Questions tagged [fluid-dynamics]
The study of the properties of fluids and gases in motion
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0answers
29 views
Dealing with spurious oscillations in particle tracking methods
I work on modelling high intensity discharge xenon-filled lamps.
The model governing the discharge is quite complex and sadly includes fluid dynamics.
After some time, I managed to implement a finite-...
0
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0answers
7 views
Compute cell values and isosurface constant from density values of particles
I am trying to reconstruct the surface for a fluid simulation based on a list of particles using the Marching Cubes algorithm. From different resources, such as http://paulbourke.net/geometry/...
2
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2answers
136 views
Automatic timestep adjustment in a CFD solver
I have developed my own 3D Finite Volume Navier-Stokes solver based on projection method for nonuniform grid. I am looking to incorporate automatic timestep adjustment at each time step based on ...
0
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1answer
57 views
Is “Gradient Computation” in Finite Volume Discretization Really 2nd order accurate?
Based on this, pp 245, we go through these steps to discretize a gradient statement, namely $\nabla\phi$:
1- Gauss theorem reads,
$$
\int_V\nabla \phi dV = \oint_{\partial V}\phi dS
$$
2- Integral ...
0
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0answers
70 views
Double mach reflection at a inclined wedge
I am running into a strange problem when solving the 2D compressible Euler equations on a inclined wedge. To elaborate, my top boundary condition seems to emitting some type of instability. I have ...
-1
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1answer
53 views
Simulating magnetic particles in a field free point generated by two opposing magnets
This is probably a long shot with such a short time, but I've been trying to get theoretical data for a project I'm working on. The project involves using a very simplified version of magnetic ...
1
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0answers
21 views
Instability in Lattice Boltzmann Solver
I wrote a Lattice Boltzmann Solver in Rust a little while back using both the BGK approximation and the TRT (two relaxation time) method on the D2Q9 lattice. In both cases I run into major stability ...
0
votes
1answer
68 views
Imposition of Dirichlet BC for Fourier pseudospectral in this paper
I was trying to implement the algorithm from the paper "Adapting a Fourier pseudospectral method to Dirichlet boundary conditions for Rayleigh–Benard convection".
I am having a hard time to ...
0
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0answers
29 views
3D Tollmien-Schlichting Waves Imposed in a Channel Flow (Are Physics correct?, etc)
So I am trying to do some further tests on a 2nd-order code Incompressible Navier Stokes equations, by studying transition to turbulence in a Poiseuille flow. Specifically, I'm interested to see ...
0
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1answer
93 views
Finite Element - Flux Calculation
I am solving an advection-diffusion equation using the FEM and am having trouble calculating my fluxes.
I start with the equation,
$$\frac{\partial n}{\partial t} = \frac{\partial j_{n}}{\partial x}\...
6
votes
3answers
225 views
Why is the FVM traditionally used in CFD, and FEM in computational structures?
Most CFD codes use FVM. Most computational structures codes use FEM.
Why is the FEM not frequently used in CFD, and why is FVM not frequently used in FEM?
3
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2answers
110 views
Finite volume discretization of non-conservative linear hyperbolic equation
Problem. Consider the one-dimensional adjoint Euler equations for $(x,t) \in \Omega \times [0,T]$ with $\Omega \subset \mathbb{R}$ and $T > 0$
$$ \varphi_t + \Big(\frac{\mathrm{d}F}{\mathrm{d} U}(x)...
1
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1answer
138 views
Normalization of polynomials for discontinuous Galerkin methods (DGM)
I was curious if someone could share their opinion on this matter. I have noticed that some people in literature normalize their Legendre polynomials, i.e. divide or multiply the polynomial by $$\...
0
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1answer
108 views
Can OpenFoam be used for interactive simulations (flying a plane)?
I'm a software engineer and I've just started to fly rc-planes. I'm currently building a self learning auto-pilot for my plane and I'm really interested in CFD. I installed OpenFOAM and ran through ...
0
votes
1answer
147 views
Heat diffusion - Is this the correct approach to include Newmann boundary conditions?
Thank you for looking at this problem. Is this the correct approach to include neumann boundary conditions? With this solution temperature is not correct, and there´s no diffusion. The model seems ...
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0answers
91 views
How to simulate water, falling under gravity, and impinging on a curved surface, which is kept/present in a domain, containing air?
TL;DR: How do I simulate a hole, at the bottom of a (full) water tank?
I am attempting to simulate water, flowing out of a hole/slit, at the bottom of a tank (Water Domain) (under the influence of ...
0
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1answer
723 views
Python Finite Difference Schemes for 1D Heat Equation: How to express for loop using numpy expression
Hello all,
I've recently been introduced to Python and Numpy, and am still a beginner in applying it for numerical methods. I've been performing simple 1D diffusion computations. I suppose my ...
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2answers
65 views
TVD for temporal dicretisation
I have come across schemes where TVD (with flux limiters) is used for spatial discretisation along with Runge-kutta for Temporal discretisation.
Can TVD be used for Temporal discretisation? If so ...
0
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1answer
65 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
votes
0answers
54 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
votes
2answers
146 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)....
0
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1answer
37 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
votes
1answer
88 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} \,,$$
where $c_1$ is a constant. The above can be discretized using the ...
1
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2answers
71 views
Guaranteed equality between binary results with increasing MPI processes
Testing on an MPI scientific code for compressible flow dynamics I noticed that the results may depend on the number of processors used for the calculation. In fact, comparing the binary files they ...
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0answers
46 views
Has there been a comparison bewteen SIMPLE/SIMPLER and JFNK for steady CFD?
I'm looking for a comparison between the Jacobian-Free Newton-Krylov (JFNK) method performance compared to the conventional CFD nonlinear solution methodologies like SIMPLE.
Does anyone know if such ...
2
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0answers
52 views
WENO methods: why the characteristic wise method resulting big errors?
I was doing my research/project using WENO as the limiter in finite volume methods to solve hyperbolic conservation law. I have no idea why the result in the characteristic wise method has a big error ...
3
votes
1answer
57 views
Plotting or Visualizing a Higher dimensional vector field
I am trying to visualize a higher dimensional vector field. Is there a way to do this. I asked this question here, I was told to post it here.
As an example, one can use
$$\begin{eqnarray}
\dot{x}...
4
votes
1answer
85 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 ...
1
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0answers
36 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 ...
3
votes
0answers
54 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
votes
1answer
83 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
341 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 ...
1
vote
1answer
43 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{\...
0
votes
1answer
137 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 ...
3
votes
1answer
111 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
165 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
votes
1answer
86 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
votes
2answers
126 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 (...
0
votes
2answers
108 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....
1
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0answers
53 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
133 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
54 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
votes
1answer
137 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
vote
2answers
558 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
vote
1answer
67 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 $\...
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0answers
101 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
124 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).
...
0
votes
2answers
103 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
140 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
votes
1answer
319 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 ...
