Perspective vibroacoustics diagnostic complex for aircraft gas-turbine engines bearing assemblies
Aeronautical and Space-Rocket Engineering
Thermal engines, electric propulsion and power plants for flying vehicles
Lyulka Experimental Design Bureau, branch of the United Engine Corporation – Ufa Engine Industrial Association, 13, Kasatkina str., Moscow, 129301, Russia
The article tackles the questions concerning peculiarities of vibroacoustic diagnostics of bearing assemblies for gas-turbine engine rotors technical condition. Possible reasons of bearing assemblies damaging and corresponding failure symptoms of individual defects, as well as procedures of their application are analysed.
The following options are possible in partucular:
flight diagnostics (while processing post-flight information, without outputting warning the pilot at this stage);
diagnostics during land approbation of the engine (aircraft-level) in operation or at the manufacturer engine test bench;
during the parking, without engine activation, by manually turning the rotors or turbostarter cold scrolling (CS).
The last item is preferable due to minimum financial and working hour costs. For implementation of such methods manual turning of the rotor and a specialist fixing data or carrying out rotor CS are required.
In the course of diagnostics of operating gas-turbine engine aimed at researching possibilities of the technical microphone installed on the engine case a number of the methods connected with a high-frequency component of a signal spectrum of effective sound pressure was revealed. The studies consisted in searching of periodic and nearly periodic vibration processes resulting from bearing assemblies defect mounted on the engine and bearings tests bench.
High frequency periodic processes occur very often either separately from nearly periodic, or together with them. They appear at identical excitation of a vibration signal with each turn. These are frequency modulation of vibration signals from damaged bearing parts, as a rule, with rotor frequency.
Physical model of the process can be easily represented on the example of slider bearing operation. In the presence of negative factors, affecting the bearing clearance reduction, and occurring due to bearing capacity decrease or oil-film wedge punching, a mutual interference of wrinkles always presenting on sliding contacting surfaces takes place. It causes the excitation of oscillations of separate parts with frequencies equal to the product of number of interactions per one shaft rotation and rotor rotation frequency and natural frequencies of interacting parts.
The vibroacoustic diagnostics complex «FIANITE 3000» was developed to realize the data obtained during the studies.
It consists of a technical microphone (piezoelectric) with the restricted directional diagram, the DP-03 device, installed in inspection ports to inspect entrance edge of high-pressure turbine blades as well as electronic analysis and indication module FIANITE 3000. After DP-03 installation into inspection port and activation of electronic analysis and indication module the measuring process will go on automatically.
The developed system of vibroacoustic diagnostics is autonomous and protected from the main interference generated by subassembly of gas-turbine engine. The total evaluation of the system revealed its very effective noise immunity and serviceability for single and periodic checkouts.
Keywords:gas turbine engines, bearings, vibroacoustic diagnostics
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