Interaction of axisymmetric supersonic twin jets

Abstract

Measurements are reported of the pressure fields within overexpanded supersonic twin jets. The flowfield was produced by two identical parallel axisymmetric Laval nozzles set in a common end wall and issuing into the ambient atmosphere. A mainstream flow in the jet is presented, with the design Mach number of 1.5, 2, and 2.5 throughout the experiments. The stagnation pressure was varied from 2.9 to 4 atm. The nozzle spacing was chosen as 14, 18, 22, and 30 mm. The twin jets are compared to circular supersonic single jets operating at the same initial flow conditions. The studies show that structure of supersonic twin jets is identical to that of low-speed twin jets. The two jets attract each other, mix and then combine to form a single jet. The flowfield, therefore, contains three distinct regions, namely, converging, merging, and combining regions. The merging between the jets occurs in the distance close to the nozzle exit for smaller nozzle spacings and higher Mach numbers. The shock cell structure as well as the mixing process vary with the exit Mach number and nozzle spacing. The spreading rate shows an irregular variation with the exit Mach number. There is a transition region between the near and far field at which the overexpanded jet starts to spread linearly with downstream distance as that of a low-speed jet