Hydrostatic pressure distribution despite fluid motion

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Discussion Overview

The discussion revolves around the conditions under which pressure distribution in a fluid can be considered hydrostatic, particularly in scenarios where fluid motion is present. Participants explore the implications of fluid velocity on pressure variation, referencing fundamental fluid dynamics principles such as the Navier-Stokes equations and the continuity equation.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants suggest that if the fluid velocity vector is horizontal everywhere, the pressure variation in the vertical direction can be considered hydrostatic.
  • Others argue that if the velocity vector is not uniform, the pressure should be referred to as "static" pressure or simply "pressure."
  • One participant questions whether the velocity vector should also be uniform for hydrostatic pressure to be applicable.
  • It is noted that if the flow is horizontal, the velocity in the vertical direction (z direction) is zero, which may lead to hydrostatic conditions based on the Navier-Stokes equations and the continuity equation.
  • Participants express varying levels of familiarity with the Navier-Stokes equations, indicating a range of expertise in fluid dynamics among the contributors.

Areas of Agreement / Disagreement

There is no consensus on whether hydrostatic pressure can be assumed in the presence of fluid motion, as participants present differing views on the conditions required for such an assumption.

Contextual Notes

Participants reference the Navier-Stokes equations and the continuity equation, but there are unresolved aspects regarding the assumptions necessary for applying these equations in the context of hydrostatic pressure.

Who May Find This Useful

This discussion may be of interest to students and professionals in fluid dynamics, particularly those exploring the relationship between fluid motion and pressure distribution.

Kqwert
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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?
 
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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.
 
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Chestermiller said:
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.
Thank you, but shouldn't the velocity vector be uniform as well?

i.e

--->
--->
--->
--->
 
Kqwert said:
Thank you, but shouldn't the velocity vector be uniform as well?

i.e

--->
--->
--->
--->
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.
 
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Chestermiller said:
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.
Thank you. Do you have any links explaining this?
 
Kqwert said:
Thank you. Do you have any links explaining this?
Do you have any background on the Navier Stokes equations and the continuity equation, or are you relatively new to fluid dynamics?
 
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Chestermiller said:
Do you have any background on the Navier Stokes equations and the continuity equation, or are you relatively new to fluid dynamics?
I am familiar with the continuity equation, but not very familiar with Navier Stokes.
 
Kqwert said:
I am familiar with the continuity equation, but not very familiar with Navier Stokes.
OK. Google the Navier Stokes equations, and examine them for a Cartesian Coordinate system.
 
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