Numerical Investigations on Dynamics and Heat Transfer in a Turbulent Underexpanded Jet

A fully elliptic Navier-Stokes equation solver in conjunction with a Reynolds stress model is validated for mildly and strongly underexpanded jets. For mildly underexpanded jets, good agreement has been found compared to available measurements for the shock reflections. The model even demonstrated some improvements over a three-dimensional modified kappa-epsilon model for turbulent predictions, which confirms the inadequacy of isotropic eddyviscosity-based models to represent properly the turbulence in those flows. For the strongly underexpanded case, the predicted Mach disk location and size are found to be in excellent agreement compared to available measurements. In addition, the predicted flow structure beyond the disk agrees with experimental observations. An attempt is also made to explain the strong coupling between some dynamic features and heat transfer aspects. The sonic line location is revealed to be an important parameter in understanding the global dynamics/heat transfer coupling. In addition, it is demonstrated that a fraction of heat dissipation may be given back to the flow and boost its temperature, which may be useful for spraying applications.