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The fluid dynamics of a microturbine system that is applied in a device for chemical and biological analysis—a so-called magic-angle spinning (MAS) probe—is investigated. The drive fluid is pressurized air at ambient temperature provided by nozzles aligned on an intake spiral, driving a Pelton-type microturbine. Computational fluid dynamics (CFD) simulations have been performed and compared with fluid dynamics measurements of the MAS system with 1.3 mm rotor diameter for spinning rates between 23 kHz and 67 kHz. The main optimization criteria of the MAS system are rotor speed and turbine stability and not primarily efficiency, which is standard for turbomachinery applications. In the frame of fabrication tolerances, a sensitivity study has been carried out by varying the nozzles diameter and the nozzle position relative to the rotor. The presented fluid dynamics study of the microturbine system includes the analysis of local fluid flow values such as velocity, temperature, pressure, and Mach number, as well as global quantities like forces and driven torque acting on the turbine. Comparison with the experimental results shows good agreement of the microturbine efficiency. Furthermore, the parameter study of the nozzle diameter reveals optimization potential for this high-speed microturbine system employing a smaller nozzle diameter.

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Modern power plants face increasing problems with windage effects in high pressure steam turbines, due to the bigger size of the rotor blades and a more flexible demand of the electricity market, which may lead to more frequent operation at low-flow conditions. So far, no theoretical model exists to fully describe these flow phenomena which would help to prevent an overheating of the turbine blades and minimize the risk of damage. The main goal of this research project therefore is to predict the part-load behavior. Measurements of the flow field of a four-stage research air turbine were carried out at low Mach numbers to better understand the aerodynamic characteristics and the flow mechanisms at part-load. The experimental data such as temperature, pressure, velocity, and flow angles, measured in 6 different planes along the turbine annulus for different rotational speeds and different relative mass flows, have been compared with the numerical results of the CFDsolver TRACE. To obtain more realistic results than in computations published earlier, a newly generated finer grid and an extension of the computational domain at the outlet were used. It is shown that with the right initialization, the CFD-Solver is capable of providing converged calculation results even for low mass flows and high rotational speeds. The results are verified with experimental data e.g. by the temperature distribution within the four-stage turbine and the pressure and temperature profiles in the measurement planes. As a general result, the highest temperatures in the turbine do not occur behind the last stage, but in the downstream third of the machine, which agrees with experiences of damage observed in real turbines.