微淹没圆形射流空化特性减压试验

Experimental study on cavitation characteristics of round jet with slight submerged outlet by decompression test

空化空蚀和掺气减蚀机理的研究是高速射流研究的重要方面。在微淹没条件下,保证闸室面积与射流出口面积比不变,对设置门槽的有压矩形闸室后接圆管射流的突扩突跌消力池空化特性进行减压试验,其中跌坎高度S（5.5 m和4.0 m）和圆管长度L2（L2/d=2、1和0,d为圆管直径）。跌坎高度S从5.5 m降低至4.0 m,门槽及圆管射流出口处消力池边墙发生空化的可能性变化仅10%。圆管长度L2/d=2和0时门槽发生空化的可能性比L2/d=1时高出40%～60%;而L2/d=0时圆管射流出口处边墙的空化可能性比L2/d=1时可高出260%,L2继续增加对空化特性的不利影响有限。增加跌坎高度S有利于水流掺气,为达到良好的掺气减蚀效果,不宜过低。因此,跌坎高度S对门槽及圆管射流出口处消力池边墙空化特性影响较小,而圆管长度L2对其空化特性影响较大。

Both of cavitation erosion and air entrainment against cavitation are important aspects of studying highspeed jets. Under the condition of slight submerged outlet and constant ratio of chamber area to outlet of jet,decompression tests are carried to study cavitation characteristics of round jet in stilling basin with sudden enlargement and abrupt drop. In which,the pressured rectangular chamber with gate slots followed by round pipe flow is located before the stilling basin. In experiments,two offset height S（ 5. 5 m and 4. 0 m） and two round pipe length L2（ L2/ d = 2,1,0,d is round pipe diameter） are tested. The experiments reveal that the probability of cavitation on gate slots and sidewalls of stilling basin reduces by 10% when the offset height decreases from 5. 5 m to 4. 0 m. Moreover,the probability of cavitation on gate slots with L2/ d = 2 and 0 increases by 40% —60% compared with layout of L2/ d = 1,while for sidewall in stilling basin the probability of cavitation with L2/ d = 0 is higher 260% compared with layout of L2/ d = 1. But its adverse effect on cavitation becomes smaller as L2 continues to increase. Furthermore,the offset height should not be too low in order to keep flows with enough aeration. Therefore,the effect of offset height S on flow cavitation of gate slot and sidewall in stilling basin is small while the effect of length of round pipe is relatively greater.