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 A15: Flow Control: Passive |
Hide Abstracts |
Chair: Sherin Bagheri, KTH Room: 203 |
Sunday, November 22, 2015 8:00AM - 8:13AM |
A15.00001: Passive control of a sphere by complex-shaped appendages Shervin Bagheri, Ugis Lacis, Stefano Olivieri, Andrea Mazzino Appendages of various shapes and sizes (e.g. plumes, barbs, tails, feathers, hairs, fins) play an important role in dispersion and locomotion. In our previous work (Lacis, U. et al. Passive appendages generate drift through symmetry breaking. Nat. Commun. 5:5310, doi: 10.1038/ncomms6310, 2014), we showed that a free-falling cylinder with a splitter plate turns and drifts due to a symmetry-breaking instability (called inverted-pendulum instability or IPL). In other words, in a separated flow, the straight position of a short splitter plate is unstable and as a consequence a side force and a torque are induced on the cylinder. In this work, we seek the three-dimensional (3D) appendage shape (on a sphere at Re$=$200) that induces the largest drift of the sphere. We find that highly non-trivial shapes of appendages on a sphere increase the side force significantly compared to trivial shapes (such as an elliptic sheet). We also find that appendages may be designed to generate drift in either direction, that is, a free-falling sphere can drift either in the direction in which appendage is tilted or in the opposite direction depending on the particular geometry of the appendage. We discuss the physical mechanisms behind these optimal appendage shapes in the context of the IPL instability. [Preview Abstract] |
Sunday, November 22, 2015 8:13AM - 8:26AM |
A15.00002: The effect of splitter plate on fluid flow and heat transfer characteristics past various bluff-body configurations Sunakraneni Soumya, K. Arul Prakash Numerical simulation of five different bluff body configurations with splitter plate is carried out to analyse the fluid flow and heat transfer characteristics for Reynolds number (Re) ranging from 50-200. The governing equations are discretized using SUPG - finite element method. The bluff body configurations considered are elliptic cylinder of axis ratios (AR$=$0.5-1.0), square cylinder, rhombus of axis ratios (AR$=$0.5-1.0), equilateral triangle, and semi-circular cylinder. The splitter plate length varied from L$=$0.0D$_{\mathrm{h}}$-6.0D$_{\mathrm{h}}$, (D$_{\mathrm{h\thinspace }}=$ Bluff body hydraulic diameter). It is observed that interaction of separated shear layers from top and bottom surfaces of the body is inhibited and vortex shedding is suppressed for certain combinations of bluff body configuration, Re and splitter plate length and wake region is modified significantly. Reduction in drag approximately of the order 2{\%} to 50{\%} is attained and overall heat transfer (Q) is increased due to splitter plate. [Preview Abstract] |
Sunday, November 22, 2015 8:26AM - 8:39AM |
A15.00003: Investigation and control of dynamic stall of an aerofoil ramp up motion Marco Edoardo Rosti, Mohammad Omidyeganeh, Alfredo Pinelli Direct Numerical Simulations of the flow around a NACA0020 aerofoil at $Re_c=20\times10^3$ undergoing a ramp up motion has been undertaken ($\alpha \in [0^{\circ},20^{\circ}], \dot{\alpha}_{\mbox{rad}} c/U_{\infty}=0.12$). New insights on the vorticity dynamics in the baseline case are discussed using a number of post-processing techniques. We will also present and discuss the effects of a passive control technique based on the use of a thin flap hinged via a torsional spring to the suction side of the aerofoil. The interaction between the flap dynamics (modelled as an infinitely thin plate) and the fluid have been carried out using an original Immersed Boundary Method applied to a finite volume solver. When the spring constant is chosen to lock the flap oscillations into the main shedding frequency, the back flow induced by the primary vortex is strongly reduced by the presence of the flap inhibiting the generation of massive separation. Moreover, the flap is capable to enhance and protract the lift overshoot typical of the dynamic stall also alleviating the subsequent lift-breakdown. These beneficial behaviour is mainly due to the establishment of a fluid structure interaction cycle that continuously regenerate the primary vortex which is ultimately responsible for the enhanced lift. [Preview Abstract] |
Sunday, November 22, 2015 8:39AM - 8:52AM |
A15.00004: Control of Vortex Shedding on an Airfoil using Mini Flaps at Low Reynolds Number Daisuke Oshiyama, Daiju Numata, Keisuke Asai In this study, the effects of mini flaps (MFs) on a NACA0012 airfoil were investigated experimentally at low Reynolds number. MFs are small flat plates attached to the trailing edge of an airfoil perpendicularly. All the tests were conducted at the Tohoku-University Basic Aerodynamic Research Tunnel at the chord Reynolds number of 25,000. Aerodynamic forces were measured using a 3-component balance and the surface flow was visualized by luminescent oil film technique. The results of force measurement show that attachment of MFs enhances lift and the enhanced lift increases with MF height. On the other hand, the results of oil flow visualization show that attachment of MFs enlarges the separated region on the airfoil rather than diminishes it. To understand the physical mechanism of MFs for lift enhancement, the flow around the airfoil was visualized by the smoke-wire method and the wake profile behind the airfoil was measured using a hot wire anemometer. It was found that vortices shed periodically from the tip of the MFs and interact with the separated shear layer from the upper surface. This unsteady vortex shedding forms a low-pressure region on the upper surface, generating higher lift. These results suggest that the height of MFs controls the frequency of vortex shedding behind the MF, forcing the separated shear layer on the upper surface flow in unsteady manner. [Preview Abstract] |
Sunday, November 22, 2015 8:52AM - 9:05AM |
A15.00005: Experimental investigation of flow past a sphere with trip Rahul Deshpande, Aditya Desai, Vivek Kanti, Sanjay Mittal The flow over a smooth sphere and a sphere with a trip was experimentally investigated in the Reynolds number range 1 x 10$^{5}$ to 5 x 10$^{5}$ through unsteady force measurements. The size of the trip is 1.5 percent of the diameter D of the sphere and measurements are made for its streamwise location from the stagnation point for 10, 20 and 30 degrees. The statistics of the drag and lateral forces were studied for a range of subcritical to supercritical Reynolds numbers to understand the effect of a trip on the critical flow regime of a sphere. Two different flow characteristics are observed over the sphere surface depending on the streamwise location of the trip. For subcritical Reynolds numbers, a significant mean side force is observed in the direction of the trip side of the sphere. On gradually increasing the Reynolds number, the flow over the sphere enters the critical regime and the direction of the side force reverses from the trip side to the non - trip side of the sphere which continues to be observed well within the early supercritical regime. [Preview Abstract] |
Sunday, November 22, 2015 9:05AM - 9:18AM |
A15.00006: Experimental Observation of Hairy Surface Exposed in Airflow Mitsugu Hasegawa, Hirotaka Sakaue The development of drag reduction method is important to reduce the consumption of limited energy in the field of engineering. While active method which needs external energy has received significant attention, passive method which means no external energy use has been focused. As one of the potential passive drag reduction method for offshore structure, aircraft, wind turbine, flexible hair implanted on the object surface has been studied. Here we make hairy surface. We conduct flow visualization to investigate the behavior of hairy surface exposed in wind tunnel. In the presentation, a current status of this experiment will be presented. [Preview Abstract] |
Sunday, November 22, 2015 9:18AM - 9:31AM |
A15.00007: Phononic subsurface: Flow stabilization by crystals Mahmoud I. Hussein, Sedat Biringen, Osama R. Bilal, Alec Kucala Flow control is a century-old problem where the goal is to alter a flow's natural state to achieve improved performance, such as delay of laminar-to-turbulent transition or reduction of drag in a fully developed turbulent flow. Meeting this goal promises to significantly reduce the dependence on fossil fuels for global transport. In this work, we show that phonon motion underneath a surface interacting with a flow may be tuned to cause the flow to stabilize, or destabilize, as desired. This concept is demonstrated by simulating a fully developed plane Poiseuille (channel) flow whereby a small portion of an otherwise rigid wall is replaced with a one-dimensional phononic crystal. A Tollmien--Schlichting (TS) wave is introduced to the flow as an evolving disturbance. Upon tuning the frequency-dependent phase and amplitude relations of the surface of the phononic crystal that interfaces with the flow, the TS wave is shown to stabilize, or destabilize, as needed. A theory of subsurface phonons is presented that provides an accurate prediction of this behavior without the need for a flow simulation. This represents an unprecedented capability to passively synchronize wave propagation across a fluid-structure interface and achieve favorable, and predictable, alterations to the flow properties. [Preview Abstract] |
Sunday, November 22, 2015 9:31AM - 9:44AM |
A15.00008: Passive Flow Separation Control Mechanism Inspired by Shark Skin India Oakley, Amy Lang The following experimental work seeks to examine shark scales as passive flow-actuated separation control mechanisms. It is hypothesized that the actuation of these scales can in fact reduce pressure drag by inhibiting flow reversal and thereby prevent flow separation. In order to examine this mechanism at a fundamental level, three-dimensional sharkskin scales were simplified and modeled as two-dimensional flaps. To further simplify the experiment, the flaps were observed within a laminar boundary layer. The laminar boundary layer was grown over a long flat plate that was placed inside a water tunnel. A rotating cylinder was also used to induce an unsteady, increasing adverse pressure gradient, which generated a reversing flow. In order to visualize the potential actuation of the two-dimensional flaps DPIV (digital particle image velocimetry) was utilized. Three main objectives for this work included, the actuation of the two-dimensional flaps, the resistance to a reversed flow as a result of flap actuation and the prevention of flow separation. However once the experiment was conducted the flaps did not perform as previously hypothesized. The adverse pressure gradient induced by the rotating cylinder did not produce a reversing flow powerful enough to actuate the flaps. [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