An aerofoil array for a gas turbine system has an inner annular platform and an outer annular platform, which extend about a longitudinal axis and radially delimit an annular channel for a gas flow; the annular channel houses a plurality of aerofoils, arranged at a substantially constant angular pitch and comprising respective central portions and respective ends connected to the platforms; the aerofoils are formed by two series of aerofoils having a different geometrical feature in order to intentionally vary the eigenfrequencies and arranged about the longitudinal axis with a sequence that is regularly repeated all along the annular channel; even though the external geometry of the aerofoils is varied, the cross-sections remain unchanged in the central portions, at any given radius with respect to the longitudinal axis.