电大流体力学选择判断问答小抄参考.doc

专业好文档一、选择1、在明渠均匀流中取一六面体，其所受的外力：作用在该六面体上有（正压力、切向力、重力）2、在水箱上接出一条等直径长细圆管，末端设有阀门以控制流量，若水箱内水面不随时间变化，当阀门开度一定时，管中水流为（恒定均匀流）3、 对实际流体，总水头总是（沿程下降）4、按短管进行水力计算的管路是（虹吸管）5、跌水的形成条件是（从缓流过渡到急流）1在明渠均匀流中取一六面体，其所受的外力：作用在该六面体上有（正压力、切向力、重力 ）2在水箱上接出一条等直径长细圆管，末端设有阀门以控制流量，若水箱内水面不随时间变化，当阀门开度一定时，管中水流为（恒定均匀流 ）3对实际流体，总水头总是（沿程下降）4.按短管进行水力计算的管路是（虹吸管 ）5.跌水的形成条件是 （ 从缓流过渡到急流 ）1在静水中取一六面体，分析其所受的外力：作用在该六面体上的力有(正压力、重力)。2在水箱上接出一条逐渐收缩锥形管道，末端设有阀门已控制流量，当水箱内水面不变、阀门开度一定时，管中水流为(非恒定非均匀流)。3按短管进行水力计算的管路是(虹吸管)4外延管嘴的正常工作条件是(管长l=(3-4)d，作用水头小于9米水柱)。 5两段长直的棱柱形渠道，通过的流量相同，(粗糙系数不同(n1>n2)，其他参数相同(i，b，m，Q)，则h01>h02)。1在静水中取一六面体，分析其所受的外力：作用在该六面体上的表面力有(正压力)2在水箱上接出一条逐渐收缩锥形管道，末端设有阀门以控制流量，当水箱内水面不变、阀门开度一定时，管中水流为(恒定非均匀流)3等直径圆管中层流的过流断面流速分布是( 呈抛物线分布 ) 4流体内部某点压强为2个工程大气压，用液柱高度为(20米水柱 ) 5总水头线与测压管水头线的基本规律之一，是：(总水头线总是在测压管水头线的上方)1流体运动的连续性方程是根据（质量守恒）原理导出的。2判断层流和紊流的临界雷诺数是(下临界雷诺数)3圆管的水力半径为二、判断题1.流体内部切应力的大小仅与流速梯度有关。 （ × ）2.真空压强是指没有大气存在时的压强。 （ × ）3.均匀流一定是恒定流。 （ ）4.动能修订系数与断面流速分布有关 （ ）5.壁面光滑的管道一定是水力光滑管 （ × ）6.若两孔口形状、尺寸完全相同，作用水头相同，一个为自由出流，一个为淹没出流，二者的流量是相同的 （ ）1.流体内部切应力的大小仅与流速梯度有关。 （ × ）2.真空压强是指没有大气存在时的压强。 （ × ）3.均匀流一定是恒定流。（ ）4.动能修订系数与断面流速分布有关 （ ）5.壁面光滑的管道一定是水力光滑管 （ × ）6.若两孔口形状、尺寸完全相同，作用水头相同，一个为自由出流，一个为淹没出流，二者的流量是相同的 （ ）1非均匀流一定是非恒定流。 (×)2流体内部切应力的大小仅与流速梯度有关。 ( × )3壁面光滑的管道一定是水力光滑管。 (×）4流体中某点的静压强大小与受压面方位无关。 ( )5明渠水流，从急流过渡到缓流，发生跌水(水跌)。 ( ×)6明渠水流的测压管水头线不可能沿程上升。 ( × )1理想流体与实际流体的区别仅在于，理想流体具有不可压缩性。( × )2无论流体作何种运动，流体内任何一个水平面都是等压面。(× )3在恒定流情况下，流线与迹线重合。( )4·对于渐变流，过流断面上动水压强分布符合静水压强分布规律( )5壁面粗糙的管道一定是水力粗糙管。( × )6在进行水力计算时，短管是指管道几何长度较短的管道。( × )1实际流体在等直径长管中流动时的总水头线是水平的直线。（× ） 2流体内切应力方向与流体运动方向相同。（ 错误 ） 3等压面与质量力垂直。（ 正确 ） 4阻力平方区内阻力系数与雷诺数无关。（ 正确 ） 三、简答题（共5小题 ，每题10分，共50分）1流体静压强的两个特征？（1）垂直指向受压面。（2）某点压强的大小与受压面的方位无关（某点压强的大小仅与该点的淹没深度有关）2、根据尼古拉兹试验，说明紊流各区沿程阻力系数 与Re和K/d的关系？（1）水力光滑区：××f（Re）（2）过渡粗糙区： f（Re,K/d）(3)粗糙区： f（K/d0）3、为什么对于孔口淹没出流无小孔口与大孔口的区别？在划分小孔口和答孔口时，若H/d>10,视为孔口各点的压强仅似相等，定义为小孔口，对于孔口淹没出流其作用水头H为上下游水面差，孔口各点的压强相等，故对于孔口淹没出流无小孔口与大孔口之分。4、何种流动为恒定流？若流体中任一点的运动要素与时间无关，或者说：流体中任一点的运动要素不随时间变化。5、圆管中层流与紊流，其断面流速分布有什么不同？圆管中层流断面流速分布为抛物线状，而圆管中紊流断面流速分布为对数曲线，紊流的断面流速分布均匀化了。1流体静压强的两个特征？（1）垂直指向受压面。（2）某点压强的大小与受压面的方位无关（某点压强的大小仅与该点的淹没深度有关）2.根据尼古拉兹试验，说明紊流各区沿程阻力系数 与Re和K/d的关系？答：（1）水力光滑区：××f（Re）（2）过渡粗糙区： f（Re,K/d）(3)粗糙区： f（K/d03.为什么对于孔口淹没出流无小孔口与大孔口的区别？答：在划分小孔口和答孔口时，若H/d>10,视为孔口各点的压强仅似相等，定义为小孔口，对于孔口淹没出流其作用水头H为上下游水面差，孔口各点的压强相等，故对于孔口淹没出流无小孔口与大孔口之分。4.何种流动为恒定流？若流体中任一点的运动要素与时间无关，或者说：流体中任一点的运动要素不随时间变化。5.圆管中层流与紊流，其断面流速分布有什么不同？圆管中层流断面流速分布为抛物线状，而圆管中紊流断面流速分布为对数曲线，紊流的断面流速分布均匀化了。1动力粘滞系数和运动粘滞系数v布什么区别?两者都反映流体的粘滞性，为动力量，v为运动量，量纲不同。3简述明渠恒定非均匀流的水力特征。答：过水断面面积A，水深h，沿程改变。即底坡线，水面线，总线头线三线不再平行，即。1等压面是水平面的条件有哪些?答：(1)必须是同一种流体。(2)必须是连续流体。 (3)必须是单一重力作用条件下。(4)必须为静止流体。 (5分)2管道内流态为紊流时，水力光滑与水力粗糙是如何定义的?答：固体边界表面存在当量粗糙度K，流体运动时在固体边界存在粘性底层艿； (1)当粘性底层艿远远大于当量粗糙度K(K-<04a)，粘性底层完全掩盖当量粗糙度K，称为水力光滑。 (3分)(2)当粘性底层不能掩盖当量粗糙度K时(K>6)，称为水力粗糙 (2分)1 流体力学中连续介质假定的含义是什么？。答案：流体是一个紧挨着一个的连续的质点所组成的，没有任何空隙的连续体，即所谓的“连续介质”。同时认为，流体的物理力学性质，例如密度、速度、压强和能量等，为空间坐标和时间的连续函数。2 描述流体运动的两种方法是什么？简述其内容。答案：（1）拉格朗日法：以流体质点为研究对象，研究质点空间位置随时间的变化过程。（2）欧拉法：以流体空间位置的质点为研究对象，研究在确定位置上，流体质点速度随时间的变化过程。3简述尼古拉兹实验中沿程阻力系数的变化规律。答案：通过尼古拉兹实验发现：在层流中仅是雷诺数Re的函数并与Re成反比；在层流到紊流过渡区，仅是Re的函数；在紊流光滑区=f1（Re），过渡区=f2（Re， ），粗糙区=f3（ ），紊流粗糙区又称阻力平方区。4.在渗流计算中达西定律与杜比公式有何区别？答案：达西定律适用于任一点的渗流流速u=kJ，其适用于恒定均匀层流渗流；而杜比公式是适用于恒定非均匀渐变层流渗流，同一过水断面上各点的渗流流速都相等且等于v= kJ。"If we don't do that it will go on and go on. We have to stop it; we need the courage to do it."His comments came hours after Fifa vice-president Jeffrey Webb - also in London for the FA's celebrations - said he wanted to meet Ivory Coast international Toure to discuss his complaint.CSKA general director Roman Babaev says the matter has been "exaggerated" by the Ivorian and the British media.Blatter, 77, said: "It has been decided by the Fifa congress that it is a nonsense for racism to be dealt with with fines. You can always find money from somebody to pay them."It is a nonsense to have matches played without spectators because it is against the spirit of football and against the visiting team. It is all nonsense."We can do something better to fight racism and discrimination."This is one of the villains we have today in our game. But it is only with harsh sanctions that racism and discrimination can be washed out of football."The (lack of) air up there Watch mCayman Islands-based Webb, the head of Fifa's anti-racism taskforce, is in London for the Football Association's 150th anniversary celebrations and will attend City's Premier League match at Chelsea on Sunday."I am going to be at the match tomorrow and I have asked to meet Yaya Toure," he told BBC Sport."For me it's about how he felt and I would like to speak to him first to find out what his experience was."Uefa has opened disciplinary proceedings against CSKA for the "racist behaviour of their fans" during City's 2-1 win.Michel Platini, president of European football's governing body, has also ordered an immediate investigation into the referee's actions.CSKA said they were "surprised and disappointed" by Toure's complaint. In a statement the Russian side added: "We found no racist insults from fans of CSKA."Baumgartner the disappointing news: Mission aborted.The supersonic descent could happen as early as Sunda.The weather plays an important role in this mission. Starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. The balloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. It will climb higher than the tip of Mount Everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratosphere. As he crosses the boundary layer (called the tropopause),e can expect a lot of turbulence.The balloon will slowly drift to the edge of space at 120,000 feet ( Then, I would assume, he will slowly step out onto something resembling an Olympic diving platform.Below, the Earth becomes the concrete bottom of a swimming pool that he wants to land on, but not too hard. Still, he'll be traveling fast, so despite the distance, it will not be like diving into the deep end of a pool. It will be like he is diving into the shallow end.Skydiver preps for the big jumpWhen he jumps, he is expected to reach the speed of sound - 690 mph (1,110 kph) - in less than 40 seconds. Like hitting the top of the water, he will begin to slow as he approaches the more dense air closer to Earth. But this will not be enough to stop him completely.If he goes too fast or spins out of control, he has a stabilization parachute that can be deployed to slow him down. His team hopes it's not needed. Instead, he plans to deploy his 270-square-foot (25-square-meter) main chute at an altitude of around 5,000 feet (1,524 meters).In order to deploy this chute successfully, he will have to slow to 172 mph (277 kph). He will have a reserve parachute that will open automatically if he loses consciousness at mach speeds.Even if everything goes as planned, it won't. Baumgartner still will free fall at a speed that would cause you and me to pass out, and no parachute is guaranteed to work higher than 25,000 feet (7,620 meters).cause there