123 research outputs found
Blood Flow Simulation of Aneurysmatic and Sane Thoracic Aorta Using OpenFOAM CFD Software
No full textCardiovascular diseases still represent one of the most deadly pathologies worldwide. Knowledge of the blood flow dynamics within the cardio-vascular system is crucial in preventing these diseases and analysing their physiology and physio-pathology. CFD simulations are highly effective in guiding clinical predictions and, more importantly, allow the evaluation of physical and clinical parameters that are difficult to measure with common diagnostic techniques. Therefore, in particular, this study is focused on investigating the hemodynamics of the thoracic aorta. Real aortic geometries regarding a sane and diseased patient presenting an aneurysm were considered. CFD simulations were performed with the OpenFOAM C++ library using patient-specific pulsatile blood flow waveforms and implementing the Windkessel pressure boundary condition for the artery outflow. The adopted methodology was preliminarily verified for assessing the numerical uncertainty and convergence. Then, the CFD results were evaluated against experimental data concerning pressure and velocity of the thoracic aorta measured with standard diagnostic techniques. The normal aorta’s blood flow was also compared against the pattern regarding the patient-specific aortic aneurysm. Parameters such as wall pressure, wall shear stress (WSS) and velocity distribution were investigated and discussed. The research highlighted that the blood flow in the aorta is strongly affected by the aneurysm onset, with the growth of recirculation zones being potentially hazardous. The outcomes of the investigation finally demonstrate how CFD simulation tools, capturing the detailed physics of the aortic flow, are powerful tools for supporting clinical activities of the cardio-vascular system
Role of the front wing/wheel setting-up on the optimal cornering performances of a Formula 1 car
No full textWe propose a hybrid approach based on meta-modelling techniques and machine-learning algorithms to determine the best car configuration for each circuit. By a specific interpolation model, we obtain an accurate estimation of the car’s speed as a function of the front wing configuration and the bend curvature. Some high-fidelity fluid dynamic simulations train the model and extend it to the entire design space. These data are then used as input for a simplified car dynamics model, providing an accurate estimate of the ideal lap time. Comparison with actual telemetry data confirms that the resulting tool is reliable, fast and easy to use
Implementation and assessment of a low-dissipative OpenFOAM solver for compressible multi-species flows
No full textA Navier–Stokes numerical wave tank with a pressure-based relaxation zone method
No full textIn the relaxation zone method for numerical wave tank modelling, the numerical fields are usually relaxed in the generation zone to the solution given by the potential theory. In the adopted procedure, the two-phase viscous flow is blended with the potential solution and this underlying inconsistency in the generation region can lead to instability in the flow. In this work, we present a new method for the wave generation in the context of the relaxation zone method which overcome the issue on the velocity forcing by introducing a body force equal to the potential pressure gradient. Results show that the method gives accurate results when compared with classical test case for wave propagation
Numerical Simulation of Interface Time Evolution by Oriented Lagrangian Particles and Level-Set Method
No full textA new computational approach for tracking evolving interfaces is proposed. The procedure is based on the coupling of lagrangian massless particles and the standard Level-Set methodology, and the use of evolution equations for fundamental vector and tensor quantities related to the geometrical properties of the interface Γ. In particular, the normal vector n and the second fundamental tensor ▽ n are linked to the particles and advected with them; in this way, the particles can be located upon Γ and enable a step-by-step calculation of the Level-Set function φ through a direct solution of the eikonal equation. No transport equation and reinitialization procedure for φ have to be taken into account and the usual numerical diffusion affecting the Level-Set approach is removed. The method is easy to code and carries out an accurate reconstruction of the front, limited only by the spatial resolution of the mesh. © 2009 by ASME
A self-adaptive oriented particles Level-set method for tracking interfaces
No full textA new method for tracking evolving interfaces by lagrangian particles in conjunction with a Level-Set approach is introduced. This numerical technique is based on the use of time evolution equations for fundamental vector and tensor quantities defined on the front and represents a new and convenient way to couple the advantages of the Eulerian description given by a Level-Set function to the use of Lagrangian massless particles. A self-adaptive mechanism suitably modifies, at each time step, the markers distribution in the numerical domain: each particle behaves both as a potential seeder of new markers on C (so as to guarantee an accurate reconstruction of the interface) and a de-seeder (to avoid any useless gathering of markers and to limit the computational effort). The algorithm is conceived to avoid any transport equation and to confine the Level-Set function to the role of a mere post-processing tool; thus, all the numerical diffusion problems usually affecting the Level-Set methodology are removed. The method has been tested both on 2D and 3D configurations; it carries out a fast reconstruction of the interface and its accuracy is only limited by the spatial resolution of the mes
Analysis of the asymmetric behavior of propeller–rudder system of twin screw ships by CFD
No full textThe interference between the hull, propeller and rudder remarkably affects the control and maneuvering capabilities of marine vehicles. In case of twin screw/twin rudder ships, the asymmetric evolution of the wake past the hull causes the asymmetric functioning of the propeller–rudder system. Systematic investigations on this aspect for twin screw ships are limited. Available experimental data carried out on simplified hull–propeller–rudder system and captive model tests do not allow to completely understand the fluid mechanism at the basis of the hydrodynamic interaction that should be taken into account in simplified maneuvering mathematical models for preliminary predictions. In this paper the hull–propeller–rudder interactions phenomena for a twin screw/twin rudder model are investigated by URANS simulations, with a particular focus on the asymmetry of the propeller–rudder system. To this aim, captive model tests consisting of pure rudder and coupled drift–yaw motions corresponding to the steady phases of turning circle maneuvers at different rudder angles (δ=15°÷35°) are performed at the speed correspondent to Fr=0.265. Moreover, a free running maneuvering simulation is also performed to gain more insight on the transient phase of the maneuver. An identity rudder lift methodology is applied to synthesize the hull–propeller–rudder interactions by means of a flow straightening coefficient; the analysis highlights that these effects are weak and invariant with respect to the rudder angle on the windward shaft, whereas on the leeward side these effects are extremely sensitive to the evolution of the hull and propeller wake
Simulation of high pressure, direct injection processes of gaseous fuels by a density-based OpenFOAM solver
No full textThe direct injection of a gaseous fuel in internal combustion engines involves under-expanded supersonic jets and complex air/fuel fluid-dynamics. Furthermore, with the high pressure ratios between the injector and the cylinder, the gaseous flow usually becomes choked even inside the injector. Knowledge of all these phenomena is essential to achieve a deeper understanding of the air–fuel mixing process that follows, influencing combustion and pollutant formation. In this framework, this study deals with the development and validation of a fully explicit, density-based solver for supersonic compressible flows, using the OpenFOAM library and featuring Runge–kutta fourth order time discretization and the Kurganov central flux splitting scheme. This methodology was applied to analyze the inner and the external flow of an innovative, multi-hole, high pressure injector for heavy-duty vehicle applications. The adoption of multi-hole patterned injectors in gaseous fuel combustion systems is believed to be an efficient way of achieving a better air/fuel mixture and, therefore, improving the combustion reaction. The present work aims to evaluate the reliability of the aforementioned mathematical approach for such kinds of complex flows and, especially, provide a comprehensive characterization of the multi-jet spray. It was found that shock waves in the internal-nozzle deeply modify the flow development and the external Mach disk as shock cells move the mixing activity on a lateral shear layer. It was also observed that a methane cloud grows downstream and, although flammable conditions are present, it later inhibits air recirculation toward the near nozzle zone
The Role of Mesh Generation, Adaptation, and Refinement on the Computation of Flows Featuring Strong Shocks
No full textWithin a continuum framework, flows featuring shock waves can be modelled by means of either shock capturing or shock fitting. Shock-capturing codes are algorithmically simple, but are plagued by a number of numerical troubles, particularly evident when shocks are strong and the grids unstructured. On the other hand, shock-fitting algorithms on structured grids allow to accurately compute solutions on coarse meshes, but tend to be algorithmically complex. We show how recent advances in computational mesh generation allow to relieve some of the difficulties encountered by shock capturing and contribute towards making shock fitting on unstructured meshes a versatile technique
Numerical evaluation of force coefficients of a yawing flat plate
No full textIn this paper the coupled role of the keel vortex and of the wave phenomena on hydrodynamic loads are investigated in the case of a yawed flat plate piercing the free surface and moving along either a straigth course or a circular path.
The flow is studied by means of an inviscid rotational model based on a integral representation for the velocity field in terms of source and surface vorticity distributions. The related integral equations are numerically solved by coupling a source panel technique together with the vortex lattice method for treating the surface vorticity integrals. The free surface conditions are linearized, while the vortex shedding has been modelled in a simplyfied nonlinear manner.
Extended comparisons with experiments and previous numerical computations show the importance of modeling the keel vortex shedding for the correct prediction of the. hydrodynamic loading. Beside, the role of free surface in determining the forces is discussed. In particular, it is numerically shown that for increasing Froude number the standard double model linearization leads to a significant overprediction of loads while the simpler Kelvin free surface condition appears to be more suitable for dealing with high Froude number cases
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