Fluid Dynamic Principles to Generate Axial Induction.ppt

Fluid Dynamic Principles to Generate Axial Induction
P M V Subbarao
Professor
Mechanical Engineering Department
I I T Delhi
Basic Methods of Solid Fluid Interactions to Extract
Wind Power ……

Mechanical Power Extraction :The fundamental
Aerodynamic Phenomena
• The type of aerodynamic forces used for generation of change in
tangential velocity across a rotor greatly influences the actual
power developed by a wind turbine.
• All bodies exposed to an airflow experience an aerodynamic force.
• The components of which are defined as aerodynamic drag (in the
direction of flow), and as aerodynamic lift (at a right angle to the
direction of flow}.
• The real power coefficients obtained vary greatly in dependence on
whether aerodynamic drag or aerodynamic lift is used for power
generation.
• A significant enhancement in power generation can be achieved in
lift machines when compared to and drag machine.
• This is due to the fact that much higher relative wind velocities can
be achieved with lift machines.

Basic Principle of Changing Angular Momentum
Drag driven WT Lift driven WT

Drag Translator
• Drag results from the relative velocity between the wind and the
device.
• The power extracted by an elementary drag is the product of the
drag force and the translation velocity.
  translator
translator
p
D
translator v
v
V
A
C
P 


2
0
2
1

translator
translator v
D
P 


Simple Drag Device
• The simplest type of wind energy conversion
can be achieved by means of pure drag
surfaces.
• The air impinges on the surface A with
velocity V0.
• The instantaneous power capture P from the
aerodynamic drag D, and the velocity Vblade
with which it moves is expressed as :
    blade
V
D
P



 

Define coefficient of drag:       A
V
C
D rel
D
2
2







V0
blade
V


Capacity of Drag Device
      blade
rel
D V
A
V
C
P













2
2



Instantaneous Power Developed by a drag device
Average Power Developed by a drag device
  


d
P
Pavg 

2
1
   
 

















 



d
V
A
V
C
P blade
rel
D
avg

 2
2
2
1

Power Coefficient of A Drag Wind Turbine
• Condition for maximum value of CPmax,
The instantaneous power coefficient  
wind
P
P
P
C

 
,
 
3
0
2
0
max,
2
2
V
A
R
A
R
V
C
C
D
p














 2
max, 1 

 
 D
P C
C
3
1
0 max 






p
C
27
4
max,
D
P
C
C 

Maximum instantaneous power coefficient
 
3
0
2
0
max,
V
R
R
V
C
C D
P








0
2
0
max, 1
V
R
V
R
C
C D
P


 









Define Blade Speed Ratio, 

Efficient Drag devices
• The aerodynamic drag coefficient of a concave surface curved
against the wind direction can hardly exceed a value of 1.3.
V0
vr
1926
.
0
max
, 
p
C

Cup anemometer
R
V0
V0 +Vb
V0-Vb

Maximum Torque Generated by A Cup Anemometer
R
 2
0
2
1

 R
V
C
A
F D
p
D 
 

 2
0
2
1

 R
V
C
A
F D
p
D 
 

     
 
2
0
2
0
max,
2
1



  R
V
C
R
V
C
R
A
R
F
F D
D
p
D
D 




 




Instantaneous Drag Coefficient


 


cos
D
C

Cup Anemometer as An Wind Speed Measuring
Devices-1

Devices-2
V0


Devices-3
V0


Lift Based Blade in Wind Turbine

Fluid Dynamic Principles to Generate Axial Induction.ppt

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Fluid Dynamic Principles to Generate Axial Induction.ppt