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This applet computes the isentropic flow relations. Isentropic means constant entropy, which implies a reversible process from the Second Law of Thermodynamics. As a gas (white area) is forced through a tube (black outline), the gas molecules are deflected by the walls of the tube. The properties of the gas will change along the length of the tube depending on the speed, or Mach number, of the gas.

The values of all the flow variables are related to one another through the Mach number, as shown on a separate slide. Therefore, selecting a value for any one variable determines the value of all the other variables. In this applet, you can select a variable by using the choice button labeled Input Variable. Directly below the selection, you can type in the value of the selected variable. When you hit the Enter key, you will see the output values change for the Mach number, the static to total pressure ratio (p/pt), the static to total temperature ratio (T/Tt), the static to total density ratio (rho/rhot), the area ratio (A/A*), the dynamic pressure ratio (q/p), and the corrected airflow per area (wcor/A). The definitions of these relations are given on a separate slide. Some of the variables (like the area ratio) are double valued. This means that for the same area ratio, there is a subsonic and a supersonic solution. The choice button at the right top selects the solution is that is presented.

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byTom Benson
Please send suggestions/corrections to: benson@grc.nasa.gov