Nozzle Flow

The first ``wind tunnel'' was not a tunnel but a rotating arm attached at the center. At the end of the arm was the object that was under observation and study. The arm's circular motion could reach a velocity above the speed of sound at its end. Yet, in 1904 the Wright brothers demonstrated that results from the wind tunnel and spinning arm are different, due to the circular motion. As a result, the spinning arm was no longer used in testing. Between the turn of the century and 1947-48, when the first supersonic wind tunnel was built, several models that explained choking at the throat have been built.

A different reason to study the converging-diverging nozzle was the Venturi meter which was used in measuring the flow rate of gases. Bendemann ^1.37 carried experiments to study the accuracy of these flow meters and he measured and refound that the flow reaches a critical value (pressure ratio of 0.545) that creates the maximum flow rate.

There are two main models or extremes that describe the flow in the nozzle: isothermal and adiabatic.