Rotating instability (RI) occurs at off-design conditions in compressors, predominantly in configurations with large tip or hub clearance ratios of s* ≥3%. RI is the source of the blade tip vortex noise and a potential indicator for critical operating conditions like rotating stall and surge. The objective of this paper is to give more physical insight into the RI phenomenon using the analysis results of combined near-field measurements with high-speed particle image velocimetry (PIV) and unsteady pressure sensors. The investigation was pursued on an annular cascade with hub clearance. Both the unsteady flow field next to the leading edge as well as the associated rotating pressure waves were captured. A special analysis method illustrates the characteristic pressure wave amplitude distribution, denoted as “modal events” of the RI. Moreover, the slightly adapted method reveals the unsteady flow structures corresponding to the RI. Correlations between the flow profile, the dominant vortex structures, and the rotating pressure waves were found. Results provide evidence to a new hypothesis, implying that shear layer instabilities constitute the basic mechanism of the RI.

Investigations into wastewater composition focusing on nonwoven wet wipesBadanie składu ścieków ze szczególnym uwzględnieniem chusteczek nawilżanych z włókniny Abstract This paper summarizes the problems caused for wastewater systems by changing wastewater composition, especially the increasing use of nonwoven wet wipes and their disposal via the toilet. The nonwoven wet wipes do not disintegrate in the sewer system as paper-based toilet does, but accumulate to large agglomerations that can block the system and clog pumps. This not only reduces the operational safety and stability of the wastewater system, but also costs the operator a lot of money. The paper introduces an approach to estimate the composition of wastewater and presents first results for the city of Berlin. Keywords: wastewater composition, solids, wet wipes, cloggingStreszczenie W artykule omówiono problemy występujące w sieciach kanalizacyjnych związane ze zmieniającym się składem ścieków, a zwłaszcza obecnością w ściekach chusteczek nawilżanych z włókniny wrzucanych do toalety. Chusteczki nawilżane wykonane z włókniny nie rozpadają się w kanalizacji tak jak papier toaletowy, ale tworzą skupiska, które mogą powodować niedrożność instalacji i rur, zagrażając bezpieczeń-stwu i stabilności eksploatacji sieci kanalizacyjnej i zwiększając koszty eksploatacyjne ponoszone przez operatora. W artykule przedstawiono metodę analizy składu ścieków i pierwsze wyniki uzyskane podczas badań przeprowadzonych w Berlinie.Słowa kluczowe: skład ścieków, ciała stałe, chusteczki nawilżane, niedrożność 126

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