基于CFD的柴油机气缸套冷却水空化特性数值分析

Numerical Simulation of Cooling-Water Cavitation of Diesel Engine Cylinder Liner by CFD

基于计算流体力学(CFD)方法对某型柴油机气缸套主推侧冷却水流场的空化动力学特性进行非定常数值模拟。通过观察缸套壁振动过程中冷却水腔内流场压力、水蒸汽汽含率和流速变化,分析了冷却水流场空化特性,研究了相关参数对模拟结果的影响。结果表明,缸套壁附近流场的绝对压力和水蒸汽汽含率均具有周期性变化特性,且与缸套壁的振动周期一致。振幅较大区域为缸套外壁面的中上区域,此处高、低压差较大(达到312.35kPa),低压在水的饱和蒸汽压附近,汽含率在4.7%～0.5%剧烈变化,此位置为冷却水主要空化区域。缸套振幅、振动频率和水温是影响冷却水空化特性的主要因素。振动频率和振幅分别增大30%,最大振幅壁面处高压分别增加50%和10%,流场空化程度增大。缸套壁振动的速度和加速度是影响流场空化程度的关键因素。

The unsteady numerical simulation of cooling-water cavitation in major thrust side of cylinder liner is performed by computational fluid dynamics（CFD） in a diesel engine. Cavitation characteristics of water flow near the liner wall are analyzed. The effects of relating factors on cavitation characteristics are investigated. Results show that the absolute pressure and volume fraction of vapor, on the liner wall, vary periodically in consistence with vibration of liner wall. Maximum pressure difference between high and low pressures appears at the maximum deformed wall, i.e. at middle upper location. Pressure difference reaches 312.35 kPa and low pressure is around the saturated vaporization pressure at this location. Volume fraction of vapor varies greatly within 4.7%-0.5%, and becomes the main cavitation erosion zone of the liner. Water temperature, vibration frequency and amplitude of cylinder liner are the main factors affecting cavitation of cooling water. The high pressure, on the maximum deformed wall, increases by 50% and 10% respectively as vibration frequency and amplitude increase by 30%. As temperature increases from 40 ℃ to 80 ℃, the high vapor ratio decreases by 45% and low vapor ratio increases by 1.1% on the maximum deformed wall. Vibration speed and acceleration of liner wall are the key factors affecting cavitation of water flow near the liner wall.