Rocket exhaust disrupter

#The thermal and pressure impingement effects of exhaust gases emanating from a rocket motor nozzle extend longitudinally well beyond the exit plane of the nozzle because of the concentrated supersonic flow pattern characteristic of the exhaust gas plume. Relatively small tactical missile rocket motors have nozzle exit velocities on the order of Mach 3.5 with recovery pressures of 300 pounds per square inch and recovery temperatures in excess of 5,000 degrees Fahrenheit. These high velocities, pressures and temperatures encountered in tactical or test firings of the rocket motor remain concentrated in the plume extending its length and result in destructive final pressure and thermal impingement effects in a relatively small area to the rear of the motor. In open environment static test firings, this necessitates strong and thermally protected structures positioned a considerable distance to the rear of the rocket nozzle, or a relatively vast open area behind the rocket. Test firings of the rocket motor into a duct or plenum require that similar features be incorporated in the plenum design to avoid destruction of the enclosure by the exhaust gas impingement. In tactical firings, the launching pad and components must also be protected. Provision of structures that can withstand the adverse temperature and pressure of the rocket motor exhaust increase the complexity and cost of the installations involved if firing safety is to be preserved.

#It is desirable, therefore, to provide an apparatus to mitigate the thermal and pressure impingement effects. Applicant3 s invention transforms the initial supersonic exhaust gas velocity to one of subsonic (or much reduced supersonic) magnitude and provides for the dispersion of the exhaust plume to reduce these effects as well as shortening the effective length of a free exhaust gas plume.

#According to the precepts of the invention, a disrupter body is positioned within the supersonic plume of a rocket motor exhaust flowing from the rocket motor nozzle. The body has a longitudinal passage, the central axis of which is subsequentially coaxial with the central longitudinal axis of the exhaust gas plume. The body and passage are sized and shaped to provide a flow area for the exhaust gases less than the cross-sectional area of the exhaust plume at the position of the body. As a consequence of the reduced flow area caused by the body, the motor exhaust gases may pass around and through the body passage only after undergoing a normal shock wave upstream of the body. The normal shock wave results in subsonic exhaust gas flow velocity downstream of the shock wave, greatly reducing exhaust temperature and pressure impingement effects farther downstream. Also, since exhaust gases pass around the body and through the body passage, the exhaust plume is dispersed.

#FIG. 1 is a side elevation view of an exhaust disrupter and plenum chamber structure with a burning rocket motor in place;

#FIG. 2 is a sectional view taken on line 2--2 of FIG. 1;

#FIG. 3 is a sectional view taken on line 3--3 of FIG. 1;

#The rocket motor exhaust disrupter apparatus of applicant's invention will be described in the context of a test firing of a rocket motor wherein the exhaust gas emanating from motor nozzle is directed into a plenum chamber or duct. It should be understood, however, that the results achieved by the apparatus would be essentially the same in an open environment in reducing the length of a free-exhaust plume and mitigating the temperature and pressure impingement effects of the plume at the launch point in tactical rocket motor firings.

#FIG. 6 illustrates the firing of a representative rocket motor 10 into a cylindrical T-shaped plenum chamber 12 without the use of applicant3 s invention. The plenum 12 has an entrance portion 14 and two exits 16 and 18. The support fixtures of the motor 10 and the plenum 12 are not shown. The rocket motor exhaust gases emanating from the motor combustion chamber exit from the motor nozzle 16 and form a concentrated plume 20. The plume 20 is illustrative of the characteristic of the supersonic flow pattern of such exhaust gases and extends well beyond the exit plane of the nozzle 16. The plume is symmetrical about the central longitudinal axis 22 of the motor 10. Within the plume 20 initial exhaust gas velocity of Mach 3 to 4 is typical, accompanied by recovery pressures of 200 pound per square inch, and recovery temperatures in excess of 5.000.degree. Fahrenheit. The velocity, pressure, and thermal characteristics of the high energy gases remain concentrated in the plume 20 resulting in a normal shock wave 23 upon impingement upon the interior of the plenum 12 in a limited region of final impingement 24 because of the shape of the plume 20. As a result, the plenum must be of substantial strength and size, and be provided with active or passive cooling means to protect the plenum structure at final impingement if the rocket motor 10 is to be safely test fired.

#An illustrated embodiment of the applicant3 s invention to reduce the final impingement effects of the exhaust gas plume 20 is illustrated in FIGS. 1 and 2. As in FIG. 6, a burning rocket motor 10 is depicted as exhausting into the interior of a plenum chamber 26 of circular cross section. The plenum 26 has an entrance section 28 and two exhaust gas exits 30 and 32. The plenum 26 is mounted in a fixed ground support structure 34 and the rocket motor 10 is held in a ground mounted test fixture 36 to establish and maintain the central longitudinal axis of the motor 10 coaxial with the central longitudinal axis 40 of the plenum entrance section 28. A disrupter body 38 is mounted on the central longitudinal axis of the plenum entrance section 28 and spaced from the motor exhaust nozzle 16 so as to be enveloped by the exhaust plume exiting the nozzle 16. The disrupter body 38 is supported in the plenum entrance section 28 by four struts 42 (FIG. 3) which attach the body to the wall of the plenum.