Turbulent/non-turbulent interface in magnetohydrodynamic channel flow

Abstract eng:
Direct numerical simulations (DNSs) are performed to show the presence of turbulent/non-turbulent interfaces in a magnetohydrodynamic (MHD) turbulent channel flow under the influence of a wall-normal magnetic field. Visualization of the vorticity field reveals flow structures consisting of two internal turbulent boundary layers (ITBLs) growing from each wall and a non-turbulent channel core. The flow structures suggest the presence of an interface between the ITBL and the core. The conditional statistics of the DNS data shows that vorticity components have sharp gradients at the interface as observed in external hydrodynamic shear flows. The Joule dissipation rate, a characteristic quantity in MHD flow, is shown to have sharp gradients at the interface. A phenomenological theory gives an estimate of the average thickness of the ITBL as a function of R, and the estimate is in close agreement with the DNS result. Here, R is the ratio of Reynolds and Hartmann numbers.

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