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The losses occur in an actual turbine due to disc and bearing friction. Figure shows the energy flow diagram for the impulse stage of an axial turbine. Numbers in brackets indicate the order of energy or loss corresponding to 100 units of isentropic work (h 01 – h 03ss). Energy flow diagram for the impulse stage of an axial turbine
Distribution in both tangential and radial directions generates secondary flow. Secondary flow generates two velocity components V y , V z , hence introducing three-dimensionality in the flow field. The two components of velocity result in flow-turning at the tailing end of the blade profile, which directly affects pressure rise-and-fall in ...
The difference between axial and radial turbines consists in the way the fluid flows through the components (compressor and turbine). Whereas for an axial turbine the rotor is 'impacted' by the fluid flow, for a radial turbine, the flow is smoothly oriented perpendicular to the rotation axis, and it drives the turbine in the same way water ...
The radial component of the fluid velocity is negligible. Since there is no change in the direction of the fluid, several axial stages can be used to increase power output. A Kaplan turbine is an example of an axial flow turbine. In the figure: U = Blade velocity, V f = Flow velocity, V = Absolute velocity, V r = Relative velocity,
Radial flow turbines are mechanically robust compared to axial turbines and they are easy to configure. As a result of that they were considered for the application before axial turbine. They are more tolerant of overspeed and temporary temperature extremes. Radial flow turbines have higher energy extraction capability in one single stage.
V f = flow velocity (axial component in case of axial machines, radial component in case of radial machines). The following angles are encountered during the analysis: α = absolute angle is an angle made by V with the plane of the machine (usually the nozzle angle or the guide blade angle) i.e. angle made by absolute velocity V and the ...
Unlike a compressor or fan, surge or stall does not occur in a turbine. This is because the gas flows through the turbine in its natural direction, from high to low pressure. As a result, there is no surge line marked on a turbine map. Working lines are difficult to see on a conventional turbine map because the speed lines bunch up.
Axial momentum theory demonstrates how the wind turbine imparts an influence on the wind which in-turn decelerates the flow and limits the maximum power. For more details see Betz's law . Since this effect is the same for both lift and drag-based machines it can be ignored for comparison purposes.