there is not any vortex shedding in channel

rasool motamedi · July 15, 2013, 10:53

hi
realy I need help
i am simulating a microchannel
length= 7500 micrometer
width=750 micrometer
and there is a vertically stirrer in channel with 400 micrometer length
walls of channel and stirrer are no slip condition
flow is laminar and multicomponent with two water data and constant property
mesh quality is 1 and I done grid study from 35000 element to 150000 element
I use adaptive timestep with max 5 and min 3
and max dt=0.001 and min dt=0.00001
inlet velocity is 4.2 m/s
my poroblem is that there is not any vortex shedding in channel in cfx
but in lattice boltzmann method and SPH method solutions we have vortex sheding and difference between mass fractions
why?

ghorrocks · July 15, 2013, 21:47

Are you sure the flow actually has shedding? This sounds like a pretty low Re number to me, it might not shed.

To get vortex shedding you need high order differencing in time and space. So this means a second order advection scheme (eg high resolution or hybrid with factor =1.0) and second order time differencing.

Also, make sure the adaptive time steps do not hit your max and min limits.

July 15, 2013, 10:53	there is not any vortex shedding in channel	#1
rasool motamedi Member rasool Join Date: Apr 2013 Posts: 41 Rep Power: 13	hi realy I need help i am simulating a microchannel length= 7500 micrometer width=750 micrometer and there is a vertically stirrer in channel with 400 micrometer length walls of channel and stirrer are no slip condition flow is laminar and multicomponent with two water data and constant property mesh quality is 1 and I done grid study from 35000 element to 150000 element I use adaptive timestep with max 5 and min 3 and max dt=0.001 and min dt=0.00001 inlet velocity is 4.2 m/s my poroblem is that there is not any vortex shedding in channel in cfx but in lattice boltzmann method and SPH method solutions we have vortex sheding and difference between mass fractions why?

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July 15, 2013, 21:47		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Are you sure the flow actually has shedding? This sounds like a pretty low Re number to me, it might not shed. To get vortex shedding you need high order differencing in time and space. So this means a second order advection scheme (eg high resolution or hybrid with factor =1.0) and second order time differencing. Also, make sure the adaptive time steps do not hit your max and min limits.