High-Volume Low-Turbulence Inlet for Aerosol Sampling from Aircraft

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9713408 Seebaugh In this project, a high-volume low-turbulence aerosol inlet for use on the NCAR C-130 aircraft will be designed, constructed, and its performance demonstrated. This inlet will enable the sampling of supermicron aerosols up to 10 micrometer aerodynamic diameter. A low turbulence inlet is required to minimize particle losses to the inlet walls. Boundary layer suction in the diffuser section of the inlet will be used as the turbulence mitigation technique. The proposed inlet will have a flow rate of 200-400 liters per minute to supply a high-volume cascade impactor system. This project will also make it possible to design similar inlets for other more general aerosol sampling applications since the target flow rate is higher than many other requirements. A reference inlet (without boundary layer suction) will be built to provide a baseline for evaluation of the turbulence reduction techniques. It will use a conical diffuser of conventional design to produce a velocity reduction (ratio of diffuser entrance to exit velocity) of a factor of 20. The reference inlet will be tested over a range of conditions corresponding to the flight envelope of the C-130 aircraft to determine the flow characteristics (time mean velocity and turbulence intensity) at the diffuser exit. A low turbulence inlet (using boundary layer suction) will be built as an enlarged version of the inlet successfully demonstrated during prior NSF project. The diffuser section will be manufactured from a cast and sintered porous plastic. About 60-80% of the inlet flow will be removed by suction to achieve the desired velocity reduction of a factor of 20. In the second year, the low turbulence inlet will be characterized and optimized in the laboratory. A flight system for the C-130 aircraft will be designed and constructed. By combining measurements of the flow characteristics at the diffuser exit and computational fluid dynamics analysis of the flow within and through the walls of the diffuser, the flow stre amlines inside the inlet and the inertial enhancement for large particles will be determined. The inertial enhancement will also be determined experimentally by measuring the size distribution of particles outside the inlet and at the diffuser exit during operation using either an optical particle counter or an aerodynamic particle sizer for several selected test conditions. The objectives of the third year effort are flight testing of the inlet and operational assistance for users of the inlet system.