Evolution and stability analysis of supersonic Coanda jets of convergent nozzle and irrotational vortex nozzle

The nozzle configuration can change the flow characteristics of the outlet jet, which will further have a significant impact on the flow structure on the Coanda profile. In this paper, the circulation control devices for convergent nozzle and irrotational vortex nozzle are designed with the same mass flow rate as the constraint, and the supersonic jet flow fields of the two nozzles at high pressure ratio are numerically studied by using the delayed detached-eddy simulation method based on shear-stress transport k–w model and compared with the flow structure obtained by Schlieren test. Moreover, the complex flow structure of supersonic jets on the Coanda profile and its evolution and flow stability are analyzed, and the features of the flow field are further extracted by dynamic mode decomposition method. The results show that the convergent nozzle presents a strong oblique shock and separation bubble structure, which leads to the enhancement of centrifugal instability. As a result, the momentum exchange between the jet and external flow is enhanced, which leads to the early formation of large-scale vortex structure in the shear layer and wall separation bubble on the jet, and the Reynolds stress distribution is more extensive. The shock wave structure on the Coanda profile of the irrotational vortex nozzle is basically eliminated. At the design pressure ratio, weak expansion waves are generated at the jet outlet, and the pressure difference is sufficient to deflect the upper layer of the jet. Therefore, the initial centrifugal instability in the upper region within the jet is weak, and the mixing between the jet and external flow is weakened, which increases the convective Mach number and delays the formation of large-scale vortices in the shear layer. At the same time, the flow in the wall boundary layer is unstable under the action of centrifugal instability, which is accompanied by the formation and shedding of vortices. The steady modal energy ratio of the irrotational vortex nozzle is 10.75% higher than that of the convergent nozzle, and the growth rate is small, so it has a more stable flow field structure.