Discussion of the VBI Calculation for the Baseline Case

The initial calculation, which will be referred to as the baseline case, predicted the unsteady flow for the 1st stage of the Purdue rig at design conditions without hub leakage flow. Because the levels of unsteadiness were low, snapshots of the 3-D flow can be used to highlight relevant flow phenomena in the vane and the rotor. A comparison of the flow with and without leakage will follow. The grid system for the VBI code was developed to provide a high-resolution orthogonal grid near the blade surface along with an orthogonal H-grid to capture wakes and shocks. There were no shocks in the Purdue rig, but Figure 3 shows a snapshot in time of Mach number and entropy contours at midspan for the baseline case. Both images in the figure show that the analysis produced a seamless solution at the interface and pitchwise periodic boundaries. The plot of entropy contours show the combined grid and flow solver did a good job of capturing and convecting the wake from the 1st blade row through the 2nd blade row. The calculated expansion ratio for the 1st stage was 1.075 with a stage efficiency of 85%. The efficiency was lower than the design value of 90.5% because of some flow separation on the rotor suction surface.

Previous steady 3-D calculations run with the ADPAC code did not indicate 1st rotor suction surface separation. For the steady ADPAC calculation, both stages of the rig were run in a multistage environment with mixing plane boundary procedures used at the interface between blade rows. Static pressure from the Rolls-Royce design code (OS069) was specified at the exit of the grid system downstream of the 2nd rotor. The steady ADPAC run predicted a mass flow of 5.97 lb./s. For the unsteady VBI run, static pressure was specified downstream of the 1st rotor. The mass flow for the VBI run was 6.05 lb./s at the inlet of the vane and 6.25 lb./s at the exit of the 1st rotor. Mass flow for the VBI run is discussed later in this report. To explain the reason for the VBI suction surface separation, Figure 4 compares the Mach number and flow angle distribution at the exit of the 1st vane.

PROPRIETARY RIGHTS LEGEND This technical data and the information embodied herein is the property of and proprietary (0 Rolls-Royce Corporation, and shall not, without prior written permission of Rolls-Hoyce Corporation, be disclosod in whole or in part to third parties. This legond shall be included on any (-¬ęproduction of this data ¬ę whole or in part. Copyright 2000 - Rolls-Royce Corporation, (unpublished)

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