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Old   August 28, 2006, 03:52
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I am involved in a project where double precision is vital. I activated 2ddp Fluent program and entered the value of temperature in the range uptop 10 decimals in the form of 304.14567545 , but after initialising the case (INIT) the value hasn't retained, it has converted to approximation values as 304.1457. I would like to know whether the FLUENT solver is really working in approximation or it has really retained all the values after decimal as my result should be in high precision. Thanking you in advance for your valuable reply.


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Old   August 28, 2006, 08:45
Default Re: DOUBLE PRECISION doubt
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I'm not saying your setup is wrong (just that I don't understand it), but where are you getting a temperature value accurate to 10 decimal places? Is it some theoretical value you're trying to apply? And what benefit do you get to having 10 decimal places over 4? I would think the numerical error in the discretization could be larger than 1e-10... The only thing I can think of with that precision is chaos theory (one of the properties of chaos is "sensitive dependence on initial conditions"), but I don't see how/why you'd be using Fluent for chaotic analyses... Typical temperature measurements are only 1 decimal place, highly accurate temperature measurements might be 2 or possibly even 3 decimal places (I've never worked with anything more accurate than .05deg, and even that I had my doubts on... I understand some other disciplines may need more accurate temperature measurements and have their own equipment for that).

Don't get me wrong. I'm not saying you don't need 10 decimal places on temperature, because I don't know the specifics of your problem. I'm just trying to understand how/where/why you have 10 decimal places on temperature.

As for your question, one way to check is a little manual, but it should work. Initialize the flowfield based on your inlet conditions. Then do an XY plot of temperature at your inlet. It should be a flat line. In the XY plot window is an axes button. Here you can change how the temperature axis represents it's values. You can adjust the range and the decimals shown on the axis. Play around with this to see if there are more than 4 decimal places being stored at the inlet (I think the maximum you can show in an XY plot is 9 decimal points using the Float format, or 9 significant figures using the Exponential format, but that'll at least tell you if Fluent is storing more than the 4 shown in the BC window).

If you can share it, I would like to learn about what you're doing that uses 10 decimal points on temperature.

Thanks, Jason
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Old   September 11, 2006, 08:20
Default Re: DOUBLE PRECISION doubt
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I apologise for my late reply as I was in vacation. I wish to thank you for your reply. The problem is based on supercritical fluid taking place in a non zero gravity environment (space), where the temperature is set to reduce in milli kelvins and the precision is required upto 7 or 8 decimal values. We have programmed a code with the help of FORTRAN and it worked and now we are trying to understand whether its capable in FLUENT package.
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