Search results for " fluid dynamics"

Flows and mixing in channels with misaligned superhydrophobic walls.

2014

Aligned superhydrophobic surfaces with the same texture orientation reduce drag in the channel and generate secondary flows transverse to the direction of the applied pressure gradient. Here we show that a transverse shear can be easily generated by using superhydrophobic channels with misaligned textured surfaces. We propose a general theoretical approach to quantify this transverse flow by introducing the concept of an effective shear tensor. To illustrate its use, we present approximate theoretical solutions and Dissipative Particle Dynamics simulations for striped superhydrophobic channels. Our results demonstrate that the transverse shear leads to complex flow patterns, which provide a…

Experimental and fluid dynamic study of continuous supercritical water gasification of glucose

2016

Abstract The supercritical water gasification (SCWG) of glucose as a model compound for H 2 production is studied in term of process development at 25 MPa and 650 °C. Gasification has been investigated using a laboratory scale continuous plant comprising a continuous down flow reactor with a volume of 200 cm 3 , a heat recovery section and pre-heat of the biomass to simulate more closely an industrial design. Feed streams (pure water and glucose solution) are introduced at the top of the vessel and products are extracted from the bottom. The reactor is equipped with various inlet points that allow to modify the inlet position of reacting streams in order to study the effect of stream mixing…

Results of Numerical Modeling of Blood Flow in the Internal Jugular Vein Exhibiting Different Types of Strictures

2022

The clinical relevance of nozzle-like strictures in upper parts of the internal jugular veins remains unclear. This study was aimed at understanding flow disturbances caused by such stenoses. Computational fluid dynamics software, COMSOL Multiphysics, was used. Two-dimensional computational domain involved stenosis at the beginning of modeled veins, and a flexible valve downstream. The material of the venous valve was considered to be hyperelastic. In the vein models with symmetric 2-leaflets valve without upstream stenosis or with minor 30% stenosis, the flow was undisturbed. In the case of major 60% and 75% upstream stenosis, centerline velocity was positioned asymmetrically, and areas of…

Flow properties and hydrodynamic interactions of rigid spherical microswimmers.

2017

We analyze a minimal model for a rigid spherical microswimmer and explore the consequences of its extended surface on the interplay between its self-propulsion and flow properties. The model is the first order representation of microswimmers, such as bacteria and algae, with rigid bodies and flexible propelling appendages. The flow field of such a microswimmer at finite distances significantly differs from that of a point-force (Stokeslet) dipole. For a suspension of microswimmers, we derive the grand mobility matrix that connects the motion of an individual swimmer to the active and passive forces and torques acting on all the swimmers. Our investigation of the mobility tensors reveals tha…

Viscous-Inviscid Interactions in a Boundary-Layer Flow Induced by a Vortex Array

2014

In this paper we investigate the asymptotic validity of boundary layer theory. For a flow induced by a periodic row of point-vortices, we compare Prandtl's solution to Navier-Stokes solutions at different $Re$ numbers. We show how Prandtl's solution develops a finite time separation singularity. On the other hand Navier-Stokes solution is characterized by the presence of two kinds of viscous-inviscid interactions between the boundary layer and the outer flow. These interactions can be detected by the analysis of the enstrophy and of the pressure gradient on the wall. Moreover we apply the complex singularity tracking method to Prandtl and Navier-Stokes solutions and analyze the previous int…

MODELIZACIÓN MEDIANTE CFD DE PARA EVALUAR LA VENTILACIÓN EN UN EDIFICIO ARQUEOLÓGICO, DATOS PRELIMINARES.

2016

[EN] The present study addresses the influences of wind flow structure, as an important factor responsible of material damage (erosion contributing) on “Casa di Diana” Mithraeum, a roman building (130 A.D.) sited on Ostia Antica (archaeological site, Rome – Italy), through the Computational Fluid Dynamics (CFD) simulations and direct measurements for its verification and validation (V&V). In this preliminary work, we present results relating to 3D reconstruction (geometry of the entire building) and the mesh importing on Fluent software. In general, the data check confirms, with ±10%, a good agreement (model) between the numerical solutions and direct measurements data by portable sensor. F…

Influence of drag and turbulence modelling on CFD predictions of solid liquid suspensions in stirred vessels

2014

Abstract Suspensions of solid particles into liquids within industrial stirred tanks are frequently carried out at an impeller speed lower than the minimum required for complete suspension conditions. This choice allows power savings which usually overcome the drawback of a smaller particle-liquid interfacial area. Despite this attractive economical perspective, only limited attention has been paid so far to the modelling of the partial suspension regime. In the present work two different baffled tanks stirred by Rushton turbines were simulated by employing the Eulerian-Eulerian Multi Fluid Model (MFM) along with either the Sliding Grid algorithm (transient simulations) or the Multiple Refe…

Regional variation of wall shear stress in ascending thoracic aortic aneurysms.

2014

The development of an ascending thoracic aortic aneurysm is likely caused by excessive hemodynamic loads exerted on the aneurysmal wall. Computational fluid-dynamic analyses were performed on patient-specific ascending thoracic aortic aneurysms obtained from patients with either bicuspid aortic valve or tricuspid aortic valve to evaluate hemodynamic and wall shear parameters, imparting aneurysm enlargement. Results showed an accelerated flow along the outer aortic wall with helical flow in the aneurysm center for bicuspid aortic valve ascending thoracic aortic aneurysms. In a different way, tricuspid aortic valve ascending thoracic aortic aneurysms exhibited normal systolic flow without su…

Numerical methods in the design process of a sailing yacht

2014

An efficient swap algorithm for the lattice Boltzmann method

2007

During the last decade, the lattice-Boltzmann method (LBM) as a valuable tool in computational fluid dynamics has been increasingly acknowledged. The widespread application of LBM is partly due to the simplicity of its coding. The most well-known algorithms for the implementation of the standard lattice-Boltzmann equation (LBE) are the two-lattice and two-step algorithms. However, implementations of the two-lattice or the two-step algorithm suffer from high memory consumption or poor computational performance, respectively. Ultimately, the computing resources available decide which of the two disadvantages is more critical. Here we introduce a new algorithm, called the swap algorithm, for t…