Roots blower is a rotary positive displacement pump which operates by pumping a fluid with a pair of meshing lobes. Recent trends in automotive industry demands high power density solutions for various applications. In comparison with legacy applications, compressors for high power density applications demand continuous operation with harsher duty cycle as well as demand higher pressure ratios. Because of longer duty cycles, it will be subjected to high heat loads which will cause a rise in temperatures of timing gears, bearings, and other components within the assembly. Accurate prediction of thermal performance is critical to design a durable and efficient roots blower for high power density applications.
Thermal analysis of an assembly of roots blower involves modelling of multi-physics phenomena. This paper details a coupled CFD analysis approach to predict temperatures of roots blower components and timing gear case oil. Timing gears are lubricated using wet sump lubrication. The oil splash within the timing gear enclosure is modelled using moving reference frame model in a multiphase splash analysis. Air flow through rotors is modelled using deforming zone method in a transient CFD analysis. An approach is presented to perform steady state conjugate heat transfer to couple physics from oil splash and air flowing through rotating lobes to predict thermal performance of roots blower assembly.
The results using this approach are validated against a test case. The temperature results from 3D CFD analysis shows a variation within 10% compared to the temperature values measured using thermocouple sensors in test setup. The approach presented in this paper helps to predict the thermal profile of solid components. This will further be utilized in designing the critical clearances and understanding bearing-housing bore distortions for improving performance and durability of roots blower.