A STUDY OF INGESTION AND DISPERSION OF ENGINE EXHAUST PRODUCTS IN TRAILING VORTEX SYSTEMS

摘要

Detailed analysis has been made of the ingestion and dispersion of engine exhaust products into the trailing vortex system of supersonic aircraft flying in the stratosphere. The rate of mixing between the supersonic jet and the co-flowing supersonic stream was found to be an order of magnitude less than would be expected on the basis of subsonic eddy-viscosity results. The length of the potential core was 66 nozzle exit radii so that the exhaust gases remain at elevated temperatures and concentrations over much longer distances than previously estimated. Ingestion started at the end of the potential core and all hot gas from the engine was ingested into the trailing vortex within two core lengths. The vortex inhibits entrainment and thermally insulates the hot gases in the core from the stratosphere. The final buoyancy phase started only ten seconds after leaving the trailing edge. The temperature rise in the wake of the supersonic aircraft is much greater than that for a subsonic transport since temperature rise was found to vary directly as speed squared and inversely as aspect ratio. The buoyancy theory incorporates an entrainment coefficient which is a function of local turbulence condi-tions. Comparison between the buoyancy calculations for the supersonic case with nondimensionalized subsonic aircraft contrail data on wake spreading showed good agreement. Velocity and temperature profiles have been specified at various stages of the wake, and the analysis in this report can be used to predict variations of concentrations of species such as NO under conditions of chemical reaction.