Analysing secondary vortex structures in an hp turbine stage using the realisable k-Ω SST model

The article analyses the effect of turbulence model selection on the pattern of development and interaction of secondary vortex structures in an HP turbine stage. The basic tool used in the analysis is FlowER, a specialised code developed for studying flow through fluid-flow machine stages and stage sections. The flow calculations performed using a standard k-ω SST turbulence model presented highly unstable behaviour of the rotor passage vortex, which periodically built up, moved up along rotor blade suction side and broke down. On the other hand, the use of the modified version, taking into account realisability constraints, has made it possible to stabilise the rotor passage vortex behaviour.Проанализировано влияние выбора модели турбулентности на характер развития и взаимодействия вторичных вихревых структур в турбинной ступени высокого давления. Основным инструментом, используемым при анализе, был решатель FlowER – специализированный код, предназначенный для исследования течений в изолированных ступенях и группах ступеней турбомашин. Расчет течения, выполненный с использованием стандартной модели турбулентности k-ω SST, показал существенно нестационарный характер канального вихря в решетке ротора, который периодически появлялся, перемещался вдоль стороны разрежения лопатки ротора в радиальном направлении и разрушался. Применение модифицированной версии решателя, учитывающей ограничения реализуемости, позволило стабилизировать поведение этого вихря

Mudflat/distal fan and shallow lake sedimentation (upper Vallesian–Turolian) in the Tianshui Basin, Central China: Evidence against the late Miocene eolian loess

The Tianshui Basin in central China contains a thick sedimentary sequence (~1400 m) of continental deposits, Aragonian to Villafranchian (Miocene-Pliocene) in age. Intense Himalayan movements around the Paleogene/Miocene boundary triggered the uplift of mountain ranges around the Tianshui Basin, providing the deposition site for continental sediments. The sedimentary infill of the basin consists of four stratigraphic units (I to IV). This paper focuses on Unit II. Most of the accommodation space was occupied by Unit I, so during the sedimentation of Unit II, the morphology of the basin was relatively flat, promoting the development of wide distal fan/mudflat areas and wide shallow lakes. Deposits include: red mudstones, pedogenic and groundwater calcretes, reworked calcrete deposits, sheet-floods, fluvial channels, rippled sandstones/siltstones, ooidal/peloidal packstones, palustrine limestones, bioturbated marls and intraclastic limestones/marls. The characteristics and organization of the deposits indicate the gradual transition from alluvial to lake environments. Within the distal fan/mudflat, the deposition of reworked calcrete clasts as one of the most striking facies of the basin may be attributed to substantial recycling of calcrete levels and red clays. At the lake margins, the presence of ooids and palustrine limestones suggests the possibility of ramplike margins within different energy settings. The origin of some of the deposits of the basin's QA-I section is under discussion, and their consideration as eolian has been recently proposed. However, we believe this possibility is precluded by the characteristics of the deposits. Our proposal has important implications for revising the interpretation of Miocene paleoclimatic conditions in central Asia