The subject of this monograph is the fluid dynamics of liquid turbomachines, particularly pumps. Rather than attempt a general treatise on turbomachines, we shall focus attention on those special problems and design issues associated with the flow of liquid through a rotating machine. There are two characteristics of a liquid that lead to these special problems, and cause a significantly different set of concerns than would occur in, say, a gas turbine. These are the potential for cavitation and the high density of liquids that enhances the possibility of damaging unsteady flows and forces.

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Hydrodynamics of Pumps

This article experimentally investigated the pressure and cavitation characteristics of high velocity flow over a surface irregularity with and without aeration in a non-circulating water tunnel system. The surface irregularity is a cylindrical protrusion made of stainless steel of 6 mm diameter and 2 mm height. Pressures with and without aeration were measured with MPX400D pressure transducers and real-timely acquired by a SINOCERA YE6263 data acquisition system. Variations in flow regimes with and without aeration were observed. Pressure profiles and their variations with air concentration upper and lower cylindrical protrusion on the invert and obvert walls were determined. Variations of cavitation number with air concentration lower cylindrical protrusion were analyzed. Also, cavitation numbers in the presence and absence of aeration were compared.

An experimental investigation of pressure and cavitation characteristics of high velocity flow over a cylindrical protrusion in the presence and absence of aeration

An experimental investigation of the cavitation characteristics of high-velocity flow over an offset-into-flow with various heights and chamfers both in the presence and absence of aeration was conducted in a cavitation tunnel of the Hydraulics Laboratory, Zhejiang University of Technology in China The 2- and 5-mm abrupt and sloping offsets into flows were employed to be models of surface irregularities Cavitation phenomena of high-velocity flow over the various offsets were carefully observed A range of air concentrations was considered Variations of wall pressures downstream and upstream of the offset were measured in terms of the air concentration The effects of air concentration and chamfer on the cavitation characteristics of the offsets were analysed In addition, the cavitation cloud over the offset-into-flow and the turbulent boundary layer over a flat plate are compared

https://www.tandfonline.com/doi/pdf/10.1080/00221680903566083

Cavitation characteristics of offset-into-flow and effect of aeration

The ski-jump-step spillway was designed using a ski-jump and an aeration basin to effectively pre-aerate flow in a stepped spillway. A new experimental study of the hydraulic characteristics of aeration basins was conducted to better understanding their pre-aeration properties and mechanisms. The plunge-pool patterns of aeration basins were classified into partially aerated, fully aerated, and vortex expelled, with increasing unit discharge. Relations between the distributions of the time-averaged pressure and the air concentration of the plunge-pools suggested that the ski-jump jet impact and the recirculating vortices are the main causes of plunge-pool air entrainment. Based on the export cross-section of the aeration basins, the bottom air concentrations remained greater than 3.0%. The sidewall air concentrations were greater than 7.5% and followed a logarithmic distribution in the vertical direction, demonstrating that the export flow attains a completely aerated state without any blackwater zones. In addition, increasing the aeration basin length was found to prevent the occurrence of a vortex expelled plunge-pool, thus promoting the appropriate pre-aeration effect under large unit discharges. doi: 10.2166/ws.2020.016 om http://iwaponline.com/ws/article-pdf/20/3/922/765904/ws020030922.pdf er 2021 Shangtuo Qian College of Agricultural Engineering, Hohai University, Nanjing 210098, China Jianhua Wu (corresponding author) College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210098, China E-mail: jhwu@hhu.edu.cn

Hydraulic characteristics of the aeration basin in a ski-jump-step spillway

Cavitation characteristics of high velocity flow past cylindrical protrusions with different heights in the absence and presence of aeration were experimentally investigated in a water tunnel at Zhejiang University of Technology. 2mm and 5mm high cylindrical protrusions with 6mm in diameter were employed. The air-water volume ratios of aerated flow were 0.96, 1.94, 2.96, 5.01 and 7.13%, respectively. Cavitation phenomena of cylindrical protrusions with different heights were observed. Variations of pressures with air-water volume ratio upper and lower the protrusions with different heights were measured. Variations of the corresponding cavitation numbers with air-water volume ratio for the protrusions with different heights were analyzed, and a comparison of cavitation numbers for the protrusions with different heights was made.

Jacob E. Warnock

Papers

Cavitation in Hydraulic Structures: A Symposium: Experiences of the Bureau of Reclamation