stokes flow. The actuation consists of applying a fixed moment and constraining the body to only move along the moment axis; this models the effect of an external magnetic torque on an object made of magnetically susceptible material. The shape of the object is parametrized by a 3-D centerline with a given cross-sectional shape. No a priori assumption is made on the centerline. Thus, we pose an infinite dimensional optimization problem and solve it with Boundary Integral and Variational methods. Sensitivities of the cost and constraints are computed variationally via shape differential calculus and a boundary integral formulation yields the boundary stresses. The optimization method can be considered as a sequential quadratic programming (SQP) approach. We report examples of locomotor shapes with and without different fixed payload/cargo shapes. [Preview Abstract] |
Sunday, November 21, 2010 5:02PM - 5:15PM |
EJ.00005: Local flow control for active building facades Srikar Kaligotla, Wayne Chen, Mark Glauser Existing building facade designs are for a passive and an impermeable shell to prevent migration of outdoor air into the building and to control heat transfers between the exterior environment and the building interior. An active facade that can respond in real time to changing environmental conditions like wind speed and direction, pollutant load, temperature, humidity and light can lower energy use and maximize occupant comfort. With an increased awareness of cost and environmental effects of energy use, cross or natural ventilation has become an attractive method to lower energy use. Separated flow regions around such buildings are undesirable due to high concentration of pollutants, especially if the vents or dynamic windows for cross ventilation are situated in these regions. Outside pollutant load redistribution through vents can be regulated via flow separation control to minimize transport of pollutants into the building. Flow separation has been substantially reduced with the application of intelligent flow control tools developed at Syracuse University for flow around ``silo'' (turret) like structures. Similar flow control models can be introduced into buildings with cross ventilation for local external flow separation control. Initial experiments will be performed for turbulent flow over a rectangular block (scaled to be a mid-rise building) that has been configured with dynamic vents and unsteady suction actuators in a wind tunnel at various wind speeds. [Preview Abstract] |
Sunday, November 21, 2010 5:15PM - 5:28PM |
EJ.00006: A Closed-loop Suction Flow Control Study over a Pitching Turret Ryan Wallace, Patrick Shea, Vaithianathan Thirunavukkarasu, Ryan Schmit, Hal Carlson, Mark Glauser Active flow control was implemented over a dynamically pitching hemispherical turret with a flat aperture in order to reduce the amount of turbulent fluctuations within the wake region. In this study unsteady suction was utilized as the control input for both open loop and closed loop control cases. The experiments were performed at the Subsonic Research Laboratory wind tunnel at Wright-Patterson Air Force Base at a high Reynolds number flow in which compressibility effects are present. It was clearly demonstrated with the open loop control cases that the suction had enough control authority to effect the baseline flow. The closed-loop control cases explored the effects of various low dimensional feedback systems, utilizing measurement-based estimation and regulators to control either fluctuating velocity or the mean velocity. The ultimate goal of the closed-loop control cases was to observe a reduction in turbulent fluctuations in the wake while reducing the amount of control input. [Preview Abstract] |
Sunday, November 21, 2010 5:28PM - 5:41PM |
EJ.00007: Feedback control of wall turbulence for drag reduction with finite spatial and temporal resolution Bettina Frohnapfel, Alexander Stroh, Yosuke Hasegawa, Nobuhide Kasagi Among various active control strategies, feedback control generally offers better control performance with smaller power consumption than predetermined control. However, it has the disadvantage of requiring numerous sensors which detect the instantaneous flow state and produce signals that are used to trigger actuators. In addition, measurable flow quantities are likely to be limited to those at the wall, where sensors can be implemented without changing the system design drastically. Most feedback control algorithms so far proposed, assume that massively arrayed sensors and actuators are provided on a wall surface. Considering the fact that physical dimensions and response times of these hardware components should be very small, i.e., less than millimeter and millisecond, fabrication and maintenance of these devices would impose an unbearable cost even with rapidly developing MEMS technology. In the present study, we take into account finite spatial and temporal resolution of wall sensing in numerical simulation and show how it affects the control results. In addition, based on the knowledge of the regeneration cycle of near-wall turbulent structures, we propose a control algorithm which yields considerable control performance with comparitively low spatio-temporal resolution. [Preview Abstract] |
Sunday, November 21, 2010 5:41PM - 5:54PM |
EJ.00008: Direct simulation of a separated boundary layer under the influence of large-scale forcing. Ayse G. Gungor, Mark P. Simens, Javier Jim\'enez The effect of large-scale forcing mimicking incoming wakes on a separated turbulent boundary layer over a flat plate is investigated by direct numerical simulation. The flow separates due to a strong adverse pressure gradient induced by suction along the upper simulation boundary, and the forcing Strouhal number $St = f l_x / U_0$ ranges from $0.25$ to $2.9$. The forcing, in which all the turbulent fluctuations except for the mean velocity defect are neglected, triggers the transition of the separated shear layer, and modifies the separated region. Each forcing pulse generates three roll-up vortices, which originate near the separation point and convect with approximately half the local free-stream velocity. The separation and reattachment points vary with the forcing frequency, but no other significant variations of the mean boundary layer properties are observed unless the separation bubble is allowed to fully reform. The separation lengths of the periodic cases can be estimated from a single recovery experiment in which the forcing is suddenly removed. [Preview Abstract] |
Sunday, November 21, 2010 5:54PM - 6:07PM |
EJ.00009: Control of vortex induced vibrations by suction and blowing K. Muralidharan, B.S.V. Patnaik K\'arm\'an vortex shedding behind bluff bodies is of interest in a wide range of technological applications. Vortex shedding past a stationary D-cylinder is controlled in our earlier investigations [1]. However, a flexibly mounted circular cylinder gives rise to vortex induced vibrations. The control of these vibrations is of both fundamental and practical interest as fluid submerged structures need suppression of vortex induced oscillations. Flow past a circular cylinder is numerically simulated by coupling mass, momentum conservation equations along with dynamical equations for the structure. An active flow control strategy based on suction and blowing is designed and implemented to assess the efficacy of this control methodology. This is achieved by suitably located suction and blowing slots on the cylinder surface. These actuators are designed such that, the suction and blowing together results in zero mass injection. This system is found to effectively annihilate the vortex induced vibrations, when the quantum of actuations is about thrice the free stream velocity. The blowing slot is located on the leeward side of the cylinder, while the suction slots are positioned at an angle of $100^{\circ}$ to the flow direction. The convective instability region is reduced, while the length of the wake formation region behind the body is controlled, with an attendant annihilation of the wake vortices. \\[4pt] [1] Patnaik BSV, Wei GW, Phy. Rev. Lett., \textbf{88}, 054502, (2002). [Preview Abstract] |
Sunday, November 21, 2010 6:07PM - 6:20PM |
EJ.00010: Dissimilar control of momentum and heat transfer in wall turbulence with traveling wave-like wall blowing and suction Yosuke Hasegawa, Nobuhide Kasagi Because of the importance of fundamental knowledge on turbulent heat transfer for further decreasing entropy production and improving efficiency in various thermo-fluid systems, we revisit a classical issue whether enhancing heat transfer is possible with skin friction reduced or at least not increased as much as heat transfer. The answer that numerous previous studies suggest is quite pessimistic because the analogy concept of momentum and heat transport holds well in a wide range of flows. In the present study, we introduce the suboptimal control theory for achieving dissimilar control in one of the most canonical thermo-fluid system, namely, turbulent flow with heat transfer in a smooth and straight channel. The Fr\'echet differentials obtained clearly show that the responses of velocity and temperature fields to a given control input are quite different due to the fact that the velocity is a divergence-free vector while the temperature is a conservative scalar. By exploiting this inherent difference, the dissimilar control can be achieved even in flows where the averaged momentum and heat transport equations have the same form. [Preview Abstract] |
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