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UNIFORM FLOW IN OPEN CHANNELS
BySaif Ur Rehman
PG-15-43
CONTENT
What is Open Channel Types of Open ChannelTypes of flowing water and controlSolution of uniform flow in Open Channel
OPEN CHANNEL
An open channel :a)The stream not completely enclosed by solid
boundaries b)It has free surface subjected only to
atmospheric pressure.c) Referred as free-surface flow or gravity flow
Open Channel
TYPES OF OPEN CHANNEL
Natural ChannelIrregular shape
i.e : river, hillsides rivulets, tidal etuaries
Artificial ChannelRegular shape
i.e : drains, culverts, sewer, tunnels
TYPES OF OPEN CHANNEL
TYPES OF FLOWING WATER AND ITS CONTROL
Rapidly Varied Flow
i.e : hydraulic jump
Non-Uniform Flow
≠ 0
Uniform Flow
= 0
Gradually Varied flow
i.e : upstream of obstruction
Open Channel
Steady Flow
= 0
Open ChannelUnsteady Flow
≠ 0
TYPES OF FLOWING WATER AND ITS CONTROL
Steady• y (depth of water) and v (velocity) remain constant
with respect to time
Unsteady Flow• y and v change with time
TYPES OF FLOWING WATER AND ITS CONTROL
Uniform• y (depth of water) and v (velocity) remain constant
along the channel.
Non - uniform Flow• y and v change along the length of the
channel
• Flow Classifications1) Depending on the Reynolds number, Re
– Laminar Flow (if Re < 2300): very slow and shallow flowing water in very smooth open channels.
– Turbulent Flow (if Re > 4000): ordinary flow in ordinary open channels.
– Transition Flow (if 2300 < Re < 4000)
TYPES OF FLOWING WATER AND ITS CONTROL
V = average channel velocityL = length of channelv = kinematic viscosity of fluid
2) Depending on Froude number, Fr
– Fr = 1 : Critical Flow
– Fr < 1 : Subcritical Flow – slow flowing water
– Fr > 1 : Supercritical Flow – fast flowing water
TYPES OF FLOWING WATER AND ITS CONTROL
V = average channel velocityg = gravity acceralationD = hydraulics water depth
TURBULENT
LAMINAR
Bernoulli’s Equation
Lhzg
Vpzg
Vp 2
222
1
211
22
Open Channel
GEOMETRIC PROPERTIES OF OPEN CHANNELS
RECTANGULAR CHANNEL TRAPEZOIDAL CHANNEL
• The terminology of geometric elementsy : depth of flow T : top width b : bottom channel widthm : side slope So : channel bottom slope v : average flow densityFr : Froude number Re : Reynold number L : length of channelQ : flow rates , Q = AV A : area of the flow P : wetted perimeterR: hydraulic radius at cross section
D : hydraulics water depth V : volume
ν : velocity E : specific energy ∆z : weir height : flow temperature q = discharge over width
(m)
GEOMETRIC PROPERTIES OF OPEN CHANNELS
UNIFORM FLOW IN OPEN CHANNEL
Uniform flow is an equilibrium condition that flow tends to if the channel :
a)constant slopeb)constant cross sectionc)constant roughnessd)depth, water area, velocity and discharge at every section of channel are constant
• CHEZY FORMULA :
UNIFORM FLOW IN OPEN CHANNEL
Where ; V = mean velocity (m/s)C = Chezy’s factor of flow resistance (m1/2/s)R = hydraulic radiusSo = slope of energy lineQ = Discharge (m3/s)
• MANNING FORMULA :Where ; V = mean velocity (m/s)
n = Manning’s coefficient of roughness (s/m1/3) R = hydraulic radiusSo = slope of energy lineQ = Discharge (m3/s)
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