# non-dimensional analysis in Fluent

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 September 4, 2005, 11:44 non-dimensional analysis in Fluent #1 Endee Guest   Posts: n/a Hi, can someone please tell how to use non-dimensioanl analysis in Fluent. Like I have a known Re of 1e5 and i want to simulate this over a circular cylinder in 3D. Cheers, Endee

 September 4, 2005, 13:51 Re: non-dimensional analysis in Fluent #2 Masood Guest   Posts: n/a hi Reynolds No. itself is dimesionless but when u apply it there should be any geometry. and u have to define it(geometry). any way in FLUENT i think u can simlate the original geometry itself and no need fr dimensionless calculation or scaling up or down to calculate results of required geometry.

 September 5, 2005, 06:42 Re: non-dimensional analysis in Fluent #3 Endee Guest   Posts: n/a hi, thanks, but can you imagine the geometry itself cant be implemented straightaway. Re=rho*vel*Dia/Meu now if rho=1.225, meu=1.7894e-5, Re=1e5 this gives for vel calculation... vel=1.7894/(1.225*dia) a) if your geometry is of dia 1 meter then vel=1.46 m/sec (is it logical at the Re)... b) if your geometri is of dia .0001 m then vel with respect to the same Re is 1460m/sec What do you say?

 September 5, 2005, 14:41 Re: non-dimensional analysis in Fluent #4 Masood Guest   Posts: n/a hi endee i can explain it like this. in simulations u can simulate logically bizarre situations which can be unrealistic. like u can simulate load distribution of urself as holding a 1000 ton boulder, it is unrealistic but can be simulated. or holding a feather in one hand and claculate load distribution. got my point.... u have to select a reasonable size fr ur problem. dimensionally u can reduce the size to very small levels but it will not be relaistic. i hope i make myself clear.

 September 6, 2005, 08:39 Re: non-dimensional analysis in Fluent #5 Jason Guest   Posts: n/a You have two unknowns (size and airspeed) so you need to match Reynold's and Mach number. Use Mach number to calculate your airspeed, and then Reynold's to calculate size. If Mach number isn't known, then you're going to have to infer if the original model was subsonic incompressible (Mach > 0.2), subsonic compressible (0.2 < Mach < 0.8), transonic (0.8 < Mach < 1.0) or supersonic (1.0 < Mach). Once you pick which Mach range you should be in, then you can calculate the range of sizes and airspeeds that would fit in this range. Then pick a combination that makes sense for your model. Hope this helps, and good luck, Jason

 September 6, 2005, 14:32 Re: non-dimensional analysis in Fluent #6 Endee Guest   Posts: n/a Dear Jason, Thanks, Thats seems much logical.. Just one relative query. If for only known Re No (1e5) and aspect ratio of cylinder (1-4), as Masood has mentioned, if i take some ratio, which is sort of illogical (like may be if i take the cylinder dia as .001m then the velocity becomes of the order of say two thousands meter/sec, will the result different if i assume dia as 1 meter with corresponding velocity of may be 2 m/sec. Because the Re is same for both cases. And that was my actual question. sincere regards, Endee

 September 7, 2005, 14:24 Re: non-dimensional analysis in Fluent #8 Masood Guest   Posts: n/a hi Jason made the point very clear. as i can say now is get to know ur problem well and the purpose of test or simulation. then u can narrow down the variables ranges to work in. good luck m8

 September 7, 2005, 16:16 Re: non-dimensional analysis in Fluent #9 Endee Guest   Posts: n/a Thats lovely, Thanks a lot, cheers Endee

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