compute shear strees
Dear all
I am beginner in openfoam, i am working on creeping flow around cylinder between two plate, how can i compute shear stress, tau, (and compare with yield stress tau0) ? which and where should i add line code? i want to display the points where tau>tau0 ,how can i display that? Best regards Jafar |
compute shear stress in interfoam
Hi fomers..:
I have completed a case with interfoam and I am interested in adding shear stress to my output files. I checked the last posts but i didn't figure out where to add this equation in my solver. volScalarField shearRate = mag(fvc::grad(U)); I would be really thanks full if any one help!:( |
Hi bagherij and arash.heidarian,
I would recommend to you to perform this calculations with the ParaView calculator, as it is easier for the start. If you still want to compute the shear stress on-the-fly within OpenFOAM, I'd suggest you to look at the coded function object, which you can include in your controlDict, see: http://www.openfoam.org/version2.0.0...me-control.php Best regards, David |
Hi guys,
i just created a similar thread according the topic: calculation of wall shear stresses in multiphase depending on mesh size? http://www.cfd-online.com/Forums/ope...tml#post595106 Maybe it is also interesting for you and you can help me to solve the problems Thank you in advance Stefan |
calcFvcGrad - U - shear stress profile
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Hi,
I am trying to get the shear stress profile in a cross section using stress = mu * (du/dr). Solver used is simpleFoam. I used the readymade tool " calcFvcGrad " on the U field which gave me 8 velocity gradients!!! But the shear stress reproduced using one of the U fields matches at the wall with the value given by "wallShearStress" tool. My doubt is what are the 8 gradients referring to. Also please let me know if the method i followed to obtain shear stress is flawed in any manner. I have attached the file generated by calcFvcGrad (I have added shear stress calculation in the same file) My geometry is a concentric annulus as show below in which i need the shear stress profile in a cross section. http://s19.postimg.org/ec8e6n89r/rotating.jpg Thanks a lot Regards AK |
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Excuse me, what's the meaning of "gradU.T()" in mathematics? is it inner product of gradU and T tensor? could you plz introduce me a source to give me a list of definition of these type of programing? |
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But there was not operation on tensors. e.g. inner product, outer ,... Regards |
1 Attachment(s)
Hi experts,
I am working with simpleFoam, with which I simulated the flow of an Hershel-Bulkley fluid. Now I wan to compute the shear strain rate. On this forum you suggested to do that this way: volTensorField gradU = fvc::grad(U); // stress tensor volTensorField tau = - mu * (gradU + gradU.T()); I'am a new foamer, so my question might seem stupid to you, but I really have to ask. Those preceeding equations, should I put them in my simpleFoam.C file? Or in my createField.H file? Because when I put them into my createField.H file like in the attachment, I got an error saying : 'grad' was not declared in the scope of volTensorField gradU (tau). The second question is should I initialize those tensor fields? With a command like: dimensionedTensor("tau",dimensionset(...), tensor(...)) I hope you will find a couple of minutes to answer me. Thanks in advance. Best regards. |
Hi,
I can't help you with your question unfortunately, because I face a similar problem. I want to get the shear rate and possibly the shear rate dependent viscosity for non-Newtonian fluids, but I don't know where to put the lines of code you referred to. A little bit of help would be great. Edit: Alright, I just found out that ParaView displays the viscosity nu, but Hyperview won't do it just as easily. Does anybody know how to get OpenFOAM to output the needed values? |
Hi "tdof",
Nonetheless thank you for you answer :). Have a good week. |
Hello,
I also have a question regarding wall shear stress for which I haven't found the answer yet. I am simulation airfoils and need the wall shear stress to identify the regions of detached flow. I use the postProcessing Utility to compute the wall shear stress, however I am not quite sure in which coordinate system OpenFOAM gives me the values. Is it the local one from my blockMesh or is it the global one? My flow direction is the x-Direction, y-Direction is upwards and z-Direction is empty since this is a 2D case. When I compute the wall shear stress OpenFoam gives me values for 0 and 1 direction. So far it makes for both the local and global coordinate system. However the 0 value is almost always negative, which doesn't make sense for the global coordinate system. ( Flow on the airfoils surface would be against the flow direction) Therefor I think wall shear stress is in the local coordinate system. can somebody confirm this please? :) thanks! |
I don't have the answer, just in case you have no starting point:
Try to understand this line Code:
ssp = (-Sfp/magSfp) & Reffp; using the OF Programmer's Guide. |
Hello,
I used interFoam to solve a two-phase flow, and I want to use the wallShearStress utility, but it works only for single-phase flow. Could anybody help me how I can change the wallShearStress to be applicable for two-phase flow? Regards, Amir |
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hei
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thank you! |
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Code:
wallShear = (-mesh.Sf().boundaryField()[patchID]/(mag(mesh.Sf().boundaryField()[patchID])) ) & (turbulence->devReff()().boundaryField()[patchID]) Kind regards, Amir |
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Hello,
I know that is an old post but i'm facing the same problem. Can anayone tell me when I can implement the wall shear stress equation in openfoam (.C or .H?) |
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