Compressible Lateral Jet And Of Rotary Jet Large Eddy Simulation

The investigation of compressible transverse jets and swirling jets is of great impor-tance due to their widespread applications. In this dissertation, large-eddy simulations are used to study three typical flows including the transverse jets into a supersonic crossflow, the pulsed jets into a supersonic crossflow and the supersonic swirling jets. The results and conclusions are briefly given as follows:(1) Numerical investigation of sonic jets injected into a supersonic crossflow was car-ried out. Results have been validated carefully against experimental data. The effects of the jet-to-crossflow momentum flux ratio and the effects of the injector geometry on various fundamental mechanisms, including shock/jet interaction, shock/vortex interaction, the jet shear layer vortices, jet penetration properties and the relevant turbulent behaviors, have been studied systematically. As a jet issuing transversely into a supersonic crossflow, some of the salient three-dimensional shock and vortical structures, such as bow, separation and barrel shocks, Mach disk, horseshoe vortex, jet shear layer vortices and counter-rotating vortex pairs, are induced. The shock structures exhibit considerable deformation-s in the circular injection, while their fluctuation becomes smaller in the elliptic injection. The jet shear layer vortices are generated at the jet periphery and their evolution, convection and penetration characteristics are obtained through trac-ing the centroid of these coherent structures. It is identified that the jet from the elliptic injector spreads rapidly in the spanwise direction but suffers a reduction in the transverse penetration when compared to those obtained in the circular injection. The turbulent fluctuations are amplified due to the jet/crossflow in-teraction. We find that the vertical Reynolds normal stress is enhanced in the downstream of the jet due to the upwash velocity induced by the counter-rotating vortex pair.(2) Numerical investigation of a pulsed jet injected into a supersonic crossflow was performed for the crossflow Mach number1.6and the mean jet-to-crossflow mo-mentum flux ratio2.2. A corresponding steady jet injection was also calculated for comparison and validation against experimental data. Various fundamental mechanisms dictating the intricate flow characteristics, including jet penetration increase, jet mixing enhancement, complex shock wave system and multi-scale vortical structures as well as their interactions, have been studied systematically. As the pulsed jet issuing transversely into the supersonic crossflow, the salient shock and vortex structures in terms of the mean and instantaneous flow field are analyzed to reveal the mechanisms relevant to the jet penetration increase and mixing enhancement. It is found that the pulsed jet fluid retaining higher mo- mentum can increase the penetration depth and the large-scale vortical structures evolved in the jet shear layer region can enlarge the penetration width. Further, the turbulent fluctuations are significantly strengthened due to the pulsation ef-fect and the shocks/vortices interaction, and the active mixing area is investigated based on the turbulent fluctuations to elucidate the jet mixing characteristics. It is noticed that the active mixing area for the pulsed jet is larger than the steady jet case, indicating that the pulsed injection can significantly enhance the jet mixing process. The dominant frequencies relevant to the unsteadiness of shock waves and vortical structures are identified to be consistent with the forcing frequency for the pulsed injection.(3) Large-eddy simulation of the underexpanded supersonic swirling jets issuing in-to a quiescent environment was carried out for two typical swirl numbers. The corresponding nonswirling jet was also calculated for comparison and validation. The swirling effects on various fundamental mechanisms dictating the intricate flow phenomena, including flow features, shock cell structures, jet spreading char-acteristics, turbulence behaviors and jet screech tone noise, has been carefully analyzed. It is found that the number of the shock cells and their length are re-duced in the swirling jets in comparison with the nonswirling jet. A recirculation zone is formed in the high swirl number case, due to the centrifugal force induced from the swirling effect. The jet shear layer becomes more unstable and the jet can spreads quickly in the radial direction due to the swirling effect, which will be of help in mixing process. Moreover, it is found that intensive turbulent fluctu-ations are generated along the jet shear layer and at the end of the jet potential core, while the pressure fluctuations are suppressed. Furthermore, we found that the jet screech tone frequency has been altered and its intensity has also been reduced due to the swirling effect.