An evaluation of a correction technique to compensate for jet temperature effects on nozzle afterbody drag at transonic Mach numbers

The objective of this investigation was to evaluate the performance of an empirical jet correction technique for correlating jet temperature effects on nozzle/afterbody drag coefficient at transonic free-stream Mach numbers. The jet correction technique utilizes experimental data to correct afterbody drag obtained with a cold jet in the wind tunnel for the effects of jet plume shape and jet entrainment associated with jet temperature changes to obtain an estimate of hot jet afterbody drag coefficient. Data used in the investigation were obtained from experiments conducted in the Arnold Engineering Development Center (AEDC) Propulsion Wind Tunnel (PWT) (16T) with two strut-mounted models at free-stream Mach numbers 0.6 to 1.5. Integrated nozzle and afterbody drag coefficient data were acquired over a jet temperature range of 500 to 2,8000R and a nozzle pressure ratio (NPR) range from jetoff to 20. Utilizing the proposed jet correction technique and cold jet entrainment data at M_infin;=0.6, afterbody drag coefficient errors associated with varying jet temperature for a 15-deg boattail are reduced to a maximum error of 50 drag counts based on body cross-sectional area, as compared to 145 drag counts by matching NPR at free-stream Mach numbers from 0.6 to 1.2. At free-stream Mach number 1.5 the technique provides a lower prediction than the actual V hot jet drag coefficient with errors as high as 70 drag counts (one drag count is equivalent to 0.0001). By matching nozzle pressure ratio or maximum plume diameter ratio at Mach number 1.5, drag coefficient errors are positive at about 70 drag counts and 25 drag counts, respectively. Since a typical fighter has a wing area which is an order of magnitude greater than body area, these drag coefficient errors in aircraft drag counts would be smaller by a factor of 10.