声空化条件下传动液体积弹性模量的时空演变

Spatiotemporal Evolution of Bulk Elastic Modulus of Transmission Fluid under Acoustic Cavitation

传动液体积弹性模量代表介质的抗压缩能力,其动态变化会影响传动系统的精准调控。以含有空气和蒸汽的ISO 4113试验油为研究对象,建立传动管内体积弹性模量均相流模型和动态模型,考虑由传动液压缩引起的温度变化以及空化效应(空气空化、蒸汽空化和伪空化),在Roe格式分解和Steger Warming通量分裂法的基础上提出一种新的数值求解方法来预测不同空化区中压力和含气率的变化,并预测体积弹性模量的时空演变。讨论压力、含气率和温度对动态体积弹性模量的影响,并比较两种模型之间的区别。结果表明:在低压区,两种模型对动态体积弹性模量的预测结果基本吻合;当压力小于1 MPa,动态体积弹性模量随压力增大而增大,随初始含气率增大而减小,而初始温度对其影响不明显;当压力在1~10 MPa内,动态体积弹性模量随压力增大而快速增大,随初始含气率和温度增大而减小,其变化率不断减小;在初始含气率小于5%的条件下,动态模型预测的动态体积弹性模量-压力曲线更平滑;当压力大于10 MPa,在均相流模型中,动态体积弹性模量随压力增大呈线性缓慢增长趋势,而在动态模型中,由于气体不断溶解,动态体积弹性模量随压力增大而趋于稳定。对比发现,均相流模型适用于低压条件,而动态模型在高压区也同样适用。

The bulk elastic modulus represents the anti-compression capacity of the transmission fluid,and its dynamic change will affect the precise regulation on transmission system.Taking ISO 4113 test oil containing air and steam as the research object,a homogeneous flow model and a dynamic model for the bulk modulus of elasticity in the transmission pipe were established.Considering the temperature change and cavitation effects(air cavitation,steam cavitation,and pseudo-cavitation)caused by the compression of transmission fluid,based on Roe scheme decomposition and Steger Warming flux splitting method,a new numerical solution method was proposed to predict the changes of pressure and void fraction in different cavitation zones,and the spatiotemporal evolution of bulk elastic modulus was predicted.The effects of pressure,void fraction,and temperature on the dynamic bulk modulus were discussed,and the differences between the two models were compared.The results show that in the low-pressure region,the prediction results of the dynamic bulk elastic modulus of the two models are basically consistent;when the pressure is less than 1 MPa,the dynamic bulk elastic modulus increases with the increase of pressure and decreases with the increase of the initial void fraction,while the effect of initial temperature is not obvious;when the pressure is within 1 MPa to 10 MPa,the dynamic bulk elastic modulus increases rapidly with the increase of pressure,decreases with the increase of initial void fraction and temperature,and its change rate decreases continuously;when the initial void fraction is less than 5%,the dynamic bulk elastic modulus-pressure curve predicted by the dynamic model is smoother;when the pressure is greater than 10 MPa,in the homogeneous flow model,the dynamic bulk elastic modulus increases linearly and slowly with the increase of pressure,while in the dynamic model,the dynamic bulk elastic modulus tends to be stable with the increase of pressure due to the continuous dissolution of gas.The comparison shows that the homogeneous flow model is suitable for low pressure,and the dynamic model is also suitable for high pressure.