射流诱导螺旋通道内二次涡演变规律及强化传热机理研究

For helical ducts, heat transfer enhancement effect of secondary flow will be weakened but the flow resistance will be increased sharply at high Reynolds number condition. For this shortcoming, the jet flow will be used to enhance heat transfer performance of helical ducts in this project. The mechanism of this technique is that at the action of longitudinal vortices induced by jet, secondary flow fields of helical duct will be improved for heat transfer enhancement. The project intends to be performed by experimental and numerical simulation method. The unsteady movement characteristics of jet-induced longitudinal vortices will be investigated to obtain their generation, development and evolution regularity in helical ducts. The change along the mainstream direction will be studied to obtain the evolution law of coupled secondary flow field, which is formed by the effect of jet-induced longitudinal vortices and secondary flow vortices induced by centrifugal force. The heat transfer enhancement mechanism of jet-induced longitudinal in helical ducts will be revealed based on the field synergy analyses of coupled flows fields and temperature fields. The effect parameters on heat transfer characteristic and flow resistance such as jet velocity ratio, jet angle and so on will be discussed. Based on the results, the flow resistance and heat transfer performance of helical ducts cooperated with jet will be quantitatively described by mathematical model. The jet flow theory can be further supplement for the research results in this project and a new heat transfer enhancement method i.e. the method of the helical duct cooperated with jet will be put forward at the same time. Moreover, the research results of this project can provide theoretical references for the design and reform of heat exchangers associated with the project to control and improve flow characteristic and strength heat transfer ability.

针对高雷诺数下，螺旋通道内二次流强化传热效果减弱但流动阻力增加迅速的缺点，本项目提出采用射流强化螺旋通道内流体的传热，其原理是通过射流的诱导作用产生射流纵向涡旋，改善螺旋通道内的二次流场，实现强化传热。本项目拟采用实验和数值模拟方法进行研究。研究螺旋通道内射流纵向涡旋运动的非定常特性，获得其在螺旋通道内生成、发展和演化规律；研究射流纵向涡协同离心二次涡所形成的耦合二次流场结构沿主流方向的变化，获得耦合二次流场的演变规律；研究耦合速度与温度场的协同性，揭示射流纵向涡强化螺旋通道传热的机理。考察射流速度比、射流角度等对流动阻力和传热特性的影响规律，建立定量描述带有横向射流的螺旋通道内传热及阻力特性的数学模型。项目研究既可以丰富射流理论，同时又提出了“射流复合螺旋通道”的新型强化传热方法。本项目的研究可为工程实际中此类流动和换热结构实施流动控制、改善流动特征以及提高换热能力提供理论参考。

利用纵向涡控制近壁流动实现强化传热是一种有效的强化方法。为了揭示射流诱导作用下的纵向涡旋对螺旋通道的强化传热机理,采用实验和数值模拟方法进行了研究。考察了射流作用下螺旋通道内复合速度场和温度场结构，研究了射流纵向涡旋对螺旋通道内流体流动特性的影响，通过研究复合二次流场分布规律,揭示了出射流纵向涡在螺旋通道内形成和演变的过程；建立了螺旋通道中流向涡的涡量计算模型,分析了涡旋强度对强化传热的影响;基于场协同原理,考察了复合速度场和温度场的协同性，揭示了射流纵向涡旋强化螺旋通道内流体传热的机理；研究了射流速度比、射流角度等因素对流动阻力系数和换热局部努塞尔数的影响规律。本项目的研究可为工程实际中相关换热设备的实施流动控制、改善流动特征以及提高换热能力提供理论参考。