Help Clarify: Wind Load or Wind Sheer?
Help Clarify: Wind Load or Wind Sheer?
(OP)
Trying to determine wind load on a smoke stack, I have read many a (fluid mechanics) text that only seem to address wind sheer. Some evaluate this wind sheer force as a drag force, and others use a similar approach - only without a drag coefficient in the (very similar) equation. So, which is correct? (Either way, they all address wind sheer only) But...
What about a normal force from the wind? Wouldn't any windward face of an object experience a normal force distributed longitudinally along said windward face? (Am I wrong? Am I misunderstanding something?) If I am correct, how does one equate wind speed to this normal force?
Any explanation or links to websites that may help clarify further would be appreciated.
Thanks in advance!
What about a normal force from the wind? Wouldn't any windward face of an object experience a normal force distributed longitudinally along said windward face? (Am I wrong? Am I misunderstanding something?) If I am correct, how does one equate wind speed to this normal force?
Any explanation or links to websites that may help clarify further would be appreciated.
Thanks in advance!





RE: Help Clarify: Wind Load or Wind Sheer?
Flexible stacks can vibrate in the wind in connection with vortex shedding, and that should be considered in the design as well.
RE: Help Clarify: Wind Load or Wind Sheer?
Also, I know that applying the fluid mechanics method is an oversimplified approach, geared for an academic exercise...not for professional practice. (Yet, I'd have to convince my boss.) As such, I am applying the most conservative Cd values (as I have found some conflicting data within the same text, for one).
In short, I did find an answer to my question. There is an overall drag coefficient (Cd) which is the sum of the friction drag coefficient (Cdf) + the pressure drag coefficient (Cdp). It seems, Cdf accounts for shear while Cdp accounts for what I was wondering about - that which is incident upon a windward surface (i.e., normal to the airstream).
Thanks again for your reply.
RE: Help Clarify: Wind Load or Wind Sheer?
RE: Help Clarify: Wind Load or Wind Sheer?
Drag=Cd*A*(rho*V*V/2); rho is the fluid's density, V is
the fluid's velocity, A is the cross sectional area of
the cylinder. Be careful of the actual definition of
Cd--there might be a different definition than the
one I've shown.
You're looking for something like Figure 2
http:
or Figure 3 here
http://ctr.stanford.edu/ResBriefs01/wang.pdf
If you finally a really detailed discussion, you might find curves that take into account surface roughness.
RE: Help Clarify: Wind Load or Wind Sheer?
If at some point, you're asked to certify that the design meets a building code or the ASME stack standard, it would be advantageous to have it in hand.