This project concerns the development of parallel computational methods for solving turbulent fluid flow problems with focus on industrial applications, such as the aerodynamics of a full aircraft at realistic flight conditions, the sound generated by the turbulent flow past the aircraft during landing and takeoff, the blood flow inside a human heart, airflow in urban areas, and geophysical flows with application to ocean based renewable energy. The massive computational cost for resolving all turbulent scales in such problems makes Direct Numerical Simulation of the underlying Navier-Stokes equations impossible. Instead, various approaches based on partial resolution of the flow have been developed, such as Reynolds Averaged Navier-Stokes equations or Large-Eddy simulation (LES). For these methods new questions arise: what is the accuracy of the approximation, how fine scales have to be resolved, and what are the proper boundary conditions? To answer such questions, a number of challenges have to be addressed simultaneously in the fields of fluid mechanics, mathematics, numerical analysis and high performance computing (HPC).
The main focus of the research at the Numerical Methods group at CST/KTH is the development of high performance, parallel, adaptive algorithms for finite element (FEM) modelling of turbulent flows and multiphysics, including fluid-structure interaction and aeroacoustics. The adaptive finite element method G2 has been developed over the past 15 years for time-resolved simulations of turbulent flows and it works as an implicit LES method with a residual based subgrid model that accounts for the unresolved scales. With mesh adaptivity based on "a posteriori" error estimates, efficient parallelization, and the use of unstructured meshes, G2 constitutes a powerful tool in Computational Fluid Dynamics, which can be used to solve time dependent problems efficiently. Within our group, there are a number of projects in various applications areas, where the new adaptive algorithms are being used and developed. These areas include aerodynamics, aeroacoustics, biomedicine, geophysics and fluid-structure interaction (FSI). Since we began utilising SNIC resources, we have obtained significant results in the development of G2.
These include: the implementation of a hybrid MPI+PGAS linear algebra backend, which enhanced the performance of the code for larger core counts as compared to the previous MPI implementation; the successful computation of the flow past a full wing-body airplane configuration in the High Lift Prediction Workshops 2 and 3, with high-impact publications, e.g. in the Encyclopedia of Computational Mechanics, a complex nose landing gear geometry and the flow past a high-lift device, both as contributions to the second NASA/Boeing/DLR workshop on Benchmark problems for Airframe Noise Computations, BANC-II in 2012. These computations were followed-up with more detailed, larger computations on the same geometries at the BANC-III workshop in 2013. In 2013 we started a FET-Open FP7 project on the simulation of the human voice based on our framework, simulation of the blood flow inside the human heart in collaboration with clinicians, and floating wind turbines in a multiphase setting.