# Help required to understand dynamic pressures

1. Aug 10, 2009

### aero_g

Hi all,

I am trying to understand the concept of dynamic and static pressures and would appreciate your help.

I've got a nozzle flow setup, such that the flow is exhausting into atmosphere. Am I right in assuming that the dynamic pressure at exit (relative to atmosphere) is equivalent to 1/2*rho*v2 and the gauge static pressure = 0?

2. Aug 10, 2009

### tiny-tim

Welcome to PF!

Hi aero_g! Welcome to PF!

(have a rho: ρ )
Yes, the gauge pressure = 0.

But I think saying "dynamic pressure at exit (relative to atmosphere)" is wrong …

I don't think there's any such thing as "gauge" dynamic pressure, so dynamic pressure is always defined as 1/2 ρv2, and Patm is irrelevant.

(from the PF Library on pressure …)

3. Aug 10, 2009

### aero_g

Re: Welcome to PF!

Hi there!

Thanks for your reply. You are right, "dynamic pressure at exit (relative to atmosphere)" is wrong …

Following that, the total pressure at exit is then = dynamic pressure (since static pressure = 0). Am I right in saying that?

4. Aug 10, 2009

### tiny-tim

Yup!

5. Aug 10, 2009

### aero_g

Thank you very much!!!!