calculating a wall shear stress heat map?

[900-50479050]

Hi, I really am a newbie at CAD and CFD so I’d be really grateful for anyones advice, but please keep it simple and walk me through it as if I were a child.

Anyway, I am designing a microflidic device on rhino3D and have exported the file to Autodesk CFD and so far have managed to generate a flow diagram with a heat map of velocity magnitude. I should mention that the CAD object is a network of channels around 0.1 mm high and wide (I may also attempt some 0.01mm channels too). I now want to work out the shear stress on the inside faces of these channels. Ive used the wall calculator function as per this guide http://knowledge.autodesk.com/support/simulation-cfd/learn-explore/caas/CloudHelp/cloudhelp/2015/ENU...

However I was really wanting to get a heat map of the shear stress in dynes/cm2 rather than tabular values. Can I do this? And If so how? Also im guessing Autodesk CFD isn’t really designed for microfluidic calculations so would be accurate at these small sizes where the Reynolds number is low and flow is laminar? (my understanding is that things should be easier to calculate than at the maco scale) ... also when I input ref temperature in the wall calculator is this the temperature of my device and the liquid flowing through it (I want both of these to equal 37oC (i understand viscosity is very temperature dependant) I’ll be using water and/or blood as the fluid.

and just one more thing.. in my fluid flow model the input for flow is in cm/h is this cm2/h (so cL/h) or is in in relation to the volume of my model? I just want to know what the flow input would be in ml/h. If anyone could help with this too that would be great!

Sorry for the long post, and possibly obvious questions, but i’d very much appreciate someone’s help.

Thanks. Paul

[Jon.Wilde]

Hi Paul,

Hopefully I can help you here. You should be able to shade the walls by Shear Stress - try right clicking off of the model within results and changing the Global Result. This changes what everything is shaded by. Then of course you can hide the external parts until you see the item of interest.

You can also right click on the Legend to change the units.

I am not quite sure what you mean referring to the wall calculator. Here you are setting a reference temperature to be used when calculating the Film Coefficient - if you do not set anything, CFD will simply use the near wall temperatures within the fluid. I can't quite visualise what you are trying to achieve here and what is causing the confusion - perhaps a diagram might help?

Your input fluid flow is whatever you define. It looks like you have used a velocity, but you could assign a flow rate instead if it helps. Using a velocity you would need to use the inlet area to calcualte the flow rate you are using.

Does that help?

Jon

[900-50479050]

Hi Jon,

Thanks for your reply. Yes that is most helpful and all very simple to do!

I've just noticed that I can input the temperature of the fluid when assigning the volume, so I think this is what I was after rather than the wall temperatures. as I was wanting to flow 37oC water through the model

Many thanks,

Paul

[Jon.Wilde]

Hi Paul,

Yes, that sounds sensible. Feel free to ask more questions if you are unsure on anything.

Thanks,

Jon