Experimental Studies on Decay and Spread Characteristics of an Overexpanded Triangular Supersonic Jet

Abstract

Experiments were conducted on overexpanded equilateral triangular supersonic jets (Mach 1.8) at Reynolds numbers 6.71 × 10⁵ and 4.81 × 10⁵ to study their decay and spread characteristics by means of measuring the jet centreline and lateral total pressure distributions. Schlieren images of the jets were also taken to study the shock patterns in the jet structure. The above Reynolds numbers correspond to the nozzle inlet total pressures of 550 kPa (6.71 × 10⁵) and 360 kPa (4.81 × 10⁵). For comparison purposes the above experiments were repeated on a circular nozzle with the same exit area and area ratio (1.44) and total pressures. The observations from the experiments reveal that the triangular jet exhibits a shorter supersonic core compared with the circular jet, i.e., reduction of 34.25% at 360 kPa and 31.11% at 550 kPa. The total pressure decay is more abrupt and a greater loss of the total pressure occurs closer to the nozzle exit plane in the case of the triangular jet compared to the circular jet. The lateral total pressure distribution reveals that the jet spreading rate is greater on the flat than on the corner side of the triangular jet.