Large-Eddy Simulation Inflow Conditions for Coupling with Reynolds-Averaged Flow Solvers

Abstract

Hybrid approaches using a combination of Reynolds-averaged Navier-Stokes (RANS) approaches and large eddy simulations (LES) have become increasingly popular. One way to construct a hybrid approach is to apply separate flow solvers to components of a complex system and to exchange information at the interfaces of the domains. For the LES flow solver, boundary conditions then have to be defined on the basis of the Reynoldsaveraged flow statistics delivered by a RANS flow solver. This is a challenge, which also arises, for instance, when defining LES inflow conditions from experimental data. The problem for the coupled RANS-LES computations is further complicated by the fact that the mean flow statistics at the interface may vary in time and are not known a priori but only from the RANS solution. The present study defines a method to provide LES inflow conditions through auxiliary, a priori LES computations, where an LES inflow database is generated. The database is modified to account for the unsteadiness of the interface flow statistics.

A Review of Embedded Large Eddy Simulation for Internal Flows

“…Although simple this method fails to provide the spatial or temporal correlations required to sustain turbulent generation downstream, as shown by Schluter et al [78] and illustrated in Fig. 3 (top).…”

Wind-structure interaction simulations of ovalling vibrations in silo groups

“…The first possibility is to use precursor databases [220,221]. In this approach, the transient unsteady boundary conditions are computed within a separate a priori wind simulation in an empty domain, e.g.…”

Inlet Conditions for Large Eddy Simulation of Gas-Turbine Swirl Injectors

“…Because of the fluctuations, the term ( v h vi) is never exactly zero, and so the term R des ii =R jj 1=2 drives the turbulent fluctuations to provide the target rms mean-velocity components and, in turn, the target axial components of the Reynolds stress. This relation was first implemented in [10] to generate a database for lookup based on an a priori RANS calculation; here, it is applied directly to control the flow. The case being simulated [25] provides experimental measurement of the flow conditions upstream of the inlet, and these were used as the target profiles for the mean and fluctuating velocity components.…”

“…Typically, this involves running a precursor simulation on a simpler geometry (e.g., a cyclic channel), to create fully developed turbulence; successive time steps of this simulation are then saved and replayed into the inlet of the main simulation. Various variants of the technique have been tried, for example, running the precursor simulation in parallel with the main simulation (thus obviating the need to store a limited database of information [9]) and scaling the data using the Reynolds stress (to adjust an existing database to another Reynolds number [10]). In the context of swirling flows, most versions of this technique make use of a method developed by Pierce and Moin [11] for generating swirl within a cyclic channel by imposing a constant tangential body force on the flow.…”

“…We also incorporate a correction method to improve the turbulence statistics for the flow, which has been applied before in the literature to generate libraries for lookup [10]; however, this is the first time that this method has been applied directly to the main domain in this manner and applied to generate a swirling flow. Our new approach was applied to the case of incompressible flow over a cylindrical sudden expansion, both with and without swirl at the inlet.…”