Numerical Investigations About the Aerodynamic Performance of the Cascade in Unsteady Environment

Abstract

The paper presents detailed parametric simulations about the unsteady flow in the cascade passageways. The studies focus on two aspects of unsteady cascade flow. One is two dimensional (2D), which describes unsteady flow characteristics only in blade-to-blade surfaces. The other is three-dimensional (3D, a linear cascade), in which more attentions are paid to the stacking of the unsteady flow of 2D cascades along all spanwise positions. In the former aspect, two different types of unsteadiness are applied at the inlet. One is an azimuthal wave structure that processes through the cascade. The other unsteadiness is spatially uniform and oscillates in time. Using each type of unsteadiness, inflow oscillations of total pressure, total temperature and inflow angle are studied for one turbine and one compressor cascades. The emphasis is focused on the aerodynamic effects of the time-average value, the amplitude and the frequency of the unsteady flow. Results show that the unsteady cascade flow produces more losses than a steady one. Some potentials towards engineering applications are also described. Finally, unsteady flow in 3D linear cascade is studied. A design freedom that can not be used under steady flow frame, Edge-Matching, is put forward. It is essentially to match phase angle of unsteady flow along the whole span so that aerodynamic, aeroelastic, aeroacoustic and heat transfer performances of turbomachinery can be optimized and compromised. With a comprehensive viewpoint, case treatment, hot streak/blade interaction, clocking and even calming effects all belong to Edge-Matching technique. It may eventually promote the daily use of unsteady design.