CFD-Method

The numerical approach is a time marching method, solving the Navier – Stokes equations with a Baldwin-Lomax turbulence model on a structured multiblock grid [8], [9]. The spatial discretization is performed with a cell centered finite volume method. The fluxes are computed with a central scheme and Jameson’s artificial viscosity [Jameson, 1991]. The time discretization is a dual time stepping method [Melson et al., 1993] with a multi stage Runge Kutta scheme. Chimera interpolation is used at the rotor stator interface (Fig. 1).

The equations are transformed to a local blade to blade coordinate system m’/ф where the stream wise coordinate is defined as m’ f £yi, with the meridional coordinate dm = s/dx2 + dr2 and ф, х,г are circumferential an­gle, axial and radial coordinate, respectively. This transformation is angle­preserving and also valid for pure radial streamsheets.

Two configurations (equivalent to 40/60 and 42/63) were generated using scaled airfoils and maintaining the axial gap. The complete computational domain in the m’/ф plane is shown in Fig. 1. Each block is discretized on a structured curvilinear H-type mesh with 64 x 192 and 48 x 192 cells for stator and rotor, respectively. The unsteady flow is calculated on three blade to blade sections at 20%, 50% and 80% span. The streamsheet thicknesses are taken from a steady through-flow calculation.