The department would like to congratulate Ferhat Kaptan on successfully passing his PhD oral exam!
Ferhat held his presentation about:„Thermo-mechanische Modellierung von Flugzeugreifen für transiente Manöver“
on monday, may 17, 2021 at the Department of Dynamics and Vibration and successfully passed his oral exam.
Abstract:
Dynamics of Coupled Turbine Blades with Variable Rotational Speed
Turbine blades are thermally and mechanically highly stressed components of turbomachinery. During operation of gas or steam turbines, they are forced into rotation by the flowing fluid, so that the fluid energy is converted into mechanical energy. In order to avoid high cycle fatigue failures, an adequate prediction of the mechanical stresses occurring during operation is of great importance. For this purpose, both static loads, e. g. caused by centrifugal forces, and high dynamic forces, caused by oscillating fluid forces in the flow channel, must be taken into account in the mechanical design. The forces caused during operation strongly depend on the turbine’s rotor speed. Thus, a variation of the rotational speed results in a corresponding change of load conditions. One of the most important challenge in the mechanical design of turbine blades is therefore to keep the vibration amplitudes as low as possible over the entire range of rotational speed.
Within the scope of this work, a calculation methodology is developed to predict the dynamic behavior of coupled turbine blades over a wide range of rotational speed. In addition to the dependence of certain structural-mechanical properties on the rotational speed, such as stress stiffening, the contact stresses in the joints areas of coupled blades are particularly dependent on the rotational speed. The developed calculation program is based on a cyclic finite element (FE) model and is connected to commercial FE programs via interfaces. The steady-state vibration response is calculated by the well-known harmonic balance method (HBM) and an alternating frequency-time scheme (AFT). By means of reduction methods, the computational load in the analysis of realistic turbine blade models with several hundred thousand degrees-of-freedom can be reduced to a fraction, so that efficient calculations of blade vibrations are possible.
To validate the calculation program, both static and rotational tests of a realistic turbine blade model are performed. The results of the tests on the rotating system are characterized by excellent reproducibility and high accuracy. The comparison shows a very good qualitative and partially quantitative agreement of the results. In particular, the measured rotational speed dependent and non-linear phenomena can be reproduced with the simulation model.
Key words: Turbine blade, shroud, rotational speed variability, vibration analyses
