I Hydrostatic pressure distribution despite fluid motion

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1. May 12, 2018

Kqwert

Hello,

in some exam questions I've looked at it is stated that the pressure distribution is hydrostatic, even though there is fluid motion. (In these cases the velocity has been constant over the section where the pressure is said to be hydrostatic). Is it really possible to assume that the pressure varies hydrostatically when there's fluid motion?

2. May 12, 2018

Staff: Mentor

If the fluid velocity vector is horizontal everywhere, then it's OK to call the pressure variation in the vertical direction hydrostatic. Otherwise, the pressure should be referred to as "static" pressure or (just plain) pressure.

3. May 12, 2018

Kqwert

Thank you, but shouldn't the velocity vector be uniform as well?

i.e

--->
--->
--->
--->

4. May 12, 2018

Staff: Mentor

If the flow is horizontal, then the velocity in the z direction is zero and, from the Navier Stokes equations and the continuity equation, it will be hydrostatic in the z direction.

5. May 12, 2018

Kqwert

Thank you. Do you have any links explaining this?

6. May 12, 2018

Staff: Mentor

Do you have any background on the Navier Stokes equations and the continuity equation, or are you relatively new to fluid dynamics?

7. May 12, 2018

Kqwert

I am familiar with the continuity equation, but not very familiar with Navier Stokes.

8. May 12, 2018

Staff: Mentor

OK. Google the Navier Stokes equations, and examine them for a Cartesian Coordinate system.