CFD assessment of orifice aspect ratio and mass flow ratio on jet mixing in rectangular ducts

Abstract

Isothermal CFD analysis was performed on axially opposed rows of jets mixing with crossflow in a rectangular duct. Laterally, the jets' centerlines were aligned with each other on the top and boltom walls. The focus of this study was to characterize the effects of orifice aspect ratio and jet-to-mainstream mass flow ratio on jet penetration and mixing. Orifice aspect ratios (LIW) of 4-to-l, 2-to-l, and l-to-l , along with circular holes, were parametrically analyzed. Likewise, jet-to-mainstream mass flow ratios (MR) of 2.0, 0.5, and 0.25 were systematically investigated. The jet-tomainstream momentum-flux ratio (1) was maintained at 36 for all cases, and the orifice spacing-to-duct height (StH) was varied until optimum mixing was attained for each configuration.The numerical results showed that orifice aspect ratio (and likewise orifice blockage) had little effect on jet penetration and mixing.

Mixing of multiple jets with a confined subsonic crossflow

“…Generally, increasing the ratio of the long to short dimension of low aspect ratio aligned slots has little effect on jet penetration. This is seen in Figures 7 and 8 from the computational results reported by Bain et al (1994). The planes shown in Figure 7 are vertical-axial ones through the orifice centers, with the corresponding vertical-transverse planes at x/H = 0.5 shown in Figure 8.…”

“…Bain et al, 1994) when extended to typical RQL conditions of MR > 2 and S/d < 2. However at those conditions the proportionality constant C has been found, both experimentally and computationally (Bain et al, 1993(Bain et al, & 1994 to be -2.5…”

“…A J of 36 was chosen, and the mass-flow ratio (MR) and orifice spacing (S/H) were maintained constant at MR = 2 and S/H = 0.425 for all, while the orifice blockages (B) varied substantially. The configurations examined were based on a numerical study by Bain et al (1994), in which orifice aspect ratio and shape were found to have little effect on the mixing performance of in-line configurations when a value of 2.55…”

Flow Coupling Effects in Jet-in-Crossflow Flowfields

“…3 The optimization of this type of mixing process has received a lot of study. [4][5][6][7][8][9][10][11][12][13][14][15][16] CFD analysis is typically used to help design the orifice pattern for effective mixing. To conserve computer resources, CFD analysis is usually performed on the interior of the combustor; the inlet boundary conditions for the air jets are specified by the designer.…”

Flow coupling effects in jet-in-crossflow flowfields

“…3 The optimization of this type of mixing process has received a lot of study. [4][5][6][7][8][9][10][11][12][13][14][15][16] CFD analysis is typically used to help design the orifice pattern for effective mixing. To conserve computer resources, CFD analysis is usually performed on the interior of the combustor; the inlet boundary conditions for the air jets are specified by the designer.…”