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oa Civil Engineer in South Africa - Belugting van vloei vanaf 'n radiaalsluis om kavitasieskade te voorkom

 

Abstract

Hoësnelheidwaterstrale ononderbroke losgelaat vanaf radiaalsluise in die dempkomme by die Zoekfonteinpypleiding-beheerwerke skep toestande wat kavitasie in die hand werk. Bronne van kavitasie is hoofsaakiik ruheid aan die betonmure en -vloere van die geute wat na die dempkomme lei en skuifsones tussen vinnig- en stadig bewegende water in die hidrouliese spronge in die dempkomme. Kavitasie vanaf die eerste bron is geminimaliseer deur die gebruik van spesiale bekisting om ultragladde betonoppervlakke te voorsien, maar hierdie maatreëls kan nie verwag word om geheel en al geslaag te wees nie en derhalwe is belugting ook gebruik.


Belugting van water losgelaat vanaf die radiaalsluise voorkom nie noodwendig kavitasie nie maar beskerm die betonoppervlakke teen die uitwerking daarvan. By Zoekfonteln word die waterstrale in lug omhul onmiddellik stroomafwaarts van die sluise om meesleuring moontlik te maak deur lug in die turbulente randlaag wat op die wateroppervlakke vorm, te meng.

High velocity water jets discharged continuously from radial gates into the stilling basins at the Zoekfonteln pipeline control works create conditions conducive to cavitation. Sources of cavitation are primarily roughtness on the concrete walls and floors of the chutes leading into the stilling basins, and shear zones between fast moving and slow moving water in the hydraulic jumps in the stilling basins. Cavitation from the first source was minimized by the use of special formwork to provide ultra-smooth concrete surfaces, but these measures could not be expected to be entirely successful, so aeration was also introduced.


Aeration of the water discharged from the radial gates does not necessarily prevent cavitation, but protects the concrete surfaces against its effects. At Zoekfontein the jets are enveloped in air immediately downstream of the gates to allow air entrainment by the mixing of air into the turbulent boundary layer that develops on the surfaces of the water.

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/content/civeng1/26/10/EJC24933
1984-10-01
2016-12-05
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