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

在本研究项目中，致力于发明一种方法，将简化的粗糙表面作为随机凹陷粗糙表面的模型。这种简化对于表面湍流的计算机模拟是必不可少的，因为计算机在存储器大小和速度上的能力都是有限的。当今，工业对不规则凹槽表面的阻力和/或换热等热流体行为的准确估计的需求急剧增加，本项目就是为了满足这一要求。建模的基本策略是首先选取规模大、高度高的重要峰，然后将选定的峰区域替换为典型形状的某些粗糙元素，如半球、圆锥体、圆柱体等。通过数值模拟，预先分别计算了正则形状粗糙元的热流体行为。通过已知局部流动和温度…来估计单元的流体力和热将更多的条件作为二维外部摄动施加到问题的流场中。因此，最终的目标是在平面上模拟复杂壁面条件下的热场流动。基于RANS模型，分别假设低雷诺数下的层流和高雷诺数下的湍流，对平面上周期性排列或交错排列的简单粗糙度单元，特别是半球粗糙单元的流体力和换热速率进行了数值模拟。利用所获得的数据证实了圆管流动中的压降与文献中所引用的实验结果重合，具有令人满意的精度。进行的第二项任务是构建一个选取主要重要山峰的方案。为此，引入了小波多分辨率分析(MRA)，并将其推广到二维。获得了去除小尺寸压痕的充分粗糙的粗糙表面。从这个简化的粗糙面出发，创建了一个由一组规范形状的粗糙元素组成的模型粗糙面，在许多情况下是半球。最重要的峰是那些具有比指定阈值更高的峰的峰，并且单个连续体积的高峰被相同体积的半球所取代。这一转换方案已经成功地建立起来。需要通过数值模拟比较模型粗糙面与原始粗糙面的阻力和换热情况，对模型表面进行验证。然而，尽管已经进行了初步比较，但该项目中可用的计算机资源不允许我们完成这一验证。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