Radial turbine
Encyclopedia
A Radial turbine is a turbine
in which the flow of the working fluid
is radial to the shaft. The difference between axial and radial turbines consists in the way the air flows through the components (compressor and turbine). Whereas for an axial turbine the rotor is 'impacted' by the air flow, for a radial turbine, the flow is smoothly orientated at 90 degrees by the compressor towards the combustion chamber and driving the turbine in the same way water drives a watermill. The result is less mechanical and thermal stress which enables a radial turbine to be simpler, more robust and more efficient (in a similar power range as axial turbines). When it comes to high power ranges (above 5 MW) the radial turbine is no longer competitive (heavy and expensive rotor) and the efficiency becomes similar to that of the axial turbines.
developed and patented his Bladeless Turbine
. One of the difficulties with bladed turbines is the complex and highly precise requirements for balancing and manufacturing the bladed rotor which has to be very well balanced. The blades are subject to corrosion
and cavitation
. Tesla attacked this problem by substituting a series of closely spaced disks for the blades of the rotor. The working fluid flows between the disks and transfers its energy to the rotor by means of the boundary layer effect or adhesion and viscosity rather than by impulse or reaction. Tesla turbine
s are typically most effective at small diameters, so they are not seen powering jet aircraft or large power plants, but for microturbine applications they have ease of manufacture and good efficiency, two characteristics that are not found in most other turbine configurations.
Euler's Turbine Equation
Euler's Turbine Equation states that
W = (U2-U1)+(V2-V1)+(W2-W1),
where U = Blade Velocity = r*omega (omega - Angular Velocity)
V = Absolute Velocity
W = Relative Velocity
For an axial machine, you have Zero Degree of Reaction that makes U2-U1 = 0.
This is one reason for the fact that axial turbines have low power output. For a radial turbine, along the flowpath, Radius reduces and hence U2 - U1 is not equal to zero, which proves that for similar turbines, radial turbine has higher power output.
can be placed at the front, in the cold part, so less lubrication oil is needed, and there are no thermal losses due to lubrication of the hot parts of the rotor.
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...
in which the flow of the working fluid
Working fluid
A working fluid is a pressurized gas or liquid that actuates a machine. Examples include steam in a steam engine, air in a hot air engine and hydraulic fluid in a hydraulic motor or hydraulic cylinder...
is radial to the shaft. The difference between axial and radial turbines consists in the way the air flows through the components (compressor and turbine). Whereas for an axial turbine the rotor is 'impacted' by the air flow, for a radial turbine, the flow is smoothly orientated at 90 degrees by the compressor towards the combustion chamber and driving the turbine in the same way water drives a watermill. The result is less mechanical and thermal stress which enables a radial turbine to be simpler, more robust and more efficient (in a similar power range as axial turbines). When it comes to high power ranges (above 5 MW) the radial turbine is no longer competitive (heavy and expensive rotor) and the efficiency becomes similar to that of the axial turbines.
Nikola Tesla's Bladeless Radial Turbine
In the early 1900s, Nikola TeslaNikola Tesla
Nikola Tesla was a Serbian-American inventor, mechanical engineer, and electrical engineer...
developed and patented his Bladeless Turbine
Tesla turbine
The Tesla turbine is a bladeless centripetal flow turbine patented by Nikola Tesla in 1913. It is referred to as a bladeless turbine because it uses the boundary layer effect and not a fluid impinging upon the blades as in a conventional turbine...
. One of the difficulties with bladed turbines is the complex and highly precise requirements for balancing and manufacturing the bladed rotor which has to be very well balanced. The blades are subject to corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
and cavitation
Cavitation
Cavitation is the formation and then immediate implosion of cavities in a liquidi.e. small liquid-free zones that are the consequence of forces acting upon the liquid...
. Tesla attacked this problem by substituting a series of closely spaced disks for the blades of the rotor. The working fluid flows between the disks and transfers its energy to the rotor by means of the boundary layer effect or adhesion and viscosity rather than by impulse or reaction. Tesla turbine
Tesla turbine
The Tesla turbine is a bladeless centripetal flow turbine patented by Nikola Tesla in 1913. It is referred to as a bladeless turbine because it uses the boundary layer effect and not a fluid impinging upon the blades as in a conventional turbine...
s are typically most effective at small diameters, so they are not seen powering jet aircraft or large power plants, but for microturbine applications they have ease of manufacture and good efficiency, two characteristics that are not found in most other turbine configurations.
Euler's Turbine Equation
Euler's Turbine Equation states that
W = (U2-U1)+(V2-V1)+(W2-W1),
where U = Blade Velocity = r*omega (omega - Angular Velocity)
V = Absolute Velocity
W = Relative Velocity
For an axial machine, you have Zero Degree of Reaction that makes U2-U1 = 0.
This is one reason for the fact that axial turbines have low power output. For a radial turbine, along the flowpath, Radius reduces and hence U2 - U1 is not equal to zero, which proves that for similar turbines, radial turbine has higher power output.
Advantages compared to axial turbines
Thanks to lower thermal and mechanical stress on the turbine tips, it is possible to boost power quite significantly by increasing the turbine entry temperature (increasing fuel input) which results in an improved mechanical efficiency. The lower mechanical stresses also enable radial turbines to handle single stage compression and expansion. As a result, the radial turbine does not need to be air cooled, which means that all the air entering the compressor is used only to drive the turbine which gives the radial design a strong advantage for co-generation applications. Another result of avoiding air cooling is that power and efficiency are kept almost constant during the lifetime of the radial turbine whereas an axial gas turbine needs to be washed often to maintain ISO performance standards. The other advantage of such a simple rotor is that the bearingsBearing (mechanical)
A bearing is a device to allow constrained relative motion between two or more parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can...
can be placed at the front, in the cold part, so less lubrication oil is needed, and there are no thermal losses due to lubrication of the hot parts of the rotor.