CFD Investigation of an Oscillating Structure Placed in a Liquid Medium

Investigation of flow structure in a system comprising of an oscillating structure immersed in a liquid medium has been extensively studied by researchers. Their applications in industrial processing are generally based on the non-linear effects produced by finite amplitude pressure variations created by the oscillating structure. The high frequency oscillations of the structure placed in the liquid medium creates a rapid series of alternating contractions and expansions pressure fields. These amplitudes associated with the high frequency oscillations are accompanied by a series of phenomena such as highly intensified radiation pressure, heat generation, acoustic streaming, agitation, cavitation, interface instabilities and friction, diffusion and mechanical rupture. The high frequency oscillations impart the translation momentum into the liquid during the first half of the cycle and absorb the same in the remainder of the cycle. This paper investigates the cavitation phenomenon, defined as creation of vapor pockets when the liquid pressure falls below the vaporization pressure of the liquid, associated with high frequency oscillations of a structure placed in a liquid medium. This has been performed using CFD analysis of such high frequency oscillations of a structure in a liquid medium using commercially available software. The grids used in the simulations are resolved fine enough to capture the physics of the flow and numerically stabilize the simulation. This transient simulation reveals high pressure gradients close to the oscillating structure due to their rapid motion, which is a function of frequency and amplitude of the vibration. The inception of cavitation phenomenon is associated with highly non-linear vapor bubble dynamics. Discussions on the velocity contours and the distribution of phases in the flow have been carried out in detail with highlights on the bubble dynamics. The use of CFD in simulating fluid structure interaction as in the case above, help us understand the nonlinear effects originating from the generation of high intensity pressure driven fields and their interaction with the medium.