Optimization and Uncertainty Reduction of Drag in Liquid and Solid Microparticle Suspensions forShock Accelerated Particles

Los Alamos National Laboratory’s Horizontal Shock Tube (HST) facility is studying acceleration of micronscale

liquid and solid droplets due to shocks for particle drag experiments in a gas. Applications include

transport of ejecta particles subject to multiple shocks. The unsteady forces on microparticles driven by a

shock are not well understood and are difficult to model. In this inherently unsteady system, it is not clear

standard drag coefficients will properly predict the motion of particles. The drag coefficient is dependent

on the particle diameter; to study these systems carefully controlled and quantified seeding of the flow

field is required. We detail how we optimized the seeding systems to introduce microparticles into our

shocktube and monitored the resulting distributions. Several nominal diameters selected ranging from 1-

10 μm were subjected to Mach 1.2, 1.3, and 1.4 shocks in air. These particles had diameter standard

deviations < 1 μm, as compared to previous work with distributions larger than +/- 2-3 μm. We

demonstrate how control of particle diameter uncertainty reduces bias in the computed drag coefficients.

Results show reduction in estimated drag compared to previous work with larger size distributions. This

can be attributed to reduction in uncertainty and systematic error. The current experiments are part of a

campaign to improve drag laws in this regime performed in conjunction with computational validation

efforts.