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The degree of reaction contributes to the stage efficiency and thus used as a design parameter. Stages having 50% degree of reaction are used where the pressure drop is equally shared by the stator and the rotor for a turbine. Figure 4. Velocity triangle for Degree of Reaction = 1/2 in a turbine
Fig-4: Velocity Diagram of Pressure compounded Impulse Turbine. The velocity diagram shown in figure 4 gives detail about the various components of steam velocity and Blade velocity. where, symbols have the same meaning as given above. An important point to note from the above velocity diagram is that the fluid exit angle (δ) is 90⁰.
Schematic diagram outlining the difference between an impulse and a 50% reaction turbine. Turbine blades are of two basic types, blades and nozzles. Blades move entirely due to the impact of steam on them and their profiles do not converge. This results in a steam velocity drop and essentially no pressure drop as steam moves through the blades.
The exit steam from one turbine is made to enter the nozzle of the succeeding turbine. Each of the simple impulse turbines would then be termed a "stage" of the turbine. Each stage comprises its ring of nozzle and blades. The steam from the boiler passes through the first nozzle ring, where its pressure drops and velocity increases. [2]
A velocity compounded impulse turbine is shown in the figure. One-stage velocity-compounded impulse turbine - Curtis Turbine. The decrease in the absolute velocity of the fluid across the two rotor blade rows (R 1 and R 2) is due to the energy transfer; the slight decrease in the fluid velocity through the fixed guide blades (F) is due to ...
An example of a velocity triangle drawn for the inlet of a turbomachine. The "1" subscript denotes the high pressure side (inlet in case of turbines and outlet in case of pumps/compressors). A general velocity triangle consists of the following vectors: [1] [2] V = absolute velocity of the fluid. U = blade linear velocity.
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With the help of these equations the head developed by a pump and the head utilised by a turbine can be easily determined. As the name suggests these equations were formulated by Leonhard Euler in the eighteenth century. [1] These equations can be derived from the moment of momentum equation when applied for a pump or a turbine.