Investigation Of The Vortex And Flow Characteristics For Jet In Crossflow

As a highly complex turbulent flow,jet is a fundamental phenomenon in the field of fluid,which always involves high energy or vortex rings etc.Due to the vast application in the engineering fields and theoretical value,the free jet,synthetic jet and jet in crossflow(JICF)has been investigated for many decades.Since the processes of the formation,entrainment,blending for the vortex rings in the JICF have great effect on the actual engineering application,the JICF is of important significance in the jet control.At present,research on the JICF are mainly focused on high Reynolds number.However,the detailed characterization for vortex rings at low Reynolds number still can not be understood.In this thesis,the large eddy simulation(LES)will be adopted to investigate the related issues for the free jet,synthetic jet and JICF,which is aimed to describe the flow mechanism of vortex ring in the JICF.The detailed content for the free jet and synthetic jet,JICF,synthetic JICF and block JICF will be listed as follows:(1)The research for the free jet and synthetic jet has been conducted based on different conditions.The corresponding content is divided into two parts: the analysis for the formation process and flow characteristics in two-dimensional free jet;and the development and evolution characteristics for the vortex ring structure in two-dimensional synthetic jet at three different Strouhal numbers.By analyzing the forming process and flow characteristics of the vortex ring structure in the free jet and synthetic jet,it will contribute to the following research on the JICF.(2)The flow characteristics of JICF at low Reynolds number will be analyzed,including the evolution of the vortex rings for two-dimensional JICF at various velocity ratios.The development of three-dimensional large scale vortex structure especially the ring-like vortices(RLV)are studied,and the forming mechanism of counter-rotating vortex pair(CRVP)are also analyzed.Finally,vorticity section,vorticity contours,the interaction among the different vortices and the velocity streamlines are expounded in detail.The mechanism of the JICF is elaborated systematically and comprehensively in this chapter.(3)Based on the analysis of the classical JICF,the research on the synthetic JICF is performed respectively at different velocity ratios.The flow characteristics between the classical JICF and synthetic JICF are also compared,including the penetration,three-dimensional vortex structure,vorticity section,streamlines in the near field and temperature profile.A new vortex named "vortex tail" has been found in the JICF at higher velocity ratio due to the enhanced interactions indicated by the increased jet momentum among the CRVP,upright vortices and shear layers.(4)The classical and synthetic JICF at low Reynolds number with and without block are performed for various velocity ratios,and the corresponding vortex characteristics have been compared.The effect of the block on the penetration for the claissical and synthetic JICF is analyzed respectively.The results in the classical JICF have revealed that the block will weaken the CRVP and RLV,and according to the contrast of the vorticity section,the effect of the block on mixed positive and negative vortices is depicted.The block will also destroy the RLV and the “vortex tail” in the synthetic JICF,and the corresponding flow characteristics of the vortices is described in detail.