II. Beyond Tesla: Impulse & Reaction Principles, Lift vs. Drag, Round Washers vs. Winglets 

April 29, 2002

Last month we announced a breakthrough in turbine efficiency due to a geometry variance from the Tesla round washer specification. Although we need to conduct further tests at higher speeds and greater inlet mass rates, the results of our tests fall right in line with basic turbine theory of design.

Any turbine becomes more efficient with an increase in rpm; bladed turbines exhibit a relatively linear increase in efficiency with rpm, whereas a disk turbine adheres to a logarithmic curve. By combining the characteristics of blades and disks in one machine, we can expect the best characteristics of both systems to reinforce each other and the negative characteristics to be left behind.

In theory that's the direction we are moving in. Let me state here & now for the record -- this club is not about proving or maintaining the exact geometries of Tesla's design. Rather, we are here to empirically develop improvements to basic turbine concepts, and end up with a better machine.

So far our test data indicates that (in the lower spin-up region) by replacing the round washers of the original Tesla design with thin-section winglets, the result is a 30% increase in efficient use of available compressed air energy.

Let's briefly examine why we obtained this result, and how this corresponds with other turbine designs.

Impulse vs. Reaction

First of all we need to define what sort of forces we are dealing with. Piston engines are strictly impulse engines -- the pistons are forced to move in the direction of expanding gases. A bucket type turbine is strictly an impulse engine. A sailboat flying a spinnaker and running downwind operates in an impulse state, whereas that same boat heading into the wind operates in a reaction state. 

Years ago, when we used to sail catamarans, we could "fly" our cat faster than the wind by drawing in the sheets and pointing just a few degrees off windward.

All modern turbines -- including bladed and disk types -- convert kinetic fluid energy to shaft horsepower through both impulse and reaction mechanisms. In a strictly bladed design, the blades move due to impulse on the underside of the (wing), a venturi or low pressure zone on the upper wing surface, and a Newtonian effect due to downwash -- or diverting streamlines from straight to angled vectors.

In the Tesla turbine some of the fluid energy is converted through impulse on the small round washers. Viscous drag on the disk surfaces accounts for another portion of energy conversion. Reaction comes into play as the fluid spirals between the disks toward the center outlets. The area we are going to focus on is the drag region behind the round washers.

In aircraft design you try to reduce parasitic drag to a minimum since it runs contrary to the intended vehicle direction. In a turbine you must increase the drag to increase energy conversion efficiencies, since the drag vector runs in the intended direction of rotation.

Lift vs. Drag

During the initial spin-up phase of our turbines, the key components in moving the disks from zero rpm to operating speed are the outer periphery washers (or winglets). Even Tesla stated that these washers were absolutely necessary for disk pack stability and strength, as well as start-up torque. Once the turbine is up to operating speed (approximately 60% of rated speed) the washers continue to add acceleration torque as loads are applied to the output shaft, to avoid dropping down into the stall region (at around 50% of rated rpm).

Even though the round washers work relatively well for generating the necessary force vectors in the desired direction, our tests indicate that through careful redesign of this key geometry, we can generate even greater forces and efficiencies. 

Reviewing our sailboat example -- a well-trimmed mainsail set at just a few degrees from windward is much more efficient than a much larger spinnaker running downwind. A round washer cannot generate a reactive force unless it is rotating about its center, since the upper and lower surfaces are identical and the downwind reactance vectors cancel each other. 

Using a non-symmetrical cambered winglet allows us to utilize all of the forces associated with aircraft -- impulse, reaction and drag -- to move in the same direction at the point of greatest torque, the outer periphery of the disk pack. Also, as the energetic fluid continues beyond the winglet region, it continues to spiral inwardly, expending even more energy through viscous boundary layer effect.

Ken Rieli

Next Page >