Hostname: page-component-78c5997874-xbtfd Total loading time: 0 Render date: 2024-11-03T09:01:39.156Z Has data issue: false hasContentIssue false
  • English
  • Français

Loss reduction on ultra high lift low-pressure turbine blades using selective roughness and wake unsteadiness

Published online by Cambridge University Press:  03 February 2016

R. J. Howell  and
K. M. Roman
R. J. Howell
Affiliation:
Department of Mechanical Engineering, Sheffield University, Sheffield, UK
K. M. Roman
Affiliation:
Whittle Laboratory, Cambridge University, Cambridge, UK
Get access Rights & Permissions [Opens in a new window]

Abstract

This paper describes how it is possible to reduce the profile losses on ultra high lift low pressure (LP) turbine blade profiles with the application of selected surface roughness and wake unsteadiness. Over the past several years, an understanding of wake interactions with the suction surface boundary layer on LP turbines has allowed the design of blades with ever increasing levels of lift. Under steady flow conditions, ultra high lift profiles would have large (and possibly open) separation bubbles present on the suction side which result from the very high diffusion levels. The separation bubble losses produced by it are reduced when unsteady wake flows are present. However, LP turbine blades have now reached a level of loading and diffusion where profile losses can no longer be controlled by wake unsteadiness alone.

The ultra high lift profiles investigated here were created by attaching a flap to the trailing edge of another blade in a linear cascade — the so called flap-test technique. The experimental set-up used in this investigation allows for the simulation of upstream wakes by using a moving bar system. Hotwire and hotfilm measurements were used to obtain information about the boundary-layer state on the suction surface of the blade as it evolved in time. Measurements were taken at a Reynolds numbers ranging between 100,000 and 210,000.

Two types of ultra high lift profile were investigated; ultra high lift and extended ultra high lift, where the latter has 25% greater back surface diffusion as well as a 12% increase in lift compared to the former. Results revealed that distributed roughness reduced the size of the separation bubble with steady flow. When wakes were present, the distributed roughness amplified disturbances in the boundary layer allowing for more rapid wake induced transition to take place, which tended to eliminate the separation bubble under the wake. The extended ultra high lift profile generated only slightly higher losses than the original ultra high lift profile, but more importantly it generated 12% greater lift.

Type
Research Article
Information
The Aeronautical Journal , Volume 111 , Issue 1118 , April 2007 , pp. 257 - 266
Copyright
Copyright © Royal Aeronautical Society 2007 

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

1. Wisler, D.C., The technical and economic relevance of understanding boundary layer transition in gas turbine engines, 1998, Minnowbrook II, 1998, Workshop on Boundary layer transition in turbomachines, NASA/CP-1998-206958.Google Scholar
2. Curtis, E.M., Hodson, H.P., Banieghbal, M.R., Denton, J.D., Howell, R.J. and Harvey, N.W., Development of blade profiles for low-pressure turbine applications, 1996, ASME 96-GT-358.Google Scholar
3. Howell, R.J., Ramesh, O.N., Hodson, H.P., Schulte, V. and Harvey, N.W., High lift and aft loaded profiles for low pressure turbines, ASME J of Turbomach, July 2001, 124, (2), pp 385–392.Google Scholar
4. Hodson, H.P., Boundary layer and loss measurements on the rotor of an axial flow turbine, ASME 83-GT-4.Google Scholar
5. Schulte, V., Unsteady Separated Boundary Layers in Axial-Flow Turbomachinery, 1995, PhD dissertation, University of Cambridge.Google Scholar
6. Engber, M. and Fottner, L., The effect of incoming wakes on boundary layer transition of a highly loaded turbine cascade, AGARD CP-571 PAPER 21.Google Scholar
7. Lake, J.P., King, P.I. and Rivir, R.B., Low Reynolds number loss reduction on turbine blades with dimples and V-grooves, 2000, 38th AIAA Aerospace Sciences Meeting and Exhibit, 10-13 January.Google Scholar
8. Ramesh, O.N., Hodson, H.P. and Harvey, N.W., Separation control in ultra-high lift aerofoils by unsteadiness and surface roughness, 2001, ISABE.Google Scholar
9. Pinson, M.W. and Wang, T., Effect of two-scale roughness on boundary layer transition over a heated flat plate: Part 1 — surface heat transfer, ASME J of Turbomach, 2000, 122, pp 301–307.Google Scholar
10. Klebanoff, P.S. and Tidstrom, K.D., Mechanism by which a twodimensional roughness element induces boundary-layer transition, Physics of Fluids, July 1972, 15, (7).Google Scholar
11. Vera, M., Hodson, H.P. and Vazquez, R., The effects of a trip wire and unsteadiness on a highly loaded low-pressure turbine blade, ASME paper number GT2004-53822.Google Scholar
12. Zhang, Z.F. and Hodson, H.P., The combined effects of surface trips and unsteady wakes on the boundary layer development of an ultra high lift LP turbine blade, ASME paper GT2004-53081.Google Scholar
13. Zhang, Z.F., Hodson, H.P. and Harvey, N.W., Unsteady boundary layer studies on ultra high lift low pressure turbine blades, Proceedings IMechE, 219 Part A: J of Power and Engineering.Google Scholar
14. Zhang, Z.F., Vera, M. and Hodson, H.P., Separation and transition control on an aft-loaded ultra-high-lift LP turbine blade at low Reynolds numbers: low-speed investigation, ASME Paper GT2005-68892.Google Scholar
15. Vera, M., Zhang, Z.F. and Hodson, H.P., Separation and transition control on an aft-loaded ultra-high-lift LP turbine blade at low Reynolds numbers: high-speed investigation, ASME Paper number: GT2005-68893.Google Scholar
16. Schulte, V. and Hodson, H.P., Unsteady wake-induced boundary layer transition in high lift LP turbines, 1996, ASME-paper 96-GT-486.Google Scholar
17. Ladwig, M. and Fottner, L., Experimental investigations of the influence of incoming wakes on the losses of a linear turbine cascase, 1993, ASME paper number 93-GT-394.Google Scholar
18. Howell, R.J., Wake-Separation Bubble Interactions in Low Reynolds Number Turbomachinery, 1999, PhD dissertation, Cambridge University.Google Scholar
19. Cox, R.N., Wall neighbourhood measurements in turbulent boundary layers using hot-wire anemometer, February 1957, ARC Report 19101.Google Scholar
20. Bearman, P.W., Correction for the effect of ambient temperature on hotwire measurements in incompressible flow, DISA Inf. 1971, (11), pp 25, 30.Google Scholar
21. Denton, J.D., Entropy generation in turbomachinery flows, 1993, 7th Cliff Garrett Turbomachinery Award Lecture, SAE Paper No 902011 also ASME paper 93-GT-435.Google Scholar