Search results for "hydrodynamic"
showing 10 items of 530 documents
The smoothed particle hydrodynamics method via residual iteration
2019
Abstract In this paper we propose for the first time an iterative approach of the Smoothed Particle Hydrodynamics (SPH) method. The method is widespread in many areas of science and engineering and despite its extensive application it suffers from several drawbacks due to inaccurate approximation at boundaries and at irregular interior regions. The presented iterative process improves the accuracy of the standard method by updating the initial estimates iterating on the residuals. It is appealing preserving the matrix-free nature of the method and avoiding to modify the kernel function . Moreover the process refines the SPH estimates and it is not affected by disordered data distribution. W…
Experimental and numerical investigation of the leading edge sweep angle effect on the performance of a delta blades hydrokinetic turbine
2020
Abstract In the last decades, an increase of energy consumption has been noted around the world. Hence, the excessive use of fossil fuels can lead to serious environmental concerns. Indeed, the use of renewable energy sources is needed to reduce the greenhouse gas effects and the CO2 emissions in the atmosphere. Small-scale hydropower could be an interesting and renewable alternative solution. The cross-flow turbines present several advantages compared to the axial-flow turbines. Therefore, increasing efforts are taken to enhance the efficiency and extend the applicability of the cross-flow turbines. In this paper, experimental investigation was carried out to evaluate the performance of a …
Numerical investigation of rain droplet impact on offshore wind turbine blades under different rainfall conditions: A parametric study
2020
The leading edge of a fiber composite wind turbine blade (WTB) is prone to erosion damages due to repeated rain droplet impact during its service life. Such damages are critical to the blade's aerodynamic as well as structural performance, ultimately resulting in substantial repair costs. An effective design of a coating material for WTB is necessary and its analysis must include variables associated with erosive rain droplets such as (1) droplet diameter, (2) impact velocity, and (3) droplet impact angle. The present paper develops and validates a coupled fluid structure interaction (FSI) computational model for simulating rain droplet impact on WTBs, where the structure domain is modelled…
The magnetohydrodynamic force experienced by spherical iron particles in liquid metal
2016
Abstract The paper contains a theoretical investigation of magnetohydrodynamic force experienced by iron particles (well-conducting and ferromagnetic) in well-conducting liquid. The investigation is performed by extending the Leenov and Kolin's theory to take into account the second-order effect. Therefore, the limits of the parent model are taken over to the present results. It is found that the effective conductivity of iron particles in liquid metal, which is important for practical application of the theoretically obtained force, is approximately equal to 1.5·106 S/m. The last result is obtained using a quasi-empirical approach – a comparison of experimental results with the results of …
Numerical and experimental study of liquid metal stirring by rotating permanent magnets
2018
In this work, we study liquid gallium stirring by rotating permanent magnets. We demonstrate possibility of easily creating different flow patterns by rotating permanent magnets, which can be industrially important for controlling heat and mass transfer processes in the system. Unlike the typical approach of simulating magnet rotation as a transient problem and time-averaging the Lorentz forces, we solve the magnet rotation as a harmonic (frequency domain) problem, which leads to forces equal to time-averaged ones and decreases the simulation time considerably. Numerical results are validated using qualitative flow structure results from the neutron radiography visualization of tracer parti…
Stability of hydrodynamical relativistic planar jets : II. Long-term nonlinear evolution
2004
In this paper we continue our study of the Kelvin-Helmholtz (KH) instability in relativistic planar jets following the long-term evolution of the numerical simulations which were introduced in Paper I. The models have been classified into four classes (I to IV) with regard to their evolution in the nonlinear phase, characterized by the process of jet/ambient mixing and momentum transfer. Models undergoing qualitatively different non-linear evolution are clearly grouped in well-separated regions in a jet Lorentz factor/jet-to-ambient enthalpy diagram. Jets with a low Lorentz factor and small enthalpy ratio are disrupted by a strong shock after saturation. Those with a large Lorentz factor an…
Quasi-Periodic Pulsations in Solar and Stellar Flares: A Review of Underpinning Physical Mechanisms and Their Predicted Observational Signatures
2021
The phenomenon of quasi-periodic pulsations (QPPs) in solar and stellar flares has been known for over 50 years and significant progress has been made in this research area. It has become clear that QPPs are not rare—they are found in many flares and, therefore, robust flare models should reproduce their properties in a natural way. At least fifteen mechanisms/models have been developed to explain QPPs in solar flares, which mainly assume the presence of magnetohydrodynamic (MHD) oscillations in coronal structures (magnetic loops and current sheets) or quasi-periodic regimes of magnetic reconnection. We review the most important and interesting results on flare QPPs, with an emphasis on the…
Relativistic MHD simulations of extragalactic jets
2005
We have performed a comprehensive parameter study of the morphology and dynamics of axisymmetric, magnetized, relativistic jets by means of numerical simulations. The simulations have been performed with an upgraded version of the GENESIS code which is based on a second-order accurate finite volume method involving an approximate Riemann solver suitable for relativistic ideal magnetohydrodynamic flows, and a method of lines. Starting from pure hydrodynamic models we consider the effect of a magnetic field of increasing strength (up to β ≡ |b|2/2p ≈ 3.3 times the equipartition value) and different topology (purely toroidal or poloidal). We computed several series of models investigating the …
The force-free twisted magnetosphere of a neutron star
2016
We present a detailed analysis of the properties of twisted, force-free magnetospheres of non-rotating neutron stars, which are of interest in the modelling of magnetar properties and evolution. In our models the magnetic field smoothly matches to a current-free (vacuum) solution at some large external radius, and they are specifically built to avoid pathological surface currents at any of the interfaces. By exploring a large range of parameters, we find a few remarkable general trends. We find that the total dipolar moment can be increased by up to $40\%$ with respect to a vacuum model with the same surface magnetic field, due to the contribution of magnetospheric currents to the global ma…
Instability of relativistic sheared jets and distinction between FRI and FRII sources
2002
We investigate the shear-driven instability of nonmagnetic relativistic jets with the bulk velocity, V , dependent on the cylindric radius, r. It is shown that instability can arise for any dependence of the velocity (or the Lorentz factor that is the same) on r. The shear-driven instability can e ectively operate in the whole volume of a jet. The growth time can be shorter than that of the Kelvin-Helmholtz instability. The considered instability leads to a turbulization of jets and can account for a distiction between the jets in the FRI and FRII sources. Urpin, V., Vadim.Urpin@uv.es