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Longitudinal vortices in wind tunnel wall boundary layers

Published online by Cambridge University Press:  04 July 2016

S. Mokhtari  and
P. Bradshaw
S. Mokhtari
Affiliation:
Department of AeronauticsImperial College, London
P. Bradshaw
Affiliation:
Department of AeronauticsImperial College, London
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Extract

Several workers have found evidence for the presence of longitudinal vortices in wind tunnel wall boundary layers near the centre line of each wall, although the only actual publication appears to be the reproduction of Bearman's work in Ref. 3. The phenomenon usually observed is shown in Fig. 1: the boundary layer is considerably thickened near the centre line. (This symmetrical and localised perturbation should be distinguished from the effect of non-uniformities in the wind tunnel screens which apparently also leads to longitudinal vortices, randomly spaced across the width of the working section). The hypothetical vortex pattern is also shown in Fig. 1: it arises because lateral pressure gradients in the wind tunnel contraction naturally deflect the slow-moving fluid in the boundary layer towards the centre line more strongly than the main ‘inviscid’ part of the flow, implying the generation of longitudinal vorticity: this is secondary flow of Prandtl's first kind.

Type
Research Article
Information
The Aeronautical Journal , Volume 87 , Issue 866 , July 1983 , pp. 233 - 236
Copyright
Copyright © Royal Aeronautical Society 1983 

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References

1. Bearman, P. W. Unpublished work at National Physical Laboratory, 1969.Google Scholar
2. Welsh, M. C. Unpublished work at CSIRO, Melbourne, 1977.Google Scholar
3 Cebeci, T. and Bradshaw, P. Momentum Transfer in Boundary Layers. McGraw Mill Hemisphere, 1977.Google Scholar
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7. Mokhtari, S. Effect of wind tunnel contraction on a two-dimensional boundary layer. MSc project report, Department of Aeronautics, Imperial College, 1982.Google Scholar