Adrien Toutant

Thermal Large Eddy Simulation in a Very Simplified Geometry of a Solar Receiver

Thermal large eddy simulations are carried out in order to study the convective flow in a solar receiver. We investigate the impact of thermal gradients on a turbulent channel flow with imposed wall temperatures for two turbulent Reynolds numbers based on the friction velocity (180 and 395). In this configuration, the flow is subsonic, while temperature variations can be strong and induce significant variations of the fluid properties. The low Mach number equations are considered. The influence of the variations of the conductivity and the viscosity is first investigated. We show that the influence of these properties can be considered constant only for weak temperature gradients. The thermal subgrid-scale modeling is studied and we conclude that for a temperature ratio of 2, we can use a constant subgrid-scale Prandtl number. Finally, we focus on the increase of the temperature ratio that emphasizes the flow dissymmetry and modifies the fluctuations profiles. The physical mechanism responsible for these modifications is explained.

High-temperature gradient effect on a turbulent channel flow using thermal large-eddy simulation in physical and spectral spaces

This paper studied nonisothermal plane channel flows using the method of thermal large-eddy simulations (TLES). Several temperature ratios (TR =TH /TC ) were investigated, where TC and TH are the temperatures of the cold and hot sides, respectively. Each TR case is further considered for two wall Reynolds numbers (Re τm ), 180 and 395, where the wall Reynolds number was defined as the average of the local wall Reynolds number values obtained for the cold and hot sides, Re τC and Re τH . For a given wall Reynolds number Re τm , it was demonstrated that the increased temperature ratio directly led to an enhanced disparity between the local wall Reynolds numbers of the cold and hot sides. Essentially, the wall Reynolds number for the cold side (Re τC ) is increased, but its companion value for the hot side (Re τH ) is decreased. In the case of large temperature ratio, the asymmetry of the mean velocity and temperature profiles is also increased. The major findings are that for high-temperature ratios, the fl...

Large Eddy Simulations of a turbulent periodic channel with conjugate heat transfer at low Prandtl number

Thermal striping is one of the possible initiator of pipe rupture. In this framework, thermal fluctuations in a heated periodic channel have been calculated using Large Eddy Simulation (LES). The fluid Prandtl number is set to 0.01 and the friction Reynolds number to 395. The Werner and Wengle Wall Function is used with the Navier-Stokes equations to reduce the computational cost. Satisfactory results can be noticed on the temperature fluctuations for low Prandtl number fluids. Several boundary conditions are considered, namely isothermal, isoflux, and conjugate heat transfer. The impacts of the wall properties on the temperature statistics for conjugated heat transfer boundary conditions are deeply analysed.

Design and proof of concept of an innovative very high temperature ceramic solar absorber

Hybrid solar gas-turbine (HSGT) is an attractive technology to foster market penetration of CSP. HSGT offers some major advantages like for example high solar-to-electric conversion efficiency, reduced water requirement and low capital cost. A very high temperature solar receiver is needed when elevated solar share is claimed. A few research works, as reported by Karni et al. [8] and by Buck et al. [1], have been dedicated to solar receiver technologies able to deliver pressurized air at temperature above 750°C. The present work focuses on research aiming at developing an efficient and reliable solar absorber able to provide pressurized air at temperature up to 1000°C and more. A surface absorber technology is selected and a modular design of receiver is proposed in which each absorber module is made of BOOSTEC® SiC ceramic (silicon carbide) as bulk material with straight air channels inside. Early stage experimental works done at CNRS/PROMES on lab-scale absorbers showed that the thermo-mechanical behavi...