日本航空宇宙学会 Acta Medica Okayama 13446460 64 4 2016 超音速壁面噴射流れ場へ上流擾乱が及ぼす影響 244 252 EN Effects of upstream disturbances on a transverse jet into Mach 2 supersonic flow were investigated by using single-time two-point spatial correlations of fluctuating velocities in the flowfield. The fluctuating velocity was measured by stereoscopic PIV. We categorized the upstream disturbances into two factors: incoming boundary layer on the injection port and weak oblique shock wave impinging ahead of the injection port. The velocity fluctuations in the upstream boundary layer had a long positive correlation region in the boundary layer. This is the evidence that very large-scale motion (VLSM) existed in the boundary layer developed on our test section. The correlation region bifurcated into the regions along the bow shock wave and the outer jet boundary. The correlation length was 10-hold longer than the boundary layer thickness. Fluctuation of the weak shock wave was induced by VLSM developed on the opposite wall to the injection wall. The velocity fluctuation due to the weak shock wave also had a long positive correlation region along the oblique shock wave. However, it had no correlation with the jet. No potential conflict of interest relevant to this article was reported.

日本航空宇宙学会 Acta Medica Okayama 13446460 63 4 2015 高速断層シュリーレンによる二次元翼バフェットの可視化 166 174 EN We visualized two-dimensional wing buffet using fast-framing focusing schlieren method. A supercritical airfoil of NASA SC(2)-0518 was used in this study. Mach number of the freestream was 0.7, and Reynolds number based on the wing code (c) was 5×106. Angle of attack without corrections (α) was changed from 4° to 6°. The present focusing schlieren system had ±18mm depth of field, which was narrow than spanwise region where the two-dimensionality of the flow field was maintained. 8,345 successive images were captured by high speed CMOS camera with 7,000 frames per second with 20μs exposure time. The present imaging system well captured the shock wave motion on the airfoil. At α = 4°, the shock wave was positioned at x/c∼0.45. The shock wave was slightly fluctuated with a frequency of 585.5Hz. Above α = 5°, the wing buffet occurred. The buffet frequency increased as increasing α. The focusing schlieren movies revealed that the shock wave was bifurcated on the wing surface, as the shock traveling upstream. The boundary layer largely separated from the leading oblique foot of the bifurcated shock wave, whereas, the bifurcated shock wave changed into a normal shock and the flow separation disappeared, as the shock traveling downstream. For both cases, many pressure waves propagated from the downstream of the shock wave to the upstream. These waves merged with the shock wave, and seem to drive the shock oscillation. No potential conflict of interest relevant to this article was reported.