Applications of Nektar++ II

Application and Verification of the Implicit Sliding Mesh Solver in Nektar++ for 3D SimulationsThis presentation outlines recent progress in applying the implicit sliding mesh solver within the Nektar++ framework to simulate unsteady stator–rotor interactions in turbomachinery. A translating mesh around a cylinder is used to generate the inflow wake and simulate wake–blade interactions on a 3D T106A low-pressure turbine blade. This setup demonstrates the capability of the solver for high-fidelity 3D simulations involving translating meshes and complex geometries.In parallel, we are validating the performance of the solver on 3D rotating meshes using Taylor–Couette flow benchmarks, considering both full-annulus and sector-domain configurations. These verification cases assess the accuracy, stability, and convergence behaviour of the solver under rotational motion. Together, these efforts lay the groundwork for future simulations of more realistic turbomachinery configurations.Development and applications of the NESO frameworkUKAEA is using Nektar++ as the fluid component of its NESO framework: a collection of software intended to model the edge plasma in a tokamak. This problem is being approached using a number of different methods ranging in fidelity and computational expense. Nektar++ has been coupled to the NESO-Particles library - this has been further extended with coupling to our atomic reactions library. The resulting code, NESO-Tokamak, will solve the Braginskii fluid equations for multiple ionic species, with source terms provided by the reactions. Axisymmetric 2D and 3D steady-state and transient transport solutions have been produced, and turbulent solutions are being worked on. The core component is a Nektar++ unsteady solver, which has been extended with several features. Another component of NESO is the meshing software NESO-fame, which produces non-conformal meshes aligned with the magnetic field in order to account for the high anisotropy of the equations.Simple generation of inflow turbulent boundary layers for iLES using Nektar++We propose a novel and simple way to generate inflow turbulent boundary layers (TBLs) that needs only a random forcing feature available from the solver and an extra (channel-like) part to be added to the domain of interest. As it does not rely on any specific physical modeling, it is more in line with implicit LES approaches, although it can also be used in a classic LES setting. The idea is basically to add a spatially developing turbulent channel flow (sustained by random forcing) to the domain so that its outlet is attached to the inlet of the domain of interest. The final trick is to set an outflow boundary condition at the upper half of the channel flow's outlet, so that only its lower part is released into the domain of interest as an inflow TBL. We note this is a type of precursor inlet TBL method, but one in which the precursor (channel) domain is carried alongside the domain of interest in a single unified simulation throughout the whole time of the computation. Although not necessarily computationally cheaper or more accurate than existing inflow TBL methods, the advocated approach has several benefits: it is extremely simple, requiring no specific TBL modeling and only minor (if any) adaptation to the solver of choice; it allows one to specify both the Reynolds number and TBL height at inflow; it does not suffer from problems that some inflow TBL methods have, such as the need for large stored databases and the artificial repetition of turbulent structures after a certain period. The methodology is demonstrated for incompressible flows in a spectral/hp continuous Galerkin (CG) implicit LES setting, but its extension to compressible flows is also discussed.