Numerical simulation of the formation of vortices around rigid cylinders inside a channel using Immersed Interface method

The numerical simulation of the flow of fluid through one or a set of objects that causes the flow to separate from the surface of them has been the subject of interest by researchers over the past few decades. One of the most important types of these objects is those with a square cross section which have important and diverse applications in different industries. One of the practical applications of these types of streams is flow around chimneys, high-rise buildings, naval structures, suspended bridges, airplane wings, ship propellers and ducts. In this research, the immersed interface method is used which is a non-conforming method to the boundary. Eulerian mesh for fluid field, and Lagrangian mesh for solid field is used. The connection of these two networks is established by the Dirac Delta function. Considering the cylinder as a rigid immersion boundary within the flow. First, the flow around a square cylinder was simulated and we surveyed different flow patterns. The changes in the number of Strouhal and the Drag coefficient were investigated in different Reynolds. The flow around the two cylinders was simulated. It was observed that with the increase of Reynolds number and the gap between cylinders, the vortex shedding (Strouhal number) would increase.

Accurate tracer particles of baryon dynamics in the adaptive mesh refinement code Ramses

We present a new implementation of the tracer particles algorithm based on a Monte Carlo approach for the Eulerian adaptive mesh refinement code RAMSES. The purpose of tracer particles is to keep track of where fluid elements originate in Eulerian mesh codes, so as to follow their Lagrangian trajectories and re-processing history. We provide a comparison to the more commonly used velocity-based tracer particles, and show that the Monte Carlo approach reproduces the gas distribution much more accurately. We present a detailed statistical analysis of the properties of the distribution of tracer particles in the gas and report that it follows a Poisson law. We extend these Monte Carlo gas tracer particles to tracer particles for the stars and black holes, so that they can exchange mass back and forth between themselves. With such a scheme, we can follow the full cycle of baryons, that is, from gas-forming stars to the release of mass back to the surrounding gas multiple times, or accretion of gas onto black holes. The overall impact on computation time is ∼3% per tracer per initial cell. As a proof of concept, we study an astrophysical science case – the dual accretion modes of galaxies at high redshifts –, which highlights how the scheme yields information hitherto unavailable. These tracer particles will allow us to study complex astrophysical systems where both efficiency of shock-capturing Godunov schemes and a Lagrangian follow-up of the fluid are required simultaneously.

Simulation of Rolling Noise Based on the Mixed Lagrangian–Eulerian Method

ABSTRACT This article presents a new method for predicting rolling noise, which is an increasingly important subject not only for roads but also for the railway transportation industry and has attracted an increasing amount of attention. Unfortunately, there are no effective numerical methods to analyze and predict rolling noise because of the required solution accuracy. For example, tires are often simplified as shells or rings in rolling noise modelling, lacking the pattern information, and leading to low accuracy. The new method presented in this article is based on the mixed Lagrangian–Eulerian method, which can be used to analyze the velocity field, acceleration field, and contact deformation of rolling contact structures with large deformations. First, two kinds of tire meshes are developed: a Lagrangian mesh for the rolling tire and an Eulerian mesh that is fixed in space and that will be used in the noise simulation. A nonrotational acceleration field is constructed by mapping the acceleration of the Lagrangian mesh onto the Eulerian mesh. Then, using that acceleration field as the acoustic source, the rolling noise can be predicted numerically using the boundary element method. Comparison between the test and simulation results shows that this method provides reasonable predications. The case studies demonstrate that the rolling noise of a tire with a block pattern is mostly caused by the impact vibration of the tire pattern. The method provides a powerful tool for investigating rolling noise, especially for patterned tires.

Numerical Prediction of Heat Transfer from Localized Heating in Enclosure Using CIP Method

In this paper, two-dimensional laminar natural-convection heat transfer of air has been numerically solved by Cubic Interpolated Method known as CIP which is based on the Eulerian mesh grid generation. For this investigation a cavity has been selected as a geometry which is being heated from bottom of the cavity at three different positions, the sides of the cavity are cold and the top of the cavity is adiabatic and no heat exchange exist there. The cavity is being heated from three different position of the bottom which is equal in length and equal but in three different position of left, center and right in equally distance. The whole simulation takes place in two various Grasshof number and air has been taken as fluid inside cavity. Prantl number has been set to 0.7 throughout the simulation. Results are presented in the form of streamlines and isothermal plots inside the cavity. The results illustrate the heat for middle heated plate is distributed symmetrically through the cavity.

Numerical Simulation of the Nozzle with Self-Oscillating Flow Using the VOF Model

The jet water shape of the nozzle will become a self-oscillating shape, if the triangle and U shape models are made into the normal nozzle. Using the VOF model , the jet shape of the nozzle will be simulated through a commercial CFD software 'FLUENT'. The VOF model (Volume of Fluid) is a surface-tracking technique applied to a fixed Eulerian mesh. It is designed for two or more immiscible fluids where the position of the interface between the fluids is of interest. The CFD simulation results shows that the jet shape of the nozzle is oscillate in a fixed period.

Trajectory-Tracking Scheme in Lagrangian Form for Solving Linear Advection Problems: Preliminary Tests

A Lagrangian linear advection scheme, which is called the trajectory-tracking scheme, is proposed in this paper. The continuous tracer field has been discretized as finite tracer parcels that are points moving with the velocity field. By using the inverse distance weighted interpolation, the density carried by parcels is mapped onto the fixed Eulerian mesh (e.g., regular latitude–longitude mesh on the sphere) where the result is rendered. A renormalization technique has been adopted to accomplish mass conservation on the grids. The major advantage of this scheme is the ability to preserve discontinuity very well. Several standard tests have been carried out, including 1D and 2D Cartesian cases, and 2D spherical cases. The results show that the spurious numerical diffusion has been eliminated, which is a potential merit for the atmospheric modeling.