
[Sponsors] 
February 13, 2006, 05:38 
about conservation of mass

#1 
Guest
Posts: n/a

Cartesian coordinat system. Inlet absolute velocity VEL=20 m/s enter in furnace at angel, say, 45 degrees. Then Uvel=20*sin(PI/4), Vvel=20*cos(PI/4). In result file can see that mass from inlet M=ro*Uvel*Area_of_Inlet, and Vvel does not take into account. I want to see mass flow M=ro*VEL*Area_of_inlet. How can I solve the problem? Is only BFC helps me?


February 13, 2006, 09:57 
Re: about conservation of mass

#2 
Guest
Posts: n/a

Please correct me if I am wrong but by setting the Vvel as you did. Vvel will be tangent to inlet so may be there is no net in flow from that component. İs that right. best regards.


February 14, 2006, 04:02 
Re: about conservation of mass

#3 
Guest
Posts: n/a

Thank u fevzi for your reply. Yes, u are right about Vvel. Think only BFC can help me.


February 15, 2006, 05:13 
Re: about conservation of mass

#4 
Guest
Posts: n/a

What is meant by "and Vvel does not take into account"? Does it mean that the NETT SOURCE printout in the RESULT file indicates zero momentum inflow rate for the velocity component parallel to the inlet plane Vvel, rather than m*Vvel, where m is the mass inflow rate?
I don't see why BFC is needed because if the VALues in the COVAL statements for the two Cartesian velocity components are 28.28 m/s and of the correct sign, then the momentum inflow rate should be correct. In the RESULT file, what COVAL statements appear for this inlet PATCH in the Group 13 printout? Also, in the VR Editor, is this inlet set up through an INLET or USERDEFINED object? 

February 15, 2006, 07:04 
Re: about conservation of mass

#5 
Guest
Posts: n/a

Thanks Mike for your reply. "Vvel does not take into account" meant that in the result file momentum does not indicates zero momentum inflow rate, but mass inflow (in result file) solve only for NORMAL velocity. Then if ABSolute velosity vector = 20 m/s, Vvel=20*sin(45 DEG)=14.14, Uvel=20*cos(45 DEG)=14.14. Net source for momentum is correct, but net mass flow in the inlet not correct, because of mass_flow_rate=ro*normal_vel*net_area. If I put (from patch and coval for P1) correct mass flow rate= ro*ABS_VELOCITY*net_area and UVel=Vvel=14.14 m/s I cann't get an convergence (because of momentum and mass do not conform).


February 15, 2006, 07:38 
Re: about conservation of mass

#6 
Guest
Posts: n/a

Thank you. It is becoming a little clearer what you are doing.
If I have understood correctly, in your case the flow enters at angle of 45deg to the inlet plane. If so, then the PATCH and COVAL statements should be: PATCH(INL,WEST,IXF,IXL,IYF,IYL,IZF,IZL,ITF,ITL) COVAL(INL,P1,FIXFLU,RHO1*14.14) COVAL(INL,W1,ONLYMS,0.0) COVAL(INL,U1,ONLYMS,14.14) COVAL(INL,V1,ONLYMS,14.14) The velocity used in the P1 patch should be Q.A where Q is the velocity vector, and A is the inlet vector area. This means that the velocity component used to define the mass inflow rate is (Q.n), where n is the unit vector normal to the inlet plane. Therefore, in the NETT source printout of the RESULT file we should see: mass inflow rate=rho1*14.14*inlet_surface_area U1 & V1 momentum inflow rate = mass inflow rate*14.14 

February 15, 2006, 09:25 
Re: about conservation of mass

#7 
Guest
Posts: n/a

Yes, Mike you are right. But point is that if u change inlet flow angel (without changing ABS_velosity) mass flow rate changed too. If u want to fix mass flow rate  u must changing ABS_velosity and as result momentum source (((. Can u tell me can I change inlet flow angel wihtout changing momentum and mass flow rates in cartesian system?


February 15, 2006, 09:29 
Re: about conservation of mass

#8 
Guest
Posts: n/a

I don't understand what you mean. It doesn't make much sense to me. I think you will have to tell me exactly how you are implementing the inflow conditions.


Thread Tools  Search this Thread 
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Mass Conservation in LES  Sas  Main CFD Forum  3  July 6, 2007 10:37 
Mass Conservation  Prabhas  FLUENT  0  December 5, 2006 01:15 
mass conservation  mange  FLUENT  0  July 20, 2006 07:08 
Mass Conservation in LES  Jaswant  Main CFD Forum  8  July 4, 2005 22:32 
Mass Conservation  Balaji  FLUENT  0  May 11, 2005 07:16 