New design for turbine blade. Can it be applied to wings?

[hatchet man]

A company called WhalePower Corp. has developed a new wind turbine bladed modeled after the flipper of a humpback whale. The new design has a saw-tooth leading edge that supposedly increases the efficiency of the blade, allowing it to operate at lower wind speeds than traditional, smooth blades.

"the tubercles channel the wind as it hits the front or "leading" edge of the blade. The channels cause separate wind streams to accelerate across the surface of the blade in organized, rotating flows. These energy-packed vortexes seem to increase the lift force on the blade.

As well, the channels prevent airflow from moving along the span of the blade and past its tip, a troubling situation on smooth blades that can cause noise, instability and lead to a loss of energy. By keeping the airflow channelled, more of the wind is captured and noise is greatly reduced."
http://www.thestar.com/article/213475

I am thinking that this could also be applied to the front and rear wings of an F1 car to help in reducing drag and potentially increasing downforce.... now if only movable aerodynamics were allowed, they could put turning vanes on the car too

My apologies if this has already been discussed or developed... I recall seeing saw-tooth edges on the trailing edge of wings but never on the leading edge.

[ginsu]

Yeah, I've seen HD video of humpback whales and you can see how the bubbles stay attached to their skin for a very long time when they surface and plunge back into the water, so I definitely believe these tubercles shapes on the leading edges could definitely work.

There was a thread similar to this a very long time ago, I know I postulated that we would see similar shaped devices on the leading edges of F1 cars. But, so far, nobody in F1 has done it. Gosh, I hope they have at least tested some of these designs to see if they work.

[kilcoo316]

I can see how it will work at higher angles of attack (cf LERX on a F-16/MiG-29 etc), but at lower speeds?


Its true that vortices do contain volumes of lower pressure along their centreline, but they also tend to increase the energy of the flow = drag.


I'll have a look around for any tech papers on it tomorrow and report back.

[mini696]

Doubtful... The airflow hits the turbine blades' leading edge perpendicular, whereas the racing wing is hit parallel.

[ginsu]

mini696, propellers and wings work off the same principles, I don't see why an advancement in one design wouldn't work for another.

From what I know about rotor aerodynamics, the flow is modeled just like an airplane wing (i.e. approx parallel to the chord). The differences lie in the fact that the wing is rotating and is generally operating in the wake of the wing that preceded it.



I guess the question is if the 'tubercles' wing would create a dirtier wake than a standard, smooth wing surface. If they do, then maybe a rotor design isn't the best use of this technology, and it may be better adapted to stand alone wing surfaces. I mean a whale flipper isn't exactly rotating, so maybe we should also be looking at plants/animals that have rotating parts ( a number of seed types come to mind).

[Ian P.]

[/quote]Doubtful... The airflow hits the turbine blades' leading edge perpendicular, whereas the racing wing is hit parallel.

In all aerodynamic evaluations the key is to consider the "relative" wind at the leading edge of the blade/aerfoil etc.
In the case of the F1 wing, the the air is moving straight toward s the wing leading edge. In the case of a propellor or turbine blade, you need to consider the direction of the wind and the direction and velocity of the blade leading edge. Get the angles right and the incident angle of the air to the blade leading edge is near zero or just where you want it. The prop driven plane is the best example. Sail boats are another good example but at the opposite end of the relative velocity scale.
Ferrari has run barge boards with saw-tooth leading edges and wings with jagged trailing edges. Not the same as the lumpy whale leading edge proposed here but I unsderstand it improves effeciency and reduces the tendancy to stall.
It will be interesting to see if this development takes hold. If it really works expect to see it show up first on home-builts and Ultra Lights.

[DaveKillens]

It seems to me this scheme is very similar to vortex generators.

[Ian P.]

Most of the vortex generators I have seen tend to be aft of the maximum thickness part of the wing. I understood this was to create additional pressure (under certain circumstances) which would delay stall.
In this design the convolutions are at the leading edge. Unique to say the least.
Probably only beneficial at low Reynolds no. which would be the case in water or low air velocities (windmills).

[kilcoo316]

Had a quick look under "leading edge serrated" and some other keywords.


Last work done was in the 70s on axial fan blades. Here is a couple of abstracts:

VORTEX SHEDDING NOISE OF LOW TIP SPEED, AXIAL FLOW FANS.

Journal of Sound and Vibration, vol. 53, no. 1, 1977, pp 25-46


Noise and performance tests were conducted on three low tip speed, half-stage, axial flow fans to determine the nature of the vortex shedding noise mechanism. Each fan was 356 mm in diameter and had eight equally spaced, variable pitch blades. The noise measurements were made in a free field environment and the fan back pressure and speed were varied during the tests. An acenaphthene coating on the blades was used to determine the regions of laminar and turbulent flow. Vortex shedding can be a significant source of noise when the fan is operated in a lightly loaded condition. Essentially it is due to instabilities in the laminar boundary layer on the suction side of the blade where these instabilities are in the form of Tollmien-Schlichting (T-S) waves. These instabilities interact with the trailing edge of the blade and generate acoustic waves which radiate from the trailing edge and form a feedback loop with the source of the instabiliites. Vortex shedding noise can contribute as much as 5 dB in overall noise level and up to 22 dB at higher frequencies (8-14 kHz). Serrations located at the leading edge, at the mid-chord, or near the trailing edge on the suction side were found to reduce the vortex shedding noise significantly. The mid-chord location was found to be the most satisfactory because, as well as eliminating the noise, the serrations provided a 3% improvement in peak efficiency. This improvement occurred because separation of the laminar boundary layer was prevented on the suction side. On the other hand, serrations placed at the other two locations tended to degrade fan performance.





CASCADE TESTS OF SERRATED LEADING EDGE BLADING AT HIGH SUBSONIC SPEEDS.

NASA CR-2472 1974

Cascade tests of two-dimensional fan rotor blade rows were performed to investigate the effects of leading edge serration on acoustic and aerodynamic performance. The test configurations covered a range of serration tooth geometries. Tests were performed to investigate effects of inlet air angle and velocity on performance. Aerodynamic performance was determined by flow surveys at the mid-span of the blade exit. Acoustic performance was determined by wake turbulence surveys and sound measurements in the semi-reverberent exhaust chamber. Measured acoustic and aerodynamic performance was comparable and indicated that a serration length of about six percent blade chord yields minimum noise generation and minimum total pressure losses.



Neither work showed any sign of an advantage in serrations at the leading edge.

[Ciro Pabón]

This is the photo published in this forum recently of Ferrari's serrated gurney flap on the trailing edge of its front wing that Hatchet Man mentions.

Why do they use it? I mean, this is not to improve the flow on the surface of the wing, is it? Does this thing reduce "stall" on the "back" surface of the gurney, as DaveKillens figure seems to suggest?

And if vortex generated by this thing equates more drag, as kilcoo316 explains, why would they want more drag here? Is this drag compensated by less underpressure on the "back" surface of the gurney, again?

[kilcoo316]

Ahh, no, the two articles I posted would not have been dealing with gurney flaps, they aren't a feature of blade design.


The serrated gurney flap apparently offers something like 95% of the downforce with 20% of the drag.

It will also tend to introduce a vortex sheet into the boundary layer wake, leading to its quicker dispersal, and allowing the rest of the car to operate more efficiently. This vorticity will also help entrain air out from under the wing, keeping energy levels up and preventing seperation towards the trailing edge (see the middle figures in DaveKillens post - but the mechanism for stopping seperation is different)