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3D Finite Element Vibrational Analysis of T385 Turbine Rotor BLISK Using SAFE Diagram

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Integrally bladed rotors (BLISK) are most stressed part of aircraft engines due to high rotational speeds, elevated temperatures and pressures. Turbine blades fail mainly due to fatigue under alternating stresses resulting from vibration of rotor systems. Non-uniform pressure field is experienced by turbine BLISK due to interaction of stator and rotor blades which acts as a source of excitation during turbine operation. The number of stator blades dictates the occurrence of resonance in the rotor BLISK during steady-state operation. Therefore, it is necessary to design a mechanically feasible rotor with respect to stator and verify its modal and harmonic response to ensure its resonance-free operation. Design and development of T385 turbine stage for 1 kN small gas turbine engine are carried out in Propulsion Division, CSIR-NAL. The dynamic behaviour of T385 turbine rotor BLISK is evaluated for vibration reliability. This paper presents vibrational analysis of the T385 turbine rotor BLISK using finite element technique to evaluate critical nodal diameter, critical frequencies and response in engine environment. The turbine speed is 50,500 rpm at the engine design point based on the inlet temperature. Detailed vibration analysis of T385 turbine is carried out using FEA to plot Campbell and SAFE diagrams. The critical nodal diameter extracted from plotted SAFE diagram is 19, which is very well agreeing with Bertini analytical formulae. The Campbell diagram is plotted for T385 turbine at critical nodal diameter of 19. The obtained critical speed from this Campbell diagram is 33,000 rpm, which ensures the rotor is safe in the operating conditions.


  • Turbine BLISK
  • Thermal stress
  • Centrifugal stress
  • Vibration
  • Nodal diameter
  • SAFE diagram
  • Campbell diagram
  • Harmonic response

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  • DOI: 10.1007/978-981-15-5701-9_45
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N :

Speed, rpm

M :

Mass, kg

C :

Damping, N s/mm

K :

Stiffness, N/mm

F n :

Frequency, Hz

ω n :

Rotational velocity, rpm

N B :

Number of blades

N V :

Number of vanes


Nozzle passing frequency, Hz


Running speed harmonics, Hz


Critical nodal diameter

d max :

Number of nodal diameters

n :

Different engine orders


Singh’s advanced frequency evaluation


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The authors acknowledge CSIR support for this project. The authors would like to thank Director, CSIR-NAL, and Head and Joint Head, Propulsion, for their support in carrying out this work. The authors also thank Propulsion Division colleagues for their support and help.

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Correspondence to Revanna Jai Maruthi .

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Jai Maruthi, R., Prathapanayaka, R., Vinod Kumar, N. (2021). 3D Finite Element Vibrational Analysis of T385 Turbine Rotor BLISK Using SAFE Diagram. In: Rao, J.S., Arun Kumar, V., Jana, S. (eds) Proceedings of the 6th National Symposium on Rotor Dynamics. Lecture Notes in Mechanical Engineering. Springer, Singapore.

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  • Print ISBN: 978-981-15-5700-2

  • Online ISBN: 978-981-15-5701-9

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