Properties of fluids and flows Flashcards
What are two important factors of a fluid?
Both liquid and air
Density
Viscosity
Name two types of flows
Laminar
Turbulent
How do you increase the turbulence in a flow?
3 factors
Increase the velocity
Lower the viscosity
Raise the density of fluid
What is the Reynolds number?
Tells you if it’s a laminar flow (low number) or turbulent flow (high number)
Not from Stephan,number in a pipe:
Low number < 2000
High number > 3000
See drive for figure
What does the Reynolds number depent on?
Re =rho*L *U/mu
L: charecteristic length
U: mean velocity
mu: viscosity
rho: densitet
OBS! Stephan bruger anden beregning - men tror ikke dette er så vigtigt!
What is the Froude number?
Ratio between wave speed and fluid speed
Fr < 1 = tranquill (subcritical)
Fr > 1 = rapid (supercritical)
Is it possible for a wave to move up stream?
< 1 Yes
> 1 No
What is a Hydraulic jump?
Change from supercritical flow (Fr > 1) to subcritical flow (Fr < 1)
Can also be the opposite way
Example: In a sink
Is a rapid flow (super critical) typical in shallow or deeper water?
Fr > 1
Shallow = rapid flow (super critical)
Deep = Tranquill flow (subcritical)
What does the Hjulstöm-Sundborg diagram show?
Errosion + transport vs. deposit of sediments depenting on the size (mm) + velocity of the water (cm/s)
High velocity: erosion + t
Medium v.: transportation
Low v.: deposition
Se drev!
What is the wave speed dependent on?
Deepth of the water
What is the rule of thumb regarding wavelength and wave depth?
Shallow water “feels” the bottom and deep water doesn’t
Shallow water:
Wavelenght > 20 *depth
Deep water:
Wavelength < 4*depth
Does the wave “feel” the bottom in shallow water?
YES
What is the wave base?
Depth were there is no influence from surface waves on bottom sediments
Name two types of transportation
Bedload:
- Saltation
- Rolling
Suspension
What is a gravity flow (mass wasting)?
Contains so much sediment that it changes the physics of the fluid
Pyroclastic flow
Turbidity flow (Bouma sequence
Mud flow
