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Fluid Dynamics of Wind

Fluid Dynamics of Wind. P M V Subbarao Professor Mechanical Engineering Department I I T Delhi. Acquisition of Basic Skills to Harvest Wind Power. "action at a distance" has stymied many of the great minds. The Big Question ?!?!?.

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Fluid Dynamics of Wind

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  1. 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?

  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 MathematicaPhilosophiaeNaturalis.“

  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. • The force of the earth's attraction causes the apple to fall, but how specifically?

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

  7. W z f We Live on A Sphere!

  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 vorticitywa, • Relative vorticitywr, • Planetary vorticityf. • 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.

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