Lecture 1 Flashcards
Distributed wind is how many KWs
<100 KW
Utility-Scale wind is how many KWs
> 100 KW
Pros of Distributed Wind turbines?
no transmission loss
better for environment
smaller, easier to install
Cons of Distributed Wind turbines?
Less efficient -> relatively higher costs
Take up land
Horizontal axis wind turbine Pros
(relative to VAWT)
(4)
- more sensitive to wind direction (can be con)
- can be put offshore
- better scalability and efficiency
- more cost efficient
Horizontal axis wind turbine cons (2)
higher capital costs
land
Vertical axis wind turbine pros
(5)
think maint/wind/environ
- 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
Vertical axis wind turbine cons (3)
- 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)
A WT model names 3.6-137 means what?
3.6 MW power generation
137 m rotor diameter
If AOA goes up, what happens?
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.
What are the best operating conditions for a wind turbine, in terms of numbers?
a = 1/3 - betz limit
a’ = 0
CL»_space; CD
aim for p-rated
The Betz limit
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
DRAW A VELOCITY TRIANGLE AND LABEL ALL ITS PARTS AND DEFINE THE PARTS NOW
look at notes
If lambda (TS) goes down, what happens to …
- power output
- a
- a’
PO goes down
a goes down
a’ goes up
How do we vary twist (alpha) to make sure we can achieve operating pt?
We want the highest CL and the lowest Cd.
Therefore, we try to keep the alpha constant.
sigma
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
2 vs 3 blades, which has a longer chord?
2
What are the natural inputs to CL and CD?
alpha and Re.
Alpha has a higher effect!
MW is how many W
10^6
Higher Re means …
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.
Weibull distro parameters A & K
What kind of curve with small A values?
What kind of curve with small K values?
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.
CL
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
CD
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
CT
Amount of thrust force generated by the rotor blades
CT = T / (0.5 * rho * A * V^2)
Lamba or Tip Speed Ratio
Whats the formula?
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
what is p rated?
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.
what is CP
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)
Vo
freestream velocity
What is CL’s affect on power?
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.
What is CD’s affect on power?
High Drag = Low Power
What is CT’s affect on power?
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.
What is the tip speed ratio’s affect on power?
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.
What is CP affect on power?
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.
For the power curve, what is the formula for the increase in P?
Vo^3
What is the Gust factor?
G = Vmax (max WS) / Vo (avg WS)
Re formula trends
inertial forces / viscous forces
inertial forces = more dominant at high Re
What is TI and what does it do at higher Re numbers?
Whats the short hand formula?
TI is turbulence intensity
Gets lower at higher Re numbers
TI = 1 / z (height from ground)
Why is there more wind during the day?
Sun drives thermal energy for wind movement
What is Zo and what happens as it gets higher?
Zo = surface roughness
Higher Zo, the more the wind slows down at the wall.
BL formula or how WT companies determine wind speed before they install turbines.
V2/V1 = log(z2/z0) / log(z1/z0)
Higher elevations means what for pressure
higher pressure
Wind creators (4)
- rotation of earth or coriolis force
- thermal energy
- pressure gradients
- centrifugal force (hurricanes)
What does it mean for WS when you have a high elevation and flat land?
Higher WS!
Blade design considerations (5)
- choose airfoil - look at CL/CD ratios about 6% - 7%
- choose alpha target
- select TSR (8-10) - most ideal is 10
- determine chord length
- determine theta (pitch angle)
If #B goes up what happens to chord
chord shortens
How does c vary along r
c ~ 1/r
What if we start to increase Re? (5)
-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
Laminar BL
- more prone to separation
- organized
Turbulant BL
- more resistant against flow
- chaotic
what is 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
What is the key difference between XFOIL and Experimental data
The key difference is that XFOIL has a hard time predicting the boundary layer over the airfoil, which causes more discrepancy at high alpha.
