Vane application is also a function of use, MPS, local ordnance requirements, and specs. For normal LP work at LT 5mps, I would use r=3w/2 for 90deg and less for no vane. I would look into SMACNA 3r radius elbow duct construction details.
In smacna chart there is option to select single vane , two vanes and three vanes. That is, there is one of one line then one of two and two of two line then one of three and two of three and three of three. If I draw a line from inner radius to outside radius the line will intersect all the three lines. My question is which one shall I select. Single vane or double vane or three vanes.
It will be a function of your required fitting or system loss based upon the Vp. We normally jump to square with vanes if we can fit a radius elbow in. If this is not a critical branch, look at the radius w/o and if the loss is good, live with it. Static regain 101. If its the critical duct, do the math, the loss table for the system will show the poor performing fittings. Your r/w = .17 and h/w = .5 The C goes from .04 @ 3v, .09 @ 2v and .21 @ 1v. It boils downs to lease cost of production that is why we don't see that many smooth w/vanes unless v is very high.
It is quicker and cheaper in most sheet metal duct shops to make a square elbow with commercial turn-vanes than to roll a back and make vanes for a curved elbow. so unless the elbow is appearance critical, cost will prevail.
B.E.
You are judged not by what you know, but by what you can do.
