Overall flow dynamics characteristics of slit-vent cylinders

PIV (Particle Image Velocimetry) experiments were conducted to reveal the influence of the Reynolds number (Re), position, and inclination angle of a slit vent on the overall flow dynamics characteristics of slit-vent cylinders. The flow mechanism of the slit vent was studied based on the quantitative evaluation of the periodic shedding vortex transformations. The experimental results indicated that the slit vent could produce a strong effect of blowing and suction on the boundary layer if the slit-vent position was in front of the flow separation point for the base cylinder. The effect of the blowing and suction caused the Kármán vortex street (KVS) to occur much earlier and strengthened the vortex shedding for the 120° and 180° slit-vent cylinders. The St values of the 180° slit-vent cylinders were least sensitive to Re as compared with the other cylinder types with Re = 2000 ∼ 5400. With the slit-vent inclination angle β varying in the range of 80°–90°, the St values of the 180° slit-vent cylinder were around 0.225 and exhibited the greatest stability.