Numerical Study of Mixing Flow Regimes Generated by Different Coaxial Jet Geometries

Document Type : Original Article

Authors

1 Corresponding author, Department of Mechanical Power Engineering, Faculty of Engineering at El-Mattaria, Helwan University, Masaken El-Helmia P.O., Cairo 11718, Egypt.

2 Department of Mechanical Power Engineering, Faculty of Engineering at El-Mattaria, Helwan University, Masaken El-Helmia P.O., Cairo 11718, Egypt.

Abstract

A computational investigation of turbulent mixing of free two air-air coaxial jets with equal densities, annular to core area ratio of 3.5 and velocity ratio of 0.5 is carried out. The flow field is considered incompressible, steady, asymmetric and turbulent. The inner and outer Reynolds numbers, based on mass averaged velocity and equivalent diameters are 8 × 104 and 7.5 × 104. Mixing flow characteristics of two different non-circular coaxial jets are obtained and compared with traditional circular coaxial jet within a relatively short length of X/Di =30. Shape and thickness of the separating wall depend on the geometry of the two coaxial jet; to maintain the AR equal to 3.5. Mixing of free jets is effective in generating the turbulence that improves the combustion and premixed flame burners performance. The simulation is performed using a finite volume scheme and a two-equation (KــــƐ) turbulence model. Results show that velocity decay along the centerline for non-circular coaxial jet is lower than that of circular coaxial jet. Also, inner potential core of non-circular cases is greater than that of circular one. In addition, the reattachment point in case of non-circular coaxial jet is reached after that of circular coaxial jet.

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