國立臺灣大學應用力學研究所張建成2006-07-262018-06-292006-07-262018-06-292000-07-31http://ntur.lib.ntu.edu.tw//handle/246246/21580本研究旨在推展先前由作者開發的二 維離散渦法，拓展至三維不可壓縮分離流 場(separated flow)的計算。此方法係結合網 格計算與隨機渦漩法之方法，一般又稱為 混成渦漩法(hybrid vortex method)。在此研 究階段，我們提出了新的定義，在此新定 義下，我們僅須將前期所提的數值算則作 些微的修改，即可直接引用，保留此一數 值算則於中高雷諾數流場計算原有高穩定 性的優點。同時為從所解渦度場求得其速 度場，我們定義了新的向量流線函數，此 向量流線函數在固體邊界滿足Dirichlet 條 件，遠域則滿足Neumann 條件，在此定義 和邊界條件下，我們可證明其所得速度場 在固體邊界直接滿足不可穿透條件(nonpenetrating condition)。為驗證此方法，我 們以環繞瞬間啟動之一球體流場為例，所 得結果和文獻上實驗比較獲致相當一致的 結果。Some time ago, the present authors proposed a hybrid vortex method for study of two-dimensional separated flows. It is hybrid in that a grid is required, and therefore is not fully Lagrangian. It is also deterministic that no random walk for diffusion is employed. The method is here extended to threedimensional separated flows. Such an extension is not at all obvious but requires new definition and formulation of the previous method. The method may be briefly described as follows. At any instant, a collection of vortices forms a patch of the flow field. The methods consists of solving the viscous vorticity equation by evolving a total vorticity associated with each vortex, and then redistributing the evolved total vorticity back to the grid at the end of each time step. The total vorticity, when divided by the volume that it occupied, yields the mean vorticity associated with the vortex. The velocity field is recovered from the vorticity field by solving a Poisson equation for a vector stream fucntion. It is shown consistent to specify the gauge that a component of the vector stream function be identically zero; this facilitates imposing Dirichlet conditions for the other two components on the body surface to satisfy the nonpenetrating condition. Vorticity is then updated on the body surface to fulfill the no-slip condition. The overall method here presented is a quite general setting for a finite body but with a particular application to flow about an impulsively started sphere. Preliminary results shows excellent comparisons with measured data in several detailed flow chatracteristics.application/pdf266039 bytesapplication/pdfzh-TW國立臺灣大學應用力學研究所離散渦漩法雷諾數向量流線函數不可穿透條件separated flowLagrangianviscous vorticity equationPoisson equationDirichlet conditionreporthttp://ntur.lib.ntu.edu.tw/bitstream/246246/21580/1/892212E002035.pdf