A New Model for Describing Inherent Unsteady Flow in Turbomachinery

Abstract

Λ new model for numerical simulation of unsteady flow in turbomachines is presented in this paper. Most turbomachinery analyses assume periodicity from blade to blade. This makes it possible to analyze one blade only. The turbomachinery is designed with unequal number of blades to avoid forced vibration problems, the asymmetry boundary condition due to unequal number of blades is one of the major difficulty in simulation rotor-stator flow with the relative motion of rotor and Stator rows. As soon as there are more than one stage in the computational domain, which is an unavoidable problem for multistage turbomachines, ultimately, the only correct nonlinear time-accurate simulation is to analyze the entire annulus in each blade row. This is simply too computationally expensive to consider for engineering application. The new model can handle this problem effectively, which divide computational domains into blade row domains and volume domains between the blade rows. The volume computational domains are the full annulus that can eliminate the periodic boundary condition limitation, the three-dimensional characteristic compatibility equations are used as complementary condition to determine the boundary conditions between the blade rows and the volumes, The asymmetry of characteristic compatibility equations represent important turbomachinery unsteady flow mechanism. The results of the 3D unsteady Euler equations numerical simulation for a two stage transonic fan is presented. The new model has proven to be effective in analysis details of unsteady rotor-stator interactions in multistage turbomachines, and encourages future investigations. The model is not only usable for numerical simulation, but maybe also beneficial to experimental measurements and analysis.