Tesla Turbine Efficiency

[BernieM]

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?

 

[Isarmann]

I was just wondering about that very point earlier today... The question that occurred to me was, "Is the boundary-layer effect more efficient in transferring energy to the turbine impeller than the 'old-style' direct-impingement method?" I did see a small video illustrating the concept of the tesla turbine just today, running on compressed air, but really it didn't show anything (even implied) about how well it works...

An unrelated article I saw earlier today was discussing the efficiency of engines and pointed out how sloppily the term is used these days... some were talking about thermal efficiency, some electrical efficiency, some mechanical efficiency... and all seemed to be hinting at (or trying to imply) that the overall efficiency of the system (power in; power out) was what was under discussion.

Although Tesla's turbine has been around, as an idea, for a long time; it seems to me that it's only been recently revived as an experimental thing... So it seems to me quite likely that there is no experimental data of the type we'd like to see-- some of the first-order research that needs doing, I would think, is to build and test models to collect exactly that kind of experiential data.

Let me know if you hear anything on this...

 

[Jupiter6]

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've read everything from 25 to 95% but have found 40-60% to be believeable, based on videos. I scavenged our engineering library on the subject but didn't find anything more than a paragraph related to the subject. Apparently, the efficiency goes down as the rotor spins faster which I imagine is due to the centrifugal force counteracting the corkscrew effect. While researching, keep in mind that these are also referred to as boundary layer turbines and fixed disc turbines. The best resource I have found so far is:http://www.teslaengine.org/

 

[Isarmann]

Yeah--- that's the kind of numbers I've seen, too; and they strike me as little different than those projections one sees based on the theoretical efficiency of Carnot cycle engines and whatnot--- not much more than a guess, really. I would consider 50% (in the middle of your reasonable range) as an acceptable compromise between optimism and foolishness, until we can get our hands on actual data...

One thought on the speed: after considering for a bit, I think your hypothesis misses the mark--- boundary layer effect is based on friction, and it won't change because of a tangental force... think of rotorcraft or airscrews--- they don't seem to 'throw off' air in the plane of the spinning disc, which they clearly would if this were a true phenomena. So what does explain the decreasing efficiency? Speed alone, I think! Consider; in most systems where you have a differential, like heat differential or what-have-you, as the differential closes, efficiency drops... Like heat engines, less efficient the closer the hot and cold sides' temperatures are.

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...

Consider: An object is moving at a given speed (100m/s) through air... there is friction, there is a boundary layer effect. Now increase or reduce speed by 1m/s--- what is the result, in terms of boundary layer effect? Negligible, it seems. Take a stationary object and subject it to a 100m/s airstream, and the effect is noticable. I think that might be a more accurate picture of why the efficiency, however high or low it is, changes as the turbine's speed increases.

 

[Jupiter6]

I kinda see what your getting at Isarmann however I don't feel air moving axially through a prop is a good comparison to a fluid corkscrewing radially inward. However, even in the tiny contact time between air and a prop blade, rotorwash does spiral outward due to a tangential component imparted by the prop blades. The boundary layer is a small part of a prop whereas it's everything in 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...

Exactly. The centrifugal force disrupts the corkscrew and creates a back pressure to the incoming fluid. I believe they call this "gating". There is literature on this avaiable on the web. I feel you and I approaching the same reasoning from opposite sides.

 

[RonL]

I think you will find the patent that Tesla filed will give you the best information of what can be expected for the turbine.

Not sure how well i remember, but two things he made reference to, was a thermodynamic conversion, and that best efficiency was achieved at about 50% turbine speed/ inlet velocity.

 

[Isarmann]

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.

 

[Isarmann]

Yes, RonL, that's what I was thinking; there must be some optimum relationship between the incoming charge speed and the turbine's speed.

Leave it to you to go to the source and make light of all our serious musings... LOL... just kidding, of course.

I should have thought to read the patent...

Have you guys noticed how often a post, which must've taken ten minutes to write, would be obviated by as little as 3-5 minutes of reading on the subject? I find myself thinking "Wikipedia, silly!" all the time on here when reading some of the less-well-informed posts...

 

[RonL]

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.

I think you are on spot with the vortex and turbine working together.
In the past I have used a vortex tube cooler, and much later found a detailed description of how it works, in a refrigeration Manuel, the air in is broken into three values
1. cold air out
2. hot air out
3. internal friction of the air against the tube wall

In my opinion this turbine is a segmented flywheel, that can transfer thermal energy from the atmosphere, a key issue, is to enhance the separation of the delta T, and pressure differences within the blades. This is the area that caused Tesla much grief (in my opinion) too much thermal difference in a small area led to blade distortion.

There might not be a free lunch here, but if not i think a good snack might be in store (as long as we have sunshine everyday)

 

[Isarmann]

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.

 

[RonL]

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.

In my mind an area of focus that most researchers miss, is how little can they get by with. The general approach is to build for high pressures, and output from the least size, which equates to higher cost in almost all respects.

I'll share a few of my thoughts and efforts to devise a plan for slower speed and more volume, no real details, but rather what and why.
First as i see it, the vortex tube puts out air at two (in general) temperatures, which is a compromise of volume at each end, the temperature varies from extreme cold at the center to very hot at the wall of the tube, air friction put an effort toward twisting the tube, and if the tube is allowed to rotate some of this energy could be recovered.

The refrigeration Manuel gave the values as follows,
air in 25 CFM,
100 PSI(794 kPa), and
temperature 100 F (38 C),
75% of the air spirals inward, expands and cools to 40 F (4 C), the other 25% of air churns in the tube, heats up to 270 F (132 C).

Air enters a spin chamber at a tangent and forms a cyclone effect, spinning at 500,000 RPM, air tries to speed up to 5,000,000 RPM while spiraling inward, is retarded by the air column in the tube, forcibly turns column with an effort equal to 1/2 horsepower.

The size of the tube is less than 1" Dia. and the spin chamber is 2" Dia. or less, an overall length of around 8".


This should give a good idea of thermal change in a vortex and this is with no moving parts.
Inserting a turbine and increasing the diameter will have a great effect on the speed of things, but a thermal change will still take place.

My plan is to use 4 canister vacuum units working in series, 1 unit on each side of the turbine pulling a vacuum at the center discharge ports, and plumed to push air toward the other two that are in series and blowing air at an increased velocity into the turbine at a tangent.
The heat from the motors will continually be cycled thru the air flow, and the insertion of jet ejector principles will allow for a replenishing of warmer air from the atmosphere.

Some cold air discharge will take place between the two vacuum units and the two pressure units.

My turbine will consist of common 10" saw blades rated for 7,000 RPM, and the center hole between 1" and 2" there is a total of 8 holes to use for bolting the pack of blades together and i will use a slightly larger spacing between the blades. The carbide tips will be left in place and hopefully act as impact blades, they are at angles that should prove useful against the air flow. The blades are about 1 pound each and i plan to use around 30 in the stack.

Another idea that i started a patent for in 1996 (but did not follow thru) is to allow the blades to move crosswise, this will produce a slide action and give the turbine a variable volume, creating the possible cycle for building and depleting pressure of the air flow.

As for taking power off the turbine, i'll leave that alone for now because the post is getting too long, hope some of this will help anyone that has an interest in Tesla's Turbine.

A good book for reference is " The Tesla Disc Turbine" by W.M.J. Cairns, I.Eng., M.I.E.D.

 

[Argentina]

I think that the end of this discucion 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 diferent turbines, at diferents presures 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 am trying to find someone who do the modeling because i have to make a thesis to end my career of mechanical engineering.

 

[Isarmann]

I agree, Argentina... I have reviewed all of Tesla's patents on the turbine, to better understand his own thinking on the advantages of the design; based on those I have some comments I will post a bit later. I think we can come up with a 'standard' design that features easily-changed major variables that should allow us to establish the numbers we seek.

 

[RonL]

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.

Hi Argentina, and Isarmann

It would be great if you find a thermal modeling program to evaluate the turbine action, and share with the forum, your findings.

It is my thinking that, the compression of air you mention above, has to be a part of the turbine's energy cycle or you have too much loss outside the system.
A closed loop system should look exactly like a heat pump, with the turbine acting as the expansion valve, and giving it the ability to expand and contract the space between the blades, while turning, is important to the pressure/vacuum buildups.

So many things can be done with the basic design, it is good to see experimenters looking at Tesla's idea.

RonL

 

[Argentina]

Im trying to get FLOWORKS ( a tool for solidworks ) and see if i can get some data if i build a small 2 o 3 disc tesla´s turbine. First i have to know how the program works and if is usefull for this kind of things.

I will tell you if a know something else.

See ya

 

[Isarmann]

Yeah, I agree that modelling software is the way to go... I'm using pro/ENGINEER from PTC, and it does include a module to do mechanical stress modelling--- but I think the key would be something more like what Argentina mentioned; thermodynamic modelling. I know of a very capable product along those lines, but I'll have to look it up--- can't remember the name. I don't think floworks is the one I've seen before... I seem to remember a different name. Regardless, once we have some models completed in any of the programs, we should be able to move them to whichever analysis software.

I do believe they will show us exactly what we're hoping to see.

 

[Argentina]

I think the first step is building the turbine with the best efficiency to transform the motion of the fluid to motion on the axle. With the less turbulence and loss of boundary layer between the disc. I don't know if the floworks works with diferent surfaces on the materials, i hope so because i think there is the key ( also on the disc speed ).

 

[Isarmann]

Yes! I could certainly see boundary-layer and surface effects being considered second-order in the minds of those who wrote the programs; but for our purposes, they're clearly first-order effects. I think Flotherm (or Flowtherm) may have been the program I was looking at before, and it's main focus is overall flow through a system, showing hotspots, eddies, and the like.

I'm sure, even if they consdiered it a secondary consideration, that these programs must take into account surface textures, especially when the walls are close--- so hopefully, at worst, changing some of the values to emphasize that portion of the modelling would still give us the general analysis we're looking for. Actual testing of a built model will firm it up... As long as the software can help us avoid major missteps, I believe it will work.

 

[Argentina]

I need the EFD.LAB, that's the program we are looking for... If someone has it, please contact me. I can't find it.

 

[ank_gl]

There are a lot of efficiency for a turbine, thermodynamic efficiency(which one can get from tables), then there is a hydraulic efficiency(in case of water turbine) or blade efficiency(indicating how well blade is taking energy from the working fluid), then is mechanical efficiency.

The case of flow irregularities(non uniform flow, turbulence, boundary layer separation, fluid friction) all cause a dip in blade efficiency,

I am not sure which efficiency are we talking about here.

And output power is parabolic with speed, and assuming constant input power, efficiency(blade efficiency) ll take a dip with rpm

 

[NateD]

Just thought I'd drop on this list and let anyone interested know that I will soon have a completed Tesla turbine built specifically for data collection purposes.


Please let me know your educational/professional backgrounds so I can write appropriate responses to your questions.


As to the question of disc efficiencies. I have concluded based on many years of thinking that the disc efficiencies will be a function of equilibrium between state properties and momentum effects of the flow field.

If you look at the basic boundary layer equations you'll see that the differential velocity is a big deal. There is of course some type of nonlinear relation between the state change throughout the flow field, the inlet pressure and the other variables in the oversimplified boundary layer equations.

I have designed my turbine assembly specifically to investigate these properties. I too have concluded after several years of internet research that no one has properly documented data. Those who have built engines in the past haven't used the proper engineering methods to distill what little data they have. And those who have used the proper methods haven't released their data to the public.

I plan on measuring the thermal efficiency and the net efficiency. And of course any other efficiency I can figure out how to calculate.

I have over 8 channels of data logging being put to use.

It should be an interesting test. Stay tuned over the next few months for some word as to how the tests go.

In the mean time feel free to post any questions you have for me.

Nate
Aero Engineer

 

[NateD]

Ok I've now gone back and read previous posts on here...

RonL on 06-04-08 at 10:40 you wrote about the Delta Ts and the pressure differences within the blades... One issue is the frictional heating of the blades. Keep in mind that the nonlinearities of the state properties of the operating fluid make calculations very difficult.

I have experimented with various CFD packages and have derived several simplified equations that might be close to estimating operation... however none of them are going to be very precise in reality (I'll be happy if I can hit within 10% of my calculated numbers when I actually test).

I would like to comment that I don't think a proper model can be derived using vortex theory without accommodating the state property changes. The state properties in the flow field are extremely variable and finding their equilibrium states has been somewhat of a problem for me in the past.

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.


Argentina... I've already tried modeling with FLOWORKS... the models I've come up with aren't exactly that accurate. The FLOWORKS (CFD) software has some distinct limitations that make it mostly unsuitable for a Tesla Engine. EFD.LAB also seems to have some limitations. I advise caution when turning to computer programs. You have to really understand CFD to be sure they are working right. In my undergrad studies I found that CFD would be great but having to write my own codes would have been a lot tougher then finishing the test engine I have designed.

Not to disappoint anyone but in my 8 years of studying this problem I have yet to find a program that properly handles a tesla engine... it is by far probably one of the most complicated fluid flow devices I have seen next to a few others out there... many others I have seen are specially written programs which can't be applied to a tesla engine.

 

[RonL]

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.

Thanks NateD,

Best wishes in your trials, and data collecting, I'll look forward to your results. (I believe the turbine has great potential)

I wonder if we are on the same page about disc spacing? the design that i did not follow through with a patent application on, allows the turbine to vary disc spacing while in operation, this will give the ability to set a cycle pattern of both, high/low air volumes and temperature.

One other thought, if not in your plans already, might be to set up an operation where the turbine is turned by an electric motor, at a very controlled and steady speed, any airflow effects would show up in the motor readings.

RonL

 

[NateD]

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

 

[RonL]

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

Nate, I do not have a degree, what little I do know comes from association of power tools, and equipment that has been used in work and home applications, I depend on the spec plate numbers (on quality equipment) for power ratings for most things.

In recent years things have changed a little, it really gets my blood rate up, when retail tools claim things like, 6.5hp, then when you look at the data plate, the motor draws 10.2 amps@115 volts, (where's the truth in advertising??)

My two largest equipment units are, a 50,000 pound (1948) fully mechanical "Link Belt" drag line, and a fully hydraulic (1990) 53,000 pound "poclain" excavator, then a compliment of smaller things all the way down to hand tools.
I have a "Bobcat" skid loader, that is powered by a 27hp engine, it weighs about 3400 pounds, and is fully hydraulic driven. Knowing and understanding how it performs work, (power, weight, traction) and without any numbers calculation, one can say why a more powerful engine would be almost a complete waste.

Doing all my own repairs gives me cause to learn how to take things to the limit, and just short of breakage. (sometimes I miss, but not often)

My studies over the last few years have been random, and unstructured, producing a quite varied array of knowledge, but without a solid foundation in the basics.

My interest in Tesla Turbines began in 1972, but until 1992 very little information was easy to find. The early years of the net has produced too much over unity, and perpetual motion talk and has tainted images of the turbine.
I do feel that will change some in the near future, and I hope to put some efforts into my own ideas, which will make use of multiple types of energy transfers.

Sorry I got a little long winded (maybe I could use a little of that to power a turbine):yuck::zzz:

Ron

 

[Argentina]

Hello...

I went to a very good technical high school and now I am in the last year of mechanical engineering in the university.
Here in argentina the m.e. is more based on materials than thermodinamics, so i have a large gap between my knowledge and the one that i want to have.

Best wishes on your investigation and i hope for good results

 

[chayced]

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.

 

[RonL]

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 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

 

[RonL]

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

Good example of my poor use of words

A clarification of the illustration used.

The SR-71 Blackbird uses power to force it's self through the air at speeds that produce tremendous heat because of friction.

If air of great pressure is forced into a spiral inside the turbine housing (producing in essence a vortex) the turbine blades are dragged along at some speed due to boundary layer adhesion, or as I have always thought (friction) corrections here please if needed:shy:

As I see it, the outer diameter is the absolute maximum of any torque application.
This highest pressure cannot be exceeded, as blade rotation keeps air from moving straight (spiral layers of diminishing energy air) to the center discharge.
Depending on energy removal from the turbine system, the velocity of air, and speed of the turbine, causes one or more layers of lesser energy(velocity) air to move to the low pressure center (I say try to pull a vacuum at this point) think of overlapping jet streams in our atmosphere.

Tesla used two terms, Viscosity and Adhesion, to me this implies friction and thermal transfer.
Based on vacuum storage, and pressure storage, my mind sees a delta T of value that exceeds durability of almost any material.
This equates to mass energy storage and cycle time.

Temperature controlled by, gas flow/energy removed.

Maybe the hardest thing for most people to comprehend, is the continued expansion of a gas into a continually declining volume. ( what helps me is to think of the volume of a cubic foot of air at the temperature of nitrogen, as opposed to 200 or 300 (C) or(F)degrees)
Once again thanks for any comments.


Ron

 

[RoaldFre]

Hi,

I've just made myself an experimental tesla turbine using 18 regular CDs, partly inspired by this forum thread.

Now I'm wondering on how to calculate the ideal converging-diverging nozzle to make it run most efficiently.
I guess the main things are the area of the convergent section (where it is smallest) and the increase in area in the divergent section(?)
I've searched the web but couldn't really find any actual equations on the subject that were usefull for designing a "de laval nozzle".
Any info is greatly appreciated :-)


RoaldFre

 

[NateD]

Chayced,

You are correct that centrifugal force (a D'Almbert's force) adds a small amount to the aerodynamic efficiency of these turbines. However this has more to do with the amount of time the air stays in contact with the discs and the fact that the force impedes the flow. I can't say for sure whether there is a net gain or loss or nulling of efficiency due to this.

You are however incorrect to claim that friction is not the action mechanism. There are two main mechanism in nearly all aerodynamic and fluidynamic effects. Friction and impulse. Even an airplane wing experiences friction. In the case of a wing the friction between air molecules is what impedes the movement of molecules from the wing. In this way the impulse effect is created. If you were to make air frictionless then molecules bumping into other molecules would produce no effect and thus you couldn't build any pressure and the relationship between static pressure and dynamic pressure would break down.

There needs to be some airflow between boundary layers to an extent however currently this extent is unknown.

BTW you can't have a boundary layer push back without viscosity and thus friction to keep the air molecules from moving in other directions.


Ron,

Induced drag on an airplane is different, though not much. Induced drag has a component of pressure drag (because the airplane has a frontal area and thus blocks the flow).

To further clerify your answer: The SR-71 gets hot because it moves air out of its way. In the process that air slides along the surface of the airplane at very high speeds and thus generates friction and thus heat. It is this heat and friction that use energy from inducing drag. And it is this drag that requires a lot of power to move the airplane through the air at nearly mach 3.

Lets clerify your use of the word turbine blades. Are you talking about a conventional turbine or a tesla turbine?

A conventional turbine relies more directly on impulse (the inertia of the air striking the blade). Drag and friction are a small part of that.

The tesla discs are dragged in a circle. As energy is absorbed by the discs and transmitted to the shaft, the gas temperature goes down and wants to contract causing the density to go up and pressure to go down. Additionally you need so much air moving through the turbine to make it work. A natural pressure drop is inevitable.

The tesla turbine will most likely never created vacuum as such a condition will require no flow at the outlet. And the laws of thermodynamics say this isn't possible.

Viscosity and Adhesion... let's discuss this more. Viscosity is a measure of how freely a fluid flows or shears. While adhesion is similar and related but describes the tendency for fluids to stick to a surface.

Neither of these have anything to do with friction or thermal transfer (directly). Though viscous effects have both a friction component and a thermal heat transfer component.

I'm not sure what you mean by vacuum storage and pressure storage. It is possible that the friction could melt the materials there are some holes in this theory.

Nate

 

[russ_watters]

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:

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

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.

 

[RonL]

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.

The most extreme example I can think of, I'm sure that most have seen with their own eyes, or at least on film, is the return of the space shuttle. Surely the reverse action can be duplicated in a wind tunnel, and in my mind this is much the same as blasting high pressure air through a Tesla style Turbine.

I think it might be significant that with supersonic aircraft, the shock wave is dispersed out into the low pressure resistance of the atmosphere, but in the turbine the pressure is forced between the blades, and has only one avenue of escape, which is to the low pressure center exhaust.

I would think the pressure drag being confined between the blades, increases the skin friction, and that both forms of resistance, while in the outside world are negative values to most mechanical things, are in fact positive to the turbine. A lot like the older friction drive systems in transmissions and construction equipment.

For the most part I think people try to get too much out of too little, and find the efficiency is not great enough to justify the efforts. Maybe lower pressure and more volume would work for some systems. Kinda like when blowing leaves with my Tim Allen leaf blower, 30 minutes of high pressure work, is totally destroyed by a quick gust of low pressure, large volume wind.

The point of the turbine is that it is so simple in construction, and forgiving in precision of build, and materials can be very common, and cost far less than most other turbines. One must be aware of limits, and design accordingly.

Ron

 

[cr0ck3t]

... I will definitely have to learn more about the centrifugal force in this situation...

A funny cartoon about 'centrifugal force'

http://xkcd.com/123/

Hope you enjoy!

 

[NateD]

Russ,

Unless I'm mistaken the aerodynamic heating on an SR-71 is almost entirely a result of the immense frictional forces present on the skin of the aircraft. In this case the skin drag is higher then the pressure drag (or more correctly perhaps they are functions of each other).

In any case skin drag is substantial and worth looking into. The energy requirement of a supersonic flight is quite huge compared to subsonic that energy goes into boundary layer effects, and of course shock waves...

If you have better insight let me know.