In nature the smaller a flying beast is the faster it flaps its wings (birds and insects). In the literature it is shown that an important mechanism used to generate lift in small creatures is unsteady separation. Bubbles form on the leading edge and gradually grow as the point of reattachment moves rearwards. Whilst the bubble is growing the lift coefficient is very high: higher than steady flow aerofoils by up to a factor of 2. I think small, low Reynolds turbines (and compressors) ought to have unsteady flow of this type. Can anyone think of how to design a turbine with such an unsteady flow mechanism?
Hi,
This is a topic that I have been interested in for several years...We have done some preliminary CFD and have a patent application filed on the topic.
The leading edge vortex does increase the lift several fold and it is possible to optimize the flapping to maximize thrust rather than lift.
It is also possible to arrange a series of such flapping devices such that they can feed off each other's LEV. There already exist tandem hydrokinetic water turbines that use this principle but not compressors. There are also some studies on optimal flapping parameters for thrust maximization rather than lift.
Another small benefit is the ground effect for internal flow when the flapping mechanism approaches a wall and changes direction (thrust augmentation).
Will send you an email...
Hi,
insect wing profiles were investigated at Cambridge Univ in 1976 and presented in a series of summer lectures. I do not know if there are any publications.
Very special profiles with bubbles, hair and holes were shown to have high lift coefficients.
A refugee for Middle East showed me for about 25 years ago how to design a fan and a wind turbine with "natural" profiles. Allah is the best designer was the message.
The fan worked with about the same efficiency as a conventional one.
Regards
Torsten
Yes there are. Ask Diva.Eng.:
http://www-diva.eng.cam.ac.uk/directory/[email protected]
Good luck
Hi,
the LEV creates a lot of lift, but at the same time it also generates a lot of drag. Efficiency is not very high. Turbines and propellers aim for efficiency most of the time, not for maximal force. If more force is required, then you install a bigger propeller or a more powerful engine. But it would be very nice to discuss this...!
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