Understanding the influence of the Rossby number on the transient dynamics over a rotating wing

Studies have demonstrated that the Rossby number greatly affects LEV stability during the steady-state phase of rotating wing motion, but its influence on transient dynamics is less clear. This research explores the effects of the Rossby number on the transient dynamics over a rotating wing, using load measurements and rotating three-dimensional velocimetry. Previous studies have indicated that an increase in the Rossby number results in a reduction in the steady-state lift. In contrast, our findings show that the maximum lift during the transient phase increases as the Rossby number increases, with the difference between the maximum and steady-state lift increasing with an increase in the Rossby number. Preliminary flow field measurements suggest that in the transient phase, the LEV grows faster with increasing Rossby number, leading to higher circulatory and, thus, a higher maximum lift. With an increase in the Rossby number, the reduced effects of rotational accelerations result in a reduced out-of-plane transport of vorticity from the LEV and, hence, a faster growth of the LEV. Eventually, as the steady state is achieved, the reduced effects of rotational accelerations result in the LEV moving farther away from the wing, resulting in a significant drop in the steady-state lift at higher Rossby numbers. This study will further quantify the vorticity fluxes that mediate LEV growth and correlate them with the lift evolution in the different phases under different Rossby numbers.