بررسي تجربي اندركنش جت مافوق صوت، جريان جانبي مادون صوت و بالك واقع در پايين‌دست جت بر ميدان جريان

EXPERIMENTAL INVESTIGATION OF THE INTERACTION BETWEEN SUPERSONIC JET, SUBSONIC CROSSFLOW AND A FIN LOCATED DOWNSTREAM OF THE JET ON THE FLOWFIELD

در اين نوشتار اثرات تداخلي ناشي از حضور بالك در ميدان گردابه‌ييِ ناشي از تخليه‌ي متعامدِ يك جتِ مافوق صوت در جريان جانبيِ مادون صوتِ تراكم‌پذير ــ كه اهميت ويژه‌يي در هدايت برخي اجسام پرنده دارد ــ مورد بررسي قرار گرفته است. براي بررسي اين اثرات، ميدان جريان با استفاده از يك ريك مخصوص در پايين‌دست بالك اندازه‌گيري شده است. نتايج حاصله نشان مي‌دهد كه اثرات حضور بالك در امتداد صفحه‌ي تقارن و در نواحي نزديك به جت بيشتر به‌صورت تقويت جفت‌گردابه‌ي چرخان است و با فاصله‌گرفتن بالك از محل تخليه‌ي جت به‌تدريج اين اثرات از بين مي‌رود. همچنين، حضور بالك در نواحي نزديك به جت با يك فاصله‌ي عرضي موجب تداخل يكي از گردابه‌ها و بالك، و گاهي نيز موجب از بين رفتن گردابه‌ي درگير با بالك مي‌شود؛ در حالي كه در نواحي دوردست اين فاصله‌ي عرضي تاثيرات اساسي بر ميدان جريان نمي گذارد و بيشتر به‌صورت آشفتگي گردابه‌ي درگير با بالك مشاهده مي‌شود.

The problem of jet into a cross flow is a classic problem in fluid mechanics and has many engineering applications. Much work has been done in the field of jet into a cross flow, however, not much of it has been involved with the interactions of supersonic jets in compressible subsonic cross flow, especially their interaction with the control surfaces located downstream. In this study, the effects of a fin located in the vortical flowfield generated by the perpendicular exhausting of a supersonic jet into a high subsonic crossflow, have been investigated. Some of the individual achievements of this research are parametric studies of jet into freestream dynamic pressure ratio (J) and the location of fins. For this purpose, a flat plate equipped with pressure holes, a fin with a NACA 0012 airfoil, a special rake to determine total pressure and a special hardware to provide supersonic jet were designed, manufactured and used. The free stream and the exhausted jet Mach numbers were held constant (0.7 and 2.5, respectively). The results related to the interactions between the jet, the freestream, and the fin downstream (the case where the fin is at the plane of symmetry) show that, when the fin is located in the near field of the jet, the strength of the counter rotating vortex pair (CRVP), due to interaction with the fin, increases. However, when the fin is located in the farfield, few changes are observed. For the case where the fin is in the near field with a lateral distance from the plane of symmetry, strong interaction between the fin and one of the vortices of CRVP is observed. In some cases, this vortex and the related jet plume were also burst. For cases where the fin is in the farfield, with a lateral distance from the plane of symmetry, the flow field is not affected by the presence of the fin and the vortices pass near the fin without much change.