螺旋桨初生空化湍流的多相流数值模拟

Multi-phase Numerical Simulation of Propeller Turbulent Cavitation Inception Flow

同时采用修正剪切应力输运(SST)湍流模型和Baseline雷诺应力模型(RSM)求取了E779A螺旋桨在无空化状态和初生空化状态下的梢涡运动轨迹,分析了涡核最小压力系数、湍动能、轴向速度分量和涡核半径沿运动轨迹的变化,并从模拟得到的梢涡卷曲起始和梢涡涡束的角度阐述了梢涡形成机理.空化模型采用改进Sauer模型,考虑了非凝结性气核质量分数、体积分数和气泡初始半径以及湍流脉动的影响,并针对轻度、中度和重度空化面积进行了可信性校验.当空化数σ>初生空化数σi时,叶梢截面压力系数分布相对不再改变的判定准则来确定.涡核中心位于螺旋线垂向截面上最小压力点,涡核边界由湍流涡频率峰值决定.数值模拟结果表明,RSM模拟梢涡路径较修正SST湍流模型稍长、局部梢涡空化范围略大、叶梢最小压力系数和轴向速度分量要小,涡核湍动能分布更为合理.但两者模拟得到的涡核运动轨迹几乎重合,并且初生空化状态下的涡核运动轨迹、最小压力系数和轴向速度分布均与各自无空化状态下非常接近,表明了初生空化状态判定的正确性和改进数值模型对梢涡运动轨迹模拟的适用性.

Both of the modified SST turbulence model and BSL Reynolds stress model were used to predict the tip vortex trajectories of E779A propeller under non-cavitation and cavitation inception conditions. The vortex core＇s minimum pressure coefficient, turbulent kinetic energy, axial velocity component and vortex size distribution related to the trajectory were analyzed at the same time, and the flow physics of tip vortex was presented from the flow field with tip vortex crimp beginning and streamtube formation. The im- proved Sauer cavitation model accounting for the effects of non-condensable gas＇s mass and volume fraction and the bubble initial radius on cavitation inception and the effect of turbulence on phase-change pressure threshold was adopted along with validation of the cavity pattern and area of E779A propeller under light- ly, moderately and heavily cavitation levels. The cavitation inception index was determined by the rule of ＂when σ〉σi, the pressure coefficient of the blade tip section is relative unaltered＂. The minimum pressure in vortex core on perpendicular cross plane was used to locate the vortex center, and vortex core bound was determined by the peak of turbulent eddy frequency. The results show that a slightly longer tip vortex trajectory appears with the BSL RSM model than the modified SST model as well as a litter bigger local tip vortex cavitation extension and more reasonable turbulent kinetic energy distribution, while the minimum pressure coefficient and axial velocity in blade tip region are smaller. On the other hand, the tip vortex trajectories captured by the two models almost superpose along with nearly the same tip vortex trajecto- ries, minimum pressure coefficient and axial velocity distribution between non-cavitation and cavitation in- ception condition of the two models respectively, which proves that the determination of cavitation incep tion by the rule is reasonable, and the adopted modified numerical models are appropriate to simulate the tip vortex trajectory.