Tommaso Murolo

(Advisor: Prof. J.C. Oefelein)

will propose a master’s thesis entitled,

Turbulence Backscatter Modeling for Large Eddy Simulations

On

Monday, July 18 at 12:00
Montgomery Knight Building 317
 

Abstract

Since Direct Numerical Simulation (DNS) is unfeasably expensive for most engineering conditions of interest due to high Reynolds numbers, Large Eddy Simulation (LES) is of great use to limit the computational cost of a high fidelity simulation. The information contained in the residual scales, which are not resolved, must be modelled to account for the small scale physics which would otherwise be lost. Deterministic closures relate the residual stresses and fluxes to resolved gradients, whereas stochastic modeling allows for small scale fluctuations uncorrelated with those at the large scales.

Among the phenomena that emerge in the filtered system of governing equations is backscatter - the flow of energy from small to large scales of turbulence (or equivalently from residual scales to resolved scales due to interactions between subgrid variance fields in the context of LES). In many applications, this reverse flow is negligible: as per Kolmogorov theory, most inert flows are statistically well described by a purely forward-scatter, i.e. an energy cascade from large to small scales. However, this trend only holds on average: these systems may very well have significant portions of their volume locally undergoing backscatter at any given moment in time. Additionally, and more importantly, backscatter becomes very significant once strong strain rates or flow dilation are introduced, as is the case for reacting flows, where chemical energy is released at the smallest scales and backscatters to the large scales. Hence, it is of great importance that LES closures are able to properly account for this reverse energy flow for physically accurate results.

This work aims at developing a stochastic LES closure that properly captures the physics of backscatter in compressible turbulence, which many commonly employed closures neglect or describe only partially. The closure will be applied in some relevant compressible conditions, and should reveal domains for which backscatter needs sophisticated modeling.

Committee

• Prof. Joseph C. Oefelein – School of Aerospace Engineering (advisor)
• Prof. Suresh Menon – School of Aerospace Engineering
• Prof. Adam Steinberg – School of Mechanical Engineering