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In modern computational studies for turbomachinery applications, time, length scales and isotropy of turbulent structures are important for representative modelling. To meet this end, experimental data are essential to validate the numerical tools. The current paper presents the development and application of a newly designed 4-senor Fast Response Probe (FRAP-4S) enabling time-resolved measurement of the three-dimensional unsteady flow velocity vector in turbomachines. The miniature multi-sensor probe demonstrates a 4mm probe-tip. In the first part of this paper 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 (LEC) 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 streamwise unsteadiness was found to be 10 times higher, compared to the crosswise components, an indication of the high degree of anisotropy. INTRODUCTION Considering the unsteady flow in an axial turbomachine, the frequency spectrum of the fluctuations is in the range of a few hertz up to several multiples of the blade passing frequency. For gaseous-flows in turbomachines, frequencies up to 50kHz are, in most cases, of practical interest (Kupferschmied et al., 2000). The time and length scales of the flow structures vary up to six orders of magnitude, due to the diverse nature of the originating mechanism (Abhari, 2006). Periodic fluctuations arise due to regular wake passing or other secondary and leakage flow features, or even shocks (Denton, 1993). On the other hand, stochastic fluctuations can be attributed to turbulence, to unsteady transition, separation of boundary layers etc. In order to understand the loss mechanisms under these conditions, experimental work and computational tools must come together to evaluate the flow structures. A comprehensive review of measurement techniques for unsteady turbomachinery flows can be found in (Ainsworth et al., 2000; Sieverding et al., 2000). Despite the advancements in numerical modelling and computational tools, turbulence models are mainly based on a series of assumptions or simplifications, which may be mathematically plausible but do not necessarily accord with the actual physics in a turbulent flow. Nevertheless, turbulence modelling is inherently connected to the design and development process in internal turbomachinery applications. In the past this numerical tools were validated through experimental investigations in simplified test rig geometries, while lately the interest is shifted towards experimental data acquisition under realistic complex flow conditions (Camp et al., 1995; Porreca et al., 2007; Lengani et al., 2012). In most studies the turbulence quantities are derived from hot-wire anemometry measurements. However the hotwire probes suffer from their inherent fragility and loss of sensitivity at high Mach numbers which makes them suitable for lightly loaded, low-speed turbomachines. To overcome this issue fast-response pressure probes equipped with embedded piezo-resistive pressure sensors have been developed for highly loaded and high-speed turbomachines. Heneka was probably the first one to attempt deriving

A novel 4-sensor fast-response aerodynamic probe for non-isotropic turbulence measurement in turbomachinery flows