## Fluids

#### I have few basic queries for nozzle flow.

• raju.chowdhury
Subscriber
1. we know that Absolute pressure is the sum of total gauge pressure and atmospheric pressure. In fluent why absolute pressure = static pressure + atmospheric pressure ?
2. I am simulating compressible gas flow in a CD nozzle. When I am plotting nozzle centerline total pressure profile, it is showing that total pressure increasing in the convergent section. I am expecting that total pressure will remain constant throughout the nozzle. Some pressure might be loss but pressure increase is not expected. What could be the reason for that?
• aitor.amatriain
Subscriber
Depends on your reference pressure. If reference pressure = 0, then absolute pressure = static pressure.
Could you post some pictures of velocity and static pressure contours?
• RK
Ansys Employee
Hello,
Please refer to this section on the user's guide for a detailed understanding on the definition of pressure in Fluent : https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v211/en/flu_ug/flu_ug_op_abs_gauge_press.html?q=absolute%20pressure
I see the change in total pressure is not so much. The error could be either numerical dissipation or coarse mesh in that region. You could use a higher order scheme for better accuracy. Please refer to this course on compressible flow in a nozzle : https://courses.ansys.com/index.php/courses/compressible-flow-in-a-nozzle/
• raju.chowdhury
Subscriber
Hi RK Thanks for your reply.
I used higher order scheme and fine mesh in that region. The pressure increase issue in the previous image solved but sudden pressure drop occurs at the throat (see the attached image). Using 1st order scheme, results matched well with isentropic theory but for the higher scheme due to the fluctuations results are not matching well with the theory.
Although the pressure increase is not too much (in the previous image), are there any other reason (except mesh and higher order scheme) to increase the pressure?

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