Changes to the vortical and turbulent structure of jet flows due to mechanical tabs

Abstract

The effect of mechanical tabs on the vortical and turbulent structures in the near fields of jet mixing flows is investigated in the present paper. In order to compare the changes of the vortical and turbulent structures of jet flows with and without mechanical tabs, flow visualization and instantaneous quantitative concentration field measurements were conducted in a water channel by using a laser induced fluorescence (LIF ) technique. The flow visualization confirmed the existence of a pair of counter-rotating streamwise vortices produced by each mechanical tab in a jet flow. The generated streamwise vortices can cause an inward indentation of ambient flow into the core jet flow and an outward ejection of core jet flow into the ambient flow. It also showed that the process of Kelvin-Helmholtz vortex pairing was accelerated, the small-scale vortical structure appeared earlier and a large-scale helical coherent structure was found in the near fields of tabbed jet flows. Based on the flow visualization and instantaneous quantitative concentration field measurements, two aspects of the effect of the streamwise vortical pairs induced by mechanical tabs on the jet mixing flows were suggested.speeds and high temperatures. Ahuja [3] reported that, C06297

Jet impingement heat transfer – Part II: A temporal investigation of heat transfer and local fluid velocities

“…As the vortices move downstream of the jet nozzle each vortex can be wrapped and develop into a three dimensional structure due to secondary instabilities. These secondary instabilities can lead to the ''cut and connect" process as described by Hui et al [1] and Hussain [2] in which the toroidal vortices break down into smaller scale motions, generating high turbulence. Vortices, depending on their size and strength, affect the jet spread, the potential core length and the entrainment of ambient fluid.…”

“…Hui et al [1] and Gao et al [4] installed mechanical tabs at the nozzle exit to instigate streamwise vortical structures. These have the effect of increasing the secondary instabilities in the jet and therefore hasten the ''cut and connect" process that breaks the vortices down into small scale turbulence.…”

Analysis of a turbulent jet mixing flow by using a PIV-PLIF combined system

“…is the detected fluorescence intensity at the measurement point (Hu et al 1999). In order to minimize the attenuation effect, a low fluorescent-dye-concentration solution ( From the equation (1), it can be seen that the intensity of induced fluorescent light detected by the image recording camera will be changed linearly with the concentration of the fluorescent dye for the constant properties of carrier flow (temperature, oxygen content, pH value etc.)…”

Large Eddy Simulation of Compressible Parallel Jet Flow and Comparison of Four Subgrid-Scale Models

“…These include the early experiments of Bradbury (1965) in which the establishment of the self-preservation in downstream of the nozzle exit is studied, and the measurement of correlations by Everitt et al (1978) which unveiled the no-similarity of large-scale statistical structures as a kind of 'local flapping' in a moving stream. Modern flow visualization techniques such as the laser induced fluorescence (LIF) and particle image velocimetry (PIV) have also been applied to study the flow details in jets by Hui et al (1999) and Tinney and Jordan (2008), respectively. The developments of the turbulent structures have been well described.…”