Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session HD: Flow Control V |
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Chair: Michael Amitay, Rensselaer Polytechnic Institute Room: 101D |
Monday, November 23, 2009 10:30AM - 10:43AM |
HD.00001: The Flow Field on Hydrofoils with Leading Edge Protuberances Derrick Custodio, Charles Henoch, Hamid Johari The exceptional mobility of the humpback whale has been linked to the use of its unique pectoral flippers. Biologists speculate that the flippers leading edge protuberances are a form of passive flow control. Force measurements on 2D hydrofoils with spanwise uniform leading edge protuberances, resembling those seen on the humpback whale flipper, were taken in a water tunnel and have revealed performance modifications when compared to a baseline NACA 63(4)-021 hydrofoil model. Qualitative flow visualization techniques and Particle Image Velocimetry (PIV) flow field measurements on the modified hydrofoils have shown that streamwise vortices originating from the shoulders of the protuberances are the likely cause of performance changes. Varying levels of interaction among adjacent streamwise vortices have been observed as a function of angle of attack and chord location. The circulation of these vortices as a function of angle of attack and spatial location was measured and an analysis of the vortex interactions will be presented. [Preview Abstract] |
Monday, November 23, 2009 10:43AM - 10:56AM |
HD.00002: Aerodynamic Control using Distributed Active Bleed John M. Kearney, George T.K. Woo, Ari Glezer Aero-effected control of lifting surfaces using distributed active bleed driven by surface pressure differences and regulated by integrated louver actuators is investigated in wind tunnel experiments. The interaction between the bleed and cross flows alters the apparent aerodynamic shape of the lifting surface and consequently the distributions of forces and moments. A modular wind tunnel model based on a Clark-Y airfoil is mounted on high-resolution isolated load cells and is equipped with independently-controlled surface louvers on the pressure and suction sides near the leading edge. The louvers are activated using integrated SMA actuators that enable time-dependent actuation. Measurements of time-resolved forces and moment show that the actuation leads to significant changes in the lift force and pitching moment over a range of angles of attack. Phase-locked PIV shows the effects of the bleed on the flow on the suction surfaces and the corresponding changes in the near wake. [Preview Abstract] |
Monday, November 23, 2009 10:56AM - 11:09AM |
HD.00003: Pseudo Volume-filling Sampling (PVS) via Bouyancy Control in Ocean Systems Robert Krohn, Thomas Bewley This project address sensing methods for modeling and prediction in structured ocean current flow applications. Well distributed measurements of important flow quantities such as the local fluid velocity, temperature, and pressure are scientifically valuable. Such measurements can be obtained from very simple sensor systems. The challenge is to distribute the sensors uniformly over the volumes of interest. Using a fleet of sensor-equipped free-drifting floats, such as those currently used in the Argo project, uncoordinated distribution has been well documented. The sensor systems are grossly underactuated, and are only capable of controlling their vertical motion, making coordinated distribution difficult. Given that an accurate estimate of the background velocity field is available, however, it is possible to ``fly'' each individual sensor system, much as a recreational balloonist can direct a balloon fairly accurately by exploiting known velocity shear within the atmosphere. The present work addresses how a network of such underactuated vehicles can be distributed uniformly over the domain of interest using variations in local flow velocities, with both global model predictive control (MPC) algorithms regulated centrally and, in certain well-defined subproblems, simple LQG algorithms implemented locally. [Preview Abstract] |
Monday, November 23, 2009 11:09AM - 11:22AM |
HD.00004: A New Sliding Discharge Actuator for Aerodynamic Flow Control Lee Neuharth, Flint Thomas The application of a three-electrode (triode) sliding discharge (TSD) actuator for aerodynamic flow control is examined. The sliding discharge actuator is a hybrid that combines the effects of both a DC corona and dielectric barrier discharge. In the configuration examined in this study, two surface mounted electrodes are placed strategically on the aerodynamic body. One is held at ground and the other is at a large negative DC bias voltage. A third electrode spanning the distance between the two surface electrodes is placed below a dielectric barrier material and is given a high-voltage AC signal. This produces a glow discharge on the aerodynamic surface in the space between the surface electrodes and there is an associated coupling of directed momentum to the ambient fluid that is the basis for flow control. Two example flow control applications of the TSD are considered: (1) the boundary layer on a flat plate and (2) separation control on a symmetric airfoil. Results from both flow control studies are summarized. [Preview Abstract] |
Monday, November 23, 2009 11:22AM - 11:35AM |
HD.00005: Aerodynamics of a golf ball with grooves Jooha Kim, Kwangmin Son, Haecheon Choi It is well known that the drag on a dimpled ball is much lower than that on smooth ball. Choi $\emph{et al.}$ (Phys. Fluids, 2006) showed that turbulence is generated through the instability of shear layer separating from the edge of dimples and delays flow separation. Based on this mechanism, we devise a new golf ball with grooves on the surface but without any dimples. To investigate the aerodynamic performance of this new golf ball, an experiment is conducted in a wind tunnel at the Reynolds numbers of $0.5 \times 10^{5} - 2.7 \times 10^{5}$ and the spin ratios (ratio of surface velocity to the free-stream velocity) of $\alpha=0 - 0.5$, which are within the ranges of real golf-ball velocity and spin rate. We measure the drag and lift forces on the grooved ball and compare them with those of smooth ball. At zero spin, the drag coefficient on the grooved ball shows a rapid fall-off at a critical Reynolds number and maintains a minimum value which is lower by 50\% than that on smooth ball. At non-zero $\alpha$, the drag coefficient on the grooved ball increases with increasing $\alpha$, but is still lower by 40\% than that on smooth ball. The lift coefficient on the grooved ball increases with increasing $\alpha$, and is 100\% larger than that on smooth ball. The aerodynamic characteristics of grooved ball is in general quite similar to that of dimpled ball. Some more details will be discussed in the presentation. [Preview Abstract] |
Monday, November 23, 2009 11:35AM - 11:48AM |
HD.00006: Experimental Investigation of Actuators for Flow Control in Inlet Ducts John Vaccaro, Michael Amitay For military applications, inlet designs are constrained by low observability requirements, which call for the use of an S-duct inlet. The inlets purpose is to limit the line-of-sight to the compressor and decelerate the incoming flow while minimizing total pressure loss, distortion, and unsteadiness. In addition, in unmanned aerial vehicles, the inlet length can determine the overall size of the aircraft. For this reason, aggressive inlets can have a large impact on overall system efficiency. Experiments have been conducted which evaluate the effectiveness of different actuation systems for active flow control in an aggressive S-duct inlet, L/D = 1.5 (at flow conditions representative of flight conditions). Comparisons will be made between: steady and unsteady blowing from a single 2-D tangential slit, spanwise varying injection from a tangential slit, and spanwise varying injection of a hybrid actuator that has both a coanda type injector along with vortex generator jets to eliminate vorticity developed by secondary flow inherent to S-ducts. Evaluations criteria will include total pressure recovery, AIP distortion levels, and unsteady pressure fluctuations. [Preview Abstract] |
Monday, November 23, 2009 11:48AM - 12:01PM |
HD.00007: Numerical Investigation of Actuators for Flow Control in Inlet Ducts Kenneth Jansen, Onkar Sahni, Michael Amitay For military applications, inlet designs are constrained by low observability requirements, which call for the use of an S-duct inlet. The inlets purpose is to limit the line-of-sight to the compressor and decelerate the incoming flow while minimizing total pressure loss, distortion, and unsteadiness. In addition, in unmanned aerial vehicles, the inlet length can determine the overall size of the aircraft. For this reason, aggressive inlets can have a large impact on overall system efficiency. Numerical simulations have been carried out which evaluate the effectiveness of steady and unsteady actuation for active flow control in an aggressive S-duct inlet, L/D = 1.5 (at flow conditions representative of flight conditions). These simulations were performed in close co-ordination with the experiments to be able to validate CFD predictions and further provide a complementary and detailed view of the flow field. Comparisons will be made between: steady and unsteady blowing from a single 2-D tangential slit. Evaluations criteria will include total pressure recovery, AIP distortion levels, and unsteady pressure fluctuations. It is noteworthy to mention that the agreement between the CFD predictions and the experimental measurements were found to be very good. [Preview Abstract] |
Monday, November 23, 2009 12:01PM - 12:14PM |
HD.00008: 3-D Interactions of Synthetic Jets and Cross-Flows - CFD Onkar Sahni, Michael Amitay, Kenneth Jansen The interaction of synthetic jets with a cross-flow was studied numerically at low Reynolds numbers and low angles of attack by using parallel adaptive flow simulations. These investigations were performed in close co-ordination with the experimental studies to precisely match the physical dimensions and parameters. The focus of the work was to explore the details of the flow structures in the vicinity of the synthetic jets. Both instantaneous and phase-averaged flow fields were collected to understand the interactions. It was found that an array of counter-rotating vortical structures formed by the synthetic jets interacts with the cross flow and develops three-dimensionalities as they advect downstream. The effect of the momentum coefficient (or blowing ratio) on the 3-D interaction was also explored. In the case of low momentum coefficient coherent vortical structures were found to be dominant whereas at high momentum coefficient coherent vortical structures breakdown forming random ones. The agreement between the CFD predictions and the experimental measurements were found to be very good. [Preview Abstract] |
Monday, November 23, 2009 12:14PM - 12:27PM |
HD.00009: Real-time PIV for Active Flow Control Applications Matthew Munson, Christian Willert, Morteza Gharib In pursuit of closed-loop control of vortex formation and separation processes on low-Reynolds number wings, a ``real-time'' particle image velocimetry system has been developed for use in the low Reynolds number oil tunnel facility at the California Institute of Technology. The use of oil as the working fluid provides slow enough dynamics that the typical latencies inherent to the PIV technique remain manageable. This system allows control decisions to be computed directly from a quantitative evaluation of features in the flow field. The performance of the system will be discussed, along with preliminary efforts toward regulation of vortex shedding processes in the wake of a low-aspect ratio rectangular wing. [Preview Abstract] |
Monday, November 23, 2009 12:27PM - 12:40PM |
HD.00010: The Design of Surface Mounted Transducer Arrays for Pressure Field Mapping in Flow Control Applications Mark Potter, Jonathan Morrison, Graham Arthur Advances in the field of flow control are leading to increasing demands being placed on pressure based instrumentation systems, in terms of sensitivity and spatial resolution. This work is aimed at accurately mapping pressure fields, in terms of both pressure and pressure-gradient fluctuations at the wall, to provide essential information for closed-loop flow control. To achieve this mapping, a capacitor-based sensor has been developed and constructed using micro fabrication techniques. Using these techniques, an array of robust surface-mounted transducers, with a sensing diameter of 800$\mu $m, has been developed with the aim of further size reductions in the future. Presented alongside the structure and fabrication methods for this design of pressure sensor is a description of the electronic systems used to determine the changes in the transducer capacitance, required for accurate sensing, along with preliminary results from a transducer array. [Preview Abstract] |
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