ABSTRACTINVESTIGATION OF THE PERFORMANCE OF LABYRINTH SEALS FOR CENTRIFUGAL COMPRESSOR APPLICATIONS By Casey Palanca Labyrinth seals were one of the first seal configurations used in modern turbomachinery and, due to their robust qualities and relatively low-cost productions, remain one of the most widely used seal configurations today. Their primary purpose is to control internal leakage between the rotating and stationary components of rotating machinery, including the centrifugal compressor. A reduction in secondary leakage flow will always be accompanied by an increase in efficiency. However, while fulfilling the objective of restricting secondary fluid flow, labyrinth seals have been known to cause adverse stability effects on the rotor. Driving forces inside the cavities from the circumferential flow path have been known to be a potential source of destabilizing vibrations. Therefore, accurately predicting these forces is a primary interest in compressor design. These forces are characterized by stiffness and damping coefficients. The present study utilizes the growing advances in CFD to understand, model, and predict the aerodynamic and rotordynamic performance of labyrinth seals. The scope of this work progresses from a well-established steady state CFD method to a more novel transient CFD approach. The benefits and disadvantages of each method are evaluated and discussed by comparing accuracy, reliability, and computational efficiency. Each method is validated with experimental data. Additionally, the proposed transient CFD method can be used to perform a reasonably accurate prediction of the frequency-dependent rotordynamic coefficients by using a Fast Fourier Transform analysis on the monitored force response and displacement data. Lastly, the transient CFD approach is expanded upon by investigating the flow characteristics of long 18 tooth on rotor balance piston labyrinth seal modeled with abradable grooves on the stator. It was discovered that the creation of abradable grooves on the stator can cause the vortex between the labyrinth teeth to change directions (clockwise to counterclockwise). This observation is used to determine the relationship between the flow pattern and rotordynamic performance. A parametric study shows the effect of abradable groove geometries and operating flow conditions on the labyrinth seal rotordynamic coefficients.
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