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variable velocity wrt position
Posted 3 feb 2012, 22:22 GMT-5 Version 4.2 1 Reply
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hi,
I want to define a variable velocity with respect to the position. for example if i define a flow in a tube, then at inlet v=U*y/a where y is height. Can you help me in this?
I am working on a problem of flow around an oscillating cylinder. Can you help me defining the oscillating cylinder?
Thank you,
Hemant Khatri
I want to define a variable velocity with respect to the position. for example if i define a flow in a tube, then at inlet v=U*y/a where y is height. Can you help me in this?
I am working on a problem of flow around an oscillating cylinder. Can you help me defining the oscillating cylinder?
Thank you,
Hemant Khatri
1 Reply Last Post 4 feb 2012, 02:51 GMT-5
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Posted:
1 decade ago
Hi
And have you tried to write out just that, i.e. in an initial condition BC, and then solved for the initial conditions (right click dependent variables in the solver node and hit Compute to selected) and observe in the Results
This works correctly if U is in "m/s" and a in "m" your velocity should then vary linearly with y from ymin to ymax, else you need to add an offset of the type U*(y-ymin)/a.
If it is for the inlet velocity along a 2D Inlet BC you might use the parabola function cte*U*s(1-s) where s is the 2D edge parameter COMSOL defines running from 0 to 1 (along the arrow direction) and cte is a constant to adapt the velocity to Umax or Uaverage or whatever you want. as int_0to1(x*(x-1)=1/6 and 0.5*(1-0.5)=1/4, so cte=6 should be for the average velocity and cte=4 for the max value if I'm right here, the easiest is to integrate the velocity with COMSOL to be sure you havent missed the cte value ;)
In 3D its more equation demanding as you need to set up the correct x,y possible z mapping
--
Good luck
Ivar
And have you tried to write out just that, i.e. in an initial condition BC, and then solved for the initial conditions (right click dependent variables in the solver node and hit Compute to selected) and observe in the Results
This works correctly if U is in "m/s" and a in "m" your velocity should then vary linearly with y from ymin to ymax, else you need to add an offset of the type U*(y-ymin)/a.
If it is for the inlet velocity along a 2D Inlet BC you might use the parabola function cte*U*s(1-s) where s is the 2D edge parameter COMSOL defines running from 0 to 1 (along the arrow direction) and cte is a constant to adapt the velocity to Umax or Uaverage or whatever you want. as int_0to1(x*(x-1)=1/6 and 0.5*(1-0.5)=1/4, so cte=6 should be for the average velocity and cte=4 for the max value if I'm right here, the easiest is to integrate the velocity with COMSOL to be sure you havent missed the cte value ;)
In 3D its more equation demanding as you need to set up the correct x,y possible z mapping
--
Good luck
Ivar