Turbulent Scalar Mixing in a Skewed Jet in Crossflow: Experiments and Modeling

Turbulent mixing of an inclined, skewed jet injected into a crossflow is investigated using MRI-based experiments and a high-fidelity LES of the same configuration. The MRI technique provides three-dimensional fields of mean velocity and mean jet concentration. The 30° skew of the jet relative to the crossflow produces a single dominant vortex which introduces spanwise asymmetries to the velocity and concentration fields. The turbulent scalar transport of the skewed jet is investigated in further detail using the LES, which is validated against the experimental measurements. Mixing is found to be highly anisotropic throughout the jet region. Isotropic turbulent diffusivity and viscosity are used to calculate an optimal value of the turbulent Schmidt number, which varies widely over the jet region and lies mostly outside of the typically accepted range 0.7 ≤ S c _t ≤ 0.9. Finally, three common scalar flux models of increasing complexity are evaluated based on their ability to capture the anisotropy and predict the scalar concentration field of the present configuration. The higher order models are shown to better represent the turbulent scalar flux vector, leading to more accurate calculations of the concentration field. While more complex models are better able to capture the turbulent mixing, optimization of model constants is shown to significantly affect the results.