Development of an Analytical Correlation between Gas Turbine Engine Smoke Production and Jet Plume Visibility.

Abstract : A jet plume visibility model computer code, which predicts the probability of detection of aircraft with visible exhaust plumes has been developed. The model first computes the plume geometry, smoke concentration in the plume and the local extinction coefficient. The average plume contrast is then computed for a specified range and observer orientation with respect to the aircraft heading. Aircraft contrast is an input to the model computer code. The probability of detection of the aircraft and exhaust plume is then computed as a function of smoke number. The model was used to calculate jet plume visibility at the nozzle exit and at the aircraft tail for several representative aircraft. Although the smoke numbers which produce no visible trails are a function of aspect angle, they were generally greater than the EPA and Air Force smoke number standards. The smoke numbers which result in a measurable increase in detection range are greater than those corresponding to plume invisibility at the nozzle exit. Esthetic nuisance smoke standards which result in plume invisibility at or near the nozzle exit will also result in no measurable increase in detection range for the tactical case. (Author)