Chemical Jettisoning Simulation (CJSIM) for Airborne Laser Aircraft

    Recent work at CDI entailed the development of a model for predicting the deposition of chemicals jettisoned into the atmosphere from an airborne laser aircraft. The model was denoted CJSIM (Chemical Jettison SIMulation) and is an evolved version of the closely related FJSIM (Fuel Jettison SIMulation) model. CJSIM offers an ideal personal computer platform for predicting the groundfall of chemicals jettisoned from altitude by aircraft; it was designed to assist USAF and DoD environmental planners and safety personnel in efficiently responding to, assessing, and documenting the impacts of chemical release events (both planned and unplanned) associated with the Chemical Oxygen Iodine Laser (COIL) while airborne.

    CJSIM directly incorporates the effects of the aircraft wake and ambient meteorology (pressure, temperature, wind speed, and wind direction) on the chemicals jettisoned from the aircraft, by using a Lagrangian droplet trajectory analysis whose predictions have been validated by numerous agricultural and forestry field studies during the development of its parent code (AGDISP) by the USDA Forest Service. Extension to the jettison heights and downwind distances anticipated here is inferred by use of the same validated analytical approach. The liquid chemical spray is initialized with the corrected drop size distribution and subjected to multicomponent evaporation effects.

    In the current release of CJSIM, the user enters pertinent chemical information, flight conditions, and meteorological values, through a user-friendly, menu-driven Microsoft Windows-based personal computer interface (Figure 1), and obtains graphical and numerical output for droplet evaporation time history and subsequent surface deposition (for liquid releases) and concentration behavior (for gaseous releases).

Figure 1: CJSIM main input screen. The B747-400 aircraft is visualized by a simple scanned drawing, depicting the sources for chemical release

    Recent improvements to the CJSIM software entailed modifications to enhance ease of use, expand the included chemical type inventory, and extend the array of jettison port locations and flow rates (or release volume) treated. Output of the model includes computations of surface area affected and total mass and volume at the surface, along with detailed histories of droplet trajectory and evaporation as well contour plots of vapor concentrations.

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