要約

The present study deals with natural convection flow in a vertical open-ended channel with wall constant heat flux. The experimental and numerical investigations are both conducted using water as the working fluid in order to get rid of radiation heat transfer and to have a pure convective flow. The numerical code is developed using Finite Differences scheme of second order in time and space to solve the elliptic two-dimensional Navier-Stokes equations under the Boussinesq assumption. Concerning the experimental apparatus, it consists of two heated walls immersed in water. Temperature and velocity measurements are provided (by thermocouple and Laser Doppler Velocimetry system) for different modified Rayleigh numbers based on the walls spacing b : Ra^*_b = 1.67×10⁶,3.6×10⁶,8.97×10⁶,1.69×10⁷,4.29×10⁷. The numerical code is first validated with a numerical benchmark for the case of natural convection in air between asymmetrically heated walls under uniform heat flux without considering radiative effects. Then, the numerical simulations are performed for the case of natural convection of water between two symmetrically heated walls by uniform heat flux and compared to experimental data. The code provides a satisfactory prediction of main quantities compared to the experimental results but only for the lowest Rayleigh numbers Ra^*_b = 1.67×10⁶,3.6×10⁶. For higher modified Rayleigh numbers Ra^*_b = 8.97×10⁷,1.69×10⁷,4.29×10⁷, the flow becomes three-dimensional and turbulent. Therefore, 2D numerical simulations fail to predict flow and heat transfer for this range of modified Rayleigh number.