Modelling of Heat Transfer and Fluid Flow through a Granular Material and External Wall Barrier

Heat and fluid flow simulations for granular material in wall barriers allow to design them in a way that maximally reduces the expenditures on utilisation of buildings. This paper demonstrates the solution to the problem of the passage of air through the external wall barrier. It shows how the temperature changes inside the wall barriers when the external temperature changes. Two types of partitions are tested: single-layer (granular material) and two-layer (granular and concrete material). The paper presents comparison of the results of the numerical model and in-house code with the experimental data. The numerical model applied is based on the unsteady equation of heat conduction (3D) and the Navier-Stokes equations. A high-order compact method in combination with the WENO scheme and predictor-corrector method are applied for the spatio-temporal discretisation. The flows of air and heat in the granular layers are modelled using immersed boundary technique, which allows to use Cartesian meshes for objects with very complex geometric shapes. The correctness of numerical model applied has been verified by comparisons with ANSYS Fluent results and experimental data obtained from measurements performed in a laboratory and in-situ

Parametric analysis of excited round jets - numerical study

A computational analysis of excited round jets is presented with emphasis on jet bifurcation phenomenon due to superposition of axial and flapping forcing terms. Various excitation parameters are examined including the amplitudes of the forcing, their frequencies and phase shift. It is shown that alteration of these parameters significantly influences the spatial jet evolution. This dependence may be used to control the jet behaviour in a wide range of qualitatively different flow structures, starting from a modification of the spreading rate of a single connected jet, through large scale deformation of an asymmetric jet, onto jet bifurcation leading to a doubly and even triply split time-averaged jet, displaying different strengths and locations of the branches. We establish that: (i) jet splitting is possible only when the amplitudes of the forcing terms are comparable to or larger than the level of natural turbulence; (ii) the angle between the developing jet branches can be directly controlled by the frequency of the axial forcing and the phase shift between axial and flapping forcing. An optimum forcing frequency is determined, leading to the largest spreading rate

Controlling spatio-temporal evolution of natural and excited square jets via inlet conditions

The paper presents numerical investigations of square jets in a wide range of Reynolds numbers with varying inlet turbulence characteristics. The research focuses on flow characteristics depending on inflow turbulent length/time scales and excitation frequencies in case of excited jets. It is found that the parameters of inlet turbulence affect the solutions qualitatively when the Reynolds number is sufficiently low. In these cases the impact of varying the turbulent time scale is considerably larger than changing the turbulent length scale. It was also observed that at sufficiently high Reynolds numbers the jets become quite independent of the inlet turbulence characteristics. This confirms findings of Xu et al. (Phys. Fluids, 2013) concerning weak/strong dependence of the jet evolution on inflow conditions. In case of excited jets the excitation frequencies play an important role and influence the jet behaviour most strongly at lower values of the Reynolds number. For some forcing frequencies a bifurcation occurs at sufficiently large forcing amplitudes. This phenomenon turned out to be independent of the assumed length and time scales of the turbulent fluctuations, both in terms of robustness as well as amplitude.</p

Modelling of Spark Ignition in Turbulent Reacting Droplet-laden Temporally Evolving Jet using LES

The turbulent jet flames in fuel sprays are of a great importance and are used in many practical applications, e.g., aircraft and automotive direct fuel injection systems. In this work we analyse the process of spark ignition in two-phase temporally evolving jet which carries the fuel spray. We focus on a dependence of the ignition on local flow structures, spark parameters and fuel droplets size. The fuel (n-Heptane) spray evaporates and mixes with the co-flowing oxidizer (air) creating a flammable mixture. The spark is modelled as a source term added to the energy equation. The goal of the research is to investigate the forced ignition and subsequent flame propagation/extinction in the low Mach number turbulent flow. The computations are carried out using Implicit Large Eddy Simulation (ILES) method by the high-order in-house LES solver. Liquid droplets are modelled in Lagrangian reference frame as point sources of mass, momentum and energy. The results show that combined effect of local fuel concentration, strain rate and scalar dissipation rate plays a main role in ignition. On the other hand, high rates of strain at the spark position cause substantial flame stretching leading to its extinction

LES of a non-premixed hydrogen flame stabilized by bluff-bodies of various shapes

Dynamics of flames stabilized downstream of different shape bluff-bodies (cylindrical, square, star) with different wall topologies (flat, wavy) is investigated using large-eddy simulations (LES). A two-stage computational procedure involving the ANSYS software and an in-house academic high-order code is combined to model a flow in the vicinity of the bluff-bodies and a flame formed downstream. The fuel is nitrogen-diluted hydrogen and the oxidizer is hot air in which the fuel auto-ignites. After the ignition, the flame propagates towards the bluff-body surfaces and stabilizes in their vicinity. It is shown that the flames reflect the bluff-body shape due to large-scale strong vortices induced in the shear layer formed between the main recirculation zone and the oxidizer stream. The influence of the acute corners of the bluff-bodies on the flame dynamics is quantified by analysing instantaneous and time-averaged results. Compared to the classical conical bluff-body the largest differences in the temperature and velocity distributions are observed in the configuration with the square bluff-body. The main recirculation zone is shortened by approximately 15% and at its end temperature in the axis of the flame is almost 200~K larger. Simultaneously, their fluctuations are slightly larger than in the remaining cases. The influence of the wall topology (flat vs. wavy) in the configuration with the classical conical bluff-body turned out to be very small and it resulted in modifications of the flow and flame structures only in the direct vicinity of the bluff-body surface

Approximate deconvolution discretisation

A new strategy is presented for the construction of high-order spatial discretisations extracted from a lower-order basic discretisation. The key consideration is that any spatial discretisation of a derivative of a solution can be expressed as the exact differentiation of a corresponding ‘filtered’ solution. Hence, each numerical discretisation method may be directly linked to a unique spatial filter, expressing the truncation error of the basic method. By approximately deconvolving the implied filter of the basic numerical discretisation an augmented high-order method can be obtained. In fact, adopting a deconvolution of the implied filter of suitable higher order enables the formulation of a new spatial discretisation method of correspondingly higher order. This construction is illustrated for finite difference (FD) discretisation schemes, solving partial differential equations in fluid mechanics. Knowing the implied filter of the basic discretisation, one can derive a corresponding higher order method by approximately eliminating the implied spatial filter to a certain desired order. We use deconvolution to compensate for the implied filter. This corresponds to a ‘sharpening’ of numerical solution features before the application of the basic FD method. The combination will be referred to as Approximate Deconvolution Discretisation (ADD). The accuracy of the deconvolved FD scheme depends on the order of approximation of the deconvolution filter. We present the ‘sharpening’ of several well-known FD operators for first- and second-order derivatives and quantify the achieved accuracy in terms of the modified wavenumber spectrum. Examples include high-order extensions up to new schemes with spectral accuracy. The practicality of the deconvolved FD schemes is illustrated in various ways: (i) by investigation of exactly solvable advection and diffusion problems, (ii) by tracking the evolution of the numerical solution to the Taylor-Green vortex problem and (iii) by showing that ADD yields spectral accuracy for the Burgers equation and for double-jet flow of an incompressible fluid.</p

Acrylates in Dental Applications

In the presented chapter, the role that is played by acrylates in dentistry has been characterized. In the introduction, subject of oral diseases has been raised as well as an issue of development of dentistry over the centuries. Furthermore, characteristics of the materials that have been used over the years to receive elements used in the form of prosthetic devices or dental implants that in the most favourable way from the user’s point of view enable the restoration of the missing piece of the dentition have been performed. Next, composition, functions and types of teeth have been described. In the following sections, materials (including dentures, adhesives, impression trays and dental crowns) widely used in dentistry and dental prosthetics in the preparation of which the key role is played by acrylates have been characterized. The preparation of prostheses was described. Particular attention has been drawn on the possibility of modification of the synthesis of acrylic materials that can lead to the improvement of their properties and result in making them more favourable from the point of view of the patient. The chapter is crowned with a brief description of the studies of properties, which are subjected to dental materials before application in the dental office

π\pi-Electron Ferromagnetism in Metal Free Carbon Probed by Soft X-Ray Dichroism

Elemental carbon represents a fundamental building block of matter and the possibility of ferromagnetic order in carbon attracted widespread attention. However, the origin of magnetic order in such a light element is only poorly understood and has puzzled researchers. We present a spectromicroscopy study at room temperature of proton irradiated metal free carbon using the elemental and chemical specificity of x-ray magnetic circular dichroism (XMCD). We demonstrate that the magnetic order in the investigated system originates only from the carbon $\pi$-electron system.Comment: 10 pages 3 color figure