Development of a Hybrid RANS/LES Model for Heat Transfer Applications

A Dual-Grid Hybrid RANS/LES Model for Under-Resolved Near-Wall Regions and its Application to Heated and Separating Flows

“…However, the buffer layer is flatter and the slope of the predicted log-layer is higher than of the reference. This is in contrast to well-agreeing profiles at P r = 1 reported by Rolfo, Uribe and Billard [24]. Extensive testing on the blending function f b for the passive scalar transport has shown that the present model is more sensitive to the choice of P r RANS t and the related mean contribution to h j than the one-simulation model.…”

“…Rolfo, Uribe and Billard [24] transferred the blending method to a hybrid SGS turbulent heat flux with a two-part expression for a Simple Gradient Diffusion Hypothesis (SGDH) model as…”

“…The blending function is a revised expression by Rolfo, Uribe and Billard [24], which includes the Smagorinsky constant C S in the denominator to make the isotropic part of the modelled τ ij less sensitive to the chosen value of C S ,…”

“…However, while a too large averaging period increases convergence time, a too short period leads to excessive fluctuations. As in the baseline Two Velocity Fields model, γ = 10Δt • u τ /δ is used for the plane channel flow, with Δt being the physical time step, u τ = √ τ w /ρ being the friction velocity, τ w being the wall shear stress and δ being the channel half width [24]. As referencing to the nominal u τ is only found feasible for the plane channel flow case with a prescribed friction Reynolds number Re τ = u τ δ/ν, γ = 0.05Δt • U b /h with U b being the bulk velocity at the hill crest and h as the hill height is used for the periodic hill test case.…”

“…Passive scalar transport has previously been demonstrated for various hybrid models in different applications, including pin matrix [21], ribbed channel [22] and impinging jet flows [23]. Rolfo, Uribe and Billard [24] presented an extension of the blending concept to the SGS turbulent heat flux as an alternative to the Simple Gradient Diffusion Hypothesis and demonstrated superior prediction of the Two Velocity Fields model to conventional LES for passive scalar transport on coarse grids.…”