Twin Impinging Jets Aligned With a Crossflow

Abstract

The flowfield created by twin impinging jets in tandem and aligned with a low velocity crossflow is studied in detail. The mean velocity, velocity fluctuation and visualization in the impingement region were obtained for a Reynolds number based on the jet exit conditions of Rej=4.3x10, an impingement height of 20.1 diameter, and for a velocity ratios between the jet exit and the crossflow VR =Vj /Uo of 7.5 to 90 with interject spacing L of 6D. The largest velocity ratios are characterized by a large penetration of the first (upstream) impinging jet, giving rise to a ground vortex due to the collision of the radial wall jet and the crossflow that wraps around the impinging point like a scarf. The second jet (located downstream) it is not so affected by the crossflow in terms of deflection, but it does not reach the ground due to the downstream wall jet that flows radially from the impinging point of the first jet along the ground. Three different types of flow pattern were identified for low, intermediate and high velocity ratios. The results help to understand the flow around a VSTOL aircraft operating in ground vicinity with front wind or small forward movement that may result in enhanced negative pressures in the underside of the aircraft causing a pitching moment and suction down force towards the ground.