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The response of a laminar separation bubble to ‘aircraft engine representative’ freestream disturbances

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Abstract

This paper investigates a large, laminar separation bubble that extends from near the leading edge and along the pressure surface of a low-pressure turbine blade. Whilst stability analyses are not performed, experiments suggest that the separation is convectively unstable at positive incidence. The separation then appears to exhibit absolute instability and, finally, global instability as the incidence of the blade becomes more negative. The conjectured onset of absolute and global instability is used to provide a possible explanation for the separation’s reduced sensitivity to ‘aircraft engine representative’ disturbances as the incidence of the blade becomes more negative.

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Abbreviations

C :

chord (m)

C X :

axial chord (m)

C P =( P 01− P)/( P 01− P 2):

static pressure coefficient

\( \bar{f} \)= fC / V 2 :

reduced (nondimensional wake passing) frequency

h :

span (m)

i :

incidence (°)

P :

pressure (Pa)

R :

reattachment point

Re 2= V 2 C / ν :

cascade exit Reynolds number

Re δ *= Vδ */ ν :

Reynolds number based on displacement thickness

s :

blade pitch (m)

s :

entropy (J/kg.K)

S :

separation point

T :

temperature (K)

\( \bar{u} \) :

mean velocity (m/s)

u RAW :

raw velocity (m/s)

u RMS :

RMS velocity (m/s)

V = V 2√ C P :

isentropic velocity (m/s)

V REV :

reverse velocity (m/s)

x :

axial direction (m)

θ :

circumferential direction (rads)

ζ S :

entropy coefficient

0:

stagnation

1:

cascade inlet

2:

cascade exit

∞:

freestream

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Acknowledgements

The authors would like to thank Rolls-Royce plc and the Defence Evaluation and Research Agency (MOD and DTI CARAD) for their generous financial support.

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Authors and Affiliations

  1. Department of Mechanical and Manufacturing Engineering, University of Melbourne, 3010, Australia

    M. J. Brear

  2. Whittle Laboratory, Engineering Department, Cambridge University, CB3 0DY, UK

    H. P. Hodson

Authors
  1. M. J. Brear
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  2. H. P. Hodson
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Correspondence to M. J. Brear.

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Brear, M.J., Hodson, H.P. The response of a laminar separation bubble to ‘aircraft engine representative’ freestream disturbances. Exp Fluids 35, 610–617 (2003). https://doi.org/10.1007/s00348-003-0709-7

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  • DOI: https://doi.org/10.1007/s00348-003-0709-7

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