fully developed turbulent pipe flow class 2 - review
DESCRIPTION
FULLY DEVELOPED TURBULENT PIPE FLOW CLASS 2 - REVIEW. FULLY DEVELOPED , STEADY, NO BODY FORCES , LAMINAR PIPE FLOW. = 0. = 0. = 0. F Sx + F Bx = /t ( cv udVol )+ cs u V d A Eq. (4.17). = (r/2)(dp/dx) Eq 8.13a. = (r/2)(dp/dx). yx = (du/dy)+u’v’ - PowerPoint PPT PresentationTRANSCRIPT
FULLY DEVELOPED TURBULENT PIPE FLOWCLASS 2 - REVIEW
= 0= 0 = 0
FSx + FBx = /t (cvudVol )+ csuVdAEq. (4.17)
FULLY DEVELOPED, STEADY, NO BODY FORCES, LAMINAR PIPE FLOW
V p2p1
w
w
l
CV
= (r/2)(dp/dx)Eq 8.13a
yx = (du/dy)
u = - (R2/4)(dp/dx)x [1 – (r/R)2]
= UC/L[1-(r/R)2]
Q = 0 uldy;V = Q/A
V/UC/L = 1/2
a
= (r/2)(dp/dx)
laminar
yx = (du/dy)+u’v’
uavg = UC/L(1-r/R)1/n
Q = 0 uldy;V = Q/A
V/UC/L = 2n2/(2n+1)(n+1)
a
turbulent
(empirical)
u(r)/Uc/l = (y/R)1/n = ([R-r]/R)1/n = (1-r/R)1/n
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.2 0.4 0.6 0.8 1
r/R
ua
vg
/Uc
l
Laminar Flowu/Uc/l = 1-(r/R)2
n=6-10
u(r)/Uc/l = (y/R)1/n
Eq. 8.30“one of the most important and useful equations
in fluid mechanics” Fox et al.
ENTER ENERGY EQUATION
Allows calculations of capacity of an oil pipe line, what diameter water main to install or pressure drop in
an air duct, ……
V12/ (2) + p1/() + gz1=V2
2/ (2) + p2/() + gz2 + hlT
hlT has units of enery per unit mass [V2]
“one of the most important and useful equations in fluid mechanics” Fox et al.
V12/ (2g) + p1/(g) + z1=V2
2/ (2g) + p2/(g) + z2 + HlT
HlT has units of enery per unit weight [L] from hydraulics during 1800’s
A ½ V(r)2 V(r)dA = (dm/dt) ½ V
2
= [A V(r)3
dA ]/ {(dm/dt) V2}
V12/ (2g) + p1/(g) + z1=V2
2/ (2g) + p2/(g) + z2 + HlT
Turbulent Flow: V(r)/Uc/l = (1-r/R)1/n
Laminar Flow: V(r)/Uc/l = 1 – (r/R)2
= [A V(r)3 dA ]/ {(dm/dt) V2}
= 1 for potential flow = 2 for laminar flow
1 for turbulent flow
V12/ (2g) + p1/(g) + z1=V2
2/ (2g) + p2/(g) + z2 + HlT
= (Uc/l/V)3 2n2 / (3 + n)(3 + 2n)* = 1.08 for n = 6; = 1.03 for n = 10
V(r)/Uc/l = (y/R)1/n
+
Hl
V1avg2/ (2g) + p1/(g) + z1 = V2avg
2/ (2g) + p2/(g) + z2 + Hl
(Eq. 8.30)
(Eq. 8.34)
Hl
V = Q/Area
BREATH
(early 20th Century turbulent pipe flow experiments)
fF = wall /{(1/2) V2}
Similarity of Motion in Relation to the Surface Friction of Fluids Stanton & Pannell –Phil. Trans. Royal Soc., (A) 1914
~1914
fF = wall /{(1/2) V2}
fF = wall /{(1/2) V2}fD = (p/L)D/{(1/2) V2} = (p/L)2R2/2{ ½ V2} = 4wall /{(1/2) V2} = 4 fF
BREATH
(rough pipe turbulent flow experiments)
Original Data of Nikuradze
Stromungsgesetze in Rauhen Rohren, V.D.I. Forsch. H, 1933, Nikuradze
p U?
p uavg2
Newton believed that drag uavg2
arguing that each fluid particle would lose all their momentum normal to the body.
Drag = Mass Flow x Change in Momentum
Drag = dp/dt (UA)U U2A
Drag/Area U2
Sir Isaac Newton (1642 – 1727)
aside
Fully rough zone where have flow separation over roughness elements and p ~ V2
k* = u*/; k* < 4: hydraulically smooth4 < k* < 60 transitional regime; k* > 60 fully rough (no effect)
White 1991 – Viscous Fluid Flow
Curves are from average values good to +/- 10%
BREATH
(Moody Diagram)
Hl = f (L/D)V2/(2g)
f = 64/Re and is proportional to in laminar flow f is not a function of /D in laminar flow f = const. and is not a function of at high
enough Re turbulent flows in a rough pipe f is usually a function of /D in turbulent flows
laminar t u r b u l e n t
fD = (p/L)D/{(1/2) V2} Darcy friction factor
ReD = UD/
For new pipes, corrosionmay cause e/D for old pipesto be 5 to 10 times greater.
Curves are from average values good to +/- 10%
fF = -2.0log([e/D]/3.7 + 2.51/(RefF0.5)]
If first guess is: fo = 0.25[log([e/D]/3.7 + 5.74/Re0.9]-2
should be within 1% after 1 iteration
For turbulent flow in a smooth pipe and ReD < 105,
can use Blasius correlation: f = 0.316/ReD
0.25 which can be rewritten as:
wall = 0.0332 V2 (/[RV])1/4)
For turbulent flow and Re < 105
can use Blasius correlation: fD = 0.316/Re0.25
Which can be rewritten as:
wall =0.0332 V2 (/[RV]) PROOF
fD = 4 fF
0.316 1/4 / (V1/4 D1/4) = 4wall/(1/2 V2)
wall = (0.0395 V2) [1/4 / (V1/4 (2R)1/4)
wall = (0.0332 V2) [ / (VR)]1/4 QED
Question?Looking at graph – imagine that pipe diameter, length,
viscosity and density is fixed.Is there any region where an increase in V
results in an increase in pressure drop?
Question?Looking at graph – imagine that pie diameter and
kinematic viscosity and density is fixed.Is there any region where an increase in V
results in an increase in pressure drop?
Instead of non-dimensionalizing p by ½ V2; use D3 /( 2L)
Laminar flow
Turbulent flow
transition
From Tritton
pD3 /(2L)
Everywhere!!!!!!!
Some history ~
“Moody Diagram”
f = function of V, D, roughness and viscosityf is dimensionless
Antoine Chezy ~ 1770:for channels: V2P = ASextrapolate this for pipe:Hl = (4/C2)(L/D)V2
Gaspard Riche de Prony (1800)Hl = (L/D)(aV + bV2)
C; a and b are not dimensionlessC; a and b are not a function of roughness
Hl
Antoine Chezy
f = function of V, D and roughnessf is dimensionless
Hl
Hl
f is a function of and D
better estimates of f
Could be dropped for rough pipes
Traditional to call f the Darcy friction factor although Darcy never proposed it in that form
Hl
Combined Weisbach’s equation with Darcy and other data,
compiled table for fbut used hydraulic radius.
= w/( ½ Vavg2) prob 8.83
Hl
Eq. 8.34
4000< ReR < 80000
Full range of turbulentReynolds numbers
“ These equations are obviously too complex to be of practical use. On the other hand, if the function which they embody is even approximately valid for commercialsurfaces in general, such extremely important information could be made readily available in diagrams or tables.”
Re
f1/f
Re/f
“The author does not claim to offer anything particularly new or original, his aim merely
being to embody the now accepted conclusionin convenient form for engineering use.”
Hl
f = [p/(g)]D2g/(LV2) f = {[p/L]D}/{1/2V2}
Hl
THE
END