发动机喷嘴内部空化初生的数值模拟研究

Numerical Simulation of Cavitation Inception in Engine Orifice

采用全空化模型研究了具有不同物性(黏性、饱和蒸汽压和表面张力)的流体在不同几何形状(入口圆角半径和长径比)喷嘴中的空化现象,用临界空化压力和临界空化数对不同条件下空化的初生进行了分析与表征。结果表明:流体的黏性越大,饱和蒸汽压越小,空化初生的临界压力就越大,而表面张力对临界空化压力没有影响;在入口圆角半径较大和喷嘴长径比较大的喷嘴中,临界空化压力较大,在流体黏性和喷嘴几何形状相同的情况下,虽然临界空化压力会随着流体饱和蒸汽压的变化而变化,但临界空化数基本保持不变;由于喷嘴几何形状的改变造成了流体方向的变化和流体与孔壁之间摩擦损耗的变化,而流体物性的变化影响了流体内部的连续性,因此,喷嘴几何形状和流体物性是影响临界空化压力和临界空化数变化的关键因素。

This paper investigated the effects of fluid characteristics and orifice geometry on cavitation inception in orifice.A full cavitation model was implemented in case of the fluids with different properties（viscosity,vapor pressure and surface tension） and the orifice with different geometries（inlet radius and length-to-radius（L/d） ratio）.The formation and development of cavitation inside the orifice were analyzed quantitatively based on both parameters of critical cavitation pressure and critical cavitation number.According to the numerical simulation,it is revealed that the critical cavitation pressure increases with the increase of fluid viscosity and the decrease of vapor pressure of fluid.But the surface tension of fluid has not relative with cavitation inception.The critical cavitation pressure also increases with inlet radius and length-to-radius ratio.In case of fluids with same viscosity and same orifice,the critical cavitation number has little variation,though the critical cavitation pressure would change with variation of vapor pressure of fluids.Both of critical cavitation pressure and critical cavitation number change from the variations of frictional loss between the wall and fluids,flow direction due to different geometries of orifice;and from the continuity variation in-side fluids due to the variation of fluid properties.