A Brief Introductionto

Fl id M h i (CE 251)Fluid Mechanics (CE 251)

Fall 2012Fall 2012Prof. Brandes

What is a Fluid?

Solid BehaviorSolid Behavior(ES 230)

G h d l

G = shear modulus

fluid behavior → infinite strain

Fluid Behavior

= viscosity (resistance to flow) = viscosity (resistance to flow)

d/dt the Rate of angular def

– So, a fluid is a substance that deforms without bound when subjected to shear i e it “flows” : bound when subjected to shear, i.e. it flows : water, air, honey, beer, etc

li i f fl id h iApplications of fluid mechanics water supply, pipelines,

conveyance systems

stormwater management

hydromachinery (pumps, turbines, propellers)

flood waves, groundwater

weather prediction, windpower, aerodynamics

medicine

i l li iA practical application:

on to some important concepts in Chapter 1 concepts in Chapter 1

THE FLUID AS A CONTINUUM – We don’t care too much what the individual

molecules are up to, we’ll look at lots of pthem together – thus, the fluid as a CONTINUOUS medium

DIMENSIONS “Dimensional Homogeneity”

– Equations derived from fundamental principles Equations derived from fundamental principles of math and physics must have the same dimensions (M, L, t, T) on both sides of the =

constantVzp

2constant

gz

2

LLfC

Re1520

)Re06.0(ln523.0

2 ??LL )(

DIMENSIONS

UNITS1. Don’t switch units (e.g., English to SI)2. Carry units through calculations, don’t add y g

what you think the units should be at the end

EX: a 55-gal drum of water weighs what?

lbsft3 lbsftlbsx

galftxgal 8.4584.6248.7

55 3

3. Check your units at the end to see that they make sense!make sense!

C ts f Fl id M h i sComponents of Fluid Mechanics1) Hydrostatics – distributed loads on submerged 1) Hydrostatics – distributed loads on submerged

objects due to static water pressures

2) Hydrodynamics - theoretical, mathematical equations of fluid flow– theorists: Newton , Bernoulli

3) Hydraulics - empirical (experimental) 3) Hydraulics empirical (experimental) measurements of fluids, fitted to mathematical functions

i t li t D Vi i R ld Nik d F d– experimentalists: Da Vinci, Reynolds, Nikuradse, Froude