Robustness of Leading-Edge-Vortex to Turbulence

Advised by Professor Xinyan Deng, Bio-Robotics Lab, Purdue University, May 2018 ~ May 2020

At Purdue, I conducted undergraduate research on a turbulence project of fluid and robotic flapping wings in Bio-inspired Robotics Lab. 

The presence of a stably attached leading edge vortex (LEV) on an insect’s wings is attributed to the aerodynamic performance they exhibit during hovering flight. Although LEV has been visualized on real insects and demonstrated by robotic analogs and through computational fluid models, the physical mechanisms are poorly understood. Prior studies have demonstrated that the stability of the LEV is sensitive to the local Rossby number, a dimensionless number associating the wing’s distance from its axis of rotation, with transitions to periodic shedding occurring at a critical point.

 Therefore, we hypothesized that, with the addition of external flow disturbances in the form of turbulence, LEV instability will occur prior to the critical Rossby number, allowing for the systematic study of this transition region. We wanted to observe the relationship between the flying altitude of each species of insect and the parameters of its wings and verified if the turbulence of the wing flight can be a buffer to the external flow. In order to measure the forces exerted on the wings with different flapping or sweeping patterns, we designed a series of experiments with a robotic wing and turbines in a big oil tank, implemented their pattern with MATLAB Simulink and overserved the flow with the method of Particle Image Velocimetry. To first verify and then investigate this phenomenon, aerodynamic force measurements obtained from dynamically scaled tank experiments will be paired with a flow quantification technique known as particle image velocimetry (PIV), providing new insights into the transition between region stability. Specifically, a robotic wing model was flapped in an oil tank and the sensor on the wing measured the lift force exerted on it to compare the position of the wing at which the lift force drops dramatically, under both laminar and turbulent conditions. The hypothesis that turbulence does not affect the transition in LEV instability which occurs under laminar flow conditions will be discussed based on the results. The results of the study would either verify the robustness of the mechanism(s) resulting LEV stability or provide an avenue for further investigation. After the experiments, I processed the PIV data with specific software, wrote a series of Matlab code for processing force data and plotting figures, analyzed and compared the figures with published academic papers, and ameliorated the raw figures with Affinity Designer. 

In this project, which involves bio-Aerodynamics, fluid, control, biology and robotics, I was exposed to different aspect of research and the interdisciplinarity of different subjects, improved my MATLAB skills, learned to design and perform a series of experiment correctly and effectively and performed academic literature reviews.

Reference: 

Sane, S. P. (2003). The aerodynamics of insect flight. Journal of experimental biology, 206(23), 4191-4208.

Juergen Kompenhans, 20171012

Cheng Bo, Roll Jesse, Liu Yun, Troolin Daniel R. and Deng Xinyan Three-dimensional vortex wake structure of flapping wings in hovering flight11J. R. Soc. Interface