Inverse heat transfer studies and the effects of propellant aluminumon TVC jet vane heating and erosion

Arnold 0. Danielson Naval Weapons Center A r p . Y ~ 5 3 3 China Lake.Ca1ifomia A recent subscale jet vane test series, accomplished largely under Air-Launched Weaponry Block Program sponsorship, was designed to determine the effeet of propellant aluminum content on vane durability in terms of leading edge erosion and shaft heating. Additionally, inverse heat transfer modeling was used to deduce details on vane heating processes under various plume conditions. The tests were normalized based on the product of exit plane pressure ratio and Mach number. This constraint focused tests on finding the minimum expected differences in vane leading edge erosion and shaft heating due to viscous, stagnation temperature and particle impingement efffeets. To date, jet vanes have been tested in the three solid propellants: Case 1, nonaluminized hydroxyl-terminated polybutadiene (NTPB) (87% solids); Case 2, 98 aluminized HTPB (88% solids); and Case 3,1896 aluminized HTPB (8% solids). This study is part of ongoing jet vane thrust vector control (JVTVC) development work a t NWC.13 Vanes designed for this work are quarterscale replicas of an NWCdeveloped integral jet vane and shaltIn addition to forming a database on vane material durability, data from this study, when combined with the full-scale vane test data, generated information with which to study the effect of scaling on vane heating. This work also provided a database for developing and refining new inverse heat transfer modeling and correlation techniques. These techniques provide a better understanding of the vane heating process. They can now be applied to the design of J W C systems in predicting shaft heating, in assessing the impact of vane design changes, and ultimately in improving predictions of thermalrelated requirements for jet vane TVC systems. This paper documents highlights of work a t NWC and the Naval Postgraduate School (NPS), beginning in 1984. The work generally divides into an experimental test series done a t NWC and an associated analysis and modeling investigation begun a t NWC, transferred early in the program to NPS for refinement and improvement.3-5 and recently extended a t NWC to the results presented in this paper. Concept of the Ex~erimental Work Experimental tests a t NWC were designed to examine various solid propellants and the heating and erosion of subscale jet vanes tested on motors us ing these propellants. Six rocket motor Brings were completed. Three firings were done to verify propellant ballistics and three were done to evaluate the thermal durability of jet vanes, all using an NWC 5 inchdiameter EVA rocket motor. The ballistic tests examined three specsc formulations of propellant containing 0, 9, and 18 wt-% powdered aluminum. After the ballistics had been confirmed, quarterscale jet vanes were fixed to the rocket motor nozzle. In these three tests, thermocouples were placed to measure vane shaft and mount temperatures. Concept of the Analytical Work The objective of the analytical study was to develop a jet vane heating model. The modeling procedure was an important theoretical aspect of this work. The intent was to develop a theoretical model that would be simple enough to provide a general tool for vane design and that could be both analytical and predictive. The approach was to structure a minimum number of thermal elements into a simple lumped-parameter vane heat transfer model, as opposed to building an overly detailed multinode finite element model. On the other hand, the model had to contain enough detail to enable the optimization of vane design and to assess vane requirements under predicted missile conditions. Therefore, part of this work was to determine how much model detail would be required to satisfy the opposing needs of simplicity for cost effectiveness and detail for information content or model value. This paper summarizes models recently developed a t NWC for three case studies: Case 1,096 aluminum propellants; Case 2, 9% aluminized p m pellants, and Case 3, 18% aluminized propellants. The process began with theoretical conjecture.4 Using parametric system identification procedures, diagrammed in Fig. I , certain unknown niodel parameters were adjusted by varying their values as necessary to align model outputs to the test data. This empirical procedure brought out information about the vane heating process itself that can be used in future vane design work. This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States.