Swirling effects on laminarization of gas flow in a strongly heated tube

A numerical study is performed to investigate thermal transport phenomena i n a process of laminarization from a turbulent flow in a strongly heated ci rcular tube in coaxial rotation. The k-epsilon turbulence and <(t(2))over b ar>-epsilon, heat transfer models are employed to determine the turbulent v iscosity and eddy diffusivity for heat, respectively. The governing boundar y layer equations ale discretized by means of a control-volume finite diffe rence technique and numerically solved using a marching procedure. When the tube is at rest, it is disclosed chat: (i) when laminarization occurs, the streamwise velocity gradient at the wall is diminished along the pow, resu lting in a substantial reduction in the turbulent kinetic energy over the w hole,tube cross section, (ii) the attenuation causes a deterioration in hea t transfer performance, and (iii) simultaneously, both the turbulent hear f lux and temperature variance diminish over the whole tube cross section in the flow direction. However, the presence of tube rotation contributes to t he promotion of laminarization of gas pow. The mechanism is that a reductio n in the velocity gradient induced by tube rotation suppresses the producti on of turbulent kinetic energy, resulting in an amplification in laminarizi ng the pow process.