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

Direction: One hour triangular unit hydrograph of a watershed has the peak discharge of 60 m3/sec.cm at 10 hours and time base of 30 hours. The $\phi$ index is 0.4 cm per hour and base flow is 15 m3m/sec.

The catchment area of the watershed is

  1. 3.24 km2

  2. 32.4 km2

  3. 324 km2

  4. 3240 km2
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Peak discharge of unit hydrograph = 60 m^3/s. Time base = 30 hours. Area under triangular hydrograph = 0.5 * base * height = 0.5 * 30 * 3600 * 60 = 3,240,000 m^3. Since it is a 1 cm unit hydrograph, 1 cm = 0.01 m. Area = Volume / Depth = 3,240,000 / 0.01 = 324,000,000 m^2 = 324 km^2.

Multiple choice

Direction: One hour triangular unit hydrograph of a watershed has the peak discharge of 60 m3/sec.cm at 10 hours and time base of 30 hours. The $\phi$ index is 0.4 cm per hour and base flow is 15 m3m/sec.

If there is rainfall of 5.4 cm in 1 hour, the ordinate of the flood hydrograph at 15th hour is

  1. 225 m3/sec

  2. 240 m3/sec

  3. 249 m3/sec

  4. 258 m3/sec
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Effective rainfall = 5.4 - (0.4 * 1) = 5.0 cm. The ordinate of the flood hydrograph = (Effective Rainfall * Unit Hydrograph Ordinate) + Base Flow. At 15 hours, the UH ordinate is calculated by linear interpolation: at 10h it is 60, at 30h it is 0. So at 15h, it is 60 * (30-15)/(30-10) = 60 * 15/20 = 45. Flood hydrograph = (5 * 45) + 15 = 225 + 15 = 240 m^3/s.

Multiple choice

Consider the turbulent flow of a fluid through a circular pipe of diameter, D. Identify the correct pair of statements.

I. The fluid is well-mixed. II. The fluid is unmixed. III. ReD < 2300 IV. ReD < 2300

  1. I, III

  2. II, IV

  3. II, III

  4. I, IV
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

For flow through a circular pipe, the flow will be _____. (A) Leminar flow Reynolds no. (Re) < 2300 Fluid flow is unmixed. (B) Turbulent flow Reynolds no. (Re) > 2300 Fluid flow is mixed.

Multiple choice

Kaplan water turbine is commonly used when the flow through its runner is

  1. axial and the head available is more than 100 m

  2. axial and the head available is less than 10 m

  3. radial and the head available is more than 100 m

  4. mixed and the head available is about 50 m
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Kaplan water turbine is a kind of reaction turbine in which axial flow took place & it is used where head available is less than 10 m.

Multiple choice

Consider the following statements regarding streamline(s):

(i) It is a continuous lines such that the tangent at any point on it shows the velocity vector at the point. (ii) There is no flow across streamlines. (iii) $\frac{dx}{u}$ = $\frac{dv}{v}$ = $\frac{dz}{w}$ is the differential equation of a streamline, where u, v and w velocities in directions x, y and z, respectively. (iv) In an unsteady flow, the path of a particle is a streamline.

Which one of the following combinations of the statements is true?

  1. (i), (ii), (iv)

  2. (ii), (iii), (iv)

  3. (i), (iii), (iv)

  4. (i), (ii), (iii)
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Stream lines: Stream lines are the Family of curves that are instantaneously tangent to the velocity vector of the flow. These shows the direction a fluid element will travel in at any point. Path lines: - Path lines are the trajectories that individual fluid particles follow.

Multiple choice

A large tank with a nozzle attached contains three immiscible, in viscid fluids as shown. Assuming that the changes in h1, h2 and h3 are negligible, the instantaneous discharge velocity is
  1. $\sqrt{2gh_3 \Big( 1+ \frac{\rho_1h_1}{\rho_3h_3}+\frac{\rho_2h_2}{\rho_3h_3}\Big)}$
  2. $\sqrt{2g(h_1 + h_2 + h_3)}$
  3. $\sqrt{2gh_3 \Big(\frac{\rho_1h_1 + \rho_2h_2 + \rho_3h_3}{\rho_1 + \rho_2 + \rho_3}\Big)}$
  4. $\sqrt{2g \Big(\frac{\rho_1h_2h_3 + \rho_2h_3h_1+\rho_3h_1h_2}{\rho_1h_1 + \rho_2h_2 + \rho_3h_3}\Big)}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$= \sqrt{2g \times \Big[\frac{\rho_1 h_1}{\rho_3} + \frac{\rho_2h_2}{\rho_3} + h_3 \Big]}\\ = \sqrt{2gh_3 \times \Big[\frac{\rho_1 h_1}{\rho_3h_3} + \frac{\rho_2h_2}{\rho_3h_3}\Big]}$

Multiple choice

Biot number signifies the ratio of

  1. convective resistance in the fluid to conductive resistance in the solid

  2. conductive resistance in the solid to convective resistance in the fluid

  3. inertia force to viscous force in the fluid

  4. buoyancy force to viscous force in the fluid
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Multiple choice

Consider a two-dimensional laminar flow over a long cylinder as shown in the figure below.

The free stream velocity is $U\omega$ and the free stream temperature $T\omega$ is lower than the cylinder surface temperature Ts. The local heat transfer coefficient is minimum at point

  1. 1

  2. 2

  3. 3

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

In laminar flow, the heat transfer coefficient is minimum where the thickness of boundry layer is maximum. The heat transfer coefficient is maximum where the thickness is minimum. For turbulent-region thickness of boundry layer is maximum at 3. For laminar region thickness of boundry layer is maximum at 2 so it will have minimum local heat transfer coefficient.