Abstract
Water tunnel experiments were conducted to study the interaction of vortical gusts with airfoil and wings. A nearly two-dimensional vortex of small core size has been produced by the transient plunging motion of an upstream airfoil. It travels with freestream and interacts with the downstream airfoil and wings. Depending on the vortex-airfoil/wing offset distance and the angle of attack of airfoil/wings, the incident vortex filament deforms, diffuses, and loses coherence, while inducing leading-edge vortex formation and shedding from the airfoil and wings. No significant spanwise flow develops in the incident vortices during the interaction. The interaction with the swept wing at each spanwise plane appears to be unaffected by the other spanwise planes. The counter-clockwise vortex induces a positive lift peak as it approaches the wing, which can be predicted by the potential flow assumption. The peak lift force is proportional to the circulation of the incident vortex and has its maximum near the zero-offset distance. The minimum lift coefficient is reached after the vortex has just passed and caused flow separation on the lower surface. The maximum lift coefficients for the finite unswept and swept wings can be estimated by making a correction for the aspect ratio and using the independence principle. The only exception is observed for the swept wing at a post-stall angle of attack for which the leading-edge vortex shedding becomes parallel to the leading-edge and increases the peak lift force.Based on the findings of vortical gust-wing interactions, the need to alleviate lift peaks arises. Previous studies have found a mini-spoiler near the leading edge is efficient in alleviating the lift force of periodic plunging airfoil. To investigate the lift alleviating performance of the mini-spoiler in gust-wing interactions, flow visualization and force measurements were performed on the airfoil, finite unswept and swept wings. The mini-spoiler is placed near the leading edge and alleviates lift through forcing flow separation. Desired lift reduction was found for a wide range of angles of attack and various wing planforms. The best performance of load alleviation was found for moderate angles of attack near stall, accompanied by great changes in the flow field. The mini-spoiler leads to lift increment at zero angle of attack. However, for those loaded situations, even in deep stall angles of attack, the mini-spoiler can reduce the lift peaks effectively. Various combinations of incident vortex sizes, geometric angles of attack and wing planforms are considered and compared.
| Date of Award | 12 Dec 2022 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Ismet Gursul (Supervisor) & Zhijin Wang (Supervisor) |