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This paper describes an experimental investigation on a state-ofthe-art compressor airfoil with three different leading edges at high subsonic flow conditions. In addition to a conventional circular and elliptical geometry which possess curvature discontinuities at the blend points, a continuous curvature leading edge is studied. The investigation considers the performance at design incidence, as well as the impact of off-design incidences. Pressure spikes near the leading edge can lead to early transition associated with higher profile losses. Goodhand and Miller [1] showed that in low subsonic conditions the avoidance of curvature discontinuities can diminish pressure spikes and therefore reduce the profile losses and enlarge the working range. In this paper, measurements are conducted to assess the potential of this concept for a high-pressure jet engine compressor airfoil operated at high subsonic conditions (M 1 = 0.7, Re d/2 = 20, 000). The results show that, at design incidence, the total pressure loss coefficient of the continuous curvature leading edge reduces by up to 15.4 % compared to the circular leading edge and by up to 3.1 % for the elliptical geometry. At off-design incidence, the reduction can be up to 40.2 % at maximum positive incidence under consideration.

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Results from a quantitative tuft flow visualization of a utility scale wind turbine undergoing a yaw movement are presented. Based on the turbine’s SCADA data suitable pre- and post-yaw timeframes were defined and the surface flowfields were analysed. A distinct asymmetry between the surface flow patterns of the 90° and 270° azimutal blade positions was observed in the pre-yaw timeframe. After the turbine yawed back into the wind the symmetry was restored. Yaw-misalignment is a source of dynamic loads which limit a turbine’s life time. The characterization of the involved flow structures and their dynamics is an essential step towards possible future load alleviation techniques. The quantitative tuft flow visualization technique is a measurement tool that can be used to assess the surface flow field.

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A detailed comparison of Hot-Wire-Anemometry (HWA) and Laser-Doppler-Anemometry (LDA) measurements in the wake of an airfoil is presented. An evaluation of the capabilities of both techniques in measuring three-dimensional turbulence in turbomachinery applications is made and potential application pitfalls are highlighted. It is shown that the HWA tends to underestimate the turbulence intensity due to damping effects, while the LDA tends to overestimate the turbulence intensity due to the optical setup. The wake flow of a single airfoil at inflow Mach numbers of 0.35 and 0.45 and corresponding Reynolds numbers of 480,000 and 630,000 are used as a reference case. Different HWA probe head designs and various wire diameter are considered, as well as different setups for the LDA measurement device. In a comparison of the two techniques, the turbulence intensity measured differs by up to 1:3 percentage points (pp) in the freestream region and 4:0pp within the wake. This is primarily due to the resolution of high-frequency fluctuations. For both measuring techniques, potential sources of errors are highlighted, especially regarding the application to turbomachinery flows.