Numerical Simulation on the Effect of Tip Clearance on the Last Stage LP Steam Turbine

Lim, Vuthy (2023) Numerical Simulation on the Effect of Tip Clearance on the Last Stage LP Steam Turbine. Masters thesis, Institut Teknologi Sepuluh Nopember.

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To maintain future supply-demand balance, there is a rising demand for flexibility of operational turbines; however, this caused the unsteadiness and imbalance in energy-supply in baseload where load conditions of turbines may vary more often between part load and overload. Especially, when the last stage of a low-pressure steam turbine operates under different flow conditions, the unsteady flow mechanism may occur due to different flow conditions leading to different flow performance. Besides this, the leakage flow field affects the blade tip clearance in a low-pressure steam turbine on the final stage of the blade and may also have a significant influence on the steam turbine’s performance. The main objective of this research aims to investigate the effect of the tip clearance on the last stage blade of a low-pressure steam turbine. A particular concern of this study is to investigate the effect of tip clearance leakage on the flow field and blade stresses in the last stage of moving the blade. Two models of rotor blades based on the geometry were adopted in the study, one is adjusted to have a uniform tip clearance value, while the other has a no tip clearance value. Three different load conditions (80%, 100% and 120% of loads) are used to investigate the variations in the flow field characteristic of tip leakage and static blade stress analysis. Three-dimensional numerical simulations of compressible steady flow were implemented by using ANSYS Fluent 19.2. The frame motion approach with mesh interface periodic and the k-omega SST turbulence model are applied to simulate compressible steady-state stator-rotor interaction. To study the stresses along the blade, a Finite Element Analysis (FEA) method is carried out using ANSYS Mechanical 19.2. The coupling approach is used to allow the flow data to be imported from the CFD model to the FEA model. The result from numerical simulation for both models is compared under three different loads. From the energy conversion efficiency, the torque is highest under high load conditions and design conditions, and the efficiency of the last stage blade is the lowest under low load conditions (80%). Due to the effect of leakage flow on the tip rotor blade, the efficiency of the turbine is reduced. The detail of the flow field is also analyzed. Moreover, the blade stress analysis indicates that the total blade deformation, Von-Mises stress, and strain shared a similar pattern for both models of rotor blades under three different loads. The stress that exceeds the blade of model tip clearance is higher than the stress on the blade of model no-tip under design load conditions and high load conditions. Comparing this highest stress to the strength of the material, the percentage is smaller than the strength of the material.

Item Type: Thesis (Masters)
Uncontrolled Keywords: Steam turbine, Tip clearance, CFD, FEA, stator-rotor interaction
Subjects: T Technology > TJ Mechanical engineering and machinery > TJ164 Power plants--Design and construction
T Technology > TJ Mechanical engineering and machinery > TJ266 Turbines. Turbomachines (General)
Divisions: Faculty of Industrial Technology and Systems Engineering (INDSYS) > Mechanical Engineering > 21101-(S2) Master Thesis
Depositing User: Vuthy Lim
Date Deposited: 25 Sep 2023 01:13
Last Modified: 25 Sep 2023 01:13

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