MODELING OF IRREGULARLY INDENTED ROUGH SURFACE FOR NUMERICAL SIMULATIONS OF TURBULENT FLOWS AND HEAT TRANSFER.

本课题致力于提出一种将简化粗糙表面作为随机锯齿粗糙表面模型的方法。由于计算机的存储容量和速度都是有限的，因此这种简化对于表面湍流的计算机模拟是必不可少的。当今工业界对精确估算不规则锯齿表面的热流体行为（如阻力和/或传热）的需求急剧增加，本项目就是为了满足这一需求。建模的基本策略是首先选取尺度大、高度高的主要峰，然后用半球、圆锥、圆柱等典型形状的粗糙度元素代替选定的峰面积。通过模拟计算，分别预先计算了典型形状的粗糙元的热流行为。在已知局部流动和热传导的情况下， ...更多信息 条件是作为二维外部扰动施加到问题中的流场。因此，本文的最终目标是用平面来模拟复杂壁面条件下的热场流动。本文采用RANS模型，在低雷诺数层流和高雷诺数湍流条件下，通过数值模拟计算了简单粗糙元件（特别是半球形粗糙元件）在平面上周期性排列或交错排列时的流体力和传热率。利用所获得的数据证实，圆形管流中的压降重现了文献中引用的实验，具有令人满意的准确性。进行的第二个任务是构建一个方案，拿起占主导地位的重要峰。为此，小波多分辨率分析（MRA）被引入并扩展到二维版本。一个充分粗化的粗糙表面，消除小规模的压痕，获得。从这个简化的粗糙表面，一个模型粗糙表面组成的一组典型的形状，在许多情况下，半球形的粗糙元素，创建。主要重要的峰是具有高于指定阈值的高峰的那些峰，并且高峰的一个单一连续体积被相等体积的半球替代。该转换方案已成功建立。为了验证模型的正确性，需要对模型表面进行数值模拟，比较模型表面和原始表面的阻力和传热情况。然而，在这个项目中可用的计算机资源不允许我们完成这一验证，虽然已经进行了初步的比较。少

In this research project, it is indented to invent a method which gives simplified rough surfaces as models of randomly indented rough ones. The simplification is indispensable for computer simulation of turbulent flows over the surfaces, since computer power both in memory size and speed is limited. Demands from industry to estimate accurately thermo-fluid behaviors such as drag and/or heat transfer of irregularly indented surfaces are increasing sharply today and this project is to meet the demands. Fundamental strategy of the modeling is firstly to pick up dominantly important peaks which are large in scale and tall in height, and then to substitute selected peak areas by certain roughness elements of canonical shape such as hemisphere, con, circular cylinder, etc.. The thermo-fluid behaviors of roughness elements of canonical shapes are calculated by simulation, separately in advance. The fluid force and heat of the elements which are estimated by knowing local flow and thermal con … More ditions are imposed as two-dimensional external perturbations to the flow field in problem. Thus, final goal is to simulate a flow with thermal field of complex wall condition by a plane surface.The task done in this project is accordingly as follows. Fluid forces and rate of heat transfer of simple roughness elements, particularly of a hemisphere, which are mounted on a plane surface, periodically in line or in a staggered arrangement have been calculated by numerical simulations, assuming laminar flow in low Reynolds number and turbulent flow in high Reynolds number, based on RANS model. It was confirmed that pressure drop in a circular pipe flow using obtained data reproduces experiments which are cited from literatures, with satisfactory accuracy. Second task conducted was to construct a scheme which picks up dominantly important peaks. For this purpose, wavelet multi-resolution analysis(MRA) was introduced and extended to two-dimensional version. An adequately coarsened rough surface which removes small scale indentation, is obtained. From this simplified rough surface, a model rough surface composed of a group of roughness elements of canonical shape, hemispheres in many cases, is created. Dominantly important peaks are those having high peaks taller than a specified threshold value and one single continuous volume of tall peaks is replaced by a hemisphere of equal volume. The scheme for this conversion has been successfully established. It is required to validate the model surface, by comparing drag and heat transfer of the model rough surface and the original one, by numerical simulation. However, the computer resources available in this project did not allow us to complete this validation, though preliminary comparisons have been carried out. Less