Flow structure and parameter evaluation of conical convergent-divergent nozzle supersonic jet flows

Supersonic gas jets in conical convergent-divergent nozzles are studied numerically using the OpenFOAM rhoCentralFoam solver. The spatiotemporal evolution of the jet flow field is analyzed. The influence of the operating conditions on the flow field is studied parametrically, including the nozzle pressure ratio (NPR), area ratio, and throat position. The behaviors and mechanisms of the double-diamond structure, throat wave, and exit wave are interpreted in detail. The results show that a conical convergent-divergent nozzle always generates shock waves. The throat shock reaches its maximum length during the initial stage, then becomes slightly shorter before becoming stationary, dominated by the exit velocity. Furthermore, it is shown that the jet flow changes from overexpansion to underexpansion with increasing NPR. With an increasing area ratio, the trend is the opposite. The throat position affects the jet divergence angle at the nozzle exit, consequently causing a variation in the core radius of the jet. It is further shown that the double-diamond structure does not always appear. The throat shock angle, exit wave angle, and shear layer width directly affect the shape of the double-diamond structure. The favorable pressure gradient of the nozzle ultimately dominates the changes in the length of the throat wave and exit wave.

Automated summary

Supersonic gas jets in conical convergent-divergent nozzles are numerically studied using the OpenFOAM rhoCentralFoam solver. The effects of operating conditions on the flow field, including nozzle pressure ratio (NPR), area ratio, and throat position, are parametrically investigated. The behaviors and mechanisms of the double-diamond structure, throat wave, and exit wave are analyzed in detail. The results indicate that shock waves are always generated in a conical convergent-divergent nozzle. The length of the throat shock reaches its maximum during the initial stage, becomes slightly shorter before becoming stationary, which is dominated by the exit velocity. Moreover, the jet flow transitions from overexpansion to underexpansion as the NPR increases, while the trend is opposite with increasing area ratio. The throat position affects the divergence angle and core radius of the jet at the nozzle exit. Furthermore, the presence of the double-diamond structure is influenced by the throat shock angle, exit wave angle, and shear layer width. The changes in the length of the throat wave and exit wave are ultimately controlled by the favorable pressure gradient of the nozzle.