Session 1: Overview and Future Directions
Session 1, 14:00 – 14:30
Session 1, 14:25 – 15:00
Session 1, 15:00 – 15:30
Session 2: Application Updates
Session 2, 16:00 – 16:20
The compressible Euler and Navier-Stokes equations in Nektar++ are discretised using explicit discontinuous spectral element methods (DSEMs), namely the discontinuous Galerkin (DG) method and the flux reconstruction (FR) approach. These two schemes have intimate underlying connections and share the benefits and disadvantages that affect the broader class of DSEMs [1,2]. In particular, one of the most efficient form of these schemes relies on the under-integration of the nonlinear terms that are eventually present in the equations being discretised (such as the equations governing compressible flows). This under-integration generates aliasing errors that can trigger numerical instabilities that may eventually lead to the crash of the simulation. Various strategies exist to tackle this issue, such as over- or consistent integration of the nonlinear terms, more stable formulations of the equations, limiters of various kind, artificial viscosity, etc. In this talk, we will present the main aliasing sources arising in DSEM methods and how we can address them using over- or consistent integration, a technique that has been explored mainly in the DG community . We will successively show how this approach can be directly applied to the FR approach and we will emphasise the intimate connections between the two schemes. We also illustrate some relevant results to show the effectiveness of these dealiasing techniques.
After having introduced the underlying numerics of the compressible flow solver, we will show some applications. Specifically, we will present a compressible viscous flow past a hump in high-speed subsonic conditions and the comparison of the associated results with triple-deck and linear/nonlinear PSE strategies.
- G. Mengaldo ‘Discontinuous spectral/hp element methods: development, analysis and applications to compressible flows’ Imperial College London, PhD Thesis, 2015.
- G. Mengaldo, D. De Grazia, D. Moxey, P. Vincent and S Sherwin, ‘On the Connections Between Discontinuous Galerkin and Flux Reconstruction Schemes: Extension to Curvilinear Meshes’. Journal of Scientific Computing, pp. 1–21, 2015.
- G. Mengaldo, D. De Grazia, D. Moxey, P. Vincent and S. Sherwin, ‘Dealiasing techniques for high-order spectral element methods on regular and irregular grids’. Journal of Computational Physics, vol. 299, pp. 56–81, 2015.
Session 2, 16:20 – 16:40
Nekkloud is a web-based interface for running Nektar++ on clusters and clouds. The tool currently supports running Nektar++ computations on PBS/TORQUE-based cluster platforms, on OpenStack private clouds and on the Amazon EC2 public cloud platform. In this talk I’ll provide an overview of Nekkloud and its features and show how its integration with the Templates and Profiles for Scientific Software (TemPSS) tool enables you to easily specify and update the configuration for your Nektar++ computations through a graphical user interface. I’ll also be looking at recent developments with Nekkloud and future plans to extend it. A tutorial on using Nekkloud will also be taking place later in the workshop schedule.
Session 2, 16:40 – 17:00
Session 2, 17:00 – 17:20
Session 2, 17:20 – 17:40
The use of stabilized spectral element methods without turbulence modelling is becoming an ever more common alternative for eddy-resolving simulations of turbulent flows. Applications to different types of flows have consistently demonstrated that implicit LES / under-resolved DNS approaches can produce accurate solutions at competitive costs. However, as no (explicit) subgrid-scale model is employed, results rely entirely on the numerical properties of the scheme of choice. Therefore, understanding the role played by the ‘numerics’ in the context of turbulence simulations is of fundamental importance to sensible usage. In this talk we focus on the continuous and discontinuous Galerkin schemes and discuss their stabilization, robustness and accuracy while also presenting some LES-like results obtained with Nektar++.
Session 2, 17:40 – 18:00
Session 3: Application Updates
Session 3, 9:00 – 9:30
This talk will describe our attempts at using Nektar++ to run embedded implicit LES simulations to gain insights into sub regions of the flow field around a F1 car dominated by vortex behaviour.
Session 3, 9:30 – 10:00
Nektar++ was extended with the ability to perform cosimulations of noise in premixed combustion systems. The different length and time scales in such setups are exploited to divide the simulation amongst a low Mach number reactive LES and an acoustics solver. In the current design, field interpolation, coordination and data exchange between these two is accomplished by an external library. The different time and length scales are accounted for by linear interpolation and the introduction of an intermediate mesh. In conjunction with spatial filtering, this receive mesh allows for the representation of the slim acoustic source term on the coarse acoustics mesh. First results obtained with this approach are presented and the implementations future direction is put up for discussion.
Session 3, 10:00 – 10:30
Session 4: New and upcoming features
Session 4, 11:00 – 11:30
Session 4, 11:30 – 12:00
Using coordinate transformations in Nektar++ incompressible flow solver
Even though Nektar++ allows us to perform simulations in complex geometries, in some situations it is useful to employ a coordinate transformation and solve the equations in the transformed domain. One example of this occurs when the transformation leads to a geometry with an homogeneous direction, since in this case we can use the more efficient Quasi-3D approach, reducing the computational cost of the simulation. In this talk, I will present new methods developed to include general coordinate transformations into the solution of the incompressible Navier-Stokes equations using spectral/hp methods. A few numerical examples will be presented, illustrating the accuracy, flexibility and computational cost of these methods. The examples will be accompanied by a description of how to use this new feature of Nektar++.
Session 4, 12:00 – 12:30
This talk will briefly describe the design and structure of the NekMesh executable for the generation of high-order unstructured meshes for complex geometries and present an overview of the generation techniques implemented in the module.