超音速燃燒衝壓引擎燃燒室加入多孔性圓柱燃燒器之模擬與分析

Abstract

本研究基於氣體動力學的理論基礎，以商用軟體FLUENT求解超音速燃燒衝壓引擎燃燒室的流場問題。在紊流模型的選擇上使用與計算情況較符合的SST k-ω紊流模組計算。此模組在壁面與邊界層附近或是高速區的流場問題皆能得到好的結果。 本文先利用商用軟體FLUENT作驗證，以此做出的模擬與文獻實驗值相佐證，並討論其流場的物理情況，確定本文所使用的數值方法可適用於超音速燃燒流場後。再加以設計與改良目前的超音速燃燒衝壓引擎燃燒室，以多孔性圓柱燃燒器做為再引燃器，放入流場中使其火焰穩定，並增加出口的動能與推進力的表現，利用不同的入口初使條件與原始流場做比較。而設計的考量有圓柱對流場造成的阻力影響以及流速大小是否造成火焰的熄滅。以燃燒室入出口而言，燃燒室的出口壓力應大於噴嘴的出口壓力以維持流體的流動，且其溫度不應過高以免材料無法負荷其高溫。在考慮以上條件後，分析加入再引燃器後的溫定流場，確定其效能確實比原始的燃燒室更佳。 最後模擬暫態流場，在原始流場下會熄滅的情況因加入多孔性圓柱燃燒器做為再引燃器使得改良後的燃燒室能在極低的氫氣質量流率下再次被引燃，且有穩定的火焰存在。

The study is based on the theory of gas dynamics. We use the software FLUENT to simulate the flow field scramjet combustion chamber. We choosed SST k-ωas turbulence model, because it can get solution which is more close to real flow field. The simulation procedure is verified against by two examples to ensure its accuracy, and we move on to design scramjet combustion chamber. Adding a porous cylinder as a burner into the flow field to improve its performance,including flame stabilization, kinetic energy and thrust improvement. Using different inlet condition to compare with the original flow field. We take some limitations into account, including the drag effect to the flow field, and flame extinction. The pressure at combustion chamber outlet should be higher than nozzle outlet for the purpose of continuous flow. The temperature at combustion chamber should avoid hot spot or it may cause damage on it. Considering the above conditions, we ensure that the performance of combustion chamber assisted by porous cylinder do better than the original one by checking the steady simulation. In the end, it could be shown that the combustion chamber assisted by porous cylinder could be ignited at extremely low hydrogen mass flow rate, which cannot be done on the original one.