Lecture 2 Flashcards
Why technique generates hydrogen bubbles in the water
Electrolysis
What is the main use of the hydrogen bubbles
Visualisation technique
Is hydrogen bubbles qualitative or quantitative
Qualitative
What is the term given to a dye added to a flow experiment
Flow tracer
How do you get a sequence of straight lines in the flume
Pulse the electrolysis
What shape bubble system is used to show flow
Square
What shape will the squares look like if the water flow is even
Even shape, pattern in even
What is it called when water moves up in the column
Ejection/ Bursting
What is it called when water moves Down in the column
Inrush/sweep
What is the most important thing in sediment entrainment and transport
Turbulence
What is ADVP
Acoustic Doppler velocity profiling
How can the Doppler effect monitor flow rate
Uses shift from scattered sound to measure velocity
What point is 0 in relation to a Doppler probe
The futhest point away
What is good about the Doppler technique
Gives a lot of detail about the flow patterns, much more than just the bubbles
What directions can water move in
Water can go downhill, back on itself, move left and right and up and down
Which technique can measure the entire flow field
Particle imagine velocimetry
What are put into the tank so that the pictures can calculate flow
Little spheres that are used to track flow
How is the image captured using the PIV
Laser flashes while camera takes photo
What is the equation for Working out movement
U=x/t
What is an ecm
Electromagnetic current meter
What forces control the behaviour of fluids
Inertial gravitational and viscous
What is the Reynolds number
Discriminates between laminar and turbulent rates
What is the equation for Reynolds number
Re=pul/u
What is the flow of the Reynolds number is less than 500
Laminar
What is a turbulence Re value
Above 2000
What is the equation for froude number
Fr=u/^gl
What is the ratio concerned with in the froude number
Ratio between Inertia and gravity
What does u represent in terms of rivers and the water system
Water velocity
What does l represent in river systems
Depth
What is the fluid state if Fr>1
Super critical
What happens if the froude number is <1
Subcritical
Which directions can water move in if the flow is subcritical
All directions
Supercritical flow is most likely where
Fast flow in shallow depths
What can froude numbers of flow impact on
Bed form creation
What froude numbers are most rivers
Less than 1
What is shear stress
Force of the flow on the river bed
What is the equation for average shear stress
T=pgRS
What is The hydraulic radius
The cross sectional area divided by the wetted perimeter
What does S stand for in the shear stress equation
Slope
How do we normally get hydraulic radius
Approximate the mean depth
What are the advantages of averaged methods
Serves an index of the total resistance by all frictional influences on the flow and easy to measure
What are the disadvantages to Average shear stress
Does not provide information on spatial variation at reach sub scale not a good index of the ability for the sediment to move to the next section
what is the no slip condition
particles in contact with a surface will move the same speed (or no speed) of that surface
What is non uniform flow
flows were cross sectional area and velocity changes
what is dynamic pressure
pressure exerted by a moving fluid
what is a stream (dingman)
any body of water flowing with measurable velocity in a channel
what is a stream reach
a stream segment with fairly uniform size and shape, slope, channel materials and flow characteristics
