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Proceedings of the Seventh International ERCOFTAC Workshop on Direct and Large-Eddy Simulation, held at the University of Trieste, September 8-10, 2008
Numerical simulations of Rayleigh–Bénard convection have become a valid complement to laboratory experiments to disentangle the complex flow dynamics. In this paper we describe some of the state-of-the-art experiments and discuss how numerical simulations help in elucidating some phenomena. In particular we show that in the high-end of the Rayleigh number there is an unavoidable deviation of the real...
The difference of droplet dynamics in reacting and non-reacting turbulent mixing layers has been investigated using direct numerical simulation. The multiphase reacting flow is described by the hybrid Eulerian-Lagrangian approach. In the reacting mixing layer, the combustion-induced evaporation causes droplet size to significantly decrease in comparison with the non-reacting case, where evaporation...
Large eddy simulations are performed on the experimental burner MERCATO operated at ONERA fed with air and liquid kerosene. The purpose of the present study is to assess the reliability of the Euler-Euler approach for two-phase flow with and without combustion. The mesoscopic Eulerian quantities for the liquid dispersed phase and the gaseous variables are advanced in space and time with a third-order...
In this work, a numerical study of combustion induced noise is performed. For this purpose, a hybrid LES/CAA approach is applied to the simulation of a turbulent jet flame. The approach is based on a low-mach number LES and linearized acoustic equations. Both LES and CAA computations are compared to experimental investigations.
A Large Eddy Simulation/Conditional Moment Closure calculation of forced ignition of a turbulent bluff-body stabilised non-premixed methane flame is performed and the results are qualitatively investigated to assess the suitability of this model for highly transient combustion phenomena. The qualitative features of the flame expansion process agree with experimental findings. Quantitatively, the time...
The flow downstream an hydraulic turbine is a swirling flow which presents a strong unsteady vortex core within the draft tube. It may trigger instabilities whose development has serious impacts on the efficiency of the system. The draft tube is also sensitive to flow separation due to the presence of a strong pressure gradient. It is still a great challenge to numerically reproduce the flow dynamics...
In this paper, we present numerical simulations of highly pulsated jet flows at 12, 000 K developing in a colder environment. Such flows are used to model plasma jets generated by direct current plasma torch. Plasma spraying is used to deposit thick coatings on a substrate. We focus here on situations where plasma jets are randomly forced by an electric arc resulting in a highly turbulent flow at...
The effects of rotation on the convective heat transfer and flow structuring in a cylindrical volume of fluid is investigated with direct numerical simulation (DNS). A formulation of the discrete equations of motion in cylindrical coordinates is solved with finite-difference approximations. At constant Rayleigh (Ra; dimensionless temperature gradient) and Prandtl (σ; characterises diffusive properties...
In this paper we present some results of an extensive campaign of direct numerical simulations of Rayleigh–Bénard convection at high Prandtl numbers (100 ≤ Pr ≤ 104) and moderate Rayleigh numbers (105 ≤ Ra ≤ 109). In particular, we examine the Nusselt and the Reynolds number dependences on Ra and Pr. A short discussion on the characteristic flow velocity is also presented.
Turbulent Rayleigh–Bénard (RB) convection is one of the classical problems in fluid mechanics, where fluid with a Prandtl number Pr = ν/k is exposed to a vertical temperature gradient between a hot lower and a cold upper surface. The Rayleigh number Ra = αgH3 ΔT/(νk) is a non-dimensional parameter to specify the ratio between the buoyancy and viscous forces, where α, ν and k denote the...
Engineering problems of climate control in buildings, cars or aircrafts, where the temperature must be regulated to maintain comfortable and healthy conditions, can be formulated as mixed convection problems, in which the flows are determined both by buoyancy and by inertia forces, while neither of these forces dominate. The objective of the present study is to investigate by means of Direct Numerical...
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