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  • Design Criterion of the Dual-Bell Nozzle Contour

    Paper number



    Dr. Hirotaka Otsu, Shizuoka University, Japan


    Dr. Masafumi Miyazawa, Shizuoka University, Japan



    The dual-bell nozzle has a base-nozzle and an extension-nozzle connected at the wall inflection where a forced, steady and symmetrical separation takes place at low altitudes. The wall inflection therefore acts as an effective nozzle exit with a small nozzle area-ratio at low altitudes. At high altitudes, nozzle flow is attached to the wall through the extension-nozzle exit, thereby providing the use of the full area-ratio. The dual-bell nozzle-contour design is critical to assure the safe and reliable operation without potential hazards of side loads and/or vibration during the launch vehicle ascent flight.
    In this study, we performed CFD analyses to determine the optimum dual-bell nozzle contour. Especially, we focused on the separation point transition from the wall inflection to the nozzle exit. Based on the present analysis, we found that the deflection angle at the wall inflection should be larger than the angle determined by a simple Prandtl-Meyer expansion. 
    Also, the time to accomplish the separation point transition from the wall inflection to the extension nozzle exit is estimated to be less than 20 ms when our design criterion of the dual-bell nozzle is applied to the booster engine of H-2A launch vehicle.  This time interval is considered to be essentially instant from the practical point of view of the safe nozzle operation.
    Abstract document


    Manuscript document

    IAC-05-C4.2.08.pdf (🔒 authorized access only).

    To get the manuscript, please contact IAF Secretariat.