Near Field of an Axisymmetric Underexpanded Jet and an Adjacent Parallel Surface

An underexpanded axisymmetric jet exhausting across an adjacent rigid planar surface generates a unique flowfield that has received little attention in the literature. To date, most published research within this area has been motivated by acoustics, and consequently little flowfield data exist. This study aims to provide such a data set for an axisymmetric jet operating at a nozzle pressure ratio of 5 and shows how variation in the plate-to-surface separation distance h/D-e results in large-scale changes in the flowfield. High-resolution planar particle image velocimetry data were obtained on the geometrical symmetry plane. These data are complemented by schlieren imagery, surface oil-flow visualization, and steady pressure-sensitive paint measurements. Data were obtained for h/D-e = 0.50, 0.55, 0.60, and for the isolated jet (for comparison purposes). The data indicate that the flowfield is dominated by a shock/boundary-layer interaction generated due to the presence of the plate and that the shock/boundary-layer interaction subsequently alters the structure of the jet. The size, strength, and location of the shock/boundary-layer interaction vary as h/D-e increases. The presence of the surface was also found to inhibit the screech cycle observed in the isolated jet case. The data presented herein form a baseline data set for an ongoing study in which the rigid surface is replaced with a compliant surface.