Fluid mechanics

shear force definition

a force tangential to a surface

What properties can be represented by a scalar field?

Scalar quantities which are not uniform but are continuously distributed

What is a steady field?

Property doesn't change with time

What is an unsteady field?

Property changes with time

What properties can be represented by a vector field?

Any vector quantity

what makes a vector field 3D?

It has x,y,z components

What do i,j,k represent in a vector field?

The components within each vector component

Streamline definition

A line to which the velocity vector is tangent at all points at a certain time instant

What do constant streamlines represent?

A steady flow

What is a streamtube?

An imaginary tube formed by streamlines

What forces are always present in fluids?

Gravity, pressure force, viscous force

What is a pathline?

The actual path followed by a fluid element

How are streamlines found using a velocity field?

dy/dx=v/u

How are pathlines found using a velocity field?

Solve differential equations with respect for t for each component

What are streaklines?

Lines obtained by joining elements that passed from the same point

What type of flow is needed for pathlines, streaklines and streamlines to coincide?

A steady flow

Examples of body forces

Gravitational force, electromagnetic force

What is a surface force?

A force distributed over a surface

What components can local stress be broken into?

Normal stress and shear stress

What is pressure in the continuum point of view?

The normal force per unit area on an imaginary surface of an infinitesimally small element of fluid surrounding that point

For a continuum point of view, what causes the viscous force?

Layers of the fluid move with different velocities relative to each other, causing continuous deformation which develops the viscous force

When does the viscous force appear?

During flow

What condition do fluids subjected to the viscous force obey?

No-slip condition

Inviscid flow definition

Flow with zero viscosity

Incompressible flow definition

Density doesn't vary with pressure

Compressible flow definition

Density varies considerably with pressure

Laminar flow definition

Ordered flow, one time scale

Turbulent definition

Chaotic flow, many time scales

Internal flow definition

Completely surrounded by boundaries

Archimedes principle

The magnitude of the buoyancy force is equal to the weight of the displaced fluid

reynolds theorem

The rate of change of a quantity in the system is equal to the rate of accumulation of the quantity in the control volume plus the net flow rate of the quantity out of the control volume.

What are the assumptions in the Bernoulli equation?

Steady flow, inviscid flow, constant density, points of application lie of the same streamline

What is the stagnation point?

All kinetic energy has been converted to pressure energy

What makes a physical phenomena unstable?

When their behaviour is disrupted by small disturbances, they don't settle in an orderly state

What does a greater Reynolds number mean?

It's easier for flow to become turbulent

What is the Reynolds number a measure of?

The importance of inertial forces versus that of viscous forces

What does it mean if inertial forces> viscous forces?

Turbulent flow

What does it mean if inertial forces< viscous forces?

Laminar flow

What components result in minor losses?

Inlets and exits, enlargements and contractions, pipe bends, valves and fittings

Assumptions of the pipe flow energy equation

Steady flow, adiabatic flow, incompressible flow, one inlet and one outlet with uniform properties at each of them

what is a fully developed internal flow (Poiseuille flow)?

one which has a constant velocity profile

pump head definition

The mechanical energy added to the fluid by the pump per unit mass of fluid