Rolling Wear of Silicon Nitride Bearing Materials

Rolling-contact fatigue test methods were used to measure the wear performance of several silicon nitride materials. Sintered, hot pressed and hot isostatically pressed materials exhibited wear rates ranging over three orders of magnitude. Hot isostatically pressed materials had the lowest wear rates. Despite the disparity in wear performance, all materials tested had useful rolling-contact fatigue lives compared to steel. Fatigue life estimates, failure modes, and rolling wear performance for theses ceramics are compared to M-50 steel. This work highlights the rapid contact stress reductions that occur due to conformal wear in rolling-contact fatigue testing. Candidate bearing materials with unacceptably high wear rates may exhibit useful fatigue lives. Rolling contact bearing materials must possess useful wear and fatigue resistance. Proper performance screening of candidate bearing materials must describe the failure mode, wear rate, and the fatigue life. Guidelines for fatigue testing methods are proposed.

Flow Visualization in a Simulated Brush Seal

A method to visualize and characterize the complex flow fields in simulated brush seals is presented. The brush seal configuration was tested in a water and then in an oil tunnel. The visualization procedure revealed typical regions that are rivering, jetting, vortical or lateral flows and exist upstream, downstream or within the seal. Such flows are engendered by variations in fiber void that are spatial and temporal and affect changes in seal leakage and stability. While the effects of interface motion for linear or cylindrical configurations have not been considered herein, it is believed that the observed flow fields characterize flow phenomenology in both circular and linear brush seals. The axial pressure profiles upstream, across and downstream of the brush in the oil tunnel have been measured under a variety of inlet pressure conditions and the ensuing pressure maps are presented and discussed.

Aero/Aeroderivative Engines: Internal Transducers Offer Potential for Enhanced Condition Monitoring and Vibration Diagnostics

Gas turbine aero engines and their ground based derivatives can benefit greatly from the enhanced condition and diagnostic data available from internal vibration transducers. This paper discusses transducer selection, illustrates typical transducer locations and mounting, and describes some of the rotor malfunctions that can be diagnosed from the vibrations data.

Model Adjustment of Small Rotors for High Speed Gas Turbines

In this paper, we present the studies which are carried out at MICROTURBO relating to rotor-bearing systems mounted in small high speed gas turbines. These studies are based on both theoretical and experimental approaches, and are aimed at providing an improved prediction of the dynamic behaviour of rotors at the design stage, in particular the critical angular velocities and sensitivity to unbalance.

An Evaluation of Waspaloy Expander Blade Tip Weld Repairs

The abrasive wear of blade tips in fluid catalytic cracking unit power recovery turbines is one of the principal ‘failure’ mechanisms for the parts. The occurrence of tip wear considerably shortens the effective life of the blade: generally well below the anticipated mechanical life of the component. This paper details the evaluation of mechanical properties and metallographic characteristics of a fully re-heat treated, Waspaloy on Waspaloy weldment for blade tip repair that will allow re-utilization of the blades.

Transient Stress Response of a Turbine Blade Under Non-Linear Damping Effects

A numerical technique to compute the stress response of a turbine blade with non-linear damping characteristics, during transient operations of the rotor has been proposed. Damping is defined as a function of vibratory mode, rotor speed and strain amplitude. The technique is illustrated by computing the stress-levels at instantaneous resonant rotor speeds for a typical step-up operation of a turbomachine.

Generalized High Speed Simulation of Gas Turbine Engines

This paper describes a real-time or faster-than-real-time simulation of gas turbine engines, using an ultra high speed, multi-processor digital computer, designated the AD100. It is shown that the frame time is reduced significantly without any loss of fidelity of a simulation. The simulation program is aimed at a high degree of flexibility to allow changes in engine configuration. This makes it possible to simulate various types of gas turbine engines, including jet engines, gas turbines for vehicles and power plants, in real-time. Some simulation results for an intercooled-reheat type industrial gas turbine are shown.

On the Design of Magnetic Suspension Systems

First, the dynamic performance of magnetic suspension systems (Figures 1–3), which are designed on the basis of linear feedback laws, are examined. Then, nonlinear control laws are developed to make the dynamics of a suspension system to be exactly that of a linear spring-mass-damper system. It is found that such control laws are not defined for all initial conditions of the supported mass. Lastly, it is shown that it is possible to achieve a true spring-mass-damper behavior for all initial conditions by using two electromagnets, but operating only one at a time.

VATEMP: The Variable Area Turbine Engine Matching Program

Variable geometry in key gas turbine components offers the advantage of either improving the internal performance of a component or of re-matching the engine cycle to alter the flow-temperature-pressure relationships. Future gas turbines are expected to use variable geometry components extensively if they are to overcome some of the problems encountered by present day engines at off-design conditions in order to give much more advanced performance. Greater attention is also being paid to the impact of installation losses on the performance of aircraft engines. A computer program called VATEMP, herein described, has been developed capable of simulating the steady-state performance of arbitrary gas turbines with or without variable geometry in almost any gas path component. Results obtained from the program led to the conclusion that variable geometry components have the potential to improve significantly the off-design performance of gas turbines.

Factors That Affect Rolling Contact Fatigue Life of Ceramics and Rolling Contact Fatigue Life of Ceramic Balls and Rollers

The rolling contact fatigue life of ceramics for rolling bearings has improved remarkably in recent years, and is now superior to that of bearing steels. This paper describes experiments to investigate the influence of manufacturing process variables on rolling contact fatigue life and compares the rolling contact fatigue life of current improved ceramics with bearing steels.