https://www.sciencedirect.com/science/article/pii/S1000936116300383Very interesting study that shows that using a winglet on the pressure side of a rotor cascade improves rotor performance, particularly by extending the stall point. In other words, the pressure side winglet creates a higher pressure ratio at a lower rotor speed. This is achieved while having a negligible impact on drag.
"On the contrary, the
pressure-side winglet greatly improves the stall margin and
introduces only a very small penalty in efficiency. At peak efficiency point, there is an efficiency reduction of about 0.27%.
The predicted penalty in rotor isentropic efficiency is due to
the additional surface offered by tip winglet which increases
the additional skin friction loss. Moreover, the pressure-side
winglet causes a slightly higher pressure ratio near the stall
point relative to the reference case..."
"By applying pressure-side winglet, the stall range predicted
by the present work is extended by 33.74%. This shows a significant improvement in the stall range of the compressor
rotor."
This is highlighted in this image.
https://files.catbox.moe/37sing.pngThe study further goes on to say
"In the condition with the suction-side winglet
applied, the shock wave/tip leakage vortex interaction is being
intensified which leads to a stronger change in the tip leakage
vortex structure. It is found that the tip leakage twists seriously
and a spiral type breakdown seems to occur at the middle of
the rotor passage. In the case with pressure-side winglet, the
tip leakage vortex trajectory is more inclined in the streamwise
direction. In addition, the distance from the first tip leakage
vortex appearance at the suction surface to the intersection
with the shock is longer than the corresponding distance in
baseline tip case. With the longer distance, the low momentum
core fluid is reenergized as tip leakage vortex mixing with main
flow."
https://files.catbox.moe/k2fytu.pngNot complete proof but evidence that pressure side winglets extend the stall range in a wing cascade, this would be useful in something like a current generation Formula 1 car that uses floor fences in a cascade arrangement. The regulations allow the use of the pressure side winglets as there is a 50mm fillet radius that is allowed on these cascades.
https://files.catbox.moe/ce7igv.jpghttps://www.fia.com/sites/default/files/fia_2023_formula_1_technical_regulations_-_issue_1_-_2022-06-29.pdf3.5.2 subsection d states
"Once each Floor Fence has been fully defined it is permitted to apply a Fillet at the
boundary between it and the Floor Body, having radius of curvature no greater than
50mm. Such a Fillet would then be considered part of the associated Floor Fence."
As far as I can tell, this means that you can apply a fillet once the floor fence is within the bounds of the actual floor, it makes no mention if the fillet can be applied at the top or bottom of the floor fence.
