| Popis: |
The effects of aircraft emissions on the chemical balance of the atmosphere has gained increasing attention in recent years. New generations of higher speed aircraft which would fly up into the stratosphere have been a particular concern. A host of experimental and analytical efforts to quantify these effects is being pursued through NASA's Atmospheric Effects of Aviation Program as well as other international efforts. Proper numerical analysis of the reacting near field region of the engine plume(s) presents several challenges. Chemical models must be constructed which are valid in the atmospheric temperature and pressure range and must include the relevant nitrogen, carbon, and sulfur species. In addition, flow field modeling is complicated by the interaction which occurs between the engine plume and the aircraft wake vortices which roll off of the wings. This phenomenon substantially affects the mixing and dilution of the plume. Results are presented here for several aircraft of various designs, speeds, and altitudes. The analysis consists of a Parabolized Navier-Stokes CFD approach coupled with a specially developed finite rate chemistry model. The focus will be on the external near field region from the exit plane of the engine to the point of wake breakup several kilometers downstream. Comparisons of analytical results to field data are shown for the ER-2, Boeing 747, and Concorde aircraft. (Author) |
