Questions tagged [fluid-dynamics]

The study of the properties of fluids and gases in motion

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0answers
132 views

What are some good debugging habits for numerical simulation?

I'm currently writing a lid drive cavity CFD code on python. Currently, my code has some issues (values jumping bear b.c). I was wondering what are some good habits in debugging numerical codes. ...
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The real myth of GPU (specifically CUDA) really speed up FEM/CFD

Now I have been believing that FEM/CFD is supposed to be faster on a GPU unit - here I am using CUDA as solid example. However, I have not been able to find a convincing paper where the benchmark ...
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3answers
5k views

Tutorial for flow around a cylinder in FEniCS

I am continuing my dive into computational fluid dynamics. I would like to build a simple test case for modelling the flow around a cylinder in FEniCS and then continue to model turbulence in order to ...
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2answers
459 views

applications of computational geometry in fields such as CFD?

Out of curiosity, I was recently trying to search what skills are required to be successful as developer in scientific computing field (e.g. CFD or similar). And to do so, I was going to through ...
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3answers
470 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?
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540 views

C - OpenMP, MPI, Serial Program

I'm part of a Computational Science course and come from a non-programming background, so please forgive me my ignorance. I'm working on a set of code in C to numerically solve the Navier Stokes ...
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5answers
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Open source codes for 2D instationary Navier Stokes equations

What open source tool can be recommended for solving 2D instationary Navier Stokes equations (in simple geometries, but with high Reynolds numbers)? Most packages I found, I'm not very lucky with. ...
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4answers
473 views

Are there any general fluid dynamics frameworks?

Are there any frameworks that could be classified as "general computational fluid dynamics framework"? What I'm thinking of is a framework that's modular and extensible in order to allow the ...
7
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2answers
959 views

What are some of the differences between using a Lagrangian and Eulerian framework to quantify passive scalar dynamics?

On one hand, one may seed the domain with particles and track their trajectories in the Lagrangian sense by implementing a Lagrangian particle tracking model. On the other hand, one may use the ...
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1answer
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computing turbulent energy spectrum from isotropic turbulence flow field in a box

I have my 3 dimensional velocity flow-field u, v and w at a given instant of time from DNS using pseudo-spectral method. I need to calculate the energy spectrum ( in Fourier space ) as a function of ...
7
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1answer
357 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 ...
7
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2answers
313 views

Stabilization of convection-dominated flow and turbulence modeling

Are stabilization techniques for convection-dominated flows like SUPG+PSPG, interior penalty methods, etc. able to handle turbulent flows without tubulence model being employed, at least up to some ...
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2answers
940 views

Feasibility and software for acoustic simulation

I'm looking at doing a finite-element simulation of air flow essentially for the purposes of approximating the response to an external audio impulse of a smallish (~10-30 cm scale), stationary 3D-...
7
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1answer
601 views

Navier-Stokes solver: How to adjust the time step based on non-linear terms?

My code solves the incompressible Navier-Stokes equation in a conducting fluid, together with the induction equation: $ \partial_t u + u \nabla u + 2\Omega \times u = -\nabla p + \nu \Delta u + (\...
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1answer
242 views

Do computational scientists typically also become domain experts?

Let's say I'm interested in fluid dynamics, specifically in fluid-structure interactions -- and I want to get into modeling, simulations and experiments. I am a mathematics student by training, ...
7
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1answer
377 views

Potential flow around a non-symmetric obstacle using stream functions

I've seen that there is a way to use the finite differences method, on a cartesian orthogonal grid, to perform calculations on potential flow about an obstacle without using the Neumann conditions, ...
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4answers
244 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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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
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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" ...
6
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1answer
6k views

Type of Navier-Stokes equation

What type equation Navier-Stokes is: Elliptic, parabolic, or hyperbolic? Should it give always the same answer no matter what is the initial condition? How these statements could be proved?
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2answers
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Solution blows up when using Runge-Kutta to solve simultaneous ODEs for liquid film equations

This is a continuation of a problem I asked over at physics exchange and math exchange. Basically I have two ODEs that I am solving in order to calculate the radial and tangential velocity of liquid ...
6
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3answers
975 views

Test Case with Known Solution for 3D Navier Stokes Equations

Is there a test case for 3D incompressible Navier Stokes Equations like the Taylor vortex in two dimensions? I know, I can easily construct 3D manufactured solutions but I would like to have ...
6
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1answer
428 views

ENO-WENO Schemes: Are ENO-WENO schemes non oscillatory for all kinds (linear/non linear) of problems?

Is there an rigorous proof of ENO-WENO schemes being non oscillatory?
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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 ?
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2answers
2k views

Finite elements for Stokes with traction boundary conditions

Suppose we are given the Stokes equations with Neumann conditions on part of the boundary: $-\nabla\cdot\boldsymbol{\sigma} = \mathbf{f}, \quad \text{and} \quad \nabla\cdot \mathbf{u} = 0 \quad \...
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2answers
1k views

Transitional flow in OpenFOAM

Is it possible to simulate transitional flow in OpenFOAM? Or, alternatively, does it make sense to use k-epsilon or k-omega model with low Reynolds number? If not, why? What kind of errors would ...
6
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1answer
173 views

A simple PDE solution question

I need to ask a question about partial derivatives. I want to solve this equation (steady state, one dimensional continuity equation): $$\frac{\partial (\rho u)}{\partial z}=0$$ which is equivalent to:...
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2answers
541 views

Simulating advection over a network of 1D pipes

I am trying to create a simulation to help visualize how different chemical components flow through a network of pipes with associated valves, pumps, and chemical inputs. In this simulation, the pipes ...
6
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1answer
748 views

ENO/WENO component-wise vs characteristic-wise

Can someone give some references to understand what's the differences between a component-wise and a characteristic-wise ENO scheme? If I'm right, the characteristic variables come from the ...
6
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2answers
239 views

CFD for high-detailed turbulence and non-linear waves

What are typical (or promising) techniques and methods in CFD to achieve high-detailed turbulence and non-linear waves interaction? And with "active" geometry (when bodies interacts with fluid in both ...
6
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1answer
536 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 ...
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1answer
194 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 ...
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2answers
2k views

9-point stencil finite difference Laplacian with variable diffusion coefficients

So I'm trying to implement a 9-point stencil discretization to the 2D difussion equation. The stencil is here. However, most of the literature deals with a Laplacian that has a constant diffusion ...
6
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2answers
198 views

Why lattice Boltzmann despite its huge number of mesh points still has worse accuracy in comparison to FEM for calculating wall shear stress?

I'm just doing a very simple experiment. I'm calculating wall shear stress based on Poiseuille flow for a pipe by using lattice Boltzmann method (LBM) and FEM to compare their values with the ...
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3answers
729 views

Fluid-structure interaction solver for cardiovascular applications

I would like to start running FSI simulations for cardiovascular applications. More precisely, I'm interested in the behaviour of aortic valve under physiological flow conditions in which the ...
6
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1answer
2k views

How to get proper parameters of SPH simulation?

I'm implementing basic fluid flow simulator using SPH method basing on e.g. https://www10.informatik.uni-erlangen.de/Publications/Theses/2010/Staubach_BA10.pdf. EDIT (dead url): https://www10.cs.fau....
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1answer
551 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 ...
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0answers
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 ...
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6answers
3k views

What is the difference between MATLAB and FORTRAN?

In our university some Ph.D students for computational methods prefer FORTRAN over MATLAB. I can't understand why? What is the difference between them when are used in computational methods like ...
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3answers
2k views

Flow past a cylinder - Projection Method - Boundary Conditions

I plan to write a code that solves the flow past a cylinder and try to see the Von-Karman vortex street. I will solve the 2-D viscous, incompressible Navier-Stokes using the projection method. The ...
5
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2answers
227 views

Inverting a pressure matrix for fluid simulation

I am implementing a fluid simulator as my numerical methods course project and I have to compute pressure at each simulation step. Basically, that means solving an equation $Ap = b$, where $A$ is a ...
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3answers
1k views

beginning Computational Fluid Dynamics

I am starting a self study course in computational fluid dynamics. I use ( An introduction to computational fluid dynamics : the finite volume method) I am learning Python programming language. The ...
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2answers
272 views

What makes turbomachinery so special in CFD

As my experience with CFD grows, I start to gain the feeling that turbomacinery is kind of special in CFD: there are special tools tailor for it. For example, ANSYS has TurboGrid or Vista TF for ...
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1answer
548 views

Riemann Solver in WENO methods

I'm reading now Shu, C.-W. (1999). High Order ENO and WENO Schemes for Computational Fluid >Dynamics. (T. J. Barth & H. Deconinck, Eds.)Lecture Notes in Computational >Science and Engineering, ...
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1answer
877 views

Package for determining power output of windmill shapes?

I'm looking for the best package for doing the following: building a 3D model (or loading externally) of a non-standard windmill shape, simulating an airflow over the model, and determining the ...
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1answer
8k views

Adjusting the time step dynamically in OpenFOAM?

I'm experimenting with OpenFOAM. In my simulation of a time-dependent, transitional flow the Courant number remains well below 1 for a certain period but then rises, eventually leading to a floating ...
5
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3answers
551 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 ...
5
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1answer
3k views

Stability of numerical method for 1D Burger's equation

I am trying to solve 1D viscous Burger's equation numerically and I cannot apply von Neumann analysis because the equation is non-linear. How do I predict the stability criteria for my system? I also ...
5
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1answer
818 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 ...
5
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1answer
2k views

CFD: Can one calculate the dimensionless wall distance $y^+$ a priori?

perhaps the most idiotic question I ever asked. people throw around the parameter $y^+$, as if it is the be all and end all of CFD (Computational Fluid Dynamics) parameters and use it as if everyone ...

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