# Fluent Code (4.2 V) Limitations

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 July 25, 1998, 04:14 Fluent Code (4.2 V) Limitations #1 John Peter Guest   Posts: n/a I am using Fluent Code for my Engineering Project. I am working on compressible fluid(air) for sub-sonic and super-sonic flow. I want to know the maximium Mach No. which can be used and also other limitations of this code. For the case of super-sonic flow the code asked for inlet boundary conditions velocities, static pressure, total temperature and turbulence quantities, would you please guide us with an example the correct use of this boundary condition. (for example for Mach No. 2). Thanks.

 July 25, 1998, 04:51 Re: Fluent Code (4.2 V) Limitations #2 John C. Chien Guest   Posts: n/a I have used Fluent's series of codes because I happened to have opportunities to use it ( in an environment that I had the opportunity to systematically study it ) for very complex 3-D applications. ( I have created a model myself with over 500 general surface patches .) I also have used both the low speed module ( called UNS) and the compressible flow module ( called Rampant ) both for stationary and rotating reference frames in turbomachinery applications. It is against my principle to state bad thing in public about anything related to CFD. I think everybody brave enough to step into this highly risky CFD field should at least receive a medal. After having said that I will give you my professional opinion: 1) define your problem, 2) determine whether it is a subsonic problem, 3) If the Mach number is less than 0.3, then use the UNS module.( this must be the over-all flow field. if you are not sure, at least over the complete boundary you would like to see the subsonic condition specified.) 4) If the Mach number is greater than 0.3, then you should use the compressible flow module (the RAMPANT module). This is the basic guideline because of the different method used in these modules. When you say Mach 2, you have no choice but to use the compressible module. ( I think the scheme used for the compressible module is similar to the one proposed by Prof. Jameson in 80's.) The low speed module(UNS) was based on ralatively old incompressible scheme (extended to include perfect gas law, or variable density flow). Don't try this scheme for transonic flow, definitely not supersonic flow ( if you do, you are just kidding yourself). I don't say I like or dislike a code, because if someone is paying you for using it you have no complaint at all. ( If it's a life and death situation, I'll help you in private.) Make it simple to remember: use incompressible flow code for incompressible flows; use compressible flow code for compressible flows. ( Over-clocking your CPU speed can be dangerous to your computer. Most of the time, it may look all right. It's risky.) Hope this will set your thinking straight.

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