An experimental study on annular impinging jets

• Main Author: Lim, Zhi Yu
• Other Authors: School of Mechanical and Aerospace Engineering
• Format: Final Year Project
• Language: English
• Published: 2016
• Subjects: DRNTU::Engineering::Mechanical engineering::Fluid mechanics
• Online Access: http://hdl.handle.net/10356/67593
• Institution: Nanyang Technological University

Dye flow visualization experiment has been conducted experimentally on an annular jet that is impinging on a flat plate at Reynolds number 1300 and separation distance 4 jet diameters apart. Laser-induced fluorescence experiment has also been conducted at Reynolds number 1300 and 2500 and separation distance of 1, 2 and 4 jet diameters apart. Particle image velocimetry experiment in the same 6 configurations are further conducted to analyse the velocity field, vorticity, vortex under the �2 criterion for vortex-core detection for the time-averaged as well as instantaneous results of 1000 image pairs. Interesting observations of vortices in the jets are found at various configurations. This report seeks to present the observations of the shape and the stability of formed vortices, as well as the possible explanations for these behaviours. Velocity profiles investigated are similar and agree with the circular jet experiments at y/D>2, where the flow is fully developed. It is found that the presence of the flat plate at 1 diameter away from the nozzle delays the formation of vortex-helix in the shear layer. It is postulated that the recirculating bubble imparts regular azimuthal perturbations that might have resulted in the formation of helical vortices along the jet shear layers instead. Under impingement configurations, this may lead to flow dynamics that vary azimuthally about the impingement point. It is also concluded that the boundary layer separation is comparable to a circular jet at a higher Reynolds number. This is in spite of the asymmetric flow behaviour at the nozzle centerline of the annular jet at flat plate distance of 4 diameters away. A significant convergent profile is produced by the jet, which turned turbulent after approximately 1 diameter distance away from the nozzle. Physically larger recirculation bubble is also observed when flat plate is at 1 diameter away as compared to the 2-diameter, 4-diameter and free jet configurations.