CAJ | 학술논문

为研究旋转失速条件下离心泵隔舌区动静干涉效应和流动特性，采用大涡模拟方法对一离心泵进行了数值模拟，得到了水泵内部流场和隔舌区压力脉动特性。对不同旋转时刻的内部流动进行分析，发现当流量小于0.75倍额定流量时，叶轮中发生了旋转失速，并且由于隔舌附近逆压梯度较大，当叶轮流道通过隔舌处时会发生“固定失速”的流动现象。对旋转失速条件下蜗壳上的压力脉动进行分析，发现蜗壳隔舌处的压力脉动幅值最高，沿着流动方向依次减小。当旋转失速发生以后，蜗壳上的压力脉动幅值约为非失速工况下的2～3倍，并随着流量减小，压力脉动主频幅值增大。在旋转失速初始阶段，隔舌区“固定失速”对压力脉动的影响较弱，旋转失速的影响占主导，蜗壳上的压力脉动主频为0.5倍叶频；而当流量进一步减小至0.25倍额定流量时，隔舌区的“固定失速”对压力脉动的影响作用增强，削弱了旋转失速的作用，蜗壳上靠近隔舌区的压力脉动主频为叶频，而远离隔舌区的位置受“固定失速”影响较小，旋转失速的影响占主导，主频仍是0.5倍叶频。该研究结果可为离心泵机组运行稳定性提供参考。
위연구선전실속조건하리심빙격설구동정간섭효응화류동특성，채용대와모의방법대일리심빙진행료수치모의，득도료수빙내부류장화격설구압력맥동특성。대불동선전시각적내부류동진행분석，발현당류량소우0.75배액정류량시，협륜중발생료선전실속，병차유우격설부근역압제도교대，당협륜류도통과격설처시회발생“고정실속”적류동현상。대선전실속조건하와각상적압력맥동진행분석，발현와각격설처적압력맥동폭치최고，연착류동방향의차감소。당선전실속발생이후，와각상적압력맥동폭치약위비실속공황하적2～3배，병수착류량감소，압력맥동주빈폭치증대。재선전실속초시계단，격설구“고정실속”대압력맥동적영향교약，선전실속적영향점주도，와각상적압력맥동주빈위0.5배협빈；이당류량진일보감소지0.25배액정류량시，격설구적“고정실속”대압력맥동적영향작용증강，삭약료선전실속적작용，와각상고근격설구적압력맥동주빈위협빈，이원리격설구적위치수“고정실속”영향교소，선전실속적영향점주도，주빈잉시0.5배협빈。해연구결과가위리심빙궤조운행은정성제공삼고。
The impeller-volute interaction around the tongue region in centrifugal pump is always very strong, which usually causes vibration and noise. The tongue region is one of the most critical regions for pressure fluctuation, and in order to reveal the impeller-volute interaction around this region under rotating stall condition, a volute-type centrifugal pump was chosen as the research object to investigate by numerical simulation. A number of reference locations were arranged in the near-tongue region for recording the pressure fluctuations. The entire computational domain including impeller and volute was divided into 4.2 million grid cells, and the time step was set as 2.3×10-4 s, totally 360 time steps per impeller revolution.. Corresponding to a Courant number, which was estimated to be smaller than 1.0. Large eddy simulation was applied to simulate the three-dimensional unsteady viscous incompressible flow in the centrifugal pump. The predictions of the numerical model were compared with experimental results of flow-head curve. Good agreement between the simulated and experiment results was obtained. The largest head deviation under different flow rates was 8%, due to the smooth wall assumption during the simulations. Several flow rates were chosen ranging from 100%to 25% of the nominal flow rate for determining the stall point. The internal flow field and pressure fluctuation characteristics at different operating points were obtained. Spectra of pressure pulsation signals were analyzed, and the frequency was normalized by the rotation frequency. The regions with lower values in the pressure field were referred as rotating cells in that the stall was always accompanied by pressure reduction. It has been found that the rotating stall phenomenon occurred as the flow rate was decreased to 0.70 of nominal flow rate. Three stall cells near the entrance of passages could be observed in the pressure distribution. As the flow rate was further decreased, the area of stall cells was larger. Under the rotating stall condition, 50% of the blade passing frequency (i.e. 3 times of rotation frequency) was presented due to the alternate stalled and unstalled passages. When the rotating stall occurred, the amplitude of pressure fluctuation was much higher than that at unstalled points. Stall cells had significant effect on the pressure fluctuations in the volute. The maximum amplitude of dominant frequency was located at the tongue whether it was under rotating stall or unstalled condition. The amplitudes at the other locations were reduced gradually along the flow direction. Furthermore, a vortex always appeared in the fixed position (near the tongue) when the blade passed the tongue. It could be called“fixed stall”phenomenon, which was caused by the non-uniform pressure distribution on the volute and strong adverse pressure gradient in the tongue region. At 0.50 of nominal flow rate, the rotating stall cells played the leading role. The dominant frequency was 3 times of rotation frequency, which was 50% of the blade passing frequency. However, when the flow rate was decreased to 0.25 of nominal flow rate, the“fixed stall”cells played the leading role. The dominant frequency was 6 times of rotation frequency, which was the blade passing frequency. This research can provide useful reference for the secure and stable operation of centrifugal pumps.