# why does my pressure contour does not increase gradient along height

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• Last Post 06 November 2019
Mrjiang posted this 06 November 2019

i analyze a right rise building in a wind tunnel simulation using CFD. i set up all the parameter: input, output,opening,ground, structure. when the analysis is completed, i plot the pressure of the structure. The pressure contour (top picture) indicate the maximum pressure is at the middle face of the structure regardless of the height. The result does make sense to me because I am expecting a result similar to the bottom picture where pressure is increase with height. can someone direct me to get similar result on it? also, if i want to export the force along the impact face or all the face of the structure how can i do so? and how can i verify if it is correct.

abenhadj posted this 06 November 2019

What are you expecting: hydro-static head due to air? The top picture does not indicated anything for me: it is almost the same colour within that range. The bottom picture is scaled between -1 and 1.

Are you accounting for buoyancy and did you activate gravity? Have you then provided a reference density?

Best regards,

Amine

Mrjiang posted this 06 November 2019

well, i am expecting a behavior of a gradually increase of force for high rise building subjected to wind force in a urban area. I am trying to obtain the Force acting on the wall surface around the building by simulating it through wind tunnel with a velocity. Also using FSI to obtain the stress at the bottom of the structure. In the CFD domain, I want to export the force that the wall surface is experiencing due to the wind velocity input or at least graph the pressure/force vs height of the structure because it is assumed that with wind velocity increase along height, therefore, the pressure gradually increase along height. However, I am having difficulty obtaining or modeling the result.

I did not account for buoyancy and activate gravity. Can you please explain why do i need to do so?

For the reference density, are you referring to the air density input?

rwoolhou posted this 06 November 2019

Depending on your mesh and inlet settings you may not see much change in pressure up the height of the building: what boundary condition did you use?

Mrjiang posted this 06 November 2019

but shouldnt the structure in the lower level have low pressure in the middle of the wall surface? but the contour shows at the lower level, the pressure at the middle of wall surface is red and constant along height.

Building: no slip wall, smooth wall