Abstract
Xiao and Jenny (2012) proposed an interesting hybrid LES/RANS method in which they use two solvers and solve the RANS and LES equations in the entire computational domain. In the present work this method is simplified and used as a hybrid RANS-LES method, a wall-modeled LES. The two solvers are employed in the entire domain. Near the walls, the flow is governed by the steady RANS solver; drift terms are added to the DES equations to ensure that the time-averaged DES fields agree with the steady RANS field. Away from the walls, the flow is governed by the DES solver; in this region, the RANS field is set to the time-averaged LES field. The disadvantage of traditional DES models is that the RANS models in the near-wall region – which originally were developed and tuned for steady RANS – are used as URANS models where a large part of the turbulence is resolved. In the present method – where steady RANS is used in the near-wall region – the RANS turbulence models are used in a context for which they were developed. In standard DES methods, the near-wall accuracy can be degraded by the unsteady agitation coming from the LES region. It may in the present method be worth while to use an accurate, advanced RANS model. The EARSM model is used in the steady RANS solver. The new method is called NZ S-DES. It is found to substantially improve the predicting capability of the standard DES. A great advantage of the new model is that it is insensitive to the location of the RANS-LES interface.
Highlights
DES (Detached-Eddy Simulation) uses unsteady RANS near walls (URANS region) and LES further away from walls (LES region)
The RANS models used in the URANS region were originally developed and tuned in steady RANS simulations
The interface between the wall region and LES is defined by Eq 6
Summary
DES (Detached-Eddy Simulation) uses unsteady RANS near walls (URANS region) and LES further away from walls (LES region). The flow is in the near-wall region governed by the RANS equations and in the outer region it is governed by the LES equations This is achieved by adding drift terms in the LES and RANS equations. Tunstall et al [3] implement and use the method in [1] and modify it (different ramp function, different constants, reducing the number of case-specific constants etc) They apply it to fully developed channel flow and a rather complex flow consisting of a pipe junction including heat transfer. The present method is in many aspects similar to that proposed in [1, 3] but it is simplified: the RANS equations are used in steady mode, a more advanced RANS turbulence model is used and the present method includes fewer drift terms and tuning constants.
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