超声速膨胀器变工况特性研究

Research on off-design characteristics of a supersonic expander

采用三维雷诺平均N-S方程和标准k-ε湍流模型,对超声速膨胀器变工况特性进行了数值研究。结果表明:进口绝对总压的上升,增加了泄漏流量,但削弱了泄漏涡强度,泄漏涡尺度变小,横向运动增强;转速的上升导致节距方向速度梯度减小,下端壁附近高速区向出口迁移,上端壁附近由泄漏流体导致的低速区影响范围缩小,斜激波向出口迁移,斜激波强度减弱,降低了泄漏和近壁面低能流体所导致的损失;进口绝对总压一定,转速越高,膨胀器膨胀比越大,等熵绝热效率越高,进口绝对总压较低(7倍标准大气压以下)将导致膨胀器膨胀比和等熵绝热效率显著降低,进口绝对总压每降低1个标准大气压,膨胀比最高降低4.1%,等熵绝热效率最高降低7.7%。

The three dimensional Reynolds-averaged Navier-Stokes equations and the k-εturbulent model are adopted to simulate numerically the off-design characteristics of a supersonic expander.It has been found that with the increasing of the absolute total pressure at inlet,the leakage flow rate increases,however,the intensity of the tip leakage vortex decreases,the size reduces,and the transverse movement enhances.With the increasing of the speed,the velocity gradient in the direction of pitch decreases,the high velocity zone near the bottom wall moves toward the outlet,the region of the low velocity zone near the casing wall which is caused by the leakage flow shrinks,the oblique shock wave moves towards outlet and the intensity weakens,the loss which is produced by the leakage flow and the low energy fluid near the wall drops.When the absolute total pressure at inlet maintains a steady value,the higher the speed,the bigger the expansion ratio and the higher the adiabatic efficiency,lower absolute total pressure（below seven times of the standard atmospheric pressure）at inlet will lead to expansion ratio andadiabatic efficiency significantly decreases,as the absolute total pressure at inlet decreases a standard atmospheric pressure,the highest of expansion ratio and adiabatic efficiency reduces 4.1% and 7.7%,respectively.