Abstract
The turbulent heat transport is anisotropic in many cases as reported by several researchers. RANS- based turbulence models use the turbulent viscosity when expressing the turbulent heat flux in the energy balance (analogy of the Reynolds stresses in the momentum balance). The turbulent (eddy) viscosity calculation comes from the Boussinesq analogy mainly and it represents just a scalar value, hence a possible anisotropy in the turbulent flow field cannot be simply transferred to the temperature field. The computational cost of a LES-based approach can be too prohibitive in complex cases, therefore simpler explicit algebraic heat flux models describing the turbulent heat flux in the time-averaged energy equation could be used to get more accurate CFD results. This paper compares several turbulence models for the case of a turbulent impinging jet and deals with a methodology of implementing a user-defined function describing the anisotropic turbulent heat flux in a CFD code.
Highlights
Several approaches like Reynolds averaged Navier-Stokes equations (RANS), LES or DNS can be used in numerical solutions of turbulent flows
Results of numerical simulations using several turbulence models were compared with experimental data from literature for a round impinging jet
Ment with experimental data was obtained with the turbulence models based on the scalar eddy viscosity (Boussinesq approximation), namely the Transition SST model [11] or Intermittency Transition model [4]. They were able to predict the secondary peak in the Nusselt number dependency on radius with reasonable accuracy in contrast to the second-order closure Reynolds Stress turbulence models
Summary
Several approaches like RANS, LES or DNS can be used in numerical solutions of turbulent flows. Reynolds-Stress Model [3] can be used to solve such problems, but the problem is that the turbulent heat flux representing similar term in the time-averaged form of the energy equation as the Reynolds stress tensor in the momentum equation (for the sake of simplicity, S h referring to other internal sources and incompressible system is assumed here) cp. Is usually described using the scalar value of the eddy viscosity and turbulent Prandtl number (which is frequently taken as constant 0.85 [4]) This approach is not able to reflect the possible anisotropy in the turbulent heat flux as pointed out by [5] and other authors. This paper compares some simulation results of a single round impinging jet with experimental data and gives focus on methodology of implementing a user-defined function in ANSYS Fluent solver describing the anisotropic turbulent heat flux on the basis of an explicit algebraic heat flux model
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