Numerical simulation was used to calculate the flow of helium gas by laminar flow model in different operating conditions. The simulation results show the net volume flow rate of helium gas through the clearance seal is zero while the net mass flow rate is not zero. The net gas leakage from compression chamber to the back-pressure chamber will bring piston shift to the compression chamber. The calculation results show the pressure wave and seal width would mostly influence the leakage. The leakage increases with charge pressure, compression ratio and seal width increasing. Piston movement has less influence on leakage. The leakage would grow with increasing of the phase shift between piston displacement wave and pressure wave and increase with work frequency increasing.%采用数值模拟的方法,基于压力波和活塞位移波的简谐变化规律,对自由活塞式斯特林制冷机压缩活塞与气缸的间隙密封内氦气建立数值模型,模拟了间隙内氦气在不同工况下的层流流动.结果显示在一个周期内,流过间隙密封的气体体积净流量为0,质量净流量不为0,净流量方向从压缩腔流向背压腔,会造成活塞在工作中向压缩腔偏移.分析结果显示压力波和间隙宽度对泄漏量的影响较大,随充气压力、压比以及间隙的增大,泄漏量增加;活塞运动对其影响较小,当活塞位移波与压力波的相位差小于90°时,相位差增大,泄漏量增加,活塞频率增大,泄漏量增加.
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