A handy toolkit that generates user-specified turbulent flow in large eddy simulations (LES) has been developed, which is based on the improved synthetic eddy method (iSEM) and implemented via a volumetric source term. It is capable of generating turbulence within a user-specified box region anywhere in the flow domain. Via a temporarily and spatially varying source term, instantaneous turbulent flow is generated downstream of the box. It is able to generate instantaneous turbulent flow at a user-specified mean velocity and Reynolds stress tensor. Compared with the improved synthetic eddy method which generates turbulence and implemented as Dirichlet boundary condition on a plane (iSEM-P), the turbulent flow generated by the volumetric source term approach (iSEM-S) has a much shorter developing distance and allows the use of a larger time step. Moreover, it improves the flexibility and allow user to generate local turbulence at the region of interest, making it particularly suitable for detached eddy simulations (DES). Both methods were tested to generate fully-developed plane-channel flow at a frictional Reynolds number of 395 and the streamwise developments of friction coefficient are compared with periodic LES. The fully-developed turbulent flow generated by iSEM-P experience a laminarisation initially and turbulence is then regenerated over a distance of x/D~5. When the new approach is used, the efficiency is greatly improved and the laminarisation-regeneration process takes a very short, negligible distance.
He et al. (Thu,) studied this question.
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