NSF Award
2451358
In general, complex flows - those observed in supersonic-to-hypersonic combustion and propulsion, fusion technologies, and astrophysics - involve multi-material mixing and span a broad range of space and time scales. Fluids participating in such flows have a wide range of molar masses, and in many cases, the flow is highly compressible. It is still a challenge for current engineering tools to predict the key flow physics that arise due to the compressibility and large material property variations. A stronger fundamental understanding of these effects on turbulent flows will significantly increase our ability to model the flow physics accurately, such as the rate of turbulent mixing that occurs in complex multi-material flows, and to perform numerical simulations of such flows with a decreased computational expense. These gained abilities will have a direct impact on the improvement and development of many high-tech products in the space, energy, and defense industries. Therefore, the focus of the proposed study is to quantify the coupled large molar-mass ratio and compressibility effects on the gravitationally driven turbulent flows. The project will also deliver an educational component by generating content for undergraduate- and graduate-level courses. It will also support outreach activities to promote interest in fluid dynamics and turbulence, and more broadly in STEM among local middle-school students.<br/><br/>Multi-material turbulence has so far mostly been studied with quasi-incompressible and Boussinesq flows with small variations in material properties. The proposed project aims to describe flow compressibility effects on Rayleigh-Taylor unstable turbulent mixing with large density variations beyond the Boussinesq approximation and the incompressible assumption. Novel direct numerical simulations of buoyancy-driven flow that resolve all spatial and temporal scales will be performed at large density ratios (>2) with highly compressible fluids using the adaptive mesh refinement to optimally deploy computational resources. Unique statistical tools will be developed to quantify the non-Boussinesq turbulent compressible mixing dynamics. The proposed simulations and statistical analyses will be used to establish a deeper understanding of turbulence transition for non-Boussinesq flows, and in particular, the small-scale flow topology of the compressible active-scalar mixing. In addition, the findings of this research are expected to inform new sub-grid-scale models and strategies to decrease the computational cost of the multi-physics complex fluid-flow simulations and validate the reduced-order models for these complex flows. This project is jointly funded by Fluid Dynamics program and the Established Program to Stimulate Competitive Research (EPSCoR).<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
