Fluid Dynamics Flashcards
What is a fluid ?
Something that flows; a substance that constantly deforms under shear stress, no matter how small
Examples of fluids
Liquids / gasses / plasmas
Density equation
Volume (kgm^-3) = mass / unit volume
p = m / V
What is the density of pure water ?
1000 kgm^-3 at 4 °C
What is relative density ?
The ratio of the density of a substance to the density of a given reference material.
Relative density equation for solids
RD = density of substance at 20°C / density of water at 4°C (1000kgm^-3)
Relative density equation for gases
RD = density of substance at 20°C / density of dry air (1.00)
Pressure definition
When a force acts perpendicular to a surface, the pressure exerted is the ratio between the magnitude of the force and the area of the surface
Pressure equation
Pressure = Force / Area
P = F / A
1 Pa = 1 N/m^2
Pressure unit conversions
1 bar = 10^5 Pa
1 atm = 1013.25 millibars , 14.69 psi = 260 mmHg
Absolute pressure equation
Absolute Pressure = gauge pressure + atmospheric pressure
What is a barometer ?
A pressure gauge that measures the pressure of the atmosphere itself
What do pressure gauges measure?
The difference between an unknown pressure and atmospheric pressure.
How does Pressure act in a fluid container? (2)
The forces that a fluid exerts into the walls of a container, and those that the wall exerts on the fluid, always act perpendicular to the walls.
And
The force exerted by the fluid is the same at all points at a given depth.
What is Archimedes principle ?
An object immersed in fluid is acted upon by an upward force that arises because pressures in a fluid increase with depth.
(Upward force on the bottom is larger than the downward force on the top).
What is buoyant force?
The difference between the upward force from the bottom and the downward force on the top of an object immersed in a fluid.
What is the buoyant force equal to?
The buoyant force is equal to the volume of the fluid displaced.
What does upthrust (upward force) equal?
The weight of the water displaced.
What is Streamline flow?
The direction of motion of individual particles is the same as that of the fluid as a whole.
Each particle of the fluid that passes a point follows the same path as those particles which passed the point before.
What is laminar flow?
Streamlined flow in which the fluid moves in layers without fluctuations or turbulence.
What is turbulent flow?
Characterised by the presence of irregular whirls and Eddies; it occurs at high velocities and when the fluids path changes direction sharply (an obstruction).
Viscosity definition
An internal friction that prevents adjacent layers of the fluid from sliding freely past each other when subjected to shear stress.
As the temp of a liquid increases, Viscosity …..
Decreases.
As the temp of a gas increases, viscosity….
Increases.