Multibladerow Forced Response Modeling in Axial-Flow Core Compressors

[+] Author and Article Information
M. Vahdati, A. I. Sayma

 Imperial College, MED, Exhibition Road, London SW7 2BX, UK

M. Imregun

 Imperial College, MED, Exhibition Road, London SW7 2BX, UKm.imregun@imperial.ac.uk

G. Simpson

 Rolls-Royce plc, P.O. Box 31, DE24 8BJ, UK

J. Turbomach 129(2), 412-420 (Jun 03, 2005) (9 pages) doi:10.1115/1.2436892 History: Received February 11, 2004; Revised June 03, 2005

This paper describes the formulation and application of an advanced numerical model for the simulation of blade-passing and low-engine order forced response in turbomachinery core compressors. The Reynolds averaged Navier–Stokes equations are used to represent the flow in a nonlinear time-accurate fashion on unstructured meshes of mixed elements. The structural model is based on a standard finite-element representation. The fluid mesh is moved at each time step according to the structural motion so that changes in blade aerodynamic damping and flow unsteadiness can be accommodated automatically. A whole-annulus 5-bladerow forced response calculation, where three upstream and one downstream bladerows were considered in addition to the rotor bladerow of interest, was undertaken using over 20 million grid points. The results showed not only some potential shortcomings of equivalent 2-bladerow computations for the determination of the main blade-passing forced response, but also revealed the potential importance of low engine-order harmonics. Such harmonics, due to stator blade number differences, or arising from common symmetric sectors, can only be taken into account by including all stator bladerows of interest. The low engine-order excitation that could arise from a blocked passage was investigated next. It was shown that high vibration response could arise in such cases.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

The core-compressor geometry and the 5-bladerow mesh. Starting from first bladerow, the blade numbers are 40, 31, 32, 38, and 50.

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Figure 2

Vibration mode shape displacement contours for Blade Mode 11

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Figure 3

Instantaneous entropy contours at 90% blade height (5-bladerow computation)

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Figure 4

Instantaneous entropy contours at 90% blade height (2-bladerow computation)

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Figure 5

Blade Mode 11/6ND modal force

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Figure 6

Clocking effects on EO excitation harmonics

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Figure 7

Whirl angle at R1 exit—measurement based versus fine mesh versus coarse mesh

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Figure 8

Steady-state Mach number contours at S2 exit

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Figure 9

The Fourier transform of the whirl angle at S2 exit for all three blockage cases

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Figure 13

1T/6ND modal force time history and its Fourier transform

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Figure 14

Maximum blade response for assembly modes of interest as a function of blockage

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Figure 10

3-bladerow mesh for blocked passage studies

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Figure 11

Instantaneous entropy contours for 25deg blocked passage

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Figure 12

Aerodynamic damping values as obtained from a transient flutter analysis Mode 1=1F, Mode 2=1T



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