An Investigation of the Gas Discharging through a High Pressure Vessel with a moving ball valve by Appling the Immersed Boundary Method
|關鍵字:||氣體釋氣過程;沉浸邊界法;座標轉換;移動邊界法;CUDA平行計算;推力分析;Gaseous Discharge Process;Immersed Boundary Method;Coordinate Transfer Method;Moving Boundary;CUDA parallel computation;Reaction and Thrust Analysis|
|摘要:||本文以三維可壓縮流計算數值程式探討且高壓氣艙球閥移動釋氣之流場狀態，將諸多數值方法結合貫通並以C++作為演算法使用之平台，流場使用有限體積法(Finite Volume Method)，將網格形變與沉浸邊界技術混合使用，兩種方法各有優缺點，而混合使用兩方法將可達到相互相補的效果。最後使用平行化計算技術OpenMP與CUDA加速流場計算速度，期以達到快速分析球閥移動釋氣之流體現象。
The aim of this thesis is to investigate gases discharged from a high pressure vessel numerically. To simulate this subject more realistically, the viscosity and compressibility of the gas are taken into consideration simultaneously. The methods of the Roe scheme, preconditioning and dual time stepping matching the LUSGS method are adopted to solve compressible flow problems during gaseous discharge processes. The non-reflecting boundary condition is used to prevent flow fields from being polluted by the reflection of the pressure wave induced by the compressible flow on the boundary. Computing procedures are performed on the Compute Unified Device Architecture (CUDA) computation platform which was recently developed and a highly effective technology for accelerating computational speed. The pressure ratio, which means the ratio of the pressure in the vessel to the pressure of outside, is larger than 1.89. Thus both subsonic and supersonic speeds of the discharged gas are investigated. Results show that the mass flow rate of this work is consistent with the existing experimental work. Due to a sudden expansion at a small opening, the phenomena of an alternating variation of the pressures of gases, rapid decrements of the temperature of gases and a quick acceleration of the velocities of gases are clearly observed in the mainstream direction. The ratio of the thrust caused by the gases released to the reaction force is less than 1 because of the dissipation of entropy generation. Also, a modified equation for predicting transient mass flow rates is derived. Results obtained by the equation have good agreements with results that calculated by the numerical method developed bt this work.