Midterm Prep Flashcards
Define a fluid
A substance that deforms continuously when acted on by a shear stress of any magnitude
How does density change for gases and liquids?
Density changes rapidly with pressure and temperature for gases. They are compressible
Density changes very slowly with pressure and temperature for liquids. They are incompressible.
What is specific gravity?
The ratio of a certain density to the density of water at 4°C.
What is viscosity?
A measure of the stickiness of a fluid
- Higher viscosity will deform more slowly
- A very strong function of temperature, but not pressure
What is the No-Slip boundary condition?
When viscosity causes a fluid to stick to a surface that it is in contact with.
y=0
u (velocity) = 0
What is a Newtonian fluid? Include examples.
The shear stress is proportional to the velocity gradient or the shear strain rate.
Examples: Water, Air, Oil
What is a Non-Newtonian fluid? Include examples.
The shear stress is not proportional to the shear strain rate.
A.K.A Funny Fluids
Examples: Polymers, mud, blood, toothpaste, silly putty
What is the bulk modulus of elasticity?
The ratio of the change in pressure to the fractional change in volume.
- Defines the compressibility of a fluid
Describe surface tension
A result from the attractive forces between liquid molecules at the interface between fluids (most significantly at a gas-liquid interface)
- A function of temperature but not pressure
Define vapour pressure
The pressure in a container with both vapour and liquid molecules when an equilibrium is reached.
- A strong function of temperature
When does vapourization occur? When does boiling occur?
Vapourization occurs when the absolute pressure is less than or equal to the vapour pressure.
Boiling occurs when the absolute and vapour pressures are equal.
What are hydrostatic forces?
The forces resulting from a fluid that is at equilibrium.
What is the Lagrangian description for fluid motion?
It follows the motion of individual fluid particles.
- Particle motion is only a function of time
What is the Eulerian description for fluid motion?
It observes fluid flow at a fixed point.
- Flow properties are described as functions of space and time
What is a pathline?
The locus of all points traversed by a specific fluid particle
What is a streakline?
The instantaneous line whose points are occupied by all particles originating from (or passing through) a specified point in the flow field.
What is a streamline?
A line which is everywhere tangential to the velocity vector
What is laminar flow?
When there is no significant mixing of neighbouring fluid particles.
What is turbulent flow?
When there is vigorous mixing of fluid particles
What is Reynold’s number?
A dimensionless parameter which can be used to describe flow and predict if it will be laminar or turbulent.
- Re < Re(crit) -> Laminar
- Re > Re(crit) -> turbulent
For pipe flow:
- Re < 2000 -> Laminar
- Re > 4000 -> Turbulent
What is a stagnation point?
Where the velocity equals zero (flow splits) in a flow field
What assumptions are associated with the Bernoulli Equation?
Flow is:
1. Steady
2. Inviscid
3. Along a Streamline
4. Incompressible (constant density)
What three pressure probes can be used to measure Bernoulli’s Equation?
- Piezometer measures the static pressure (P1)
- Pitot Probe measures the total (stagnation) pressure
- Pitot-Static Probe measures the difference between the total and static pressures (used to determine velocity)
