Viewing 15 posts - 16 through 30 (of 32 total)
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• #2869
LaurentDelaon
Participant

hi mathias,

is cylinder 2d use air ? how represent air ?
can I put pression for inflow and outflow? like a delta P ?

laurent

#2870
Nicolas
Participant

1. In general different fluids can be characterized by their density and their kinematic viscosity. While assuming a isothermal fluid to be incompressible, both quantities remain constant throughout the simulation and therefore are used as input parameters for the ‘UnitConverter’ set up.
In the particular case of ‘cylinder2d’ the density (‘physDensity’) is set to 1.0 kg m-3 which indeed is supposed to resemble an air-like fluid. The kinematic viscosity however is not fixed but scales with the cylinder radius and the Reynolds number (Re). This way the Reynolds number can be used as an input parameter in the beginning (‘simulation setup’), which allows for the investigation of different flow regimes. Nevertheless if desired any physical quantity may be set as a fixed input parameter for the ‘UnitConverter’ as well.

2. In the example ‘cylinder2d’ a velocity boundary is applied at the inlet and a pressure boundary at the outlet (‘addVelocityBoundary’ and ‘addPressureBoundary’ in ‘prepareLattice’). In order to specify a pressure difference a pressure boundary has to be applied at the inlet as well by replacing the corresponding velocity instruction in ‘prepareLattice’ by

sLattice.defineRho( superGeometry, 3, rho);

In order to prevent shocks, a smooth start-up can be added by gradually changing the initialized pressure on either side to the desired (here 0.1 Pa) one. This can be done in ‘setBoundaryValues’ by defining a functor which has the information of the density corresponding to the pressure in lattice units by

AnalyticalConst2D<T,T> rho(converter.getLatticeDensityFromPhysPressure(.1*frac[0]);

#2873
LaurentDelaon
Participant

thank’s you very much for your explainations : thats really help me!
I have also progress with the use of cylinder2d example I have replace with sucess the cylinder by a rectangle.
You complemantary explains should permit to understand better that I try to do:
a moving rectanle in a air flow like a simple valve (I have a real demonstrator with pression measures)

thank’s again Nicolas.

#2875
LaurentDelaon
Participant

Hi Nicolas

I have two way for moving object during simulation. (1)moving cleaning and 2)porosity)
I try first way to
a) rename geometry to fluid (clearing of last material position object)
b) move it to next position (with the good material)
should I do other thing than just adjust on geometry or do I modify the slattice ?
what is the connection with collision and stream calculus? with sLattice ? is it transparent ?
I’m work with cylinder2d.
thank’s.
Laurent.

#2877
mathias
Keymaster

Dear Laurent,

these are very specific questions. I recomment a/ you come to our spring school and/or b/ contacting us for a cooperation.

Best
Mathias

#2878
LaurentDelaon
Participant

Hi mathias
yes they are specifics simples questions on OpenLB…
on a very simple example it’s seem difficult to obtain clearly reponses.

And so, I contact you on the forum OpenLB, isn’t it?
what is the usage of your forum ???
I ‘am try to comes to your spring school but I need to obtain responses currently now.

Laurent.

#2880
mathias
Keymaster

Hi Laurent,

As we are a non-profit group of free people, you may understand that we are working on that forum in our free time on our free will. Working with moving boundaries goes beyond a simple question. We have currently no example published explainng it. You can have a look in

M.J. Krause, F. Klemens, T. Henn, R. Trunk, and R. Nirschl. “Particle flow simulations with homogenised lattice Boltzmann methods”. In: Particuology 34 (Oct. 2017), pp. 1–13. issn: 1674-2001. doi: http://doi.org/10.1016/j.partic.2016.11.001. url:http://www.sciencedirect.com/science/article/pii/S167420011730041X.

You are welcome to help us in the forum and answer the questions of others or you can provide documentation which I am happy to revise and include in our documentation file. You can welcome to contact me!

Best
Mathias

#2885
LaurentDelaon
Participant

Hi Mathias ,

Not a deep help for me : I need information on how work the openLB on general principles.
I can’t read and analysis all the OpenLB code…
I can’t answer to my own questions for the moment so you should do wait a little time before I answer to other’s questions , no ?
help me to realise my project and you can use it to include it on your forum.

#2888
mathias
Keymaster

To get started I recomment reading our documentation (pdf) and have a look at all the examples. Then, you can get through the code by using doxygen which is available online on our website. You can further come to Karlsruhe give a talk and have a one day discussion with our expert on moving geometries.

Best
Mathias

#2889
LaurentDelaon
Participant

Hi Mathias,
I can’t come to Karlsruhe for the moment, but I can try to commmunicate via modern tool like internet email or forum…

Laurent

#2907
LaurentDelaon
Participant

Hi Mathias,

I have a question base on cylinder2d :

How can I change the color of cylinder (which is blue actually) ? put it in white by example…

regards.

Laurent.

#2908
albert.mink
Moderator

Dear Laurent,

whether something is colored blue, red or whatever depends probably on your post-processing software and is not directly related to OpenLB.
I suppose that by “blue” you mean material number 1. The design of OpenLB strictly requires material number of 1 for fluid cells and other for boundaries. That means you better DO NOT change your material number in OpenLB, but adjust your color mapping to get ‘your color’ in your post-processing software.

Cheers
Albert

#2910
LaurentDelaon
Participant

Hi Albert,

In example cylinder2D the material cylinder is 5 (and 0)
The color I speak is the result of simulation and the blue color of the cylinder is the same blue color of the zero value velocity. So the material 1…
So you saiy to me it’s normal because the material 5 of cylinder don’t move… result that material 1 simulation velocity is null and have the blue color…

Can I affect boundary inflow pressure instead of velocity in cylinder2d ? How I change the pressure value ? think’s is it the rhoF valu 1 ? what is the correpondance with physical units ? Pa or bar ?
Seem not totaly clear to me…

Regard’s.

#2911
Marc
Participant

Dear Laurent,

It is possible to change the inflow pressure. You can set a second pressure boundary at the inflow. The value of the density equals 1 is mostly related to a pressure of 0 Pa. The converter of OpenLB uses the SI System for physical quantities.

Best Marc

#2915
LaurentDelaon
Participant

hi marc
We have realise lot of things with openlb but I have minor miss-understand:
In cylinder2d how can I put 100400Pa inlet and 100200Pa outlet ?
I understand how doing inletPa pressure with material_3 outletPa pressure with material_4.

But seem I have pb to setting pressure… Should I do modify N? Re ? or other thing ?

Another question : is the pressure equivalent of the totale pressure ?

regards.

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