Modelling unsteady turbulent forced convection inside tubes using a low-Reynolds-number k ε model

The study of turbulent forced convection in unsteady flow regimes is of both fundamental interest and considerable practical importance because of the widespread occurrence of such flow regimes in engineering systems. Since the complexity of the equations governing turbulent flow, obviously precludes direct analysis, even for steady flow, investigators must turn to experimentation and modelling in order to study this problem. Whilst a considerable body of work does exist on the hydrodynamics of unsteady turbulent shear flow, very few studies also consider heat transfer and in consequence it is not well understood. The present study was motivated by unsteady heat transfer measurements made in water pipe flow undergoing harmonic oscillation. Although the experiment was complicated by variable viscosity and density effects, the results suggested that measured Nusselt numbers could differ significantly from those obtained using a pseudo-steady correlation (a correlation strictly applicable to steady flow evaluated at the instantaneous conditions of an unsteady flow). This study primarily aims to assess the degree to which the widely used low-Reynolds-number k-ε turbulence model reproduces the previous experimental data. (Author)