Simulations of an Underexpanded Round Jet using the Lattice-Boltzmann Method

In order to minimize the acoustic and infrared signatures of aircraft engines as well as tackling vibrational challenges induced by their close-coupled integration on the airframe, a deep understanding of the jet development in the near field is required. The ability to accurately simulate the jet physics at an affordable cost early in the design process is instrumental to achieving this objective. In this paper, the Lattice-Boltzmann Method is used to simulate an underexpanded jet exiting from a round convergent nozzle at a nozzle pressure ratio 2.4. Results are compared to experimental measurements from the open literature. A mesh resolution study is first conducted to weigh cost accuracy trade-off. Simulations are compared to experiment demonstrating the Lattice-Boltzmann Method approaches ability to properly capture the shock-cells location and the shear-layer development. The influence of taking into account both the nozzle inlet boundary layer and the incoming turbulence level on the jet development is then assessed. The results show an improvement of the shock-cell positioning by introducing some upstream turbulence, for a negligible rise of the computational cost.