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장조원,손명환,은희봉,Chang, Jo-Won,Sohn, Myong-Hwan,Eun, Hee-Bong 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.3
An experimental study was carried out to investigate near-wake characteristics of an elliptic airfoil oscillating in pitch. The airfoil was sinusoidally pitched about the half chord point between -5$^{\circ}$and +25$^{\circ}$angles of attack at the freestream velocities of 3.4 and 23.1 m/s. The corresponding Reynolds numbers based on the chord length were 3.3$\times$10$_{4}$ and 2.2$\times$10$^{5}$ , respectively. A hot-wire anemometer was used to measure the near-wake flow variables at the reduced frequency of 0.1. Ensemble-averaged velocity and turbulence intensity profiles were presented to examine the near-wake characteristics depending on the Reynolds number. The axial velocity deficit in the near-wake region tends to decrease with the increase in the Reynolds number as found in many stationary airfoil tests. Turbulence intensity in the near-wake region have a tendency to decrease with the -increase in the Reynolds number during the pitch-up motion, whereas it shows different feature during the pitch-down motion according to the separation characteristics.
마하수 3.0에서 스파이크를 붙인 무딘물체의 열전달에 관한 실험적 연구
장조원 空軍士官學校 1989 論文集 Vol.27 No.-
At supersonic speeds, the separation ahead of a blunt body caused by a spike or conical windshield greatly influences pressure drag & heat transfer rate of a blunt body. The effect of separated flow caused by spike or conical windshield has been experimentally investigated to see heat transfer rate at a nose section of flatnosed axially symmetric bodies. The tests were conducted in the Seoul National University's 200x200(mm) supersonic wind tunnel at a Mach number of 3.0 and Reynolds numbers per unit length from 4.75 x 10^7 to 5.29 x 10^7. The temperature distributions along the forward-face of blunt bodies dquipped with a spike or conical windshield have been measured by varying spike-length. The visualization using schlieren optical technique showed two distinct flow patterns, which are the open type with a simple wake and the closed type with complicated separated flows. The experimental results have shown that the use of a spike or conical windshield protruding from a flat-nosed cylinder decreased the heat transfer to a fraction of that measured on a flat-nosed body without a spike; the reduction effect in heat transfer was significant at the short spike-length of blunt body with a single conical windshield.