CFD Online Discussion Forums

hi all,

I am modeling hybrid rocket combustion. I use axi-symmetric model. My motor consists of a cylindrical combustion chamber and a convergent nozzle.

I model only the cylindrical port. So my grid is in the shape of a rectangle. From the left surface oxidiser comes in. From the top surface fuel comes in. The bottom line is the axis and on the right side a convergent nozzle is fitted.

The model grid can be found in "http://picasaweb.google.com/guru.palani" inside Projects folder.

As a first step, I keep the full inlet of the port (left side of rectangle) for oxidizer inlet and as I said the top surface becomes the inlet for fuel. So as such, there is a cross flow between oxidiser and fuel.

Now, the problem is, I require the fuel to come out normally from the fuel inlet boundary.(top surface of the rectangle), which I am not getting.

I use, density based solver, ideal gas approximation for fluids (so I could not use velocity inlet condition), and mass flow inlet boundary condition for both fuel and oxidiser.

And moreover as I switch on the reaction, after some iterations, I see reverse flow in fuel inlet which is something very much disliked, because any change in the fuel flux makes the flame to go off.

When I specify the normal mass flux, if reverse flow happens then it means that the boundary condition I specified (defined mass flux normal to the boundary) has not been satisfied. How do I tackle it..??

I need fuel to enter into the port normal to the surface at all the time.What should I do???

Is there a possibility to specify velocity at the boundary for compressible calculations???

Is there a possibility to specify some porous wall kind of boundary???I saw porosity can be defined at a zone and not at the boundary. Or is there a way to model some permeable membrane type of boundary???

Any sort of help would be highly appreciated.

Thanks in advance, Palani.