Determination of ϵ at inlet boundaries

Abstract

Different methods for the determination of accurate values for the dissipation rate ϵ at the inlet boundary of a computational domain, are studied. With DNS data for a fully developed channel flow and pipe flow, it is shown that the method suggested by Rhee and Sung (2000), in which the k–ϵ turbulence model is used to compute both k and ϵ from a given velocity profile, is not reliable and can result in very poor results. The method is found to be extremely sensitive to the details of the imposed velocity profile. An alternative procedure is proposed, in which only the ϵ transport equation is employed, with given profiles for the mean velocity and the turbulence kinetic energy. This way, accurate and reliable profiles are obtained for ϵ. Another procedure, based on the turbulent mixing length, was suggested by Jones (1994). The problem. The problem is then shifted towards the determination of the mixing length at the inlet boundary of the computational domain. An expression for this mixing length is proposed in this paper, based on the mentioned DNS data. Finally, the method proposed by Rodi and Scheuerer (1985) is included for comparison reasons. The different procedures are first validated on the fully developed channel and pipe flow. Next, the turbulent flow over a backward‐facing step is considered. Finally, the influence of the inlet boundary condition for ϵ is illustrated in the application of a turbulent piloted jet diffusion flame.

Premixed and nonpremixed generated manifolds in large-eddy simulation of Sandia flame D and F

“…At the inflow plane the fluctuations of the velocity components are uncorrelated, but the instability of creating the turbulence is strong, such that in the shear layers, within a few gridpoints from the inlet, correlation shear stress values larger than 0.5 are encountered. It is remarked that Reynolds-averaged simulations of this flow are known to be sensitive to prescription of the inflow turbulence and inflow turbulent dissipation rate in particular [43].…”

Subgrid Scale Modeling in Large-Eddy Simulation of Turbulent Combustion Using Premixed Flamelet Chemistry

“…For this purpose we select the partially premixed diffusion flame, Sandia Flame D. For this flame a large amount of experimental information is available [12,13]. The flame has also been simulated many times, both LES [14][15][16][17][18][19][20][21] and RANS [22][23][24][25][26][27].…”

Rate-Controlled Constrained Equilibrium (RCCE) simulations of turbulent partially premixed flames (Sandia D/E/F) and comparison with detailed chemistry

“…This form applies variation in mixing length with y only in the cells next to the wall when y < 0:22R. Both Nikuradse and Merci et al [60] proposed alternative expressions which incorporate variation of the mixing length with y for all the jet radius (see Merci et al [60]). Alternatively, constant mixing length assumption throughout the jet radius has also been used (e.g.…”