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Design, Numerical Simulation and Experimental Investigation of Radial Inflow Micro Gas Turbine
Author(s): Samip Shah, Salim Channiwala, Digvijay Kulshreshtha, GAURANG CHAUDHARI
Keywords: Turbine Design; Volute Design; Small Gas Turbine
The paper describes an investigation in to the design and performance of radial inflow turbines having a capacity of 25kW with the mass flow rate as 0.1028kg/s, turbine inlet stagnation temperature 1200K and pressure as 2.82 bar. The design speed of turbine rotor is 1,50,000 rpm. With these input data, first a non-dimensional design philosophy is deduced to design a turbine rotor. The turbine rotor dimensions are non-dimensionalized by rotor inlet radius and the fluid and rotor velocities are non-dimensionalized by the inlet stagnation speed of sound. The design approach is largely one dimensional along with empirical correlations for estimating losses used to obtain the main geometric parameters of turbine. After that a modified vortex design procedure is developed to derive the non-dimensional volute geometry as a function of azimuth angle for actual flow condition. Once a specific turbine is designed, the flow is analyzed in detail using a three-dimensional Computational Fluid Dynamics (CFD) code in order to assess how accurately the performance is predicted by simple meanline analysis. Finally, a fully instrumented experimental setup is developed. The experimental investigations have been carried out to study the temperature and pressure distribution across turbine and total-to-static efficiency is calculated. The limitations of surging and choking in compressor as well as in the bearings to take up load at such high speed has allowed the tests to be conducted upto 70000 rpm only, with turbine inlet temperatures ranging from 900 K to 1000 K and a pressure ratio upto 1.79, which developed power in the range of 1.69 kW to 10.22 kW. The uncertainty bands are in order of ±13.76% to ±3.12%. It is observed that the CFD results are in good agreement with test results at off design condition. CFD models over predicted total to static efficiency by order of 7-8% at lower speed. These deviations are reduced as turbine runs close to design point.