An Experimental Study of Flows in Planar Nozzles

The paper describes an experimental investigation of the characteristics of low-Mach number flow of air from four planar nozzles. The nozzles had rectangular (rounded) inlets from a circular duct and aspect ratio of 3 at the exit. In general, two types of spiraling secondary flows were observed at nozzle exits. One type was observed in the vicinity of the midplane of the nozzles near the upper and lower walls, and the other type in the vicinity of the side walls in the corners. Experiments have shown that the secondary flows located in the vicinity of the midplane are produced by the contraction from the circular duct to the rectangular inlet, while the secondary flows located in the vicinity of the side walls are produced by the boundary layer migration toward the convex inner wall sections of the nozzles. The secondary flows have low total pressure associated with them. A comparison of discharge coefficient is made for the nozzles examined. The experiments were performed at the Reynolds numbers, based on the average flow speed at the nozzle exit and nozzle throat width, in the range of 3.4 × 10³ to 2.5 × 10⁴.