Numerical simulation of turbulent mixed convective pipe flow

Abstract

In the present study, three-dimensional numerical simulation of turbulent mixed convection in a smooth horizontal pipe filled with air is carried out using finite volume method. The variation of flow and thermal characteristics in the fully developed turbulent region is observed with the variation of Reynolds number (Re = 5×74100, 33130, 23000, 10480, 7410) for modified Richardson number (0.1 ≤ Riq ≤ 10), while the modified Grashof number (Grq) is kept constant at 5.49×108. The mathematical model of the present problem consists of Reynolds-Averaged Navier-Stokes and energy equations along with the realizable k-ε turbulence model. At first, validation of the present results is performed in terms of the variation of isotherm contour, axial velocity contour, dimensionless mean axial velocity (u+) and mean temperature (T+) profiles in the inner and outer region of the pipe with the previous work. Secondly, the effect of the variation of Re and the corresponding Riq in the mixed convection regime is observed on variation of the axial velocity and isotherm contours, u+ and T+ profiles. The results show that the axial velocity profile becomes asymmetric in the fully developed region for lower Re and higher Riq. However, with increasing Re and decreasing Riq, the flow is dominated by forced convection and the velocity profile becomes symmetric again. On the other hand, u+ and T+ profiles show similar increasing trend with increasing Re and decreasing Riq from inner to outer region of the pipe.