## Numerical modeling of separated flows at moderate Reynolds numbers appropriate for turbine blades and unmanned aero vehicles

G. Castiglioni, J.A. Domaradzki, V. Pasquariello, S. Hickel, M. Grilli (2014)*International Journal of Heat and Fluid Flow* 49: 92-99. doi: 10.1016/j.ijheatfluidflow.2014.02.003

Flows over airfoils and blades in rotating machinery, for unmanned and micro-aerial vehicles, wind turbines, and propellers consist of a laminar boundary layer near the leading edge that is often followed by a laminar separation bubble and transition to turbulence further downstream. Typical RANS turbulence models are inadequate for such flows. Direct numerical simulation (DNS) is the most reliable, but is also the most computationally expensive alternative. This work assesses the capability of Immersed Boundary (IB) methods and Large Eddy Simulations (LES) to reduce the computational requirements for such flows and still provide high quality results.

## Large-eddy simulation of supersonic turbulent boundary layer over a compression-expansion ramp

M. Grilli, S. Hickel, N.A. Adams (2013)*International Journal of Heat and Fluid Flow *42: 79-93. doi: 10.1016/j.ijheatfluidflow.2012.12.006

Results of a large-eddy simulation (LES) of a supersonic turbulent boundary layer flow along a compression–expansion ramp configuration are presented. The numerical simulation is directly compared with an available experiment at the same flow conditions. The compression–expansion ramp has a deflection angle of *β* = 25°, the free-stream Mach number is *Ma*_{∞} = 2.88, and the Reynolds number based on the incoming boundary layer thickness is *Re _{δ}* = 132 840.

## Wall-modelled Implicit Large-Eddy Simulation of the RA16SC1 Highlift Configuration

M. Meyer, S. Hickel, C. Breitsamter, N.A. Adams (2013)*AIAA paper* 2013-3037. doi: 10.2514/6.2013-3037

Industrially applied Computational Fluid Dynamics still faces a challenge when it comes to the accurate prediction of the complex flow over realistic highlift configurations. In this paper we demonstrate that the flow over the 3-element RA16SC1 highlift configuration can be efficiently and accurately predicted with Implicit Large-Eddy Simulation (ILES) on Cartesian adaptive grids.

## Experimental and numerical investigation on shockwave / turbulent boundary layer interaction

M. Grilli, L.S. Chen, S. Hickel, N.A. Adams, S. Willems, A. Gülhan (2012) *AIAA paper* 2012-2701. doi: 10.2514/6.2012-2701

We report on an experimental and computational effort to study the interaction of a compressible turbulent boundary layer with an oblique shock wave. A wide range of shock intensities has been considered in the experiments through a variation of the free-stream Mach number.

## A parametrized non-equilibrium wall-model for large-eddy simulations

S. Hickel, E. Touber, J. Bodart, J. Larsson (2012)

Proceedings of the 2012 Summer Program, Center for Turbulence Research, Stanford University.

Wall-models are essential for enabling large-eddy simulations of realistic problems at high Reynolds numbers. The present study is focused on approaches that directly model the wall shear stress, specifically on filling the gap between models based on wall-normal ordinary differential equations (ODEs) that assume equilibrium and models based on full partial differential equations that do not. We develop ideas for how to incorporate non-equilibrium effects (most importantly, strong pressure-gradient effects) in the wall- model while still solving only wall-normal ODEs.

## Analysis of unsteady behavior in shockwave turbulent boundary layer interaction

M. Grilli, P.J. Schmidt, S. Hickel, N.A. Adams (2012)*Journal of Fluid Mechanics* 700: 16-28. doi: 10.1017/jfm.2012.37

The unsteady behaviour in shockwave turbulent boundary layer interaction is investigated by analysing results from a large eddy simulation of a supersonic turbulent boundary layer over a compression–expansion ramp. The flow dynamics are analysed by a dynamic mode decomposition which shows the presence of a low-frequency mode associated with the pulsation of the separation bubble and accompanied by a forward–backward motion of the shock.

## Large Eddy Simulation of turbulence enhancement due to forced shock motion in shock boundary layer interaction

O.C. Petrache, S. Hickel, N.A. Adams (2011) *AIAA paper* 2011-2216. doi: 10.2514/6.2011-2216

We present Implicit Large-Eddy Simulations of a shockwave-turbulent boundary layer interaction with and without localized heat addition. For an entropy spot generated ahead of the shock, baroclinic vorticity production occurs when the resulting density peak passes the shock.

## Wall modeling for implicit large-eddy simulation and immersed-interface methods

Z.L. Chen, S. Hickel, A. Devesa, J. Berland, N.A. Adams (2013) *Theoretical and Computational Fluid Dynamics *28: 1-21. doi: 10.1007/s00162-012-0286-6

We propose and analyze a wall model based on the turbulent boundary layer equations (TBLE) for implicit large-eddy simulation (LES) of high Reynolds number wall-bounded flows in conjunction with a conservative immersed-interface method for mapping complex boundaries onto Cartesian meshes. Both implicit subgrid-scale model and immersed-interface treatment of boundaries offer high computational efficiency for complex flow configurations.

## Implicit LES applied to zero-pressure-gradient and adverse-pressure-gradient boundary-layer turbulence

S. Hickel, N.A. Adams (2008)*International Journal of Heat and Fluid Flow* 29: 626-639. doi: 10.1016/j.ijheatfluidflow.2008.03.008

Well resolved large-eddy simulations (LES) of a fully turbulent flat-plate boundary-layer flow subjected to a constant adverse pressure gradient are conducted. Flow parameters are adapted to an available experiment. The Reynolds number based on the local free-stream velocity and momentum thickness is 670 at the inflow and 5100 at the separation point. Clauser’s pressure-gradient parameter increases monotonically from 0 up to approximately 100 since a constant pressure gradient is prescribed. The adverse pressure gradient leads to a highly unsteady and massive separation of the boundary layer. The numerical predictions agree well with theory and experimental data.

## Implicit large-eddy simulation applied to turbulent channel flow with periodic constrictions

S. Hickel, T. Kempe, N.A. Adams (2008)*Theoretical and Computational Fluid Dynamics* 22: 227-242. doi: 10.1007/s00162-007-0069-7

The subgrid-scale (SGS) model in a large-eddy simulation (LES) operates on a range of scales which is marginally resolved by discretization schemes. Accordingly, the discretization scheme and the subgrid-scale model are linked. One can exploit this link by developing discretization methods from subgrid-scale models, or the converse. Approaches where SGS models and numerical discretizations are fully merged are called implicit LES (ILES).