Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session R21: Vortex Dynamics VII |
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Chair: Mohamed Farhat, EPFL Room: 324-325 |
Tuesday, November 22, 2011 12:50PM - 1:03PM |
R21.00001: How leakage flow influences the hydrodynamic damping of a vibrating blade Matthieu Dreyer, Etienne Cartier, Steven Roth, Mohamed Farhat The hydrodynamic damping of a structure is of particular importance in many engineering applications. In the case of axial turbines, the presence of a gap between the rotor tip and the shroud induces a leakage flow creating a tip vortex whose roll up process is highly dependent on the clearance size. The blade response to an excitation in the presence of this flow is however poorly characterized. In the present study, the hydrodynamic damping of a Naca hydrofoil in a water tunnel is investigated with respect to the gap width. An innovative device was designed to excite the hydrofoil in non-intrusive way: an underwater electric discharge creates a fast growing and collapsing bubble which generates strong shockwaves. The structural response is monitored with a Laser Vibrometer. Assuming a single degree of freedom system, the hydrodynamic damping for the first two eigen modes (bending and torsion) is identified for different values of upstream velocity, incidence angle and tip clearance size. [Preview Abstract] |
Tuesday, November 22, 2011 1:03PM - 1:16PM |
R21.00002: Counter rotating open rotor flow field investigation using stereoscopic Particle Image Velocimetry Eric Roosenboom, Andreas Schroeder, Reinhard Geisler, Dieter Pallek, Janos Agocs, Klaus-Peter Neitzke Counter rotating open rotor (CROR) propulsive systems are again considered as fuel efficient alternatives to conventional propulsion systems. In the present paper details of dedicated experiments on a generic CROR model are studied using stereoscopic Particle Image Velocimetry. The CROR model has 10 front blades and 8 aft blades, with blade design similar to modern propellers for high disk loadings. Recent progress in Particle Image Velocimetry applications to propeller flow analysis is used to further develop the technique for application to CROR systems. Stereoscopic Particle Image Velocimetry (SPIV) has been applied for the flow field investigation behind a counter rotating open rotor (CROR) model in order to enable experimental insight in the complex flow phenomena of multiple vortex structures. The paper discusses a dedicated triggering strategy for the determination of the phase positions of both propellers using the phase delays and revolution periods. Results of the PIV measurements are presented and the topological events of the rotor-interactions are discussed. [Preview Abstract] |
Tuesday, November 22, 2011 1:16PM - 1:29PM |
R21.00003: A comparison between the growth of leading-edge and tip vortices on a low aspect ratio plate using 3D-PTV Colin Hartloper, David Rival, David Wood, Matthias Kinzel The vortex formation process on an impulsively started flat plate at 45 degree incidence is studied using both direct force measurements as well as 3D-PTV. The focus of this experiment has been to study the competing evolution of leading-edge and tip vortices for a range of start-up motions. The 3D-PTV measurement volume, located in the tip region of the plate, provides detailed insight into the roll-up of the shear layers at early stages of the motion. By quantifying the evolution of circulation at various spanwise and tip locations, we are able to relate the unsteady generation of force to the instantaneous vortex topology present around the plate. [Preview Abstract] |
Tuesday, November 22, 2011 1:29PM - 1:42PM |
R21.00004: Influence of outlet geometry on the swirling flow in a simplified model of a large two-stroke marine diesel engine S. Haider, T. Schnipper, K.E. Meyer, J.H. Walther, S. Mayer We present Stereoscopic particle image velocimetry measurements of the effect of a dummy-valve on the in-cylinder swirling flow in a simplified scale model of a large two-stroke marine diesel engine cylinder using air at room temperature and pressure as the working fluid and Reynolds number 19500. The static model has stroke-to-bore ratio of 4, is rotationally symmetric and the in-cylinder swirling flow is enforced by angled ports at the inlet. We consider a case analogous to engine when the piston is at bottom-dead-center. In absence of an exhaust valve the overall axial velocity profile is wake-like and flow reversal is observed on the cylinder axis, close to the inlet. Downstream, the flow reversal disappears and instead a localized jet develops. The corresponding tangential velocity profiles show a concentrated vortex with decreasing width along the downstream direction. By placing a concentric dummy-valve at the cylinder outlet, the magnitude of reverse flow at the inlet increases, the strong swirl is diminished and the axial jet disappears. We compare these findings with previous measurements in vortex chambers and discuss the relevance of these results with respect to development of marine engines. [Preview Abstract] |
Tuesday, November 22, 2011 1:42PM - 1:55PM |
R21.00005: The effect of non-zero radial velocity on the impulse and circulation of starting jets Michael Krieg, Kamran Mohseni Vortex ring formation dynamics are generally studied using two basic types of vortex generators. Piston cylinder vortex generators eject fluid through a long tube which ensures a purely axial jet; whereas, vortex ring generators which expel fluid through a flat plate with a circular orifice produce 2-D jets (non-zero radial velocity). At the nozzle exit plane of the orifice type vortex generator the radial component of velocity is linearly proportional to the radial distance from the axis of symmetry, reaching a maximum at the edge of the orifice with a magnitude around 10 \% of the piston velocity (the ratio of the volume flux and the nozzle area). As the jet advances downstream the radial velocity quickly dissipates, and becomes purely axial less than a diameter away from the nozzle exit plane. The radial velocity gradient in the axial direction plays a key role in the rate at which circulation and impulse are ejected from the vortex generator. Though the radial component of velocity is small compared to the axial velocity, it has a significant effect on both the circulation and impulse of the starting jet because of this gradient. The extent of circulation and impulse enhancement is investigated through experimental DPIV data showing that the orifice device produces nearly double both circulation and energy (with identical piston velocity and stroke ratios). [Preview Abstract] |
Tuesday, November 22, 2011 1:55PM - 2:08PM |
R21.00006: Effects of ground plane topology on vortex-ground interactions in a forced impinging jet Jayson Geiser, Kyle Corfman, Ken Kiger The phenomenon of a three-dimensionally unstable vortex-ground interaction is studied, motivated by the problem of sediment suspension by vortex-wall interactions from landing rotorcraft. In the current work, the downwash of a rotorcraft is simplified using a prototype flow consisting of an acoustically forced impinging jet. The goal of the current investigation is to quantify the effects of disturbances to the ground-plane boundary layer on the three-dimensional development of the vortex ring as it interacts with the ground plane. A small radial fence is employed to perturb the natural evolution of the secondary vortex, which typically exhibits azimuthal instabilities as it is wrapped around the primary vortex. The fence is observed to localize and intensify the azimuthal development, dramatically altering the mean flow in this region and generating corresponding azimuthal variations in the turbulent near-wall stresses. Multi-plane ensemble-averaged stereo PIV is employed to obtain volumetric, phase averaged data sets that are subjected to a triple decomposition to fully quantify turbulence effects. The effects of the radial fence are examined at both a high and low Reynolds number flows (Re = $\Gamma/\nu$ = 50,000 and 10,000, respectively), and the data is analyzed in the context of structures leading to significant sediment mobilization. [Preview Abstract] |
Tuesday, November 22, 2011 2:08PM - 2:21PM |
R21.00007: Mach Number Effect on the Characteristics of a Free Pulsed Jet Isaac Choutapalli An experimental study was carried out on a free pulsed jet over a Mach number range of 0.3 to 0.8. The data was obtained using Particle Image Velocimetry (PIV). The global flow field of the pulsed jet showed that over the range of Mach numbers considered, the centerline velocity decay, jet spreading and the normalized mass flow rate for a given Strouhal number (St = fd/Uj; where f is the frequency of pulsation, d is the nozzle exit diameter and Uj is the time-averaged axial velocity at the nozzle exit) are only weakly dependent on the nozzle exit Mach number. The phase-averaged results show that the vortex ring circulation is also weakly dependent on the nozzle exit Mach number for a given Strouhal number. The vortex ring pinch-off was found to be independent of the nozzle exit Mach number but dependent on the pulsing frequency. [Preview Abstract] |
Tuesday, November 22, 2011 2:21PM - 2:34PM |
R21.00008: High-speed schlieren videography of vortex-ring impact on a wall Benjamin Kissner, Michael Hargather, Gary Settles Ring vortices of approximately 20 cm diameter are generated through the use of an Airzooka toy. To make the vortex visible, it is seeded with difluoroethane gas, producing a refractive-index difference with the air. A 1-meter-diameter, single-mirror, double-pass schlieren system is used to visualize the ring-vortex motion, and also to provide the wall with which the vortex collides. High-speed imaging is provided by a Photron SA-1 digital video camera. The Airzooka is fired toward the mirror almost along the optical axis of the schlieren system, so that the view of the vortex-mirror collision is normal to the path of vortex motion. Vortex-wall interactions similar to those first observed by Walker et al. (JFM 181, 1987) are recorded at high speed. The presentation will consist of a screening and discussion of these video results. [Preview Abstract] |
Tuesday, November 22, 2011 2:34PM - 2:47PM |
R21.00009: ABSTRACT WITHDRAWN |
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