CFD analysis of turbulent forced convection in a plane channel with a built-in triangular prism

Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.Turbulent forced convection in a heated two-dimensional channel with a centrally built-in prism with a triangular cross section is computationally investigated by different turbulence modelling strategies. These include Reynolds Averaged Numerical Simulations (RANS), Unsteady RANS (URANS) and Large Eddy Simulations (LES). RANS and two­-dimensional URANS (2D URANS) are performed for a range of Reynolds numbers (Re) extending from 2,500 to 250,000. The Prandtl number is kept at the value of 0.7 (corresponding to air) in all computations. Three dimensional URANS (3D URANS), as well as LES (which are by definition three­-dimensional) are additionally performed for Re 2,500. In RANS and URANS, the Shear Stress Transport (SST) model is employed as the turbulence model. It is shown that the heat transfer at channel walls can be augmented by presence of the triangular prism, and the prediction quality depends on the modelling approach applied in the analysis. It is demonstrated that the effect of the unsteady motion of the coherent vortex structures behind the prism are mainly responsible for the heat transfer augmentation, and their influence cannot adequately be represented by RANS, calling for an unsteady approach, such as URANS or LES. The comparison between the predictions of 2D URANS and 3D URANS as well as LES shows, on the other hand, that this flow unsteadiness is also intimately related with flow three-dimensionality, as the time-averaged Nusselt numbers vary depending on the dimensionality assumed.ej201

Lattice Boltzmann analysis of laminar forced convection in a plane channel with a built-in triangular prism

Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.ej201

A note on modelling non-rectangular boundaries by the Lattice Boltzmann Method

The classical Lattice Boltzmann Method is based on an orthogonal, equidistant lattice structure. Thus, representation of non-rectangular boundaries deserves further attention. Besides the straightforward possibility of representing a non-rectangular boundary by a staircase, there are more sophisticated approaches in the literature for an accurate modelling of a non-rectangular boundary. In the present paper, three such methods arc compared with each other, and with the straightforward staircase approximation on two laminar flow test cases. As the reference solution, results obtained by a commercial CFD code are used, which are obtained by an exact representation of the non-orthogonal boundaries, using non-orthogonal finite volume discretisation. The results show that the so-called extrapolation method's performance is slightly inferior compared to the other methods; however, all methods exhibit a comparable overall accuracy