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

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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