An Analytical Study on Design and Performance of Dual-Bell Nozzles

We performed theoretical and CFD analyses of dual-bell nozzles, to explore possible application of this advanced nozzle concept to current and near-term launch vehicles. The theoretical analysis, performed with the help of a recently proposed nozzle-flow separation model, determined optimum performance gains to be obtained by applying dual-bell nozzles to cryogenic and liquid-oxygen/kerosene engines of existing launch vehicles. The CFD calculations determined the nozzle contour design criterion that will provide the reliable nozzle operation without potential hazards of side loads and/or vibration. The CFD analysis also confirmed the correlation between separation criterion and transition altitude that determines the dual-bell nozzle performance. The dual-bell nozzle has proved to provide significant launch vehicle flight performance gains when we design the nozzle contour according to the design criterion determined here. We have also shown that the efficient light-weight dual-bell nozzle can be manufactured by accommodating a radiation-cooling system to the extension-nozzle wall with lightweight materials.