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January 28, 2005, 15:44 
supersonic mixing : boundary condition

#1 
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I am doing a 3d simulation of a mixing problem where a sonic jet is injected into supersonic crossflow. I am using second order extrapolation boundary condition at the exit. But I am getting negative densities at the exit boundary condition. Any suggesations ? Amol


January 28, 2005, 15:50 
Re: supersonic mixing : boundary condition

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Is the wall normal velocity into the domain or out? Is the wall normal velocity subsonic or supersonic?
What is your intent for the boundary? Do you want a nonreflecting boundary, a force free boundary, or maybe one where some quantities are fixed? 

January 28, 2005, 16:17 
Re: supersonic mixing : boundary condition

#3 
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I guess the earlier discription was very short. so this:
A a sonic (Mach 1) jet is injected into a constant area duct. The crossflow (flowing across the duct) is of Mach 2. I am having trouble at the exit boundary where flow leaves the computational domain. Right now I am doing a inviscid mode simulation and hence the velocity normal to exit boundary is supersonic. But in practise, the flow at the exit will be a supersonic boundary layer having both subsonic and supersonic layers. My intent for the boundary is to have a smaller computational domain. THanks for the reply Runge_Kutta (cool name). 

January 28, 2005, 17:12 
Re: supersonic mixing : boundary condition

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For outflow boundaries one should specify this number of boundary conditions:
Euler Subsonic: 1 Euler Supersonic: 0 NavierStokes Subsonic: N_dim + 2 + (N_species  1) Navier Stokes Supersonic: N_dim + 1 + (N_species  1) where N_dim is the number of dimensions in your simulations and N_species is the number of species in for which you are solving a species equation. Take each boundary grid point on a point by point basis and classify it as inflow/outflow, subsonic/supersonic. Next, be careful about Euler boundaries in a NavierStokes calculation (things like inviscid slip walls). Right now, you are not permitted to impose any BCs for an Euler supersonic outflow. That will change when you add diffusive terms. 

January 28, 2005, 17:16 
Re: supersonic mixing : boundary condition

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I am using a commercial code for the simulation and I have to use the boundary conditions avilable with software. The list is at : http://www.aerosft.com/Gasp/Manual/reference/x1885.html
The most relevant boundary condition I found was extrapolation from within the cell. Thanks a lot for the help. 

January 28, 2005, 17:32 
Re: supersonic mixing : boundary condition

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First, you and GASP aren't talking to each other. It sounds like GASP isn't interested in Euler flows. Maybe you should presume that all is NavierStokes and proceed accordingly.
Navier Stokes  Supersonic outflow : All wallnormal components of the viscous stress tensor = 0. (n dot tau = 0) The wall normal heat flux is zero (n dot q = 0) All wall normal species diffusion velocities are zero. Navier Stokes  Subsonic outflow : Both tangential wallnormal components of the viscous stress tensor = 0. (n dot tau dot t1 = n dot tau dot t2 = 0) where t1 and t2 are two tangential unit vectors to the surface. The wall normal heat flux is zero (n dot q = 0) All wall normal species diffusion velocities are zero. The last BC is usually specified based on nonreflection criteria. 

January 28, 2005, 18:20 
Re: supersonic mixing : boundary condition

#7 
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Thanks a lot.


January 28, 2005, 20:00 
experimental data on bed to wall heat tranfer

#8 
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Hi Everybody
I am looking for experimental data on bed to wall heat transfer in bubbling fluidized beds. Could anyone cite some references. rahel 

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