FE Review Course – Fluid

Mechanics

Spring 2012

Frank T.-C. Tsai, Ph.D., P.E.

Dept. of Civil & Environmental Engineering, LSU

ftsai@lsu.edu

(O) 578-4246

Get the handbook!!

• SUPPLIED-REFERENCE HANDBOOK

• 8th edition, 2nd revision, April 2011

Visualize questions

• Draw diagrams

• Annotate diagrams with numbers,

symbols, equations, etc.

• Find right equations from the reference

handbook

• Skip questions if you cannot quickly find

equations from the reference handbook

CoOH

fluid

CoOH

fluidSG

4@24@2

/d

dpEv

vE

c

4 cosh

d

1 mm 4 0.025 1

1000 0.82 9810 d

(Page 62)

Units and Scales of Pressure

Measurement

Standard atmospheric pressure

Local atmospheric pressure

Absolute zero (complete vacuum)

Absolute pressure

Gage pressure

1 atmosphere

101.325 kPa

14.7 psi

10.34 m H20

760 mm Hg

Suction vacuum

(gage pressure) Local

barometer

reading

6894.76 Pa/psi

atmgageabs ppp Absolute pressures are often indicated as psia, and

gage pressure as psig.

Fluid Statics •Pressure vs. elevation

•Manometers

•Force over submerged plane and

curved surfaces

•Buoyancy

Fluid Statics •Pressure vs. elevation

•Manometers

•Force over submerged plane and

curved surfaces

•Buoyancy

(z=0 at water surface and z is negative below surface)

(for gas)

12 Wabove fluid ofweight ,projection verticalon the FFFFF vRh

submergedfluidbuoyancyF "= g

For curved surface, separate the pressure force into horizontal and vertical part. The

horizontal part becomes plane surface and the vertical force becomes weight.

If an object is submerged in several different fluids, must calculate the

buoyancy in each of them, then add together. When using buoyancy in

problems, FBD is often needed.

31 3

12* 0.53

3 12

z

(page 63)

The diameter of the pipe is 0.3 m.

g

Vz

p

2EGL

2

ag

++=z

p+=

gHGL

Pressure head (w.r.t.

reference pressure)

velocity

head

Elevation head (w.r.t.

datum)

Piezometric

head

zg

vp

2

2

zp

EGL: line connecting

(total head line)

HGL: line connecting

(piezometric head line)

Example EGL & HGL

(page 64)

60+20 mph=80mph=117.3 ft/s

W Q h

Turbine :

Dimensionless parameters

Example

If a flow rate of sm /2.0 3 is measured over a 9 to1 scale model of a weir, what flow rate

can be expected on the prototype?

Flow over a weir is an openchannel flow. Use Froude number for modeling.

24332

222

mm

pp

m

p

m

p

m

p

p

p

m

m

lv

lv

Q

Q

l

l

v

v

gl

v

gl

v

If the model force is at 1000N, what will be the force on the prototype?

72993)(

)(22

22

22

2222

m

p

m

p

pmlv

lv

F

F

lv

F

lv

F

(use drag force)

(continuity eq.)

2 2 2F VQ V A V

F

WW Q h h

Q

point ,friction Turbineafter Lh h h h

before Pumpafterh h h