管内自由衰减旋流阻力与换热的衰减特性

Friction and Heat Transfer Decaying Characteristics of Free Decaying Swirl Flow in Pipe

针对管内自由衰减旋流局部流动、阻力及换热特性理论研究的不足，根据流体力学动量矩定理，从理论上推导了管内自由衰减旋流当地最大切向速度、当地阻力系数以及当地换热努塞尔数沿管长衰减的解析式，理论解与试验结果吻合良好．并且揭示：①旋流初始切向速度比越大、雷诺数越小或管壁粗糙度越大，则管内当地最大切向速度、当地阻力系数以及当地换热努塞尔数的衰减也就越快；②管内自由衰减旋流当地阻力系数的衰减要比当地换热努塞尔数的衰减来得迅速。

According to the momentum moment theorem of fluid dynamics, the analytical decaying equations of the local maximum tangential velocity, the local friction factor and the local Nusselt number of the free decaying swirl flow in pipe were obtained. The theoretical equations are in good agreement with the experimental data and show that:(1) if the initial tangential to axial velocity ratio is larger, or the Reynolds number is smaller, or the wall roughness is larger, then the local maximum tangential velocity, the local friction factor and the local Nusselt number decay more rapidly along the axial distance; (2) under the same conditions, the friction factor decays more rapidly than the Nusselt number, and this helps to increase the thermodynamical performance of the enhanced heat transfer of the free decaying swirl flow in a tube.