The grid system for the þstage compressor geometry is shown in
Fig. 1.
The experimental compressor geometry consists of an inlet guide vane
(IGV) followed by two nearly identical stages. The only difference
between the stages is that the first-stage rotor is closed 
relative
to the second-stage rotor. The only deviation from the original design
was that the axial gaps between the rotors and stators were
increased slightly to permit the incorporation of a radial-circumferential
traverse system. All airfoils are defined by
NACA 65-series sections with circular-arc mean camber lines.
There are 44 airfoils in each row.
The hub and casing are at a constant radius along the axis of the
compressor. These features make the compressor ideal for
computational modeling.
The computation was performed using the midspan experimental geometry. It was assumed that the flow is periodic from airfoil to airfoil in the circumferential direction, so the flow through only one airfoil-to-airfoil passage was computed. In addition, the experimental IGV geometry was unavailable at the time this calculation was initiated, so a 0.8%-thick parabolic arc airfoil was used. These assumptions are not expected to significantly affect the comparison between the computation and the experiment.
Two types of grids are used to discretize the flow about each of the airfoils, as seen in Fig. 1. An inner "O" grid, generated using an elliptical method, is used to resolve the viscous effects near the airfoil. The "O" grid is then overlaid on an algebraically generated, sheared Cartesian outer grid. The outer grids are allowed to slip past each other to model the relative motion between rotors and stators. Using this system, 12 grids are required to fully discretize the flow field through the þstage compressor.
Two different grids were used to study the effect of grid refinement
on the solution. Every other point in the coarse grid is displayed
in Fig. 1. The inner grids have 
grid points each,
and the outer grids have 
grid points each. The inlet
and exit grids have 
and 
grid points each,
respectively. The total number of points in all 12 zones of the
coarse grid is 53,173.
Experimental data exists only for the second stage of the compressor.
In order to reduce the computational time required for a grid
refinement study, grid refinement was done only in the second stage
of the compressor. The second-stage inner grids were refined to have
points each while the second-stage outer grids were refined
to have 
grid points each. The exit-grid size was
increased to 
. Thus, the fine-grid cells are one quarter
the area of the coarse-grid cells. The total number of points for
the fine-grid system was 116,732.