Characterization of Unsteady Phenomenon during Pitching Motion
The aerodynamic response of airfoils in motion has garnered significant attention due to the critical need to accurately predict unsteady aerodynamic loads. This demand arises from engineering challenges such as separated flows, noise prediction, and flutter analysis. Modern engineering problems increasingly require the evaluation of structural nonlinearities, which in turn necessitate using time-domain aerodynamic models to capture the complex dynamics involved.
Predicting aerodynamic loads in unsteady flows is challenging, particularly at high angles of attack where flow separation occurs. These loads significantly impact aircraft efficiency, especially by influencing the lift generated by the wings. This study focuses on the phenomena associated with low-Reynolds-number flows over airfoils during pitching motion. We experimentally investigate the instantaneous pressure fluctuations on a NACA 0018 airfoil at Reynolds numbers ranging from 2 to 3 × 10^5.
Miniature pressure sensors were embedded within the airfoil to measure instantaneous pressures and the resulting aerodynamic loads. The primary objective of this study is to develop a model capable of accurately predicting aerodynamic loads during motion in the time domain. We introduce modifications to three existing models and propose a new model, by combining and refining the Wagner’s and Goman-Khrabrov’s models. The modification adjusts the instantaneous lift coefficient slope from the theoretical value of 2π to the value obtained from static experiments.
Furthermore, we analyze the effects of various flow parameters on the development and location of the laminar separation bubble (LSB) along the wing. The study examines the influence of reduced frequency, Reynolds number, and angle of attack on the LSB’s. This research offers new insights into theoretical lift coefficient models, the impact of different flow characteristics on the LSB, and the unsteady Kutta condition.
The work is towards M.Sc. degree under the supervision of Professor Emeritus Moti Karpel and Dr. Oksana Stalnov
