Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session E17: Flow Control: Instabilities |
Hide Abstracts |
Chair: Matthew Juniper, University of Cambridge Room: 205 |
Sunday, November 22, 2015 4:50PM - 5:03PM |
E17.00001: Experimental sensitivity analysis and control of thermoacoustic systems Matthew Juniper, Nicholas Jamieson, Larry Li, Georgios Rigas We report the results of an experimental sensitivity analysis on a thermoacoustic system: an electrically heated Rijke tube. We measure accurately the change of the linear stability characteristics of the system, quantified as shifts in the growth rate and oscillation frequency, that is caused by the introduction of a passive control device. In the case presented here, the control device is a mesh, which causes drag in the system. The rate of growth is slow, so the growth rate and frequency can be measured over many hundred cycles in the linear regime with and without control. This means that the shift in growth rate and frequency can be calculated very accurately. These measurements agree well with the theoretical predictions from adjoint-based methods of Magri \& Juniper (JFM 2013, 719, 183-202). The results suggest that adjoint-based methods can accurately predict the effect of different passive control devices on the stability of a thermoacoustic system, opening new avenues for the development, implementation and validation of control strategies for more complex thermoacoustic systems. [Preview Abstract] |
Sunday, November 22, 2015 5:03PM - 5:16PM |
E17.00002: Tollmien-Schlichting wave cancellation by feedback control Hari Vemuri, Jonathan Morrison, Eric Kerrigan Tollmien-Schlichting (TS) waves are primary instabilities in the boundary layer and, by actively interfering with their growth, the transition process can be delayed. In this study the experimental results of both open-loop and real-time feedback control will be shown for 3D TS waves excited within a flat-plate boundary layer. They are excited at a 0.75mm pin-hole source driven by a speaker. A 0.75 mm thin, dual slot geometry is used for actuation by another speaker and a wall hot-wire sensor manufactured in-house is used as the sensor for feedback control. The spatial transfer function models between the source and sensor (G$_{\mathrm{s}})$ and the actuator and sensor (G$_{\mathrm{a}})$ obtained by classic frequency sweep techniques are used to synthesize various types of robust, stabilizing controllers (K). The transfer function G$_{\mathrm{s}}$ determines the unstable range of frequencies whereas G$_{\mathrm{a}}$ together with K determines the stability of the closed-loop. A second traversing hot-wire is used to record the performance of the controller downstream. It is shown that the experimental transfer functions agree remarkably well with numerical calculations as do the predicted results from feedback control. Preliminary experimental feedback control results for various other actuator configurations will also be presented. [Preview Abstract] |
Sunday, November 22, 2015 5:16PM - 5:29PM |
E17.00003: Controlling Spatiotemporal Chaos in Active Dissipative-Dispersive Nonlinear Systems Susana Gomes, Marc Pradas, Serafim Kalliadasis, Demetrios Papageorgiou, Grigorios Pavliotis We present a novel generic methodology for the stabilization and control of infinite-dimensional dynamical systems exhibiting low-dimensional spatiotemporal chaos. The methodology is exemplified with the generalized Kuramoto-Sivashinsky equation, the simplest possible prototype that retains that fundamental elements of any nonlinear process involving wave evolution. The equation is applicable on a wide variety of systems including falling liquid films and plasma waves with dispersion due to finite banana width. We show that applying the appropriate choice of time-dependent feedback controls via blowing and suction, we are able to stabilize and/or control all stable or unstable solutions, including steady solutions, travelling waves and spatiotemporal chaos, but also use the controls obtained to stabilize the solutions to more general long wave models. We acknowledge financial support from Imperial College through a Roth PhD studentship, Engineering and Physical Sciences Research Council of the UK through Grants No. EP/H034587, EP/J009636, EP/K041134, EP/L020564 and EP/L024926 and European Research Council via Advanced Grant No. 247031. [Preview Abstract] |
Sunday, November 22, 2015 5:29PM - 5:42PM |
E17.00004: ABSTRACT WITHDRAWN |
Sunday, November 22, 2015 5:42PM - 5:55PM |
E17.00005: ABSTRACT WITHDRAWN |
Sunday, November 22, 2015 5:55PM - 6:08PM |
E17.00006: An investigation of natural and forced transition in a laminar separation bubble via time-resolved Particle Image Velocimetry John Kurelek, Serhiy Yarusevych The transition process in a laminar separation bubble (LSB) formed on the suction surface of a NACA 0018 airfoil at a chord Reynolds number of 100,000 and an angle of attack of $5^{\circ}$ is studied experimentally. Both natural and forced transition are evaluated using controlled acoustic disturbances. Time-resolved Particle Image Velocimetry and surface pressure measurements are used to investigate the streamwise and spanwise flow development in the bubble. For all the cases examined, the transition process is characterized by the formation of strongly periodic shear layer vortices in the LSB due to the amplification of disturbances in the bubble's fore portion. These structures feature strong spanwise coherence at roll-up; however, they deform rapidly and begin to break down upstream of the mean reattachment point. The vortex breakup is shown to be initiated by spanwise deformation of the vortex filaments, linked to the formation of streamwise structures. This is followed by the formation of turbulent spots, which expand rapidly near mean reattachment. The results demonstrate that the acoustic disturbance environment can have a strong influence on the characteristics of the vortices and their breakup, thereby affecting flow transition and the overall dynamics of the LSB. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700