| 摘要 |
<p>The tubular outflow mouthpiece issues over the highest point of the bed upper surface, and has components for momentary by-pass of its through flow profile. This by-pass functions when the flow through the mouthpiece profile is obstructed by material which has penetrated from the granular bed. Thie causes the outflow profile hydraulic resistance to increase locally and momentarily, with fluid flowing into the bypass at the upstream end of the blockage, and back into the profile at the blockage downstream end. The blockage is eroded by fluid flowing past it to the throughflow profile, and the hydraulic resistance is restored, with the by-pass function being stopped. The mouthpiece has at least one aperture in its wall with a width and length greater than the size of the bed material granules, and covered on the mouthpiece outside with at least one casing of elastic sprung material. The casing maintains the apertures closed when fluid flows through the mouthpiece outlet, and can widen its dia. when the blockage increases the fluid pressure in the throughflow profile so that the by-pass is formed outside the fixed body of the mouthpiece.</p> |
