The current work describes the design, development and testing of a miniature fast response aerodynamic probe (FRAP) with 4 sensors (4S), able to perform measurements in unsteady three-dimensional flow field. Moreover, the calibration and first results with the newly developed probe is also provided. The miniature FRAP-4S demonstrates a 3 mm tip diameter, which represents a 25% reduction in diameter size, in comparison to a first generation FRAP-4S, without any loss in terms of measurement bandwidth. The 3 mm outer casing of the probe is additively manufactured with a high-precision binder jetting technique. In terms of aerodynamic performance, the probe demonstrates high angular sensitivity up to at least ± 18° incidence angle in both directions.

To evaluate the measurement accuracy of the newly developed FRAP-4S, measurements are performed at the Laboratory for Energy Conversion (LEC) in both a round axisymmetric jet and an one-and-a-half stage, unshrouded and highly-loaded axial turbine configuration. Turbulence measurements performed with the miniature FRAP-4S are compared against hot-wire studies in round free-jets found in the literature. Good agreement in both trends but also absolute values is demonstrated. Moreover, the performance of the probe is compared against traditional instrumentation developed at LEC, namely miniature pneumatic and FRAP-2S probes. The results indicate that the FRAP-4S, despite its larger size in comparison to the other probes tested, can resolve the main flow patterns, while the highest deviations occur in the presence of highly skewed and sheared flows. Furthermore, the additively manufactured probe was proven to be robust after more than 50 hours of testing in representative turbine environment configuration. Finally, it should be highlighted that the newly developed FRAP reduces measurement time by a factor of three in comparison to FRAP-2S, which directly translates to reduced development time and thus cost, during turbomachinery development phase.

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