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I see a lot of references to the 'efficiency' of the Tesla turbine, however, I can't find any actual data. Does anyone have a handle on actual achievable efficiencies of the tesla turbine?
I see a lot of references to the 'efficiency' of the Tesla turbine, however, I can't find any actual data. Does anyone have a handle on actual achievable efficiencies of the tesla turbine?
I'm thinking that, as the speed of the turbine approaches the speed of the stream of working fluid, the boundary layer effect becomes less and less...
I definitely think we're on the same page, and think you might be right; we're talking about the same thing... But there is a lot of imprecision out there when it comes to explaining the mechanism of agreed-upon phenomena, so I always find it interesting to try to come to understanding of the actual effect at work. I will definitely have to learn more about the centrifugal force in this situation; thanks for the steer on the word "gating". But leaving that aside for a moment (let's say we come up with a method that will negate that effect entirely), wouldn't you think there will still be an efficiency drop as the linear speed of the turbine approaches the speed of the stream driving it? So, assume there is no disruption of the corkscrew at all--- won't we still have efficiency drop as an expected result of the speed differential approaching zero?
I actually found out about Tesla turbines because of work I've been doing on vortex phenomena of all types; it seems like vorticies are one of those (I think of them as 'magic') areas of science where you get a synergistic payoff from what goes in... Of course, there's no such thing as a free lunch, but some things (like latent heat, for example) really seem to have potential benefits that in some way 'go beyond' what you might expect.
I wouldn't be suprised if the 'corkscrew' or vortex effect in the Tesla turbine is an important (if not indeed critical) component of how it functions in the first place.
Hehehe... I like that.
I really wonder about the thermodynamic component myself... I'd really love to see tests done (or do them myself) to establish some of these things we're wondering about.
I think that the end of this discussion is to build a series of different sizes of turbines and variables. Compress air and get how much energy it takes to do it, then expand it on the different turbines, at different pressures and speed to see how much energy you recover. If nobody wants to modeling the system by computer to get the best values of the turbine, disc, gap dimensions and speed of the fluid in motion. The practice will be the only way out. I'm trying to find someone who do the modeling because i have to make a thesis to end my career of mechanical engineering.
The test engine I designed and am now building has more then enough variables for a proper parametric study. I can vary direction, disc diameter, disc spacing, and fluid entrance parameters. As I said it'll be enough data to keep me busy for at least 6 months.
When I started looking at the Tesla Turbine I too looked at varying the disc spacings. I have concluded since that there are better ways to control the throttle. What I have done is designed the engine around max operating power. Varying the spacing of the discs sets up many problems that there are better solutions to dealing with in my opinion. One big issue I've thought about with a variable geometry version is sealing the case properly so there aren't big leaks.
Additionally varying rotor spacing makes things unnecessarily complicated. As an engineer I stick to the KISS methodology.
As to the motor idea... its worth looking into, though I think there is a big difference in the way the air moves when forced into the engine vs when the engine is being used as a pump.
Though I suppose if one could characterize the engine operation as a pump one could superimpose the results onto a forced fluid version. And therefore get a hybrid math model. I'm still not sold on the idea.
The very same data should jump out once my tests are done. The hardest parameter to measure of course is pressure distribution across the discs. But really the most important is to fully characterize the parameters that change as operating and engine parameters change.
What backgrounds do the people on this forum have?
I have a BS in Aerospace Engineering with a specialty in propulsion systems.
Nate
I think there are a lot of misconceptions with regard to Tesla turbines. The first of which is a misconception that centrifugal force acts against efficiency. Quite the opposite in fact. . In a Tesla turbine this fluid enters at a high velocity at the outside of the disks, where rotational velocity is high, and exits in the center where rotational velocity is low. If it were not for the centrifugal forces on the stream as is spiraled down the fluid would quickly find the center of the turbine. In having a centrifugal force the fluid itself is forced to have a nearly constant difference in velocity from the disks for the entire spiral downward. This is nearly pointless with water or other liquids, but with steam or even air this allows for extracting energy continuously and uniformly through varying densities. I'm not saying that the turbine has some sort of magical efficiency properties, but the balancing of forces on the fluid does allow a single simple turbine to act on a wide range of fluid densities.
Another misconception: the Tesla turbine does not act from friction, but instead boundary layer interaction. Friction is used in some designs to aid in low speed torque, but it's not desirable for efficiency. If you are going to build a Tesla turbine for efficiency testing then both nozzle design and disk spacing are key. If I'm not mistaken the actual airflow should exist between the two boundary layers of the surrounding disks, and only in a small gap there. That way there is a balance between the fluid stream pressing on the boundary layer, and the boundary layer pressing back. Minimal friction with force still being imparted from a moving fluid to a nearly stationary one with a small difference in velocities between the two.
Hope that helps a little.
I don't know how to say in words what I think, but in my mind is this not the same thing as induced drag on the surfaces of an airplane? The SR-71 Blackbird uses titanium because of the thermal build up due to the airflow.
The plane moves through the air, while the air is forced through the turbine.
I guess I don't really have a good understanding of how boundary layer and friction differ.
It seems to me that friction is the zone in which air is in solid contact with the surface and some distance out where slippage is almost resistance free.
Thanks in advance for any thoughts.
Ron
There are two kinds of drag. The drag that occurs in the boundary layer (the entire boundary layer) is skin friction drag. Skin friction drag is drag that slows down the airflow in the vicinity of the object and the boundary layer is characterized by the velocity profile near the object (roughly parabolic velocity profile).I don't know how to say in words what I think, but in my mind is this not the same thing as induced drag on the surfaces of an airplane? The SR-71 Blackbird uses titanium because of the thermal build up due to the airflow.
The plane moves through the air, while the air is forced through the turbine.
I guess I don't really have a good understanding of how boundry layer and friction differ.
It seems to me that friction is the zone in which air is in solid contact with the surface and some distance out where slippage is almost resistance free.
Thanks in advance for any thoughts.
Ron
I haven't been paying attention to this thread, frankly, because I see no point to it. Tesla wasn't known for his fluid dynamics and a turbine he invented wouldn't necessarily have been any good even a hundred years ago, so why bother? In any case:
There are two kinds of drag. The drag that occurs in the boundary layer (the entire boundary layer) is skin friction drag. Skin friction drag is drag that slows down the airflow in the vicinity of the object and the boundary layer is characterized by the velocity profile near the object (roughly parabolic velocity profile).
The other type of drag is pressure drag, which is due to the shape of the object creating a pressure disturbance in the air. Pressure drag is generally the bigger of the two.
In supersonic aircraft, skin friction drag is an insignificant factor. Virtually all of the drag and therefore virtually all of the heating is due to pressure drag from the shock wave.
... I will definitely have to learn more about the centrifugal force in this situation...