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 D3: Multiphase Flow II: Cavitation |
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Chair: Roger Arndt, University of Minnesota Room: 303 |
Sunday, November 20, 2011 2:10PM - 2:23PM |
D3.00001: Ventilated Supercavities Ellison Kawakami, Roger Arndt Drag reduction and/or speed augmentation of marine vehicles by means of supercavitation is a topic of great interest. During the initial launch of a supercavitating vehicle, ventilation is required to supply an artificial cavity until conditions at which a natural supercavity can be sustained are reached. A study has been carried out to determine various aspects of the flow physics of a supercavitating vehicle at Saint Anthony Falls Laboratory. During the present experimental work, the ventilated supercavity formed behind a sharp-edged disk was investigated using several configurations. Results regarding cavity shape and closure, as well as ventilation requirements versus cavitation number and Froude number are presented. In addition, effects related to flow choking in a water tunnel test section are discussed. Results obtained are similar in character to previously reported results, but differ significantly in measured values. An attempt was made to correlate results from water tunnel experiments to open flows, where there are no effects of flow choking. Supercavitation parameters, especially the minimum attainable cavitation number are found to be strongly affected by tunnel blockage and Froude number. [Preview Abstract] |
Sunday, November 20, 2011 2:23PM - 2:36PM |
D3.00002: Scaling of Partial Cavity Drag Reduction Steven Ceccio, Simo Makiharju, Sarah Schinasi, Marc Perlin Experiments to examine ventilated partial cavities configured for drag reduction were conducted at the U.S. Navy's W. B. Morgan Large Cavitation Channel (LCC) and at the University of Michigan's 1:14$^{th}$ scale model of the LCC. Experiments were focused on the gas flux required to form and maintain stable partial cavities. The models and free surface forming gates were geometrically similar, and the experiments were performed over the same range of Froude numbers. The Reynolds numbers based on downstream distance were up to 80 million for the large and 1.8 million for the small-scale experiments. And, during the small-scale experiments the Weber number was varied by a factor of two to assess the effect of surface tension on the required air flux. The measured air fluxes normalized by flow speed, model span and step height varied by one to two orders of magnitude with the change of Reynolds number, and this is primarily due to the different gas entrainment process at the cavity closure. Variation of the Weber number at the small scale modestly changed the required gas fluxes. [Preview Abstract] |
Sunday, November 20, 2011 2:36PM - 2:49PM |
D3.00003: Numerical Simulation of Cavitating Flows Aswin Gnanaskandan, Krishnan Mahesh We are developing the capability to simulate cavitating flows (e.g sheet to cloud cavitation transition) in complex geometries. The compressible flow solver (Park \& Mahesh, AIAA Paper 2007-0722) has been extended to solve for multiphase flows on unstructured meshes. A multi-phase medium is constructed using a homogenous equilibrium model that assumes thermal equilibrium between the liquid phase and the vapor phase. The algorithm solves the compressible Navier Stokes Equations for the liquid/vapor medium along with the transport equation for the liquid's mass fraction. A characteristic-based shock capturing scheme is extended to handle non-ideal gases and mixtures, and applied in a predictor-corrector approach. The base scheme is non-dissipative and this approach ensures that the shock-capturing is active only in the regions of discontinuity. We will present details of this algorithm, its implementation, and validation. [Preview Abstract] |
Sunday, November 20, 2011 2:49PM - 3:02PM |
D3.00004: Large Eddy Simulation of cavitating turbulent flows Sergei Chumakov, David Cook, Frank Ham, Uwe Iben Large Eddy Simulation of a turbulent cavitating flow has been performed using the explicit spatially-filtered compressible Navier-Stokes solver Charles. The unstructured finite volume method uses a blended central-upwind scheme in single-phase regions to minimize artificial damping of resolved turbulence scales and switches to a lower-order reconstruction and an HLLC approximate Riemann solver to capture discontinuities associated with the phase change. Time discretization is performed with an explicit third order Runge Kutta scheme. Comparison between the simulations results and classic 1-D Riemann problems with and without cavitation are presented, as well as comparison with the cavitating flow experiments from the current literature. [Preview Abstract] |
Sunday, November 20, 2011 3:02PM - 3:15PM |
D3.00005: Cavitation inception criteria for hydrokinetic turbine blades Ivaylo Nedyalkov, Martin Wosnik Cavitation can adversely affect the performance of hydrokinetic turbines, and cause noise, vibration and even erosion. In some cases, unstable operation can be caused by cavitation-induced flow instabilities. A theoretical model for cavitation inception criteria on the blades of hydrokinetic turbines was developed by deriving cavitation numbers using turbine momentum theory and Airy wave theory. The cavitation number on a turbine blade element is calculated as a function of tip speed ratio, axial and angular induction factors at the rotor - which depend on the turbine's operating condition - and location on the blade, blade rotation angle, free stream velocity, wave-induced pressure oscillation, wave-induced velocities, time-dependent turbine hub submergence, vapor pressure, and free stream turbulence. With cavitation maps for specific hydrofoil shapes, which exist for some basic foil shapes, or can be obtained from inexpensive experiments in a small high-speed water tunnel where velocity and pressure can be controlled independently, the physical cavitation inception limits $\sigma_{i}$ and $(\sigma/2\alpha)_{i}$ can be determined. With this model, safe deployment depths and safe tip speed ratios for specific turbines installed at a given site can be predicted. The model is compared to the common cavitation inception scaling with lift coefficient or Reynolds number. [Preview Abstract] |
Sunday, November 20, 2011 3:15PM - 3:28PM |
D3.00006: General linear theory for sound waves accompanied with evaporation and condensation Masashi Inaba, Takeru Yano, Masao Watanabe When a sound wave in a vapor is reflected at an interface between the vapor and its liquid, the evaporation and condensation occurs in addition to the partial penetration of the wave into the liquid. Although the sound propagation outside the boundary layer is as usual governed by the linear wave equation, the boundary condition at the interface should carefully be treated in the kinetic theory of gases even if the Knudsen number (Kn) defined by the ratio of the mean free path of gas molecules to a typical wavelength is sufficiently small compared with unity. We therefore execute a general analysis of the entire flow field by using the ES-BGK model of the Boltzmann equation applicable to polyatomic gases and a general kinetic boundary condition at the interface. As a result of the asymptotic analysis for small Kn with the assumption that an acoustic Mach number is sufficiently small compared with Kn, we retrieve the linearized Euler equations outside the boundary layer and the so-called slip boundary conditions for the Euler and boundary layer equations. The coefficients in the slip conditions are determined by the Knudsen layer analysis. The effect of phase changes on the waves is illustrated by a simple example of plane standing wave. [Preview Abstract] |
Sunday, November 20, 2011 3:28PM - 3:41PM |
D3.00007: Fluid-structure interaction response and stability of flexible hydrofoils in cavitating flow Yin Lu Young, Antoine Ducoin, Eun Jung Chae There is an increasing interest in the use of passive/active control mechanisms to take advantage of the fluid-structure interaction response of flexible lifting bodies to improve propulsive efficiency and performance from ambient flow. However, design of these flexible lifting bodies are not trivial, particularly for heavily loaded and cavitating, off-design conditions, because of potential hydroelastic instability failure mechanisms such as divergence or flutter. Hence, the objectives of this research are to (i) develop and validate an efficient coupling procedure to predict the hydroelastic response of flexible hydrofoils in unsteady flows, and (ii) investigate the influence of fluid density and viscosity on the FSI response and stability of flexible hydrofoils in cavitating flows. A multiphase CFD code is coupled with a simplified 2-DOF model to represent the spanwise bending and twisting response of a flexible hydrofoil. The influence of coupling algorithms on the accuracy and stability of the numerical predictions are discussed. [Preview Abstract] |
Sunday, November 20, 2011 3:41PM - 3:54PM |
D3.00008: Three-dimensional investigation of the response of bubble/particle motion to grid generated turbulence Sam Raben, Pavlos Vlachos Multiphase turbulent flow can be found in numerous different environments, from biological applications to industrial mineral processing. Often it is desirable to know how the discrete phase, bubbles and/or particles, respond to the turbulent fluctuations present in the surrounding flow. Previous works have developed empirical and semi- empirical relationships for the slip velocity, RMS motion, and collision rates for these discrete phases. These relationships were based upon 1- or 2-D samplings of the flow and therefore were approximations for the field as a whole. This work evaluates the validity of these relationships through the use of Tomographic PIV. Tomographic imaging it capable of providing not only information about the three-dimensional flow field but also motion of the discrete phases as well. An experiment was conducted in grid-generated turbulence where solid particles and bubbles where added. By fully resolving the motion of the flow field and objects present therein, the RMS and slip velocity could be calculated directly. This direct calculation was used to evaluate the validity of the currently available models. [Preview Abstract] |
Sunday, November 20, 2011 3:54PM - 4:07PM |
D3.00009: Influence of the bubbles on the turbulence in the liquid in hydrodynamic cavitation through a venturi Sylvie Fuzier, Olivier Coutier Delgosha, S\'ebastien Coudert, Antoine Dazin The physical description of hydrodynamic cavitation is complex as it includes strongly unsteady, turbulent and phase change phenomena. Because the bubbles in the cavitation area render this zone opaque, nonintrusive experimental observation inside this zone is difficult and little is known about the detailed bubble, flow structure and physics inside. A novel approach using LIF-PIV to investigate the dynamics inside the cavitation area generated through a venturi is presented. The velocity in the liquid and of the bubbles are measured simultaneously and correlated with areas of various bubble structure. The influence of the bubble structure on the turbulence in the liquid is also studied. [Preview Abstract] |
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