The study of the properties of fluids and gases in motion

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63 views

WENO reconstruction of flux involving derivative terms

I have a set of modified compressible Euler equations that I would like to solve using a WENO method. The issue is that the modified flux function involves derivative and filtering terms and I'm not ...
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1answer
50 views

How to model waterflow when only a couple of sample points available

Figure below depicts a cross section of a creek for which I am trying to measure the water flow for that section. What we have as inputs are a bunch of sample points on the river. For each sample ...
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1answer
78 views

Dual time stepping for fluid dynamics

I'm attempting to implement the Weiss and Smith preconditioner in an existing finite volume code and I am struggling with the idea of dual time stepping. My inner time steps are predictor-corrector, ...
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0answers
44 views

How to create a mesh with boundary layers and y+ < 1 using snappyHex,OpenFOAM? [closed]

I have been tirelessly trying out different permutation and combination of layer control parameters, so that I can get proper boundary layers and y+ < 1, but to no good effect, when I increase ...
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0answers
72 views

High-order continuous Galerkin Navier-Stokes solver in deal.II

I looked at the list of publications related to deal.II, but it seems that when it comes to Navier-Stokes equations, everyone speaks about Discontinuous Galerkin solver in their papers. I know there's ...
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1answer
122 views

Euler's equations 1d for pipe, Inlet boundary conditions

$\def\rmin{{\mathrm{in}}}$ $\def\l{\left}\def\r{\right}$ $\def\tagl#1{\tag{#1}\label{#1}}$ I am using the one-dimensional finite volume method to calculate the air flow in some tube. For subsonic ...
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0answers
44 views

Turbulence: Suggest research papers similar to this experiment

I am trying to find the effect on turbulence characteristics when flow passes through a converging section. For this experiment I will use a PIV system to gather data about the flow. However, I could ...
3
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1answer
79 views

Euler's equations for a tube with varying cross-section

$\def\pd{\partial}$ $\def\l{\left}\def\r{\right}$ $\def\mdot{{\dot{m}}}$ $\def\eps{\varepsilon}$ Consider a tube with longitudinal coordinate $x$ from $0$ to $l$ and varying cross-section $A(x)$. ...
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1answer
59 views

2d pseudo-spectral turbulence simulation with random initial velocities

I am trying to write a 2d pseudo-spectral DNS code with random initial velocities. This is kind of a classic simulation where the very tiny vortices group together forming larger and larger vortices ...
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0answers
40 views

Numerical strategy to detect the point of detachment over the wall of cylinder in the simulation of unsteady flow over circular cylinder

I am working on unsteady simulation of flow over circular cylinder where we get Kármán vortex street. Kármán vortex street is a repeating pattern of swirling vortices caused by the unsteady separation ...
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1answer
47 views

“boundary” vs “interface”?

I am working with biofilm and there are many documents talking about boudary conditions while others talks about interface or both of boundary and interface. So, boundary and interface are the same ...
1
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0answers
109 views

A Simple Standard Test Case for Pipe Flow

Original Question I am familiarising myself with OpenFOAM and want to run a simple pipe flow case. I would like to be able to compare my computational pipe-flow results to a well established case ...
3
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2answers
102 views

Darcy Flow - Solution by Finite Difference

I'd like to model the fluid flow through a porous medium using finite differences. Since I am new to this numerical technique, I have a simple question. I use the following set of equations to ...
3
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0answers
82 views

Transport Equation in a Tube: Source Term on Boundary

I'm modeling mass transport in a flow reactor. The flow reactor is a tube, which allows me to use cylindrical symmetry in solving the Convection-Diffusion-Reaction (CDR) Equation, which governs the ...
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1answer
156 views

Reconstructing fluxes

Given a standard advection equation, we write the update as $$ q_i^{n+1}=q_i^n+\frac{\Delta t}{\Delta x}\left(F_i^{n+1/2}-F_{i+1}^{n+1/2}\right) $$ with $F_i^{n+1/2}=F\left(q_i^n,\,q_i^*\right)$ and ...
2
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0answers
48 views

When a flow changes its character from time-periodic to chaotic?

In this simple benchmark describing the flow around a disc in the plane with stationary bc, for low Reynolds numbers the solution is stationary and for higher RN it is periodic in time. Is there a ...
6
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2answers
102 views

Simulating advection over a network of 1D pipes

I am trying to create a simulation to help visualize how different chemical components flow through a network of pipes with associated valves, pumps, and chemical inputs. In this simulation, the pipes ...
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2answers
114 views

Inverting a pressure matrix for fluid simulation

I am implementing a fluid simulator as my numerical methods course project and I have to compute pressure at each simulation step. Basically, that means solving an equation $Ap = b$, where $A$ is a ...
3
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1answer
131 views

Problem in Discretizing Convection-Diffusion-Reaction equation

I'm trying to solve the Convection-Diffusion-Reaction (CDR) equation on a rectangular domain, using cylindrical coordinates and Finite Difference Methods (FDM) (this approximates a flow reactor). ...
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0answers
40 views

Anyone knows why surface-to-ambient radiation is not applicable to interior boundaries in comsol?

I have a 2D model consisting of a square piece of electrical insulator and in the middle I have a thin rectangle acting as a wire. I'm running a current through it so I heat it up to 500 K. Clearly it ...
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1answer
55 views

zero pressure gradient flat plate CFD++

I'm trying to perform a trasient simulation of a subsonin flow over a flat plate in CFD++. I want to impose a ramp profile on the velocity at the inlet, like for instance a smooth step, and look at ...
3
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0answers
227 views

Immersed boundary method

I'm trying to use immersed boundary method for the 3D flow problem (Navier-Stokes equations), but I'm maybe misunderstood something in this method. Main principles I took from this book. I use the ...
2
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0answers
94 views

can we calculate y+ apriori?

perhaps the most idiotic question I ever asked. people throw around the parameter $y^+$, as if it is the be all and end all of CFD parameters and use it as if everyone and their dog know how to ...
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0answers
52 views

openFOAM RAS to LES

I successfully ran a RANS simulation of industrial fan with all wall BCs, pimpleDyMFoam solver and spallart-almaras RAS model. I got results upto some time, I would like to continue that simulation ...
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0answers
105 views

how to visualize velocity from Lagrangian particle tracking method

I have few particle's position and velocity information as a function of time. Particle is following a trajectory path, while doing so, one particle may disappear, other particle may appear. Particle ...
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1answer
187 views

Lid driven cavity flow problem to solve with the help of projection method and use coding in fortran 90 [closed]

I want to solve Lid driven cavity flow with the help of projection method i want to make own fortran program to solve two dimensional unsteady flow. I propose to solve the equations in the following ...
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1answer
131 views

how to specify an arbitrary surface for field average in openfoam?

So, I am running this openfoam simulation and I need areaAverage velocity and pressure on a surface,currently the entire plane is being read, I wan't to specify my own in sampleSurfaceDict, ...
3
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1answer
95 views

Can one use incompressible flow approximation for fluid flow in heated pipes?

I was wondering if the use of incompressible flow approximation for fluid flow in heated pipes is reasonable. A previous question (Definition of incompressible flow) seemed to focus on Natural ...
3
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4answers
189 views

Looking for analytic solutions to time dependent fluid flow problems

I'm looking for analytic solutions to time dependent fluid flow problems (can be compressible or incompressible, Euler or Navier-Stokes equations). The main thing though is that I'd like there to be ...
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0answers
99 views

Problem with initial/boundary conditions for 1D flow simulation

I am trying to simulate numerically the flow between the atmospher and a pipe in Matlab, where the initial condition within the pipe is ...
11
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2answers
357 views

Discontinuous Galerkin: Nodal vs Modal advantages and disadvantages

There are two general approaches to representing solutions in the discontinuous galerkin method: nodal and modal. Modal: Solutions are represented by sums of modal coefficients multiplied by a set ...
5
votes
2answers
125 views

What are some of the differences between using a Lagrangian and Eulerian framework to quantify passive scalar dynamics?

On one hand, one may seed the domain with particles and track their trajectories in the Lagrangian sense by implementing a Lagrangian particle tracking model. On the other hand, one may use the ...
5
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1answer
134 views

Riemann Solver in WENO methods

I'm reading now Shu, C.-W. (1999). High Order ENO and WENO Schemes for Computational Fluid >Dynamics. (T. J. Barth & H. Deconinck, Eds.)Lecture Notes in Computational >Science and Engineering, ...
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1answer
204 views

Basic Finite Element Method (FEM) question: assembly and re-assembly

I'm reading up on the Finite Element Method (in Zienkiewicz's Book) , so I understand better what I'm doing in FEniCS and COMSOL. Currently, I'm wondering about this: Using FEM to solve fluid flow ...
3
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0answers
73 views

N-body simulation for particles

I would like use N-body simulation for measure a torque on an object in a liquid (helium). It's a 2D study. On the site : http://www.browndeertechnology.com/docs/BDT_OpenCL_Tutorial_NBody-rev3.html I ...
4
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2answers
286 views

beginning Computational Fluid Dynamics

I am starting a self study course in computational fluid dynamics. I use ( An introduction to computational fluid dynamics : the finite volume method) I am learning Python programming language. The ...
5
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5answers
429 views

Open source codes for 2D instationary Navier Stokes equations

What open source tool can be recommended for solving 2D instationary Navier Stokes equations (in simple geometries, but with high Reynolds numbers)? Most packages I found, I'm not very lucky with. ...
6
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2answers
178 views

Feasibility and software for acoustic simulation

I'm looking at doing a finite-element simulation of air flow essentially for the purposes of approximating the response to an external audio impulse of a smallish (~10-30 cm scale), stationary ...
0
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0answers
55 views

Using Lattice Boltzmann for something different from Navier Stokes

First of all: is it possible to use the Lattice Boltzmann method if no equilibrium distribution exists? Secondly, if I have a PDE, how do I derive the corresponding collision function?
3
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1answer
302 views

Stability of numerical method for 1D Burger's equation

I am trying to solve 1D viscous Burger's equation numerically and I cannot apply von Neumann analysis because the equation is non-linear. How do I predict the stability criteria for my system? I also ...
5
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0answers
135 views

Negative viscosity stabilized by fourth order terms

I am trying to solve a "Navier-Stokes"-type problem where the viscosity is negative. Of course this renders the equation unstable and thus I add a fourth order term, so the entire equation becomes: ...
2
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0answers
71 views

What are the governing equations solved in coupled atmosphere-ocean models?

In (hydrostatic) atmospheric general circulation models, for example the so-calle Primitive Equations, consisting of the horizontal momentum equation, the hydrostatic balance, the continuity equation, ...
1
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1answer
97 views

Simulate aerodynamics of a general shape object

I'm trying to code a simple physics simulator in C++ but I'm stuck on the air resistance issue. Surfing the Internet I only find a drag coefficient for very basical area shapes when the air is ...
2
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0answers
37 views

Solving nonlinear wave equation in a dispersive infinite waveguide

I would like to solve a three-dimensional nonlinear wave equation in an infinite cylindrical waveguide numerically. Since the waveguide is dispersive, shocks are less likely to form. Both the ...
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0answers
32 views

Spectra of the energy flux VS transfer spectra?

In direct numerical simulation of turbulence what is the advantage to look at the spectra of the energy flux rather than the transfer spectra? The transfer spectra corresponds to the triple-velocity ...
0
votes
1answer
93 views

What is the time_step and how many iterations required for convergence purpose in fluids simulation [closed]

My question seems elementary: I use a new numerical method to do fluids dynamics simulation. I use t=0.001s as the time step. But I don´t know how many iterations I need to achieve velocity ...
3
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0answers
95 views

How to estimate if a velocity field is statistically homogeneous?

For a 3D velocity field $\mathbf{u}$ obtained by direct numerical simulation. Assuming that the field is defined on a periodic domain $\mathcal{P}$ of periodicity $L_x$ in the $x$ direction, $L_y$ ...
3
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1answer
186 views

Non-linear ordinary differential equation in the modeling of the oscillation of a meniscus

I am trying to model the oscillation of a fluid miniscus in a straw when the miniscus is displaced from its equilibrium level. The results was the following non-linear ODE: $$y''= 1/y - 1.$$ This ...
2
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2answers
203 views

CFD mesh generation

Is there any libraries(python is preffered) for generation rectangular 3d mesh (for using with the finite difference method), which will be consistent with boundaries? (I've asked this question at ...
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0answers
65 views

Boussinesq thermal equations & Ansys numerical models

I have to model the boussinesq thermal equations on a 2D Semicircular canal of Ear with Ansys software.. I'm not so familar with Boussinesq eqations and I have trouble with finding the parameters to ...