A method for estimating jet entertainment effects on nozzleafterbody drag
Abstract
A highly simplified analysis was used to derive an expression for estimating the induced afterbody drag caused by the turbulent jetmixing process. The approach estimates the induced velocity produced by the jetmixing process and uses small perturbation concepts to estimate the resulting pressure change on the afterbody surface from which the induced afterbody drag coefficient is obtained. The theoretical induced afterbody drag (entrainment drag) is combined with the maximum jet plume diameter blockage condition to form a correlation method that accounts for the effect of jet area ratio, exit angle, total temperature, molecular weight and ratio of specific heats for a given external stream Mach number, Reynolds number, and afterbody geometry. For verification, the correlation method was used to predict the drag of an H2 and C2H4 jet from the measured drag of an N2 jet and to predict the drag of a hot jet from the measured drag of a cold jet for both the 15 and 25deg AGARD afterbody configurations in the Mach number range from 0.6 to 1.5. The average accuracy of the correlation method is better than 10% for both afterbody configurations and is 40 to 50 % more accurate than a correlation method based only on the blockage parameter. A brief numerical study indicates that the major parameter which correlates the jet entrainment effect is the product of the jet gas constant and total temperature.
 Publication:

Final Report
 Pub Date:
 February 1980
 Bibcode:
 1980aro..reptR....B
 Keywords:

 Afterbodies;
 Drag;
 Jet Flow;
 Turbulent Jets;
 Drag;
 Mathematical Models;
 Numerical Analysis;
 Turbulent Mixing;
 Fluid Mechanics and Heat Transfer