Numerical Simulation of Confined Multiple Transverse Jets

Abstract

Behavior of unconfined transverse jets has been studied extensively, but little work is reported on the flow characteristics of confined transverse jets. The latter has been numerically investigated using a number of RANS codes. The computational results obtained from these codes have been evaluated against the existing experimental data, and the results of a Large-Eddy Simulations (LES) code reported in the literature. Furthermore, an extensive validation effort has been conducted to characterize the performance of the codes for predicting the flow within a propulsion-related mixing configuration. The validation case involves eight circumferentially spaced transverse jets issuing radially into an axisymmetric main flow, a configuration relevant for gas turbine burners and new liquid rocket engine preburners. The main flow Reynolds number was 1.7 x 10 5 and the jet-to-main flow momentum flux ratio was sixteen. The momentum and scalar mixing was investigated through the solution of the Reynolds-Averaged Navier Stokes (RANS) equations. The solutions of three commercial RANS solvers, Fluent, STAR-CCM+, and CFD++, are compared to experimental data and large-eddy simulation (LES) results available in literature. Due to demonstrated periodicity, only a one-eighth pie-shaped section of the geometry was considered. The different commercial codes used the same geometry, grid, boundary conditions, and variations of the k-ϵ turbulence model. The LES results obtained from literature used a different grid, but the same geometry. All numerical simulations using the above mentioned codes capture salient flow structures such as the counter-rotating vortex pair (CRVP). Experimental data used for validation of the codes include mean axial velocity and jet fluid mixture fraction profiles (at three distinct axial locations), jet trajectory, turbulent kinetic energy distributions, and velocity and mixture fraction cross-plane distributions. All CFD results except CFD++, exhibit symmetrical solutions about the center plane. The current investigation shows that although all codes considered predict the experimental data with various degrees of accuracy, Fluent using the standard k-ϵ turbulence model with the standard wall function, and LES results compare exceptionally well with the experimental data for this flow regime and configuration. NomenclatureA, b, c = empirical constants C = local mean mass fraction of the jet C = average mass fraction of the jet over the cross sectional area A D = diameter J = momentum flux ratio m  = mass flow rate n = number of jets Q = volume flow rate r = velocity ratio x = streamwise coordinate y = cross stream coordinate j = subscript for jet flow Us = Unmixedness

Numerical and Experimental Investigation of Confined Turbulent Multiple Transverse Jets

“…A recent study summarized by Davoudzadeh et al explored the CFD validation to an existing eight jet configuration documented in the literature 1 . The current validation effort builds upon this previous study through the consideration of fewer jets and different measurement locations.…”