why we use large blades in low pressure turbine?

Question

why we use large blades in low pressure turbine ans use small blades in high pressur turbine?>

Answer 1

If you're talking about different stages in the same machine, then the high-pressure section has a smaller diameter because the mass flow per unit area is larger. In general, high-pressure turbine blades tend to be relatively stubby because stress and deflection would be too great otherwise. Also, the shape of the high-pressure blade becomes impractical at long aspect ratios.

Answer 2

Small blades in high pressure turbine because, in the turbine, there are restrictive nozzles for venturi effect: restrict the fluid stream causes rise in velocity, which adds to the energy of the fluid just before it turns the blades. A bunch of small blades work much better than one large blade.

A low-pressure turbine, however, works opposite a high-pressure turbine. In this case, the blades are causing the motion of the air, rather than the reverse. Greater surface area causes more air motion.