Abstract
The performance of the twin-screw supercharger with design adapted for automotive use depends on the volume and the total losses of the air flow through the rotors more than on any other thermo-fluid aspects of the supercharger behaviour. Therefore to accurately predict the efficiency of the twin-screw supercharger for a particular engine system accurate flow calculation is required. Relationships between flow and performance of the helical screw supercharger were investigated to create a parametric model of helical rotors capable to relate the geometry of their conjugated profiles to different rotor configurations required by different design and performance criteria such as size, compression ratio, internal leakage and volumetric efficiency. The leakage analysis and loss correlations in twin-screw superchargers resulted through a preliminary design process which defined typical leakage paths as generated by the conjugated rotor profiles geometry and the resulting functional clearances. The proposed paper will present the method designed by the authors for validation of the preliminary design process. Validation of preliminary rotor profile models integrated with flow data was achieved through comparison of CAD-CFD models based on the 3D mathematical model of the supercharger with experimental laser velocimetry (LDV) measurements. Previous to this research the CFD analysis as applied to twin-screw superchargers had not yet been developed to a level permitting the confident design from only computational results. Fundamental CFD modelling was used to explain different practical observations and for trend analysis. By integration of the velocity fields in CFD models overall performance parameters such as mass flow rates, velocity distribution profiles and leakage were derived. Accurate experimental velocity data derived from independent variation of input speed and fluid characteristics through dynamic similarity were investigated with LDV laser velocimerty measurements on a special test rig with the reference twin-screw supercharger with asymmetric rotor profiles. Overall performance match of CFD simulation data and LDV experimental measurements were subject for data calibration. Theoretical predictions will be verified by pressure data.
Keywords:supercharger, engine design, CFD simulation, automotive, performance