The study of the properties of fluids and gases in motion
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0answers
4 views
Importance of the Time Step Value for the Accuracy of a Transient CFD Simulation Coupled to an Optimisation Algorithm
My understanding is that one should use a time step $\Delta t < \frac{h}{v}$ (where h - smallest mesh element, v - velocity) to get an accurate result.
But how important is this really for the ...
2
votes
0answers
56 views
Which turbulence model: k-epsilon or k-omega?
I'm modelling a tidal harbour in Ansys Fluent and want to include a turbulence model in my simulation. I want to predict the water movements around a pontoon which is situated in the harbour. Which ...
1
vote
1answer
44 views
Vortex Panel Method implementation
I'm trying to understand and implement panel methods for a two-dimensional airfoil.
I haven't found yet a very detailed explanation on how to implement it, and there are some things I don't' still ...
1
vote
2answers
119 views
Simple CFD method
I am looking for a simple method to compute potential flow (then non-viscous) around an obstacle. The method I am looking for must NOT use coordinate transformation, panel methods, finite element ...
5
votes
1answer
104 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?
7
votes
2answers
98 views
Mesh Independence Study: Is the Independent Mesh Really the Best One?
I am running a mesh independence study. I start with Mesh 1 and proceed up to Mesh 4, each time doubling the number cells in the mesh. In parallel, I am comparing my computational results to ...
10
votes
1answer
106 views
CFD: Does order of time stepping scheme affect steady state solution? If yes why?
I am trying to solve Ideal MHD equation using semi discrete methods, ENO spatial reconstructions and TVD RK time stepping. I am getting different steady state solutions with different temporal order. ...
8
votes
1answer
98 views
Pressure as a Lagrange Multiplier
In the incompressible Navier-Stokes equations,
\begin{align*}
\rho\left(\mathbf{u}_t + (\mathbf{u} \cdot \nabla)\mathbf{u}\right) &= - \nabla p + \mu\Delta\mathbf{u} + \mathbf{f}\\
...
5
votes
1answer
108 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, ...
2
votes
1answer
72 views
calculation time in Fluent
I'm making a model of a square box where water comes in and the water level rises. I want it to be a transient, turbulent, VOF-model. The velocity of water entering changes in time ($-0.2$ to $0.2$ ...
4
votes
0answers
45 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 ...
0
votes
0answers
49 views
Transient Fluid Dynamics
Eventually, I would like to numerically simulate the transient compressible flow in an axial compressor during start-up.
However, I know that this is a very challenging undertaking (to say the least).
...
8
votes
4answers
348 views
Is CFD used in animations / movies / art?
This is not a technical question, and is asked just out of curiosity.
Are CFD simulations used in animation movies? (something like shallow water equations, explosion problem etc.)
In other words, ...
5
votes
2answers
149 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 ...
4
votes
1answer
56 views
Is stabilization of energy equation needed when momentum equation needs it?
When SUPG/PSPG stabilization is added to momentum equation of flow problem, is needed stabilization for energy equation also? I would guess that when stabilization for velocity works fine so one gets ...
1
vote
0answers
75 views
What methods exist to solve for the fluid flow past a cylinder using finite differences on a Cartesian grid?
I'm interested in finite-difference approaches to the incompressible Navier-Stokes equations that can handle complex geometry without the use of an unstructured mesh or a non-Cartesian grid. To be ...
1
vote
1answer
42 views
CFD (Fluent) define a inlet for a tidal basin
I'm still pretty new in the CFD modelling world.
Can anyone advise me how to define a inlet for a tidal basin in Fluent?
The water level and the velocity at the inlet vary in time due to the tide ...
1
vote
1answer
50 views
What is a “wake” in the context of CFD?
I am getting into computational fluid dynamics (CFD). One of my professors mentioned that a cylindrical wake would be a good starting point to learn about turbulence modelling when using CFD software. ...
4
votes
2answers
102 views
Poiseuille flow
I have probably a very stupid problem. I can't solve a simple Poiseuille flow in a straight 2-D channel driven by a pressure drop. Results are complete nonsense. (Setting zero pressure on the outflow ...
6
votes
0answers
176 views
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 ...
1
vote
2answers
101 views
How to define a cylinder surrounded by a clustered cartesian mesh
I am trying to model a flow past a cylinder using the projection method. I am a bit confused on how to define the circular cylinder in my computational domain.
I know that the cylinder has the ...
5
votes
1answer
100 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 ...
2
votes
2answers
182 views
CFD: multiphase flow modeling of a laminar flow reactor
I am planning to model the laminar flow reactor shown in the picture below using computational fluid dynamics (CFD). The laminar flow reactor is used to study a multiphase flow: a layer of sheath air ...
1
vote
1answer
42 views
Traction on the boundary - how to compute from velocity field
can you help me? I have a fluid simulation in 2D, where I compute by finite differences on the grid the velocity field and pressure. So this is my output from the program. Now I have to show how the ...
1
vote
1answer
120 views
CFL evolution techniques for Implicit methods
I am working on implicit schemes for Euler equations. Implicit methods allow one to use large CFL values, but is there some way to evolve CFL number from a much smaller value than desired value to ...
5
votes
1answer
85 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 ...
5
votes
2answers
193 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 ...
1
vote
2answers
148 views
Is there any 1-D test case for incompressible flow codes?
There is quasi 1-D C-D nozzle test case for compressible flow codes, like that "is there any 1-D test case for incompressible flow codes?"
6
votes
5answers
283 views
Definition of incompressible flow
As all knows incompressible flow doesn't exist in reality, its an assumption introduced to simplify governing equations. We can not apply this assumption straightforward. Generally Mach ...
7
votes
4answers
210 views
What is the simplest method for solving incompressible Navier-Stokes equations?
By "the simplest" I mean the simplest to learn and implement from scratch. I hope my question can more or less be answered.
3
votes
1answer
156 views
Effecient CFD programming techniques
I'm trying to make highly efficient CFD programming complex for solving combustion problems. I've finished writing core which realises mathematical model, and now I'm concerned about code performance. ...
1
vote
1answer
117 views
4th order Padé scheme formula derivation
I am trying to derive the formula of the 4th order Padé scheme that passes through the points $x_i$, $x_{i-1}$ and $x_{i+1}$
$$\Big(\frac{\partial\phi}{\partial x} \Big)_i = ...
3
votes
0answers
68 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 ...
1
vote
0answers
34 views
Can I use RANS to see the effect of mixed convection?
my question is: can I use a RANS simulation to see the effect of mixed/natural convection?
Actually I have also a second question: I would like to do this in Comsol multiphysics, but it seems that it ...
5
votes
1answer
171 views
Higher order Lax-Wendroff type scheme?
Suppose we want to solve a hyperbolic conservation law $u_t+f(u)_x=0$. I really like to use Lax-Wendroff, which reads
$u_j^{n+1} = u_j^n -\frac{\Delta t}{\Delta ...
3
votes
0answers
78 views
General case Kutta condition
I'm working on a 2D inviscid fluid simulation using a "panel method", with Potential being used to enforce the no-through boundary condition. I'm trying to incorporate the Kutta condition, which says ...
4
votes
1answer
150 views
Boundary conditions in fluid simulation
I'm working on a 2D fluid sim using vortex particles/"vortons" as described in Fluid Simulation for Video Games. Which I think is the same things as the "discrete vortex method". Basically you ...
4
votes
1answer
187 views
Dirichlet-Neumann boundary condition solution becomes unstable - Pressure Correction Method
I am simulating incompressible flow over a cylinder at Reynold number of 500. I am solving navier stokes equation using pressure correction method. My solution becomes unstable after certain time ...
2
votes
0answers
99 views
Create 2D plot from two data sets in ParaView
I'm currently running a CFD simulation for an internal flow and need to compare my computed results to experimental data. The experimental data is saved as a comma separated file with columns for ...
7
votes
0answers
96 views
Connections between Differential Forms and the second order Finite Volume Method
Reading today about the theory of differential forms, I was left impressed how much it reminded me of second order Finite Volume Method (FVM).
I'm struggling to figure out is thinking this way just ...
1
vote
1answer
117 views
Finite element stabilization schemes for incompressible flow
I am looking for an easy to implement stabilization scheme that can be used with equal order ($P_1-P_1$ or $Q_1-Q_1$) finite elements for fluid flow. Is there something like this or should I stick to ...
4
votes
3answers
128 views
nuclear reaction fluid modelling
I'm pretty ignorant regarding the dark arts of numerical codes and modelling, but i'm interested in trying to pursue it for a particular pet project. It regards modelling of nuclear reactions like ...
2
votes
1answer
126 views
Where can I find Ansys Fluent for ubuntu?
I am new to Ansys Fluent (the Ansys CFD product). Is it a windows-only software?
My institute owns copies that work on windows only.
Online tutorials on how to install Fluent on ubuntu aren't clear.
6
votes
0answers
80 views
How to solve a compressible flow through a porous medium with a changing inlet concentration
I'm trying to solve the transient behaviour of a compressible flow through a porous media (porosity is $\epsilon$). Where the fraction of B in A ($ \phi$) changes with time. The equations that I found ...
6
votes
1answer
123 views
Hybrid spatial schemes for CFD: any downside to blending versus switching?
Aside from extra computational cost due to having to compute both fluxes over a certain region, is there any downside to blend two flux evaluations for a hybrid scheme in a finite volume method? The ...
9
votes
2answers
212 views
What are some good data-types for unstructured cell-centered FVM CFD code?
I'm interested in an advice for efficient data structures for cell browsing in unstructured cell-based finite volume CFD.
One example that I encountered (in dolfyn cfd code) goes like this (I'll show ...
7
votes
4answers
292 views
Fourier pseudo-spectral method and numerical dissipation
Performing a direct numerical simulation of isotropic turbulence with Fourier pseudo-spectral method (Orzag & Patterson, PRL, 1972) using FFT.
For a background of the method, which is widely used ...
2
votes
1answer
61 views
How to add perturbation to a base state in physical grid space?
For study 3D instabilities problem i.e a base state (velocity field and temperature field) and an additional perturbation.
The method must be independent of the type of instabilities considered but ...
8
votes
3answers
143 views
How to estimate the impact of small scale on large scale in fluid dynamics?
Assuming that a direct numerical simulation is performed, what is a good method for estimate the impact of small scale on large scale in fluid dynamics ? For example is it pertinent to compare two run ...
2
votes
1answer
815 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 ...
