Chap1 open channel flow
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Transcript of Chap1 open channel flow
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HYDRAULICS
UNIFORM FLOW IN OPEN CHANNELS
ByErni Syuhada Bt Mazwil Ishan
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HYDRAULICS ENGINEERING
• A scientific fluid flow particularly in water thoroughly in pipe, open channel, orifice and embankment, including the problem related to energy and pressure.
• Related to water or fluid in dynamic condition.
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CONTENT
What is Open Channel Types of Open ChannelTypes of flowing water and controlSolution of uniform flow in Open Channel
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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
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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
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TYPES OF OPEN CHANNEL
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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
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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
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TYPES OF FLOWING WATER AND ITS CONTROL
Uniform• y (depth of water) and v (velocity) remain constant
along the channel. Figure 2.0
Non - uniform Flow• y and v change along the length of the
channel
Figure 2.0
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• Flow Classifications1) Depending on the Reynolds number, Re
– Laminar Flow (if Re < 500): very slow and shallow flowing water in very smooth open channels.
– Turbulent Flow (if Re > 1000): ordinary flow in ordinary open channels.
– Transition Flow (if 500 < Re < 1000)
TYPES OF FLOWING WATER AND ITS CONTROL
V = average channel velocityL = length of channelv = kinematic viscosity of fluid
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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
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TURBULENT
LAMINAR
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TYPES OF FLOWING WATER AND ITS CONTROL
Critical Section (In uniform and non-uniform flow)1) If So < Sc, y > yc : Subcritical flow2) If So = Sc, y = yc : Critical flow3) If So > Sc, y < yc : Supercritical flow
Figure 3.0
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Bernoulli’s Equation
Lhzg
Vpz
g
Vp 2
222
1
211
22
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Open Channel
GEOMETRIC PROPERTIES OF OPEN CHANNELS
RECTANGULAR CHANNEL TRAPEZOIDAL CHANNEL
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• The terminology of geometric elementsy : depth of flow T : top width b : bottom channel widthm : side slope So : channel bottom slope v : average flow density
Fr : 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
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Type of channel
TOP WIDTH, T
AREA, A WETTED PERIMETER, P
RECTANGULAR B By B + 2yTRAPEZOIDAL B+2my By + my2 B+2y √ 1+m2
GEOMETRIC PROPERTIES OF OPEN CHANNELS
Where,
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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 constante)channel bed, water surface and energy line are parallel, So = Sw = Sf)y1 = y2 , V1 = V2
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• 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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UNIFORM FLOW IN OPEN CHANNEL
Closed conduits flowing partly fullCorrugated metal storm drains 0.010Concrete culvert 0.024Unfinished concrete 0.013Clay drain tile 0.014Lined or built up channelsUnpainted steel 0.012Planed wood 0.012Unplaned wood 0.013Trowel – finished concrete 0.013Rough concrete 0.017Glazed brick 0.020Brick in cement mortar 0.013Excavated channelsClean earth (straight channel) 0.022Earth with weeds (winding channel) 0.030Natural streamsClean and straight 0.030Weedy reaches, deep pools 0.100
Typical values of Manning’s coefficient, n
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SOLUTION IN OPEN CHANNEL
• Conveyor FactorFrom eq
We obtain ; For Chezy
For Manning
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• Section Factor, Z For Chezy ;
For Manning;
SOLUTION IN OPEN CHANNEL
• Thus, normal depth, yo can be obtain by using trial and error method
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SOLUTION IN OPEN CHANNEL
• Example :Given trapezoidal channel 10m wide with side slope of 1:1.5. Bed slope is 0.0003. The channel with concrete lining, n = 0.012. Calculate the velocity, V and flow rate, Q when the flow depth is 3.0m. If the flow rate is 50m/s, determine the slope, So of channel.