Les under prediction drag

hosseiniazim · January 12, 2021, 09:38

Hi every body
I am trying to predict a boat drag with Large Eddy Simulation . but i have large under prediction drag .about 36% less than real drag.any one can help me with it?

ping · January 13, 2021, 04:07

i have never heard of anyone using les for boat drag and this sounds like a big waste of resources considering the mesh and timesteps that would be required.
well constructed models using standard 2 equation rans turbulence models will get you to within a percent or two of measured towing tank data for most types of boats.

hosseiniazim · January 13, 2021, 07:33

yes i know i can use k-e or k-w models .but i want to know why drag from LES has large under predicted results? what is problem? how i can fix it?

ping · January 13, 2021, 07:42

well as i implied in my first answer, cases need an extremely fine mesh and very short timesteps when using les and this is one of the reasons it is rarely used for real engineering problems since it is very impractical and cases take too long to solve even on massive super computers

hosseiniazim · January 13, 2021, 08:31

i see.thank you for your answer.can you tell me what is the appropriatey+ value for LES?

January 12, 2021, 09:38	Les under prediction drag	#1
hosseiniazim New Member Azim Join Date: May 2020 Posts: 11 Rep Power: 5	Hi every body I am trying to predict a boat drag with Large Eddy Simulation . but i have large under prediction drag .about 36% less than real drag.any one can help me with it?

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January 13, 2021, 04:07		#2
ping Senior Member Ping Join Date: Mar 2009 Posts: 556 Rep Power: 20	i have never heard of anyone using les for boat drag and this sounds like a big waste of resources considering the mesh and timesteps that would be required. well constructed models using standard 2 equation rans turbulence models will get you to within a percent or two of measured towing tank data for most types of boats.

January 13, 2021, 07:33		#3
hosseiniazim New Member Azim Join Date: May 2020 Posts: 11 Rep Power: 5	yes i know i can use k-e or k-w models .but i want to know why drag from LES has large under predicted results? what is problem? how i can fix it?

January 13, 2021, 07:42		#4
ping Senior Member Ping Join Date: Mar 2009 Posts: 556 Rep Power: 20	well as i implied in my first answer, cases need an extremely fine mesh and very short timesteps when using les and this is one of the reasons it is rarely used for real engineering problems since it is very impractical and cases take too long to solve even on massive super computers

January 13, 2021, 08:31		#5
hosseiniazim New Member Azim Join Date: May 2020 Posts: 11 Rep Power: 5	i see.thank you for your answer.can you tell me what is the appropriatey+ value for LES?