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

An ideal horizontal flow setting basin is 3 m deep having surface area 900 m2. Water flows at the rate of 8000 m3/d, at water temperature 20oC (m = 10-3 kg/m.s) and p = 1000 kg/m3). Assuming Stokes law to be valid, the proportion (percentage) of spherical sand particles (0.01 mm in diameter with specific gravity 2.65), that will be removed, is

  1. 32.5

  2. 67

  3. 87.5

  4. 95.5
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The removal efficiency is calculated using the ratio of settling velocity to surface overflow rate. The settling velocity is determined by Stokes Law, and the surface overflow rate is the flow rate divided by the surface area. Comparing these values yields the percentage of particles removed.

Multiple choice

A very wide rectangular channel carries a discharge of 8m3/s per m width. The channel has a bed slope of 0.004 and Manning’s roughness coefficient, n = 0.015. At a certain section of the channel, the flow depth is 1 m.

What Gradually Varied Flow profile exists at this section?

  1. M2

  2. M3

  3. S2

  4. S3
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

First, calculate normal depth (yn) using Manning's equation and critical depth (yc). Since the bed slope is steep (S0 > Sc) and the actual depth is less than normal depth, the flow profile is S3.

Multiple choice

A very wide rectangular channel carries a discharge of 8 m3/s per m width. The channel has a bed slope of 0.004 and Manning’s roughness coefficient, n = 0.015. At a certain section of the channel, the flow depth is 1 m.

At what distance from this section the flow depth will be 0.9 m? (Use the direct step method employing a single step)

  1. 65 m downstream

  2. 50 m downstream

  3. 55 m downstream

  4. 60 m downstream
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Using the direct step method for GVF, the distance is calculated by delta_x = (E2 - E1) / (S0 - Sf_avg). Calculating the specific energy at depths 1 m and 0.9 m and the average friction slope leads to 50 m.

Multiple choice

A pipeline (diameter 0.3 m, length 3 km) carries water from point P to point R (see figure). The piezometric heads at P and R are to be maintained at 100 m and 80 m, respectively. To increase the discharge, a second pipe is added in parallel to the existing pipe from Q to R. The length of the additional pipe is also 2 km. Assume the friction factor, f = 0.04 for all pipes and ignore minor losses.

What is the increase in discharge if the additional pipe has same diameter (0.3 m)?

  1. 0%

  2. 33%

  3. 41%

  4. 67%
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice

A pipeline (diameter 0.3 m, length 3 km) carries water from point P to point R (see figure). The piezometric heads at P and R are to be maintained at 100 m and 80 m, respectively. To increase the discharge, a second pipe is added in parallel to the existing pipe from Q to R. The length of the additional pipe is also 2 km. Assume the friction factor, f = 0.04 for all pipes and ignore minor losses.

If there is no restriction on the diameter of the additional pipe, what would be the maximum increase in discharge theoretically possible from this arrangement?

  1. 0%

  2. 50%

  3. 67%

  4. 73%
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice

An average rainfall of 16 cm occurs over a catchment during a period of 12 hours with uniform intensity. The unit hydrograph (unit depth = 1 cm, duration = 6 hours) of the catchment rises linearly from 0 to 30 cumecs in six hours and then falls linearly from 30 to 0 cumecs in the next 12 hours. $\psi$index of the catchment is known to be 0.5 cm/hr. Base flow in the river is known to be 5 cumecs.

Peak discharge of the resulting direct runoff hydrograph shall be

  1. 150 cumecs

  2. 225 cumecs

  3. 230 cumecs

  4. 360 cumecs
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

 

Multiple choice

An average rainfall of 16 cm occurs over a catchment during a period of 12 hours with uniform intensity. The unit hydrograph (unit depth = 1 cm, duration = 6 hours) of the catchment rises linearly from 0 to 30 cumecs in six hours and then falls linearly from 30 to 0 cumecs in the next 12 hours. $\psi$index of the catchment is known to be 0.5 cm/hr. Base flow in the river is known to be 5 cumecs.

Area of the catchment in hectares is

  1. 97.20

  2. 270

  3. 9720

  4. 2700
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

 

Multiple choice

Water is pumped from a well tapping an unconfined aquifer at a certain discharge rate and the steady state drawdown (X) in an observation well is monitored. Subsequently, the pumping discharge is doubled and the steady state drawdown in the same observation well is found to be more than double (i.e. more than 2X). This disproportionate drawdown is caused by

  1. well losses

  2. decrease in the saturated thickness of the aquifer

  3. nonlinear flow

  4. delayed gravity yield
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

 

Multiple choice

Direct step method of computation for gradually varied flow is

  1. applicable to non-prismatic channels

  2. applicable to prismatic channels

  3. applicable to both prismatic and non-prismatic channels

  4. not applicable to both prismatic and non-prismatic channels
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

 Direct step method, employs the formula $dx = \frac{\triangle E}{S_0 - S_1}$ and only applicable when, there is no change in the cross-sectional area of channel, i.e., Prismatic channel.

Multiple choice

The depth of flow in an alluvial channel is 1.5 m. If critical velocity ratio is 1.1 and Manning’s n is 0.018, the critical velocity of the channel as per Kennedy’s method is

  1. 0.713 m/s

  2. 0.784 m/s

  3. 0.879 m/s

  4. 1.108 m/s
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

 $y = 1.5m, n = 0.018\\ \text{Critical velocity as per kennedy's equation}\\ \hspace{1.7cm}V = 0.55 my^{0.64}\\ \hspace{2cm} = 6.55 \times 1.1 \times (1.5)^{0.64}\\ \hspace{2cm} = 0.784 m/s$