[techctrl]

Hello,


If a surface integral value (such as pressure) is negative, what does it imply?

If I generate a force report in the positive Y direction for two horizontal walls, the vector value of one is positive and the other is negative. But the surface integral values of both (which are scalar values) are negative.

This has me confused, any clarification provided would be appreciated.

[jsm]

Hi,

You are comparing pressure and force that are entirely different. Don't compare the signs of these properties.

Pressure is scalar quantity and it has no signs. In general, fluent will show gauge pressure and it will not add the operating pressure. If it is confusing you, then plot the absolute pressure instead of static pressure. And the most possible reason for negative pressure is re-circulation nearer to the walls.

In other hand, force is vector quantity and what ever the sign you are getting in Fluent is the force acting direction.

[techctrl]

Originally Posted by jsm

Hi,

You are comparing pressure and force that are entirely different. Don't compare the signs of these properties.

Pressure is scalar quantity and it has no signs. In general, fluent will show gauge pressure and it will not add the operating pressure. If it is confusing you, then plot the absolute pressure instead of static pressure. And the most possible reason for negative pressure is re-circulation nearer to the walls.

In other hand, force is vector quantity and what ever the sign you are getting in Fluent is the force acting direction.

Thank you for the explanation.

You are correct that I shouldn't compare a scalar and vector quantity. I was mostly just curious as to why the pressure values end up being negative, which you clarified for me.

One more thing; does the pressure force on a wall surface and the pressure distribution on that same wall act in the same direction? If I were to draw the pressure profile on a wall surface, it should be in the same direction as the force vector, yes?

[jsm]

It is difficult to answer without considering the shape of wall and that is the reason we are using software to understand it.