Wind Tunnel Tests of a Shrouded Aircraft Inlet

We describe tests of a shrouded aerosol inlet for a high-altitude jet aircraft. Both the lip of the inlet and the shroud are NACA (National Committee for Aeronautics, now known as NASA, or National Aeronautics and Space Administration) airfoils. Wind tunnel tests show a smooth growth of the boundary layer in the inlet, with an undisturbed core more than I m back from the entrance. The shroud makes the inlet performance insensitive to angle of attack. Aerosol transmission tests showed accurate sampling, although the Stokes numbers accessible in the wind tunnel were less than 0.2. AEROSOL SCIENCE AND TECHNOLOGY 28:33-39 (1998) O 1998 American Association for Aerosol Research INTRODUCTION The problem of bringing aerosols from outside a jet aircraft into aerosol instruments without changing the number or composition of aerosols is a difficult problem. The Airborne Aerosol Inlet Workshop held in 1991 found that many existing aircraft aerosol inlets were inadequate (Baumgardner et al., 1991). In particular, 50-90% losses of aerosols have been observed in aircraft inlets (Huebert et al., 1990). As the Mach number becomes larger, isokinetic sampling is important not only to maintain representative aerosol numbers but also to avoid ram heating. Such heating is over 20 K if the flow is brought to stagnation from a Mach number of 0.7, enough to affect volatile species on the aerosols. We are building an aircraft version of a new instrument to analyze the chemical composition of single particles (Murphy and *The Author to whom correspondence should be addressed. ' Also with the Cooperative Institute for Research in Environmental Sciences, University of Colorado. Aerosol Science and Technology 28:33-39 (1998)