Computation of Unsteady Transonic 3D Flow in Oscillating Turbomachinery Bladings by an Euler Algorithm with Deforming Grids.

Abstract

A numerical method is presented for obtaining the unsteady fully 3-D transonic flow field in an isolated row of oscillating blades. Two important features characterize the present analysis. The first is the use of a flux-vector-splitting algorithm, which is well known for its excellent shock-capturing properties and its numerical robustness. The second feature is the coupling of the unsteady flow calculation with an interactive grid generation, a method which enables the code to treat every possible oscillation mode of the blade assembly. After each step a new boundary-fitted grid for all blade channels under consideration is generated, taking into account the movement of the blades. Written in an implicit form, the Euler code allows for rather large time steps, thus guaranteeing the calculation of the necessary aerodynamic coefficients with reasonable time effort - even for low reduced frequencies. The present investigations are restricted to special prescribed eigenmodes of the blades, namely tuned modes where all blades perform oscillations with the same frequency, same amplitude, and a constant interblade phase angle. Results of unsteady pressure and lift coefficients are presented for heaving motions of the blades at different interblade phase angles. A comparison with experimental results from a special standard configuration of the "Workshop on Aeroelasticity in Turbomachines" gives an insight into the reliability of the present method.