A New Paradigm for Flow Analyses and a Novel Technique to Enhance the Thrust from Scarfed Nozzles
- Paper number
IAC-08.C4.2.1
- Author
Dr. I-Shih Chang, The Aerospace Corporation, United States
- Coauthor
Dr. Sin-Chung Chang, NASA Glenn Research Center, United States
- Coauthor
Dr. Robert L. Glick, United States
- Coauthor
Dr. Chau-Lyan Chang, NASA Langley Research Center, United States
- Year
2008
- Abstract
Purpose: The purpose of this paper is to present a new paradigm for flow analyses and a novel technique to enhance the thrust from scarfed nozzles. The new paradigm, the space-time conservation element and solution element (CESE) method, is built upon rigorous mathematical theorems and extensive physics considerations and is a true unsteady and genuinely multi-dimensional flow solver. The CESE method treats space and time as a single entity, solves the dependent variables of governing equations and their spatial derivatives simultaneously, and provides accurate solutions for Euler and Navier-Stokes (N-S) flows. The CESE method is applied in this study to solve the flow-fields of scarfed nozzles, which are used frequently for vectoring control of a space propulsion subsystem. Scarfing a nozzle reduces weight and length of the nozzle; but it also lowers the thrust produced from the nozzle. A novel technique proposed by Robert Glick to enhance the thrust from scarfed nozzles is investigated. Detailed results of the investigation and the flow-fields obtained from the CESE method for scarfed nozzles are presented.
Methodology: One of the Alternate Launch Abort System (ALAS) design options for NASA Orion Crew Exploration Vehicle (CEV) involved a faired-tower design. This alternate design would have scarfed nozzles for both the jettison motor and the abort motor. The low thrust produced from the scarfed nozzles is a concern. The idea behind Robert Glick’s technique to enhance the thrust from scarfed nozzles is to convert a portion of efflux momentum into a net pressure force in the flight direction by introducing an obstruction at the scarf plane and creating an oblique shock and a flow separation and recirculation zone in the scarfed nozzle. To test workability of the technique, the space-time CESE method in conjunction with an unstructured mesh generator is applied to solve the N-S flows associated with a nonsymmetric 2D scarfed nozzle. The CESE method captures distinctive features of complicated wave interaction patterns automatically during unsteady flow development and provides accurate flow-fields for evaluating different scarfed nozzle configurations.
Results: Three different scarfed nozzle configurations (without an obstruction, with a mild-obstruction, and with a long-obstruction at the scarf plane) are investigated. The corresponding computational meshes and the computed Mach contours and pressure distributions have been obtained. Without an obstruction at the scarf plane, a smooth flow is observed in the scarfed nozzle. Mild-obstruction produces a positive force gain in the flight direction. Long-obstruction results in a shock wave interacting with the lower nozzle wall and negating the net force gain in the flight direction. The novel technique to enhance the thrust from scarfed nozzles has another merit: the lateral force required for safe operation of the ALAS can be obtained passively and effortlessly by using different sizes of obstruction for scarfed nozzles on the four sectors of the ALAS shown in Fig. 1. Since scarfing an axisymmetric nozzle will produce a 3D nozzle, further study of obstruction-length optimization for scarfed nozzles requires 3D flow analyses.
Conclusions: The paper includes substantive technical content on a new paradigm for flow analyses and a novel technique to enhance the thrust from scarfed nozzles. The solutions obtained from the new paradigm are more accurate than those from other existing methods in Computational Fluid Dynamics (CFD). Application of the new paradigm for flow analyses yields detailed results for evaluating different scarfed nozzle configurations. The 2D analysis results indicate that the proposed novel technique has the potential to enhance the thrust from scarfed nozzles without much effort.
The material in the paper is the results of authors’ independent research and is new and original. The paper has not been presented elsewhere, and the attendance of at least one of the authors at the 59th IAC in Glasgow, Scotland to present the paper is assured.
- Abstract document
- Manuscript document
IAC-08.C4.2.1.pdf (🔒 authorized access only).
To get the manuscript, please contact IAF Secretariat.