[boccardi]

Hi everyone!
I am analizing a supersonic turbine vane (NGV subsonic and rotor supersonic) with ansys CFX. The domain has a subsonic part which is the same in 3 different simulation (so all of them have the same chocking area) and i had some changes far from the choking area. Since i have in all the simulation the same inlet and outlet conditions and the same choking area (I checked I have M=1 always in the same spot), shouldn't i have to find the same massflow in all three of them, no matter what geometric changes i do in the supersonic part?
Cause I find 3 different values of massflow (massflow change even about 30%!!!)

I am imposing total pressure and static temperature at inlet and pressure at outlet.


What am I missing?


Thank you!

[Opaque]

Originally Posted by boccardi

Hi everyone!
I am analizing a supersonic turbine vane (NGV subsonic and rotor supersonic) with ansys CFX. The domain has a subsonic part which is the same in 3 different simulation (so all of them have the same chocking area) and i had some changes far from the choking area. Since i have in all the simulation the same inlet and outlet conditions and the same choking area (I checked I have M=1 always in the same spot), shouldn't i have to find the same massflow in all three of them, no matter what geometric changes i do in the supersonic part?
Cause I find 3 different values of massflow (massflow change even about 30%!!!)

I am imposing total pressure and static temperature at inlet and pressure at outlet.

By using static temperature, you may have different total temperature for each case, correct? Therefore, not the same model.

What am I missing?


Thank you!

If you specify static temperature at the inlet, you are not comparing the same models.

[boccardi]

Thanks for your answer Opaque.
Sincerely I didn't get your answer. I am specifying at inlet the same value of total pressure and static temperature in all 3 cases. So since I have the same boundary conditions (both at inlet and outlet) and the same geometry in the subsonic domain and in choking area, I am expecting to have the same mass flow

[Opaque]

Originally Posted by boccardi

Thanks for your answer Opaque.
Sincerely I didn't get your answer. I am specifying at inlet the same value of total pressure and static temperature in all 3 cases. So since I have the same boundary conditions (both at inlet and outlet) and the same geometry in the subsonic domain and in choking area, I am expecting to have the same mass flow

They may have the same boundary conditions, but not the same potential/stagnation conditions. The "Total available energy" can be different. Total Temperature defines the total available energy upstream. Static temperature does not.

I was surprised you did not use "Total Temperature" boundary condition for a highly compressible flow model.

[boccardi]

Thanks for the answer! Ok I am new in this, so I'll try to use total temperature and see what is going on