Learning Forum

[maaz007]

Can anyone guide/help me in mesh generation of screw compressor for analysis in ANSYS CFX/FLUENT (which ever feasible for this type of analysis, i dont know which one to use). i am new to ansys.

[peteroznewman]

Read this post.

[maaz007]

I have read the discussion and it mentions to use 2D as a starting point but i cant use 2D because in screw compressor the compression is done axially. Please let me know how to mesh the fluid and solid? do i have to subtract the solid from the fluid or i will insert the solid in a FULL fluid (without a screw shaped cavity)? 

Regards

[peteroznewman]

Did you follow the Immersed Body example in the discussion?  You mesh the fluid cavity without the screw and you mesh the screw separately. Doing a 2D model just makes the solution faster and gives you confidence that you know how to build a valid model that runs before you spend the effort on the 3D case.

[maaz007]

Yes i followed that example but unfortunately the meshing portion is excluded from that example. it only focuses on Preprocessing and onwards. Also is there any method other than immersed body method to carry out this type of simulation?

 

[Rob]

You can try overset in Fluent or full moving mesh: neither will be simple.  Can you post a couple of images of what you want to model: it's very easy for a poor translation to confuse on here. 

[maaz007]

you mean the simplest of all methods will be the immersed solid method? I have attached the screenshots of the compressor

[Rob]

Immersed solids (CFX) or Overset (Fluent) will be easiest within the solver. Mesh requirements may make it more complicated. 

[maaz007]

I am having a problem with extract volume. when i import this geometry into ansys spaceclaim, it shows the model as a combination of surfaces rather than solid bodies. so the extract volume says it only works for solids

[peteroznewman]

Go to the Repair Tab and click the Missing Faces tool to convert a set of faces into a solid.

[maaz007]

I have run the simulation using immersed solid method by making the 2 rotors as immersed solids but i have a problem. after the solution when i draw streamlines in cfd post, the lines are crossing the rotors i.e. they are not considering it as a solid. i mean how can fluid cross the rotors when i have marked it as immersed solid domain. any ideas? 

 

[Rob]

I'd suggest starting a new thread in the Fluids section: I don't know and Amine & others tend not to look in here. 

[maaz007]

nevermind. i want to confirm that u told me to go for immersed solids method, does it cater for the compression being taken place due to screw movements as its a compressor.

[Rob]

If you've got the geometry gaps correct and set it up then yes, the feature will mimic whatever you're trying to model. Including screw pumps etc.  If you plot pressure contours can you see that?

[maaz007]

i have two concerns regarding this:
1- the pressure rise shown in contours is neglible where as a high value was expected.
2- the ANSYS CFX Solver modelling guide tells that immersed solid doesnt cater for the compression effects very well and also not works with total energy or thermal energy models. but i have to enable the total energy model otherwise how would the compression be taken into account by the solver?

[Rob]

 As there's a thread in fluids I've copied your post there.   I can't answer this (I don't use CFX enough) and Amine tends not to look in here, as I mentioned yesterday.