THE INFLUENCE OF SHROUD LOOSENESS ON THE NATURAL FREQUENCY OF TURBINE BLADES MODEL

• Main Author: Kamil Husain, Fajar
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/82793
• Institution: Institut Teknologi Bandung

The turbine is one of the most widely used prime movers for electricity generation. Among the important components of a turbine is the shroud, which serves to reduce stress concentration when the blade experiences high stress. In some cases, the shroud is prone to loosening, which can potentially damage the turbine blades. Due to the significant impact of loosening on turbine performance, this study aims to investigate the effect of loosening that occurs on the shroud towards the natural frequency of the turbine blade model. In this research, theoretical calculations were first performed on a cantilever beam that serves as a model of a turbine blade. These calculations were carried out in two conditions: the fixed-free condition as a model of the turbine blade without a shroud, and the fixed-fixed condition as a model of the turbine blade with a shroud that does not experience loosening. The cantilever beam was then simulated using the Finite Element Method (FEM) application, Ansys 2023 R2. This analysis was also used in the simulation of the turbine blade model with an added shroud. This analysis serves to observe the behavior and mode shapes of the blades with variations in shroud stiffness. In addition to being analyzed with FEM, the model was also made into a test object by welding the shroud model to the ends of the blades. Next, an FRF test was conducted on this test object by applying an excitation force using an impact hammer. The acceleration signal was then measured using accelerometers and recorded using a data acquisition device. The data was then processed with a laptop with Matlab software, resulting in magnitude and coherence graphs in the frequency domain. From these two graphs, the natural frequency value of the test object was obtained, and the results of the FRF test analysis were compared with the simulation results. FEM analysis on the model shows that loosening in the shroud model can be detected by observing a decrease in natural frequency ranging from 17% to 33% in all analyzed mode shapes. However, in practice, the vibration modes of the model do not consistently occur in each blade, so the FRF testing method is only effective for observing this phenomenon in the first mode shape.