DIY Tesla Impulse Turbine

[Toymaker]

First, this project is not yet finished, and I need to find/purchase larger air fittings, including a valve, before I'm able to move forward.

Not much to see from the outside. The only testing so far has been done using my shop air compressor, set to 100 psi max. The brass fittings are standard 3/8" air hose quick disconnect mounted to a 1/4" ball valve. This hardware has proven to be woefully inadequate to provide the needed air flow.


Below is the stack of 24 disks mounted onto the splined drive shaft. These photos were taken before the swarf was removed from each disk. Each disk has 40 flat plates machined around the circumference which act as a simple impulse turbine. The flat impulse plates are wider than the disks, resulting in a 1mm open space between each disk pair.


22 disks look like the photo below, while each of the 2 end disks are only "single sided".


The left pic shows the disk stack inside the housing along with 6 brass nozzles, and the ceramic bearing. The right photo shows a bearing retainer plate which holds the bearing and 8mm O-rings which seal the nozzle connections to central air inlet. It's nearly impossible to see, but the right photo also shows a 1mm wide channel which will retain another O-ring.



Below is one of the 6 brass nozzles showing the 24 holes, each 0.041" diameter. A simple drilled hole is not the best shape for an air nozzle, but I don't have any cutting tools which could make a proper divergent nozzle shape in a hole this small. Each nozzle protrudes through bottom of the outer case which allows the angle of the air jets to be easily changed.


The top left pic is the other side of the bearing retainer plate and shows the 6 air channels which feed high pressure air into the 6 nozzles. The triangular holes vent the low pressure air outside the case. The 1mm channels around each of the 6 triangular holes will hold O-rings when they arrive from e-Bay.

The bottom left pic shows the inside surface of the outer-most end plate; again, a 1mm thick O-ring seals the circumference of the plate.

Pic on the right shows the water pump (opened) the turbine will hopefully drive.


Hopefully, this little turbine will develop enough power to drive the above water pump, but at present time the 3/8" air hose leading from my shop air compressor to the turbine is way too small to carry the volume of air the turbine needs. The below video was made where I placed wooden plugs inside all 6 nozzles, blocking 20 of the 24 holes in each brass nozzle, drastically limiting the turbine's power.

 

[Toymaker]

Guess I should have opened this thread under, "A Work in Progress" ??
Oh well, here's a quick progress update:

Still using the same 1/4" ball valve and misc. pipe fittings, but eliminating the compressor tank's pressure regulator by tapping directly into the air tank made a huge difference. In these two video's I un-blocked 13 nozzle holes on each of the 6 nozzles, resulting in the turbine having about 1/2 power at any given air pressure.

In both videos, the initial air pressure starts at 90 psi and drops rapidly as the air compressor cannot keep up with the air draining through the turbine; you can clearly hear the turbine rpm dropping in the first video. Also, I believe I need to modify the centrifugal water pump as I believe the blades are spaced together too closely in the eye; I will try making 3 of the 6 blades "half blades". Also, in order to use all 24 nozzle holes in each of the 6 nozzles, I still need to buy a 1/2" ball valve and the various 1/2" fittings to match.

For now, despite my wife's commentary, I'm pleased with these initial results.

 

[Nerd1000]

Interesting setup.

Turbomachines are a fascinating area that I've only slightly dipped my toes in. The maths is far more complicated than a reciprocating machine!

 

[steve schwartzkoph]

Guess I should have opened this thread under, "A Work in Progress" ??
Oh well, here's a quick progress update:

Still using the same 1/4" ball valve and misc. pipe fittings, but eliminating the compressor tank's pressure regulator by tapping directly into the air tank made a huge difference. In these two video's I un-blocked 13 nozzle holes on each of the 6 nozzles, resulting in the turbine having about 1/2 power at any given air pressure.

In both videos, the initial air pressure starts at 90 psi and drops rapidly as the air compressor cannot keep up with the air draining through the turbine; you can clearly hear the turbine rpm dropping in the first video. Also, I believe I need to modify the centrifugal water pump as I believe the blades are spaced together too closely in the eye; I will try making 3 of the 6 blades "half blades". Also, in order to use all 24 nozzle holes in each of the 6 nozzles, I still need to buy a 1/2" ball valve and the various 1/2" fittings to match.

For now, despite my wife's commentary, I'm pleased with these initial results.

View attachment 147324

View attachment 147325


View attachment 147326

About 23 years ago when I was running my business, we built what I believe to be a true Tesla Turbine.
The Discs were 20" diameter and I believe there were 19 of them. They were no vanes or blades on them and just relied on the boundary layer of the Discs to rotate them. We made the first of 60 units and they were powered by a huge parabolic dish that turned water into steam from the sun. It even had a condenser to reclaim the water from the steam.

 

[Toymaker]

About 23 years ago when I was running my business, we built what I believe to be a true Tesla Turbine.
The Discs were 20" diameter and I believe there were 19 of them. They were no vanes or blades on them and just relied on the boundary layer of the Discs to rotate them. We made the first of 60 units and they were powered by a huge parabolic dish that turned water into steam from the sun. It even had a condenser to reclaim the water from the steam.

Do you recall how much power your turbines produced? Did you use one or multiple nozzles? What was the spacing between discs ?

The discs on my tiny turbine are only 2.4" (61mm) diameter, and as you alluded to, they are not pure Tesla blades, but rather a hybrid design, combining pure impulse and Tesla design together. Placing impulse blades on the discs while still allowing for open space between each disc pair (the Tesla part of the design) was just a crazy idea I wanted to try. At this stage in the testing, I'm quite pleased with the power developed by my hybrid turbine, but I must admit that I don't know how much additional power, if any, the impulse blades produce.

At this time, by biggest challenge is the impellor inside the water pump; I'm almost certain a better impellor design will move more water and produce higher pressures. Below is the impellor I started with. The next version will be quite different.

 

[Nerd1000]

How did you mill the blades on the pump impeller?

On a related note, a conventional impulse turbine would be very much like the pump, just running in reverse.

 

[steve schwartzkoph]

Do you recall how much power your turbines produced? Did you use one or multiple nozzles? What was the spacing between discs ?

The discs on my tiny turbine are only 2.4" (61mm) diameter, and as you alluded to, they are not pure Tesla blades, but rather a hybrid design, combining pure impulse and Tesla design together. Placing impulse blades on the discs while still allowing for open space between each disc pair (the Tesla part of the design) was just a crazy idea I wanted to try. At this stage in the testing, I'm quite pleased with the power developed by my hybrid turbine, but I must admit that I don't know how much additional power, if any, the impulse blades produce.

At this time, by biggest challenge is the impellor inside the water pump; I'm almost certain a better impellor design will move more water and produce higher pressures. Below is the impellor I started with. The next version will be quite different.

View attachment 147413

The spacing between the discs was .047" and it had one 2" dia. nozzle that transitioned into a rectangle and was distributed across the top of the entire width of the disc pack and it could be adjusted from zero to full open. I only built the turbine to my customers specifications and I was not privy to the power it produced. It was being used for power generation, so I'm sure it produced some serious HP. I only tested it on compressed air in my shop and I never saw it run on steam.

 

[Toymaker]

How did you mill the blades on the pump impeller?

On a related note, a conventional impulse turbine would be very much like the pump, just running in reverse.

About 12 years ago I built the small benchtop CNC milling machine you see below; it runs with an old Dell Optiplex 780 computer running Mach3. I purchased the mini-mill milling head (spindle, gearbox, motor, & speed control) and fabricated the X-Y-Z frame from mostly 1/2" aluminum plate.


Unfortunately I didn't take any video of milling the aluminum impellor, but I did make a short video of milling a slightly larger impellor I made from nylon.

Below shows the nylon impellor inside the the plastic housing, still wet from a recent test run.


Powered only with a fractional HP motor, the plastic pump above throws an impressive stream of water.

 

[Steamchick]

I like the "conventional" pumps. I can see some thinking behind a combined impulse and Tesla turbine, but as both extract max power at max gas velocity, the impulse bit at largest diameter probably extracts most of the power from the air jets. The "exhaust" from the impulse bits will be travelling typically at around half velocity, but mixed with a bit of air jet that slips through the slot, possibly a little higher. So realistically, as the impulse vane travels around half the velocity of the impulse air, 1/4 of the energy is retained in the exhaust. How much of the turbulent exhaust can be realised as energy transferred into the "Tesla" part of the turbine, I am not sure. But I figure that the Tesla bit will be too slow and turbulent to do much. Tesla turbines increase efficiency as disc speed increases. Impulse turbines extract less power, but torque is developed at lower rotor speeds, more suited to a water turbine per your design. A Tesla turbine is more suited to a Tesla pump - both with plain flat discs, witH 2 ~ 3 mm gaps, but different diameters.
Good fun!
Enjoy,
K2

 

[Toymaker]

I like the "conventional" pumps. I can see some thinking behind a combined impulse and Tesla turbine, but as both extract max power at max gas velocity, the impulse bit at largest diameter probably extracts most of the power from the air jets. The "exhaust" from the impulse bits will be travelling typically at around half velocity, but mixed with a bit of air jet that slips through the slot, possibly a little higher. So realistically, as the impulse vane travels around half the velocity of the impulse air, 1/4 of the energy is retained in the exhaust. How much of the turbulent exhaust can be realised as energy transferred into the "Tesla" part of the turbine, I am not sure. But I figure that the Tesla bit will be too slow and turbulent to do much. Tesla turbines increase efficiency as disc speed increases. Impulse turbines extract less power, but torque is developed at lower rotor speeds, more suited to a water turbine per your design. A Tesla turbine is more suited to a Tesla pump - both with plain flat discs, witH 2 ~ 3 mm gaps, but different diameters.
Good fun!
Enjoy,
K2

I agree the majority of work extracted from the gases jetting out from the nozzles will likely be accomplished by the impulse blading, which is my plan, however, as you pointed out, there's still a large amount of energy within that gas stream that will otherwise be wasted if not for the Tesla section. The initial jet of gasses from any one nozzle will push the impulse blades only as far as the next jet of gases from the next nozzle, at which point those gases from the upstream nozzle will be pushed inward into the 1mm gaps between the discs where those gases will continue to expand thereby creating continued momentum. I'm fairly certain most, if not all, turbulence generated from the impulse blading will be redirected by the high velocity nozzle gases pushing the slower gases inward, combined with viscous interaction of disc rotation. Whatever small amount of energy is lost from redirecting turbulent gas flow from the impulse blades will be regained as those redirected gases will now transfer more useful energy to discs via their continued expansion.

Whatever amount of energy the Tesla section is able to extract, whether it's only 5% or as I suspect, much more, is energy that would otherwise have been lost, but is now added as useable torque.

 

[Steamchick]

From a video I saw years ago of a Tesla Turbine demonstrating how it performed efficiently, it "crawled" up the revs to around 60,000 - 70,000rpm, but then there was a point at which the gas velocity and disc surface speed started to interact much better, when it accelerated incredibly rapidly up to over 100,000rm when the efficiency (measured by generator output went very high. Below that "critical speed", the turbine worked but efficiency wasn't anything to write home about. (20%~40%? - Can't remember much!). But I think I remember they proved Tesla's claims of 89% efficiency when in the "high-speed" mode.
The difficulty was making a power train to suit the very high speeds, materials that didn't fatigue (Tesla recorded that his discs only had a short running life because they stretched and cracked! - He lacked today's clever materials!).
Anyhow, I think that the maths suggest that the turbine should be "one or the other". I.E. a "reaction" (momentum exchange) or Impulse turbine for low speeds, or a Tesla "Surface friction" disc turbine at very high speeds. (10~ 100 times the speeds of an impulse turbine?).
I should even go so far as to suggest a fine pitched helical groove in each plate could be an alternative to make an impulse turbine like a friction turbine?
I have not thought very much about this, but I wonder how to determine the hole size in the middle for the exhaust? There will be a relationship between the gas pressure and temperature at the nozzle per hole size and number of holes (mass of gas per time), and the gas pressure after expansion (and loss of heat as work transferred to the discs?) = the same mass of gas per time at a lower pressure = larger volume requiring the larger holes in the discs for exhaust. But I have not spent the time to work it out. Has anyone done that?
ON "direction of jets"... I understand that the jet is usually designed so it is tangential to the centre of the "impulse" vane? From other expanding jet stuff I have read, the jet of gas will expand at about 9degrees of internal angle of cone (Any better knowledge anyone?). So you can draw your impulse vanes, jets and cones of expansion and see what should be about right? I think Impulse turbines are usually designed to have one blade just taking the gas as the previous blade is turning out of alignment from the cone of impulse jet. - That's why there are many impulse vanes on these turbines - I think?
Thanks for sharing your ideas, you have made me think about how much I don't know about turbine design! - Part of the pleasure of sharing ideas on this site.
Thanks,
K2

 

[Steamchick]

Here are some papers I have found that I should study!

https://www.akademiabaru.com/doc/ARFMTSV62_N1_P122_137.pdf
https://www.researchgate.net/figure...e-Tab-2-Geometrical-parameters_fig1_250166615
https://www.e3s-conferences.org/articles/e3sconf/pdf/2019/39/e3sconf_supehr18_03008.pdf
Lots of reading there - and more besides!
K2

 

[Steamchick]

Hi Ray,
This paper seems to discuss something that may help your design....(?)
But this takes the tangential air-flow from inlet, using the casing to re-direct the flow around an arc of the disc to the exhaust, instead of to the middle (like you and Tesla). (I am surprised he just uses about 1/4 of the arc of the turbine instead of maybe 80%? - Surely a longer path would be more efficient?).
Perhaps there is a weakness in his design that the gas velocity at exhaust cannot be less than the disc velocity, otherwise the discs would pump the gas through the turbine after some transitional point where the gas slows to disc speed?
Another possible disadvantage of his design is that the boundary layer of gas at the periphery is losing energy by friction to the casing, not driving the discs?
I think the significant advantage of the Tesla turbine is that the air path is not just a small arc at the circumference, but a very long spiral path from outside at high speed to middle at significantly lower speed - after expansion of the gas - while keeping the gas velocity close to the disc surface velocity. When the Tesla Turbine mode is achieved, the natural helical path of the gas achieves the very high efficiencies (energy transfer from steam to moving metal) he claimed. But the disc surface needed to be close to the gas velocity... = sonic! Also at each "turn" of the helix, the gas jet is slightly slower than the jet at one turn further out and slightly faster than one turn further in, but it will find its natural helix due to laminar flow, velocity of gas versus metal, etc. Rather than any "Engineered" path!

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9548558/
People, tell me to stop if my musings are OFF-Track from what you want to read?
Thanks,
Ken

 

[Steamchick]

Yet another...

K2

 

[Toymaker]

Here are some papers I have found that I should study!

https://www.akademiabaru.com/doc/ARFMTSV62_N1_P122_137.pdf
https://www.researchgate.net/figure...e-Tab-2-Geometrical-parameters_fig1_250166615
https://www.e3s-conferences.org/articles/e3sconf/pdf/2019/39/e3sconf_supehr18_03008.pdf
Lots of reading there - and more besides!
K2

Thanks for the references K2.

Here's yet another study,...this one focusing on small diameter discs: cm-scale Tesla Turbines

 

[Toymaker]

I redesigned and machined a new impellor over the past few days which resulted in another small improvement in performance. Left image is the old impellor,... Right image is the new design with 14 shortened, thinner blades. The new impellor is 2" diameter.
The new impellor threw the water stream several meters further and the stream was noticeably more coherent.

The test was performed still having half the turbine nozzles blocked off, which as noted earlier, is required due to the size limitations of my shop air compressor tank, which as seen in the video, supplies only a few seconds of useful air pressure.

I've ordered more brass rod and will re-make all the nozzles with much smaller holes, which I hope will allow me to operate the turbine with my limited air compressor, and use all the nozzles, instead of only half; if needed, smaller holes can always be drilled out to a larger diameter when I transition to running on steam.

 

[Toymaker]

I machined 6 new nozzle arrays as shown below. Holes in the top array are noticeably smaller, 0.026" diameter compared to 0.041" diameter. Doing a little math shows the total area for the larger hole nozzles to be 0.19 sqr in, and the total area for the new, smaller hole nozzles to be 0.076 sqr in. Due to my compressor's relative small tank size, I was forced to block off half the holes in the larger holes nozzles, resulting in a total useable nozzle area of about 0.1 sqr in.; the results of that configuration are shown in post #16. The smaller nozzle holes allow using the entire length of each 0.026"-hole nozzle array, but since total nozzle area for the new arrays is smaller, I expected similar, or even less developed power compared to the original nozzles. I'm pleasantly surprised that the new nozzle arrays produce more power than the original nozzles.

I need to find a much larger source of either compressed air or steam to continue testing; time to put this project on the shelf and get my monotube boiler working

 

[Steamchick]

I suspect (but am guessing!) that the smaller holes are putting proportionally more air in the turbine slots and at a higher velocity, and less air impinging on the outer metal surface of the rotor where it simply goes around the outside and out the exhaust?
Gas velocity is everything in the turbine. - And putting it where you want it, versus NOT putting it where you do NOT want it is the key to efficiency.
What was the pressure gauge steady at with the larger holes, and what is it steady at now?
K2

 

[Steamchick]

I guess you realise you can measure the flow of water (Time to pump a known quantity from the reservoir) vesus water pressure (measure how high it will squirt! - 32feet high is 1 bar pressure) therefore determine how much useful work the turbine is performing?
K2

 

[Toymaker]

I guess you realise you can measure the flow of water (Time to pump a known quantity from the reservoir) vesus water pressure (measure how high it will squirt! - 32feet high is 1 bar pressure) therefore determine how much useful work the turbine is performing?
K2

That's a nice idea, but, as you could see in the videos, each test run lasts only a few seconds, and with constantly decreasing output as the compressor's air tank rapidly empties through the nozzles. Given the limited test set-up I have, there's not enough time to take any meaningful measurements,...and for now, that's OK as these first few test runs were only meant as a proof-of-concept, and I'm happy with the results thus far. Meaningful tests will have to wait for a much better source of compressed air, or more likely, a source of steam.