翻译原文--利用非恒定流理论分析虹吸式屋面排水系统-外文文献(编辑修改稿)

翻译原文--利用非恒定流理论分析虹吸式屋面排水系统-外文文献(编辑修改稿)内容摘要：

ydraulic conditions within the horizontal pipework will beinCRuenced by several bends and possibly connections fromadditional roof outlets.3. Verticalpipework. For a siphonic roof drainage systemto function properly two pieces of vertical pipework mustbe present: the FFrst is a small length (–∼0:5 m) whichconnects the outlet to the horizontal pipework. The secondconnects the horizontal pipework to the point of discharge,assumed to be at atmospheric pressure.. Priming of the test rigUnderstanding the priming action within a siphonic testrig is of fundamental importance. If, for what ever reason,an installed system cannot prime at the design rate of inS. Arthur, . SwaSOeld/Building and Environment 36 (2020) 939–948 943CRow the system will fail to meet its design criteria. Thepriming action described in this section will consider thehydraulic conditions which prevail in a siphonic systemwhere the inCRow to the roof gutter rises rapidly to equalor exceed than the observed inCRow capacity of the test rig(. the design condition). To analyse the priming actionof the test rig, pressures were recorded at several pointsalong the horizontal pipework at data sampling rates from10 to 1000 Hz, CRow depths in the gutter were measuredusing pressure transducers at a similar frequency. Additionally, as the entire system was transparent, CRows wereanalysed by eye, with the aid of still photography and using an EPSRC Loan Pool highspeed video camera (up to500 frames per second). The priming procedure observedmay be deconstructed into the elements listed below:1. Initial gutter inCRow. The FFrst step in the priming procedure is for the water depth in the roof gutter to slowlyincrease. Initially, the pressures in the siphonic systempipework are equal to ambient atmospheric pressure (plusthe CRow depth). Flow in the vertical pipework at thisstage was observed to be annular. Flows in the horizontalpipework were observed to be subcritical. As the depthat the roof outlet increases, this causes supercritical CRowto develop at the start of the horizontal pipework, and theobserved formation of a distinguishable hydraulic jumpjust downstream (Fig. 4a).2. Importance of Bend 1. As Fig. 1 indicates, a shortsection of vertical pipe is attached to the siphonic roofoutlet. This short length of pipe then connects, via bend1, to the horizontal part of the test siphonic system. Laboratory tests have indicated that if only a single verticallength of pipe is connected to the siphonic roof outlet (.no horizontal pipework is included in the system), the hydraulic resistance is insuSOcient to allow the developmentof full bore CRow in the vertical section — irrespective ofthe depth of CRow in the roof gutter.3. Hydraulicjump. As the CRow slowly increases with timethe jump gradually moves towards the downstream end ofthe horizontal pipe. Simultaneously, the downstream (subcritical) depth of the jump slowly increases. Eventually, arate of inCRow is reached where the depth downstream ofthe hydraulic jump is equal to the pipe diameter, at thisjuncture full bore CRow has developed in the horizontalpipework (Fig. 4b). At this juncture, a volume of air bees trapped between the jump and the upstream end ofthe horizontal pipe (above the supercritical CRow). Simultaneously, full bore CRow conditions propagate downstream.4. Main vertical pipe. When full bore CRow conditionsreach bend 2, the vertical pipe begins to FFll. As full boreCRow develops in the main length of vertical pipe, the massof water in the pipe causes depressurisation of the CRowin the upstream pipework (. the ambient pressure fallsbelow atmospheric pressure). This causes the inCRow intothe system to increase. This increased inCRow causes thefull bore CRow to develop at the upstream end of the horiFig. 4. Movement of trapped air within the system during priming. (TheFFgure assumes the roof outlet is fully submerged and the inCRow containsno air.)zontal pipe. The air pocket (described above) then movesalong the horizontal pipework at the ambient velocity ofthe CRow (Fig. 4c). When this air pocket passes bend 2and enters the vertical pipe (Fig. 4d) it causes a partialrepressurisation of the entire system. However, once theair pocket leaves the vertical pipe the system can beefully primed — other than the presence of small amountsof entrained air which enter the system (normally lessthan 5%).Fig. 5 shows data collected for a typical priming eventin the test rig. Each of the zones delineated in the FFgureare described in Table 2.7. Air induction into siphonic systemsWithin siphonic roof drainage systems there are threeprinciple entry routes for air into the system CRow, andthese may be listed as follows。 1. Airwhichexistedwithinthesystembeforetherainfallevent considered began. Before there is any inCRow into asiphonic system, the volume within the pipework is almost944 S. Arthur, . SwaSOeld/Building and Environment 36 (2020) 939–948Fig. 5. Ambient pressures in the system during priming. It can be seen that the CRows within the system move quite quickly from a free surface CRowcondition to full bore CRow. The FFgure clearly shows that the repressurisation is generated at the downstream end of the system, and then propagatestowards the upstream end. This is indicated by the time lag observed between the observation of the repressurisation at the downstrean and upstreampressure monitoring points.Table 2Zone descriptions, as delineated in Fig. 5Zone Description1 Development of full bore CRow in the horizontal pipeword2 Filling of main length vertical pipe3 Repressurisation caused by air pocket4 System primedentirely FFlled with air. Welldesigned systems allow thisair to exit from the system both via the roof outlet, asthe inCRow gradually builds, and via the di。