A theoretical, experimental and CFD analysis of regenerative flow compressors and pumps for microturbine and automotive fuel applications

Regenerative flow compressors and pumps, hereafter known as RFC/RFP are rotodynamic machines capable of producing high heads at very low flow rates. They can produce heads equivalent to that of several centrifugal stages from a single rotor with comparable tip speed. The compression process is usually not regarded as efficient. Typically regenerative compressors produce less than 50% efficiency but still they have found many applications, because they allow the use of fluid dynamic compressors in place of positive displacement compressors for duties requiring high heads at low flow rates. Recently Capstone Turbine Corporation has made use of RFC in low pressure (0.2--15 psig) natural gas compression required by its Model C30 microturbine system. Moreover, due to compact size and self priming characteristics of the regenerative pumps, Delphi Automotives has utilized RFP for automotive fuel pumping application.; A detailed discussion of fundamentals, hypothesis of operation, applications, limitations, challenges and future trends in regenerative turbomachines is presented. Experimental data on Capstone single and multistage RFC with radial blades is analyzed in the form of various non-dimensional parameters. A mathematical model to describe the complex three dimensional corkscrew flow pattern in radial and non-radial blade RFC/RFP is presented. Governing equations for blade and channel region are developed and various losses are correlated with geometric and aerodynamic parameters. A performance prediction code for RFC based on these governing equations and loss models is developed and performance results are compared with test data on Capstone multistage RFC. An extensive sensitivity analysis from the code is performed, based on which some design changes are suggested for performance improvement. Moreover, a generalized design procedure for radial and non-radial blade RFC is proposed in this work.; Application of regenerative turbomachines in automotive fuel pumping is discussed in detail. Delphi Automotives replaced radial blades by non-radial blades to improve performance. Performance of Delphi fuel pump is predicted from the code and compared with test data and some design improvements are suggested after performing a sensitivity analysis on various geometric parameters. Details of CFD analysis on a 3D model of the fuel pump using commercial software "STAR CD" are presented. The regenerative pump with non-radial blades produces hydraulic efficiencies around 40% surpassing all the existing regenerative fuel pump designs in the automotive industry. However, there is still a lot of room for improvement in hydraulic efficiency by employing aerodynamically designed aerofoil blades. Therefore, need was felt to investigate RFC/RFP with aerofoil blades. A compressible flow theory for aerofoil blade RFC is presented in this work. Theoretical performance results are compared with published test data on aerofoil blade RFC. Extensive sensitivity analysis from the code is performed and design changes are suggested for performance improvement. Theoretical analysis shows that aerofoil blading introduced in these turbomachines can enhance isothermal efficiency above 60%. Based on suggested design changes, a new RFC model with aerofoil blades is developed and a CFD analysis is performed. Currently work is in progress to optimize the inlet manifold of aerofoil blade RFC.