Aerodynamic analysis of a Micro Turbine centrifugal compressor

Micro Turbine technology has developed rapidly during the last two decades. Major research issues related to this technology are the scale effects on aerodynamic turbomachinery performance, which include relatively high viscous losses due to the low Reynolds number of the flow through the cascades and also to the relative magnitude of size-independent losses. Micro Turbine Technology B.V. is developing a micro turbine for domestic combined heat and power units and combined auxiliary power unit/parking heaters for trucks. This paper describes the analysis of the micro turbine single stage centrifugal compressor by means of a numerical steady-state model, which approximates the real, time-dependent flow physics with satisfactory results and shorter computational time with respect to an unsteady approach. A commercial three-dimensional (3D) Reynolds-averaged Navier-Stokes computational fluid dynamics (CFD) code is adopted for this study. The simulations allow to understand the most significant flow phenomena of the 3D compressor flow field and to solidify the role of CFD as a consistent analysis tool, especially when accurate measurements are impossible to perform. The numerical results are compared with experimental data and the flow field analysis highlights some critical flow phenomena such as relative Mach number higher than unity in the in-ducer and secondary flow structures with their associated losses in the impeller.