本研究旨在探討弧形前壁面構型對於凹槽駐焰器流場特性的影響。凹槽駐焰器因能有效產生低速迴流區，提升燃料混合與火焰穩定性，廣泛應用於超音速燃燒推進系統中。過去研究多聚焦於長深比與後壁面斜角等幾何參數，對前壁面設計之探討則相對有限。為此，本研究設計兩種凹槽構型，分別為具垂直前壁面之基礎型凹槽，以及具弧形前壁面之前弧型凹槽，進行流場觀測與性能比較。實驗利用反射式震波風洞搭配粒子影像測速技術（PIV），在馬赫數2的自由流條件下，量測凹槽內的瞬時速度場，以探討弧形前壁面設計對凹槽內部流場結構與低速迴流區特性的影響。
研究結果顯示，基礎型構型之剪切層受槽內壓力震盪影響，易產生上下擺動，導致低速迴流結構不穩定；反之，弧形前壁面則可有效降低剪切層擺動並引導其深入槽底，使低速迴流呈現穩定且完整之主迴流結構。進一步比較性能指標發現，剪切層深入槽內可提升迴流區平均渦度，雖縮小迴流面積並限制環流量，但經評估可推測其不致降低迴流與剪切層之間的質量交換，甚至能強化剪切層將主流氣流導入迴流區內部的趨勢，促進主流與低速迴流之間的循環與交換，進而提升燃燒效率與穩定性。
綜合而言，弧形前壁面的設計能穩定促進剪切層深入槽內，形成完整且高渦度的主迴流，對燃料混合產生潛在助益。並且依據邊界速度分析，可推論此構型有助於提升將剪切層上之新鮮空氣輸送至低速迴流區內部的能力，強化迴流區與主流間的循環與交換。

This study examines the impact of a curved front wall configuration on the flow characteristics of cavity flameholders. Cavity flameholders are widely used in supersonic combustion systems to enhance fuel–air mixing and stabilize flames through low-speed recirculation. Prior research has primarily emphasized geometric parameters like length-to-depth ratio or aft wall angle, with limited focus on front wall design. To bridge this gap, this study compares two cavity configurations—a baseline with a vertical front wall and a modified version with a curved front wall—via flow field observation and performance analysis. Experiments were performed in a reflected shock tunnel using Particle Image Velocimetry (PIV) under Mach 2 free-stream conditions to capture instantaneous velocity fields within the cavity.
Results show that the baseline cavity exhibits unsteady shear layer motions, driven by pressure oscillations, leading to fragmented and unstable recirculation structures. In contrast, the curved front wall suppresses these oscillations, guiding the shear layer deeper into the cavity and forming a stable, complete primary recirculation structure. Performance analysis indicates that while deeper shear layer penetration reduces recirculation zone size, it increases the mean vorticity. Moreover, the enhanced boundary velocity in y-direction further suggests a stronger ability to entrain fresh air into the recirculation zone, thereby improving the exchange between the mainstream and the recirculation zone.
Overall, the curved front wall design demonstrates a significant potential to promote stable shear-layer penetration, strengthen recirculation dynamics, and enhance fuel–air mixing, offering clear advantages for flameholder applications in supersonic combustion.

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