射流泵极限工况下空化流动

Cavitating Flow in Jet Pump under the Operating Limits

极限工况发生时,液体射流泵喉管中段至末端的汽液两相空化流动为均相泡状流。基于定常、等温及水平流动假设和Wood声速公式,导出极限工况发生时射流泵喉管中段至末端一维均相泡状流的控制方程组。依据该控制方程结合射流泵壁面沿程压力测试结果,计算喉管中段至末端液汽两相流动的马赫数。从喉管的中段至末端液汽两相流动的马赫数逐渐增加,在压力最低点附近达到最大,其最大值为0.94,十分接近1。进一步分析表明,极限工况发生时,射流泵喉管中段至末端液汽两相空化流表现为两相临界流动,其流速达到当地液汽两相流声速,流动出现臃塞,从而导致一定工作压力下吸入流量不再随出口压力的降低而增加,而是保持不变。揭示射流泵极限工况发生的机理,对其深入研究具有重要意义。

The liquid-vapor two-phase cavitating flow from the middle section to the end of throat tube is observed and verified to be homogeneous froth flow when jet pump works under the operating limits. Based on the assumption of the steady isothermal horizontal flow and the Wood sound velocity equation, the one-dimensional governing equation of homogeneous froth flow from the middle section to the end of throat tube under the operating limits, is derived. With the aid of the measurement data of pressure distribution along the wall of the jet pump, the Mach number of the liquid-vapor two-phase flow from the middle section to the end of throat tube is calculated by the derived governing equation. It is found that the Mach number increases gradually from the middle section to the end of throat tube, and reaches the maximum value 0.94, very close to 1, at nearby the lowest point of pressure. Further analysis indicates that under the operating limits, the liquid-vapor Cavitating flow from the middle section to the end of throat tube performs as critical two-phase flow, and the flow velocity reaches the local sound velocity of the liquid-vapor two-phase flow. The flow is choked and results in the appearance of the operating limits that the entrained flow rate will keep unchanged and not increase with the decrease of outlet pressure under a certain driving pressure. The mechanism of flow within a jet pump under operating limits is revealed and this is of significance to the further research work.