1. P M V Subbarao Professor Mechanical Engineering Department I I T Delhi
Fluid Dynamics of Wind
P M V Subbarao
Professor
Mechanical Engineering Department
I I T Delhi
Acquisition of Basic Skills to Harvest Wind Power

2. "action at a distance" has stymied many of the great minds
The Big Question ?!?!?
The question we need to answer is how can a force occur without any countable finite bodies & apparent contact between them?
"action at a distance" has stymied many of the great minds

3. Reality of Fluids : A Resource of Gradients
At the end of the 1640s, Pascal temporarily focused his experiments on the physical sciences.
Following in Evangelista Torricelli’s footsteps, Pascal experimented with how atmospheric pressure could be estimated in terms of weight.

4. How to Create Force with Only One Solid???
Newton developed the theories of gravitation in 1666, when he was only 23 years old.
Some twenty years later, in 1686, he presented his three laws of motion in the "Principia Mathematica Philosophiae Naturalis.“

5. Think about Field Let's focus on Newton's thinking.
Consider an apple starting from rest and accelerating freely …...
Until the apple hits the ground, the earth does not touch the apple so how does the earth place a force on the apple?
Something must go from the earth to the apple to cause it to fall.
The force of the earth's attraction causes the apple to fall, but how specifically?
The earth must exude something that makes acceleration of apple.
This something exuded by the earth was called as the gravitational field.
We can start by investigating the concept called field.

6. Variables Describing the Atmosphere
Thermodynamic variables
Pressure, p
Density, r
Temperature, T
Dynamic variables
Velocity, (three parameters!)
Vorticity, (three parameters!)

7. We Live on A Sphere! f z W

8. Vorticity in A Rotating Frame of Reference
When the vorticity in the atmosphere of a planet is to be defined, it is important to remember that the planet itself is spinning.
The spinning earth (a solid body) adds some vorticity to atmosphere.
In a rotating reference frame:
Consider the rotation effect:
The vertical component of the vorticity is

9. Distribution of Vorticity in A Rotating Frame of Reference
The vertical component of the vorticity at a given latitude f is:
Absolute vorticity wa,
Relative vorticity wr,
Planetary vorticity f.
For the Earth f is positive in NH and negative in SH.
The planetary vorticity is typically much bigger than the relative vorticity!?!?!?!?

10. Relative vorticity
The relative vorticity is positive for counterclockwise rotation:
In the NH this is the circulation around low pressure systems has positive relative vorticity (hurricanes, typical tornadoes, mid-latitude cyclones).
In the SH the relative vorticity is negative for the low pressure centers as the motion is clockwise.