bookcover.pngI’ve decided it’s time to consolidate my blogs into one magnificent blog! Seriously, you’ll find posts about fluid dynamics at this new url, along with all of the existing posts, and posts about other topics as well. How can you find the fluid mechanics posts? Just click on FLUIDS in the Categories list in the sidebar. You’ll also know a fluid dynamics post when you see one because of the featured image. I hope to see you there!

Reynolds Number

This video does an outstanding job of making the Reynolds Number meaningful. More about the use of the Reynolds Number in scale model testing in future posts!

Did Jon Lester Cheat?

Baseball in GloveThere are claims that Boston pitcher Jon Lester cheated in the Series opener against St. Louis in Boston on Wednesday night. These claims are based upon an observable blob of something – I think I’d rather not know precisely what – in his glove. The substance in his glove does not necessarily equate to cheating. It’s what Lester did or did not do with the substance that counts.

A major league pitch moves through the air at speeds of 90 mph or more. As the ball moves forward, it is subject to aerodynamic forces known as the Magnus Force – a variation of the Bernoulli effect. In the case of the Magnus Force, it is the spinning of the ball and the raised surface of the stitches that create a whirlpool of rotating air around the ball. The moving air exerts pressure – think Bernoulli effect – and the ball moves in the direction of least resistance. A perfect curve ball curves right at the plate because of the Magnus Force.  Continue reading

Euler’s Equations

Leonhard Euler (1707-1782) is known for his contributions to fluid dynamics. Specifically, his work discoveries in infinitesimal calculus, his derivation of Bernoulli’s equation, and his equation for inviscid fluid flows.

Euler’s equation for inviscid flows, those without friction, first appeared in 1757 in an article entitled, “Principes genereaux du mouvement des fluids.” This equation focuses on the fluid flow as a whole and analyzes the fluid velocity at a fixed point.

By using this equation, estimations on the effect of friction can be made when investigating aerodynamic problems. His equation is still in use today.

Related Posts:
Leonhard Euler
Viscid vs Inviscid Flows

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Leonhard Euler

EulerLeonhard Euler (1707-1782) is widely considered the preeminent mathematician of the 18th Century. Euler worked closely with Bernoulli while they lived in St. Petersburg. He envisioned pressure as a point that could vary from point to point throughout a fluid. His differential equation for a fluid accelerated by gradients of pressure led him to create “Bernoulli’s Equation,” based upon Bernoulli’s work.

Continue reading

Daniel Bernoulli

UnknownDaniel Bernoulli (1700-1782) was a member of a well-respected family of Swiss scientists and mathematicians. His book, “Hydrodynamica,” published in 1793, coined the term “hydrodynamics.” Bernoulli’s fluid flow equations contributed to the success of the modern practice of testing scale models early in the design process. Continue reading

Look Out!


Pitot Tubes

What does a pitot tube look like? Here are a few examples. The first is a pitot tube. The second is a pitot tube affixed to the underside of an airplane wing, facing into the wind. The third is a diagram of the way a pitot tube is used to give readings a pilot can use during flight. Wait! There’s more!

Henri Pitot

PitotHenri Pitot (1695-1771) was a hydraulic engineer who invented a device that is still in use today. That device, the pitot tube, measures the velocity of a fluid flow at a given point. Pitot used his pitot tube to measure the flow of water in rivers and canals.


Diagram of Modern Pitot Tube

The pitot tube is a deceptively simple device. Pitot’s original tube had two tubes. The first was a tube that stuck straight up, open ad one end and inserted vertically into the water. This tube measured the static pressure – the pressure of the water at rest. The second tube was bent at a right angle. The open end of the right angle faced directly in the fluid flow. Pitot used his tubes to measure the velocity of the Seine River. He stood on a bridge and lowered his apparatus into the water. Wait! There’s more!

An Ocean of Air

In 1644, Evangelista Toricelli wrote, “We live submerged at the bottom of an ocean of air.” We don’t feel the force of the pressure of this fluid any more than aquatic creatures feel the force of the water on all sides. Why? Because there is a uniformity of pressure in both cases; gravity exerts pressure on all sides.

Imagine for a moment that everything on the Earth and above its surface could exist under the water, or vice versa, without any change in appearance or properties. If we visualize  horizontal bands atop one another, it would break the habitable area into observable layers. Grass, trees, plants, insects, ground-dwelling animals would all be in the same layer as the plants, crabs, bottom-feeders, and sand dwelling creatures beneath the surface of the ocean. There would be fish swimming in the layer above our heads with the birds. Airplanes would soar further above, in a layer with the whales. Dolphins would escape the surface of the ocean, accompanied by rockets, at the topmost layer above Earth. It would be a jumbled and magnificent scene.  Wait! There’s more!

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