Multidisciplinary Approach to Aerospike Nozzle Design

A model of a linear aerospike rocket nozzle that consists of coupled aerodynamic and structural analyses has been developed. A nonlinear computational fluid dynamics code is used to calculate the aerodynamic thrust, and a three-dimensional finite-element model is used to determine the structural response and weight. The model will be used to demonstrate multidisciplinary design optimization (MDO) capabilities for relevant engine concepts, assess performance of various MDO approaches, and provide a guide for future application development. In this study, the MDO problem is formulated using the multidisciplinary feasible (MDF) strategy. The results for the MDF formulation are presented with comparisons against separate aerodynamic and structural optimized designs. Significant improvements are demonstrated by using a multidisciplinary approach in comparison with the single-discipline design strategy. 1.0 Introduction A multidisciplinary analytic model of a linear aerospike rocket nozzle has been developed; this model includes predictions of nozzle thrust, nozzle weight, and effectivevehicle gross-liftoff weight (GLOW). The linear aerospike rocket engine is the propulsion system proposed for the X-33 and the VentureStar (Fig. 1) reusable launch vehicle (RLV). The model has been developed to demonstrate multidisciplinary design optimization (MDO) capabilities for relevant engine concepts, assess performance of various MDO approaches, and provide a guide for future application development. The MDO approach is a methodology for the design of complex engineering systems and subsystems that coherently exploits the synergism of mutually interacting phenomena. Traditional methods of design, analysis, and optimization have been based on the approach where disciplines are isolated. This work has focused on developing and implementing a baseline MDO problem using the multidisciplinary feasible (MDF) strategy. This paper presents the results for single-discipline and multidisciplinarily optimized aerospike rocket nozzle designs. The aerospike rocket engine consists of a rocket thruster, cowl, aerospike nozzle, and plug base region (Fig. 2). The aerospike nozzle is a truncated spike (or plug nozzle) that adjusts to the ambient pressure and potentially integrates well with launch vehicles. The flow-field structure changes dramatically from low altitude to high altitude on the spike surface and in the base region. Additional flow bleeds into the base region to create an aerodynamic spike (giving the aerospike its name), which increases the base pressure, and the contribution of the base region to the aerospike thrust. In the early 1960’s, aerospike and plug nozzles were the focus of development projects in the United States, Italy, and Germany. More recently, they have been proposed as the propulsion system for the RLV program for NASA and studied in the Advanced Rocket Propulsion Technologies and Future European Space Transportation Investigations Programme for ESA. This effort is focused on developing a multidisciplinary approach by utilizing preliminary analysis methods in a design methodology for the aerospike nozzle. The contour of the aerospike nozzle has been traditionally designed by using both simple methods and more elaborate methods based on calculus of variations. These design approaches are adequate for determining an aerodynamic contour that approximates or exactly satisfies a design for maximum thrust at one design condition (usually vacuum). However, the nozzle contour is usually modified as the design of the engine progresses. For example, the length of the nozzle may be varied to improve the thrust-to-weight ratio of the engine. In addition to structural weight effects, the thermal cooling system, propulsionvehicle integration, thruster contour design, and the fuel-oxidizer delivery system are a few of the topics that are significant in the aerospike nozzle design.