A labyrinth seal is commonly used to decrease the flow leakage loss between rotating and static components in aero engines. It is susceptible to aeroelastic instability because of its low stiffness. The aim of this study was to establish methods to predict and suppress it effectively. To achieve this, both numerical and experimental investigations are conducted using ansyscfx and ansys mechanical. These solvers are coupled to simulate the flutter precisely. Also, to assess the accuracy of the simulation qualitatively and quantitatively, a test rig is built. In the first part of this study, the accuracy of the numerical method is confirmed for several test cases with different seal clearance variations. Flutter inception is evaluated in detail for various pressure ratios and rotation speeds. The numerical results show good agreement with the experimental results. It is also confirmed that the aeroelastic instability is very sensitive to the seal clearance variations. These results show the same tendency as those in previous works. In the second part of this study, this paper tries to develop a flutter suppression method with higher leakage performance. This is achieved by changing the seal geometry. To detect the important geometric parameters, the contribution of each geometric component to aeroelastic instability is carefully analyzed. On the basis of this, the seal geometry is modified and its performance is evaluated. The optimized labyrinth seal shows good performance in terms of flow leakage and aeroelastic stability. Through this study, a new flutter suppression method is established.

This paper deals with an application of computational fluid dynamics (CFD) to partial admission stages in a steam turbine. The calculation of partial admission stages requires unsteady analysis and full circle modeling. Therefore, quasi-3-dimensional (Q-3D) analysis of the mean radius is conducted to reduce computational load. First, an experiment using the air turbine is carried out. The result is in good agreement with the result of CFD analysis under the same conditions as the experiment, and the application of the Q-3D method to partial admission stage analysis is validated. Using this method, 2-stage analysis of partial admission is conducted. The influence of the circumferential position of the admitted arc on stage efficiency is discussed. The efficiency difference is related to the windage loss caused by pressure distribution in the circumferential direction. It is found that there is an optimum circumferential position of the admitted arc from the point of view of turbine efficiency.

A labyrinth seal is commonly used to decrease the flow leakage loss between rotating and static components in aero engines. It is susceptible to aeroelastic instability because of its low stiffness. The aim of this study is to clarify the physical mechanism of labyrinth seal flutter and to establish a method to predict and suppress it effectively. To achieve this, both numerical and experimental investigations are conducted using ANSYS CFX and ANSYS Mechanical. These solvers are coupled to simulate the flutter precisely. Also, to assess the accuracy of the simulation qualitatively and quantitatively, a test rig is built. In the first part of this study, the accuracy of the numerical method is confirmed for several test cases with different seal clearance variations. Both one-way and two-way fluid structure interaction (FSI) analyses are performed. Flutter inception is evaluated in detail for various pressure ratios and rotation speeds. The numerical results show reasonably good agreement with the experimental results. It is also confirmed that the aeroelastic instability is very sensitive to the seal clearance variations. These results show the same tendency as those in previous works [1–5]. In the second part of this study, this paper tries to develop a flutter suppression method without deteriorating the flow leakage performance. This is achieved by changing the seal geometry without changing the seal clearance variation. To detect the important geometric parameters, the contribution of each geometric component to aeroelastic instability is carefully analyzed. On the basis of this, the seal geometry is modified and its performance is also evaluated. The optimized labyrinth seal shows good performance in terms of flow leakage and aeroelastic stability. Through this study, a new method to suppress the flutter with low flow leakage is established.

This paper deals with an application of Computational Fluid Dynamics, CFD, to partial admission stages in a steam turbine. Calculation of partial admission stages requires unsteady analysis and full circle modeling. Therefore quasi-3 dimensional analysis on the mean radius is conducted to reduce computational load. First, an experiment of air turbine which has one stage is carried out. This result shows a good agreement with the result of CFD analysis which has the same condition as the experiment, and applying the Q-3D method to partial admission stage analysis is validated. Using this method, 2 stage analysis of partial admission are conducted. The influence of circumferential position of admitted arc on stage efficiency is discussed. The efficiency difference is related to the windage loss which is caused by pressure distribution in the circumferential direction. It was found that there is an optimum circumferential position of admitted arc from the point of view of turbine efficiency.

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