- #1
leviterande
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Hi,
I have became confused about a "certain situation" belonging to Bernoulli Principle :a "wind on flat roof situation" more precisely. The big misconceptions on the net didn't make it easier. There are very contradicting explanations from experts on the web. However, I hope to get a clarification and help from this forum.
Consider fig. 1 and fig. 2 (sorry for the inaccurate drawings)
-Fig.1- Wind past a FLAT roof example
See figure 1. In books, plenty of examples and questions are given on calculation of uplift force on FLAT ROOFS of houses. WIndspeed and area of the FLAT roof is given to calculate the upward net uplift on the roof. Now if I understand this correctly, the only REAL reason for the lower pressure above roof/uplift force on a FLAT roof is because the constriction of the incoming flowing wind hitting the side wall. After this wind stream hits the sidewall, it now bends/flows up towards and around the roof where now the streamlines gets therefore closer together and reaches now a higher velocity and thus the pressure here gets lower too around and above the flat roof (all because of conservation of momentum of the initial wind velocity and Bernoulli). The flat Roof feels upward lift due to the higher indoor pressure compared to the upper outdoor air. So, the airflow-constriction i.e. the sidewall of the house is the original CAUSE for the lower pressure on the roof and thus the uplift force on the roof(?) correct? I believe so
-Fig. 2- WInd past a FLAT ROOF but wind doesn't hit the sidewall i.e. no airflow constriction
To demonstrate my point, see now the hypothetical fig. 2. It is the same example as fig. 1 except now, the wind stream portion is flowing higher from the ground and is just flowing right above the FLAT roof without meeting the "sidewall constriction" or at least minimally touching the sidewall. Now in this hypothetical situation, my question is very simple: would there be a lower pressure on the roof and thus an uplift force on the roof in fig 2.? I explained this to several people and got mixed answers...
I believe that there would be no force on the flat roof in figure 2 because there is no constriction or change/deflection of airflow(?), right?
Your input is highly appreciated as I am really wanting to know. I tried some experiments but here, even slight crudeness unfortunately destroy results.
Thanks
I have became confused about a "certain situation" belonging to Bernoulli Principle :a "wind on flat roof situation" more precisely. The big misconceptions on the net didn't make it easier. There are very contradicting explanations from experts on the web. However, I hope to get a clarification and help from this forum.
Consider fig. 1 and fig. 2 (sorry for the inaccurate drawings)
-Fig.1- Wind past a FLAT roof example
See figure 1. In books, plenty of examples and questions are given on calculation of uplift force on FLAT ROOFS of houses. WIndspeed and area of the FLAT roof is given to calculate the upward net uplift on the roof. Now if I understand this correctly, the only REAL reason for the lower pressure above roof/uplift force on a FLAT roof is because the constriction of the incoming flowing wind hitting the side wall. After this wind stream hits the sidewall, it now bends/flows up towards and around the roof where now the streamlines gets therefore closer together and reaches now a higher velocity and thus the pressure here gets lower too around and above the flat roof (all because of conservation of momentum of the initial wind velocity and Bernoulli). The flat Roof feels upward lift due to the higher indoor pressure compared to the upper outdoor air. So, the airflow-constriction i.e. the sidewall of the house is the original CAUSE for the lower pressure on the roof and thus the uplift force on the roof(?) correct? I believe so
-Fig. 2- WInd past a FLAT ROOF but wind doesn't hit the sidewall i.e. no airflow constriction
To demonstrate my point, see now the hypothetical fig. 2. It is the same example as fig. 1 except now, the wind stream portion is flowing higher from the ground and is just flowing right above the FLAT roof without meeting the "sidewall constriction" or at least minimally touching the sidewall. Now in this hypothetical situation, my question is very simple: would there be a lower pressure on the roof and thus an uplift force on the roof in fig 2.? I explained this to several people and got mixed answers...
I believe that there would be no force on the flat roof in figure 2 because there is no constriction or change/deflection of airflow(?), right?
Your input is highly appreciated as I am really wanting to know. I tried some experiments but here, even slight crudeness unfortunately destroy results.
Thanks