Grid system for VBI analysis

The composite mesh for the VBI calculations used an O-grid embedded in a background H-grid to model each blade passage. For rotors, a degenerate O-grid was used to model the flow in the tip clearance region. A 2-D section of the grid showing the midspan geometry is shown in Figure 1. Every other grid point in each of the grids is shown. The H-grid dimensions for the vane were 112x54x50. The H-grid dimensions for the rotor were 92x46x50. The dimensions for the O-grid in both blade rows were 146x24x50. The rotor tip clearance grid was 146x12x6. The total number of points used for the vane was 477,600. The total number of points used for the rotor was 397,312.

Figure 1. Illustration of the Composite mesh for the 1st stage of the Purdue low speed turbine rig showing the embedded O-grid in a background H-grid.

Figure 1. Illustration of the Composite mesh for the 1st stage of the Purdue low speed turbine rig showing the embedded O-grid in a background H-grid.

Boundary information for the outer boundary of the O-grids and the hole boundary of the H-grids was passed at each time step using trilinear interpolation. This grid scheme was chosen initially to provide an orthogonal mesh with adequate resolution for wake tracking. It was particularly attractive because there is no shear in the H-grid regardless of the blade stagger angle. This scheme is unattractive because the combined flow solver/grid system is not particularly conservative. An additional problem arises with this approach when applied to compressor blading. The problem with compressors is that the thin, high stagger blades require a very dense background grid, and there is a high probability that the code which determines the interpolation stencils for boundary points (PEGSUS) will not be able to provide a unique stencil for all points. Even for turbines, the preprocessing step to find all of the interpolations can be time-consuming. The most vulnerable aspect of the subsequent calculation is the lack of strict conservation.

PROPRIETARY RIGHTS LEGEND This technical data and tha information embodied herein is the property of and proprietary to Rolls-Royce Corporation, and shall not, without prior written permission of Rolls-Royce Corporation, be disclosed in whole or In part to third parties. This legend shall be included orĀ» any reproduction of this data in whole or in part. Copyright 2000 - Rolls-Royce Corporation, (unpublished)

0 0

Post a comment