Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session E3: Multiphase Flows III |
Hide Abstracts |
Chair: Deniz Tolga Akcabay, University of Michigan Room: 325 |
Sunday, November 24, 2013 4:45PM - 4:58PM |
E3.00001: Computation of Cavitating Flow in a Francis Hydroturbine Daniel Leonard, Jay Lindau In an effort to improve cavitation characteristics at off-design conditions, a steady, periodic, multiphase, RANS CFD study of an actual Francis hydroturbine was conducted and compared to experimental results. It is well-known that operating hydroturbines at off-design conditions usually results in the formation of large-scale vaporous cavities. These cavities, and their subsequent collapse, reduce efficiency and cause damage and wear to surfaces. The conventional hydro community has expressed interest in increasing their turbine's operating ranges, improving their efficiencies, and reducing damage and wear to critical turbine components. In this work, mixing planes were used to couple rotating and stationary stages of the turbine which have non-multiple periodicity, and provide a coupled solution for the stay vanes, wicket gates, runner blades, and draft tube. The mixture approach is used to simulate the multiphase flow dynamics, and cavitation models were employed to govern the mass transfer between liquid and gas phases. The solution is compared with experimental results across a range of cavitation numbers which display all the major cavitation features in the machine. Unsteady computations are necessary to capture inherently unsteady cavitation phenomena, such as the precessing vortex rope, and the shedding of bubbles from the wicket gates and their subsequent impingement upon the leading edge of the runner blades. To display these features, preliminary unsteady simulations of the full machine are also presented. [Preview Abstract] |
Sunday, November 24, 2013 4:58PM - 5:11PM |
E3.00002: Understanding and Toward Controlling the Hydroelastic Response and Stability of Hydrofoils in Cavitating Flows Deniz Tolga Akcabay, Yin Lu Young This study examines the hydroelastic behavior of hydrofoils in cavitating flows. The hydrofoil was modeled as a 2-D structure which can undergo spanwise bending and twisting deformations and the flow is modeled through the unsteady RANS equations. The results show that: 1) amplitude of the dynamic load fluctuations on the hydrofoil can exceed their mean values as the highest load fluctuations and vibrations occur when maximum cavity length is close to foil trailing edge, and the fluctuations decrease when in stable supercavitation; 2) lock-in can lead to dynamic load amplifications and focusing of the frequency at the system resonance frequency, and the system resonance frequency varies with cavitation volume due to changes with fluid added mass; 3) viscous effects, in general, tend to delay static divergence, but unsteady cavity/vortex shedding can lead to flutter and lock-in; 4) the mean hydroelastic loads/deformations are bounded by the stall limit and quasi-steady potential flow estimates for the fully wetted and supercavitating regimes; and 5) transient, viscous fluid-structure interaction models are needed to predict the dynamic response and stability of flexible hydrofoils. Finally, results will be shown to illustrate potential strategies that could be used to minimize cavitation and enhance stability. [Preview Abstract] |
Sunday, November 24, 2013 5:11PM - 5:24PM |
E3.00003: An acoustically accurate method to simulate turbulent cavitating flows Aswin Gnanaskandan, Krishnan Mahesh An acoustically accurate method involving transport of energy equation has been developed to simulate cavitating flows to study sheet to cloud cavitation transition in complex geometries. The algorithm uses a compressible homogeneous equilibrium model and solves transport equation for the vapor's mass fraction along with the compressible Navier-Stokes equation for the mixture. The internal energy equation is demonstrated to discretely outperform the total energy equation. A novel characteristic based filtering method has been developed for multiphase flows and is applied in a predictor-corrector approach, ensuring zero dissipation away from discontinuities. A dynamic Smagorinsky model is used for both Navier Stokes and the scalar transport equation. The algorithm has been validated for a variety of problems. Details of the methodology along with simulation results will be discussed. [Preview Abstract] |
Sunday, November 24, 2013 5:24PM - 5:37PM |
E3.00004: Measurements on a cavitating wedge Harish Ganesh, Simo Makiharju, Steven Ceccio Three types of cavitation on a wedge; incipient, transient, and periodic shedding, were chosen to perform extensive flow measurements to establish a reliable experimental dataset for CFD validation. Two time-synchronized high-speed video cameras were used to film the cavitation events from the top and side. A common time base was used to synchronize the cameras with unsteady pressure pulse signature during the cavitation cloud collapse, surface impedance probes implanted on the wedge surface, and flow properties measurement devices. This enabled the possibility to correlate the processes observed in the video to measured flow properties. The whole process was repeated by replacing the high speed video cameras with a time resolved X-ray densitometry system to measure the void fraction distribution synchronously with other flow measurements. Based on all the measurement data, significant physical processes that dominate the cavitation dynamics were identified. [Preview Abstract] |
Sunday, November 24, 2013 5:37PM - 6:03PM |
E3.00005: Apker Prize Lecture: Using 3D Printing and Stereoscopic Imaging to Measure the Alignment and Rotation of Anisotropic Particles in Turbulence Guy Marcus, Shima Parsa, Stefan Kramel, Rui Ni, Greg Voth We have developed a general methodology to experimentally measure the time-resolved Lagrangian orientation and solid body rotation rate of anisotropic particles with arbitrary aspect ratio from standard stereoscopic video image data. We apply these techniques to particles advected in a $R_\lambda \approx 110$ fluid flow, where turbulence is generated by two grids oscillating in phase. We use 3D printing technology to design and fabricate neutrally buoyant rods, crosses (two perpendicular rods), and jacks (three mutually perpendicular rods) with a largest dimension of 7 times the Kolmogorov length scale, which makes them good approximations to tracer particles. We have measured the mean square rotation rate, $\dot{p}_i \dot{p}_i$, of particles spanning the full range of aspect ratios and obtained results that agree with direct numerical simulations. By measuring the full solid-body rotation of jacks, we provide a new, extensible way to directly probe the Lagrangian vorticity of a fluid. We also present direct measurements of the alignment of crosses with the direction of their solid body rotation rate vector---in agreement with direct numerical simulations. [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