Uncertainty reduction of unsteady drag coefficient measurements for monodispersed micronsized particles*

The Los Alamos National Laboratory Horizontal Shock Tube (HST) studies response of shock-accelerated particles in a gas. When subjected to the highly unsteady flow of a shock, normal drag coefficients may not properly predict the motion of the particles. These experiments were done as a part of an ongoing campaign to improve drag laws in this regime and are performed in conjunction with computational efforts. Individual particle positions were obtained using a high speed eight-pulse particle tracking technique. Solid particles of several nominal diameters selected from the range of 1-10 μm were subjected to 1.2, 1.3, and 1.4 Mach number shocks in air. The nominal particle diameter was obtained from vendor specifications and physical measurement of the size distribution before injection into the shock tube. These particles had diameter standard deviations < 1 μm, as compared to previous work with distributions larger than +/- 1-2 μm. We will demonstrate how control of the particle diameter uncertainty reduce the bias in the computed drag coefficients. As a result, we see a reduction in estimated drag as compared to previous measurements with polydispersed diameter distributions. This can be attributed to reduction in uncertainty and systematic error.