Questions tagged [fluid-dynamics]
The study of the properties of fluids and gases in motion
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16 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 ...
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0answers
48 views
Wrapped BVP with an unknown boundary for fluid modeling
I have a model about a fluid being extruded on a moving bed as in the 3D printing process. The model is a boundary-value problem where the right boundary is the point where the fluid attaches to the ...
2
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0answers
28 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
51 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
$$\begin{eqnarray}
\dot{x}...
3
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1answer
57 views
How to go from turbulent RANS to laminar Navier-Stokes and Euler
SU2 is an open-source CFD suite that is built around a RANS-solver. The main PDE that is solved, is the following:
$$
\frac{\partial}{\partial t} \mathbf{U} + \nabla \cdot \mathbf{F^c} - \nabla \cdot ...
1
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0answers
26 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
61 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{\...
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1answer
80 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
62 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
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1answer
28 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
31 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 ...
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0answers
72 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
117 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
71 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 ...
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2answers
99 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
98 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
45 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
109 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
45 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
101 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 ...
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2answers
224 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 ...
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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
71 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 ...
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0answers
75 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
99 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 ...
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2answers
116 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
$$\frac{\partial u(t,x)}{\partial t}+\frac{\partial u(t,x)}{\...
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1answer
211 views
Finite volume software packages
There are many software packages for the finite element method, of which the most popular are listed e.g. on Wikipedia. When it comes to the finite volume method, I'm not aware of any similarly ...
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1answer
94 views
FFT Poisson Solver for non-uniform grid
I have a 3D solver for the incompressible Navier-Stokes equations which uses a FFT library for the Poisson equation with a uniform grid on all directions. In 2D the Poisson equation is given by:
$$
...
2
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3answers
312 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 $\Delta x$:
$$ \frac{\partial \rho}{\partial t} + u \...
1
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0answers
69 views
(Approximate) Incremental Projection Method for Navier-Stokes equations
I am trying to implement an incremental projection method for the 2D incompressible Navier-Stokes. The type of projection method I am trying is
$$
\frac{u^{*} - u^{n}}{dt} = - \nabla p^{n} - u \cdot ...
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1answer
260 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
83 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 ...
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1answer
77 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
54 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
184 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 ...
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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
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1answer
135 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
185 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
47 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 ...
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2answers
215 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 ...
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0answers
68 views
Definition of CFL number in Arbitrary Lagrangian-Eulerian framework
In an Eulerian frame of reference, the CFL number is defined as $$\sigma=\frac{u \Delta t}{\Delta x}$$
with $u$ the magnitude of the fluid velocity. A restriction such as $\sigma<1$ for time ...
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1answer
157 views
Robust/Tested Solver for incompressible 2D Euler (Fluid dynamics) Equation
I am trying to locate suitable computational algorithms for a optimization problem that requires repeated solution of transient 2D incompressible Euler equation on a 2D domain (say rectangular).
My ...
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0answers
53 views
Reconstruction of cells information when given mesh in polyMesh format
The polyMesh format used in OpenFOAM is an intelligent format for which 'cells' file, i.e. the file giving list of nodes that make a cell, is not needed. The way to reconstruct geometry data such as ...
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1answer
60 views
Are there generic formulations of Riemann solvers?
I have been following Toro's book on Riemann solvers to implement a finite-volume scheme for computational fluid dynamics. The Riemann solvers presented in the book seem to be fairly tightly coupled ...
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0answers
114 views
Solution to 1D consolidation problem python implementation
A solution to the 1D consolidation problem is given by
$$\frac{\partial}{\partial t} p = c_{v} \frac{\partial^{2}}{\partial y^{2}} p$$
where $p$ is the pore water pressure, $c_v$ is the ...
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3answers
918 views
Galerkin method: Test functions vs. Basis functions
I'm a novice to finite element and I'm finding quite hard to find the actual difference between Test function(s) and Basis function(s).
I would be glad if somone could explain me that and point out ...
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2answers
169 views
Boundary conditions for streamlines in enclosed flow
I am trying to solve Lid driven square cavity flow problem of Stokes equation using finite element method. I have boundary conditions for velocity as zeros on every boundary but u=1 on top boundary. ...
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3answers
422 views
Pressure boundary condition in lid driven cavity using finite element method
Thank you all
1.) I am trying to solve lid driven cavity problem for an incompressible Stokes and Navier Stokes equations using general "Mixed" finite element method. dirchlet boundary conditions are ...
