Inlet Boundary Conditions for Embedded Les

The paper evaluates a new method to prescribe synthesized turbulent inlet boundary conditions. The method can also be used when prescribing turbulent fluctuations at an interface between (U)RANS and LES regions when the flow enters the LES region. When making LES, DES or hybrid LES-RANS a precursor channel DNS is often used. The disadvantage of this method is that it is difficult to re-scale the DNS fluctuations to higher Reynolds numbers. In the present work synthesized isotropic turbulent fluctuations are generated at the inlet plane with a prescribed turbulent length scale and energy spectrum. A large number of independent realizations are generated. A correlation in time between these realizations is introduced via an asymmetric, nontruncated time filter. In this way the turbulent time scale of the synthesized isotropic turbulent fluctuations is prescribed. The method has previously been validated for DNS channel flow at Reτ = 500 [1]. In that study it was found that the present approach is at least as good as using inlet boundary conditions from a pre-cursor DNS. It is employed in the present study in hybrid LES-RANS of the flow around a threedimensional hill and the flow over the downstream part of a bump. The sensitivity to the strength (amplitude) of the inlet fluctuations is investigated. Most of the bump simulations include only a central slice of the domain. One simulation was also carried out in which the sidewalls are included, which creates strong secondary flow.