Design and analysis of a viscous film dynamometer for wide range turbocharger turbine performance mapping

• Main Author: Boyd, Michael
• Other Authors: Spence, Stephen ; Kim, Sung
• Published: Queen's University Belfast 2018
• Subjects: 620
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.737782

The transient nature of automotive exhaust gas flow is a significant obstacle to turbocharger turbine optimisation, with the need to optimise performance for pulsating flow and maintain acceptable performance across a wide range of engine operating conditions. Standard industrial testing methods are incapable of applying the desired power absorption, due to the inherent limitations of radial compressors, and therefore are limited in their ability to map turbine characteristics. Firstly, this project investigated existing technologies and identified a design approach which allowed development of a novel turbine dynamometer for small automotive turbine applications. The design approach was documented with consideration of component sizing, stress, rotordynamics, component assembly and instrumentation requirements. A novel model for determining viscous torque within a high speed oil film operating under shear stress was developed. A prototype test rig was designed and commissioned based on an existing turbocharger unit which was modified to accept a novel loading device. This prototype device was used to test the turbine over a wide range of conditions, and was used to validate the new viscous model. A second test rig was developed with an expanded feature set, based on the findings of the prototype. Velocity ratio values from 0.075 to 0.596 were achieved and a new loading device configuration was implemented to allow for continuous loading variation during tests. Measured efficiency values were shown to match well with CFD simulations. Instability within the oil film of the device was identified and studied, indicating areas where this was likely to occur and suggesting that shaft vibration interacting with cavitation regions was causing fracture of the oil film. A CFD analysis of the oil film was used in conjunction with experimental data to identify flow phenomena which caused the initiation of this film fracture.