LES and DES for complex geometries

SNIC 2019/3-79


SNIC Medium Compute

Principal Investigator:

Lars Davidson


Chalmers tekniska högskola

Start Date:


End Date:


Primary Classification:

20306: Fluid Mechanics and Acoustics



Compressible CFD. High-fidelity CFD methods are used for the simulation of compressible flows in engineering turbomachinery applications with the aim to gain a better understanding of the underlying physical principles and to push the limits for industrial use of CFD. All simulations are done using the Chalmers-developed CFD code G3D::Flow, which has been used extensively on SNIC resources in the past and shown very good scaling properties. The flow simulation methodologies applied in the project are based on (Unsteady) Reynolds-Averaged Navier-Stokes ((U)RANS), Large Eddy Simulation (LES) and Delayed Detached Eddy Simulation (DDES). In order to accelerate URANS simulations of turbo machinery flows, a time-spectral approach known as the Harmonic Balance method has been implemented in G3D::Flow. Despite the use of Harmonic Balance, large-scale turbomachinery simulations require in the order of 65 000 core hours for one single design and operating condition. DDES and LES, where Harmonic Balance may not be applied, typically require substantially larger resources. The computational effort needed varies between the different research projects, but all activities are in the large-scale simulation range, which stems from the use of computational grids with sizes in the order of 100 million cells or, depending on method, problems with roughly 700-2500 million degrees of freedom. Access to large-scale computational resources is needed in order to be able to realize the investigations signed up for in ongoing and planned research activities. Some examples of projects: * Robust optimization methods for transonic blade design (ROKS) - Vinnova (NFFP6) * Integrated Duct Aerodynamics (IDA) - H2020 Clean Sky 2 * Ultra-low Emission Technology Innovations for Mid-century Aircraft Turbine Engines (ULTIMATE) - H2020 * Validation of improved turbomachinery noise prediction models and development of novel design methods for fan stages with reduced broadband noise (TurboNoiseBB) - H2020 * Heat load distribution In hot parts of industrial Gas turbines burning HYDROGEN rich fuel (HIGH2) - Energimyndigheten The PhD project "Industrialization of CFD methods for improved predictions of complex aeronautical flows (CIAO)" is financed by NFFP/Vinnova. To meet requirements on more cost effective aeronautical products with enhanced capabilities and a reduced environmental footprint, improved flow simulation techniques are needed. With improved flow simulation techniques accurate predictions of complex unsteady fluid flows, such as separated flows which e.g. can generate noise, leading to engine disturbances and structural fatigue, can be made. Hybrid RANS (Reynolds-Average Navier-Stokes)-LES (Large-Eddy Simulation) techniques are considered to be sufficiently accurate and computationally affordable for the aeronautical industry and will be explored and developed for industrial needs in this project. Industrially adapted hybrid RANS-LES modelling (HRLM) techniques thus have the potential to improve product quality, give a more efficient design process with shorter time-to-market for new products and products with a reduced environmental impact. Moreover, HRLM techniques have a great potential to complement or replace wind tunnel and flight tests. There are however improvements needed to adapt these methods for general industrial geometries and flow conditions before being considered as the new state-of-art industrial design tool. The project focuses on the development of RANS-LES interface methodologies, numerical methods adapted for hybrid RANS-LES models in an industrial environment and methods for generating synthetic turbulence in the RANS-LES interface region to give a rapid and accurate transition from RANS to LES. The outcome of the project will be scientific publications as well as establishing a new industrial standard and best practice for turbulence modelling. The FOI code EDGE will be used. In the EU project ULTIMATE we will use the C3SE resource for different research topics: * High-fidelity aeroacoustic simulations of novel counter-rotating propeller designs. * Validation and verification of state-of-the-art aeroacoustic models and methods for predicting tonal, and broadband, noise in turbomachinery. * Research on NOx emissions arising from pulsed detonation combustion using reduced chemistry models for Jet-A—air mixtures. * Investigating the aerodynamic performance of axial turbomachinery, operating under intermittent combustion.  The flow field variation is predicted using URANS models, and detailed chemistry mechanisms are employed to predict the performance and post-combustion properties of pulsed detonation combustion, operating with different fuel-air mixtures.