A data set consisting of one-year vertical profiles of horizontal wind speed obtained with lidar at Braunschweig Airport, North German Plain, is analyzed with respect to the low-level jet (LLJ). The observations reveal a typical LLJ altitude between 80 and 360 m, a frequency of occurrence up to almost 9% for some altitudes, and a typical wind speed between 4 and 9 m s À1 . LLJ events occurred most frequently in summer during the night. In the winter, LLJs were observed both during day and night. The Weibull distribution for wind speed is presented for different heights. The most probable wind speed of the Weibull distribution increases from 4 m s À1 at 40 m altitude to values exceeding 7 m s À1 for altitudes above 240 m. There is a significant difference for the Weibull parameters determined with a monthly, seasonal and annual data set. The contribution of the LLJ to the overall wind speed distribution is analyzed. An LLJ event occurred on 52% of the days over the year, with a total measurement time of 739 h. As the typical rated speed for onshore wind turbines is in the range from 11.5 to 14.5 m s À1 and the typical hub height is in the range of 100 to 150 m, it can be expected that wind turbines are affected by the LLJ.

Highly-loaded turboprop intake was investigated for two different shaft connection types to assess the configuration sensitivity on performance. Turboprop intakes inherently have S-shape to bend around the gearbox, which have significant effects on the flow. Previous geometric sensitivity analysis on uninstalled, isolated single scoop S-ducts with shaft penetration showed higher recovery and lower distortion trends for long intakes with shorter ducts. The major pressure loss was observed over the bore due to the penetrating shaft. It is expected that changing the configuration to wrap-around will overcome the loss introduced by flow around the bore. The two configurations were compared by varying the S-duct curvatures using computational methods. The results showed an increase in recovery with lower total pressure distortion levels for wrap-around configuration of the same sizes. The gain in the recovery by the configuration change was observed to be similar to the gain when the ducts were shortened. However, wrap-around S-duct suffered from higher swirl distortion than shaft penetration of the same size but these were observed to be lower than the shaft penetration type with short ducts. Distortion intensities showed opposite trends for the two configurations, with wrap-around producing low distortion in circumferential whereas high in radial direction. The results will be used as the basis for the turboprop intake design and its over-the-wing integration on the high-lift aircraft.

The impact of stator clocking on performance and flow of a 2.5-stage axial compressor has been investigated. Stator clocking, the circumferential indexing of adjacent stator rows with equal blade counts, is known as a potential means to modify the flow field in multistage turbomachinery and increase overall efficiencies of both turbines and compressors. These potential effects on turbomachine performance are due to wake-airfoil interactions and primarily depend on the alignment of the downstream stator row with the upstream stator wake path. The present survey describes and discusses the experimental research on stator clocking effects in a low-speed 2.5-stage axial flow compressor, using front loaded CDA blade sections and cantilevered stator rows with identical blade counts. Conventional static pressure tappings were used to locate global peaks in compressor performance for varying Stator 2 clocking positions at different flow coefficients. Results of unsteady total pressure measurements obtained by means of a high-frequency pressure transducer, embedded in the Stator 2 leading edge, give information on Stator 1 wake propagation. Traverse data from pneumatic 5-hole probes show the impact of stator indexing on Stator 2 exit total pressure at different blade spans. Regardless of flow coefficient, the variations of overall compressor efficiency due to Stator 2 clocking are around 0.2% and are exhibiting a near-sinusoidal trend over the clocking angle. It is shown that total pressure measurements at mid-span of Stator 2 leading edge suggest best overall performances for design and low loading conditions, if the Stator 1 wakes pass through mid-passage of Stator 2. At high loading, however, maximum efficiency locates the wake path directly at the leading edge. Due to a considerable span-wise skewness of the upstream stator wake, the aerodynamic clocking position for Stator 2 varies from hub to tip. While it is shown again that this effect weakens the advantages of airfoil indexing on a global scale, stator clocking shows much more potential if only a single blade section is considered.

When reaching the stall point of an axial-flow pump, the pump head characteristic becomes unstable and the pump head suddenly drops. Before this happens however, at even higher flow rates the NPSH3 and the pump body and shaft vibrations increase dramatically. For effectively increasing the available operating range, it is essential to find a solution for all three problems without reducing the pump efficiency at design. The paper describes an experimental investigation on the outlined subject that gives insight into the flow phenomena leading to stall. Based on this knowledge a very simple type of casing treatment was chosen and investigated. It was found to satisfy all mentioned requirements. Subject to the investigations is a highly loaded axial-flow pump having a nq of 150 (SI units). The overall pump performance was investigated measuring pump head, efficiency, NPSH3, and casing as well as shaft vibrations. Further-more, oil flow pictures taken at the pump casing and at the rotor blades, and video captures of the cavitating core of the tip clearance vortex were analyzed for understanding the flow phenomena leading to stall (see also related paper Part I, Schrapp et al. (2004)). From the video captures it was realized that the behavior of the tip clearance vortex which was found to perform so-called spiral-type vortex breakdown is triggering stall inception in this machine.

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