cartesian Vs. Cylin-pol.
 

hi, I am simulating jet flow in a geometry which is primarily cylindrical. To be precise, an axisymmetric jet flows from a tube contained concentrically inside a cylindrical enclosure.

I have done it both in cartesian as well as cyl-pol. co-ordinates. the results however are coming out to be different. The reason I have assigned to it is as follows:

Since, the jet axis is arbitrary i.e., not aligned with either x or y or z, and due to structured grid approach of phoenics,(there are no cell faces perp.to axis of jet) flow along jet axis is not simulated properly and a spread more than what is actually occuring is depicted.

In Cyl-pol. co-ordinates, axial flow is simulated correctly, as jet axis is along Y axis for any jet orientation. But, will it be able to simulate transverse spread of the jet accurately enough.

If you find my reasoning correct, please answer to my query. If you dont, please explain to me the reason for discrepancy that should occur while changing co-ordinate system as it is highly undesirable for any software.

Thanks in advance

Arnie

Re: cartesian Vs. Cylin-pol.
 

There might be numerical smearing happening or maybe your cell apsect ratio is long in the main plume direction.

But why cant you not align the flow with say the Z axes in cartesian when you can with cyl-polar??

Look to see if the two cases are converged fully, it may be that the cyl polar one has done better and this may be somewhat due to the possibility that with polar you have aligned the main plume direction to an axes.

Run the cartesian again and align the pume direction to the z-axes, grind some convergence out and take a look, is the result appreciably different to your original run with inclined orientation.

Also There are things like HOS which might help, see numerical diffusion.

Re: cartesian Vs. Cylin-pol.
 

hi Mick, Thanks for pondering over my problem. Actually my problem involves obstructions in the path of the jet due to which I cant align as you said. Also, in cyl-pol syst., I have given jet axis to be along Y-direction so that I can chng the jet orientation easily. Changing jet orientation is very important in my case so as to study the efficiency of the jet. I would like to know what is HOS? Regards Arnie

Re: cartesian Vs. Cylin-pol.
 

HOS is higher order schemes.