Two-equation hybrid RANS-LES models: a novel way to treat k and ω at inlets and at embedded interfaces

A novel method for prescribing k and omega at inlets and RANS-LES interfaces in embedded LES is presented and evaluated. The method is based on the proposal byHambato use commutation terms at RANS-LES interfaces. Commutation terms are added to the k and omega equations in the region near the inlet (i.e. the RANS-LES interface). The proposed method can also be used when prescribing inlet values for k and omega in hybrid LES-RANS. The commutation terms are added in embedded LES at the LES side of the RANS-LES interface. The influence of the extent of the region where the commutation terms are added is investigated. It is found that it is most efficient to add commutation terms in only one cell layer adjacent to the interface; in this way, tuned constants are avoided. The commutation term in the omega equation is derived from transformation of the k and e equations. When the commutation terms are used in only one cell layer, the commutation term in the k equation corresponds to a negative convection term. Hence, the commutation term can be omitted and a homogeneous Neumann inlet boundary condition can be used. The commutation term in the omega equation is retained. The novelmethod is evaluated for channel flow(Re-t = 8000), boundary layer flow(Re-theta = 11, 000) and backward-facing step flow(Re-H = 28, 000). Hybrid LES-RANS is used for the first two flows and embedded LES for the backwardfacing step flow.