A TRAJECTORY BOX MODEL FOR AIRCRAFT EXHAUST PLUMES

A trajectory box model describing the expansion and cooling of jet air craft plumes at cruise altitude in the wake regime is presented. The f orcing along the trajectory takes into account turbulent entrainment r ates for the distinct dynamical regimes. (jet, vortex, and dispersion) , with special emphasis on the proper treatment of jet mixing. The mod el is used to study the plume evolution, especially the overall plume dilution history, behind a subsonic B 747 and a planned supersonic air liner under cruising conditions. The accuracy with which microphysical ly relevant quantities like plume temperature and water saturation rat io can be predicted with the box model is discussed by comparing the r esults to spatially resolved, two-dimensional model calculations of je t mixing. As an application, the gas phase chemical conversion of NO i nto HNO2, of NO2 into HNO3, and of SO2 into H2SO4 taking place in the early jet regime is investigated using a simplified plume chemistry. M aximum conversion rates and their sensitivity to variations of the OH exit plane concentration are examined by means of analytical expressio ns.