Flow behavior around a square cylinder subject to modulation of a planar jet issued from upstream surface

• Published in: Journal of fluids and structures Vol. 51; pp. 362 - 383
• Main Authors: Huang, R.F., Hsu, C.M., Chiu, P.C.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2014
• Subjects: Cylinder wake; Cylinders; Deflection; Flow control; Flow visualization; Fluid dynamics; Fluid flow; Fluids; Infrared radiation; Oscillating; Smoke; Square cylinder; Upstream; Flow control; Flow visualization; Cylinder wake; Square cylinder
• ISSN: 0889-9746; 1095-8622
• DOI: 10.1016/j.jfluidstructs.2014.10.001

The flow behavior in the up- and downstream regions of a square cylinder subject to the modulation of a planar jet issued from the cylinder׳s front surface was studied using the laser-assisted smoke flow visualization method and hot-wire anemometer measurement. Reynolds numbers were from 1628 to 13000. The drag force experienced by the square cylinder was obtained by measuring the surface pressures on the up- and downstream faces. The temporally evolving smoke flow patterns in the up- and downstream regions were synchronously revealed through the smoke flow visualization. The frequency characteristics of the instability waves in the up- and downstream regions were synchronously detected by the two hot-wire anemometers. Four characteristic flow modes were observed within the different ranges of the injection ratios. At the low injection ratios (IR<1), the ‘swinging jet’ appeared. The jet swung periodically leftward and rightward and formed a fluid bubble on the front surface. The fluid bubble contained a pair of counter-rotating vortices and presented a periodic variation in its height. At moderately low injection ratios (1<IR<4.3), the ‘deflected oscillating jet’ appeared. The jet was deflected in either the left or the right direction and wrapped around one of the edges of the square cylinder. Both the swinging and oscillating motions of the jet in the swinging jet and deflected oscillating jet modes were induced by the periodic feedback pressure signals generated by the vortex shedding in the wake. At the moderately high (4.3<IR<8.3) and high (IR>8.3) injection ratios, the ‘deflection jet’ and ‘penetrating jet’ appeared. The jet detached from the cylinder׳s front surface and penetrated a long distance into the upstream region due to large jet momentum. Neither periodic jet oscillation in the upstream region nor vortex shedding in the wake was observed. The drag coefficient was found to be decreasing quickly with increasing the injection ratio. •Flow around a square cylinder changed by a planar jet issued from upstream surface.•Four characteristic flow modes were found in upstream region.•Swinging and oscillating jets appeared at small and moderate injection ratios.•Upstream instabilities were induced by downstream vortex shedding.•Downstream periodic instabilities disappeared at large injection ratios.