Far Spacing

DPIV plots of median velocity at the far spacing configuration are shown in Fig. 5. Due to the limit in laser sheet width, the flow field was not captured near the wake generator trailing edge. The wake shedding frequency is not easily determined as it was at close spacing. Hot wire measurements obtained downstream of the wake generator show the blade-pass frequency of 7.7 kHz

Figure 6. Far spacing, 75% span, median velocity

wake generator. An observation made from the instantaneous fbw visualiza­tion images (not presented here) suggest a phase locking of the wake shedding to the bow wave perturbation but random motion of the vortices as they con – vect downstream. At far spacing, two or three shed vortices are present at any given time in the gap between the wake generator and rotor. At close spacing, there is only one vortex present. As a result the averaged instantaneous images at far spacing do not show as clear a view of the wake region as close spacing. Nevertheless, plots of median velocity still illustrate important details of the far spacing ft>wfield.

Analysis of Fig. 5 shows bands of low and high velocity in the ft>w field that are a result of the rotor bow shock and expansion zone. At far spacing, the rotor bow shock is not as well defined because it is weaker than at close spacing. This is evident from the peak velocity magnitude observed in the DPIV images. The peak velocity at far spacing is approximately 220 m/s while at close spacing it is 245 m/s. Due to the increased axial gap between the rotor leading edge and wake generator the rotor bow shock has dissipated into more of a bow wave at the location it interacts with the wake generator trailing edge.

The wake generator wake has mixed out more resulting in a wider and shal­lower wake. The interaction of a weaker wake with a weaker bow shock does not split the rotor bow shock into two clearly defined regions such as was ob­served at close spacing.

3. Summary

A DPIV system for use in transonic turbomachinery has been described. Re­sults from an experiment conducted in the SMI rig are presented that show the complex flow field associated with the interaction of a downstream transonic rotor with an upstream stator. The effect of changing the axial gap between blade-rows is studied and the DPIV plots are presented as an experimental data set for time accurate CFD validation.

At close spacing, the wake shedding is synchronized with the rotor blade – pass frequency. The interaction of the rotor bow shock and wake generator causes the wake to expand downstream of the shock. The shock is split into two regions above and below the wake. As the shock approaches the wake gen­erator trailing edge, the velocity increases and the shock to turn more normal to the freestream flow.

At far spacing the wake convects downstream in a chaotic fashion. Bands of high and low velocity are evident from the rotor bow shock and expansion waves downstream of the shock. The interaction between the rotor bow shock and wake generator is much weaker than the close spacing interaction. The wake has mixed out more at the location it interacts with the shock and does not split the shock in two nor turn the shock normal to the freestream flow.

Acknowledgments

The wake generators, rotor, and stator were built by Pratt & Whitney. From the CARL group at Wright-Patterson AFB the authors would like to recognize Dr. Herb Law, Robert Wirrig, Ron Berger, Terry Norris, Bill Ullman, and Chris Blackwell for their assistance in gathering the data. The assistance of Dr. Sivaram Gogineni and Dr. Larry Goss of ISSI in setting up the DPIV system is also recognized. Post processing of the results was assisted by Justen England and Nathan Woods. The authors thank the Propulsion Directorate management for supporting the research and allowing the presentation and publication of this paper.

References

Sanders, A. and Fleeter, S. Experimental Investigation of Rotor-Inlet Guide Vane Inter­actions in Transonic Axial-Flow Compressor. AIAA Journal of Propulsion and Power, 16(3):421-430, 2000.

Smith, L. H. Wake Dispersion in Turbomachines. ASME Journal of Basic Engineering,

:668-690, 1966.

Smith, L. H. Wake Ingestion Propulsion Benefit. AIAA Journal of Propulsion and Power, 9(1):74—82, 1993.

Van Zante, D. E., Adamczyk, J. J., Strazisar, A. J., and Okiishi, T. H. Wake Recovery Per­formance Benefit in a High-Speed Axial Compressor. ASME Journal of Turbomachinery, 124:275-284, 2002.

Van de Wall, A. G., Kadambi, J. R., and Adamczyk, J. J. A Transport Model for the Deterministic Stresses Associated With Turbomachinery Blade Row Interactions. ASME Journal of Turbomachinery, 122:593-603, 2000.

Gorrell, S. E, Okiishi, T. H., and Copenhaver, W. W. Stator-Rotor Interactions in a Tran­sonic Compressor, Part 1: Effect of Blade-Row Spacing on Performance. ASME Journal of Turbomachinery, 125:328-335, 2003.

Gorrell, S. E, Okiishi, T. H., and Copenhaver, W. W. Stator-Rotor Interactions in a Tran­sonic Compressor, Part 2: Description of a Loss Producing Mechanism. ASME Journal of Turbomachinery, 125:336-345, 2003.

Strazisar, A. J. Investigation of Flow Phenomena in a Transonic Fan Rotor Using Laser Anemometry. ASME Journal of Engineering for Gas Turbines and Power, 107:427^35, 1985.

Ottavy, X., Trebinjac, I., and Voullarmet, A. Analysis of the Interrow Flow Field Within a Transonic Axial Compressor: Part 1 – Experimental Investigation. ASME Journal of Turbomachinery, 123:49-56, 2001.

Ottavy, X., Trebinjac, I., and Voullarmet, A. Analysis of the Interrow Flow Field Within a Transonic Axial Compressor: Part 2 – Unsteady Flow Analysis. ASME Journal of Tur­bomachinery, 123:57-63, 2001.

Calvert, W. J. Detailed Flow Measurement and Predictions for a Three-Stage Transonic Fan. ASME Journal of Turbomachinery, 116:298-305, 1994.

Law, C. H. and Wennerstrom, A. J. Two Axial Compressor Designs for a Stage Matching Investigation. Technical Report AFWAL-TR-89-2005, Air Force Wright Aeronautical Laboratory, WPAFB, OH, 1989.

Creason, T. and Baghdadi, S. Design and Test of a Low Aspect Ratio Fan Stage. AIAA Paper 88-2816, 1988.

Gorrell, S. E., Copenhaver, W. W., and Chriss, R. M. Upstream Wake Infliences on the Measured Performance of a Transonic Compressor Stage. AIAA Journal of Propulsion and Power, 17(1):43-48, 2001.

[1] Gorrell, S. E. An Experimental and Numerical Investigation of Stator-Rotor Interactions in a Transonic Compressor. PhD thesis, Iowa State State University, Ames, Iowa, 2001.

Chriss, R. M, Copenhaver, W. W., and Gorrell, S. E. The Effects of Blade-Row Spacing on the Flow Capacity of a Transonic Rotor. ASME Paper 99-GT-209, 1999.

Estevadeordal, J., Gogineni, S., Goss, L., Copenhaver, W., and Gorrell, S. Study of Wake-Blade Interactions in a Transonic Compressor Using Flow Visualization and DPIV. ASME Journal of Fluids Engineering, 124(1): 166-175, 2002.

Copenhaver, W., Estevadeordal, J., Gogineni, S., Gorrell, S., and Goss, L. DPIV study of near-stall wake-rotor interactions in a transonic compressor. Experiments in Fluids, 33:899-908, 2002.

Hart, R. The Elimination of Correlation Errors in PIV Processing. In 9th International Symposium on Applications of Laser Techniques to Fluid Mechanics, Lisbon, Portugal, 1998.

Westerweel, J. Fundamentals of Digital Particle Imaging Velocimetry. Measurement Sci­ence and Technology, 8:1379-1392, 1997.

J., Estevadeordal, Gogineni, S., Goss, L., Copenhaver, W., and Gorrell, S. DPIV Study of Wake-Rotor Synchronization in a Transonic Compressor. AIAA Paper 01-3095, 2001.