A new displacement-based approach to calculate stress intensity factors with the boundary element method

The analysis of cracked brittle mechanical components considering linear elastic fracture mechanics is usually reduced to the evaluation of stress intensity factors (SIFs). The SIF calculation can be carried out experimentally, theoretically or numerically. Each methodology has its own advantages but the use of numerical methods has be-come very popular. Several schemes for numerical SIF calculations have been developed, the J-integral method being one of the most widely used because of its energy-like formulation. Additionally, some variations of the J-integral method, such as displacement-based methods, are also becoming popular due to their simplicity. In this work, a simple displacement-based scheme is proposed to calculate SIFs, and its performance is compared with contour integrals. These schemes are all implemented with the Boundary Element Method (BEM) in order to exploit its advantages in crack growth modelling. Some simple examples are solved with the BEM and the calculated SIF values are compared against available solutions, showing good agreement between the different schemes

Breakup of elongated droplets in microfluidic T-junctions

We show experimentally, and explain theoretically, what velocity is needed to break an elongated droplet entering a microfluidic T-junction. Our experiments on short droplets confirm previous experimental and theoretical work that shows that the critical velocity for breakup scales with the inverse of the length of the droplet raised to the fifth power. For long elongated droplets that have a length about thrice the channel width, we reveal a drastically different scaling Taking into account that a long droplet remains squeezed between the channel walls when it enters a T-j unction, such that the gutters in the corners of the channel are the main route for the continuous phase to flow around the droplet, we developed a model that explains that the critical velocity for breakup is inversely proportional to the droplet length. This model for the transition between breaking and nonbreaking droplets is in excellent agreement with our experiments.FWN – Publicaties zonder aanstelling Universiteit Leide

X-ray tomography for fully-3D time-resolved reconstruction of bubbling fluidized beds

A new X-ray computed tomography technique for the purpose of imaging fluidized beds is presented. It consists of an experimental set-up with three stationary X-ray source and flat panel detector pairs, a geometric calibration and data processing workflow, and an image reconstruction algorithm. The technique enables sparse-angular tomographic reconstruction in large 3D regions of fluidized beds at framerates up to 200 Hz, and therefore images bubbles along their whole trajectories through the volume. It allows for a unique analysis of bubble dynamics in fluidized beds, including bubble velocities, bubble transformations, i.e., time evolution of the bubble distributions in space, and bubble\xe2\x80\x93bubble interactions. In this article, we first analyze the main limitation of the technique, the sparse angular resolution, through numerical simulations. We then test the experimental set-up through imaging a series of phantoms. Lastly, we demonstrate results from a Geldart B bubbling fluidized bed

Direct Numerical Simulation of Turbulent Heat Transfer Modulation in Micro-Dispersed Channel Flow

The object of this paper is to study the influence of dispersed micrometer size particles on turbulent heat transfer mechanisms in wall-bounded flows. The strategic target of the current research is to set up a methodology to size and design new-concept heat transfer fluids with properties given by those of the base fluid modulated by the presence of dynamically-interacting, suitably-chosen, discrete micro- and nano- particles. We run Direct Numerical Simulation (DNS) for hydrodynamically fully-developed, thermally-developing turbulent channel flow at shear Reynolds number Re=150 and Prandtl number Pr=3, and we tracked two large swarms of particles, characterized by different inertia and thermal inertia. Preliminary results on velocity and temperature statistics for both phases show that, with respect to single-phase flow, heat transfer fluxes at the walls increase by roughly 2% when the flow is laden with the smaller particles, which exhibit a rather persistent stability against non-homogeneous distribution and near-wall concentration. An opposite trend (slight heat transfer flux decrease) is observed when the larger particles are dispersed into the flow. These results are consistent with previous experimental findings and are discussed in the frame of the current research activities in the field. Future developments are also outlined.Comment: Pages: 305-32

Heat transfer in particle-laden wall-bounded turbulent flows

In present work heat transfer in particle-laden wall-bounded turbulent flows has been study with the fluid-particle one way interaction approach. Direct Numerical Simulation of the flow, combined with Lagrangian particle tracking technique has been performed to study the problem. In presented configuration small solid and dense particles carrying by fluid forces are influence by turbulent non-isothermal flow. Numerical computation was performed for various grids for Reynolds number 180, 395 and the molecular Prandtl number 1.0. The effect of particle diameter and density as well as the effect of the Reynolds and Prandtl number on the statistical quantities was examined. The flow field, spatial pattern of particle concentration and particle temperature were presented. It has been shown that particles finally were distributed not uniformly nor hydrodynamic nor thermally.Applied Science