Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session E16: Flow Control: Active IControl
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Chair: Kunihiko Taira, Florida State University Room: 603 |
Sunday, November 19, 2017 4:55PM - 5:08PM |
E16.00001: Controlled Wake of a Moving Axisymmetric Bluff Body E. Lee, B. Vukasinovic, A. Glezer The aerodynamic loads exerted on a wire-mounted axisymmetric bluff body in prescribed rigid motion are controlled by fluidic manipulation of its near wake. The body is supported by a six-degree of freedom eight-wire traverse and its motion is controlled using a dedicated servo actuator and inline load cell for each wire. The instantaneous aerodynamic forces and moments on the moving body are manipulated by controlled interactions of an azimuthal array of integrated synthetic jet actuators with the cross flow to induce localized flow attachment over the body's aft end and thereby alter the symmetry of the wake. The coupled interactions between the wake structure and the effected aerodynamic loads during prescribed time-periodic and transitory (gust like) motions are investigated with emphasis on enhancing or diminishing the loads for maneuver control, and decoupling the body's motion from its far wake. [Preview Abstract] |
Sunday, November 19, 2017 5:08PM - 5:21PM |
E16.00002: Active control of flow-induced vibrations of a cylinder using piezo actuators Jason Dahl, Ersegun Deniz Gedikli The flow-induced vibration of continuous structures typically finds compatible conditions where the wake of the structure produces forces such that the coupled excitation of the structure follows large amplitude, figure eight motions, which can contribute to fatigue damage. In the present study, piezo actuators are embedded in a cylinder, with the actuators oriented to apply a force in-line with the flow. The cylinder is placed in a uniform free stream, which excites vibrations of the structure. The piezo actuators were applied to excite the second structural mode frequency in the in-line direction. This excitation produces an incompatible excitation of the structure between the in-line and cross-flow directions, leading to vibration suppression. The piezo actuators were also actuated at a flow speed just before a jump in the response branch of the cylinder, which was observed to cause a premature jump in amplitude, resulting in increased motion. The piezo actuators are also observed to be ineffective at altering the response when the cross-flow motion is very large. The present study demonstrates control of vortex-induced vibrations using purely in-line excitation of the structure, indicating the strong coupling between these directions in vortex-induced vibrations. [Preview Abstract] |
Sunday, November 19, 2017 5:21PM - 5:34PM |
E16.00003: Coupled Control of Flow Separation and Streamwise Vortical Structures. Travis Burrows, Bojan Vukasinovic, Ari Glezer The flow in offset diffusers of modern propulsion systems are dominated by streamwise vorticity concentrations that advect of low-momentum fluid from the flow boundaries into the core flow and give rise to flow distortion and losses at the engine inlet. Because the formation of these vortices is strongly coupled to trapped vorticity concentrations within locally-separated flow domains over concave surfaces of the diffuser bends, this coupling is exploited for controlling the streamwise evolution of the vortices and thereby significantly reduce the flow distortion and losses. The scale and topology of the trapped vorticity are manipulated at an operating throat Mach number of 0.64 by using a spanwise array of fluidic oscillating jets that are placed upstream of the separation domain. The present investigations demonstrate that the actuation alters the structure of both the trapped and streamwise vortices. In particular, the distribution of the streamwise vortices is altered and their strength is diminished by actuation-induced streamwise vorticity concentrations of opposite sense. As a result, the actuation leads to significant suppression of pressure distortion at the engine inlet (by as much as 60{\%}) at an actuation level that utilizes less than 0.4{\%} of the diffuser's mass flow rate. [Preview Abstract] |
Sunday, November 19, 2017 5:34PM - 5:47PM |
E16.00004: Abstract Withdrawn
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Sunday, November 19, 2017 5:47PM - 6:00PM |
E16.00005: Influence of unsteady perturbations on a wall-normal vortex Qiong Liu, ByungJin An, Motohiko Nohmi, Masashi Obuchi, Kunihiko Taira We numerically examine the influence of unsteady perturbations on a wall-normal vortex. The present study considers a model vortex similar to a Burgers vortex with no-slip boundary condition prescribed along its symmetry plane. The boundary layer generated along the symmetry plane of the model vortex gives rise to a significant difference from the Burgers vortex, which has dynamical implications in examining vortical flows near wall boundaries. We utilize three-dimensional direct numerical simulations (DNS) to examine the input-output response of the vortex with respect to various perturbations introduced near its vortex core. The perturbed flow exhibits the emergence of instabilities and changes to the behavior of vortex breakdown. The influence of various perturbation parameters is considered in order to characterize the features of dynamical response, including changes to the azimuthal velocity and pressure profiles. Moreover, vortical structures obtained from DNS and companion water tunnel experiments are examined in detail with proper orthogonal decomposition (POD) to highlight key energetic features. [Preview Abstract] |
Sunday, November 19, 2017 6:00PM - 6:13PM |
E16.00006: Separation control on curved boundaries Kamal Kumar R, Manikandan Mathur Flow separation and its characteristics are an important consideration in the field of bluff body aerodynamics. Specifically, the location and slope of the separation, and the size of the re-circulation bubble that forms downstream of the bluff body significantly affect the resulting aerodynamic forces. Recent theories based on dynamical systems (Haller, 2004) have established criteria based on wall-based quantities that identify the location and slope of separation in unsteady flows. In this work, we adapt the closed-loop separation control algorithm proposed by Alam, Liu \& Haller (2006) to curved boundaries, and demonstrate the effectiveness of the same via numerical simulations on the flow past a cylinder in the vortex-shedding regime. Using appropriately placed wall-based actuators that use inputs from shear stress sensors placed between the actuators, we demonstrate that the separation characteristics including the re-circulation bubble length, can be desirably modified. [Preview Abstract] |
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