Passive Jet Flow Control Method for Suppressing Unsteady Vortex Shedding from a Circular Cylinder

A numerical simulation is performed to investigate a passive jet flow control method for suppressing the alternating vortex shedding from the circular cylinder. A hollow pipe is tightly set on the circular cylinder, and two arrangement cases for the holes are employed: one is a five-hole case, which means that five suction holes are set near the front stagnation point and five jet holes set near the rear stagnation point of the cylinder. The other is the full-hole case, which means the holes are equidistantly arranged on the hollow pipe. The incoming flow enters the suction holes and jets into the near wake from the outlet holes. Consequently, the wake vortex shedding alternately is manipulated or destroyed. The numerical simulations of baseline cases (without control) are first conducted to verify the reliability of the numerical model. Next, the two controlled cases (five hole-case and full-hole case) are investigated at the Reynolds number R = 10(3)-10(5). It is found that a remarkable mitigation for the aerodynamic forces of the cylinder is revealed at the high Reynolds number: the in-line drag coefficient can be reduced by approximately 40.00%. At the same time, the cross-flow lift fluctuation has been completely suppressed with a control effectiveness of more than 98.00%. The swirling strength distributions and corresponding streamline results around the circular cylinder are then described, which are employed to present the essential physics regarding why the unsteady vortex shedding is suppressed by the passive control method. Finally, the stability of the flow field is discussed based on the linear stability theory. The absolute instability region near the cylinder shrinks substantially at the high Reynolds number, even changing into a convective instability region completely for the five-hole cases. (C) 2016 American Society of Civil Engineers.