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Research Papers

Experimental and Computational Fluid Dynamics Based Determination of Flutter Limits in Supersonic Space Turbines

[+] Author and Article Information
Pieter Groth, Hans Mårtensson

Department of Aerothermodynamics, Volvo Aero Corporation, SE-461 81 Trollhättan, Sweden

Niklas Edin

Department of Turbines and Rotors, Volvo Aero Corporation, SE-461 81 Trollhättan, Sweden

J. Turbomach 132(1), 011010 (Sep 16, 2009) (8 pages) doi:10.1115/1.3072491 History: Received August 28, 2008; Revised September 16, 2008; Published September 16, 2009

Turbines operating at high pressure in high velocity flow are susceptible to flutter. As reduced frequencies become sufficiently low, negative aerodynamic damping will be found in some modes. Ensuring that the total system damping is positive over the entire turbine operating envelope for all modes is of utmost importance in any design since flutter in a turbine often causes blade failures. This is in contrast to the normal engineering approach, which is to require a positive aerodynamic damping. A unique test campaign with a 1.5 stage supersonic space turbine has been performed. The turbine was operated at simulated running conditions over a large operating envelope in order to map out flutter limits. During the test, flutter was intentionally triggered at seven different operating conditions. Unique data have been obtained during the test that supports validation of design tools and enables better understanding of flutter in this type of turbine. Based on the data the flutter boundary for the turbine could be established. Using computational fluid dynamics (CFD) tools flutter was predicted at all operating points where the flutter limit was crossed. Both in predictions and as evidenced in test the two nodal diameter backward traveling mode was the most unstable. In addition to this predicted values of aerodynamic damping at flutter agreed well with damping estimated from measured amplitude growth.

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Figures

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Figure 1

Drawing of test turbine

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Figure 2

Instrumented blisk

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Figure 3

Operating conditions in test

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Figure 4

Maximum displacement of rotor

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Figure 5

Flutter events and flutter boundary

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Figure 6

Waterfall diagram at the time of flutter in test 8

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Figure 7

Strain gauge response of the 2ND mode versus time when flutter occurred during test 3

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Figure 8

Strain gauge response of the 2ND mode versus time when flutter occurred during test 5

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Figure 9

Strain gauge response of the 2ND mode versus time when flutter occurred during test 8

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Figure 10

Maxima of strain gauge response of Fig. 9 versus time

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Figure 11

Computational mesh

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Figure 12

Contours of relative Mach number in test 8 in (a) prior to flutter in (b) at onset of flutter (white Mach=2.3, dark blue Mach=0.04)

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Figure 13

Contours of the imaginary part of unsteady pressure in test 8 in (a) prior to flutter in (b) at onset of flutter

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Figure 14

Scaled critical damping versus nodal diameters for backward traveling disk modes

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