Session: 14-02: Brush/Labyrinth Seal

Paper Number: 153688

Investigation of a Straight Through Labyrinth Seal with an Air-Curtain using Computational Fluid Dynamics and 1D Modelling 

Labyrinth seals are widely used in gas turbine engines to minimize and or control Secondary Air System air flow routed to various engine components. These non-contact seals operate, based on the principle of creating a tortuous path for the leakage flow, which causes a reduction in pressure and increase of losses, thereby limiting the amount of gas that escapes. Due to their ability to function under high-speed and high-temperature conditions, labyrinth seals are the work horses of gas turbine engines. An important feature in the performance of labyrinth seals is the "air-curtain" effect, which enhances their sealing capability in addition to all the geometrical features employed. The air-curtain effect occurs when high-pressure air is intentionally introduced into the seal pockets, creating a barrier that opposes the flow of leakage flow. By increasing additional resistance to leakage, the air-curtain effect significantly improves the overall efficiency of the seal at the expense of the additional flow used, especially in applications where minimizing and/or controlling leakage flow is critical. In turbomachinery, this effect helps maintain system pressure and enhances the durability of the components, making it a key factor in the optimal design of labyrinth seals.

Current study aims to investigate the effects of an air curtain on a representative straight-through labyrinth seal. Firstly, a straight through labyrinth seal, developed in-house without air-curtain, is tested and modeled numerically in ANSYS Fluent and the results are compared resulting in a good match. Additionally, another test case from Durham University, which focuses on air curtain effects, is modeled and numerical results are compared with test data. Next, a comprehensive analysis matrix is created, including variables such as the seal pressure ratio (PR_seal), non-dimensional mass flow rate (%W) of the air curtain to the inlet flow, and inlet swirl effects. A total of 45 cases are analyzed using 2D axisymmetric CFD simulations with rotation. Based on the 2D results, the inlet swirl has no contribution to minimize the leakage reduction for the different seal pressure ratios, when the air-curtain flow is injected at the first seal pocket. Moreover, when seal pressure ratio increases, jet pressure ratio (PR_jet) goes down to capture same leakage reduction compared to lower pressure ratios. Overall, the 2D analyses show that the most effective sealing is provided between 0.2-0.3 %W inlet flow and around jet pressure ratio of 2. Afterwards, the case that provides the greatest reduction in main leakage flow is identified and examined in detail. The influence of the air curtain's position—specifically its location within the pocket, axial position, the angle of the curtain hole within the pocket, and the swirl effect of the curtain hole — are investigated using 2D analyses. The most effective case is selected and further modeled using a 3D sector model. Finally, to simplify engineering evaluations and reduce computational costs, the integration of the air curtain feature into a 1D design tool, Altair Flow Simulator (FS), is explored. According to 2D axisymmetric analysis results, a regression analysis is carried out and an obtained correlation is implemented to the FS as a multiplier.

 

Presenting Author: OMER UYAV TUSAS ENGINE INDUSTRY - TEI

Presenting Author Biography: Omer Uyav graduated with a Bachelor's degree in Mechanical Engineering from Kocaeli University and completed his Master's degree in the same field at Bogaziçi University in Türkiye. He has been working as a thermal system design engineer at TEI for the past four years.

Authors:

Avni Ertas TUSAS ENGINE INDUSTRY
OMER UYAV TUSAS ENGINE INDUSTRY
ERINC ERDEM TUSAS ENGINE INDUSTRY