Learning Forum

[GKokkinos]

Dear Community,

I am a new member to this community and I would like to start by expressing my gratitude to everyone who spends his/her time to answer questions and help fellow ANSYS users.

I have a 2D axisymmetric model of a converging-diverging nozzle with an exhaust region. The structured mesh is used and the inlet BC is pressure inlet, with 3 x10^6 gauge total pressure and 3 x 10^5 supersonic initial pressure. The inlet temperature is 623k.  At the pressure outlet, the gauge pressure is 0Pa and the temperature is 293K. I use a density-based solver, Realizable K-e, Non- Eq wall Fn. I use Implicit formulation, Roe-FDS and least-squares Cell-based where the flow is second-order upwind and the rest first order. The geometry of is this one (The red lines are the pressure outlet (0 Pa gauge pressure and 293K ). The white lines are the wall, and the blue line is defined as the pressure inlet.):

This gives the following velocity profile on the axis of symmetry (shown in images)

The issue is:  I want to split the model into the nozzle and exhaust region. I start with the nozzle geometry shown below and the same inlet conditions described above. The exhaust region is again defined as pressure outlet and left as default. 

The velocity profile along the axis is  shown below. This is what was expected. It is the same as with the full nozzle + exhaust region model except that it stops at the end of the nozzle. 

Then I export the static pressure, total pressure and total temperature profiles at the outlet of the nozzle. 

Then I try to create the exhaust region as shown below:

The red lines are the pressure outlet (0 Pa gauge pressure and 293K ). The white lines are the wall, and the blue line is defined as the pressure inlet. I use the static pressure profile in the Supersonic/Initial pressure box, the total pressure profile in the Total pressure box and the total temperature profile in the total temperature box. In the initialisation pane, I click on the "USE SPECIFIED INITIAL PRESSURE ON THE INLETS". 

My model doesn't converge, it throws an error "Wrong type". I do not know how to make it work. I can see that the profile data and the Interpolated data are the same. However after it throws an error, when I try to plot the pressures at the inlet they are slightly different than the input profile and the interpolated profile shown in order below:

Does anyone got any clue as to what is going on? Should my inlet BC be different (its supersonic)? Should my reference Values be different ( i have it as default)? 

Any help is greatly appreciated... I spent hours and hours on this Thank you very much beforehand for spending the time to read through it. Let me know for any further clarifications.

Best regards,

G.K.

 

[DrAmine]

Please insert the pictures in your test and not as attachement.

[DrAmine]

For supersonic pressure inlets both fields are required: the stagnation pressure and the static pressure.

[GKokkinos]

Hi Amine,

Thank you very much for taking the time to reply. I tried including the pictures inline with the text but it threw an error saying that the string can only have 6000 characters. 

As for the supersonic inlet, where should the stagnation pressure be inserted?

I can only see the boxes of Gauge Total Pressure and Supersonic/Initial Gauge Pressure. I took the total pressure profile from the nozzle's outlet and the static pressure profile and put it in the GTP and the S/IGP respectively. 

Best regards,

George 

[DrAmine]

Insert the pictures in several posts if you want.

 

Total Pressure at Inlet is stagnation Pressure.

[GKokkinos]

Thank you once again Amine. 

I have edited my post successfully to include the images. 

I will try what you said: replace the total pressure with the stagnation pressure and I will update this post. 

On a different note, when I used the PRESSURE BASED SOLVER instead of the DENSITY SOLVER for the exhaust region, it worked (converged quickly) and it gave me this velocity profile which complements the nozzle's :

Any idea why this would happen?

Best regards,

George

[DrAmine]

Again the total pressure you are exporting as profile you need to use it in the total pressure field. The static pressure as profile in the supersonic pressure field. All other things remains the same. 

 

And please use a recent version: 18.x is not supported.

[GKokkinos]

I understand, thank you! Due to some compatibility issues, I am unable to update the ansys version at the moment. 

Unfortunately, what you suggest is exactly what I am doing. However, it doesn't work with the density-based solver but apparently it works with a pressure solver. Would you please explain why this is happening?

Best regards,

George 

[DrAmine]

I cannot explain it without looking into the case and testing with new version. If pressure based solver is working for you that you a solution.

[GKokkinos]

Thank you very much for all your help Amine. 

Best regards,

George