介面計算方法於液氣兩相流之動態及相變化研究

Abstract

不論在自然界或工程系統中，常會存在兩種互不相融的流體運動問題，過去常以實 驗方法做探討，近年來，數值方法快速發展，以計算流力模擬此雙流體問題成為重要分 析方式，在此種計算中，一項重要課題，就是要能準確預測流體間的介面問題，這在液 氣的兩相流中尤其重要，因在介面處，兩者的性質，如密度及黏滯性有極大的差異，這 在數值模擬上造成極大的困擾。過去數年，我們針對雙流體的流場問題，發展出兩套計 算方法，一屬介面捕捉法，採用高解析的差分混合限制型的下風差分，另一採介面重建、 加上先預測後修正的介面追蹤法，能有效的處理介面的運動，及避免數值的擴散及耗 散。本計畫將繼續發展這些計算方法，將延伸至三維模擬，第一年主要針對氣體進入液 體儲存槽中形成氣泡，及液滴撞擊壁面的動態問題做探討，第二年考慮相的變化，將加 入氣化模式，第三年利用此相變化的計算方法探討薄膜沸騰的熱傳問題。

Flows involving two immiscible fluids can be found in nature environment or engineering systems. Experiments were often employed to study such flow problems. However, the fast development of numerical methods in the past has made CFD an important tool for such flow analysis. The most important issue in analyzing these flows is to predict the sharp interface between the two fluids accurately. This is especially true in the two-phase flow of liquid and vapor because the great differences in density and viscosity between the two phases cause difficulties in numerical calculations. In the past several years, we have developed two numerical schemes for interfacial flows. One is of interfacecapturing type which blends high-resolution differencing schemes with bounded downwind scheme. Another is of interface-tracking type which uses interface reconstruction technique together with a predictor-corrector procedure. Numerical dissipation and dispersion can be overcome and the interface can be accurately predicted. These methods are going to be further developed and extended to deal with three-dimensional problems. In the first year of this project, we will study the phenomenon of bubble formation as air flows into a tank filled with liquid. Another concern is the impact of a liquid droplet on a solid wall. The target of the second year is to take account of phase change in the two-phase flows. Vaporization models will be added into the calculation procedure. In the last year, we will study the film boiling problems using the developed methods.