Surface roughness effects on the heat transfer due to turbulent round jet impingement on convex hemispherical surfaces

The effect of surface roughness on the convective heat transfer from a heated convex hemispherical surface due to a turbulent round cold air jet impingement has been investigated numerically using the ANSYS FLUENT CFD code. Initially, the performance of a few turbulence models, namely, the RNG k–ɛ model, the realizable k–ɛ model, the standard k–ω model, and the SST k–ω model, in the prediction of the convective heat transfer for such a flow configuration, is evaluated against experimental data. Based on this evaluation, the SST k–ω model is chosen and employed to further investigate the surface roughness effect on the jet impingement heat transfer process for the above mentioned configuration. The flow and geometric parameters for this study are the jet exit Reynolds number (Re), the jet diameter (d), the diameter of the hemispherical surface (D), the distance of the impingement surface from the jet exit (L), and the equivalent average sand grain roughness height of the hemispherical surface (ks). Computations have been performed for various combinations of these parameters for a range of their values. It is observed from the results that, the local and average Nusselt number at the hemisphere surface is enhanced with increasing surface roughness height. Thus it is concluded that the impinging jet heat transfer will be augmented if roughness is added to the hemispherical surface.