Fluid Mechanics (381-400)

Updated: Apr 23, 2020

381. Flow of air can be considered to be incompressible within 1% error if the

Mach Number of flow is less than 0.2


Newtonian -Water Ideal Plastic -Oil paint Thyxotropic -Printer's ink Pseudo plastic -Blood

383. In order that a droplet of water at 20°C (σ=0.0728 N/m) has an internal pressure 1kPa greater than that outside it, its diameter should be nearly

0.3 mm

384. Glycerine (specific weight 1260 kg/m³ dynamic viscosity 8.00 x 10⁻² kg-sec/m²) is spread freely to a thickness of 1 mm between a bottom stationary plate and a top moveable plate of 10 cm area. The top plate is to be moved at a uniform

speed of 1 m/s. The force to be exerted on the top plate is 0.08 kg

385.Fluid Properties

1. The variation of kinematic viscosity between liquids and gases is much

less than the variation of dynamic viscosity.

2. Surface energy is caused by relative forces of cohesion and adhesion

between the fluids

3. Bulk modulus of water is 3,00,000 units and that of gas is 15 units. This

indicates that gas is 20,000 times more compressible than water

386. Consider the following statements relating hydrostatic forces on submerged


1. The pressure centre is always below the centroid of any plane submerged

surface that is not horizontal.

2. Total force on a curved surface is the product of the average force and the

submerged area.

3. The vertical component of force on a body completely submerged in a

static reservoir of fluid is equal to the weight of the fluid displaced by the



Force developed in a pipe bend-Momentum Equation Pitot static tube -Energy Equation Flow through smaller passage produces higher velocity-Continuity Equation Vortex flow-Moment of momentum


Cavitation-Fluid pressure reduces to vapour pressure limit Seperation- Adverse pressure gradient in widening boundaries of flow Stagnation point-Absence of fluid velocity wake-Bluff body in flow


1.In free vortex flow, the flow velocity is in tangential direction only and

varies inversely as the distance from the origin.

2. In a free vortex, flow is rotational at the core and irrotational away from it.

3. In a forced vortex, flow is rotational, that is, fluid particles undergo rotation

about their mass centre.


1. In a source, equipotential lines are


2. Flownet is a representation of 2-dimensional irrotational flow of

incompressible fluid.

3. In uniform flow region, streamlines will be parallel and equidistant.


Reynolds Number-Viscous force Froude number-Gravity force Weber number-Surface energy force Mach number-Elastic force


a) In the study of flow between two fixed parallel plates, the flow is

assumed two dimensional.

b) Velocity distribution for laminar flow between two parallel plates shows

that velocity varies directly with pressure gradient.

c) In case of flow between parallel plates, variation of shear is linear


a) Water hammer occurs in a situation when there is unsteady flow in a pipe.

c) Propagation of high pressure through elastic media gives rise to water


d) For water hammer to develop, the valve at the end of a pipeline must be

fully closed.

394. Which one of the following pairs of types of flow and situations correctly matched ?

a) Non-uniform flow...velocity changes magnitude with distance

b) Steady flow ... velocity does not change with time

c) Tranquil flow ... Froude number of flow is less than

395. For a circular channel (with r as the radius of the channel) to be efficient

depth of maximum velocity must be 1.62 r

396. The loss of energy in a hydraulic jump formed in a rectangular channel is given by (Symbols have the usual meanings)


a) Specific energy is the total energy above the floor of an open channel.

b) For a given specific energy, two depths exist and these are called

alternate depths.

c) Critical velocity occurs at Froude number =1.

398. Which one of the following pairs of situations and types of water surface

profiles is correctly matched ?

a) Mild slope; flow over free overall :M

c) Critical slope; flow downstream of a sluice gate: C

d) Critical slope; flow behind an overflow weir : C


M₂-Convex downwards;upstream asympototic to normal depth with depth decreasing in d/s direction S₁-Convex.upwards and depth increasing in flow direction asymptotic to NDL at d/s end C₁-Convex upwards;asymptotic to horizontal at d/s end; depth increasing with d/s A₃-Depth increasing downstream and meeting at an angle to CDL; a curve with an inflexion point

400. Consider the following fluids:

1. Blood

2. Molasses

3. Slurry of clay in water

Among these, non-Newtonian fluids would include

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