Section 1: fluid/sediment equations

Question 1

Reynolds number equation

Answer 1

Re= ρud/µ (may be l instead of d)

Question 2

What does the Reynold number show

Answer 2

Ratio of inertial to viscous forces

Question 3

What forces are represented in the Reynolds number

Answer 3

ρ is fluid density
u is fluid velocity
d(/l) is a length parameter such as the diameter of a pipe or length of submerged object
µ is fluid viscosity

Question 4

When does the flow become turbulent, at what Reynolds number

Answer 4

> 2000

Question 5

Features of Laminar flow

Answer 5

Low velocity, low Reynolds number
In linear paths generally parallel to the boundary of the flow
At constant velocity
Fluid motion is predictable
May be analysed by mathematical theory

Question 6

Features of Turbulent flow

Answer 6

High velocity, high Reynolds number
Irregular sinuous paths
With veolicty changing (subject to accelerations/decelerations)
Fluid motion is unpredictable
Cannot be analysed with mathematical theory, requires empirical/experimental study

Question 7

Froude Number equation

Answer 7

Fr=u/√gh

Question 8

What does the Froude number show

Answer 8

Ratio of inertial to gravity forces

Question 9

What forces are presented in the Froude number

Answer 9

u is fluid velocity
g is acceleration due to gravity
h is the a length parameter such as the depth of a flow or the length of an object moving on the water surface

Question 10

Essential characteristics of turbulent flow

Answer 10

Disorder (irreproducible in detail)
Efficient mixing
Vorticity, irregularly distributed in time and space

Question 11

What is the assumed acceleration due to gravity unless otherwise stated

Answer 11

9.81 m s-2

Question 12

SI base units of ρ

Answer 12

kg m-3

Question 13

Si base units of u

Answer 13

m s-1

Question 14

SI base units of d and h

Answer 14

m

Question 15

SI base units of μ

Answer 15

kg m-1 s-1

Question 16

SI base unit of g

Answer 16

m s-2

Question 17

Viscosity equation

Answer 17

τ = μ* du/dz

Question 18

What forces are presented in the viscosity

Answer 18

τ is shear stress
μ is fluid viscosity
du/dz is rate of change of local fluid velocity (u) in the direction z normal to the shearing surfaces at any point
z is direction u is depth?

Question 19

What is viscosity

Answer 19

A measure of the resistance of a fluid to deformation eg shearing or extension

Question 20

Bernoulli Equation

Answer 20

p + ρu^2/2 + ρgh

Question 21

What are the forces present in the Bernoulli Equation

Answer 21

p is static pressure (uniform in all directions) - pressure at a point on a body moving with the fluid
ρu^2/2 is dynamic pressure (pressure on surfaces perpendicular to flow) - kinetic energy per unit volume
ρgh is manometric height - gravitational potential energy per unit volume

Question 22

What is the Bernoulli Equation

Answer 22

The sum of a pressure term, a velocity term and a gravitational/height term that remain constant
Static pressure + dynamic pressure = total pressure

Question 23

What is U2 > U1
P2 < P1

Answer 23

Fluid velocity varies inversely with fluid pressure
If fluid has to travel through narrowing, velocity gets faster and pressure decreases

Question 24

Stoke Law Equation

Answer 24

w = gD^2(ρs - ρl) / 18μ

Question 25

What are the forces present in Stoke Law

Answer 25

w is settling velocity
D is grain diameter
ρs is density of solid particle
ρl is density of fluid

Question 26

Fluid drag force (drag coefficient CD)

Answer 26

FD / ρu^2D^2

Question 27

Dimensionless fluid drag force CD

Answer 27

CD= f (ρud/ μ)