三岔式非穩態流場粒子分離器之數值模擬

Abstract

本研究為三岔型粒子分離器內部非穩態流場之二維數值模擬。在分析過程中，入口處基態流場假設為均勻流加上週期性的震盪流場，分析模型的外型主要概分為兩部分:一輸入流道加上三岔型分離流道。此模型在三岔口處會產生渦流使粒子往兩側輸出流道移動而與流體分離。 首先本研究參考文獻中的實驗操作參數，諸如入口層流的平均流速、流場震盪的頻率、兩側流道的張角角度和中央輸出流道的長度；然後對流場作完整的分析，之後再藉由改變參數的組合，觀察流場變化來推論粒子分離之物理機制。同時亦能得到最佳化的參數以及提供粒子分離的實驗裝置之參考。 最後根據本研究數值模擬的結果得知，此裝置在粒子分離機制上最主要的兩個因素為：主流道的Ka值至少為5.72以上(Ka為一震盪流場中的無因次參數)；並且中央輸出流道要短於兩側輸出流道。

This study mainly simulates two dimensional behavior of an unsteady-flow particle separator with triple outlet channels. The geometry of this device was referred to the previous study. During the analysis, we regard the flow field as the combination of laminar flow and periodic oscillating flow. The analytic models, in principle, are divided by two components, which are the main channel and trifurcate zone. When the inlet is subjected to the oscillating velocity profile, there will be two vortices which are generated upstream of the center channel. The vortices will increase the flow resistance of the center channel, and rotating directions of the vortices are able to lead the particles to move toward the side channels. First of all, the flow phenomenon of the particle separator was observed at 1/16 step in the whole period. Secondly, the flow fields of the particle separator were investigated in various parameters, such as the flow velocity, oscillating frequency, the incline angle between the two side channels and the length of the center channel. Base on the results of this simulation, two important separating factors of this device were obtained. The dimensionless factor of the flow field, Ka, should be above 5.72, and the length of the center channel should be shorter than the side channel.