所謂背景噪音是因為風洞的測試段壁面有不同的配置，如左右側有實心壁面或是透孔壁面的不同，使得風洞內有不同的背景噪音，其對流場的干擾，導致流場展現出來的行為有所不同，可壓縮凸角流場乃針對自由流馬赫數為0.6～0.9之間的凸角模型實驗，本研究針對成功大學航太研究中心的穿音速風洞，進行兩種壁面、六個凸角角度和四個自由流馬赫數的可壓縮凸角流場研究。
利用表面平均壓力和壓力擾動量的分佈，顯示凸角角度增加或是自由流馬赫數增加都會讓凸角流場中的擴張波強度增加，下游的分離泡也隨之變大，伴隨而來的震波也因條件的不同，在位置、型態和行為上都有不同的展現，例如震波震盪的型態從單一震波轉變成λ-震波；利用參數的結果，在最小壓力係數圖或是最大馬赫數圖上都顯示此參數在次音速凸角流場和穿音速凸角流場之間有可定義的分界，即φ=6.80為區隔，可以有效的控管流場是否會產生震波甚至邊界層分離的狀態；最後分析透孔壁面和實心壁面的擴張波強度，透孔壁面和實心壁面的震波震盪頻率、流場不穩定性的差異。

Boundary layer flow in the vicinity of a sharp corner has been investigated by many researchers, particularly for the compression corner in supersonic speed. For a convex corner flow, it is possible to formulate the interaction law in an explicit form which would relate the displacement effect of the boundary layer to the pressure induced in the inviscid part of subsonic and supersonic flows. In transonic flow, there are not many studies which explain the flow properties as a result of the viscous-inviscid interaction near the corner point. Thus an experimental program was conducted to investigate the compressible convex-corner flow with solid or perforated side wall. Presence of perforated side walls induces stronger tunnel background noise, which affects the expansion and recompression process near the corner. For the test cases of shock-induced separation, the size of separation bubble also tends to decrease. Oscillation frequency of shock wave is about 150 Hz and 100 Hz for the test cases of perforated and solid side walls, respectively. This indicates higher tunnel background noise tends to enhance the shock excursion phenomena.

1. Chung, K., “Transition of Subsonic and Transonic Expansion-Corner Flows,” Journal of Aircraft, Vol. 37, No.6, 2000, pp. 1079-1082.

2. Chung, K., “Unsteadiness of Transonic Convex-Corner Flows,” Experiments in Fluids, Vol. 37, No. 6, 2004, pp.917-922.

3. Chung, K., “Investigation on Transonic Convex-Corner Flows,” Journal of Aircraft, Vol. 39, No.6, 2002, pp. 1014-1018.

4. Dolling, D.S., “Fifty Tears of Shock-Wave/Boundary Layer Interaction Research：What Next？,” AIAA J. Vol.39, No. 8, 2001, pp. 1517-1531.

5. IBRAHIM TURKYILMAZ, “An Investigation of Separation Near Corner Points in Transonic Flow,” Journal of Fluid Mechanics, Vol. 508, 2004, pp.45-70.

6. Johnson, D.A., “Transonic Flow about a Two-Dimensional Airfoil-Inviscid and Turbulent Flow Properties,” AIAA 78-1117, AIAA 11th Fluid and Plasma Dynamics Conference, Seattle, Wash., July 10-12, 1978, 21p.

7. Lee, B.H.K., “Transonic Buffet on a Supercritical Airfoil,” Aeronaut J. May, 1990, pp. 143-152.

8. Lee, B.H.K., “Self-Sustained Shock Oscillations on Airfoils at Transonic Speeds,” Aerospace Sciences, Vol. 37, issue 2, 2001, pp. 147-196.

9. Mabey, D.G., Welsh, B.L., and Cripps, B.E., “Periodic Flows on a Rigid 14% Thick Biconvex Wing at Transonic Speeds,” TR-81059, Royal Aircraft Establishment, May 1981.

10. Mason, W.H., “Fundamental Issues in Subsonic/Transonic Expansion Corner Aerodynamics,” AIAA Paper 93-0649, Jan. 1993.

11. Stanewsky, E., and Little, B.H., “Studies of Separation and Reattachment in Transonic Flow,” Journal of Aircraft, Vol. 8, No.12, 1971, pp.952-958.

12. Verhoff, A., Stookesberry, D., and Michal, T., “Hodograph Solution for Compressible Flow Past a Corner and Comparison With Euler Numerical Predictions,” AIAA Paper 91-1547, 1991.