In modern computational studies for turbomachinery applications, time, length scales and isotropy of turbulent structures are important for representative modelling. To this end, experimental data are essential to validate the numerical tools. The current article presents the development and application of a newly designed 4-sensor Fast Response Aerodynamic Probe (FRAP-4S) enabling time-resolved measurement of the three-dimensional unsteady flow velocity vector in turbomachines. The miniature multi-sensor probe demonstrates a 4 mm probe-tip. In the first part of this article the design, manufacturing and calibration results of the FRAP-4S are presented in detail. To assess the newly developed probe accuracy, comparison against traditional instrumentation developed at the Laboratory for Energy Conversion is also provided. In the second part of this work, measurements are performed at the rotor exit of a one-and-a-half stage, unshrouded and highly-loaded axial turbine configuration. The results showed increased level of unsteadiness and turbulence levels with peak-to-peak fluctuation from 5 to 35%. More importantly, in some regions stream-wise unsteadiness was found to be ten times higher, compared to the cross-wise components, an indication of the high degree of anisotropy.

This work describes the design, development and testing of a miniature FRAP with 4 sensors, able to perform measurements in unsteady 3D flow field. Moreover, the calibration and first results with the newly developed probe is provided. The miniature FRAP-4S demonstrates a 3 mm tip diameter, which represents a 25% reduction, in comparison to a first generation FRAP-4S, without any loss in measurement bandwidth. The 3 mm outer probe-cell is additively manufactured with a binder jetting technique. In terms of aerodynamic performance, the probe demonstrates high angular sensitivity up to at least ±18° incidence angle in both directions. Evaluating the measurement accuracy of the newly developed FRAP, measurements are performed at LEC in both a round axisymmetric jet and 1.5-stage, unshrouded and highly-loaded axial turbine. Turbulence measurements are compared against hot-wire studies in round free-jets found in literature. Good agreement in trends and absolute values is demonstrated. Moreover, the performance of the probe is compared against miniature pneumatic and FRAP-2S probes. The results indicate that FRAP-4S, despite its larger size in comparison to the other probes tested, can resolve the main flow patterns, while highest deviations occur in highly skewed and sheared flows. Furthermore, the additively manufactured probe was proven robust after more than 50 hours of testing in representative turbine environment configuration. Finally, the newly developed FRAP reduces measurement time by threefold in comparison to FRAP-2S, which directly translates to reduced development time and thus cost, during turbomachinery development phase.

The aim of this work is to describe the design of an innovative test rig for investigating the expansion of saturated fluids in the two-phase region. The experimental test rig was thought up and built by TPG of the University of Genoa. It will be equipped by probes and some optical accesses that permit high speed video recording and laser measurements. It will be useful for the study of the quality ratio, vapour and liquid droplet thermodynamic properties and their speed.

A novel turbo expander based on the Tesla turbine is proposed to be applied to a heat pump or refrigeration cycle to improve the overall cycle efficiency. Initial numerical modelling of this turbo expander at representative conditions was carried out using the homogeneous relaxation model (HRM) to assess the influence of phase change on performance. The presence of a dense cloud of liquid droplets within the rotor was predicted to produce a significant back pressure on the turbine nozzle postponing the phase change. This was expected to occur in the vicinity at the outlet of the nozzle, but high volume fractions of liquid was predicted to penetrate deeper inside the rotor, especially at higher RPM. The resulting lower velocities of the liquid flow at the inlet of the rotor was predicted to significantly degrades the performance of the turbine. It is thus important for a successful implementation of this concept to remove as much liquid droplets as possible before the flow enters the rotor in order to minimise the back pressure.

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