蜗壳及尾水管的水力计算

第二章蜗壳及尾水管的水力计算第1节蜗壳水力计算一.蜗壳尺寸确定水轮机的引水室是水流进入水轮机的第一个部件，是反击式水轮机的重要组成部分。引水室的作用是将水流顺畅且轴对称的引向导水机构。引水室有开敞式、罐式和蜗壳式三种。蜗壳式是反击式水轮机中应用最普遍的一种引水室。它是用钢筋混凝土或者金属制造的封闭式布置，可以适应各种水头和流量的要求。水轮机的蜗壳可分为金属蜗壳和混凝土蜗壳两种。1.蜗壳形式蜗壳自鼻端到进口断面所包围的角度称为蜗壳的包角，水头大于40m时一般采用混凝土蜗壳，包角；当水头较高时需要在混凝土中布置大量的钢筋，造价可能比混凝土蜗壳还要高，同时钢筋布置过密会造成施工困难，因此多采用金属蜗壳，包角。本电站最高水头为174m，故采用金属蜗壳。2.座环参数根据水轮机转轮直径D1查[1].P128页表2—16得：座环出口直径:mmDb27252600180019001800200026002850座环进口直径:mmDa32503100180019001800200031003400蜗壳常数K=100（mm）、r=200（mm）3.蝶形边锥角ɑ取4.蝶形边座环半径mkDraD725.11.0225.325.蝶形边高度hmkbh29.055tan1.0276.0tan206.蜗壳圆形断面和椭圆形断面界定值smhs51.055cos29.055cos7.座环蝶形边斜线LmhL354.055sin8.座环蝶形边锥角顶点至水轮机轴线的距离mahrrD522.155tan29.0725.1tan1二.蜗壳进口断面参数计算1.蜗壳进口流量Q0的计算由HLD10运转综合特性曲线查得:Pr=35833.3(kW)、Hr=158.75（m）、ηT=0.905)/(4.25905.075.15881.93.3583381.93smHPQTrrr)/(3.244.25360345360300smQQr2.蜗壳进口断面面积F0的计算)(2.2113.242000mvQF根据水头查设计手册图2—21得：v0=11m/s3.蜗壳进口断面半径ρ0的计算)(84.014.32.200mF4.进口断面圆心至水轮机中心线的距离α0查[1].P128表2—16金属蜗壳座环尺寸系列得：k=0.1m、Da=3.25m、Db=2.725m)(5.229.084.0725.1222200mhraD5.蜗壳系数C的计算2300202000202000aaCaaC6.进口断面外半径R0maR34.384.05.2000三.蜗壳圆形断面参数计算1.蜗壳圆形断面参数计算：见表2—1表2—1蜗壳圆形断面计算表断面号13450.1501.7250.5180.08410.6580.8080.6530.8592.5333.39CiiDrCriD22h22hCriDix2ixiiaiR四.蜗壳椭圆形断面参数计算1.蜗壳椭圆形断面参数计算：见表2—2表2—2蜗壳椭圆形断面计算表断面号LAR2R1151350.0720.00420.00170.1790.4960.3540.8320.5080.5062.1432.65161200.0640.00330.00130.1590.4640.3540.7340.4550.4912.0782.57171050.0560.00250.00100.1390.4300.3540.6390.4000.4742.0102.4818900.0480.00190.00080.1190.3940.3540.5460.3430.4571.9402.4019750.0400.00130.00050.0990.3560.3540.4560.2830.4391.8682.3120600.0320.00080.00030.0790.3140.3540.3690.2210.4201.7912.2121450.0240.00050.00020.0600.2680.3540.2850.1550.4001.7112.1122300.0160.00020.00010.0400.2150.3540.2050.0840.3791.6252.0023150.0080.00010.00000.0200.1490.3540.1290.0080.3571.5321.89四.蜗壳单线图的绘制HLD10蜗壳单线图见附图423300.1431.7250.4950.08410.6410.7840.6150.8362.5093.3533150.1371.7250.4730.08410.6230.7600.5780.8142.4853.3043000.1301.7250.4500.08410.6050.7350.5410.7902.4603.2552850.1241.7250.4280.08410.5860.7100.5040.7672.4353.2062700.1171.7250.4050.08410.5660.6840.4680.7432.4093.1572550.1111.7250.3830.08410.5460.6570.4320.7182.3823.1082400.1041.7250.3600.08410.5250.6300.3960.6932.3553.0592250.0981.7250.3380.08410.5030.6010.3610.6682.3262.99102100.0911.7250.3150.08410.4810.5720.3270.6412.2972.94111950.0851.7250.2930.08410.4570.5410.2930.6142.2662.88121800.0781.7250.2700.08410.4310.5090.2600.5862.2342.82131650.0721.7250.2480.08410.4040.4760.2270.5572.2012.76141500.0651.7250.2250.08410.3750.4410.1940.5272.1662.69iaCisin1aCisin12aCi22cotCri12iiaiR第2节尾水管尺寸的计算一.尾水管基本尺寸的确定1.尾水管型式的选择水流在转轮中完成了能量交换后，将通过尾水管流向下游，这是尾水管的基本作用。但是尾水管还有一个作用是使水轮机转轮出口处的水流能量有所降低，从而增加转轮前后的能量差。回收一部分水流能量。尾水管有直锥型、弯曲型和弯肘型三种型式。大型立式机组，由于土建投资占电厂总投资的比例很大，故一般选用弯肘形尾水管以降低水下开挖量和混凝土量。2.尾水管的高度h尾水管的高度h是指水轮机底环平面到尾水管底板的高度，它对尾水管的恢复系数、水轮机运行稳定性及电站开挖量有直接影响。高度h越大，锥管段的高度可取大一些，因而降低了锥管段出口即肘管段进口及其后部流道的流速，这对降低肘管中的水力损失有利。一般情况下，通过尾水管的流量愈大，h应采用较大的值，但h增大受到水下挖方量的限制。h的确定，与水轮机型式有关。由于混流式和定桨式水轮机在偏离最优工况运行时，尾水管中会出现涡带，引起机组振动，如果h太小，则机组振动加剧，故h选择时应综合考虑能量指标和运行稳定性。根据经验，h一般可作如下选择：对于D1D2的低比速混流式水轮机，h≥2.2D1。取h=2.5D1。参考表2—3，标准弯肘型尾水管可选4H系列。表2—3标准弯肘形尾水管主要参数单位：m尾水管型式1/DhD1hLB5D44hh6L1h54A4C4E4E4H4H201.9152.302.302.502.502.702.301.001.001.001.001.001.001.001.9152.302.302.502.502.702.303.504.504.504.504.504.503.502.202.382.502.502.741.742.171.101.171.231.231.3521.3521.041.1001.1701.2301.2301.3521.3521.0400.5500.5840.6170.6170.6700.6700.5101.4171.5001.5901.5901.7501.7501.4101.0001.2001.2001.2001.3101.3100.9373.肘管的选择肘管段的形状十分复杂，因为水流要在肘管内拐弯90°，同时要由进口圆形断面逐渐过渡到出口为矩形断面。它对尾水管的恢复系数影响很大，且肘管中的水力损失最大。肘管难以用理论公式计算，通常采用推荐的标准肘管，图2—4所示为4号系列肘管。图中各部分的尺寸参数列于表2—4中。4H型肘管主要参数见表2—4和2—5表2—44H型标准肘管主要参数单位：m尾水管参数1/DhD1hLB5D44hh6L1h54H2.512.54.52.741.3521.3520.671.751.31D1=1.9m4.751.94.758.555.212.56882.56881.273.3252.489参考表2—5可选出肘管各部分参数:表2—54号系列肘管各部分参数表单位：m参数类型D4h4B4L1h6aR6R7a1a2R84A4C4E4H201.1001.1701.2301.3521.0401.1001.1701.2301.3521.0402.2002.3822.5002.7402.1701.4171.5001.5901.7501.4100.5500.5840.6170.6700.5100.3950.4220.4460.4870.3690.9401.0001.0601.1600.8790.6600.7030.7450.8150.6401.2051.2751.3501.4781.1350.0870.0930.0980.1070.0800.6340.6770.7100.7820.590注：表中数值是对D1=1m而言。表2—54号系列肘管各部分参数表单位：m尾水管参数D4h4B4L1h6aR6R7a1a2R84H1.3521.3522.741.750.670.4871.160.8151.4780.1070.782D1=1.9m2.572.575.23.3251.2730.9252.21.552.80.21.54.进口单边锥角β对于混流式水轮机进口单边锥角β取值范围为7°—9°。取β=8°由比转速ns查[1].P26图1—29得：h1=0.024×1.9=4.56(cm)h2=0.148×1.9=28.12(cm)h3=h–h1–h2–h4=475–4.56–28.12–256.88=185.44(cm)5.尾水管进口直径D3)(210212132133213cmtghhhhDtgDhhhh6.出口扩散段查[1].P132，顶板仰角ɑ=10°—13°，取ɑ=12°。支墩的尺寸如下：cm68.676.52013.015.01.05Bb—)(72.27068.67463cmbRcmbr92.1668.6725.03.02.0cmDl2669.14.14.11二.尾水管单线图的绘制HLD10尾水管单线图见附图5