Starting pressure and hysteresis behavior of an annular injection supersonic ejector

An analytical model to predict the primary stagnation pressure that starts an annular injection supersonic ejector is presented. If the length of the mixing chamber is longer than the critical length, the starting pressure increases proporionally to the mixing chamber length, which differs from conventional ejectors using central injection. To describe the dependency of the starting pressure on the mixing chamber length, we assume that the ejector starts when the exiting supersonic primary How reaches the second throat. In the present model, we use a subsonic mixing model to calculate the secondary How pressure in the mixing chamber. Applying the obtained pressure as a back pressure condition, the distance that the supersonic primary flow develops is calculated. Comparing the distance to the mixing chamber length, we derive a minimum pressure requirement diagram that accurately predicts the starting pressure and hysteresis for a given geometry.