Turbulent flow through a high aspect ratio cooling duct with asymmetric wall heating

Abstract

We present well-resolved large-eddy simulations of turbulent flow through a straight, high aspect ratio cooling duct operated with water at a bulk Reynolds number of $Re_{b}=110\times 10^{3}$ and an average Nusselt number of $Nu_{xz}=371$. The geometry and boundary conditions follow an experimental reference case and good agreement with the experimental results is achieved. The current investigation focuses on the influence of asymmetric wall heating on the duct flow field, specifically on the interaction of turbulence-induced secondary flow and turbulent heat transfer, and the associated spatial development of the thermal boundary layer and the inferred viscosity variation. The viscosity reduction towards the heated wall causes a decrease in turbulent mixing, turbulent length scales and turbulence anisotropy as well as a weakening of turbulent ejections. Overall, the secondary flow strength becomes increasingly less intense along the length of the spatially resolved heated duct as compared to an adiabatic duct. Furthermore, we show that the assumption of a constant turbulent Prandtl number is invalid for turbulent heat transfer in an asymmetrically heated duct.

Collaborative Research for Future Space Transportation Systems

“…Based on the reference experiment [49], the flow field in the thermal entrance region of a straight high aspect-ratio water-cooling duct with an aspect ratio AR = 4.3, a Reynolds number of Re b = 1.1 × 10 5 and an average Nusselt number of Nu = 371 was investigated by LES and RANS simulations. The validation of the LES with DNS data and the good agreement between numerical LES and experimental PIV results for velocity and Reynolds stress profiles are reported in [50]. Figure 19 depicts the temperature and secondary flow development along the heated domain in the lower duct quarter.…”

Assessment of RANS Turbulence Models for Straight Cooling Ducts: Secondary Flow and Strong Property Variation Effects

“…Using other turbulence models than the BSL RSM, the results deviate further from the LES, see [17]. When heating is applied the secondary flow strength becomes weaker along the duct, [19]. The RANS captures this behaviour only for the large vortex, whereas the small vortex strength slightly increases.…”

“…For the LES database of [19] the incompressible NSE with the Boussinesq approximation are applied. The transport properties are evaluated using the IAPWS correlations.…”

“…In the following, the RANS results of the BSL RSM turbulence model in combination with different turbulent heat flux closures are compared to the LES of [19]. Figure 2 shows the cross-sectional flow and temperature field and Fig.…”

“…In the first part of the present study an asymmetrically heated high aspect ratio cooling duct (HARCD) at Re b = 110 • 10 3 and a moderate heating of T W − T b = 40 K is investigated using the BSL RSM and various turbulent heat flux closure models with ANSYS CFX. This setup has been studied experimentally, [28], and using a LES, [16][17][18][19] serving as comparison database. In the second part a cryogenic transcritical channel at Re b = 16 • 10 3 is investigated with the BSL RSM and various turbulent heat flux closure models with ANSYS FLUENT.…”