轮缘间隙对轴流泵内部非定常流场的影响

Effect of tip clearance on unsteady flow in axial-flow pump

为研究轴流泵轮缘间隙泄漏流的非定常特征及其对泵外特性的影响,采用基于S-A模型的DES方法和滑移网格技术,对轴流泵在设计流量下的内部湍流进行了数值计算,重点分析了4组轮缘间隙下泵内非定常流场特性及压力脉动特性.在设计轮缘间隙下,计算所得泵扬程和效率与试验数据吻合良好,最大相对误差分别为2.0%和3.0%.计算结果表明:随轮缘间隙增大,水泵扬程和效率均呈下降趋势;轮缘泄漏涡强度和影响范围随轮缘间隙增大而增大,当轮缘间隙为3.3‰D2时,轮缘泄漏涡扩散至相邻叶片出口边;不同轮缘间隙下,叶轮区压力脉动频率均以叶频为主;靠近叶片进口的叶轮室内壁压力脉动幅值随轮缘间隙的增大呈减小趋势,叶轮室中部压力脉动随轮缘间隙增大而增大;叶轮出口断面的压力脉动频域特性在不同轮缘间隙下均以1倍叶频为主,脉动幅值随轮缘间隙增大而减小.

In order to study the influence of the tip clearance on the unsteady flow and performance of the axial-flow pump,adopting the Spalart-Allmaras model based detached eddy simulation（DES） method and sliding mesh technique,numerical simulations of internal turbine flow of the axial-flow pump under designed conditions were carried out.The internal unsteady flow and its pressure pulsations of four different tip clearance sizes were simulated and analyzed.With the designed tip clearance,the predicted pump head and efficiency matched well with the measured data,and the maximum relative errors were less than 2.0% and 3.0%,respectively.The numerical results show that the pump performance,especially the head and efficiency tend to decrease as tip clearance becomes bigger;the intensity and range of the tip clearance vortex increase as the tip gap grows.When the gap reaches 3.3‰D2,the tip clearance vortex expands to the trailing edge of the neighboring blade.The results also show that the blade passing frequency dominated the pressure fluctuations in the impeller.The increase of the blade tip gap led to a reduction of the maximum pressure fluctuation amplitude on the front part of the impeller casing,but an increase on the middle part of the impeller casing.Pressure fluctuations in the impeller-vane gap region are dominated by the blade passing frequency（fn）,while the maximum pressure fluctuation amplitude was observed to decrease as the tip clearance size increases.