Effect of environmental disturbances on crossflow instability

Wind tunnel experiments on the receptivity of three-dimensional boundary layers were performed in a range of freestream turbulence intensities, Tu , from 0.01%—the lowest level ever achieved in this type of work—up to 0.41%. This work confirms that for T u = 0.01 % , and presumably below this level,...

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Bibliographic Details
Published in:	Experiments in fluids Vol. 64; no. 2
Main Authors:	Placidi, Marco, Ashworth, Richard, Atkin, Chris J., Rolston, Stephen
Format:	Journal Article
Language:	English
Published:	Berlin/Heidelberg Springer Berlin Heidelberg 01-02-2023 Springer Nature B.V
Subjects:	Amplitudes Cross flow Disturbances Engineering Engineering Fluid Dynamics Engineering Thermodynamics Fluid- and Aerodynamics Heat and Mass Transfer Research Article Surface roughness Three dimensional boundary layer Turbulence Wind tunnel testing Wind tunnels
Online Access:	Get full text
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Summary:	Wind tunnel experiments on the receptivity of three-dimensional boundary layers were performed in a range of freestream turbulence intensities, Tu , from 0.01%—the lowest level ever achieved in this type of work—up to 0.41%. This work confirms that for T u = 0.01 % , and presumably below this level, the transition process is dominated by stationary modes. These are receptive to surface roughness and generate Type-I and Type-II secondary instabilities that eventually cause the transition to turbulence. The saturation amplitude of these stationary waves is highly sensitive to the level of environmental disturbances; the former is here recorded to be the highest in the literature, with the latter being the lowest. Travelling modes are still present; however, their influence on the transition process is marginal. At matched surface roughness levels, when the level of environmental disturbance is enhanced to T u ≥ 0.33 % , the travelling modes acquire more importance, strongly influencing the laminar/turbulent transition process, whilst the initial amplitude and growth of the stationary modes are hindered. For this level of Tu , is the interaction of steady and unsteady disturbances that produces highly amplified waves (Type-III), that quickly lead to nonlinear growth and anticipated turbulence. Finally, a simple rule of thumb is proposed, where the transition front was found to move forward by roughly 10 % chord for an increase in one order of magnitude in the Tu levels. Graphical abstract
ISSN:	0723-4864 1432-1114
DOI:	10.1007/s00348-023-03579-x