A simple variable Mach number nozzle for aerodynamic engine tests was designed and calibrated. In this new nozzle, only one hydraulic actuator made freestream Mach number change from 2 to 4 during a run of the wind tunnel. The optimization of the nozzle contours was conducted by the 2-D computational simulation. The CFD results predicted that the deviation of Mach number from the averaged value was less than 1% and flow angle was less than 1 degree in the test region. The results of the calibration tests of the nozzle showed that the deviations of Mach number distributions in the test core (60mm×60mm) were less than 1.5% from Mach 2 to 3.5 and 3.5% at Mach 4. This result assured that this nozzle was suitable for aerodynamic engine tests. The aerodynamic tests of scramjet engine models in acceleration/deceleration conditions were carried out with this nozzle. Air capture ratio and internal drag were measured. When freestream Mach number decreased, the soft unstart in the inlet was observed around Mach 3. It resulted in increase of the internal drags.
