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-   -   there is not any vortex shedding in channel (http://www.cfd-online.com/Forums/cfx/120816-there-not-any-vortex-shedding-channel.html)

rasool motamedi July 15, 2013 10:53

there is not any vortex shedding in channel
 
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?
:confused::(:mad:

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.


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