Unsteady Tip Clearance Flow in a Blade Passage
Summary
In the passage flow of a turbomachine, the interaction between inflow
vortices and wakes, shed from fixed stators or inlet-guide vanes, and the
rotor blades (Figure 1) can create a highly unsteady behavior in the tip
clearance flow. This unsteadiness in tip clearance may cause undesirable
phenomena downstream of a rotor-blade section, such as intermittent
cavitations due to high pressure fluctuations in axial propulsion pumps or
noise generation in air-breathing engines. Prior studies by
Ma (2003), Mish
et al. (2003) and Staubs (2004) established an informative conclusion that
the unsteadiness in the tip leakage vortex downstream is influenced by the
blade-tip pressure fluctuation. Therefore, the purpose of this study is to
reveal the relationship of the unsteadiness in the tip clearance flow,
blade-tip pressure and a tip leakage vortex in the passage in order to
provide better understanding to this problem and use the results for a
further development of simplified analytic solutions.
Figure 1. Diagram of Stator-Rotor Interaction
A linear cascade model
(Virginia Tech Low Speed Cascade Tunnel)
and a
moving wall with vortex generators were used to simulate a stator-rotor
interaction in an idealized laboratory environment as show in Figure 2.
Detail velocity measurement under different flow conditions are being made
using single-sensor and four-sensor hotwire probe system of the type
described by Wittmer et al. (1999) in the tunnel’s center blade passage.
Some of the preliminary results are shown in the PDF file (.5M).
Figure 2. Linear Cascade Model
References
Ma R., “Unsteady Turbulence Interaction in a Tip Leakage Flow Downstream of a Simulated Axial Compressor Rotor”, Ph. D. dissertation, Virginia Tech, June 2003.
Mish P., Stabs J., Intaratep N., and Devenport W. J., “Characterization of Unsteady Loading Occurring in a Linear Cascade Produced by Simulated Stator-Rotor Interaction”, the 16th International Symposium on Air Breathing Engines, August 30 – September 5, 2003, Cleveland, OH, ISABE 2003-1225.
Staubs J., Master Thesis, Aerospace and Ocean Engineering Dept., Virginia Tech, expecting 2004.
Wittmer K S, Devenport W J and Zsoldos J S, "A Four Sensor Hot Wire Probe System for Three Component Velocity Measurements", Experiments in Fluids, vol. 24, pp 416-423, 1998. See also vol. 27, no. 4, pp. U1, September 1999.
Last Updated: 07/31/2004