离心泵内流场PIV测试中示踪粒子跟随性的计算

示踪粒子的选取依据不同的流场而不同,对于离心泵内流场合适的示踪粒子是保证PIV试验精度的关键.基于固液两相流理论,重点考虑黏性阻力和旋转因素对粒子的影响,对离心泵内部湍流场中的示踪粒子进行了受力分析.然后在BBO方程基础上引入外部势力,建立了离心泵内流场中示踪粒子的拉格朗日运动方程,并采用Fourier积分变换的数学方法首次推导出适应于离心泵内流场的PIV测试用示踪粒子跟随性计算公式.利用离心泵内流场的PIV测试结果采用相平均处理的方法计算了试验所用的示踪粒子的跟随程度,计算结果表明：粒子径向的跟随性比周向差,选择示踪粒子时优先考虑径向的跟随性;而由于离心泵叶轮旋转和曲率的影响,即使采用相平均处理,粒子的速度也不代表水流速度,粒子跟随性最大偏差度为4.55%.计算结果可以检验所用示踪粒子的可靠性,为离心泵内流场选取合适的示踪粒子提供理论依据.

Analysis on tracing ability of PIV seeding particles in flow fields of centrifugal pumps

PIV seeding particles selection is flow field-dependent,so that the selecting suitable seeding particles to flow field in centrifugal pumps is the key thing to allow the accuracy of PIV measurement to be guaranteed. Based on the particle-liquid two-phase turbulent flow theory, the forces acting on the seeding particles, mainly including the viscous resistance and the forces caused from centrifugal acceleration field in a centrifugal pump were analyzed. Then the Lagrange equation of a seeding particle was established by introducing an external potential force into the BBO equation. Using the Fourier integral transform, a formula, which is applicable for PIV measurement of flow field in a centrifugal pump, for calculating the seeding particle tracing ability was deduced initially. Utilizing the PIV phase- averaged measurement results of the flow field in a centrifugal pump, the seeding particle tracing ability was estimated. The results turned out the particle tracing ability in the radial direct is poorer than that in the circumferential one, thus the seeding particles should be selected according to the priority of tracing ability in the radial direction. Even though the results of PIV measurement are processed with a phase-averaged technique, the velocity of seeding particles doesn＇t represent the real velocity of fluid because of the effects of impeller rotation and streamline curvature, and causing a maximum error is as high as about 4.55%. The formula can be used to examine the reliability of seeding particles to improve the accuracy of PIV flow measurement in centrifugal pumps.