Experimental and Numerical Analysis of Finite Wing inGround Effect at Low Reynolds Numbers

• Main Authors: Po-Lun Lo, 羅博倫
• Other Authors: 朱錦洲
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/tfj99w

碩士 === 國立臺灣大學 === 應用力學研究所 === 106 === This study is aimed to investigate the influence of ground effect during the landing process of the airfoil NACA 4412 under static and dynamic experimental force measurements in a water tunnel that has moving ground simulation with numerical validations. Airfoils of 5‑cm chord length (C) and 3° pitch angle (θ) at various aspect ratios (AR=2, 3, & 4) are vertically immersed in the water with a narrowed‑neck support linked between the load cell above water surface and the airfoil beside the conveyor belt. The conveyor belt is designed to synchronize with the inflow velocity (U) in order to remove the boundary effects generated by the velocity difference at the side wall, and is capable of matching Reynolds numbers (Re) from 5,000 to 10,000 as utilize in the present study. The forces exerted on the airfoil are measured by a 2‑D load cell under the two prescribed situations, namely static ground effect (SGE) and dynamics ground effect (DGE).In SGE, the forces exerted on the airfoil are measured statically at various clearance and angle of attacks α=θ+γ, where γ is chosen to match with those in the DGE. As in DGE, the forces are measured at a continuous descending motion of normalized constant velocity vf=vf*∕U=tan(γ) towards the ground (moving conveyor), so‑called dynamic. It is emphasized that γ is the inflow angle relative to the descending airfoil determined by vf, and α in DGE is varied from 6° to 25° (with θ=3°).The results show that the ground effect in either SGE or DGE is essential to the airfoil only when the clearance decreases below a unit chord length (C), and the influence becomes rather tremendous as the clearance deceases below 0.5C. Next, it is found that the lift coefficient CL increases with increasing α in SEG and DGE cases under the same Re. However, the increment of CL ceases when a critical α is achieved in SGE. When α is low‑to‑moderate, CL is shown to increase with increasing Re in both SGE and DGE cases. In addition, the lift curve with respect to the clearance in SGE and DGE are almost the same when α is low‑to‑moderate, and thus the results in SGE can be reasonably applied to that in DGE. However, when dealing with α beyond a certain angle, the analysis of DGE must be taken into account in order to prevent an error that could reach about 30 to 40%.