Metastable separated structures in turbulent flow around circular and oval dimples

The mechanisms are discussed that determine the structure of the separated turbulent flow of an incompressible fluid around a cylindrospherical dimple which is oval in plane and located on a flat wall transverse to the rectangular channel. In the case of short dimples, including a demispherical dimple, there are three equilibrium states of Reynolds-averaged flow: one symmetric state and two reflective asymmetric single vortex states. Here, the asymmetric states are metastable, whereas the symmetric state is unstable; therefore, the real flow around such dimples has the character of spontaneous aperiodic switchings between these two asymmetric metastable states. As the length of dimple increases, the symmetric state of the flow stabilizes and the possible asymmetric equilibrium states become unstable. As a result, the real flow acquires a quasi-stationary character. As the length of the dimple increases further, the flow character remains, but the structural topology of the internal flows in the dimple becomes complicated.