Effects of Upstream Disturbances on Dynamic Stall of Constant- rate Pitching Airfoil

• Main Authors: Chao, Chish-chung, 趙志忠
• Other Authors: Chen Jerry-min
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/69858254815784609540

碩士 === 國立中興大學 === 機械工程學系 === 85 === The effects of upstream local disturbances on the aerodynamic characteristics ofan airfoil pitching at a constant-rate is studied experimentally.The experimentswere conducted in an open- type wind tunnel.The test model was the NACA 0012 airf-oil. The disturbed flow field was produced by a thin rod placed upstream of thetest airfoil. The surface pressures of the airfoil were measured to examine its aerodymamic performance under various test conditions. The results demonstrate that the upstream disturbances, produced by the rod parallel to or below the pit- ching axis, have significant influence on the static airfoil at higher angles of attack, causing a delay in stall angle and an increase in maximum lift coeffi-cient. For the dynamic airfoil, such disturbances also leads to a delay in lift and moment stall. The largest influence occurs when the rod is located below the pitching axis of the airfoil. For higher pitch rates, it is found that the upstr-eam influence on the airfoil retains but is less intensified. Different horizon-tal locations of the rod make no discernable effects on the pressure distrib-utions for the dynamic cases. The lift coefficient plateau phenomenon happenswhen the airfoil is operated at pitch rates higher than k=0.01. The LCP becomesunclear when the rod is located below the pitching axis, and meanwhile there appears a smooth pitching moment stall rather than a sharp drop observed for the undisturbed case.