An LES investigation on turbulent flow in a centrifugal impeller affected by normal-distributed inflow perturbations

Abstract

The inflow of a rotating centrifugal impeller is normally perturbed by an upstream stationary component; therefore, the development of turbulent flow is different from the case with steady and uniform inflow. In this work, we performed a large-eddy simulation on turbulent flow in a centrifugal impeller, considering perturbation from the inflow and emphasizing the development of perturbation and its influence on flow in the impeller. The inflow perturbation is applied for the streamwise (w-) velocity and is time-varying as generated by a random number generator. A normal-distributed pattern of perturbation is always assumed with the intensity of perturbation, defined as the ratio between the perturbation amplitude and the mean velocity, set as fv = 0%, 5%, 10%, and 20%, where fv denotes the perturbation intensity. The inflow perturbation notably affects the passage flow. The velocity fluctuation and secondary flow increase in intensity as the perturbation intensity increases from fv = 0% to 10%, while a further increase to fv = 20% slightly weakens the velocity fluctuation. Although this phenomenon is less obvious in terms of the time-averaged characteristics of velocity, the Reynolds stress terms CtCa and CrCa under time-averaging still reflect a clear variation trend, and the Reynolds stresses are observed significantly on the blade suction surface.