Thermal Effects on Cryogenic Cavitating Flows around an Axisymmetric Ogive

Abstract

Cavitation in cryogenic fluids generates substantial thermal effects and strong variations in fluid properties, which in turn alter the cavity characteristics. In order to investigate the cavitation characteristics in cryogenic fluids, numerical simulations are conducted around an axisymmetric ogive in liquid nitrogen and hydrogen respectively. The modified Merkle cavitation model and energy equation which accounts for the influence of cavitation are used, and variable thermal properties of the fluid are updated with software. A good agreement between the numerical results and experimental data are obtained. The results show that vapor production in cavitation extracts the latent heat of evaporation from the surrounding liquid, which decreases the local temperature, and hence the local vapor pressure in the vicinity of cavity becomes lower. The cavitation characteristics in cryogenic fluids are obtained that the cavity seems frothy and the cavitation intense is lower. It is also found that when the fluid is operating close to its critical temperature, thermal effects of cavitation are more obviously in cryogenic fluids. The thermal effect on cavitation in liquid hydrogen is more distinctively compared with that in liquid nitrogen due to the changes of density ratio, vapour pressure gradient and other variable properties of the fluid.

Numerical study of thermodynamic effects on liquid nitrogen cavitating flows

“…(4) represent for the evaporation and condensation rates during mass transfer process. The liquid-vapor evaporation and condensation rates for the present transport equation-based cavitation model [7-9,23,3 1,33, [45][46][47][48] are respectively shown as following:…”

“…C dest and C prod are two empirical coefficients, respectively, which are defined as C dest = 3.8, C prod = 20 [47,48], U 1 is the reference velocity scale, and t 1 is the reference time scale, which is the characteristic length scale L c divided by the reference velocity scale U 1 (t 1 = L c /U 1 ). a l is liquid volume fraction, p v is the saturated vapor pressure.…”

“…Reviewing the state-of-the-arts numerical method for attached cavitating flows, homogeneous model, Favre-averaged NavierStokes equations and turbulence closures, and a transport equation-based cavitation model is capable handling because of its satisfactory robustness and reasonable prediction capability for simulating the cavitating flows [7][8][9]23,31,33,[45][46][47][48]. Based on the framework which is coupled with energy equation, the liquid nitrogen cavitating flows are numerical investigated, the present aims are to study thermodynamics effects on cryogenic cavitating flows and analyze the specific effects on cavitation mass transportation process and flow field structure.…”