Analysis of Thermal Effects in a Cavitating Orifice Using Rayleigh Equation and Experiments

Abstract

The focus of this research is the experimental and analytical study of the cavitation phenomena in internal flows in presence of thermal effects. Experiments have been done on water and nitrogen cavitating flow in orifices. Transient growth process of the cloud cavitation induced by flow through the throat is observed using high-speed video images and analyzed by pressure signals. Cavitation of thermo-sensible fluid, as cryogenic fluid, presents additional complexities (as compared to that in water) because thermal effects are important. The different cavitating behavior at different temperature and different fluid is related to the bubble dynamic inside the flow. To investigate possible explanations for the influence of fluid temperature on cavitating internal flow, initially, a steady, quasi-one dimensional model has been implemented. The nonlinear dynamics of the bubbles has been modeled by Rayleigh-Plesset equation. In the case of nitrogen, thermal effects in the Rayleigh equation are taken into account by considering the vapor pressure at the actual bubble temperature Tc, which is different from the liquid temperature T far from the bubble. A convective approach has been used to estimate the bubble temperature. The quasi-steady one dimensional model can be extensively used to conduct parametric studies useful for fast estimation of the overall performance of any geometric design. For complex geometry, three-dimensional CFD codes are necessary. In the present work comparison have been done with numerical predictions by the CFD Fluent code in which a simplified form of the Rayleigh equation taking into account thermal effects has been implemented by external user routines.