## Verification and Validation of Immersed Boundary Solvers for Hypersonic Flows with Gas-Surface Interaction

Baskaya, A.O., Capriati, M., Ninni, D., Bonelli, F., Pascazio, G., Turchi, A., Magin T., Hickel, S. (2022)

AIAA Aviation Forum, Chicaco. AIAA paper 2022-3276. doi: 10.2514/6.2022-3276

Verification and validation results of two immersed boundary solvers, INCA and CHESS, for atmospheric entry flows characterized by complex fluid thermochemistry and gas-surface interactions (GSI) are presented. Results are compared with those obtained with the body-conforming solver US3D, which is coupled to the same external thermochemistry library, Mutation++, as INCA and CHESS. In these campaigns, the INCA solver has shown an almost perfect agreement with the body-conforming reference solver and other reference results from literature.

## Adaptive reduced-order modeling for non-linear fluid-structure interaction

Thari, A., Pasquariello, V., Aage, N., Hickel, S. (2021) *Computers and Fluids* 229: 105099. doi: 10.1016/j.compfluid.2021.105099

We present an adaptive reduced-order model for the efficient time-resolved simulation of fluid–structure interaction problems with complex and non-linear deformations. The model is based on repeated linearizations of the structural balance equations. Upon each linearization step, the number of unknowns is strongly decreased by using modal reduction, which leads to a substantial gain in computational efficiency.

## Large-eddy simulation of turbulent, cavitating flow inside a 9-hole Diesel injector including needle movement

Örley, F., Hickel, S., Schmidt, S.J., Adams, N.A. (2017)*International Journal of Engine Research* 18:195-211. doi: 10.1177/1468087416643901

We investigate the turbulent multiphase flow inside a nine-hole common rail Diesel injector during a full injection cycle of ISO 4113 diesel fuel into air by implicit large-eddy simulation (LES). The simulation includes a prescribed needle movement obtained from a one-dimensional multi-domain simulation.

## A cut-cell finite volume-finite element coupling approach for fluid-structure interaction in compressible flow

Pasquariello, V., Hammerl, G., Örley, F., Hickel, S., Danowski, C., Popp, A., Wall, W.A., Adams, N.A. (2016) *Journal of Computational Physics* 307: 670-695. doi: 10.1016/j.jcp.2015.12.013

We present a loosely coupled approach for the solution of fluid–structure interaction problems between a compressible flow and a deformable structure. The method is based on staggered Dirichlet–Neumann partitioning. The interface motion in the Eulerian frame is accounted for by a conservative cut-cell Immersed Boundary method. The present approach enables sub-cell resolution by considering individual cut-elements within a single fluid cell, which guarantees an accurate representation of the time-varying solid interface.

## Cut-element based immersed boundary method for moving geometries in compressible liquid flows with cavitation

Örley, F., Pasquariello, V., Hickel, S., Adams, N.A. (2015) *Journal of Computational Physics* 283: 1-22. doi: 10.1016/j.jcp.2014.11.028

The conservative immersed interface method for representing complex immersed solid boundaries or phase interfaces on Cartesian grids is improved and extended to allow for the simulation of weakly compressible fluid flows through moving geometries. We demonstrate that an approximation of moving interfaces by a level-set field results in unphysical oscillations in the vicinity of sharp corners when dealing with weakly compressible fluids such as water. By introducing an exact reconstruction of the cut-cell properties directly based on a surface triangulation of the immersed boundary, we are able to recover the correct flow evolution free of numerical artifacts.

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

Meyer, M., Hickel, S., Breitsamter, C., Adams, N.A. (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.

## An innovative approach to thermo-fluid-structure interaction based on an immersed interface method and a monolithic thermo-structure interaction algorithm

Grilli, M., Hickel, S., Adams, N.A., Hammerl, G., Danowski, C., Wall, W.A. (2012) * *

*AIAA paper*2012-3267. doi: 10.2514/6.2012-3267

We present a loosely-coupled approach for the solution of the thermo-fluid-structure interaction problem, based on Dirichlet-Neumann partitioning. A cartesian grid finite volume scheme, with conservative interface method is used for the fluid and a finite-element scheme for the thermo-structure problem. Special attention is given to the transfer of forces, temperatures and to the structural positions.

## Numerical modelling and investigation of symmetric and asymmetric cavitation bubble dynamics

Lauer, E., Hu, X.Y., Hickel, S., Adams, N.A. (2012) *Computers and Fluids* 69: 1-19. doi: 10.1016/j.compfluid.2012.07.020

In this paper, we investigate the high-speed dynamics of symmetric and asymmetric cavitation bubble-collapse. For this purpose, a sharp-interface numerical model is employed, that includes a numerically efficient evaporation/condensation model.

## Numerical investigation of collapsing cavity arrays

Lauer, E., Hu, X.Y., Hickel, S., Adams, N.A. (2012) *Physics of Fluids *24: 052104. doi: 10.1063/1.4719142

## Implicit Large Eddy Simulation of cavitation in micro channel flows

Hickel, S., Mihatsch, M., Schmidt S.J. (2011)

In *proceedings of the WIMRC 3rd International Cavitation Forum* ; Warwick, UK.; ISBN 978-0-9570404-1-0. arXiv: 1401.6548

We present a numerical method for Large Eddy Simulations (LES) of compressible two-phase flows. The method is validated for the flow in a micro channel with a step-like restriction. This setup is representative for typical cavitating multi-phase flows in fuel injectors and follows an experimental study of Iben *et al. *(2010).

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

Chen, Z.L., Hickel, S., Devesa, A., Berland, J., Adams, N.A. (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.

## A conservative immersed interface method for large-eddy simulation of incompressible flows

Meyer, M., Devesa, A., Hickel, S., Hu, X.Y., Adams, N.A. (2010) *Journal of Computational Physics* 229: 6300-6317. doi: 10.1016/j.jcp.2010.04.040

We propose a conservative, second-order accurate immersed interface method for representing incompressible fluid flows over complex three dimensional solid obstacles on a staggered Cartesian grid. The method is based on a finite-volume discretization of the incompressible Navier–Stokes equations which is modified locally in cells that are cut by the interface in such a way that accuracy and conservativity are maintained.

## Assessment of implicit large-eddy simulation with a conservative immersed interface method for turbulent cylinder flow

Meyer, M., Hickel, S., Adams, N.A. (2010) *International Journal of Heat and Fluid Flow* 31: 368-377. doi: 10.1016/j.ijheatfluidflow.2010.02.026

The success of Large-Eddy Simulations (LES) of wall-bounded turbulence depends strongly on an accurate representation of the flow near the boundaries. Since in implicit LES the truncation error of the numerical discretization itself functions as SGS model, the order of accuracy of the discretization should be maintained near the boundary. In this paper, we analyze the performance of implicit LES for predicting turbulent flows along complex geometries.

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

Hickel, S., Kempe, T., Adams, N.A. (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).