高功率密度液力变矩器空化特性研究

High power-density torque converter is prone to cavitation due to high circular velocity and low local pressure, consequently leading to performance degradation. Both experimental and numerical studies are carried out on the cavitation phenomena in a torque converter. A series of hydraulic performance tests are performed under different wheel speeds and charging pressures to reveal the relation between cavitation and operating/charging conditions. A full wheel transient cavitation model based on Rayleigh-Plesset equation is built to capture the two-phase cavitating flows inside torque converter under variant operating conditions. The stress-blended eddy simulation (SBES) model is adopted to calculate the turbulent behavior inside the torque converter. Both experimental and numerical results revealed that cavitation might occur under high pump speed, low speed ratio and low charging pressure conditions, and the cavitation degree increased with a decreasing speed ratio. The worst-case-scenario for cavitation is the stall operating condition. Large amount of cavitation bubbles are generated in the stator domain, blocked the main circular flow and reduced the mass flow rate, resulting in capacity degradation as high as 31%. The full wheel transient cavitation model is able to predict the cavitating hydraulic performance precisely. By considering cavitation, the maximum prediction error for torque ratio, capacity factor and efficiency is reduced from 30% to 5%.