本研究選用計算流體力學軟體ANSYS FLUENT進行凹槽機構對液態燃料噴注的超音速燃燒流場影響，首先是根據Wang等人在2015年所發表之文獻，將本研究所建立的數值模擬方法之計算結果與實驗壁面壓力分佈做比對，並捕捉到噴注上游因逆向壓力梯度所產生的連續迴流現象。接著根據Zhang等人在2002年所發表之文獻，在L/D值大於14以上時凹槽內流場會轉為封閉型態，而本研究藉由數值計算成功模擬出封閉型凹槽流場，再次驗證本研究數值方法的可靠及準確性。在參數分析的部分，建立兩組不同凹槽L/D值的燃燒室模型，分別為L/D值為3.0與4.5，其中，L為凹槽長度，而D為凹槽深度，L/D值即為凹槽之長深比。首先觀察不同凹槽L/D值的燃燒現象，在L/D值為3.0的燃燒室內之火焰燃燒溫度比L/D值為4.5的燃燒溫度還高。不論L/D值為3.0或4.5的模型，由於噴注孔半徑固定的條件下，煤油噴注量11.3g/s與13.4g/s時相比，較大的噴注量會擁有較快的噴注速度，因此13.4g/s的煤油較能注入燃燒室中心，所以其燃燒範圍才會在出口附近分佈較廣，但缺點是燃料較無法流入凹槽內進行反應，因此凹槽內的燃燒產物水比11.3g/s時相較少了許多，凹槽內溫度也較低。由計算結果可得知兩者凹槽內迴流區的結構差異性，在L/D值為3.0的凹槽流場中，因為其凹槽深度較深，故在深度中間的截面中可以觀察到四到六個不對等且結構範圍較小的迴流區，凹槽內流場較為複雜且左右兩邊有些微不對稱；而L/D值為4.5的凹槽流場則因為凹槽深度較淺，故在深度中間的截面中則觀察到四個結構完整的迴流區，整體型態上較為對稱。在噴注擺動的方面，因為不同L/D值的凹槽會影響其內部迴流區結構，而這些迴流區同時也會擾動凹槽上方的流場，造成煤油氣產生S型擺動現象，使這些流入凹槽內燃燒的煤油氣也左右不對稱，因此在互相影響之下，才會導致凹槽內流場有些微不對稱的情形發生。在與平板燃燒室比較後可以發現，由於平板燃燒室內無凹槽內迴流區的擾動，所以其燃料噴注後方之流線相對要平穩許多。

This study uses the computational fluid dynamics software ANSYS FLUENT to analyze the effects of cavity mechanism on a supersonic combustion flow field with liquid fuel injection. First, according to Wang et al. (2015), our numerical simulation results are compared with the experimental wall pressure distribution and the accuracy of our numerical method is proved. During the parameter analysis, two 3D cavity models of L/D = 3.0 and 4.5 are established, where L is the cavity length and D is the cavity depth.
First, we observe the different L/D combustion phenomena. The flame temperature in the L/D = 3.0 combustor is higher than the flame temperature in the L/D = 4.5 combustor. Regardless of whether using the L/D = 3.0 or 4.5 model, due to the radius of the injection hole being fixed, the large kerosene mass flow rate has faster jet speed, so the 13.4g/s kerosene can be injected into the center of the combustor easily, and the combustion range can be distributed widely in the combustor outlet. But the disadvantages of 13.4g/s are that less fuel flows into the cavity to burn and the cavity temperature is low. According to the simulations results, we can obtain the difference in the structure of the recirculation between these two cavity models. In the L/D = 3.0 cavity flow field, four to six irregular recirculations are observed in the middle cross section because the depth of cavity is deep, the flow field is more complex and the left and right sides are slightly asymmetrical. In the L/D = 4.5 cavity flow field, four structural integrity recirculations are observed in the middle cross section because the depth of the cavity is shallow, and the overall structure is more symmetrical. In the injection oscillation part, different L/D values of the cavity can affect its internal recirculation structure, and the recirculation will also interact with the flow field above the cavity, resulting in the kerosene having an S-type oscillation phenomenon, so the kerosene flowing into the cavity is also asymmetrical. After comparison with the plate combustor, we can find that the flow field of the fuel injection is relatively smooth because there is no cavity recirculation to interact with the flow field in the plate combustor.

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