Aspect Ratio - Single and double precision

MissCFD · October 23, 2016, 19:46

Hey,

Can someone tell me why when we run in double precision, the acceptable range for aspect ratio increases ?

Furthermore, can somebody please explain me why in CFX-Solver Manager User's Guide (3.2.1.5), it is written that a good quality (OK) for aspect ratio is less than 10 000 whereas in CFX-Solver Modeling Guide (15.3.2.3), the acceptable range for aspect ratio is less than 1 000 ?

Thank you very much for you help !

ghorrocks · October 24, 2016, 03:28

Increasing the aspect ratio of the elements means the diffusion of the mesh increases. If the diffusion swamps the fluid signal then the simulation will be inaccurate. Double precision numerics allows smaller fluid signals to be defined and so can handle worse quality meshes before they get swamped in diffusion.

The difference in recommended aspect ratio is because it is just a general guide based on judgement. The actual requirement varies simulation to simulation. So different people made different estimates of a general requirement - but it should be taken as no more than a guide as some simulations are more sensitive and some are less sensitive.

October 23, 2016, 19:46	Aspect Ratio - Single and double precision	#1
MissCFD Senior Member Join Date: Aug 2014 Posts: 160 Rep Power: 12	Hey, Can someone tell me why when we run in double precision, the acceptable range for aspect ratio increases ? Furthermore, can somebody please explain me why in CFX-Solver Manager User's Guide (3.2.1.5), it is written that a good quality (OK) for aspect ratio is less than 10 000 whereas in CFX-Solver Modeling Guide (15.3.2.3), the acceptable range for aspect ratio is less than 1 000 ? Thank you very much for you help !

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October 24, 2016, 03:28		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,852 Rep Power: 144	Increasing the aspect ratio of the elements means the diffusion of the mesh increases. If the diffusion swamps the fluid signal then the simulation will be inaccurate. Double precision numerics allows smaller fluid signals to be defined and so can handle worse quality meshes before they get swamped in diffusion. The difference in recommended aspect ratio is because it is just a general guide based on judgement. The actual requirement varies simulation to simulation. So different people made different estimates of a general requirement - but it should be taken as no more than a guide as some simulations are more sensitive and some are less sensitive.