J. Axel Glahn

Impact of Rotational Speed on the Discharge Characteristic of Stepped Labyrinth Seals

Current and future gas turbine engines are subject to increasing performance requirements and improved fuel efficiencies. The resultant engine cycles increase core flow temperatures requiring additional cooling flow while requiring a reduction in parasitic leakage by more than 25% to meet the performance goals. The achievement of the reduced leakage requires that seal design concepts be tested and improvements validated in engine like conditions before they are introduced into the actual engine. A previous paper [1] described a set of rotating seal designs that have been tested in various combinations of rotating and static design features for low leakage potential. This paper is a continuation of the previous effort and focuses in particular on the effect of rotational speeds on the discharge characteristic of various stepped labyrinth seal designs. Leakage reductions will be characterized in terms of CD /DD,0 (i.e. ratio of leakage rate with rotation over leakage rate without rotation) as a function of circumferential to axial through flow velocity, U/Cax . For large velocity ratios of U/Cax > 5, leakage reductions of more than 20% were observed. Experimental data are compared with literature [2].Copyright

Rim Seal Ingestion in a Turbine Stage From 360-Degree Time Dependent Numerical Simulations

Numerical simulations of turbine rim seal experiments are conducted with a time-dependent, 360-degree CFD model of the complete turbine stage with a rim seal and cavity. The turbine stage has 22 vanes and 28 blades and is modeled with a uniform flow upstream of the vane inlet, a pressure condition downstream of the blades and three coolant flow conditions previously employed during experiments at Arizona State University. The simulations show the pressure fields downstream of the vanes and upstream of the blades interacting to form a complex pressure pattern above the rim seal. Circumferential distributions of 15 and 17 sets of ingress and egress velocities flow through the rim seal at the two modest coolant flow rate conditions. These flow distributions rotate at wheel speed and are not associated with the numbers of blades or vanes. The seal velocity distribution for a high coolant flow rate with little or no ingestion into the stator wall boundary layer is associated with the blade pressure field. These pressure field characteristics and the rim seal ingress/egress pattern provide new insight to the physics of rim seal ingestion. Flow patterns within the rim cavity have large cells that rotate in the wheel direction at a slightly slower speed. These secondary flows are similar to structures noted in previous a 360-degree model and large sector models but not obtained in a single blade or vane sector model with periodic boundary condition at sector boundaries. The predictions of pressure profiles, sealing effectiveness and cavity velocity components are compared with experimental data.© 2012 ASME

De-Oiler System for Improved Oil Containment

Oil containment is a critical design requirement that affects overall system safety and reliability of gas turbine engines. This paper examines a new method to enhance oil containment by use of an improved de-oiler that creates a favorable bearing compartment differential pressure environment even at low power settings. Typically gas turbine engines require seals to contain oil within the bearing compartment. These seals, both contacting and non-contacting configuration styles, rely on secondary airflow to buffer the sealing interface and force oil mist and droplets back into the compartment. This is not difficult to achieve at high or moderate power conditions since there is generally sufficient air flow and pressure available to meet the sealing requirements. However, at idle conditions, the engine low-pressure compressor (LPC) may not turn fast enough to produce sufficient airflow to buffer the seals. To address these concerns the authors propose a method where the de-oiler creates a vacuum at idle speed, which results in favorable compartment seal differential pressures and also acts as a restrictor at higher speeds, where limiting the contact pressure and increasing the service life of mechanical seals become desirable design goals. The paper will examine a specific case study with both analytical and experimental results.Copyright