# Question about Relative Velocity

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 August 8, 2013, 08:22 Question about Relative Velocity #1 New Member   Ding Chao Join Date: Aug 2013 Posts: 5 Rep Power: 4 Hi,everyone I am modeling a bubble flow useing CFX,and I need use relative velocity in CCL. I find that the slip velocity have no unit in the CFX reference_Guide,and I don't know this is why.Could anyone explain to me the question? Could I use this expression to calculate the relative velocity? Vr=sqrt((air.Velocity u-water.Velocity u)^2+(air.Velocity v-water.Velocity v)^2+(air.Velocity w-water.Velocity w)^2) If anyone know the answer,please help me!

 August 8, 2013, 18:58 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 11,053 Rep Power: 86 Seems strange. I would have thought slip velocity would be in m/s. Also make sure you are using the correct variable. There is "Slip Velocity" for ASM models, "particle Slip velocity" for particles, "Slip Velocity Magnitude". There should be no need to calculate this, it should already be a variable in the solver. You just have to find the right variable name.

August 8, 2013, 21:10
#3
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Ding Chao
Join Date: Aug 2013
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Quote:
 Originally Posted by ghorrocks Seems strange. I would have thought slip velocity would be in m/s. Also make sure you are using the correct variable. There is "Slip Velocity" for ASM models, "particle Slip velocity" for particles, "Slip Velocity Magnitude". There should be no need to calculate this, it should already be a variable in the solver. You just have to find the right variable name.
Thank you for your reply,but I don't understand what does the "Velocity of an algebraic slip component to the continuous" mean.Why it have no unit? What does the algebraic mean?
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 August 8, 2013, 22:11 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 11,053 Rep Power: 86 I don't understand it either. It might be a documentation mistake. Also we might be misunderstanding the variable. I am not sure which is the case.

August 8, 2013, 23:02
#5
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Ding Chao
Join Date: Aug 2013
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Quote:
 Originally Posted by ghorrocks I don't understand it either. It might be a documentation mistake. Also we might be misunderstanding the variable. I am not sure which is the case.
Thank you all the same!what do you think that if I use" Vr=sqrt((air.Velocity u-water.Velocity u)^2+(air.Velocity v-water.Velocity v)^2+(air.Velocity w-water.Velocity w)^2)"to calculate the relative velocity between gas and liquid?Is it accurate?

 August 8, 2013, 23:26 #6 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 11,053 Rep Power: 86 I suspect the value you get from your equation should be the same as Slip Velocity Magnitude, providing you are doing an ASM model. Is it the same?

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