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Industrial Aerodynamics 4 > Meteorology > Flashcards

Meteorology Flashcards

1
Q

How far does the troposphere extend and why is it significant?

A

11km, it is where weather occurs

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2
Q

What characterises a region of convergent flow?

A

Air flows in toward a central point at ground level and rises before diverging near the upper limit

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3
Q

What characterises a region of divergent flow?

A

Air flows together high in the troposphere and descends before parting near the ground

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4
Q

What force causes wind flow to deviate from a straight path?

A

Coriolis force

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5
Q

What is a typical size and speed of a depression?

A

4000km diameter
15-25 m/s

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6
Q

Which type of front causes severe weather?

A

Cold front

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7
Q

What is the lapse rate?

A

Decrease in temperature with height

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8
Q

What is the equation for the polytropic law?

A

p=k * rho^n

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9
Q

What is the equation of state?

A

p=rho * R * T

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10
Q

What does adiabatic mean?

A

No transfer of heat or mass outside the system

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11
Q

What is the density ratio?

A

rho2/rho1 = (p1/p2)^(gamma-n/gamma*n)

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12
Q

What is n in these equations? What is its equation?

A

Polytropic index
n = g/(g-RL) where L is lapse rate

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13
Q

What is assumed for Earth-fixed motion?

A

Linear acceleration di V/dt = 0
Rotational acceleration di Omega/dt = 0

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14
Q

What is the pressure gradient force?

A

-delta p/rho

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15
Q

What are the forces denoted by Ff and g respectively?

A

Friction force
Gravity force

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16
Q

What is the equation for coriolis force relative to motion?

A

-2 * Omega * Vm

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17
Q

Gravity force is not used directly in acceleration calculations, what is used instead?

A

Effective gravity force
g - Omega(Omega * r)

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18
Q

What are the unit vectors s, n and k?

A

s is along the particle path
n is normal to the path
k is vertically up from the Earth’s surface

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19
Q

How is coriolis force different to the other involved forces when resolving into s and n?

A

Coriolis force only has an n component, all others have both

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20
Q

What is the coriolis parameter f?

A

2 * Omega * sin phi

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21
Q

What are the conditions for geostrophic wind?

A

Negligible friction
Negligible curvature
Pressure gradient and coriolis force are balanced

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22
Q

What is the equation for geostrophic wind speed?

A

Vg = -1/(f*rho) * dp/dn

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23
Q

How do you begin the derivation of gradient wind speed?

A

(dv/dt)s = 0
(dv/dt)n = v^2/r

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24
Q

If centripetal acceleration is positive, what is the direction of circulation?

A

Anti-clockwise

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25
Q

What direction is cyclonic flow in the northern hemisphere?

A

Anti-clockwise

26
Q

What is the equation for solutions of gradient wind speed?

A

Vgr = -fr/2 * (1+- sqrt(1+ 4Vg/fr))

27
Q

For a regular low in the northern hemisphere (acw circulation) which solution for Vgr is used?

A

The negative

28
Q

What is the Rossby number?

A

Ratio of centrifugal to coriolis actions
Ro = v/f*r

29
Q

What does it mean when the Rossby number is large?

A

Coriolis force can be neglected

30
Q

What is cyclostrophic wind speed? What is the equation?

A

Gradient wind speed neglecting coriolis force
Vc = sqrt(-r/rho * dp/dn)

31
Q

What is the radius of maximum winds in relation to the fitting factors A and B?

A

Rw = A^(1/B)

32
Q

What is the name of the height, delta, at which wind speed becomes equal to gradient wind speed?

A

Boundary layer depth

33
Q

What is the equation for maximum shear stress at the ground surface?

A

Tao 0 = rho * u^2
Where u is friction velocity

34
Q

What is z0?

A

Roughness length, used to scale relative height z

35
Q

What is the function g(x) which relates x = z/z0 to y = Vz/u*?

A

2.5ln(x) + (34.5fz)/u*

36
Q

For what heights is the mean velocity equation using z0 applicable?

A

Up to 300m
Below 30m the 34.5fz/u* part is neglected

37
Q

What is the power law Vz/Vr?

A

Vz/Vr = (z-d/r-d)^alpha
Where d is the zero level, r is reference height and alpha is tabulated based on terrain

38
Q

How is turbulent wind speed quantified?

A

A sum of mean and fluctuating components

39
Q

How is turbulence intensity found?

A

Standard deviation of wind speed divided by mean wind speed

40
Q

What is the gust factor Ktao?

A

Peak wind speed (V^)/ mean wind speed (V-)

41
Q

What is the autocovariance function used for?

A

Measuring the persistence of turbulent eddies

42
Q

What is the autocovariance function Cuu(Tao)?

A

The time-averaged product of velocity and times t and t+tao

43
Q

What is the autocorrelation function rhouu?

A

rhouu(tao) = Cuu(tao)/variance

44
Q

What is the equation for time period of turbulence?

A

The integral of autocorrelation by tao

45
Q

Similarly to time based covariance and correlation equations, what else can be represented in this way?

A

Velocity measured simultaneously at two different points in SPACE

46
Q

How is the Power Spectral Density equation Suu defined?

A

Variance = integral of Suu over frequency range n

47
Q

What is the PSD function used for?

A

Finding the frequency distribution of kinetic energy of fluctuations

48
Q

What are the 3 types of anemometer?

A

Pressure
Rotation
Research (Hot wire/sonic)

49
Q

What are advantages and disadvantages of pressure anemometers?

A

+ Robust, low maintenance
+ Quick response to fluctuation
- Many factors affecting calibration
- Poor accuracy at high yaw

50
Q

What are advantages of rotation anemometers?

A

+ Calibration unaffected by temperature, humidity etc
+ Linear response
+ Robust
+ Omnidirectional

51
Q

What are disadvantages of rotation anemometers?

A
  • Slow response at low wind speeds
  • Cannot record wind direction
  • Differently calibrated for smooth and turbulent flow
  • Overspeeding possible
52
Q

What are generally the main advantage and disadvantage of research anemometers?

A

Very accurate
Very expensive

53
Q

What distribution is commonly used to approximate cumulative probability of wind speeds in storm conditions?

A

Weibull distribution

54
Q

What is the notation Px signifying? What about Pxn?

A

Px is the probability that the extreme value is less than x in any one year
Pxn is the probability x is not exceeded in n years

55
Q

How do you create a quadratic in the gradient wind speed derivation?

A

Substitute in the equation for geostrophic wind speed

56
Q

In what direction does coriolis force act relative to wind motion as viewed from above?

A

To the right of wind direction in the Northern Hemisphere, to the left in the Southern Hemisphere

57
Q

Why is (dV/dt)s = 0 in gradient wind?

A

Flow is steady so there is no streamwise acceleration

58
Q

How do you convert bar to Pascals?

A

Divide by 1e-5

59
Q

What is the equation for peak wind speed in a hurricane?

A

sqrt(B/rho*e (pn -pc))

60
Q

What is typically assumed of Omega if no information about rotational acceleration is given?

A

Omega = 2pi/86400
Where 86400 is the number of seconds in a day

61
Q

What is true in adiabatic conditions?

A

n = gamma

Industrial Aerodynamics 4 (4 decks)

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