Fluids and Flows

Question 1

Name two important characteristics for Fluids and Flows

Answer 1

Density (ρ) & Viscosity (μ)

Question 2

Name the two types of flows

Answer 2

Unidirectional flows (currents) & Oscillatory flows (waves)

Question 3

What is fluid turbulence?

Answer 3

Fluid movement where the flow is chaotic and unpredictable

Reducing the velocity or raising the density will reduce the turbulence

Question 4

What does Reynolds number (Re) describe?

Answer 4

It describes if the flow will be laminar or turbulent

Re < 500 = Laminar
Re > 2000 = Turbulent
In between it’s a transitional flow

Question 5

Name reasons for turbulence

Answer 5

• High flow velocities
• Low viscosity
• Obstructions or sharp changes in the flow path (like a rock)

Question 6

What does the Froude number (Fr) describe?

Answer 6

it describes the relative importance of inertial forces to gravitational forces in a flow.
(At one point waves won’t be able to move upstreams anymore)

Question 7

When is a flow supercritical and when is it subcritical?
Froude number (Fr)

Answer 7

Fr > 1 = supercritical flow (rapid) - dominated by inertia
Fr = 1 = critical flow - gravity and inertia in balance
Fr < 1 = subcritical flow (tranquil) - dominated by gravity

Question 8

What is a hydraulic jump?

Answer 8

Sharp change from supercritical flow to subcritical flow

Question 9

What does Hjulströms diagram show us?

Answer 9

It show us the flow velocity needed to move different grainsizes and when they will erode, transport and deposit

Question 10

There is two types of particle movement. Which two?

Answer 10

Suspension and Bedload transport

Suspension is when particles are moved within the body of fluid

Bedload is when particles roll, slide or bounce (saltation) along the bottom of the fluid flow

Question 11

What is a density flow?

Answer 11

When a mixture of fluid and sediment gets the ability to move down a slope

Question 12

Name a few types of density flows

Answer 12

Sediment gravity flow
- Mudflow
- Sand moving down dune
- Tubidity flow

Pyroclastic density flow
- Hot ash and gasses

Question 13

What differentiates waves in shallow and deep water

Answer 13

Waves in shallow water will “feel” and react to the bottom

Oscillatory motion in shallow water, will create ripples on the bottom

Oscillatory motion in deep water will die out, before it reaches the bottom