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1、水利水电工程专业英语——水电站与水轮机篇1.EnergyandPowerofWaterFlow1.水流的能量和功率Asmayberecalledfrommechanicsoffluids,theenergyandpowerofaquantityofwaterinsteadyflowfromAtoBcanbedeterminedusingBernoulli’stheoremforspecificenergy.FromtheprincipleofconservationofenergyitfollowsthattheenergyeAatAequalstheenergye
2、BatBplustheenergyeABreleasedasthewaterflowsfromAtoB.Assumingthattheweightofthewateris1N,Bernoulli’sequation,whichineffectexpressesthelawofconservationofenergy,maythenbewrittenasZA+PAρg+aAVA22g=ZB+PBρg+aBVB22g+eAB（1）回顾流体力学，可以使用伯努利定理的比能来确定从A到B的一定量的稳定水流的能量和功率。根据能量守恒定律，A点的能量eA等于B点的能量eB加上水流
3、从A到B的能量损失eAB。假设水体的质量是1N，那么实际上表述能量守恒的伯努利方程可以写作：ZA+PAρg+aAVA22g=ZB+PBρg+aBVB22g+eAB（1）WhereZAandZBarerespectivelytheelevationsaboveadatumplaneO-OofthecentersofgravityofthestreamcrosssectionsatAandB(m),PAandPBarerespectivelythepressuresatthecentersofgravityofthecrosssectionsatAandB(Pa),ρi
4、sthewaterdensity(kgm-3),VAandVBarerespectivelytheaveragevelocitiesofwateratAandB(ms-1),gisthefreefallaccelerations(ms-2),andaAandaBarenumericalcoefficientsaccountingforanon-uniformvelocitydistributionoverthecrosssections(theyarealwayslargerthanunityandgenerallyrangebetween1.03and1.1).其
5、中ZA和ZB分别表示A和B处水流断面重心在基准面O-O以上的高程（m），PA和PB分别是A和B处水流断面重心的压力（Pa），ρ是水的密度（kgm-3），VA和VB分别是A和B处水的平均速度（ms-1），g是自由落体加速度，且aA和aB是考虑断面非均匀分布速度的数字系数（它们通常比单位的大，且通常范围为1.03-1.1）。Thefirstterms,z,oneithersideofEq.(1),knownastheelevationheadsorpotentialheads,definethespecificpotentialenergyofwaterduetothe
6、elevationwithrespecttotheselecteddatum.Thesecondterms,Pρg,calledthepressureheads,definethespecificpotentialenergyofwaterduetotherespectivepressure.Thetotalspecificpotentialenergymay,therefore,bewrittenase=z+Pρg.Itisthesameforanypointofacrosssection,sinceanincreaseinzalwaysproducesamatc
7、hingdecreaseinPρg.Accordingly,thepotentialenergyatacrosssectionmaybeevaluatedintermsoftheelevationsofthepointslyingonthefreesurfaceofthatcrosssection,assumingthatPρgande=h(wherehistheelevationofthepointsonthefreesurfaceabovethedatumplane).Finally,thethirdterms,VB22g,referredtoastheve
