Early evolution of the compressible mixing layer issued from two turbulent streams
Résumé
Direct numerical simulation of the spatially developing mixing layer issuing from
two turbulent streams past a splitter plate is carried out under mild compressibility
conditions. The study mainly focuses on the early evolution of the mixing region,
where transition occurs from a wake-like to a canonical mixing-layer-like behaviour,
corresponding to the filling-up of the initial momentum deficit. The mixing layer
is found to initially grow faster than linearly, and then at a sub-linear rate further
downstream. The Reynolds stress components are in close agreement with reference
experiments and follow a continued slow decay till the end of the computational
domain. These observations are suggestive of the occurrence of incomplete similarity
in the developing turbulent mixing layer. Coherent eddies are found to form in
the close proximity of the splitter plate trailing edge, that are mainly organized in
bands, initially skewed and then parallel to the spanwise direction. Dynamic mode
decomposition is used to educe the dynamically relevant features, and it is found to be
capable of singling out the coherent eddies responsible for mixing layer development.
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