Implementation Of Nonstaggered Grid Division And Refinement And Its Application In Numerical Simulation Of Wind Flow Around Buildings

Owing to many advantages such as high efficiency and low cost, numerical simulation techniques are paid more and more attentions and are more and more widely used in the prediction of wind load on and wind environment around buildings. The rationality of numerical prediction results not only depends on the turbulent model and iterative numerical method adopted but also on the quality and layout of the division grid.The structured grid scheme has been widely used in the numerical simulation of wind flow around buildings due to advantages of simple formulation and save of computational time. However, the structured grid now commonly used in the numerical prediction is an unchanged grid that is determined and arranged before computation. Such a fixed grid is usually difficult to fit in with the change of wind velocity and pressure gradients in different areas of the actual wind flow, and consequently the local changes of flow condition and their effect on the building cannot be effectively caught. The primary objective of this dissertation is to establish a self-adaptive grid division and refinement scheme and successfully apply it to the numerical simulation of wind flow around buildings and building complexes.For convenience of grid refinement implementation the nonstaggered grid system based on the structured orthogonal grid scheme is adopted. In order to eliminate the possible pressure wiggles when nonstaggered grid is used, except for the use of the momentum interpolation method (small wiggles still appear when the method is adopted alone), a new method is proposed and applied in the same time. In the new method a pressure-gradient difference term is added to the flow velocity in each control volume interface when dealing with the pressure-correction equation. This overcomes the problem of pressure wiggles completely when nonstaggered grid is applied to the numerical simulation of wind flow around buildings. Through proper handling of boundary conditions under nonstaggered grid system, a new grid division scheme with one division performance being applicable to the computation of a problem under different wind directions. In order to improve the accuracy and efficiency of numerical prediction, a semi-adaptive and layer-patch refinement method based on the idea of adaptive mesh refinement (AMR) is proposed and applied to the numerical simulation of wind flow around buildings based on the pressure correction iterative algorithm. The main process of the method is: after the converged solution for a certain layer of grid is obtained, all elements that are required to be refined based on error analysis are automatically found and output. As the distribution of the elements to be refined is often discrete and irregular, regular square blocks consisting of elements to be refined need to be manually built and input to the computer. The computation for the refined layer grid is then carried out and the procedure is repeated until the final convergence criterion is satisfied.Based on the above grid division and refinement scheme, a computer program named WSMR is developed. Using the program two and three-dimensional numerical simulation of wind flow around single or multiple buildings can be achieved and the detailed flow condition including wind velocities, pressures and time-average characteristics of turbulence can be obtained. In order to attain the required accuracy efficiently multi-layer local refinements can be carried out based on the initial division grid.Using the developed computer program the wind flow around a cubic building model, a rectangle-section tall building and a gable-roof building are first numerical predicted, respectively. Inthe prediction the single-area and multi-area grid refinement approaches are respectively used and the numerical results are compared with the wind-tunnel test results and the numerical results without grid refinement obtained by other researchers. This indicates that the proposed nonstaggered grid and refinement scheme is not only valid and easy to be car...