A computer program which is capable of computing performance of a fixed geometry two dimensional extemal compression supersonic inlet installed in a ramjet engine which satisfies the required air mass flow rate for the engine to operate at off design condition, was developed. The program can calculate quantity of possible air flow which may income through the inlet under the critical operation that is state of operation such as normal shock wave stands on the throat position of the air inlet, and required air flow for the engine which the ramjet engine requires to generate combustion gas that is exhausted through a jet nozzle of the engine under given engine operating condition and critical air inlet operation. When possible air flow exceeds required one, possible air flow decreases down to required one by subcritical operation. When possible air flow is less than required one, a pressure recovery factor of the air inlet is lower down till required air flow decreases down and equal to possible one by supercritical operation. It was found that influence of the inlet/nozzle characteristics on the position, i.e. the strength, of the normal shock wave is very sensitive. In particular, in supercritical regime where a ramjet engine is considered to stably operate, the pressure losses due to the normal shock wave becomes predominant compared to all the other losses, such as due to the oblique shock waves, combustor and nozzle. Thus, the characteristics significantly affect the global engine performance. Useful correlation for predicting the pressure recovery in super critical regime was also found from the numerical results, which is an exponential function of the flight and design Mach numbers and gas propenies. The correlation gave a good agreement with the available experimental data of an actual ramjet engine.
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