液態燃料側向噴注於馬赫2流場觀察顯示下游噴霧產生不穩定之擺動現象，對燃料氣化消散距離產生重大影響。本研究對造成噴注不穩定特性因素進行初步的探討，應用視流紋影法及高速攝影機分析弓形震波的變化，同時擷取噴注平板壁面上壓力訊號，利用快速傅立葉轉換進行頻譜分析，並將兩者對於噴霧消散現象影響進行比較。實驗分析顯示，噴注前之邊界層分離引發之斜震波與弓形震波會相互作用造成弓形震波振盪，進而影響震波下游壓力及速度的變化。在垂直噴注條件下，震波主振盪頻率於10kHz以下，而在較高動量通量噴注之振盪頻率會降至5kHz以下，同時具備較顯著的噴霧擺幅。在前傾45°噴注之弓形震波振盪頻率較垂直噴注為大，且可以觀察到高於10kHz的震盪頻頻率出現，燃料消散距離也比垂直噴注縮短許多。近壁面動態壓力感測顯示，噴注下游近壁面渦流主要的壓力響應頻率約在50kHz至150kHz，同時壓力訊號隨測試下游量測距離快速衰減，但噴霧仍保持擺動現象。經視流影像觀察，下游噴霧擺動頻率與弓形震波震盪頻率相近，推論影響燃料消散距離之主要因素是由弓形震波與分離震波相互作用引發下游壓力之不穩定性所主導。

Observation of the phenomenon of liquid fuel laterally injected into Mach 2 airflow shows the downstream fuel spray swings violently. The phenomenon greatly enhances the contact (mix) between the liquid spray and the surrounding supersonic airflow to cause the droplets to quickly evaporate. The distance that the droplets of the spray evaporate is defined as the spray dissipation distance. The swing motion of the spray may be caused by the occurrence of uneven and unstable pressure field. The objective of this thesis research is to analyze the sources of this unstable pressure effect.
Coupled with Schlieren photography and high-speed camera, the experimental observations are performed in a shock tunnel. The images of the bow shock induced by the liquid injection as well as the dynamic pressure measurements on the flat plate model wall are taken and analyzed. The observation shows the oblique shock induced by the boundary layer separation ahead of the liquid jet interacts and causes the bow shock to oscillate and may lead to downstream pressure field oscillation. For the right-angle fuel injection, the oscillation frequencies are found under 5KHz at lower jet momentum flux, to 10KHz at higher momentum flux. For 45 forerake of fuel injection, the bow shock oscillation frequency further increases to above 10KHz, accompany with a much shorter spray dissipation distance than that of right-angle injection.
The dynamic pressure measurements at the near wall show that the frequency response of the wake vortices behind the fuel injection are mainly in 50KHz to 150KHz and damping out quickly along the downstream where the spray swings violently. These observations infer that the interaction of the separation shock with bow shock may be the crucial source of downstream pressure unstable thus lead to the spray swing motion and quick dissipation phenomenon.

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