Convective heat transfer and reacting flows
Authors: Kumar Abhishek , Hin Chi , Threlfall Ed 
Published: June 2024

This session focuses on the applications that involves heat transfer and comprises the following talks
1. Radially heated Taylor-Couette flow in Nektar++
2. Flow structures arising from the interplay between shear and buoyancy
3. NESO - A Nektar++-based framework for fusion plasma physics

Radially heated Taylor-Couette flow in Nektar++

Taylor-Couette (TC) flow involves fluid motion between rotating concentric cylinders, one of the key problems in fluid dynamics. Its behaviour varies from axisymmetric Taylor vortices to turbulence through different patterns. The flow dynamics become more complicated when a temperature difference is applied between the two cylinders, leading to radial heat transfer coupled with centrifugal acceleration. The combination is pivotal in altering the stability conditions of TC flow. In this study, we aim to focus on the effects of ‘sinusoidal’ radial heating on the TC flow dynamics.

In TC flow problems, most codes utilise the Fourier-spectral method in the axial and azimuthal directions due to the invariance of these directions. However, in our case, as we introduce sinusoidal heating, the Fourier-spectral approach becomes inadequate for the axial direction. This is where the capabilities of Nektar++ become valuable. In this context, we are developing a solver within the Nektar++ framework that operates in cylindrical coordinates. It will use spectral-element discretisation in the radial and axial plane while retaining the Fourier-spectral method in the azimuthal direction. We have obtained some preliminary results, which we will present and discuss during this workshop.

Flow structures arising from the interaction between shear and buoyancy

This study investigates Rayleigh-Bénard-Poiseuille (RBP) flow, combining buoyancy and shear effects, in a large domain (Γ = 12.57) with a Prandtl number (Pr) of 1. Rayleigh (Ra) ranges from 3000 to 10000 and Reynolds (Re) from 0.1 to 2000, aiming to understand the interactions between buoyancy and shear-driven mechanisms. Six flow regimes were identified: (a) Spiral Defect Chaos (SDC), (b) Ideal Straight Rolls (ISRs), (c) Wavy Rolls, (d) Intermittent Rolls, (e) Longitudinal Rolls, and (f) Shear Flow Turbulence. The research expands previous work by examining how shear (Re) influences SDC and if buoyancy (Ra) encourages the transition to shear flow turbulence. A detailed analysis of these regimes will be presented in the workshop.

NESO - A Nektar++-based framework for fusion plasma physics

Project NEPTUNE (part of the UK's ExCALIBUR programme) aims to provide a modern framework for simulating fusion plasma physics, with an emphasis on plasma turbulence and transport of neutral species in magnetically-confined fusion devices. This framework, called NESO (for NEPTUNE Exploratory SOftware), consists of a Nektar++-based plasma fluid solver, coupled to a performance-portable particle simulation code written in SYCL (NESO-Particles). The ultimate goal is a code capable of approaching the exascale on a large GPU-based supercomputer and this will be achieved using the nascent GPU capabilities of Nektar++.

This talk will present the current status of the NESO code including several plasma physics examples.