Fluid mechanics

Question 1

What is a fluid?

Answer 1

It is a substance existing as a liquid or a gas

Question 2

How can solids and liquids be distinguished?

Answer 2

They can be distinguished on the substance’s ability to resist an applied shear stress

• a liquid continuously deforms
• a solid can resist applied shear stress by deforming but eventually stops when constant shear stress is applied

Question 3

What is a continuum?

Answer 3

a continuous, homogenous matter with no holes

Question 4

What is the continuum assumption?

Answer 4

the assumption that the fluid properties vary continuously throughout the fluid

Question 5

How are the properties of a fluid defined?

Answer 5

properties such as temperature, density and pressure are taken to be well defined at infinitesimal volume elements

• small in comparison to the length scale of the system
• large in comparison to the molecular length scale

Question 6

What is the definition of density?

Answer 6

It is defined as mass per unit volume

Question 7

What is the definition of specific gravity?

Answer 7

It is defined as the ratio of the density of the fluid to the density of water at some specified temperature

Question 8

What is the definition of specific weight?

Answer 8

It is the gravitational force per unit volume of fluid

Question 9

What is pressure?

Answer 9

It is force per unit area

Question 10

Describe the Lagrangian method

Answer 10

It involves following individual fluid particles and determining how the fluid properties associated with the particles change as a function of time.

Question 11

What is a fluid particle?

Answer 11

It is defined as a body of fluid having finite mass and internal structure but negligible dimensions

Question 12

Describe the Eulerian method

Answer 12

A finite volume is defined through which the fluid flows in and out.
The fluid properties are described by defining the necessary properties(pressure, velocity, density e.t.c) as functions of time and space

Question 13

Define a control volume

Answer 13

A volume in space through whose boundaries matter, mass, momentum and energy can flow

Question 14

Define a streamline

Answer 14

A line drawn on the flow such that it is tangential to the velocity vector at all times.
No flow passes through a streamline.

Question 15

Define stream-tube

Answer 15

A closed surface containing streamlines. No flow crosses the boundary of the stream-tube.

Question 16

Define a path-line

Answer 16

A path traversed by a given fluid particle over time.

Question 17

How can pathlines be determined?

Answer 17

They can be determined experimentally by using a neutrally buoyant tracer particles and taking time exposure photographs

Question 18

Define a streakline

Answer 18

A locus of fluid particles that have passed sequenetially through a prescribed point in the flow.

Question 19

How can streak-lines be generated experimentally?

Answer 19

Continuously injecting tracer fluid(dye in liquid, smoke in gas) at the starting point.