DNS of a Spatially Developing Turbulent Mixing Layer from Co-flowing Laminar Boundary Layers

Abstract

Understanding the development of a turbulent mixing layer is essential for various aerospace applications. In particular, experiments found that the flow development is highly sensitive to inflow conditions, which are difficult to reproduce in the flow simulations. In previous direct numerical simulations (DNS) of temporarily and spatially developing turbulent mixing layers, idealized inflow conditions based on mathematical approximations of the mean velocity profile were used to facilitate turbulent flow conditions. The current paper presents results of DNS of a spatially developing turbulent mixing layer, where coflowing laminar boundary layers over a splitter plate are used as inflow conditions; no artificial perturbations are seeded into the flow. The goal is to closer replicate a naturally developing mixing layer. The flow conditions used in simulations closely match those in experiments by Bell & Mehta (1990). DNS were conducted using the spectral-element code Nek5000. Effects of the splitter plate thickness and the computational domain size in the spanwise direction on the flow development are analyzed. Profiles of the mean flow velocity and the Reynolds stresses are compared with the experimental data.

Analysis of uncertainty sources in DNS of a turbulent mixing layer using Nek5000

“…Understanding uncertainty in DNS results will add a value to the dataset. The current paper continues our previous effort [14] in this direction.…”

“…In particular, studies of a spatially developing two-dimensional mixing layer [15] and a temporarily evolving three-dimensional mixing layer [16] showed that the nature and magnitude of flow perturbations imposed at the inflow strongly affect the flow development and turbulence statistics. When co-flowing boundary layers separated by a splitter plate are used as inflow conditions in simulations of a spatially developing mixing layer, the plate thickness at the trailing edge and the T trailing edge shape have a significant effect on the flow features and turbulence intensity [14,17]. Results of DNS were also found to be sensitive to the spanwise size of the computational domain [14].…”

“…When co-flowing boundary layers separated by a splitter plate are used as inflow conditions in simulations of a spatially developing mixing layer, the plate thickness at the trailing edge and the T trailing edge shape have a significant effect on the flow features and turbulence intensity [14,17]. Results of DNS were also found to be sensitive to the spanwise size of the computational domain [14]. Overall, due to the simulation cost, there is only a limited number of studies on the uncertainty analysis in DNS of a mixing layer and particularly, of a spatially developing mixing layer.…”

“…The choice of parameters was driven by a search for their optimal combination for conducting cost-effective accurate DNS in a domain long enough to achieve a self-similar regime in a turbulent mixing layer. The initial domain used in [14] was found to be short in the streamwise direction for this purpose.…”

“…Two grids were used in the simulations: one from [14] and the other with higher resolution of the wake behind the splitter plate and the mixing layer area. Possible effects of the grid resolution on the simulation results are discussed in the paper, but their detailed analysis was not among the objectives of the current study.…”