18-03-2014, 11:15 AM
Blade Nomenclature
Blade Nomenclature[.ppt (Size: 434.5 KB / Downloads: 146)
Axial Flow Turbines
Most of the gas turbines employ the axial flow turbines.
The chapter is concerned with axial flow turbines.
The radial turbine can handle low mass flows more efficiently than the axial flow machines.
■ The velocity triangles for one axial flow turbine stage and the nomenclature employed are shown. The gas enters the row of nozzle blades with a static pressure and temperature P1, T1, and a velocity C1, is expanded to P2, T2, with an increased velocity C2 at an angle α2.
■ The rotor blade angle will be chosen to suit the direction β2 of the gas velocity V2 relative to the blade at inlet.
■ V2 and β2 are obtained from the velocity diagram of known C2, α2, and U.
► Assumptions
■ Consider conditions at the mean diameter of the annulus will represent the average picture of what happen to total mass flow.
■ This is valid for low ratio of tip radius to root radius.
■ For high radii ratio, 3-D effects have to be considered.
■ The change of tangential (whirl) mass is . This amount produces useful torque.
■ The change in axial component produces the axial thrust on the rotor.
■ Also there is an axial thrust due to P2 – P3.
■ These forces (net thrust on turbine rotor) are normally balanced by the thrust on the compressor rotor.