Compressible flow for an ejector

[ramrecon]

Hi all,

I am asking to check if you could give feedback on a device I made, a simulation a gas ejector (in this case the working fluid is only air).

I want to see the suction capabilities of the ejector with it current geometry, the motive pressure is 9 bar_a and the ejector discharges the air to the atmosphere at 0 gauge.

I'm not quite sure what to specify as for the inlets and outlets, my inlet is specified as a Total pressure of 9 bar_a, the outlet (discharge) is 0 gauge pressure and the suction port is an Unknown.

My turbulence model is the k-e with IWF turned on, no special enhancements in the wall area except for regions on the nozzle and at the diffuser.

Do you have any feedback on this particular problem? Do I need to extend me outlets further ?

And thank you for your excellent support on these forums, I am very impressed with the quick feedbacks and dedication! 🙂

[Jon.Wilde]

Hi,

Your setup generally looks great. Although you might like to consider a 1/2 model to halve the run time 🙂

Good use ot mesh and regions by the looks of it.

Do you know if the Total Temp value set in the Solve -> Physics box applies to both inlets? We need some sort of Total Temp assigned but as of yet I am not sure if you need it on both inlets or just in the solve box.

What exists in reality at the suction port? Is it open to atmosphere?

How is the main inlet fed?

Your inlets/outlets look long enough I think, just be sure to check the outlet, that the flow is nice and smooth by the time is exits. If not, then extend it.

Hope that helps,

Jon

[ramrecon]

Hi Jon, 

Thanks for the quick reply. 

In reality the suction port pressure would be around 0,1 bar_a but I am really interested in how much suction the ejector can provide given the mass flow rate through the main inlet (mass flow rate is ~1,1 kg/s).

I changed the inlets since I posted the last post in such a way that I fixed the static pressure at the main inlet to 9 bar_a and introduced a velocity of 40 m/s.

Suction port boundary condition: Unknown (since I want to determine the suction/pressure)

Discharge: Open to atmospheric conditions

The total temperature is set in the Solve -> Physics tab to ~26°C.

My field really is not in the compressible flow region I am more in the incompressable so forgive me if I am forgeting the important bits 🙂

Regards,

[Jon.Wilde · Accepted solution]

No problem, that is what we are here for 🙂

Best to stick to mass flow rates if you know them, although a velocity should be fine too (just good practice).

Check this page out, I find it pretty useful: Internal Compressible Flow

You might also need to up the pressure in the Material Environment to 9 bar.  Check the inlet density is correct within results. You can run 0 iterations and verify this before running the full solve.

Your setup might be OK, I am just not sure if the unknown will be enough, could be.

Let us know how it runs?

Thanks,

Jon

[ramrecon]

Hi Jon,

I just completed the analysis and it seems to be giving good results, when looking at mass flow rates through the ejector, flow is being brought up at the suction port and being discharged at the outlet.

And I verified the density at the main inlet it is valid for air at 9 bar.

I am running the model again now with the SST model (ADV5) + enhanced mesh layering at the boundary to see the different results.

So far it seems to be looking good 🙂 Thanks for the advice.

ps. sorry for the late response but I just had a baby boy about 4 hours after I wrote my last reply 😄