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Questions tagged [fluid-dynamics]

The study of the properties of fluids and gases in motion

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16 views

Using Modules; creating files and importing ? Please see attached links [on hold]

I am a super n00b beginner, I have been teaching myself python concepts for the last couple of months using juptyer notebook, and lessons in CFD & similar subjects that I am conceptually familiar ...
0
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0answers
38 views

Classifying a nonlinear numerical instability

I am using a piece of code to study magnetohydrodynamics and I have encountered a problem. The code is solving the ideal MHD equations, i.e. the Euler equations with the Lorentz force and Faraday's ...
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1answer
34 views

What's a time centered Riemann problem?

I am trying to understand the meshless methods as described in https://arxiv.org/pdf/1409.7395.pdf. I'm having trouble understanding the following step: (Page 7, just after equation 17) Now, rather ...
2
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0answers
45 views

Why do stabilized formulations for the Navier-Stokes equation maintain the convergence rate for high order polynomial interpolation?

I have a quick questions which has been troubling me lately. When reading the FENICS Finite Element Book they assess various approaches to solver the Stokes equation. Obviously, they discuss the ...
3
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2answers
120 views

Asymptotic error of forward Euler

I'm trying to understand the asymptotic error behaviour of forward Euler (finite difference method), as timesteps are decreased (refined), so I feel trust in the method of manufactured solutions (MMS)....
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0answers
34 views

Lax-Friedrich's Method in Conservative Form. (Burger's equation)

I don't understand how to calculate conservative form in general. So the idea is that you imitate the integral for Finite-Volume methods. Then your flux cannot be evaluated in your node but in your ...
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1answer
35 views

Modeling Diodes in Autodesk CFD

I'm extremely new to Autodesk CFD, and I'm working on a project that deals with diodes heating up and cooling down based on a fixed temperature regulated by a temperature switch. Basically, I have a ...
2
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1answer
79 views

Numerically solving a partial differential equation

I am trying to numerically solve the following PDE, $$\frac{\partial u^A}{\partial t} = c_1\frac{\partial^2 u^A}{\partial^2x} \,,$$ where $c_1$ is a constant. The above can be discretized using the ...
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2answers
62 views

Guaranteed equality between binary results with increasing MPI processes

Testing on an MPI scientific code for compressible flow dynamics I noticed that the results may depend on the number of processors used for the calculation. In fact, comparing the binary files they ...
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0answers
33 views

Has there been a comparison bewteen SIMPLE/SIMPLER and JFNK for steady CFD?

I'm looking for a comparison between the Jacobian-Free Newton-Krylov (JFNK) method performance compared to the conventional CFD nonlinear solution methodologies like SIMPLE. Does anyone know if such ...
2
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0answers
31 views

WENO methods: why the characteristic wise method resulting big errors?

I was doing my research/project using WENO as the limiter in finite volume methods to solve hyperbolic conservation law. I have no idea why the result in the characteristic wise method has a big error ...
3
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1answer
52 views

Plotting or Visualizing a Higher dimensional vector field

I am trying to visualize a higher dimensional vector field. Is there a way to do this. I asked this question here, I was told to post it here. As an example, one can use $$\begin{eqnarray} \dot{x}...
4
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1answer
63 views

How to go from turbulent RANS to laminar Navier-Stokes and Euler

SU2 is an open-source CFD suite that is built around a RANS-solver. The main PDE that is solved, is the following: $$ \frac{\partial}{\partial t} \mathbf{U} + \nabla \cdot \mathbf{F^c} - \nabla \cdot ...
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0answers
28 views

How to remove sigularities from 3D Vortex Lattice Method

I'm trying to solve aerodynamics of whole aircraft by vortex lattice method (or deeper here). The problem is that sometimes trailing vortex filaments from Horse Shoe Vortexes of main wing hits panels ...
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0answers
62 views

Oscillations in force coefficients from CFD simulations

I have carried out a CFD simulation (with finite volume method) to investigate the unsteady force enforced to the vehicle body. The horizontal tail keeps flapping in sinusoidal function. As a result, ...
3
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0answers
43 views

Should I expect computational gains using a second-order splitting method here?

I am trying to solve a three-dimensional baroclinic transport problem. The hydrodynamic (three-dimensional shallow water) equations are: \begin{align} \nabla \cdot \vec{v} = 0, \tag{1} \\ \frac{\...
2
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1answer
81 views

When writing a research article, how to deal with deviations from theoretical expectations due to numerical errors?

We research the aerodynamics of the vehicle. Usually, there exists turbulence, which will cause the time-varying measurement of the force. The unsteady flow field determines we could not get a ...
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2answers
77 views

Demo example for OpenFOAM with CUDA

I am looking for a simple usage example/demo of OpenFOAM + CUDA and would like to understand how exactly OpenFOAM benefits from CUDA. The thing is I do not have any background in fluid dynamics and so ...
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1answer
31 views

Loss of energy when using Roe Solver for solving onedimensional Shallow Water Equations

I have written a Roe solver with Harten entropy fix code in Matlab to numerically solve the one-dimensional Shallow Water Equations. : \begin{eqnarray} \dfrac{\partial h(x,t)}{\partial t} + \dfrac{\...
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0answers
40 views

Poincare map for Arnold-Beltrami-Childress Magnetic Field in Python

I want to plot the Poincare map for Arnold-Beltrami-Childress magnetic field for parameters $A=1, B=0.816, C=0.5773$ in Python for the Poincare section $z=0$. Also, I am not able to understand what ...
1
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0answers
73 views

Comparison between FEM and FDM methods for flow simulations

What are the main differences between finite element and finite difference approach for incompressible flow simulations? I have a vague idea about how FE methods rely on minimizing the residual over ...
4
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0answers
131 views

A good 2D finite difference for the continuity equation

How could I go about solving the continuity equation below in 2D? $$\frac{\partial \rho}{\partial t} + \nabla \cdot \left(\rho u\right)=0$$ I saw that a similar question was posted here: A good ...
2
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1answer
73 views

build a simple incompressible solver with spectral method

I am trying to build a simple solver for the incompressible fluid in a periodic box to learn the spectral method. I am following the textbook (Peyret R. Spectral methods for incompressible viscous ...
2
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2answers
103 views

Algorithm to generate water flow map, given a terrain

I've posted the same question at GameDev Stack Exchange, but unfortunately I am not getting any response. So I am going to post ( and reword) it here. Hopefully I can get an answer! I have a terrain (...
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2answers
99 views

Conservative formulation for compact finite difference schemes

At the Section 4.2 of this paper (which is very well known in the computational fluid dynamic community), the author claims that it is enough, for the compact finite difference formulation in eq. 4.2....
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0answers
48 views

fourth order Poisson iterative solver --in Matlab

I want to calculate the stream function $\psi$ starting from a velocity field $(u,v)$ (such that $u=-\frac{\partial\psi}{\partial y}$ and $v=\frac{\partial\psi}{\partial x}$). I thus calculate the ...
3
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0answers
117 views

Finite Element Stabilization for Drift-Diffusion/Advection-Diffusion Equations

I've tried my best to look through the relevant suggested similar questions when posting this, and hopefully this contains enough new material to not be considered a duplicate. I'm currently trying ...
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0answers
49 views

Stokes flow around rigid body

I'm trying to simulate Stokes flow in 2D around an arbitrary polygon (representing a rigid body). I'd like to get both the effect of the body on the flow velocity and the forces on the body by the ...
0
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1answer
112 views

Unphysical Behaviour Characteristic-Wise WENO5-Z

I am currently working on a scheme that uses finite differences WENO5-Z with 3rd Order Runge-Kutta time integration for solving the Euler equations. The code projects the conserved variables and ...
1
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2answers
277 views

Which python library for GPU sparse linear system solver library

I have a fluid dynamic solver written in python which I want to accelerate by moving the most expensive computations to the GPU. Ideally all arrays and sparse matrices used in my code should remain on ...
1
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1answer
62 views

Defining dimensionless tempearture for Periodic flow systems

Given a flow inside a square duct with constant temperature at the walls $(T_{w1} = T_{w2} = T_w)$ the physical property in terms of temperature that repeats itself in a periodic fashion is the $\...
3
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0answers
79 views

Non-reflecting boundary conditions for compressible Navier-Stokes equations

I have some questions about the implementation of non-reflecting OUTFLOW boundary condition for Navier Stokes equations. Following Poinsot, Lele "Boundary Conditions for Direct Simulations of ...
2
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0answers
82 views

Simulation of surface tension-dominated interfaces

I want to simulate the shape of the free surface in a small fuel tank in microgravity, which is very slowly being emptied. The tank is not symmetric, the geometry is given by CAD (e.g. step file). ...
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2answers
100 views

Second derivative in coordinate invariant form

To solve stationary, incompressible, inviscid and irrotational flow around a circular cylinder, I am using general coordinates. Since the flow is symmetrical, we only consider the upper half of the ...
1
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2answers
123 views

Find classical solution of transport equation with FDM

We know the classical solution of transport equation is determined by one initial (boundary?) condition, for example, the solution of $$\frac{\partial u(t,x)}{\partial t}+\frac{\partial u(t,x)}{\...
0
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1answer
242 views

Finite volume software packages

There are many software packages for the finite element method, of which the most popular are listed e.g. on Wikipedia. When it comes to the finite volume method, I'm not aware of any similarly ...
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1answer
106 views

FFT Poisson Solver for non-uniform grid

I have a 3D solver for the incompressible Navier-Stokes equations which uses a FFT library for the Poisson equation with a uniform grid on all directions. In 2D the Poisson equation is given by: $$ ...
2
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3answers
353 views

Finite volume piecewise linear 2D advection develops instability

I'm developing a finite volume solver for the simple twodimensional advection equation with constant velocities $u, v$ and constant mesh spaces $\Delta x$: $$ \frac{\partial \rho}{\partial t} + u \...
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0answers
73 views

(Approximate) Incremental Projection Method for Navier-Stokes equations

I am trying to implement an incremental projection method for the 2D incompressible Navier-Stokes. The type of projection method I am trying is $$ \frac{u^{*} - u^{n}}{dt} = - \nabla p^{n} - u \cdot ...
0
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1answer
307 views

Proper boundary conditions for potential flow around cylinder

I am computing the stationary, incompressible, inviscid and irrotational flow around a circular cylinder using a discretization in general coordinates. I derived a PDE and proper boundary conditions ...
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1answer
87 views

Simulating Stokes flow with an obstacle

I was asked to compute the Stokes flow (i.e. a low Reynolds fluid) near and obstacle. This is the first time I face a fluid and I am lost. What reference/general ideas/big theorems can you recommend ...
2
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1answer
80 views

Computational Fluid Dynamics: Question on a third-order accurate finite difference approximation

According to this paper the following finite difference approximation is third-order accurate: $$\frac{d\rho_j}{dx}\approx\frac{2-\eta}{3}\frac{\rho_{j+1/2}-\rho_{j-1/2}}{\Delta x}+\frac{1+\eta}{3}\...
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0answers
55 views

Vortex Lattice Method: better basis than horse-shoe vortex?

I read several introductory texts about potential flow and vortex lattice method. Basically, it is fitting of some velocity field described by conditions on velocity at some control points using basis ...
5
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3answers
204 views

How can I make sure the flow is divergence-free when I use moving mesh?

I am using projection method and P2/P1 finite element method to solve the incompressible Navier-Stokes equations while the mesh is constantly adapted as the body moves (edge swapping, splitting and ...
1
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0answers
77 views

Computational approaches to analyse numerical solutions

I apologise beforehand if the question isn't well defined or is too broad, I'm just having some difficulty finding the information I need. I also apologise if this should have been asked on stack ...
6
votes
1answer
136 views

Pressure definition/convergence issues for the Incompressible Navier-Stokes when using a stabilized P1-P1 finite element formulation

I believe this might be a recurring topic, but i have not found a post that directly related to this issue. I come from a finite volume background and my experience is more with predictor-corrector ...
7
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4answers
189 views

In Matlab, how can I be consistent with units?

I am modeling some aerodynamics equations and am using meters / centimeters, kilograms, and seconds. I've heard that, "matlab doesn't know units". So, how can I make sure that it does? Just ...
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0answers
50 views

Detecting stability in solutions to coupled nonlinear equations in aerodynamics,

I'm studying a quasi-steady force model (published in a fluid dynamics journal) that consists of coupled, nonlinear ODEs that describe unsteady aerodynamics -- recently, my advisor and I have found ...
0
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2answers
218 views

How to represent CFD result when I use grid-centered FVM?

My variables are stored at the center of the cells. How can I transfer these values to grid points? If I calculate the algebraic average value there may be a shock.
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0answers
38 views

CFD Mass exchange across a reactive front

I have a CFD solver at hand which can deal with 2 phases and so far is able to exchange momentum and energy across the interface, where both phases meet. How this is done is well documented in the ...