Determination of Serviceability Limits of a Turboshaft Engine by the Criterion of Blade Natural Frequency and Stall Margin

This paper analyzes the health and performance of the 12-stage axial compressor of the
TV3-117VM/VMA turboshaft operated in a desert environment. The results of the dimensional
control of 4800 worn blades are analyzed to model the wear process. Operational experience
and two-phase flow simulations are used to assess the effectiveness of an inlet particle separator.
Numerical modal analysis is performed to generate the Campbell diagram of the worn blades and
identify resonant blade vibrations which can lead to high cycle fatigue (HCF): mode 7 engine order 30
in the first stage and mode 8 engine order 60 in the fourth. It is also shown that the gradual loss of
the stall margin over time determines the serviceability limits of compressor blades. In particular,
the chord wear of sixth-stage blades as high as 6.19 mm results in a reduction of the stall margin
by 15–17% and a permanent stall at 770–790 flight hours. In addition, recommendations setting out
go/no-go criteria are made to maintenance and repair organizations.