Computing Turbulent Flow Field of Swirl Jet.

Document Type : Research Studies

Author

Mechanical Power Department., College of Engineering Zagazig University., Zagazig., 44519., Egypt.

Abstract

A computing of a turbulent jet subjected to fluidic excitation and it's effect on the jet evolution was conducted. The jet was subjected to vortex generating jets placed at the exit of the main jet nozzle exit to generate Swirl Jet. The main jet had a Ren about 17000, and the VGJ to main jet momentum ratio were 0.055, 0.095, 0.078 and 0.285. The velocity ratio between the VGJs and main jet (CR = Cvgi/Cjet) was varied up to unity. The activation of VGJ was tangential (α=0), (α=45 degree) and (α=90 degree). 
In non-reacting Swirl Jets, the dynamics of the flow field structure were computed using a three-dimensional Navier-Stokes code (CFDRC, 2000). The governing equations are discretized on a structured grid using an upwind difference scheme. The macroscopic behaviour of the jet evolution is discussed with the turbulent pressure and velocities. The transport of jet fluid is compared with the unexcited jet. 
The use of Vortex Generator Jets to enhance the mixing between a turbulent jet and the surrounding fluid is shown to offer improvement and control over the jet evolution. VG)'s enhance the jet spreading angle over unexcited jet. The Swirl Jet with injection angle (α =45) and the higher momentum injection gives maximum higher Turbulent Kinematics Energy than the Baseline Jet by 18.5, 29,4, 38.7 or 122.6% for momentum ratios equal 0.055, 0.078, 0.095 and 0.285 respectively. With Swirl Jet excitation the high stress region located at a cylinder layer of diameter 0.8 of nozzle diameter and moving horizontally in a section from 2 to 3 z/D from upstream according to momentum ratio. These computational data are compared with the experimental results obtained with a four-wire hot-wire velocity probe by the author (Mostafa, 2000). The results show great agreement with the experimental results at different conditions of Swirl Jet flow. 

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