Questions tagged [fluid-dynamics]

The study of the properties of fluids and gases in motion

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16
votes
2answers
2k views

(how to) write simulations that run faster?

I have started using python as the programming language for doing all my assignments in CFD. I have a very little experience in programming. I am from mechanical engineering background and am pursuing ...
7
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1answer
352 views

Numerical solution of hyperbolic PDEs with nonconvex flux

In some hyperbolic PDEs the flux is nonconvex. One example is equations in magnetohydrodynamics. What are the complications in the wave structures of such problems? What general precautions one should ...
10
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2answers
2k views

Euler equations in 2d

As an assignment in college, I did a 1d simulation. The problem statement was to solve 1d shock tube problem involving compressible ideal gas as working fluid. For this problem, I solved system of ...
3
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2answers
633 views

Entropy fix for godunov scheme

For non linear system of hyperbolic PDE, The finite volume methods work well (because of inherent conservation). Godunov scheme is a very elegant solution philosophy. For linear system, it is nothing ...
17
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2answers
4k views

Disadvantages of common discretization schemes for CFD simulations

The other day, my computational fluid dynamics instructor was absent and he sent in his PhD candidate to substitute for him. In the lecture he gave, he seemed to indicate several disadvantages ...
2
votes
0answers
138 views

Would anyone give some review on adjoint methods in shape optimization method <in fluid dynamics>? [closed]

Modification Is a continuous adjoint approach a reliable/promising method for optimizing the shape of an airfoil under conditions of unsteady turbulence flow? Original Question I saw lots of people ...
8
votes
2answers
1k views

Taxonomy of ILU preconditioners

I learned that for BiCGStab solver for sparse linear systems it's pretty much always necessary to use a preconditioner. I realized by now that choosing a good one is problem dependent. Surfing the ...
6
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3answers
1k views

How to quickly implement and test a turbulence model?

What is the best software for quickly implement and test a Reynolds Averaged Navier-Stokes turbulence model ?
19
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6answers
14k views

How to get started with OpenFOAM for CFD

I'm looking at using OpenFOAM for solving basic internal flows in CFD. What is the best way to get started, and could anyone please point me to a good online reference to go to with any questions I ...
8
votes
1answer
533 views

Finite difference scheme for compressible nonisothermal flow in porous media

My challenge is to solve the following system of equations, which describe gas combustion in porous media: 1) Continuity $\varepsilon \frac{\partial \rho_g}{\partial t} +\frac{\partial}{\partial x} \...
11
votes
1answer
1k views

Optimal transport warping implementation in Matlab

I am implementing the paper "Optimal Mass Transport for Registration and Warping", my goal being to put it online as I just cannot find any eulerian mass transportation code online and this would be ...
6
votes
3answers
1k views

Is lattice Boltzmann suitable for simulation of incompressible Stokes flow?

We have a flow that is dominated by adhesion forces from the substrate and surface tension from the free surface. The material is nearly solid and at rest first, and gets a bit less solid by heating. ...
6
votes
3answers
4k views

How to find QR decomposition of a rectangular matrix in overdetermined linear system solution?

While trying to find cell-centered gradients in finite volume method computation of incompressible fluid flow I get over-determined linear system. This is a well known "cell based least-square" ...
22
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2answers
4k views

A good finite difference for the continuity equation

What would be a good finite difference discretization for the following equation: $\frac{\partial \rho}{\partial t} + \nabla \cdot \left(\rho u\right)=0$? We can take the 1D case: $\frac{\partial \...
5
votes
1answer
751 views

Finite-difference discretization for a convective term

How does one discretize the classical convective term in a transport equation using finite differences? I know the finite volume schemes out ther i.e. upwind, central differencing etc. Are there ...
13
votes
4answers
328 views

How to create a random 3D domain representing a plant's root structure?

I would like to model laminar flow of water from roots to the stem of a plant. At the very end of the roots, the tubes vary from millimeter to centimeter scale in diameter and length. As we get closer ...
3
votes
2answers
424 views

What numerical methods are recommendable for simulating two phase immiscible fluid flow through a pipe with high capillary pressure?

I'm simulating two phase immiscible drainage (air displacing water) in a rectangular domain of size .6mm x 2.4mm (2 dimensions) using Ansys FLUENT software. I am using an implicit Volume of Fluid ...
10
votes
1answer
256 views

Why do we have to rerun the CFD solver for higher Reynolds number?

I started to learn OpenFOAM from the Cavity tutorial which is provided at the web-site. When experimenting with different Reynolds numbers, in section "2.1.8.2 Running the code", tutorial says to ...
4
votes
0answers
288 views

How does one handle the source term in the Shallow Water Equations when using the discontinuous galerkin method? [closed]

I use the discontinuous galerkin method to solve the steady flow 1D shallow water equations with a bump at the bottom. This flow is frictionless. I use the runge-kutta method to approximate the time ...
3
votes
2answers
1k views

Looking for a library or algorithms to perfom clipping 3D unstructured meshes by a set of surfaces

We have a 3D (volume) unstructured, possibly hybrid, degenerative irregular mesh data structure that we are capable of generating (mostly composed of hexahedra and general polyhedra, using a mix of ...
12
votes
3answers
2k views

finite volume method: unstructured mesh vs octree adaptation + cell cutting

I'm working with the OpenFOAM C++ Computational Continuum Mechanics library (it can deal with fluid-solid interaction, MHD flows...) which uses arbitrary unstructured meshes. This was driven by the ...
17
votes
5answers
2k views

Is there a good, easy-to-use, high quality open source CFD solver out there?

My thesis is on developing numerical methods for model reduction in combustion. I run my methods purely on the chemistry part of combustion simulations, and I have plenty of case studies for 0-D ...
6
votes
1answer
518 views

Benchmarking performance in CFD: how to compare machines and codes?

Informally in our lab, we have developed 2 metrics to compare CFD solvers over the range of machines we have access to. One is called COMP, which stands for COde Machine Performance. This single ...
5
votes
2answers
149 views

Which tool/metric do you recommend to evaluate the quality and validity of a Large Eddy Simulation?

The idea behind Large Eddy Simulation is to solve explicitely the scales of the flow that are resolved by the computational grid and to model the sub-grid scales. Ideally, the cut-off between these ...
9
votes
1answer
1k views

What is the most accurate interpolation method for a 3D-flowfield on a structured grid?

I solve multi-species, compressible Navier-Stokes equations on a 3D structured grid. I have obtained a solution on a given grid (let's say a relatively coarse one). I want now to refine my grid and ...
18
votes
4answers
581 views

Which methods can ensure that physical quantities remain positive throughout a PDE simulation?

Physical quantities like pressure, density, energy, temperature, and concentration should always be positive, but numerical methods sometimes compute negative values during the solution process. This ...
12
votes
1answer
403 views

What spatial discretizations work for incompressible flow with anisotropic boundary meshes?

High Reynolds number flows produce very thin boundary layers. If wall resolution is used in Large Eddy Simulation, the aspect ratio may be on the order of $10^6$. Many methods become unstable in this ...
31
votes
4answers
2k views

Why is local conservation important when solving PDEs?

Engineers often insist on using locally conservative methods such as finite volume, conservative finite difference, or discontinuous Galerkin methods for solving PDEs. What can go wrong when using a ...
23
votes
4answers
1k views

When is a high order method useful for computational fluid dynamics simulations?

Many numerical approaches to CFD can be extended to arbitrarily high order (for instance, discontinuous Galerkin methods, WENO methods, spectral differencing, etc.). How should I choose an ...