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Questions tagged [fluid-dynamics]

The study of the properties of fluids and gases in motion

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Simple turbulence model appropriate for buoyancy-driven cavity like problem

Which turbulence model is suitable for resolving incompressible buoyancy-driven flow of a fluid within an cylindrical ampoule? I prefer turbulence model which is sufficiently simple so that fully ...
Jan Blechta's user avatar
6 votes
0 answers
2k views

What is the best OpenFOAM RAS turbulence model for a motorbike/vespa problem?

I am learning OpenFOAM as a hobby and using my Vespa racing as the topic to apply it to. The objective is to produce modifications that improve the top speed (as well as getting some values such as ...
internetscooter's user avatar
6 votes
0 answers
1k views

How does GAMG in OpenFOAM really work?

I use OpenFOAM for CFD simulations. A very popular preconditioner is GAMG which needs a low number of iterations per a time step in SIMPLE or PISO solvers that are used to simulate the fluid flow. I ...
user avatar
5 votes
0 answers
345 views

Galerkin Least-Squares stabilization for FEM solution advection (hyperbolic) equations

I am playing with Galerkin Least-Squares stabilization to solve advection diffusion problem in the context of the finite element method. This works very well for steady-state advection-diffusion ...
BlaB's user avatar
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5 votes
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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 ...
grizzlyjoker's user avatar
5 votes
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189 views

Is it generally unstable to use in multidimensional simulations finite difference schemes with higher orders than 2?

I'm part of a team trying to generalize a 1D Advection-Diffussion-Reaction code we inherited by extending it to 2D by using dimensional splitting, i.e. solving advection and diffusion for x and y ...
mathdummy's user avatar
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5 votes
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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: $$...
Jesper's user avatar
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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, ...
Dilaton's user avatar
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5 votes
1 answer
570 views

Finite volume a posteriori error estimation

I'm wondering what alternatives there are to a grid convergence study to judge solution accuracy for a given grid resolution when doing steady-state RANS simulations on an automatically generated ...
akid's user avatar
  • 719
4 votes
0 answers
213 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 ...
John Snow's user avatar
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How to implement boundary conditions on Finite Difference WENO5 scheme for the Euler equations

I'm implementing a Finite Difference WENO5 with Lax-Friedrich flux splitting on a uniform, structured grid to solve the 2D Euler equations of fluid dynamics on a rectangular domain in cartesian ...
CFD_padawan's user avatar
4 votes
0 answers
420 views

Algorithm for face based data-structure - CFD

Good morning I'm trying to develop an unstructured CFD code to solve Euler equations in a finite-volume (cell-centered) context (learning purposes). I was able to build from a cgns file some basic ...
LM_O's user avatar
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3 votes
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What EXACTLY are the "outflow" and "pressure outlet" BCs in ANSYS Fluent?

I am just starting my MSc and we have been given an assignment in which we must model two-dimensional, laminar, incompressible Poiseuille flow in a channel. We are supposed to use a VELOCITY INLET ...
K.defaoite's user avatar
3 votes
0 answers
73 views

Is it possible to shift the numerical results in order to compare it with the analytical solution?

I'm using lattice Boltzmann method (LBM) to do simulation of flow in a pipe. The diameter of the pipe is 0.02 m and its height is 0.1 m. I put a parabolic velocity profile at the inlet: $$\mathbf{u}(\...
Mithridates the Great's user avatar
3 votes
0 answers
83 views

Choosing good modelling method for solving Boltzmann equation

I'm writing a solver for Boltzmann Equations (BE) including a force term in rarefied plasma, for my PhD. The aim is to see if an instability occurs inside an electric streamer (theoretically it should,...
Paweł J's user avatar
3 votes
0 answers
101 views

Is the matrix exponential and the Jordan canonical form actually useful for solving differential equations?

All of my yearlong graduate-level Linear Algebra course notes from my professor—an algebraist/representation theorist—shows his love for the exponential map $e^A$ and the Jordan canonical form—and one ...
user36348's user avatar
3 votes
0 answers
155 views

What is appropriate boundary condition for Poisson pressure equation?

I'm doing CFD simulations in unstructured grids. Well, it's a bit different from conventional unstructured grids that are used mainly in FEM or FVM as tetrahedral meshes. Mine is a voxelized mesh of ...
Mithridates the Great's user avatar
3 votes
0 answers
109 views

numerical instabilities in Fluid Dynamics, Finite Element Method

I'm looking for references to understand where the numerical instabilities come from in hydrodynamics in general, and notably when the Péclet number: $Pe>1$. I'm using the finite element method. ...
J.A's user avatar
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3 votes
0 answers
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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{\...
A. B. Marnie's user avatar
3 votes
0 answers
238 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 ...
Chronum's user avatar
  • 321
3 votes
0 answers
234 views

Rhie--Chow interpolation on PDE level

The Rhie--Chow [1] interpolation seems to be a standard tool in the Finite-Volume discretization of incompressible flows. It is commonly defined on the discrete level [2]. In the lecture notes [3] --...
Jan's user avatar
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3 votes
0 answers
81 views

Cavity Flow CFD Boundary conditions and strange waves

So I have a PDE that I use to describe how material flows through a volume(2D or 3D). $$\frac{\partial C}{\partial t} + \vec{u} \cdot \nabla C = (D' + D )\nabla^2C$$ Now using finite differences I get ...
Aviv Moshe Albeg's user avatar
3 votes
0 answers
401 views

Euler Equation Eigensystem with Gravity in the Energy Flux

I am modifying a conservative form of the Euler equations with gravity in the energy flux (see previous question: Energy Conservation in Conservation Laws with Source Terms) for use in a Riemann ...
Wes Lowrie's user avatar
3 votes
0 answers
61 views

Discretizing boundary conditions for vortex methods

I am working on a fluid simulation using vortex methods. For this I must compute the vortex sheet on my boundaries given as: $$ \gamma(\mathbf{x}) - \frac{1}{\pi}\int_S \frac{\partial}{\partial\mathbf{...
Alex's user avatar
  • 31
3 votes
0 answers
373 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 ...
seb's user avatar
  • 994
3 votes
0 answers
706 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 ...
erthalion's user avatar
  • 163
3 votes
0 answers
260 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 ...
Ludovic's user avatar
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3 votes
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220 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, $L_y$ ...
ucsky's user avatar
  • 419
3 votes
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Create 2D plot from two data sets in ParaView

I'm currently running a CFD simulation for an internal flow and need to compare my computed results to experimental data. The experimental data is saved as a comma separated file with columns for x,y,...
tonymac's user avatar
  • 211
2 votes
0 answers
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Lowest order Raviart Thomas elements

I have questions regarding the implementation of Lowest order Raviart Thomas elements on quadrilaterals, some papers use the basis functions in this form: for example the right edge: $N = \left[\dfrac{...
Amr Ashraf Ibrahim Ibrahim's user avatar
2 votes
0 answers
80 views

Preventing an Overflow in Exponential Integrating Factor

The following is the Discrete Spectral Vorticity Evolution PDE for incompressible flow: $$ \frac{\partial \Omega_{pq}}{\partial t} = \nu \left( \frac{\partial^2 \Omega_{pq}}{\partial x^2} + \frac{\...
Jacob Ivanov's user avatar
2 votes
0 answers
124 views

Starting point to use Trilinos linear algebra packages?

I have experience with classical linear algebra packages in C++ like Eigen, Blaze, etc. I have never wrote my own PetSC back-end solver but I used/modified several of them. In a new project I would ...
Kürşat Yurt's user avatar
2 votes
0 answers
121 views

Solute transport around a solid obstacle

I am a newbie in CFD and single/multiphase flow and transport in general. As part of my quest to learn, I am trying to model solute transport around a solid object in the center of a 2D domain. The ...
oma11's user avatar
  • 55
2 votes
0 answers
87 views

Multigrid method: linear solver and modified residual

I am trying to better understand the FAS multigrid algorithm for Euler equation in FV discretization. The usage of the modified residual (the residual with forcing) inside the different cases: ...
albiremo's user avatar
  • 410
2 votes
0 answers
157 views

What is temporal order of accuracy of the PISO algorithm?

A few Computational Fluid Dynamics (CFD) codes implement the so called PISO (Pressure-Implicit with Splitting of Operators) algorithm for pressure-velocity coupling. My concern is what is actual ...
Johntra Volta's user avatar
2 votes
0 answers
538 views

How are finite volume method boundary conditions implemented without using ghost-cells?

I'm currently trying to implement my own FVM code in cpp, but when I try to calculate the laplacian of a test function, given by \begin{align}\phi_0=\sin(2\pi x)\sin(2\pi y),\end{align} I get ...
Tepa's user avatar
  • 31
2 votes
0 answers
139 views

How does the "Stable Fluids" algorithm by Jos Stam relate to the SIMPLE and PISO algorithms?

The "Stable Fluids" paper (*) by Jos Stam starts by acknowledging that "Our method cannot be found in the computational fluids literature, since it is custom made for computer graphics applications. ...
cesss's user avatar
  • 131
2 votes
0 answers
44 views

Decoupling of the fluid viscosity and incompressibility constraint in a partitioned scheme

I am new here and this is my very first question: I hope I respect all the criteria and rules. I am just getting started with partitioned approaches for solving FSI problems. I am interested in a ...
user111283's user avatar
2 votes
0 answers
75 views

Defining appropriate test function spaces for the finite element solution of Euler's fluid equations

I have the following coupled equations for the conservation of mass and momentum of a compressible fluid : \begin{equation} \rho_t + (\rho u)_z = 0, \end{equation} $$ (\rho u)_t + (\rho u^2)_z + \...
Dan Burrows's user avatar
2 votes
0 answers
166 views

Velocity self-advection stability problem with QUICK upwind scheme

I'm trying to implement a finite-difference fluid solver (incompressible, inviscous) using the QUICK scheme for advection. Mostly I've been following the Norris thesis chapter 2 (https://ses.library....
omgold's user avatar
  • 21
2 votes
0 answers
336 views

CFD and finite volume method: Dirichlet boundary conditions for the Euler equations

Please point me to an answer if one already exists, but after some searching, I still can't find the answer to what seems like a very simple question. There are plenty of references out there for ...
emprice's user avatar
  • 255
2 votes
0 answers
717 views

Understanding MP-PIC implementation in OpenFOAM

The multiphase particle-in-cell (MP-PIC) method is characterized by mapping particle properties from the Lagrangian coordinates to the Eulerian grid. However, the implementation of this method in ...
Jakub Klinkovský's user avatar
2 votes
0 answers
47 views

Verification on pressure predictor method for CFD code

I have developed a python code for a lid-drive cavity model. However, my results are not converging. The algorithm of my code looks like this: Euler Momentum Equation looks like this: $$\frac{u^{n+1}...
Kelvin Loh's user avatar
2 votes
0 answers
72 views

Solving a simple Shallow Water model

Hi. I have a question at Mathematics and they suggested post here, once it's not common. I transcript as following. Many thanks I need to solve with basic methods this simple Shallow Water Model: $...
Quiet_waters's user avatar
2 votes
0 answers
112 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 ...
BlaB's user avatar
  • 1,157
2 votes
0 answers
122 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 ...
Mr. Robot's user avatar
2 votes
0 answers
260 views

Outflow boundary condition - second derivative of velocity

Consider a fluid flow simulation in a pipe. At the outflow, instead of explicitly imposing a boundary condition, I linearly extrapolate information from the interior (for velocity components). This ...
Rhinocerotidae's user avatar
2 votes
0 answers
136 views

Order of local and global truncation error in a finite volume scheme

Can the order of the local truncation error be higher than the order of global truncation error in a finite volume method?
random_acct's user avatar
2 votes
0 answers
135 views

How one could choose the value of viscous coefficient for obtaining stable solution of Burgers' equation?

Burgers' equation is a fundamental PDE used in various fields such as number theory, gas dynamics, heat conduction, elasticity, etc. It is crucial especially for developing numerical models for ...
Loading...'s user avatar
2 votes
0 answers
421 views

Collocated Grid Navier Stokes Solver

I want to solve Navier Stokes equations on a collocated grid. Earlier, I was using a MacCormick scheme based solver where I discretized predictor step in forward differences and corrector step in ...
Tanmay Agrawal's user avatar