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

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

Consider steady, incompressible and irrotational flow through a reducer in a horizontal pipe where the diameter is reduced from 20 cm to 10 cm. The pressure in the 20 cm pipe just upstream of the reducer is 150 kPa. The fluid has a vapour pressure of 50 kPa and a specific weight of 5 kN/m3. Neglecting frictional effects, the maximum discharge (in m3/s) that can pass through the reducer without causing cavitation is

  1. 0.05

  2. 0.16

  3. 0.27

  4. 0.38
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Multiple choice

You are asked to evaluate assorted fluid flows for their suitability in a given laboratory application. The following three flow choices, expressed in terms of the two-dimensional velocity fields in the xy-plane, are made available. P. u = 2y, v = - 3x Q. u = 3xy, v = 0 R. u = 2x, v = 2y Which flow(s) should be recommended when the application requires the flow to be incompressible and irrotational?

  1. P and R

  2. Q

  3. Q and R

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

Multiple choice

The velocity profile of a fully developed laminar flow in a straight circular pipe, as shown in the figure, is given by the expression u(r) = -$\frac{R^2}{4 \mu} \Big(\frac{dp}{dx}\Big) \Big(1-\frac{r^2}{R^2}\Big)$, where $\frac{dp}{dx}$ is a constant. The average velocity of fluid in the pipe is
  1. -$\frac{R^2}{8 \mu} \Big(\frac{dp}{dx}\Big)$
  2. -$\frac{R^2}{4 \mu} \Big(\frac{dp}{dx}\Big)$
  3. -$\frac{R^2}{2 \mu} \Big(\frac{dp}{dx}\Big)$
  4. -$\frac{R^2}{\mu} \Big(\frac{dp}{dx}\Big)$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Multiple choice

Water, having a density of 1000 kg/m3, issues from a nozzle with a velocity of 10 m/s and the jet strikes a bucket mounted on a Pelton wheel. The wheel rotates at 10 rad/s. The mean diameter of the wheel is 1 m. The jet is split into two equal streams by the bucket, such that each stream is deflected by 1200, as shown in the figure. Friction in the bucket may be neglected. Magnitude of the torque exerted by the water on the wheel, per unit mass flow rate of the incoming jet, is

  1. 0 (N.m) / (kg/s)

  2. 1.25 (N.m) / (kg/s)

  3. 2.5 (N.m) / (kg/s)

  4. 7.5(N.m) / (kg/s)
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Multiple choice

The gap between a moving circular plate and a stationary surface is being continuously reduced, as the circular plate comes down at a uniform speed V towards the stationary bottom surface, as shown in the figure. In the process, the fluid contained between the two plates flows out radially. The fluid is assumed to be incompressible and in viscid.

The radial velocity vr at any radius r, when the gap width is h, is
  1. $vr=\frac{V_r}{2h}$
  2. $v_r=\frac{V_r}{h}$
  3. $v_r=\frac{2Vh}{r}$
  4. $v_r=\frac{Vh}{r}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation