第五章习题参考答案（仅限参考）

1.a 2.b 3.d 4.c 5.d

L?vm26．解： ?p??d2

假设雷诺数小于2300，有λ?6464??Revmd，代入上式得：

L?vm264?L?vm264?L?vm?p????

d2vmdd22d22d2?p2?0.152?0.965?106??1.84m/s 则vm??464?L?64?4?10?920?1000Re?vmd??1.84?0.15?690?2300，符合假设 ?44?103.14?0.152?1.84Q?Avm?vm??0.03?m3s?

44另一种简单计算方法：

假设雷诺数小于2300，有

?d2?p2d2?p0.152?0.965?106vm?R???1.84m/s ?48?L32?L?32?4?10?920?1000Re?vmd??1.84?0.15?690?2300，符合假设

4?10?43.14?0.152?1.84Q?Avm?vm??0.03?m3s?

447．解： vm??d24Q4?0.03??0.425?ms? ?d23.14?0.32Re?λ?vmd??0.425?0.3?1063?2300 ?41.2?1064?0.06 ReLvm2300.4252?hf???0.06???0.06m

d2g0.32?9.819 / 17

8．解： vm?4Q4?0.05??1.02?ms? ?d23.14?0.252Re?vmd??1.02?0.2555?2.5?10?10 ?61.007?10?d?0.0013?0.0052；查莫迪图得λ?0.031

0.25Lvm21001.022?hf???0.031???0.66m

d2g0.252?9.810.3294Q2?60?1.4?ms?v??9．解： m ?d23.14?0.0524??p?L?vm2?h???????

?g?d?2g??2?pL2?6168.610????0.03??6.29?6?0.29 22?vmd1000?1.40.05L?vm2?700?1.132???2.9?3?0.02??6.64m 10．解：?h?????????d?i2g?0.15?2?9.81i?11．解：Re?vmd??vmd??0.25?0.305?1.235??5269?10

1.78?10?5λ?0.3164?0.037 0.25Red4?()211??2?p?L??vm238?4?(d)3 3211?0.396??0.305?0.037?1.23?0.252???5.58Pa380.390.00121200004Q60?60?25?ms? ?12．解：vm??d23.14?d24?解得d=1.3m

10 / 17

Re?vmd??25?1.365?2.07?10?10

1.57?10?5?d?0.0005?0.000385；查莫迪图得λ?0.0155 1.3L?vm2?120?252??h?????????2.5?11?0.0155??921.57m ??d2g1.32?9.81?i??i??p??g?h?1.23?9.81?921.57?11120Pa

pi?pM?pa??p??1.569?1.01325?0.11??105?2.471?105Pa

1750060?60?11.9?ms? 13．解：vm?4Q?2?d3.14?0.7224?Re?vmd??11.9?0.725?5.46?10

0.157?10?4（1）

?d?0.2?0.000278；查莫迪图得λ?0.0147 720Lvm228.611.92?hf???0.0147???4.21m

d2g0.722?9.81（2）

?d?2?0.00278；查莫迪图得λ?0.0265 720Lvm228.611.92?hf???0.0365???7.60m

d2g0.722?9.81第六章习题参考答案（仅限参考）

1．解：Rex???x17?36==3.4?10 ?15?10?6?x?5 Rex5x5?3??8.13?10?3m Rex3.4?106??2．解：Rex???x30.17x5==2?10 ?15?10?611 / 17

x?0.1m

??xcr50?0.96Re?==3?103．解：x

?15?10?6crReL???L50?37==1.0?10 ?6?15?101.292CfL??0.41?10?3

ReL0.074?3CfT??2.95?10

ReL0.2A*??CfT?CfL?Rexcr?7620(若查表，则A*=8700)

Ff?Cf2???2?0.074A*????bl???bl?9.86N ?0.22ReL?2?ReL（查附录1，对应的ρ=1.205kg/m3） 4．解：ReL????L=379.6 ???5?x ????max?5?x?0.128m ???CfL?1.328?0.068 ReL2???Ff?2CfL2bl?1.70N

12 / 17