Large eddy simulation of energy gradient field in a centrifugal pump impeller

Abstract

Large eddy simulation of the fluid flow in a centrifugal pump impeller is conducted at design load and quarter load, and the energy gradient field is analyzed to reveal the behavior of internal flow. A universal equation for calculating the energy gradient function, which is defined as the ratio of energy increase (transversal gradient of the mechanical energy gradient) to energy loss (stream-wise gradient of the work done by shear stress), is adopted. Research results show that positive and negative 0.3 for the logarithm of energy gradient function are critical values that reflect dominant energy increase and dominant energy loss, respectively. The large eddy simulation results indicate that the magnitude and shape of energy gradient field are affected by turbulent fluctuation. The energy gradient field in the impeller at mid-height has more small-scale features than those in the impeller at zero and one heights. The regions of dominant energy increase and dominant energy loss are highly distinct at both design load and quarter load. In some large areas, neither dominant energy increase nor dominant energy loss is observed at quarter load in the impeller passage. These results, which are mainly attributed to a highly separated flow, are not evident at design load. The region of dominant energy increase at design load is larger than that at quarter load, particularly close to the volute. The magnitude of mean logarithm of energy gradient function at quarter load is evidently smaller than that at design load, but its value remains higher than 1.0.