Reynolds Number (Re) Re = R = A/P V = mean velocity / = (which is kinematic viscosity) Re = VR( ...
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Transcript of Reynolds Number (Re) Re = R = A/P V = mean velocity / = (which is kinematic viscosity) Re = VR( ...
![Page 1: Reynolds Number (Re) Re = R = A/P V = mean velocity / = (which is kinematic viscosity) Re = VR( / ), where Driving Forces Resisting Force Re.](https://reader038.fdocuments.us/reader038/viewer/2022110402/56649e4d5503460f94b44136/html5/thumbnails/1.jpg)
Reynolds Number (Re)
Re =
R = A/PV = mean velocity/ = (which is kinematic
viscosity)
Re = VR(/), where
Driving Forces
Resisting Force
Re < 500 Laminar FlowRe > 750 Turbulent Flow
![Page 2: Reynolds Number (Re) Re = R = A/P V = mean velocity / = (which is kinematic viscosity) Re = VR( / ), where Driving Forces Resisting Force Re.](https://reader038.fdocuments.us/reader038/viewer/2022110402/56649e4d5503460f94b44136/html5/thumbnails/2.jpg)
Flow Types
• Laminar:– Water particles move
along paths that do not disrupt the movement of neighboring particles.
– Most resistance is caused by intermolecular viscous forces.
– Resistance is velocity
• Turbulent Flow– Water particles move in all
directions and velocity constantly fluctuates
– Most resistance is generated along channel perimeter; related to channel shape, particle size, and concentration.
– Resistance is square of velocity
![Page 3: Reynolds Number (Re) Re = R = A/P V = mean velocity / = (which is kinematic viscosity) Re = VR( / ), where Driving Forces Resisting Force Re.](https://reader038.fdocuments.us/reader038/viewer/2022110402/56649e4d5503460f94b44136/html5/thumbnails/3.jpg)
Manning EquationDescribes Flow and Resistance
in Open Channels
V = 1.49/n(R2/3)(S1/2)
n = Manning’s roughnessCoefficient
Slope = water surface slope
Assumes English units.
![Page 4: Reynolds Number (Re) Re = R = A/P V = mean velocity / = (which is kinematic viscosity) Re = VR( / ), where Driving Forces Resisting Force Re.](https://reader038.fdocuments.us/reader038/viewer/2022110402/56649e4d5503460f94b44136/html5/thumbnails/4.jpg)
Velocity Distribution in Open Channels
![Page 5: Reynolds Number (Re) Re = R = A/P V = mean velocity / = (which is kinematic viscosity) Re = VR( / ), where Driving Forces Resisting Force Re.](https://reader038.fdocuments.us/reader038/viewer/2022110402/56649e4d5503460f94b44136/html5/thumbnails/5.jpg)
Sediment Transport Terminology
• Entrainment: the processes that initiate the motion of a particle.
• Competence: the size of the largest particle a stream can entrain under any give set of hydraulic conditions.
• Capacity: the maximum amount of sediment that the stream can carry given the current hydraulic conditions.
• Load: amount of sediment that is actually carried by the stream.
• Sediment discharge: time rate of movement through a cross-section (weight/time; tons/day)
![Page 6: Reynolds Number (Re) Re = R = A/P V = mean velocity / = (which is kinematic viscosity) Re = VR( / ), where Driving Forces Resisting Force Re.](https://reader038.fdocuments.us/reader038/viewer/2022110402/56649e4d5503460f94b44136/html5/thumbnails/6.jpg)
Load TypesClassification Based on Mode of Transport
• Suspended Load: Particles transported mainly or entirely in suspension through the supporting action of turbulence.
• Bedload: Sediment which moves by skipping, sliding, and rolling along the channel bed. Remains within a few grain diameters of the channel bed.
![Page 7: Reynolds Number (Re) Re = R = A/P V = mean velocity / = (which is kinematic viscosity) Re = VR( / ), where Driving Forces Resisting Force Re.](https://reader038.fdocuments.us/reader038/viewer/2022110402/56649e4d5503460f94b44136/html5/thumbnails/7.jpg)
Load TypesClassification Based on Bottom
Sediment Characteristics
• Wash Load: Particles so fine that they are not found in appreciable amounts in the channel bed.
• Bed Material Load: Particle sizes that are found in great quantities in the stream bed.– Most bed material load is actually transported in
suspension.
![Page 8: Reynolds Number (Re) Re = R = A/P V = mean velocity / = (which is kinematic viscosity) Re = VR( / ), where Driving Forces Resisting Force Re.](https://reader038.fdocuments.us/reader038/viewer/2022110402/56649e4d5503460f94b44136/html5/thumbnails/8.jpg)
Variations in Suspended Sediment
Concentration with Discharge
![Page 9: Reynolds Number (Re) Re = R = A/P V = mean velocity / = (which is kinematic viscosity) Re = VR( / ), where Driving Forces Resisting Force Re.](https://reader038.fdocuments.us/reader038/viewer/2022110402/56649e4d5503460f94b44136/html5/thumbnails/9.jpg)
Influence of Manning’s n on Resistance and Suspended
Sediment
![Page 10: Reynolds Number (Re) Re = R = A/P V = mean velocity / = (which is kinematic viscosity) Re = VR( / ), where Driving Forces Resisting Force Re.](https://reader038.fdocuments.us/reader038/viewer/2022110402/56649e4d5503460f94b44136/html5/thumbnails/10.jpg)
Methods Used to Describe Entrainment
• Critical Bed Velocity
– Impact or momentum of the water mass on the exposed part of the particle.
– 6th power law: Size of particle entrained increases with the 6th power of the velocity.
– Very difficult to measure
Velocity (V)
Water
![Page 11: Reynolds Number (Re) Re = R = A/P V = mean velocity / = (which is kinematic viscosity) Re = VR( / ), where Driving Forces Resisting Force Re.](https://reader038.fdocuments.us/reader038/viewer/2022110402/56649e4d5503460f94b44136/html5/thumbnails/11.jpg)
Methods Used to Describe Entrainment
• Critical Tractive Force
– Dragging force is exerted on the exposed part of the particle.
– = DS• (Duboy’s Equation)
– Fairly Easy to measure
Depth (D)
Water Surface
Slope (S)
![Page 12: Reynolds Number (Re) Re = R = A/P V = mean velocity / = (which is kinematic viscosity) Re = VR( / ), where Driving Forces Resisting Force Re.](https://reader038.fdocuments.us/reader038/viewer/2022110402/56649e4d5503460f94b44136/html5/thumbnails/12.jpg)
Shield’s Dimensionless Values
• Dimensionless Shear Stress
=
(f - s) d
Dimensionless ReynoldsNumbers
R* = V*d
V * = (gRS)1/2
d = Intermediate grain diameter
R = Hydraulic Radius
- Specific weight of solid and fluid
![Page 13: Reynolds Number (Re) Re = R = A/P V = mean velocity / = (which is kinematic viscosity) Re = VR( / ), where Driving Forces Resisting Force Re.](https://reader038.fdocuments.us/reader038/viewer/2022110402/56649e4d5503460f94b44136/html5/thumbnails/13.jpg)
Dimensionless Shields Plot
![Page 14: Reynolds Number (Re) Re = R = A/P V = mean velocity / = (which is kinematic viscosity) Re = VR( / ), where Driving Forces Resisting Force Re.](https://reader038.fdocuments.us/reader038/viewer/2022110402/56649e4d5503460f94b44136/html5/thumbnails/14.jpg)
Hjulstrom Plot
![Page 15: Reynolds Number (Re) Re = R = A/P V = mean velocity / = (which is kinematic viscosity) Re = VR( / ), where Driving Forces Resisting Force Re.](https://reader038.fdocuments.us/reader038/viewer/2022110402/56649e4d5503460f94b44136/html5/thumbnails/15.jpg)
Tractive Force vs. Critical Velocity?
![Page 16: Reynolds Number (Re) Re = R = A/P V = mean velocity / = (which is kinematic viscosity) Re = VR( / ), where Driving Forces Resisting Force Re.](https://reader038.fdocuments.us/reader038/viewer/2022110402/56649e4d5503460f94b44136/html5/thumbnails/16.jpg)
Stream Power
• = QS• = wdvS• = (dS)v• = S
![Page 17: Reynolds Number (Re) Re = R = A/P V = mean velocity / = (which is kinematic viscosity) Re = VR( / ), where Driving Forces Resisting Force Re.](https://reader038.fdocuments.us/reader038/viewer/2022110402/56649e4d5503460f94b44136/html5/thumbnails/17.jpg)
East Fork River Bedload Trap
Flow
Bedload Trap