Physics

Fluid Mechanics and Hydraulics

361 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

An isolated 4-hour storm occurred over a catchment as follows:

Time 1st hour 2nd hour 3rd hour 4th hour
Rainfall (mm) 9 28 12 7

The$\phi$ index for the catchment is 10 mm/h. The estimated runoff depth from the catchment due to the above storm is

  1. 10 mm

  2. 16 mm

  3. 20 mm

  4. 23 mm
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Total rainfall = 9 + 28 + 12 + 7 = 56 mm. Phi index = 10 mm/h. Runoff occurs when rainfall > phi. Hours 1, 2, 3, 4 have rainfall 9, 28, 12, 7. Rainfall > 10 occurs in hours 2 (28-10=18) and 3 (12-10=2). Total runoff = 18 + 2 = 20 mm.

Multiple choice

A rectangular open channel needs to be designed to carry a flow of 2.0 m3/s under uniform flow conditions. The Manning’s roughness coefficient is 0.018. The channel should be such that the flow depth is equal to half the width and the Froude number is equal to 0.5.

Keeping the width, flow depth and roughness the same, if the bed slope of the above channel is doubled, the average, boundary shear stress under uniform flow conditions is

  1. 5.6 N/m2

  2. 10.8 N/m2

  3. 12.3 N/m2

  4. 17.2 N/m2
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

 $\tau = \omega RS_0, \text{Now}, S_0 = 0.0042\\ R = y/2 = \frac{0.836}{2} = 0.418 \\ \therefore \tau = 9810 \times 0.418 /times 0.0042 \\ \hspace{0.8cm} = 17.22 N/m^2$

Multiple choice

A plain sedimentation tank with a length of 20 m, width of 10 m and a depth of 3 m is used in a water treatment plant to treat 4 million litres of water per day (4 MLD). The average temperature of water is 20°C. The dynamic viscosity of water is 1.002 x 10–3 N.s/m2 at 20° C. Density of water is 998.2 kg/M3. Average specific gravity of particles is 2.65.

What is the minimum diameter of the particle which can be removed with 100% efficiency in the above sedimentation tank?

  1. 11.8 x 10–3 mm

  2. 16.0 x 10–3 mm

  3. 50 x 10–3 mm

  4. 58 x 10–3 mm
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

 

Multiple choice

A flood wave with a known inflow hydrograph is routed through a large reservoir. The outflow hydrograph will have

  1. attenuated peak with reduced time-base

  2. attenuated peak with increased time-base

  3. increased peak with increased time-base

  4. increased peak with reduced time-base
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

 Main function of any reservoir in the flood routing is to reduce the peak and increase the time base so that there will be less damage on the downstream of flow.

Multiple choice

Water emerges from an ogee spillway with velocity = 13.72 m/s and depth = 0.3 m at its toe. The tail water depth required to form a hydraulic jump at the toe is

  1. 6.48 m

  2. 5.24 m

  3. 3.24 m

  4. 2.24 m
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Using the hydraulic jump formula: y2 = (-y1 / 2) + sqrt((y1^2 / 4) + (2 * v1^2 * y1 / g)). Given v1 = 13.72, y1 = 0.3, g = 9.81. Froude number Fr = 13.72 / sqrt(9.81 * 0.3) = 13.72 / 1.716 = 7.99. y2 = 0.3/2 * (sqrt(1 + 8 * 7.99^2) - 1) = 0.15 * (sqrt(1 + 510.7) - 1) = 0.15 * (22.6 - 1) = 3.24 m.