Advanced nuclear energy holds promise as a reliable, carbon-free energy source capable of meeting our nation's commitments to addressing climate change. A wave of investment in fission and fusion power within the United States and around the world indicates an important maturation of academic research projects into the commercial space. The design, certification, and licensing of novel reactor...
We perform simulations of Rayleigh-Bénard convection (RBC) at Rayleigh numbers ranging from 105 to 1012 and a fixed Prandtl number of 0.7. To simulate the canonical RBC setup with infinite horizontal extents, we employ a Cartesian box of aspect ratio 4 and periodic sides. We use the GPU accelerated spectral element solver, NekRS, on the GPU cluster, JUWELS Booster, at...
Despite very successful complex geometry calculations using Nek over the years, gridding complex geometry cases remains a challenge. I will present some recent complex geometry cases using Nek and discuss possible new methodologies to simplify the gridding process. First, h-p adaptivity can be used to develop a suitable grid, starting from a fairly coarse mesh. However, the dynamic adaptive...
The propagation of internal waves in continuously stratified or rotating fluids differs radically from those of more traditional wave flows. It is worth mentioning that the dispersion relation connects the frequency only with the direction relative to gravity or rotation and does not determine the wavelength. Additionally, wave packets propagate perpendicular to the phase velocity. The...
High-frequency ventilation (HFV) is a medical ventilation technique that uses fast yet shallow inflations, resulting in small peak pressures, thereby protecting lungs from over-distension. While several mechanisms have been proposed for gas transport during HFV, this process is still not well understood, and it is likely the treatment as it stands is sub-optimal. Nonlinear mean streaming and...
Hydrogen and Ammonia-based fuels will play a pivotal role for future carbon-free combustion systems. Direct numerical simulation (DNS) plays a pivotal role in establishing comprehensive understanding of the complex interactions of turbulence and the flame and forms the basis on which novel combustion models can be developed. We will be presenting the current activities on turbulent combustion...
It is well known that Nek5000/RS's spectral element method (SEM) delivers
spectacular convergence in the limit that the solution is well-resolved. Less
understood, however, is the behavior of the SEM for marginally-resolved
solutions that are frequently encountered in practice, particularly in the case
of large-eddy simulations, where the turbulence is inherently under-resolved.
We...
We discuss results of recent Exascale studies with NekRS. Through numerous simulation examples, we illustrate that NekRS sustains 80% parallel efficiency for local problem sizes, n/P, ranging from 3M points per MPI rank on OLCF's Frontier (2 ranks per AMD MI250X) to 5M points per rank on ALCF's NVIDIA A100-based Polaris. On 72,000 ranks of Frontier, NekRS sustains 0.39 TFLOPS per rank or a...
The implementation and performance of non-zonal hybrid Reynolds Averaged Navier-Stokes (RANS)/Large Eddy Simulation (HRLES) approaches in Nek based on the k-tau RANS model will be presented. Results will be compared with direct numerical simulations (DNS) for benchmark cases such as the turbulent flow over the Periodic Hill geometry and the Plane Asymmetric Diffuser. Wall modeling approaches...
The calculation of Lyapunov Exponents by using the perturbation solver in nek5000 will be discussed. This work was started by Anand Jayaraman and Paul Fischer (Jayaraman, et.al., PRE 2006) and has been used over the years to better understand chaos and turbulence in Rayleigh-Benard convection. Leading order Lyapunov exponents were calculated for small systems and moderate Rayleigh number to...
In order to accelerate development of magnetic confinement fusion from experimental tokamaks to power plants, detailed computational multiphysics approaches are being developed to enable predictive modelling and in silico design. A key step towards this goal is identifying a highly scalable computational fluid dynamics code to tackle the large, challenging fluids problems involved. NekRS is...
Hydrodynamics of dolphin swimming has long been an attractive topic, yet few studies have focused on the function of its iconic dorsal fin. Here, we present high fidelity numerical simulations for flow around a 3-D wall-mounted dolphin dorsal fin based on a scanning from a real dolphin. The spectral element method is applied through NEK5000 to ensure high accuracy and efficiency of the...
A comprehensive series of direct numerical simulations (DNS) is performed to investigate the early flame kernel development (EFKD) in a lean premixed H2-air mixture in decaying homogeneous isotropic turbulence and engine-relevant thermodynamic conditions. Systematic variations of turbulent intensity and integral length scale were assessed, resulting in Karlovitz number between 1.9 and 21. The...
The primary objective of this study is to employ a DNS framework to replicate the intricate phenomena of a laboratory-scale soot configuration, specifically the UCAM RQL (Rich-burn Quick-quench Lean-burn) Burner . The moment-based soot model MOMIC was integrated into the high-order CFD code Nek5000 with the development of an in-house plugin, establishing a framework to assess the accuracy and...
To resolve multiphase flow, specifically dispersed phase flow, tracking the dispersed phase's trajectory is crucial. The Euler-Lagrange approach is adopted to predict the interaction between the dispersed phase (microbubble) and the continuous phase (turbulence). The Lagrangian tracking code, ppiclF (parallel particle-in-cell library written in Fortran), and the spectral element method code,...
Hydrogen-based fuel burning faces challenges due to intrinsic premixed flame instabilities that affect flame morphology. This study introduces a three-dimensional (3D) Direct Numerical Simulation (DNS) dataset using a low-Mach formulation and a deficient reactant thermochemical model with NekRS, comparing flame characteristics to a well-established two-dimensional (2D) dataset...
This article applies density-based topology optimization in order to design roughness elements capable of generating stable streaks to damp the growth of Tollmien-Schlichting (TS) waves in a boundary layer. First a steady baseflow is established, then the unsteady linearized Navier-Stokes equations are evolved to assess the spatial growth of the TS waves across the flat plate. The...
