×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Creating roof turbulence on a flat roof

Creating roof turbulence on a flat roof

Creating roof turbulence on a flat roof

(OP)
Would creating turbulence on a flat roof by installing multiple small ridges reduce the likelihood of the roof lifting in a strong wind?

RE: Creating roof turbulence on a flat roof

Like dimples on a golf ball (350 to 375 from what I understand), it would at the very least reduce skin friction, enabling the roof to fly farther once detached.

As for lift, I am not an aeronautical, but if you add curvature to the top surface, do you not increase lift, at least up to a point?

Mike McCann
MMC Engineering

RE: Creating roof turbulence on a flat roof

The uplift at edges is caused, primarily, by the air flowing off the wall creating a low pressure region, before the flow reattaches to the roof. The code does not really contemplate whether the roof surface creates laminar or turbulent airflow, and whether the air is smoothly attached to the roof or not, this phenomenon exists. Even lower local pressures occur where vortices are formed in this unattached flow (faster airflow equates to lower pressures, hence the typical airfoil shape.)

There could be local effects due to roof texture or shape which are not accounted for in the code/standards. I would expect harsher design demands with the proposed irregularities. Wind tunnel testing would probably need to be done to validate such a design.

RE: Creating roof turbulence on a flat roof

(OP)
Thanks Mike & TXStructural.

I was hoping for an answer that said yes, more turbulent flow on the roof would reduce the airspeed and therefore likelihood of it detaching, so that I could reduce the structure but .. its better to know the answer than not.

Cheers

RE: Creating roof turbulence on a flat roof

Creating turbulent flow that affects the roof membrane system is not a good idea. The fastening of a roof membrane system against uplift does not contemplate the potential for fatigue from many cycles of load as would be produced by turbulent flow. It's tough enough to fasten a roof membrane system against uplift without adding more issues to the mix.

RE: Creating roof turbulence on a flat roof

(OP)
Thanks Ron, I'll stick with the standard guidelines.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close