We present well-resolved RANS simulations of two generic asymmetrically heated cooling channel configurations, a high aspect ratio cooling duct operated with liquid water at (Formula Presented) and a cryogenic transcritical channel operated with methane at (Formula Presented). The former setup serves to investigate the interaction of turbulence-induced secondary flow and heat transfer, and the latter to investigate the influence of strong non-linear thermodynamic property variations in the vicinity of the critical point on the flow field and heat transfer. To assess the accuracy of the RANS simulations for both setups, well-resolved implicit LES simulations using the adaptive local deconvolution method as subgrid-scale turbulence model serve as comparison databases. The investigation focuses on the prediction capabilities of RANS turbulence models for the flow as well as the temperature field and turbulent heat transfer with a special focus on the turbulent heat flux closure influence.

We present well-resolved RANS simulations of a high-aspect-ratio generic cooling duct configuration consisting of an adiabatic straight feed line followed by a heated straight section ending with a 90° bend. The configuration is asymmetrically heated with a temperature difference of ∆T = 40 K. As fluid liquid water is used at a Reynolds number of Reb = 110 × 10 ³. The setup follows an experimental reference case, which has also been investigated using a well-resolved LES. The current investigation focuses on the prediction capabilities of different RANS turbulence closure models for the duct flow field, defined by the interaction of secondary flows and turbulent heat transfer. In the straight duct only turbulence-induced secondary flow is present, which becomes weaker along the heated duct due to the viscosity reduction, leading in turn to a reduced mixing. In the curved section, the stronger pressure-induced secondary flow superimposes the turbulence-induced one increasing the mixing of hot and cold fluid. A well-resolved LES serves as comparison database for the straight duct results.

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 × 10³ and an average Nusselt number of Nuxz = 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.

We present the results of well-resolved large-eddy simulations (LES) of an asymmetrically heated high aspect ratio cooling duct (HARCD) with an aspect ratio of AR = 4.3 for two different wall temperatures. The temperature difference with respect to the bulk flow is ∆T = 40 K, respectively ∆T = 60 K. The HARCD is operated with liquid water at a Reynolds number of Re_b = 110 ⋅ 10³ based on bulk velocity and hydraulic diameter. The generic HARCD setup follows a reference experiment. The main goal of the present study is the numerical investigation of the interaction of turbulent heat transfer and the turbulent duct flow, specifically the heating induced changes in mean flow and turbulent statistics with a spatially developing temperature boundary layer. Furthermore, we investigate the influence of asymmetric wall heating on streamwise vorticity and its dynamics as well as the turbulent Prandtl number and the effect of the secondary flow on its distribution.

We present well-resolved large-eddy-simulations (LES) of a straight, high-aspect-ratio cooling duct (HARCD) at a bulk Reynolds number of Re = 110 • 10³ and an average Nusselt number of Nu = 371. The geometry and boundary conditions have been defined together with Rochlitz et al. (2015), who conducted the experimental measurements for this case. Water was chosen as coolant. The current investigation focuses on the influence of asymmetrical wall heating on the flow field and specifically on the influence of the turbulence-induced secondary flow on turbulent heat transfer, the spatial development of the temperature boundary layer and the accompanying viscosity modulation. Due to the viscosity drop in the vicinity of the heated wall we observe a decrease in turbulent length scales and in turbulence anisotropy, resulting in a decrease of turbulent mixing and the secondary flow strength along the duct.