Turbine blades having alternating resonant frequencies

Claim 1

A steam turbine rotor assembly comprising: a rotor rotatable at a predetermined running speed, a plurality of first free standing elongated, low aspect rotor blades, each having a first resonant frequency, a plurality of second free standing elongated, low aspect rotor blades, each having a second resonant frequency, wherein the plurality of first and second rotor blades are alternatingly connected to the rotor in at least one row, and wherein adjacent blades of the at least one row have alternating first and second resonant frequencies, each of the plurality of first and second rotor blades having a base portion and an air foil portion including a leading edge, a trailing edge, a concave surface, a convex surface, and a tip, and the tips of the plurality of second rotor blades of the at least one row being profiled for increasing the resonant frequency thereof, said alternating first and second resonant frequencies providing means for preventing unstalled flutter in the at least one row at non-resonant frequencies wherein each profiled tip includes an L-shaped recess formed substantially longitudinally from the leading edge to the trailing edge in the concave surface of the airfoil portion of the blade at the tip, said L-shaped recess defining an extension running from the trailing edge along the top and terminating before the leading edge.