Prediction of impeller speed dependence of cavitation intensity in centrifugal pump using cavitating flow simulation with bubble flow model

Abstract

We developed a numerical method of estimating not only cavitation erosion area but also cavitation intensity that depends on the impeller speed of pumps. Our numerical simulation code with a bubble flow model simulates the bubble pressure and the bubble nuclei distribution in a cavitating flow in detail. We simulated impulsive bubble pressure that varied within microseconds in a centrifugal pump. The cavitation intensity was estimated by analyzing the bubble pressure and the bubble nuclei distribution. The erosion area on the impeller blade in our pump test was visualized by using a method involving dye. The plastic deformation rate of an aluminum sheet attached in the erosion area was measured, and the cavitation intensity was estimated using an experimental database. The erosion area and cavitation intensity were measured at high and low impeller speeds. The erosion areas were both located on the suction side of the impeller blade, and they were distributed between the shroud and the mid-point of the blade near the leading edge. The measured cavitation intensity at high-speed was twice that at low-speed. The predicted areas of high cavitation intensity agreed well with the erosion areas in the experiment though the predicted areas slightly shifted to the leading edge. The predicted cavitation intensity at highspeed doubled that at low-speed as well as the experimental result. Therefore, we confirmed that the numerical method of estimating cavitation intensity was accurate. Next, we added three calculations while changing the impeller speed to obtain a function of cavitation intensity variations. The predicted function was a function of the impeller speed to the power, and this also corresponded to the experimental. Our code is thus effective for estimating the cavitation intensity that increases on the suction side of the impeller blade in a centrifugal pump when the impeller speed is changed.