Learning Forum

[Yash Nitnaware]

sir i am doing non-premixed combustion simulation of C4H6 and O2 in ansys fluent, I have put the operating pressure for non-premixed combustion as 1200000Pa, inlet mass flow rate as 0.1 kg/s and fuel inlet as 0.024 kg/s and the exit pressure outlet as 0.57806 bar. But in the pressure i am getting negative pressure at the throat.

why am i getting negative pressure at the throat?

 

[vinaraya]

Hi Yash, the absolute pressure in Flunet is equal to gauge static + operating pressure. In your case, I would expect the velocities are high in the throat area (please post picture of velocity magnitue and mach number). In such cases, it would better to look for total pressure (gauge static + dynamic pressure) - this total pressure is in gauge. As fluent doesnt have an explicit post-processing variable called absolute total pressure - you could create a Custome Field function (total pressure + Operating pressure of 12bar) and check the contour. 

Additionally, you can try to give realistic expected limits for pressure in the limits panel. This will limit the pressure from moving to unphysical values.

Regards,

Vijay

[Yash Nitnaware]

thank you sir, for this suggestion.

[Yash Nitnaware]

but after putting the limit values , i am still getting the negative values at throat

 

[vinaraya]

Hi Yash, have you checked the absolute total pressure as mentioned earlier ? can you check the velocity magnitude/Mach number contours + are we seeing any flow separation (you can check the vector plot for that) + check the mesh resolution (keep the y+ close to 1). What turbulence model are you using (use the k-w SST model if you are currently using the k-e model).