Symmetrization of laminar viscous fluid flow in a flat diffuser by periodic impaction on the inlet flow velocity

This paper shows a method of symmetrization of an asymmetric flow of a vis-cous incompressible fluid in a flat diffuser using a weak periodic vibration ef-fect on the velocity input flow. The results are obtained for a viscous incom-pressible fluid by simulation based on numerical solving of the Navier-Stokes equations. The results of numerical simulation have shown one of the ways of symme-trization of asymmetric laminar flows of a viscous incompressible fluid in a flat diffuser with a weak periodic effect on the input flow velocity. It is shown that vibration effects, even at amplitudes less than 1% of the velocity can symmetrize the fluid flow in the diffuser. Richardson's "annular effect" for a harmonic oscillating fluid flow in the diffuser was shown.Comment: arXiv admin note: text overlap with arXiv:2203.0465

Simulation of Water Entry and Exit of a Circular Cylinder Using the ISPH Method

Simulations of free surface flows, as well as flows with moving boundaries in general, are quite difficult to describe with the classic, mesh-based Eulerian methods, such as finite difference, finite volume, and finite element methods. Meshless Lagrangian methods or a combination of Eulerian-Lagrangian methods that have the ability to describe the free surface with large deformations have been developing in the past fifteen years. In this paper, the Lagrangian incompressible smoothed particle hydrodynamics (ISPH) method for simulating the dynamics of an incompressible viscous fluid flow is presented. The ISPH method is an attractive choice for the simulation of incompressible fluid flow because it is based on the simple SPH formulations, and it solves the pressure field implicitly using the projection scheme of solving the Navier-Stokes equations. A computer code for the simulation of the viscous incompressible fluid flow based on the ISPH method is developed. Water entry and water exit of a rigid body are very important phenomena in marine hydrodynamics and there have been many studies and experiments on the topic. The cases of two-dimensional water entry and water exit of a circular cylinder at a forced constant velocity were studied in order to verify and validate the method. Numerical simulations of a rigid circular cylinder falling onto initially calm water at a constant entry velocity were carried out. Also numerical simulation of the water exit of a circular cylinder, initially fully immersed, was performed. The obtained numerical results are in good agreement with the experimental and analytical ones found in the literature

Simulation of Water Entry and Exit of a Circular Cylinder Using the ISPH Method

Simulations of free surface flows, as well as flows with moving boundaries in general, are quite difficult to describe with the classic, mesh-based Eulerian methods, such as finite difference, finite volume, and finite element methods. Meshless Lagrangian methods or a combination of Eulerian-Lagrangian methods that have the ability to describe the free surface with large deformations have been developing in the past fifteen years. In this paper, the Lagrangian incompressible smoothed particle hydrodynamics (ISPH) method for simulating the dynamics of an incompressible viscous fluid flow is presented. The ISPH method is an attractive choice for the simulation of incompressible fluid flow because it is based on the simple SPH formulations, and it solves the pressure field implicitly using the projection scheme of solving the Navier-Stokes equations. A computer code for the simulation of the viscous incompressible fluid flow based on the ISPH method is developed. Water entry and water exit of a rigid body are very important phenomena in marine hydrodynamics and there have been many studies and experiments on the topic. The cases of two-dimensional water entry and water exit of a circular cylinder at a forced constant velocity were studied in order to verify and validate the method. Numerical simulations of a rigid circular cylinder falling onto initially calm water at a constant entry velocity were carried out. Also numerical simulation of the water exit of a circular cylinder, initially fully immersed, was performed. The obtained numerical results are in good agreement with the experimental and analytical ones found in the literature

Conditions at the downstream boundary for simulations of viscous incompressible flow

The proper specification of boundary conditions at artificial boundaries for the simulation of time-dependent fluid flows has long been a matter of controversy. A general theory of asymptotic boundary conditions for dissipative waves is applied to the design of simple, accurate conditions at downstream boundary for incompressible flows. For Reynolds numbers far enough below the critical value for linear stability, a scaling is introduced which greatly simplifies the construction of the asymptotic conditions. Numerical experiments with the nonlinear dynamics of vortical disturbances to plane Poiseuille flow are presented which illustrate the accuracy of our approach. The consequences of directly applying the scalings to the equations are also considered

Simulation of flows with violent free surface motion and moving objects using unstructured grids

This is the peer reviewed version of the following article: [Löhner, R. , Yang, C. and Oñate, E. (2007), Simulation of flows with violent free surface motion and moving objects using unstructured grids. Int. J. Numer. Meth. Fluids, 53: 1315-1338. doi:10.1002/fld.1244], which has been published in final form at https://doi.org/10.1002/fld.1244. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.A volume of fluid (VOF) technique has been developed and coupled with an incompressible Euler/Navier–Stokes solver operating on adaptive, unstructured grids to simulate the interactions of extreme waves and three-dimensional structures. The present implementation follows the classic VOF implementation for the liquid–gas system, considering only the liquid phase. Extrapolation algorithms are used to obtain velocities and pressure in the gas region near the free surface. The VOF technique is validated against the classic dam-break problem, as well as series of 2D sloshing experiments and results from SPH calculations. These and a series of other examples demonstrate that the ability of the present approach to simulate violent free surface flows with strong nonlinear behaviour.Peer ReviewedPostprint (author's final draft