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A dual-bell nozzle has been tested in the ONERA-R2Ch wind tunnel within the CNES PERSEUS program. The wall pressure distributions and the thrust for the two §ow regimes have been characterized in the nozzle pressure ratio (NPR) range from 51 up to 597. A hysteresis on the transition NPR between the two §ow regimes has been observed according to the evolution of NPR. The duration for the switch between the two §ow regimes is less than 10 ms. The hysteresis of about 20% on the NPR has also a direct e¨ect on the thrust. The total thrust of the dual-bell nozzle becomes higher than the thrust of the isolated base nozzle without extension for NPR > 1500. The hysteresis phenomenon has been modeled with the use of supersonic separation criteria and by making the assumption that incipient separation occurs immediately after the transition for increasing NPRs, while e¨ective separation occurs just before the transition for decreasing NPRs.

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