Large eddy simulation is applied to solve the unsteady three-dimensional viscous flow in the whole impeller-volute configuration of a centrifugal fan. The results of the simulation are used to predict the impeller-volute interaction and to obtain the unsteady pressure, velocity, and vorticity fluctuations in the impeller and volute casing. The simulation at the design point is carried out with the wall-adapting local eddy-viscosity subgrid-scale model and a sliding mesh technique is applied to consider the impeller-volute interaction. The results show that a strongly unsteady flow field occurs in the impeller and volute casing of the fan, and the flow is characterized with obvious pressure and vorticity fluctuations, especially at the tongue and at the blade wake region. The large pressure fluctuation at the tongue and the large fluctuation of the blade wake vorticity appear as the blade wake is passing the tongue. Acoustic analogy and vortex sound theory are used to compute the radiated dipole and quadrupole sound fields, which are in good agreement with the experiment. The sound results show that the vortex sound theory is convenient for the broadband noise computation, and the dipole sound is much higher than the quadrupole sound. The dipoles, distributed over the volute tongue surface, are the dominant sound source of the fan.
Research on the Rotating Jet Noise Based on the Vortex-Sound Theory
