扰流管束振荡流动强化换热研究

When the flow is instable or there is some spoiler structure in the flow field, the fluid flow will probably be asymmetric or be self-sustained oscillating. This is a phenomenon caused by the nonlinear nature of the system. Self-sustained oscillations occur in many industrial applications, in which cases initial and boundary conditions are completely steady and symmetrical, and the studies on the phenomenon is of great significance. The objective of this project is to investigate the conditions of the formation and development process of self-sustained oscillation as well as its impact on the flow and heat transfer by numerical simulation and experiment, and to study the heat transfer enhancement caused by the oscillation. The numerical simulation is an effective method to study the nonlinear characteristics of the flow, and the experimental validation of the numerical model is an important guarantee of the research work. For experiment, laser interferometry will be used to measure the temperature field; Smoke flow visualization method will be employed to visualize the flow field; Thermography will be used to record the temperature of the solid surface. The heat transfer and flow characteristics of self-sustained oscillation flow beyond the experimental conditions could be studied by validated numerical model, in detail. The formation and development of the elf-sustained oscillation and its influence to the heat transfer characteristic could be numerically simulated in detail as well as the physical mechanism of the heat transfer enhancement caused by the self-sustained oscillation.

当流动不稳定和有一定扰流结构下，流体流动会形成偏斜流动或者自维持振荡，这是一种由系统内部的非线性本质引起的现象。这种在初始及边界条件完全均匀对称的情况下产生的自维持振荡在许多工业应用都曾出现，对该现象的研究具有重要意义。本项目通过数值模拟与实验相结合来研究流体自维持振荡现象出现的条件，形成和发展的过程及其对传热的影响，以及由自维持振荡引发的强化传热。数值模拟是研究流动非线性特征的有效方法，但数值模型的实验验证是研究工作进行的重要保证。实验采用采用激光干涉的方法测试流体的温度场，用烟可视化方法显示流场，由红外热像仪测量固体表面温度场。经过验证的数值模型可以研究多种参数下的自维持振荡流动与传热的特点，尤其是入口雷诺数从小到大的变化过程中也就是流动从层流向湍流发展过程中自维持振荡的产生、发展及其对流动和传热的影响，以及由自维持振荡引发的强化传热的机理。

本课题的研究背景是扰流管束的振荡流动和强化换热问题。对于扰流强化换热问题，以往学者多采用对称的和稳态的模型进行研究。而事实上，由于流动和传热本质上是非线性问题，除了对称解或稳态解以外，还可能存在非对称的和非稳态的解。本课题针对上述不足，抽象出的科学问题是扰流管束非线性特性流动和换热问题，其中包括扰流管束对流传热机理及非线性特性的研究，以及物理参数和几何结构变化对流动和传热规律的影响。通过对这些相关物理机理和规律的研究，为存在管束结构的相关换热设备的强化换热设计，提供理论基础和参考数据。. 课题以扰流管束流动和换热问题为背景，建立由简单到复杂的不同扰流圆管和扰流管束的流动和换热的物理和数学模型，发展相关数值模拟方法。通过数值计算并辅以实验分析，给出所研究问题的流动和换热特性和其中存在的非线性特性，以及给出相关物理条件和几何机构变化对扰流管束的流动和传热特性及非线性特性的影响。在此基础上，进一步分析振荡流动对传热的影响以及强化传热的规律，为利用振荡流动引起的强化换热和改善换热设备性能奠定理论基础和提供参考数据。