Turning Vanes Required

Do you want turning vanes with your duct work? Yes, if you are considering a square corner and you want to minimize your fan power requirement. Don't take my word for it, instead consider this Computational Fluid Dynamics (CFD) study that compares a vaneless square corner with both small turning vanes and large turning vanes.

Turning Vane CFD StudyTurning Vane CFD StudyVelocity magnitude contours on the symmetry plane

The velocity magnitude contours on the symmetry plane of each configuration show recirculation zones (blue) downstream of the corner. Notice how the zone reduces in size with the introduction of the turning vanes and is smallest for the large turning vanes. You can also see that the maximum flow velocity (red) is reduced adjacent to the recirculation with the turning vanes, even though each simulation maintains the same volume flow rate.

Turning Vane Pressure Loss ComparisonTurning Vane Pressure Loss Comparison

How does this seemingly improved flow pattern for the turning vanes translate into actual savings? The pressure drop for the large turning vanes is a whopping 62% less than the vaneless corner. Given that you select a fan based on the system pressure drop and the volume flow rate, the large turning vanes will save you power and equipment costs. What's not to like?



Turning Vanes

Turning Vanes Required
Submitted by Richard Smith on June 6, 2013 - 08:32

This model is for positive pressure to the inlet & outlet of the 90 elbow. What is needed is a model of a negative pressure on the inlet of the 90 elbow.
The forces of pulling air through an elbow are not the same as pushing and since the turbulence from the mass of the air smashing into the wall of the elbow is less, then the pressure drop will be less.

The question is how much less? There is a video produced by SMACNA showing helium bubbles passing through a clear glass duct and elbows. The bubbles show how small changes in deminsion and angle make big improvements in air flow.

Perhaps a government grant could be proposed to verify the computational model