Experimental thermodynamic and rotordynamic analyses of automotive turbochargers using fluid film bearings with different groove shapes

• Autor(a) principal: Luiz Henrique Jorge Machado
• Data de Publicação: 2022
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Repositório Institucional da UFMG
• Texto Completo: http://hdl.handle.net/1843/44370
• topic: Turbocharger; Experimental analysis; Floating ring bearing; Axial groove; Acoustic emission; Engenharia mecânica; Turbocompressores; Emissão acústica; Mancais; Estudos experimentais

This work presents an experimental study of the influence of the axial groove shape of semi-floating ring bearings on the dynamic and thermodynamic behavior of small turbochargers used in the automotive and aeronautical industries. A hot flow test bench using LPG gas for turbocharger tests at different speed and mass flow conditions is used for the development of this study. Seven different turbochargers with semi-floating ring bearings with different axial groove shapes are selected for the evaluation of dynamic and thermodynamic response under different operating conditions, including pre-surge and surge. Each semi-floating ring bearing has in its internal part two end areas to bear the rotor and one middle area for the free flow of the lubricant. The bearings are manufactured by conventional machining processes directly by the turbocharger manufacturer. The electrical discharge machining (EDM) process is used for the exclusive manufacture of grooves, which are: triangular, half-ellipse, quarter-ellipse, quarter-ellipse inverted, rectangular, trapezoidal and circle (or half-moon). The comparative analysis of the thermodynamic behavior is carried out through performance and efficiency tests of compressors and turbine-rotor assemblies at constant speed and mass flow. Temperature, pressure and air and gas mass flow transducers are installed at various points upstream and downstream of the compressor and turbine in the test bench. For the study of rotor dynamics, frequency spectra and diagrams of the journal precession orbits are obtained from the measurement of vibrations at different stationary speeds and constant operating airflows. Waterfall plots are performed on acceleration and deceleration of turbochargers. Accelerometers and displacement transducers (proximity probes) are used to pick up the vibration signals on turbochargers under different turbocharger operating conditions. Synchronous and subsynchronous responses are also obtained and analyzed for each turbocharger for the range of rotational speeds from approximately 0 to 145,000 rpm. Acoustic emission signals are captured under steady-state speed and flows. Several treatments are performed on these data, with different electronic filters and statistical analysis. Correlations are made of the acoustic emission data with the change only in the operating speed, only in the mass flow of air from the compressor, with the pre-surge and surge condition. A preliminary evaluation of the dimensions of the grooves of the analyzed bearings is carried out by means of dimensional metrological analysis before the tests to certify that the amount of lubricant and the effective area of rotor-bearing contact are within the determined in the design. The experimental results obtained allow the creation of important thermodynamic performance maps and dynamic response curves of the seven turbochargers analyzed, providing relevant subsidies for the selection of the most appropriate axial groove shape of the floating ring bearing for a given turbocharger operating condition. Additionally, it is possible to show that acoustic emission data using a bandpass filter between 50 and 100 kHz with kurtosis analysis have strong characteristics for detecting the pre-surge condition in small turbochargers.