Fluid Mechanics II 2010 (2006 Ad).pdf - DSpace at CUSAT

BTS (C) — IV — 10 — 015 F
B. Tech Degree IV Semester Examination, April 2010
Time : 3 Hours
Cusat Digital Library Service http://dspace.cusat.ac.in/
CE 405 A/B FLUID MECHANICS H
(2006 Scheme)
PART - A
(Answer ALL questions)
I. (a) Compare specific energy curve and specific force curve.
State the conditions under which the rectangular section of an open channel
will be most economical. Derive these conditions.
Distinguish between backwater curve and draw down curves. Give examples
for each.
Sketch the jump position on a stilling basin for various tail water conditions.
Prove that the maximum efficiency of a jet impinging on a series of moving
flat plates is 50%.
(t) How can the best performance curve be obtained with the help of characteristic
curves of a reaction turbine?
Discuss few methods adopted to increase the efficiency of centrifugal pumps by
altering the shape of the casing.
Discuss the condition under which negative slip occurs in reciprocating pumps.
PART — B
Maximum Marks : 100
II. (a) In a rectangular channel 3.5 m wide laid at a slope of 0.0036, uniform flow occurs
at a depth of 2 m. Find how high can the hump be raised without causing afflux.
If the upstream depth of flow is to be raised to 2.5 m, what should be the height
of the hump? Take Manning's n equal to 0.015.
(8 x 5 = 40)
(4 x 15 = 60)
(b) Water flows in a channel of the shape of isosceles triangle of bed width 'a' and
sides making an angle of 45° with the bed. Determine the relations between depth
of flow 'd' and bed width 'a' for maximum velocity condition and for maximum
discharge condition. Use Manning's formula and note that 'd' is less than 0.5 a.
OR
(8)
III. (a) A flow of 100 litres per second flows down in rectangular laboratory flume of width
0.6 m and having adjustable bottom slope. If Chezy's C is 56 determine the bottom
slope necessary for uniform flow with a depth of flow 0.3 m. Also fmd the conveyance
and state of flow (ie. tranquil or rapid).
(7)
(b)
A trapezoidal channel has a bed width 10 m and side slopes of 2 horizontal to 1 vertical.
at a section 200 m downstream the bed rises by 0.08 m gradually, bed width increases
to 0.15 m and side slopes become 3 horizontal to 1 vertical. Rise in bed level, increase
in bed width and flattening of side slopes are gradual. Flow rate in the channel is
200 m3 /s and the flow depth at the upstream section is 7 m. If Manning's n = 0.035,
estimate the depth at the downstream section.
(8)
(Turn Over)
(7)

IV. (a) State and discuss the assumptions made in the derivation of the dynamic equation for
gradually varied flow starting from first principles derive equation for the slope of the
coater surface in gradually varied flow with respect to (i) channel bed (ii) horizontal.
(b) Show that the gradually varied flow equation for flow in a rectangular channel of variable
width B may be expressed as
Qty dB
dY S - +(j
dx
dx
1
n2 B
gie
(a)
OR
Show that the head loss in a hydraulic jump formed in a rectangular channel
VII.
(b)
(vi —V2)3
may be expressed as AE =
2 g(V, - V2).
2
A horizontal rectangular channel 3 m wide and 2 m water depth conveys water at
18 m3/s. If the flow rate is reduced to 2/3 of it's original value, compute the magnitude
and speed of the upstream surge. Assume that the front of the surge is rectangular and
friction in the channel is neglected.
(a) Explain with sketches the working of an oil pressure governor. (7)
(b) Show from the first principles that the peripheral coefficient of a pelton wheel is 0.5. (8)
OR
Show that in a turbine with radial vanes at inlet and outlet and operating under head 'h',
if the velocity of flow at outlet is C times that at inlet, the peripheral velocity `u' and the
hydraulic efficiency 'Rh' are given by
2gh 2
u
-
2 + c 2 tan 2 a ' 2 + c 2 tan2 a
where a is guide de blade angle
Assuming that the radial component of flow of fluid through a centrifugal pump
remains constant and that the fluid enters radially, prove that the ratio of the pressure
head Hp to the velocity head Hv created by an impeller neglecting the losses is given
by Hp ((II—VAcot Pi , where U1 is the speed of impeller at outlet, Vf,
Hv U, +Vf, cot 13
is the veloety of flow and /3 is the exit angle of impeller blades. Hence show that
, — Vf, cot p)
ideal efficiency of the impeller is given by ri =(U.
2U,
OR
Working from the first principles show that, in a single acting reciprocating pump
the work done against pipe friction, if large air vessels are fitted near to the cylinder
on both suction and delivery pipes, compared with that done if there are no air vessels
is (%2 g2).
***
(15)
(15)
(15)