choosing boundary condition settings

seedl · November 5, 2015, 17:37

high every one!
i am trying to simulate a low reynolds insect body ( house fly and bee ) aerodynamics.
i want to know how to choose the turbulent intensity and turbulent viscosity ratio for velocity inlet and pressure outlet.
i just want to compare the insects body's in aerodynamics . and just need to use a reasonable data for my experiment because the value itself is not important but the ratio of drag force of body's which are different that have equal volumes is important.
so the ratio of drag force after solving should be true and drag itself just should be reasonable.
so what's your idea about default 5% of turbulent intensity and 10 percent of turbulent viscosity ratio?!
and it's default values in outlet...!

Steffen595 · November 8, 2015, 18:20

http://www.cfd-online.com/Wiki/Turbulence_intensity

the air is not moving, the insect is, so lowest turbulence?
the air just has to go out of the way, before it hits the insect., just move the inlet a bit back.

LuckyTran · November 9, 2015, 00:37

Well you need to know the origin of turbulence before you can specify it.

If the insect is flying in quiescent air (like in a laboratory or in a glass-jar) then there isn't any turbulence and you should be doing a laminar simulation (or 0% turbulence intensity simulation).

If the insect is flying around inside my home with the a/c and ceiling fans spinning , etc. then the turbulence is generated by these objects.

Either way I think it's better to specify the intensity and length scale since these are most likely the quantities available from correlations or measurements and such.

The outlet turbulence quantities are only needed if reverse flow is encountered.

November 5, 2015, 17:37	choosing boundary condition settings	#1
seedl New Member Join Date: Oct 2015 Posts: 3 Rep Power: 10	high every one! i am trying to simulate a low reynolds insect body ( house fly and bee ) aerodynamics. i want to know how to choose the turbulent intensity and turbulent viscosity ratio for velocity inlet and pressure outlet. i just want to compare the insects body's in aerodynamics . and just need to use a reasonable data for my experiment because the value itself is not important but the ratio of drag force of body's which are different that have equal volumes is important. so the ratio of drag force after solving should be true and drag itself just should be reasonable. so what's your idea about default 5% of turbulent intensity and 10 percent of turbulent viscosity ratio?! and it's default values in outlet...!

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November 8, 2015, 18:20		#2
Steffen595 Senior Member Join Date: May 2012 Location: Melbourne Posts: 161 Rep Power: 13	http://www.cfd-online.com/Wiki/Turbulence_intensity the air is not moving, the insect is, so lowest turbulence? the air just has to go out of the way, before it hits the insect., just move the inlet a bit back.

November 9, 2015, 00:37		#3
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,665 Rep Power: 65	Well you need to know the origin of turbulence before you can specify it. If the insect is flying in quiescent air (like in a laboratory or in a glass-jar) then there isn't any turbulence and you should be doing a laminar simulation (or 0% turbulence intensity simulation). If the insect is flying around inside my home with the a/c and ceiling fans spinning , etc. then the turbulence is generated by these objects. Either way I think it's better to specify the intensity and length scale since these are most likely the quantities available from correlations or measurements and such. The outlet turbulence quantities are only needed if reverse flow is encountered.