Jure Marn

Two-dimensional large-eddy simulation of turbulent natural convection due to internal heat generation

Abstract Two-dimensional numerical simulations of laminar and turbulent natural convection in a fluid with internal heat generation in a square cavity are presented. The simulations were carried out at Rayleigh numbers 106–1011 and Prandtl numbers 0.25 and 0.6. The turbulent fluid motion was captured with a large-eddy simulation (LES) model. The Rayleigh–Taylor instabilities at the upper boundary and the Kelvin–Helmholtz instabilities at the side boundaries cause first local and then global transition from laminar to turbulent motion. Lower Prandtl numbers enhance heat transfer through the bottom region, whereas higher Prandtl numbers enhance heat transfer through the upper region of the simulation domain. The simulations also reveal that the Rayleigh–Nusselt number relation is not uniformly linear in a log10–log10 diagram.

On incompressible buoyancy flow benchmarking

Nowadays, the use of computational fluid dynamics (CFD) codes has become routine, although there are still some unresolved basic issues. The crucial step in the testing of numerical codes is benchmarking. Accurate solutions of benchmarks represent reference points for code development. As studies have revealed, the already existing benchmarks for natural-convection flows do not satisfactorily validate numerical codes. The authors propose the advection of a hot rectangular plume in a cold fluid placed in a rectangular cavity as a new benchmark for incompressible buoyancy flows. Our attention was focused on low-viscosity flows at zero thermal diffusivity. Together with the benchmarks configuration, the results of numerical calculations are presented to serve as a reference point for further investigations.Nowadays, the use of computational fluid dynamics (CFD) codes has become routine, although there are still some unresolved basic issues. The crucial step in the testing of numerical codes is benchmarking. Accurate solutions of benchmarks represent reference points for code development. As studies have revealed, the already existing benchmarks for natural-convection flows do not satisfactorily validate numerical codes. The authors propose the advection of a hot rectangular plume in a cold fluid placed in a rectangular cavity as a new benchmark for incompressible buoyancy flows. Our attention was focused on low-viscosity flows at zero thermal diffusivity. Together with the benchmarks configuration, the results of numerical calculations are presented to serve as a reference point for further investigations.

Systemic approach to innovations – standards vs software

Purpose – In this paper we tried to apply some system theory in the complex problems of intellectual property management by presenting some relevant current issues regarding standards and possibilities of computer software protection. Systemic approach to involvement in lucrative business of software is examined, from the point of innovations incorporated within standards and software.Design/methodology/approach – Two competing concepts are confronted: public accessible standards, and public exclusionary patents, both in the area of software development and software patenting. Actual examples of controversies are presented, and commented.Findings – Patents are legalized monopolies. Monopolists exact higher prices than free market enterprises. Our results indicate that there needs to be balance between public interest in free access to technological information and monopolies. Owing to the lack of system theory applied in this problem solving processes the issues remain unsolved and also unclear to many in...

Two-step validation process of particle mixing in a centrifugal mixer with vertical axis

Two-step approach of validation is proposed to validate a numerical model, capable of accurate prediction of mixing power characteristics of a centrifugal mixer with vertical axis. Two sets of experiments and two sets of numerical simulations are presented—the first set to determine physical characteristics of the particles comparing the numerical simulations results with experimental data, and the second set to validate predicted behavior of anchor type vertical axis impeller for mixing of same particles. Zeolite particles were used for actual calculations. After determining shear modulus, coefficient of interaction, static friction coefficient, and rolling friction coefficient through optimization process based on numerical simulations with subject function of diameter and angle of repose derived from experiment, using these values in numerical simulation of impeller mixer mixing zeolite particles led to results, which were in good agreement with results of the second set of experiments. The obtained zeolite material parameter values can therefore serve as a solid basis for discrete elements method based numerical simulation of zeolite granular materials.

Modelling of Flyash Water Mixture Flows

Present paper deals with modelling of a laminar flow of shear-thickening non-Newtonian fluid. First, approach with the Quadratic model to rheological modelling of such a fluid is presented. Secondly, the laminar flow of non-Newtonian fluid in a pipe bend is studied by numerical means to obtain the pressure loss coefficient prompted by disagreement between the empirical correlations and numerically obtained results. Finally, the comparison between two rheological models is presented.Copyright

Hydrodynamic of Bubble Boiling Regime With Artificially Produced Nucleation Site

In presented work a hydrodynamic of bubble boiling process in quiescent water has been investigated using PIV (Particle Image Velocimetry) experimental technique. Velocity distribution in narrow region over the artificially produced nucleation site that was active during the partial developed nucleate boiling has been presented in more details. Experimental methodology is based on specially arranged boiling measurement procedure and it includes a statistic cross-correlation function for the raw velocity vectors estimation and validation protocol where refined velocity filed of bubbling process is attained. Review of vertical velocity components in natural convection and bubble boiling regime at two selected temperatures along the boiling surface is given and some comparison is carried out. Vertical velocity profiles around the rising bubbles are presented in qualitative manner and vertical pumping characteristics of boiling process vs. natural convection are compared.Copyright

Electrostatic Ash and Water Flow Mixture Modeling

Slurry flow consisting of 63% electrostatic filter ash and 37% water is subject of investigation reported in this contribution which tries to determine the most appropriate rheological model. The authors have modeled experimental data obtained from actual experimental setup, i.e. pipe viscometer and derived model parameters for Power Law as well as for Sisko model. Based on this analysis a numerical simulation of experiment has been attempted using well known Power Law model and taking the advantage of CFX 4.3 numerical code. This was mainly attempted in order to verify use of the same numerical package later for purpose of building a library of friction coefficients to be used in pipe flow analysis with lumped parameters computer code.

Non Newtonian Driven Cavity Flow ComparisonBetween Boundary Element And Finite DifferenceMethods

An important class of fluids, namely generalized Newtonian fluids, have been the subject of considerable research in the area of petroleum engineering and biomechanics. This contribution deals with a comparison between velocity-vorticity formulation used in the Boundary element method and the Finite difference method. Both methods decompose material properties into its constant contribution. The formulation is applied in its two dimensional form for flow in a driven cavity, believed to be a widely used benchmark problem for a wide array of fluid dynamics problem.