Flashcards
Chapter 1 Flashcards MAE 331
Cards in this deck (29)
- 1Fluid Mechanics• Broad field of study concerned with the behavior of
liquids and gases at rest or in motion
• Fluid statics – fluid is at rest or moving as solid body
• Fluid dynamics – fluid is in motion - 2What is a fluid?A fluid is a substance that deforms
continuously when subjected to a shear stress,
no matter the magnitude of that shear stress - 3If you continue to apply forcethe
substance will continue to flow and
deform - 4For common solids (e.g. steel)a
shearing force will cause an initial
deformation (usually very small), but will
not continuously deform - 5Fluid Classification ContinuumNewtonian, Non-Newtonian
Gas, liquid
Steady, unsteady
Viscous, inviscid
Compressible,
incompressible
Laminar, turbulent - 6Fluid Classification Method of AnalysisTheoretical
Experimental
Computational - 7Continuum• We treat the fluid as a continuum
We assume that all the fluid characteristics
we are interested in vary continuously
throughout the fluid; e.g. pressure,
density, velocity, etc. - 8We look at fluid in amacroscopic rather
than microscopic sense; in general, the
fluid in the pipe is moving from left to right
– “the average” - 9Microscopic viewmolecules are moving
in random directions - 10Densityp"rho"= M/L^3
- 11VelocityV=L/T
- 12ForceF = M(L/T^2)
- 13PressureP = F/L^2 = (M/LT^2)
- 14VISCOSITYM/LT
- 15• °R =°F + 459.67
- 16• K =°C+ 273.15
- 17Fluid Properties Density:greek symbol “rho” – p – mass/volume
slug/ft^3
kg/m^3 - 18Fluid Properties Specific Weight:Greek symbol “gamma” – y –
weight/volume
y= rho "p" * g
units lb/ft^3
N/m^3 - 19Fluid Properties: Specific Gravity – SG –Dimensionless quantity that
quickly shows if a fluid is less dense or more dense than water
SG = p/p water y/y water = 1 - 20Ideal Gas Law P = pRT• P = absolute pressure, T = absolute temperature, R = gas constant, p = density
- 21Pressure FormulaPabs = Patm + Pgage
Patm = 14.7 psia
Pgage = Pabs - Patm - 22ViscosityGreek symbol
“mu”: - 23“no-slip” condition• Fluid in contact with the plate “sticks” to the plate
- 24Fluids for which the shearing stress is linearly related to the rate of shearing strain (du/dy) are designatedNewtonian fluids
- 25Shear thinninge.g. latex paint
- 26Shear thickeninge.g. bullet proof vest
- 27• Inviscid/Viscous Flow• Inviscid fluid is one in which µ = 0 (never strictly true)
• Effect of viscosity is sometimes negligible for certain types of engineering applications
• If you cannot make inviscid assumption, the fluid is viscous - 28Compressible & Incompressible Flow• All fluids are compressible to some level
• But many fluids can be assumed incompressible
• Most liquids – good assumption as incompressible
• Incompressible – r is constant in time and space;
density does not change with pressure
• For majority of course we assume incompressible
• For gases (i.e. air) we use Mach number (M) to
determine whether we can assume
incompressible - 29Mach number (M)M=v/a
a = sqrt(yRT)