On the Interaction of Turbulent Shear Layers with Harmonic Perturbations |
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Authors: | Yuli Lifshitz David Degani Anatoli Tumin |
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Institution: | (1) Faculty of Mechanical Engineering, Technion-Israel Institute of Technology, Haifa, 32000, Israel;(2) Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, AZ 85721, USA |
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Abstract: | The problem of coherent perturbations in a turbulent shear layer is considered for the purpose of developing a mathematical
model based on a triple decomposition that extracts the coherent components of random fluctuations. The governing equations
for the mean and the coherent parts of flow are derived, assuming the eddy-viscosity equivalence for the random part of flow,
and solved by iterations to provide a coupled solution of the problem as a whole. Calculations agree well with experimental
data in the upstream part of the layer where the mean–coherent flow interaction is the most important. In this region, the
interaction changes the mean flow velocity distribution in such a manner that the neutral stability curve is shifted upstream
relative to its position in the undisturbed layer and the perturbation intensity decreases further downstream. Experiments
show that the coherent waves suppress the turbulent Reynolds stress production downstream of this region, but the model fails
to predict the layer spreading correctly probably due to an inadequate turbulence closure of the mean flow. For the case of
a turbulent mixing layer, we suggest a new closure relation that takes into account this coherent-random interaction. |
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Keywords: | Turbulent shear layers Periodic excitation |
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