One of the greatest challenges in computational fluid dynamics (CFD) is the correct representation of turbulent and transitional flows (Link Turbulence & Transition). With sufficient computational resources they can be computed using scale-resolving methods such as direct numerical simulation (DNS) or large eddy simulation (LES). These methods resolve the relevant turbulent scales to correctly predict the mean flow field and statistical correlations and require little to no modelling assumptions. Such scale resolving simulations (SRS) can be considered as a kind of numerical test rig. They can be used, on the one hand, to gain very detailed insight into complex turbulent flows, especially highly separated flows which primarily occur at off-design operating conditions of aero engines. On the other hand, high fidelity data can be used to validate and refine statistical turbulence models used in the day-by-day design process of turbomachinery components.
The strategic goal is to qualify TRACE to serve as a numerical test rig for turbomachinery components at design and off-design or even unusual operating conditions (e.g. compressor surge, wind milling, high-altitude relight, blade-off, bird-strike) by extending its capabilities with respect to SRS. This is a crucial step towards the virtual engine. While the experience in solver development is based at the Institute of Propulsion Technology, the new Institute of Test and Simulation for Gas Turbines will supply computational resources and integration of these simulations within the concept of the digital twin.
An extreme variety of models and methods for SRS exists in the CFD community at universities all over the world. However, not only due to limited computational resources have these methods not yet been routinely applied in an industrial environment. At the interface between fundamental research and the aerospace industry, it is DLR’s responsibility to develop practical and usable solutions. These require research concerning boundary conditions, discretization methods, transitional flows, mesh generation and online as well as post-processing methods, and high-performance computing.
Both TRACE’s structured finite volume and unstructured discontinuous Galerkin solvers have been validated and compared in a series of large eddy simulations for reference cases. Recently, a first simulation of a low-pressure turbine blade has been conducted.