Publications

Reynolds-number scaling analysis on lift generation of a flapping and passive rotating wing with an inhomogeneous mass distribution

Published in Chinese Journal of Aeronautics, 2023

1. A coordinative relationship between active stroking and passive rotating motion is demonstrated in flapping wing system. Moreover, the phase shift between wing rotation and stroke reversal depends on active stroking motion. And advanced rotation is obtained when driving Reynolds number smaller than 100.
2. The mean lift coefficient decreases with the increase in Reynolds number, and increases with the increase in additional torque.
3. The additional torque can be used as a control parameter for modulating wing roation and lift generation.

Recommended citation: Qin, S., Hang H., Xiang, Y., and Liu, H. (2023). Reynolds-number scaling analysis on lift generation of a flapping and passive rotating wing with an inhomogeneous mass distribution. https://doi.org/10.1016/j.cja.2023.09.030

Active tail flexion in concert with passive hydrodynamic forces improves swimming speed and efficiency

Published in Journal of Fluid Mechanics, 2021

1. Passive bending is more efficient but could reduce swimming speed compared to rigid flapping, but the addition of active bending could enhance both speed and efficiency;
2. The phase difference between the posterior and anterior sections of the body is an important kinematic factor that influences performance;
3. Active antiphase flexion, consistent with the passive flexion phase, can simultaneously enhance speed and efficiency in a region of the design space that overlaps with biological observations.

Recommended citation: Hang, H., Heydari, S., Costello, J. H., and Kanso, E. (2022). Active tail flexion in concert with passive hydrodynamic forces improves swimming speed and efficiency. https://doi.org/10.1017/jfm.2021.984

Scaling analysis of the circulation growth of leading-edge vortex in flapping flight

Published in Acta Mechanica Sinica, 2021

1. Formation time of Leading edgs vortex (LEV)) in flapping wings experiment stays in the range of 2.5–5.5, agrees with the scaling formation number predicted by other vortices;
2. The mode of wing rotation plays a controllable role in the formation number of LEV by modulating the characteristic length scale that feeds the formation of LEV. After reaching the formation number, the LEVs stably remain attached on the flapping wing and even further grow at some spanwise locations because of vorticity transport;
3. Before the leading ledge vortex reach pinch off, the formation time calculated by the circulation of the LEV has a linear relationship with the formation time predicted by the kinematics of flapping wings, which implies the circulation growth of LEV can be predicted based on wing kinematics.

Recommended citation: Xiang, Y., Hang, H., Qin, S., and Liu, H. Scaling analysis of the circulation growth of leading-edge vortex in flapping flight. Acta Mech. Sin. (2021). https://doi.org/10.1007/s10409-021-01134-7

An objective-adaptive refinement criterion based on modified ridge extraction method for finite-time Lyapunov exponent (FTLE) calculation

Published in Journal of Visualization, 2019

In the calculation of inite-time Lyapunov exponent (FTLE), using a physics-based refine criterion is able enhance computation efficiency faster than a universal refine criterion based on error or gradient calculation.

Recommended citation: Hang, H., Yu, B., Xiang, Y., Zhang, B., and Liu, H. (2020). An objective-adaptive refinement criterion based on modified ridge extraction method for finite-time Lyapunov exponent (FTLE) calculation. Journal of Visualization, 23(1), 81-95. https://doi.org/10.1007/s12650-019-00605-1