53 / 2019-09-04 16:39:01

Drag reduction of a circular cylinder by sensitivity analysis

drag reduction sensitivity analysis active control passive control

We have established an algorithm to calculate the sensitivity of lift/drag forces to a variety of boundary perturbations, including active, passive and mixed perturbations, which refer to non-zero velocity on the body surface, surface roughness, and surface vibration, respectively. The algorithm is then applied to a circular cylinder flow in both two and three-dimensional conditions for sub-optimal drag reduction. The passive control, consisting of spanwise uniform roughness and periodic waviness concentrated around the separation line and localized in the spanwise direction, is observed to reduce drag significantly. Similarly, in the active counterpart, the control consisting of spanwise uniform suction and periodic suction/blowing reduces drag by 20% at maximum control velocity 2% of the free-stream velocity (or momentum coefficient 10−4) at Reynolds number Re = 190. Such a drag reduction is owing to the suppression of interactions of detached shear layers and a spanwise mismatch of shedding vortices. This control is much more efficient than the previously tested spanwise uniform suction or periodic suction/blowing, both requiring maximum control velocity above 8% (or momentum coefficient above 10−3) to achieve similar drag reduction effects. The control effectiveness, defined as the ratio of the control-reduced drag power and the maximum input power, is above 20, up to Re = 1000, the highest Reynolds number considered in this work.