The three-dimensional turbine model is based on the Large Scale Rotating Rig (LSRR) geometry used in the experiments performed by Dring, et al. (1986a,1986b) and Joslyn and Dring (1989). The LSRR is a 1-1/2 stage turbine with a 27-inch midspan radius, 6-inch span and airfoil aspect ratios of approximately unity. The turbine hub and casing are at constant radii. The axial gap between the first stator and rotor is approximately 50% of the first-stage average axial chord, while the gap between the rotor and the second stator is approximately 67% of their average chord. The rotor tip clearance is approximately 1% of span. A large experimental database exists for this turbine, including time-averaged pressures at several span wise locations on each airfoil, traverse data behind each airfoil, and surface flow visualizations.
The experimental configuration has 22 airfoils in the first stator row and 28 airfoils in each of the rotor and second stator rows for a total of 78 airfoils. A three-dimensional computation of the flow through the complete turbine configuration would be prohibitively expensive. To reduce the cost of the computation, the number of stators in the first row was increased to 28 and the size of the stators was reduced by a factor of 22/28 to maintain the same blockage. The flow is then assumed to be periodic from passage to passage, thereby allowing a reduction to a single blade or vane in each of the rows.
The grids used to describe the hub and airfoil surfaces of the turbine are shown in Fig. 1 The stator O-grid contains 214 points in the wrap-around direction, 26 points in the surface-normal direction and 51 points in the radial direction. The rotor O-grid contains 214 in the wrap-around direction, 45 points in the surface-normal direction and 51 points in the radial direction. The additional points in the rotor grid exist to discretize the rotor tip region. The dimensions of the H-grids vary, but average 123 points in the axial direction, 81 points in the circumferential direction and 51 points radially. The dimensions of the H-grids used to discretize the inlet and outlet regions of the turbine stage are 34 by 81 by 51. These relatively fine grid dimensions were arrived through the use of a two-dimensional code to evaluate the grid density needed to support the convection of the wakes with minimal dissipation. The total number of grid points used for the grid system was approximately 2.7 million grid points.