ANALYSIS OF STEADY AND UNSTEADY TURBINE CASCADE FLOWS BY A LOCALLY IMPLICIT HYBRID ALGORITHM

For the two-dimensional steady and unsteady turbine cascade flows, the Euler/Navier-Stokes equations with Baldwin-Lomax turbulence model are solved in the Cartesian coordinate system. A locally implicit hybrid algorithm on mixed meshes is employed, where the convection-dominated part in the flowfield is studied by a TVD scheme to obtain high-resolu tion results on the triangular elements, and the second- and fourth-or der dissipative model is introduced on the O-type quadrilateral grid i n the viscous-dominated region to minimize the numerical dissipation. When the steady subsonic and transonic turbulent flows are investigate d, the distributions of isentropic Mach number on the blade surface, e xit flow angle, and loss coefficient are obtained. Comparing the prese nt results with the experimental data, the accuracy and reliability of the current approach are confirmed. By giving a moving wake-type tota l pressure profile at the inlet plane in the rotor-relative frame of r eference, the unsteady transonic inviscid and turbulent flows calculat ions are performed to study the interaction of the upstream wake with a moving blade row. The Mach number contours, perturbation component o f the unsteady velocity vectors, shear stress, and pressure distributi ons on the blade surface are presented. The physical phenomena, which include periodic flow separation on the suction side, bowing, chopping and distortion of incoming wake, negative jet, convection of the vort ices and wake segments, and vortex shedding at the trailing edge, are observed. It is concluded that the unsteady aerodynamic behavior is st rongly dependent on the wake/shock/boundary layer interactions.