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Analysis of Vortex-induced Counter Torque and Fin Pressure on a Finned Body of Revolution

出版	Sandia National Laboratories, 2005
URL	http://books.google.com.hk/books?id=yQi1pyr9S_QC&hl=&source=gbs_api
EBook	FULL_PUBLIC_DOMAIN

註釋Finned bodies of revolution firing lateral jets in flight may experience lower spin rates than predicted. This reduction in spin rate is a result of vortices generated by the interaction between the lateral jets and freestream air flowing past the body. The vortices change the pressure distribution on the fins, inducing a counter torque that opposes the desired spin. Wind tunnel data measuring roll torque and fin pressures were collected for a full-scale model at varying angle of attack, roll angle, airspeed, and jet strength. The current analysis builds upon previously written code that computes torque by integrating pressure over the fin surfaces at 0 degree angle of attack. The code was modified to investigate the behavior of counter torque at different angles of attack and roll angles as a function of J, the ratio of jet dynamic pressure to freestream dynamic pressure. Numerical error analysis was applied to all data to assist with interpretation of results. Results show that agreement between balance and fin pressure counter torque at 0 degree angle of attack was not as close as previously believed. Counter torque at 4 degree angle of attack was higher than at 0 degree, and agreement between balance and fin pressure counter torque was closer. Plots of differential fin pressure coefficient revealed a region of high pressure at the leading edge and an area of low pressure over the center and aft regions of the tapped surface. Large differences in the counter-torque coefficient were found between various freestream dynamic pressures, especially at Mach 0.95 and 1.1. Roll angle had significant effect only for cases at angle of attack, where it caused counter torque to change unpredictably.