摘要 :
The flow structures, wake-flow characteristics and drag coefficients of a square cylinder at various Reynolds numbers (Re) and incidence angles were experimentally studied in an open-loop wind tunnel. The cross section of square c...
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The flow structures, wake-flow characteristics and drag coefficients of a square cylinder at various Reynolds numbers (Re) and incidence angles were experimentally studied in an open-loop wind tunnel. The cross section of square cylinder is characterized by the aspect ratio (AR) and blockage ratio (BR) of 25% and 4%, respectively. The Reynolds number is changed from 4000 to 36,000 and the incidence angle is adjusted from 0° to 45°. The flow patterns near/behind the square cylinder were determined using the smoke-wire scheme. The global velocity fields and streamline patterns were analyzed using the particle image velocimetry (PIV). Additionally, the flow-topology method was applied to analyze the flow patterns by calculating the separatrices, alleyways and critical points. Experimental results showed that the flow structures around the square cylinder exhibit three modes-leading-edge separation, separation bubble and attached flow. The surface-pressure profile, drag coefficient (C_D), lift coefficient (C_L) and vortex shedding frequency were detected/calculated using a pressure transducer and hot-wire anemometer. The lift coefficient did not significantly vary with Re. The minimum C_D occurs at =12°, whereas the minimum C_L occurs at =13°. The minimum projected-Strouhal-number (St_d) occurs at =0° while the maximum St_d occurs at =15°.
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摘要 :
This study examines several finite length NACA 0012 airfoils to explore how the angle of attack (α), the sweep angle (Λ) and the Reynolds number (Re) affect the junction vortex and horseshoe vortex. Upstream floor roughness and ...
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This study examines several finite length NACA 0012 airfoils to explore how the angle of attack (α), the sweep angle (Λ) and the Reynolds number (Re) affect the junction vortex and horseshoe vortex. Upstream floor roughness and turbulence intensity (T.I.) influence the wing-junction flow was also studied. The junction-flow structures at low Reynolds numbers were visualized using the smoke-wire technique. The smoke-streak flow patterns were classified into two characteristic modes - horseshoe vortex and non-horseshoe vortex. The horseshoe-vortex patterns were further categorized as the junction-vortex mode and non-junction-vortex mode. The velocity vectors were measured using the particle-image velocimetry (PIV), and the data was utilized to calculate the junction vorticity (Ω). Experimental results indicate that the straight wing has the maximum junction vorticity. The Ω decreases with increasing α and Λ and with decreasing Re. The Ω decreases with increasing T.I. The upstream T.I. generated by the mesh fences was more significant than that produced by sandpapers.
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