LES-CHT for a Rotating Cavity With Axial Throughflow

Abstract

The flow and heat transfer within rotating cavities is often discussed as a conjugate problem: the temperature distribution within the cavity disks drives the large-scale flow structure within the cavity, and the cavity aerodynamics influence the heat transfer to the disks. However, most simulations of rotating cavities only consider the fluid domain in isolation. This is particularly true for turbulence resolving approaches such as large eddy simulation (LES). The large timescale disparity between the fluid time steps used in LES and the characteristic solid time-scale complicates the use of LES with conjugate heat transfer (CHT). A further issue is that an under-resolved solid mesh artificially amplifies higher frequency temperature fluctuations from the fluid. This paper addresses these challenges with a new method for LES-CHT where the low-frequency temperature fluctuation caused by the large-scale flow structure is accounted for using a multi-scale frequency domain approach. We investigate two cases: axially heated disks made of a low conductivity material, and disks made from a higher conductivity material with a temperature set by radial conduction from the shroud. The formation of small-scale flow structures on both the disk and shroud is dependent on the heating configuration of the cavity - indicating that high-fidelity thermal boundary conditions should be used when simulating rotating cavities. The formation of heating induced vortical flow structures near the disk is particularly interesting, as this is unexpected from the laminar Ekman layer modelling argument usually used to consider this region.

Conjugate heat transfer: Some fundamentals and recent progress

“…Furthermore, for cases with distinctive low frequency disturbances which penetrate through a whole solid domain, a small number of temperature harmonics may be solved in the solid domain. This capability is demonstrated in a recent extension of the Fourier spectral framework, applied to buoyancy-driven cavity flows by Hickling and He [46]. The LES-CHT results for a cavity flow have also revealed a new type of thermally-driven turbulent flow instability [46], showcasing the potential of LES-CHT development for further applications.…”

“…This capability is demonstrated in a recent extension of the Fourier spectral framework, applied to buoyancy-driven cavity flows by Hickling and He [46]. The LES-CHT results for a cavity flow have also revealed a new type of thermally-driven turbulent flow instability [46], showcasing the potential of LES-CHT development for further applications.…”

Conjugate Modeling of a Closed Co-Rotating Compressor Cavity

“…The characteristic timescale of the solid was found to be significantly longer than that of the fluid, leading to long convergence times for transient cases. Recent work by Hickling and He [23] assessed the sensitivity of conjugate boundary conditions. LES was used for the fluid domain coupled with a 3D steady-state solid domain.…”