Nozzle Experiments by Richard Gideon

March 2003

Recently I have been thinking about nozzles for the Tesla turbine. All the drawings that I have seen show either one or two nozzles with the second one being used to make a reversible turbine. I then began to wonder what if the two nozzles were pointed in the same direction. Might this be a viable alternative to increase the power of a turbine without going to a larger diameter or thicker rotor? From here obviously the next question was how about 3 or 4 nozzles, etc.

As I have stated before I believe theory and some common sense make a good starting point but to really prove an idea there is nothing like a working model. Hence I designed a test turbine with multi-nozzles each of which could be individually easily turned on or off.

My first concern was my extremely limited air supply. Obviously it would make no sense to build turbine so big that I would not have enough air to run it. After some experimenting I found that my air compressor could supply a reasonable amount of air for a reasonable amount of time through sixteen 1/8" diameter holes. Thus I determined that my rotor case would have sixteen 1/8" diameter nozzles. At this size I made no attempt to use a convergent/divergent design, they are just plain old round holes. Then because of the 1/8" diameter nozzles a 4-disc rotor is all that was needed to effectively cover their openings.

The rotor case basically consists of two concentric rings. The inner ring has the 16 equally spaced nozzle holes. The outer ring has 16 threaded holes in line with the nozzle holes. This allows me to insert a screw onto which I have turned a sharp point on its end. The sharp point then acts as a needle valve and can shut off air to the nozzle. Conversely backing the screw out allows air through the nozzle. Supply air is delivered to the space between the inner and outer rings which functions as a manifold and delivers air to all the nozzles. I fitted a pressure gauge to the manifold so I could directly measure the pressure

in the manifold and thus helped in maintaining a constant pressure for all the tests.

I ran three types of tests, one for maximum RPM, one for torque at 6000 RPM and one to measure the time needed to use up a given amount of air. Each of these tests where run with the following nozzles open.

First – 1 nozzle open, then 2 open, then 3 open, then 4, then 6, then 8, and finally all 16 open.

The results are shown in the following graphs.

The graphs for maximum RPM and torque are self-explanatory.

With the time graph I was trying to show efficiency, albeit in a round about way. I started each test run when my compressor had just shut off and the air tank was filled to its maximum pressure. I then timed how long the turbine could run before the compressor would restart at its lower limit. Between these two pressure points I figured I have a more or less constant volume of air to work with. Thus by comparing the time needed to use up this given quantity of air to speed gives an indication of how efficiently the each different combination of nozzles preformed.

In conclusion it appears that if you are only interested in maximum torque, then the more nozzles the better. However if operating efficiency is important then 3 to 4 nozzles appears to be the limit.

Richard Gideon
Spotteddogs@iwic.net

Another great job of engineering from Richard Gideon. Tesla mentioned in his work with the turbine that 12 or more nozzles would be feasible and increase the power density of the engine. With high quality engineering results obtained so easily from the Tesla turbine, did the entire automotive world make a mistake in developing the piston engine instead? -- Ken