Breakdown in a boundary layer exposed to free-stream turbulence |
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Authors: | J Mans E C Kadijk H C de Lange A A van Steenhoven |
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Institution: | (1) Department of Mechanical Engineering, Technische Universiteit Eindhoven, P.O. Box 513, Eindhoven, 5600, The Netherlands |
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Abstract: | The natural secondary breakdown modes of a flat plate boundary layer exposed to a free-stream turbulence level of 6.7% are
characterised by experimental visualisations. The used experimental set-up is a water channel and no external triggering of
the instabilities is used. The visualisations show the presence of two secondary instability modes, a sinuous (antisymmetric)
and a varicose (symmetric) mode. The amplitudes of both instabilities increase, according to a non-linear profile, in upstream
direction. The amplitudes also experience temporal growth. When a critical amplitude is reached, roll-up structures appear.
These structures develop and finally merge, resulting in a turbulent spot. The development of the amplitude is similar in
both modes. However, the amplitude of the varicose instability varies between 0.38 and 0.63 2 π A/ λ] and the sinuous amplitude between 0.11 and 0.23 2 π A/ λ]. The propagation velocities of the sinuous and varicose instabilities are 0.91 u/u
blas] and 0.87 u/u
blas] respectively. This shows that both modes are located in a low speed streak. |
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Keywords: | |
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