不同流体介质的空化热力学效应

Thermal effect on cavitation in different fluids

为了分析不同流体介质的空化热力学效应,本文采用数值模拟的方法计算了不同温度的水体、液氮和液氢的空化流动。计算基于均相流模型,采用能较好描述流场非定常特性的FBM湍流模型和考虑热力学效应的修正空化模型,并在能量方程源项中考虑了空化的影响,数值模型和随温度不断更新的物质属性均通过软件二次开发引入。结果表明:对三种不同的流体介质水体、液氮和液氢,空化热力学效应影响依次增强,在同一流体介质中,流体介质的工作温度越接近物质临界点,空化的热力学效应越明显。热力学效应明显主要表现在:空穴长度的缩短程度更大,蒸汽含量降低较多,压降和温降增大。同时发现,流体介质的物质属性决定了热力学效应的影响程度,物质属性主要影响参数包括饱和蒸汽压、液汽密度比和热传导系数,饱和蒸汽压变化梯度增大,液汽密度比和热传导系数变低,上述三种物质属性的变化趋势,导致了该流体介质或者该工作温度下的空化热力学效应较强。

In order to analyze the thermal effect in different liquids,the computations are conducted in wa⁃ter,nitrogen and hydrogen with different temperatures by numerical methods.The computations based on the homogenous multiphase model are conducted around a hydrofoil for three temperatures by implementing FBM turbulence model,which can describe the unsteady cavitation characteristics more exactly and the re⁃vised cavitation model considering the thermal effect.The energy equation considers the cavitation influence in the source term.The numerical models and the variable thermal properties of the fluid are implemented with software.The results show that for water,nitrogen and hydrogen,the thermal effect becomes increasingly obvious,and in the same fluid,the thermal effect is more significant when the operational temperature is near to the critical point.The thermal effect is obviously shown in a shorter cavity length,a more decreased vapour volume fraction and a more distinct pressure and temperature depression.The material properties decide the intensity of the thermal effect on cavitation,the influence material parameters include the saturated vapor pressure,the liquid/vapour density ratio and the thermal conductivity.When the gradient of saturation vapor pressure is larger,the liquid/vapour density ratio and the thermal conductivity decrease,so the thermal effect for this liquid or the operational temperature range is more obvious.