1.

Segment V11.1: Lighter Flame
(Related to Textbook Section 11.1 - Ideal Gas Relationships)

For an ideal gas the relationship among the pressure, density, and temperature is given by the ideal gas law. A change in pressure, temperature, or gas constant (type of gas) changes the density.

Density differences can be made visible by use of a Schlieren optical system that uses the fact that the speed of light in a gas is a function of its density. Because butane has a different density than air (different gas constant), unlit butane gas escaping from the lighter is visible as a small plume. When the lighter is lit, air surrounding the flame is less dense (higher temperature) than the room air. A large buoyant plume is produced. (Iowa State University Mech. Engr. Schlieren system courtesy of Professor W. J. Cook)

2.

Segment V11.2: Compressible Flow Visualization
(Related to Textbook Section 11.3 - Categories of Compressible Flow)

The speed of light in a gas is a function of the gas density. This allows the use of a Schlieren optical system to visualize compressible flows. An arrangement of lenses, mirrors, and a knife edge can deflect the light rays and produce images that show these density differences.

A very sensitive, large-field Schlieren apparatus is used to reveal the plume of warm, lower density air shed by the human body. Also shown are the density variations that result from the complex oblique shock and expansion waves in a supersonic jet of air issuing from a nozzle at the right. (Video courtesy of Professor G. S. Settles, Director, Gas Dynamics Lab, Penn State University.)

3.

Segment V11.3: Rocket Engine Start-Up
(Related to Textbook Section 11.4.2 - Converging-Diverging Duct Flow)

A converging-diverging nozzle is used to accelerate a gas to supersonic speeds. The nozzle exit pressure is determined by the stagnation pressure upstream of the nozzle and nozzle area ratio. Unlike subsonic flows, the exit pressure for supersonic flows need not be equal to the surrounding pressure.

At lift-off conditions, the nozzles of the Space Shuttle rocket engines are overexpanded. The nozzle exit pressure is less than the surrounding sea level atmospheric pressure. As shown in a computational fluid dynamics (CFD) simulation of the start-up of the Space Shuttle engines, this situation causes a complex multidimensional flow in the exhaust plume. (Video courtesy of NASA. CFD simulation created by Dr. Carey Cox; copyright Mississippi State University Engineering Research Center.)

4.

Segment V11.4: Supersonic Nozzle Flow
(Related to Textbook Section 11.4.2 - Converging-Diverging Duct Flow)

For a given converging-diverging nozzle, there is one pressure ratio (exit pressure/stagnation pressure) that produces isentropic choked flow. Otherwise, complex shock and expansion waves occur.

Air is shown exiting into the atmosphere from a nozzle on the right. As the stagnation pressure in the tank is raised, the flow, which begins as a subsonic jet, develops oblique shock waves (overexpanded flow). Isentropic flow (no waves) is produced when the pressure ratio is raised further to that value determined by the nozzle area ratio. Finally, for still higher stagnation pressure, expansion waves and shock waves develop (underexpanded flow). (Schlieren video provided by Professor G. S. Settles, Director, Gas Dynamics Lab, Penn State University.)

5.

Segment V11.5: Blast Waves
(Related to Textbook Section 11.5.3 - Normal Shock Waves)

Blast waves are essentially moving shock waves. The pressure rise across the wave depends on the amount of energy released and the distance from the explosion.

The loud "bang" of a firecracker is a very weak shock wave (pressure rise on the order of only 0.00001 psi) that travels at the speed of sound. A nuclear bomb blast wave is extremely strong. Thousands of feet from the explosion the pressure rise across the blast wave can be hundreds of psi, causing massive damage to structures. Miles from the explosion a blast wave is seen racing across the water and ruffling the palm trees. (Video courtesy of the Department of Energy)