Abstract:
The current study demonstrates a numerical investigation of laminar to turbulent transitional flow and forced convection heat transfer over a smooth heated flat plate at zero pressure gradient for both isothermal and isoflux surface boundary conditions. Seven different turbulence models namely low Re k-ε, shear stress transport, Spalart-Allmaras , standard k- ε, standard k-ω, Length VELocity, and Algebraic yPlus, are selected along with Reynolds Averaged Navier-Stokes and thermal energy equations for numerical simulation. The numerical results are compared with direct numerical simulation and experimental data for different momentum thickness Reynolds number, Reθ = 400 and 2240 and Prandtl number, Pr = 0.71. From the comparative study, it is found that Spalart-Allmaras model has good agreement with both DNS and experimental results and can be used to predict the flow and heat transfer for various Reynolds and Prandtl numbers. The effects of Reynolds and Prandtl numbers over the mean properties of the hydrodynamic and thermal boundary layers are studied within the range of 600 ≤ Reθ ≤ 900 and 0.025 ≤ Pr ≤ 7. It is observed that both the magnitude and distribution of these mean properties are strongly influenced by the variation of the governing non-dimensional numbers. Prandtl number effects are more prominent in the thermal field and Reynolds number has more dominance over the momentum field. The visualizations of these effects are also presented. A recent approach is used to identify the onset of transition from laminar to turbulent flow. A similar approach is also developed and applied to predict the onset of transition from laminar to turbulent heat transfer. It is exposed that heat transfer can be laminar or turbulent even though the flow field is in a different stage e.g. laminar. The flow field is observed to be fully turbulent at Reθ = 800. For both constant surface temperature and constant heat flux boundary conditions, the heat transport phenomenon does not switch to turbulent regime up to a certain Prandtl number even though the momentum field is in fully turbulent regime. Present study shows that when Reθ = 900 and Pr ≤ 0.71 the heat transfer is not fully turbulent, despite the flow is turbulent. Completely opposite case is also observed at Reθ = 600 for Pr higher than 4 where the heat transport occurs in fully turbulent mode though the flow is not turbulent. In addition, average Nusselt number correlations during transitional flow and heat transfer have been developed for 2×105 ≤ ReL ≤ 3.5×105 and 0.71 ≤ Pr ≤ 4 for both isothermal and isoflux boundary conditions and found acceptable when compared with existing correlations.
