In this study, a numerical experiment was performed as what obtains relative velocity fluctuation by oscillating an object with comparatively large amplitude in the direction of flow. Follow pattern and instantaneous fluid force around an In-line forced oscillating symmetrical airfoil (NACA0012) with attack angle of 5 degrees caused not separation in stationary situation were investigated using a vortex method at the Reynolds numberRe=4.05×105, in ranges of the oscillation amplitude ratio 2a/c=0.5,1.0,1.5 and 2.0 and the oscillation frequency ratiof/fK=0.25,0.5,1.0 and 2.0 (here,a:half-amplitude of oscillation,c:chord-length,f:oscillation frequency,fK:natural Karman vortex shedding frequency from a stationary airfoil with the attack angle of 90 degrees). As a result of calculations, Separation was observed by oscillating condition even if it was the airfoil of attack angle not separating. It is found that the separation was dependent on the velocity ratio. The characteristics of fluid force are changed by oscillation.
In this study, a visualization experiment was performed in order to confirm the flow pattern around airfoil with relative velocity fluctuation by in-line forced oscillating in the direction of flow. An airfoil NACA0012 with attack angle of 5 degrees produce the separation in the steady state was observed by the experiments using dye streak method at Reynolds number Re=3.6x103. The investigation of the attack angle which does not separate in such low Reynolds number was performed, and it was confirmed that the separation occurs to 3 degrees. And the airfoil with attack angle of 2 degrees which does not cause separation in steady state, was forced to oscillate with two kinds of relative velocity ratio (umax/U=0.4 and 0.8, here, umax and U denote maximum moving speed of airfoil and main flow velocity, respectively.). The flow separation on the surface of airfoil with attack angle which does not produce the separation in the steady state is occurred even if the maximum moving speed of airfoil umax is in the range which does not exceed main flow velocity U.
In this study , a visualization experiment was perfl )rmed 洫 order to conflrm the flow pattem around air 兪 )il with relative veloo 貢 ty fluctUation by ln−1ine forced oscillat 洫 g in the direCtion of flow. As a result , airfbil NACAOOI2 with aUack angle of 5 degreos p τoduco the sepamtion the stationa 【 y condition was observed by the experiments using dye s甘 eak me 血 od at Reynolds number Rei ・ 3. 6xlO3. The 血vestigation of the attack angle which does net separate in such low Reynolds number was pe痴 ed, and it was confirmed that the separation occurs to 3 degrees , And air 剱 with attack angle of2degrees which does not cause sepalation in stationary con 〔lition , was fbrced to oscillate with 2 kinds ofrelative velocity ratio( 触 1ひ = 0. 4 , 0. 8) . The flow separation on the su 血 ce of airfoil with attack angle which does not produce the separation in the stationary condition is produced even ifthe movement speed of airf( }il is in the range which does not exceed main flow veloci 旬 . Key W ( ) rds :Separation , in − line Forced Oscillation , Low Reynolds number , NACAOO12 , Dye Streak Methed
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