Numerical simulation of reciprocating turbulent flow in a plane channel

Computational results were obtained for oscillatory flow with zero time mean (reciprocating flow) in a plane channel using a finite-volume method. A forcing term that varied cosinusoidally in time was imposed, and its frequency and amplitude were made to vary so as to span a range of regimes from purely laminar to fully turbulent. The results were validated against analytical solutions and literature data. In turbulent flow, although the computational grid did not fully resolve all the turbulence scales, the results were judged to be sufficiently accurate to capture all the essential features of the problem. The present computational results confirmed the existence of four main flow regimes (laminar, disturbed laminar, intermittently turbulent, and fully turbulent), already identified in the previous literature. One of the most interesting results was that the relation between the amplitudes of the forcing term and of the flow rate was found to be approximately linear both in the laminar and in the turbulent regimes; the reasons for this peculiar behavior were investigated and discussed. The influence of oscillation frequency and forcing term amplitude on transition to turbulence was also studied; results were compared with transition criteria proposed in literature, and a flow regime chart was proposed. Finally, the effect of unsteadiness on heat transfer was investigated by imposing different temperatures at the opposite walls of the channel and computing mean and fluctuating temperature distributions and heat transfer rates. The Nusselt number was found to increase significantly even in the disturbed laminar regime and to vary as Re0.8 (as in steady turbulent flow) in the turbulent regime.