THREE-DIMENSIONAL NUMERICAL SIMULATION OF FLOW THROUGH THE TWIN-SCREW SUPERCHARGER: CLEARANCE FLOW PATTERNS AND LEAKAGE LOSS ANALYSIS FOR HELICAL ROTORS WITH SYMMETRIC AND ASYMMETRIC ROTOR PROFILES

摘要

Given the supercharging significance for the automotive engines, this research focused on identification of supercharger and supercharger components with higher efficiency by criteria of flow characteristics. Of particular interest for this research has been the twin-screw supercharging compressor with design adapted for automotive use (the twin-screw supercharger). The performance of this supercharger type depends on the volume and total losses of the air flow through the supercharger rotors more than on any other thermo-fluid aspects of the supercharger behaviour; therefore, to accurately predict efficiency of the twins-crew supercharger for consideration in matching a supercharger to a particular engine system, accurate flow calculation is required. To define gas dynamics in the internal flow system of a twin-screw supercharger and for leakage prediction in the preliminary design process, experimental research is required. Leakage analysis and loss correlation in twin-screw superchargers include evaluation of performance for supercharger rotors with symmetric and asymmetric geometric profile design. Compressibility effects in the twin-screw supercharger are important, and methods based on the one-dimensional flow theory cannot account for variation of flow properties at a section, which is characteristic for real flows, therefore there is a need for methods of three-dimensional analysis in which the effects of flow non-uniformity at a section are considered. This paper presents research investigation of relationships between flow and performance in the twin-screw supercharger based on the three-dimensional (3D) parametric model of the supercharger rotors [1] to relate the rotor conjugated profile geometry and typical leakage paths to different rotor configurations characterised by typical flow patterns. This approach is required by particular designs, which specify performance criteria such as rotor size, internal leakage and volumetric efficiency.