Experimental investigations on separation control and flow structure around a circular cylinder with synthetic jet

Abstract

Circular cylinder separation control and flow structure influenced by the synthetic jet have been experimentally investigated in a water channel. The synthetic jet issues from a slot and ejects toward upstream from the front stagnation point of the cylinder. It has been found that, similar to the traditional synthetic jet which is positioned near the separation point or inside the separation region, the present synthetic jet arrangement constitutes an efficient way to control flow separation of the circular cylinder, but with a different control mechanism. The present synthetic jet leads to an upstream displacement of the front stagnation point and the formation of a vortex pair near both sides of the exit orifice. When Re U based on the synthetic jet average exit orifice velocity is about lower than 43, a closed envelope forms in front of the windward side of the cylinder during the blowing cycle of synthetic jet, which acts as an apparent modification for the cylinder configuration. When Re U is high enough, an open envelope forms upstream of the cylinder, and the flow around the cylinder becomes much energetic. Thus, regardless of Re U , the present synthetic jet can improve separation for flow around a circular cylinder. With regard to the leeward side, as Re U increases, the flow separation region behind the cylinder gradually disappears. The flow over cylinder may be fully attached when the open envelope forms upstream of the cylinder and Re U is greater than 344. Then, the flow past the cylinder will converge near the back stagnation point of the cylinder, where a new vortex pair shedding periodically is generated due to the high shear layer. flow control, synthetic jet, flow around a cylinder, vortex structureThe synthetic jet is a kind of new active flow control technology improved by the research group of Glezer [1] in the late 1990s. They carried out a deep study on the synthetic jet formation and evolution mechanism, and divided the flow field into two different regions: near-field region and

Active control of the wake behind the cylinder

“…This finding is in agreement with [7]. If the SJs were placed at the rear stagnation point (Į = 180°) the wake behind the cylinder was symmetric.…”

“…Open envelope was observed if the SJs were placed at the front stagnation point (Į = 0°). This is in good agreement with [7]. Figures 14 and 15 show visualization for C f = 3.99 and C f = 5.98, respectively.…”

“…(4) in the text below) were optimal, then the drag coefficient was reduced about 30%. If the SJ was placed in the rear stagnation point, small close envelope was formed during the extrusion part of the period [7]. During the intrusion part of the period the vortex pair is convected downstream from the both sides of the cylinder and interacts with the wake.…”

Review of zero-net-mass-flux jet and its application in separation flow control

“…(a) The velocity distributions at different stream-wise positions with L=2.0 and Re U 0 =2500, 5000, 10000 [27] ; (b) the normalized velocity distributions with L=17.0-80. 8 and Re U 0 =734-2200, including that of the continuous jet [28] .…”

“…The ZNMF jet was first used as a laboratory flow control method by Wiltse and Glezer [3] in 1994, after that it attracted more and more attentions. Now, the ZNMF jet is a hot topic in fluid mechanics researches, and there are many universities and institutes in China that are conducting relative research work, including National University of Defense Technology [4][5][6] , Beijing University of Aeronautics and Astronautics [7][8][9][10][11] , Nanjing University of Aeronautics and Astronautics [2,[12][13][14] , Northwest Polytechnic University [15,16] and Tsinghua University [17,18] . Many reviews about this subject have been published [4,19] .…”