Application of the improved cavitation model to turbulent cavitating flow in fuel injector nozzle

摘要

Cavitation phenomenon occurring inside diesel injector nozzles plays a key role in atomization of fuel spray. The most common approach to numerically model the cavitating flow is Volume-Of-Fluid (VOF) method, which employs the governing equations for a perfect gas-liquid mixture often in combination with a transport equation for liquid or gas volume fraction. A mass transfer model is required to evaluate the phase change between liquid and vapor. Most of the mass transfer models use the simplest bubble dynamics model, Rayleigh (R) equation which is sometimes called simplified Rayleigh-Plesset (RP) equation, to simulate the growth and collapse of bubbles based on the vapor saturation pressure P_v. We have found that R equation over-predicts cavitation when local pressure is slightly below P_v. We have proposed the Modified Rayleigh (MR) equation taking into account the critical pressure P_c, and showed its validity in some simple test cases with uniform pressure. In this study, the applicability of the MR equation to turbulent cavitating flows in a fuel injector nozzle is examined. OpenFOAM is used for the numerical simulation of turbulent cavitating flows in an one-side rectangular nozzle whose images have been captured by a high-speed camera and the turbulent velocity has been measured by a Laser Doppler Velocimetry (LDV). Turbulent effect is taken into account using RNG k-ε model. The numerical results are compared with the experimental data and the turbulent recirculation flow, re-entrant jet and cloud cavitation shedding are well simulated by the MR model.