## Shock Waves

#### Glenn Research Center

Shock waves occur whenever an object moves faster than the speed of sound and the object abruptly constricts the flow. Shock waves are very small regions in a gas where the gas properties change by a large amount. Scientists call this a high gradient region, which just means a large change of variable over a very small distance. Across a shock wave, the air pressure increases almost instantaneously. The air temperature and density also increase across a shock wave, while the Mach number and speed of the flow decrease. If the shock wave is oriented perpendicular to the flow direction it is called a normal shock. (In this case, "normal" means perpendicular, not ordinary, or average, or usual). If the shock wave is inclined to the flow direction it is called an oblique shock. There are rather simple algebraic equations which describe the change in flow variables across a normal or an oblique shock wave.

This simulator solves the equations for flow past a sharp wedge using the free stream Mach number and wedge angle as inputs. Inputs to the program can be made using the sliders, or input boxes at the upper right. To change the value of an input variable, simply move the slider. Or click on the input box, select and replace the old value, and hit Enter to send the new value to the program. Output from the program is displayed in output boxes at the lower right. The flow variables are presented as ratios to free stream values. The graphic at the left shows the wedge (in red) and the shock wave generated by the wedge as a line. The line is colored blue for an oblique shock and magenta when the shock is a normal shock. The black lines show the streamlines of the flow past the wedge. Notice that downstream (to the right) of the shock wave, the lines are closer together than upstream. This indicates an increase in the density of the flow.

You can download your own copy of this simulator for use off line. The program is provided as Shock.zip. You must save this file on your hard drive and "Extract" the necessary files from Shock.zip. Click on "Shock.html" to launch your browser and load the program.

• Sources of Drag:
• Compressible Aerodynamics:
• Interactive Shock Waves:
• Inlet:

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