Physics

Fluid Mechanics and Hydraulics

376 Questions

Fluid mechanics and hydraulics questions address the principles of fluid flow, pipe resistance, and open channel dynamics. The topics include Bernoulli equation, Navier-Stokes equation, and hydrograph calculations. These concepts are crucial for civil and mechanical engineering competitive examinations.

Fluid flow equationsOpen channel flowPipe frictionHydraulic jumpHydrograph analysis

Fluid Mechanics and Hydraulics Questions

Multiple choice

A single pipe of length 1500 m and diameter 60 cm connects two reservoirs having a difference of 20 m in their water levels. The pipe is to be replaced by two pipes of the same length and equal diameter d to convey 25% more discharge under the same head loss. If the friction factor is assumed to be the same for all the pipes, the value of d is approximately equal to which of the following options?

  1. 37.5 cm

  2. 40.0 cm

  3. 45.0 cm

  4. 50.0 cm
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

 

Multiple choice

Directions: The ordinates of a 2-h unit hydrograph at 1 hour intervals starting from time t = 0, are 0, 3, 8, 6, 3, 2 and 0 m3/s. Use trapezoidal rule for numerical integration, if required.

What is the catchment area represented by the unit hydrograph?

  1. 1.00 km2

  2. 2.00 km2

  3. 7.92 km2

  4. 8.64 km2
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The volume of the unit hydrograph is the area under the hydrograph curve. Using the trapezoidal rule: Volume = (1/2) * [ (0+0) + 2*(3+8+6+3+2) ] * (1 hour * 3600 s/h) = 22 * 3600 = 79200 m^3. Since it is a unit hydrograph (1 cm of runoff), Area = Volume / Depth = 79200 m^3 / 0.01 m = 7,920,000 m^2 = 7.92 km^2.

Multiple choice

Match the following:

 
Equation Physical interpretation
(P) $\triangledown \times \bar{V}$ = 0 (I) Incompressible continuity equation
(Q) $\triangledown. \bar{V}$ = 0 (II) Steady flow
(R) $\frac{D\bar{v}}{Dt}=0$ (III) Irrotational flow
(S) $\frac{a\bar{V}}{at}=0$ (IV) Zero acceleration of fluid particle

  1. P - IV, Q - I, R - II, S - III

  2. P - IV, Q - III, R - I, S - II

  3. P - III, Q - I, R - IV, S - II

  4. P - III, Q - I, R - II, S - IV
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Multiple choice

A mild-sloped channel is followed by a steep-sloped channel. The profiles of gradually varied flow in the channel are

  1. M3, S2

  2. M3, S3

  3. M2, S1

  4. M2, S2
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

 In the mild sloped channel $y_n > y > Y_c$ and steep sloped channel $y_n < y < y_c$ in the flow condition for smooth transition of flow from mild sloped channel to steep sloped channel. Profile formed in mild sloped channel $M_2$ and in steep sloped channel is $S_2$. $$\\$$ Note:- $Y_c$ remains constant for the given discharge and width of the channel

Multiple choice

The flow in a rectangular channel is subcritical. If width of the channel is reduced at a certain section, the water surface under no-choke condition will

  1. drop at a downstream section

  2. rise at a downstream section

  3. rise at a upstream section

  4. not undergo any change
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In a subcritical flow, the flow is controlled by downstream conditions. Reducing the width (a constriction) increases the velocity and decreases the depth at the constriction. To maintain the subcritical state, the water surface drops at the constriction and downstream.

Multiple choice

For a rectangular channel section, Group I lists geometrical elements and Group II gives proportions for hydraulically efficient section.

   
Group I Group II
       
P Top width 1 $\dfrac{y_e}{2}$
Q Perimeter 2 $y_e$
R Hydraulic Radius 3 $2y_e$
S Hydraulic Depth 4 $4y_e$

ye is the follow depth corresponding to hydraulically efficient section. The correct match of Group I with Group II is

  1. P - 2, Q - 4, R - 1, S - 3

  2. P - 3, Q - 1, R - 4, S - 2

  3. P - 3, Q - 4, R - 1, S - 2

  4. P - 3, Q - 4, R - 2, S - 1
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

 

Multiple choice

Directions: Carry One Mark Each.

Couette flow is characterized by

  1. steady, incompressible, laminar flow through a straight circular pipe

  2. fully developed turbulent flow through a straight circular pipe

  3. steady, incompressible, laminar flow between two fixed parallel plates

  4. steady, incompressible, laminar flow between one fixed plate and the other moving with a constant velocity
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Couette flow: In fluid dynamics, Couette flow is the laminar flow of a viscous fluid in the space between two parallel plates, one of which is moving relative to the other. The flow is driven by virtue of viscous drag force acting on the fluid and the applied pressure gradient parallel to the plates.

Multiple choice

Directions: Carry One Mark Each.

Three parallel pipes connected at the two ends have flow-rates Q1, Q2 and Q3, and the corresponding frictional head losses are hL1, hL2 and hL3, respectively. The correct expressions for total flow rate (Q) and frictional head loss across the two ends (hL) are

  1. Q = Q1 + Q2 + Q3; hL = hL1 + hL2 + hL3

  2. Q = Q1 + Q2 + Q3; hL = hL1 = hL2 = hL3

  3. Q = Q1 = Q2 = Q3; hL = hL1 + hL2 + hL3

  4. Q = Q1 = Q2 = Q3; hL = hL1 = hL2 = hL3
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation