Learning Forum

[raju.chowdhury]

I want to simulate the flow in a nozzle with a pressure 15 bar (abs). I only know the throat and exit diameter, throat length, diffuser length (not accurate, may be 2-3 mm difference from the actual geometry) of the nozzle. Is it possible to find nozzle exit velocity with the known information?nI tried to simulate by considering a arbitary nozzle inlet diameter (greater than throat but less than exit diameter). But not getting the expected pressure at the inlet boundary (At inlet getting 10.45 bar (abs)) . Any idea how to overcome the problem?n

[Kalyan Goparaju]

Hello, nCan you give a bit more information regarding the problem you are trying to simulate? Are you expecting a supersonic flow through the nozzle or subsonic? nThanks, nKalyann

[raju.chowdhury]

Supersonic velocity.n

[RK]

Hello, nYou can use the a_e/a_star relation to determine the corresponding pressure ratio and hence the Mach number. From the Mach number you can get the exit velocity. You will also have to find out the ratio of the temperatures of throat to exit. You can refer to any text book on compressible flow, where you might find an example for such calculations. n

[Aitor]

If you know inlet pressure, why do you say that you are obtaining a value of 10.45 bar? Inlet pressure should be a boundary condition of the problem.n

[raju.chowdhury]

My understanding is: if I give an input as 15 bar pressure, after simulation results I will get the same pressure at inlet. But instead of 15 bar, I am getting 10.45 bar. Why at inlet different pressure is showing?n

[RK]

Use a pressure inlet boundary condition and make sure you are setting the right value (depending on the set operating pressure value). n

[raju.chowdhury]

I am using pressure inlet boundary condition and using the right value as well.n

[Kalyan Goparaju]

Pressure inlet boundary condition sets the total pressure. Are you getting 10.45 bar when checking total pressure at the inlet or static pressure? n

[raju.chowdhury]

Hi Kalyan,nI was checking static pressure. Total pressure giving the same pressure that I given as input pressure. Thanks a lot.n