Experimental study of a natural convection flow in a cubic enclosure with a partially heated inner block

In many industrial contexts, buoyancy driven flows are the only cooling strategy in case of breakdown of the forced convection cooling system. In order to study those flows in a simplified configuration, a buoyancy-driven flow is generated inside a cubic enclosure by a partially heated block (Ra = 1.4 × 109). The flow is studied experimentally in the vertical median plane, in the part of the enclosure where the flow is generated i.e. close to the heated side of the block. Velocity fields, mean profiles and RMS statistics are analyzed. The results show the presence of boundary layer flows with a central zone nearly at rest and stratified. RMS velocities are intensified with elevation.

Computational fluid dynamics simulation of buoyant mixing of miscible fluids in a tilted tube

Buoyancy-driven flows and mixing of fluids with different densities occur frequently both in nature and as part of industrial processes within chemical and petroleum engineering. This work investigates the buoyant exchange flow of two miscible fluids in a long tube with closed ends at varying tilt angles using OpenFOAM. The study focuses on the evolution of the concentration field and front velocities of the mixing zone at different inclinations. Numerical results based on a miscible solver agree with previous experiments and direct numerical simulations. Treating the fluids instead as immiscible with no surface tension leads to unrealistically high front velocities at intermediate inclinations.

New H 2 O weighted sum of gray gases model for natural convection flows within large cavities

Radiation heat transfer plays a significant role in buoyancy driven flows for large scale facilities. In the analysis of nuclear containment safety during severe accidents, it has been found that the thermal radiation particularly affects the temperature distribution and containment pressurization due to the humidity environment. In order to model thermal radiation, one of the main challenges is the description of nongray gas property for the steam-air mixtures. The weighted sum of gray gases model (WSGG) is a reasonable method in engineering applications because of its computational efficiency. There are many WSGG models available for combustion applications, but none of them is dedicated for low temperature applications. Furthermore, most of the existing WSGG models only provide the fixed partial pressure ratios (e.g., p H 2 O = 2p CO 2 for methane). To overcome this limitation, a tailored WSGG model is derived by the Line-by-Line model for a gas mixture composed of arbitrary concentrations of H 2 O. This tailored WSGG model is valid for the pressure path length ranging from 0.0001 to 10 atm · m, and for the temperature from 300 to 1200 K. The WSGG correlations are verified against the Line-by-Line benchmark solutions with isothermal/non-isothermal temperatures and homogeneous/non-homogeneous concentrations. The results demonstrate the ability and efficiency of the new tailored WSGG formulation.

On the choice of finite element for applications in geodynamics

Geodynamical simulations over the past decades have widely been built on quadrilateral and hexahedral finite elements. For the discretisation of the key Stokes equation describing slow, viscous flow, most codes use either the unstable Q1 × P0 element, a stabilised version of the equal-order Q1 × Q1 element, or more recently the stable Taylor-Hood element with continuous (Q2 × Q1) or discontinuous (Q2 × P−1) pressure. However, it is not clear which of these choices is actually the best at accurately simulating typical geodynamic situations. Herein, we are providing for the first time a systematic comparison of all of these elements. We use a series of benchmarks that illuminate different aspects of the features we consider typical of mantle convection and geodynamical simulations. We will show in particular that the stabilised Q1 × Q1 element has great difficulty producing accurate solutions for buoyancy-driven flows – the dominant forcing for mantle convection flow – and that the Q1 × P0 element is too unstable and inaccurate in practice. As a consequence, we believe that the Q2 × Q1 and Q2 × P−1 elements provide the most robust and reliable choice for geodynamical simulations, despite the greater complexity in their implementation and the substantially higher computational cost when solving linear systems.

Numerical Simulation Of Thermodiffusion Subjected To Different Gravity Fields

In this work, a typical thermodiffusion experiment on a binary mixture is simulated numerically using a two-dimensional computational fluid dynamics (CFD) code. Three scenarios for gravity have been studied: residual, pure oscillatory, and microgravity micro-accelerations. It was found that less separation of mixture components in the presence of strong gravity fields is due to the formation of buoyancy-driven flows. For the case of pure oscillatory gravity, the effects of the frequency and amplitude are discussed in detail. A critical vibrational Rayleigh number is proposed above which the diffusion process is highly affected by the external excitation. For the case of the microgravity environment, quasi-steady accelerations and g-jitter, both of which are found on the International Space Station, have been considered. Results show g-jitter has a minimal effect on the thermodiffusion experiment. The effects of the residual gravity field were also found to be insignificant in stimulating a strong convection flow.

Numerical Simulation Of Thermodiffusion Subjected To Different Gravity Fields

In this work, a typical thermodiffusion experiment on a binary mixture is simulated numerically using a two-dimensional computational fluid dynamics (CFD) code. Three scenarios for gravity have been studied: residual, pure oscillatory, and microgravity micro-accelerations. It was found that less separation of mixture components in the presence of strong gravity fields is due to the formation of buoyancy-driven flows. For the case of pure oscillatory gravity, the effects of the frequency and amplitude are discussed in detail. A critical vibrational Rayleigh number is proposed above which the diffusion process is highly affected by the external excitation. For the case of the microgravity environment, quasi-steady accelerations and g-jitter, both of which are found on the International Space Station, have been considered. Results show g-jitter has a minimal effect on the thermodiffusion experiment. The effects of the residual gravity field were also found to be insignificant in stimulating a strong convection flow.