Skip to main content Accessibility help
Hostname: page-component-559fc8cf4f-8sgpw Total loading time: 0.278 Render date: 2021-02-24T18:45:04.034Z Has data issue: true Feature Flags: { "shouldUseShareProductTool": true, "shouldUseHypothesis": true, "isUnsiloEnabled": true, "metricsAbstractViews": false, "figures": false, "newCiteModal": false, "newCitedByModal": true }

Unsteady boundary-layer transition in low-pressure turbines

Published online by Cambridge University Press:  01 July 2011

Whittle Laboratory, University of Cambridge, Cambridge CB3 0DY, UK
Whittle Laboratory, University of Cambridge, Cambridge CB3 0DY, UK
E-mail address:


This paper examines the transition process in a boundary layer similar to that present over the suction surfaces of aero-engine low-pressure (LP) turbine blades. This transition process is of significant practical interest since the behaviour of this boundary layer largely determines the overall efficiency of the LP turbine. Modern ‘high-lift’ blade designs typically feature a closed laminar separation bubble on the aft portion of the suction surface. The size of this bubble and hence the inefficiency it generates is controlled by the transition between laminar and turbulent flow in the boundary layer and separated shear layer. The transition process is complicated by the inherent unsteadiness of the multi-stage machine: the wakes shed by one blade row convect through the downstream blade passages, periodically disturbing the boundary layers. As a consequence, the transition to turbulence is multi-modal by nature, being promoted by periodic and turbulent fluctuations in the free stream and the inherent instabilities of the boundary layer. Despite many studies examining the flow behaviour, the detailed physics of the unsteady transition phenomena are not yet fully understood. The boundary-layer transition process has been studied experimentally on a flat plate. The opposing test-section wall was curved to impose a streamwise pressure distribution typical of modern high-lift LP turbines over the flat plate. The presence of an upstream blade row has been simulated by a set of moving bars, which shed wakes across the test section inlet. Further upstream, a grid has been installed to elevate the free-stream turbulence to a level believed to be representative of multi-stage LP turbines. Extensive particle imaging velocimetry (PIV) measurements have been performed on the flat-plate boundary layer to examine the flow behaviour. In the absence of the incoming bar wakes, the grid-generated free-stream turbulence induces relatively weak Klebanoff streaks in the boundary layer which are evident as streamwise streaks of low-velocity fluid. Transition is promoted by the streaks and by the inherent inflectional (Kelvin–Helmholtz (KH)) instability of the separation bubble. In unsteady flow, the incoming bar wakes generate stronger Klebanoff streaks as they pass over the leading edge, which convect downstream at a fraction of the free-stream velocity and spread in the streamwise direction. The region of amplified streaks convects in a similar manner to a classical turbulent spot: the leading and trailing edges travel at around 88% and 50% of the free-stream velocity, respectively. The strongest disturbances travel at around 70% of the free-stream velocity. The wakes induce a second type of disturbance as they pass over the separation bubble, in the form of short-span KH structures. Both the streaks and the KH structures contribute to the early wake-induced transition. The KH structures are similar to those observed in the simulation of separated flow transition with high free-stream turbulence by McAuliffe & Yaras (ASME J. Turbomach., vol. 132, no. 1, 2010, 011004), who observed that these structures originated from localised instabilities of the shear layer induced by Klebanoff streaks. In the current measurements, KH structures are frequently observed directly under the path of the wake. The wake-amplified Klebanoff streaks cannot affect the generation of these structures since they do not arrive at the bubble until later in the wake cycle. Rather, the KH structures arise from an interaction between the flow disturbances in the wake and localised instabilities in the shear layer, which are caused by the weak Klebanoff streaks induced by the grid turbulence. The breakdown of the KH structures to small-scale turbulence occurs a short time after the wake has passed over the bubble, and is largely driven by the arrival of the wake-amplified Klebanoff streaks from the leading edge. During this process, the re-attachment location moves rapidly upstream. The minimum length of the bubble occurs when the strongest wake-amplified Klebanoff streaks arrive from the leading edge; these structures travel at around 70% of the free-stream velocity. The bubble remains shorter than its steady-flow length until the trailing edge of the wake-amplified Klebanoff streaks, travelling at 50% of the free-stream velocity, convect past. After this time, the reattachment location moves aft on the surface as a consequence of a calmed flow region which follows behind the wake-induced turbulence.

Copyright © Cambridge University Press 2011

Access options

Get access to the full version of this content by using one of the access options below.


Alfredsson, P. H. & Matsubara, M. 1996 Streaky structures in transition. In Transitional Boundary Layers in Aeronautics (ed. Henkes, R. & van Ingen, J.), pp. 374386, Elsevier.Google Scholar
Asai, M., Minagawa, M. & Nishioka, M. 2002 The instability and breakdown of a near-wall low-speed streak. J. Fluid Mech. 445, 289314.Google Scholar
Cai, C. & Harrington, P. B. 1998 Different discrete wavelet transforms applied to denoising analytical data. J. Chem. Inf. Comput. Sci. 38 (6), 11611170.CrossRefGoogle Scholar
Coull, J. D. & Hodson, H. P. 2010 Predicting the profile loss of high lift low pressure turbines. ASME Paper GT2010-22675.Google Scholar
Coull, J. D., Thomas, R. L. & Hodson, H. P. 2010 Velocity distributions for low pressure turbines. Trans. ASME, J. Turbomach. 132 (4), 041006.CrossRefGoogle Scholar
Diwan, S. S. & Ramesh, O. N. 2009 On the inflectional instability of a laminar separation bubble. J. Fluid Mech. 629, 263298.CrossRefGoogle Scholar
Durbin, P. A., Zaki, T. A. & Liu, T. 2009 Interaction of discrete and continuous boundary layer modes to cause transition. Intl J. Heat Fluid Flow 30, 403410.CrossRefGoogle Scholar
Ginoux, J. 1965 Streamwise vortices in laminar flow. In Proc. AGARDoGRAPH '97, Part II, Paris.Google Scholar
Halstead, D. E. 1996 Boundary layer development in multi-stage low pressure turbines PhD thesis, Iowa State University.Google Scholar
Hodson, H. P. 1983 The detection of boundary layer transition and separation in high speed turbine cascades In Proc. Seventh Symp. Measurement Techniques for Transonic and Supersonic Flow, Aachen, Germany, 2123 September.Google Scholar
Hughes, J. D. & Walker, G. W. 2001 Natural transition phenomena on an axial compressor blade. J. Turbomach. 123 (2), 392401.CrossRefGoogle Scholar
Inger, G. R. 1975 Three dimensional disturbances in reattaching separated flows. In Proc. AGARD Conf., no. 168, Gottingen.Google Scholar
Jacobs, R. G. & Durbin, P. A. 1998 Shear sheltering and the continuous spectrum of the Orr–Sommerfeld equation. Phys. Fluids 10 (8), 10.1063/1.869716.CrossRefGoogle Scholar
Jacobs, R. G. & Durbin, P. A. 2001 Simulations of bypass Transition. J. Fluid Mech. 428, 185212.CrossRefGoogle Scholar
Lewalle, J., Ashpis, D. E. & Sohn, K.-H. 1997 Demonstration of wavelet techniques in the spectral analysis of bypass transition data. NASA Technical Publication 3555.Google Scholar
Marxen, O., Lang, M., Rist, U., Levin, O. & Henningson, D. S. 2009 Mechanisms for spatial steady three-dimensional disturbance growth in a non-parallel and separating boundary layer. J. Fluid Mech. 634, 165189.CrossRefGoogle Scholar
Matsubara, M., & Alfredsson, P. H. 2001 Disturbance growth in boundary layers subjected to free-stream turbulence. J. Fluid Mech. 430, 149168.CrossRefGoogle Scholar
McAuliffe, B. R. & Yaras, M. I. 2010 Transition mechanisms in separation bubbles under low and high freestream turbulence. Trans. ASME, J. Turbomach. 132 (1), 011004.CrossRefGoogle Scholar
Opoka, M. M. & Hodson, H. P. 2008 Experimental investigation of unsteady transition processes on high-lift T106A turbine blades. J. Propulsion Power 24 (3), 424432.CrossRefGoogle Scholar
Orth, U. 1993 Unsteady boundary-layer transition in flow periodically disturbed by wakes. Trans. ASME, J. Turbomach. 115 (4), 707713.CrossRefGoogle Scholar
Pfeil, H., Herbst, R. & Schröder, T. 1982 Investigations of the laminar-turbulent transition of boundary layers disturbed by wakes ASME Paper 82-GT-0406.Google Scholar
Roshko, A. & Thomke, G. J. 1966 Observations of turbulent reattachment behind an axi-symmetric downstream facing step in supersonic flow. AIAA J. 4, 975980.CrossRefGoogle Scholar
Schlichting, H. 1979 Boundary Layer Theory. 7th edn. McGraw-HillGoogle Scholar
Schubauer, G. B. & Klebanoff, P. S. 1955 Contributions on the mechanics of boundary layer transition. NACA TN 3489 and NACA rep1289.Google Scholar
Solomon, W. J., Walker, G. J. & Hughes, J. D. 1999 Periodic transition on an axial compressor stator: incidence and clocking effects: Part II – Transition onset predictions. Trans. ASME, J.Turbomach. 121 (3), 408415CrossRefGoogle Scholar
Stanislas, M., Okamoto, K., Kähler, C. J. & Westerweel, J. 2005 Main results of the Second International PIV Challenge. Exp. Fluids 39, 170191. (see also p. 35 and p. 37 of the Minutes of the Second International PIV Challenge: Scholar
Stieger, R. D. & Hodson, H. P. 2004 The transition mechanism of highly loaded low-pressure turbine blades. Trans. ASME, J. Turbomach. 126 (4), 536543.CrossRefGoogle Scholar
Stieger, R. D. & Hodson, H. P. 2005 The unsteady development of a turbulent bar wake through a downstream low-pressure turbine cascade. Trans. ASME, J. Turbomach. 127 (2), 288394.CrossRefGoogle Scholar
Watmuff, J. H. 1999 Evolution of a wave packet into vortex loops in a laminar separation bubble. J. Fluid Mech. 397, 119169.CrossRefGoogle Scholar
Wheeler, A. P. S., Sofia, A. & Miller, R. J. 2007 The effect of leading-edge geometry on wake interactions in compressors. ASME Paper GT2007-27802.Google Scholar
White, F. M. 1999 Viscous Fluid Flow 2nd edn. McGraw-Hill.Google Scholar
Wissink, J. G., Rodi, W. & Hodson, H. P. 2006 The influence of disturbances carried by periodically incoming wakes on the separating flow around a turbine blade. Intl J. Heat Fluid Flow 27 (4).CrossRefGoogle Scholar
Wu, X., Jacobs, R. G., Hunt, J. C. R. & Durbin, P. A. 1999 Simulation of boundary layer transition induced by periodically passing wakes. J. Fluid Mech. 398, 109153.CrossRefGoogle Scholar
Yarusevych, S., Kawall, J. G. & Sullivan, P. E. 2008 Separated-shear-layer development on an airfoil at low reynolds numbers AIAA J. 46 (12), 30603069.CrossRefGoogle Scholar
Zhang, X. F. & Hodson, H. P. 2007 Effects of Reynolds number and freestream turbulence intensity on the unsteady boundary layer development on an ultra-high-lift airfoil. ASME Paper GT2007-27274.Google Scholar
Zhang, X. F., Hodson, H. P. & Harvey, N. W. 2005 Unsteady boundary layer studies on ultra-high-lift low pressure turbines Proc. IMechE, Part A: J. Power and Energy 219, 451460.CrossRefGoogle Scholar

Full text views

Full text views reflects PDF downloads, PDFs sent to Google Drive, Dropbox and Kindle and HTML full text views.

Total number of HTML views: 0
Total number of PDF views: 350 *
View data table for this chart

* Views captured on Cambridge Core between September 2016 - 24th February 2021. This data will be updated every 24 hours.

Send article to Kindle

To send this article to your Kindle, first ensure is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about sending to your Kindle. Find out more about sending to your Kindle.

Note you can select to send to either the or variations. ‘’ emails are free but can only be sent to your device when it is connected to wi-fi. ‘’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

Find out more about the Kindle Personal Document Service.

Unsteady boundary-layer transition in low-pressure turbines
Available formats

Send article to Dropbox

To send this article to your Dropbox account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Dropbox.

Unsteady boundary-layer transition in low-pressure turbines
Available formats

Send article to Google Drive

To send this article to your Google Drive account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Google Drive.

Unsteady boundary-layer transition in low-pressure turbines
Available formats

Reply to: Submit a response

Your details

Conflicting interests

Do you have any conflicting interests? *