Swirling Effects on Laminarization of Gas Flow in a Strongly Heated Tube

A numerical study is performed to investigate thermal transport phenomena in a process of laminarization from a turbulent flow in a strongly heated circular tube in coaxial rotation. The k-ε turbulence and t²-ε_t, heat transfer models are employed to determine the turbulent viscosity and eddy diffusivity for heat, respectively. The governing boundary layer equations are discretized by means of a control-volume finite difference technique and numerically solved using a marching procedure. When the tube is at rest, it is disclosed that: (i) when laminarization occurs, the streamwise velocity gradient at the wall is diminished along the flow, resulting in a substantial reduction in the turbulent kinetic energy over the whole tube cross section, (ii) the attenuation causes a deterioration in heat transfer performance, and (iii) simultaneously, both the turbulent heat flux and temperature variance diminish over the whole tube cross section in the flow direction. However, the presence of tube rotation contributes to the promotion of laminarization of gas flow. The mechanism is that a reduction in the velocity gradient induced by tube rotation suppresses the production of turbulent kinetic energy, resulting in an amplification in laminarizing the flow process.