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Wind Turbines > Lecture 1 > Flashcards

Lecture 1 Flashcards

1
Q

Distributed wind is how many KWs

A

<100 KW

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2
Q

Utility-Scale wind is how many KWs

A

> 100 KW

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3
Q

Pros of Distributed Wind turbines?

A

no transmission loss
better for environment
smaller, easier to install

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4
Q

Cons of Distributed Wind turbines?

A

Less efficient -> relatively higher costs
Take up land

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5
Q

Horizontal axis wind turbine Pros
(relative to VAWT)
(4)

A
  • more sensitive to wind direction (can be con)
  • can be put offshore
  • better scalability and efficiency
  • more cost efficient
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6
Q

Horizontal axis wind turbine cons (2)

A

higher capital costs
land

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7
Q

Vertical axis wind turbine pros
(5)
think maint/wind/environ

A
  • responds better to changes in wind direction
  • easier and cheaper to maintain because you have physical access to the generator
  • better for urban environments
  • can withstand higher turbulance levels
  • can operate at lower wind speeds
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8
Q

Vertical axis wind turbine cons (3)

A
  • lower efficiency
  • lower operational range. Likes their ideal wind speed and little else
  • high fatigue because the blade always has the wind on it in the same area of the blade. (Requires more maintanence)
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9
Q

A WT model names 3.6-137 means what?

A

3.6 MW power generation
137 m rotor diameter

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10
Q

If AOA goes up, what happens?

A

This means that the blades are angled more towards the incoming wind.

Results in an increase in the lift force generated by the blades, which can cause the wind turbine to produce more power.

If the angle of attack is increased too much, the blades may stall, which means that the lift force decreases significantly and the wind turbine produces less power.

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11
Q

What are the best operating conditions for a wind turbine, in terms of numbers?

A

a = 1/3 - betz limit
a’ = 0

CL&raquo_space; CD

aim for p-rated

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12
Q

The Betz limit

A

the maximum amount of power that can be extracted from the wind by a wind turbine is approximately 59.3% of the total kinetic energy of the wind

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13
Q

DRAW A VELOCITY TRIANGLE AND LABEL ALL ITS PARTS AND DEFINE THE PARTS NOW

A

look at notes

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14
Q

If lambda (TS) goes down, what happens to …

  • power output
  • a
  • a’
A

PO goes down
a goes down
a’ goes up

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15
Q

How do we vary twist (alpha) to make sure we can achieve operating pt?

A

We want the highest CL and the lowest Cd.

Therefore, we try to keep the alpha constant.

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16
Q

sigma

A

blade solidity or how much we are blocking the wind.

sigma = (BC) / (2pi*r)

sigma_optimal = 1/r

the only thing we change is B

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17
Q

2 vs 3 blades, which has a longer chord?

A

2

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18
Q

What are the natural inputs to CL and CD?

A

alpha and Re.

Alpha has a higher effect!

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19
Q

MW is how many W

A

10^6

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20
Q

Higher Re means …

A

More steep CL curve and higher alphas.

In the CD plot, the Re goes down, because the ratio of drag force to vis force increases.

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21
Q

Weibull distro parameters A & K
What kind of curve with small A values?
What kind of curve with small K values?

A

Weibull curve = wind probability

A: mean wind speed: controls scale or height
Small A values = shallow curve

K: wind conditions: controls width.
Small k values = skinny curve.

22
Q

CL

A

Amount of lift generated by an airfoil (such as a wind turbine blade)

CL = L / (0.5 * rho * V^2 * S)

L = lift force generated by the airfoil
rho = density of the fluid (air)
V = velocity of the fluid (air) relative to the airfoil
S = reference area of the airfoil

23
Q

CD

A

Amount of drag generated by an airfoil

CD = D / (0.5 * rho * V^2 * S)

where:
D = drag force acting on the airfoil
rho = density of the fluid (air)
V = velocity of the fluid (air) relative to the airfoil
S = reference area of the airfoil

24
Q

CT

A

Amount of thrust force generated by the rotor blades

CT = T / (0.5 * rho * A * V^2)

25
Q

Lamba or Tip Speed Ratio

Whats the formula?

A

Determines the efficiency of the turbine in extracting power from the wind.

The relationship between the rotational speed of the rotor blades and the speed of the wind.

TSR = omega * R / V

where:
omega = rotational speed of the rotor blades (in radians per second)
R = radius of the rotor blade
V = velocity of the fluid (wind) passing over the rotor

26
Q

what is p rated?

A

P rated refers to the rated or maximum power output of a wind turbine.

The rated power output is typically specified by the manufacturer and is dependent on factors such as the size of the turbine, the design of the rotor blades, the generator efficiency, and the wind speed at the turbine site.

27
Q

what is CP

A

amount of power that a wind turbine can extract from the wind

CP = P / (0.5 * rho * A * V^3)

where:
P = power extracted by the rotor blades
rho = density of the fluid (air)
A = rotor area
V = velocity of the fluid (air)

28
Q

Vo

A

freestream velocity

29
Q

What is CL’s affect on power?

A

High CL = High Power

However, increasing the lift coefficient too much can also lead to increased drag and decreased efficiency, as well as increased wear on the turbine components.

30
Q

What is CD’s affect on power?

A

High Drag = Low Power

31
Q

What is CT’s affect on power?

A

High CT = High power

However, increasing the CT too much can also lead to decreased efficiency, as well as increased stresses on the turbine components.

This is because a higher CT can lead to increased turbulence and flow separation around the blades, which can result in increased drag and reduced efficiency.

Additionally, the increased thrust force can lead to increased stresses on the turbine components, which can reduce the reliability and lifespan of the turbine.

32
Q

What is the tip speed ratio’s affect on power?

A

TSR = Rw/V

If in optimal range (8 -10) then it will corresponds to high power.

At low TSR values, the turbine is not able to extract all of the available power from the wind, as the blades are not rotating fast enough to fully utilize the available energy.

At high TSR values, the turbine can experience increased turbulence and flow separation around the blades, which can lead to increased drag and reduced efficiency.

33
Q

What is CP affect on power?

A

High Cp = High Power

This is because a higher CP indicates that the turbine is able to extract a larger fraction of the available power from the wind, resulting in a higher power output.

34
Q

For the power curve, what is the formula for the increase in P?

A

Vo^3

35
Q

What is the Gust factor?

A

G = Vmax (max WS) / Vo (avg WS)

36
Q

Re formula trends

A

inertial forces / viscous forces

inertial forces = more dominant at high Re

37
Q

What is TI and what does it do at higher Re numbers?

Whats the short hand formula?

A

TI is turbulence intensity

Gets lower at higher Re numbers

TI = 1 / z (height from ground)

38
Q

Why is there more wind during the day?

A

Sun drives thermal energy for wind movement

39
Q

What is Zo and what happens as it gets higher?

A

Zo = surface roughness

Higher Zo, the more the wind slows down at the wall.

40
Q

BL formula or how WT companies determine wind speed before they install turbines.

A

V2/V1 = log(z2/z0) / log(z1/z0)

41
Q

Higher elevations means what for pressure

A

higher pressure

42
Q

Wind creators (4)

A
  • rotation of earth or coriolis force
  • thermal energy
  • pressure gradients
  • centrifugal force (hurricanes)
43
Q

What does it mean for WS when you have a high elevation and flat land?

A

Higher WS!

44
Q

Blade design considerations (5)

A
  1. choose airfoil - look at CL/CD ratios about 6% - 7%
  2. choose alpha target
  3. select TSR (8-10) - most ideal is 10
  4. determine chord length
  5. determine theta (pitch angle)
45
Q

If #B goes up what happens to chord

A

chord shortens

46
Q

How does c vary along r

A

c ~ 1/r

47
Q

What if we start to increase Re? (5)

A

-generate less lift
-stall will become wider
-flow less likely to separate from airfoil
-viscous forces increase, so drag increases
-less likely to stall at lower speeds

48
Q

Laminar BL

A
  • more prone to separation
  • organized
49
Q

Turbulant BL

A
  • more resistant against flow
  • chaotic
50
Q

what is a

A

By how much are we slowing down the wind?

the axial induction factor (also known as thrust coefficient or power coefficient) is a dimensionless parameter that describes the efficiency of the turbine in converting the kinetic energy of the wind

51
Q

What is the key difference between XFOIL and Experimental data

A

The key difference is that XFOIL has a hard time predicting the boundary layer over the airfoil, which causes more discrepancy at high alpha.

Wind Turbines (1 decks)

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