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December 15, 2002, 23:58 
fluidparticle: turbulence change

#1 
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Dear researchers who are Modeling Particulate flow in a turbulent primary liquid flow:
I was expecting some modulation of turbulence of the primary liquid flow as I injected particles (then used 2way coupling). Unfortunately, I don't see any difference of the fluid properties (e.g., turbulence kinetic energy for example) before and after the particle injections in the primary liquid flow.. Can anyone shed some lights in this matter?? Alisa 

December 16, 2002, 20:08 
Re: fluidparticle: turbulence change

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How are the linear momentum and particle equations coupled?
What volume fraction of particles are in the flow, and what is the Stokes number for your particular case? 

December 16, 2002, 23:36 
Re: fluidparticle: turbulence change

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1) The Momentum equation is:
F=Sum[18*mu*Cd*Rep*Ur/(rop*dp^2*24)+Fothers]mp*DelT This term is used as momentum sink in the primary mometum equation and source in the particulate flow equations. Fothers is the sum of pressure force, virtual mass force, saffman lift force. 2) This is a steady state process and the volume fraction of the particles is ~ 1 %, The Stoke number is [rop*uf*dp^2/(9*mu*L0)] ~20 at the plane of injection. Regards, Alisa 

December 18, 2002, 09:32 
Re: fluidparticle: turbulence change

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can you also tell us the density of the particle? that will give the mass loading of the particles.
if the mass loading is signifacnt, then the particles will affect the flow. you will have to provide more information. regards, chidu... 

December 18, 2002, 15:00 
Re: fluidparticle: turbulence change

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The density of the particles is 950 kg/m^3 (buoyant particle), water as a liquid fluid (density 1000 kr/m^3)
The mass flow rate is 1% od the liquid flow rate (mass/s) Now pls advice me what might be wrong? Alisa 

December 19, 2002, 05:54 
Re: fluidparticle: turbulence change

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So looks like your mass loading is 0.01 or 1%. This is quite a small mass loading. To see some change in the flow in a global sense you might need mass loadings of atleast 0.1.
What is your flow configuration? Also your particle is not that buoyant. It is almost neutral. Basically your Stokes number is high, so I am assuming that the number of particles in the domain are quite small. Is this true? Regards, Chidu... 

December 20, 2002, 07:34 
Re: fluidparticle: turbulence change

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Are you doing a 4way coupling, meaning that you calculate source terms for kepsilon or just source terms for the momentum equations (2way)? Jan


December 20, 2002, 13:59 
Re: fluidparticle: turbulence change

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Hi Chidu, Do you have any reference to this statement : To see some change in the flow in a global sense you might need mass loadings of atleast 0.1. ??
I believe that I have seen papers where even though the mass loading is less than 10%, there is an effect. When you say, the mass loading has to be atleast 10%, do you also mean that I can't use Lagrangian partic particle tracking?? Will be eagerly waiting for your response. Alisa 

December 20, 2002, 14:05 
Re: fluidparticle: turbulence change

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Hi, I never used 4way coupling. In fact I am using a software called "FLUENT", I am not sure how difficult it would be to use 4way coupling in FLUENT.
I am only using 2way coupling. And I am using Cloud particle modeling as well. Do you have any good reference of 4way coupling? And do you agree with the Chidu, like he/she thinks that to have an effect on the turbulence, I need at least 10% mass loading?? Regards Alisa 

December 21, 2002, 09:30 
Re: fluidparticle: turbulence change

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Hi Alisa,
My statement was not a strict limit. All I meant was 1% mass loading is quite small and it is quite possible that you would not see any change. I didn't say that you can't using Lagrangian particle tracking (LPT) for mass loadings of 10% or more. It depends on the density of the particle. If it is many times heavier than the fluid then a high mass loading can be easily achieved even for dilute suspensions. May I ask for references which show observable differences for mass loadings of 1%? If you look at some of the papers on twoway coupling using DNS (Prof. Elghobashi Phys.Fluids 1993 work) their lowest mass loading is 23%. regards, Chidu... 

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