The effect of a 2D planar jet was investigated to manipulate the separation bubble behind the vertical fence. The pulsating and continuous blowing jets were generated in front of or behind the fence. The experiments were carried out in a circulating water channel. The parameters used for controlling the jet included the distance between the slit nozzle and fence, the speed of the jet, and the frequency of the pulsating jet. The velocity fields were measured using phase-averaged DPIV method. From the results, the mechanism of reduction of the separation bubble and the quantitative effects of parameters to reduce the separation bubble behind the fence were found. A maximum reduction of 87% compared with the reattachment length of the uncontrolled fence flow was achieved using the front continuous jet. The controlled fence wakes have higher flow fluctuations and less sheltering effect than that of uncontrolled fence wake.
In this study, we experimentally investigated the effect of rear-located pulsating jet to reduce the separated flow region behind the vertical fence. The separation bubble behind the fence is the representative feature of fence wake. Control of fence wake can be used for various purposes such as the reduction of drag, increasing or decreasing the mixing, etc. The vertical fence was submerged in the turbulent boundary layer in the circulating water channel. Reynolds number based on the fence height and upstream flow velocity was 3000. The parameters used for controlling the pulsating jet included the frequency, jet speed and distance between the fence and slit nozzle. In addition, we investigated the effect of continuous jet on the fence wake. Phase averaged DPIV method was applied to measure the instantaneous velocity fields around the fence. And the obtained results were compared with those of uncontrolled fence flow. The obtained results quantitatively show the decrease of reattachment region brought by the pulsating jet. And the specific jet condition which were effective to reduce the separation bubble behind the fence were found.
Abstract. We carried out the experiments which controled the periodic jet in front of the fence to alter the fence wake. The experiments were performed in circulating water channel and the vertical fence was submerged in the boundary layer. The frequency, jet nozzle distance and speed of jet passing the slit were investigated. Each case divided into 20 phases and phase-averaged results were compared with uncontrolled fence flow. From the results, we found the specific frequency and nozzle distance which were good for reducing the reattachment length. In this case, the reattachment length was decreased 35% compared with the uncontrolled fence flow.
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