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An Experimental Facility Design to Determine Rotordynamic Coefficients due to Tip Clearance Asymmetry in Axial Turbines FREE

[+] Author Affiliations
Seung Hyub Oh

Korea Aerospace Research Institute, Taejon, Korea

Seung Jin Song, Yong Shik Hong

Inha University, Inchon, Korea

Paper No. 97-AA-018, pp. V001T03A006; 7 pages
doi:10.1115/97-AA-018
From:
  • ASME 1997 Turbo Asia Conference
  • ASME 1997 Turbo Asia Conference
  • Singapore, September 30–October 2, 1997
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-7867-5
  • Copyright © 1997 by ASME

abstract

Many liquid rocket engines for space launch vehicles use high performance turbopumps to deliver fuel and oxidizer to the thrust chamber. Such turbopumps have been plagued by rotordynamic instability caused by non-axisymmetric turbine tip clearance. Yet, there is dearth of experimental data on this phenomenon, and reliable damping data are non–existent. This paper describes a new experimental facility designed and built to obtain aerodynamic stiffness and damping forces in an unshrouded turbine with a whirling rotor.

The experimental facility consists of an air supply system, single turbine stage test section, instrumentation, and auxiliary systems. The test turbine is a 1: 1 replica of an unshrouded turbine stage used in an actual turbopump. This impulse turbine has a design flow coefficient of 0.76 and work coefficient of 5.9. To measure aerodynamic stiffness forces, the turbine casing is mounted so that it is eccentric relative to the turbine rotor which is concentric with the turbine shaft. Thus, static turbine tip clearance asymmetry is obtained. To obtain aerodynamic damping forces, the turbine casing is mounted concentric relative to the turbine shaft, and the turbine rotor is mounted eccentric relative to the shaft. Thus, synchronous forward whirling condition, or dynamic turbine lip clearance asymmetry, is simulated. Currently, the mean tip clearance is 2% of the rotor blade span, and the specified eccentricity is 1% of the rotor blade span. This test rig facilitates acquisition of both stiffness and damping rotordynamic forces due to turbine aerodynamics. In contrast, past experiment designs required two separate drives — one for rotation and second for whirling motion — to simulate whirling turbine. Therefore, the new facility offers a comparably inexpensive and reliable alternative testing method.

Instrumentation consists of pilot static probes, thermocouples, and optical encoder (tachometer) to monitor turbine operating conditions. Proximity probes are used to measure tip clearance. Steady pressure data are obtained through a set of static pressure taps on the casing. Dynamic pressure data are obtained through flush-mounted, Kulita unsteady pressure transducers. Finally, steady and dynamic velocity data are acquired via 2–D hot wire probes. Thus, steady and unsteady flow fields in turbines with statically offset rotor and whirling rotor, respectively, can be measured.

Copyright © 1997 by ASME
This article is only available in the PDF format.

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