Reducing the uncertainty of unsteady drag coefficient measurements for micron-sized particles

At Los Alamos National Laboratory’s Horizontal Shock Tube (HST) facility we are studying acceleration of shocked isolated micron-scale liquid and solid droplets in a gas. Unsteady forces on microparticles driven by a shock wave are not well understood and difficult to model, therefore standard drag coefficients may not predict the motion of particles. Our current experiments are part of an ongoing campaign to improve drag laws in this regime and performed in conjunction with validation and computational efforts. We detail the optimization of our micron-sized particle seeding systems for both liquid and solid particles, including monitoring resulting distribution. This assisted in reducing random and systematic uncertainty of resultant drag coefficient measurements. This work was done by carefully controlling and tuning liquid spray injector and particle solution concentration. Sifting of solid particles was also performed prior to injecting into test section. We minimize moisture and electrostatic forces which cause clumping by implementing a new grounded stainless-steel particle recirculation system. As final step we created synthetic data to evaluate our processing technique. As a result, we see a reduction in estimated drag which can be attributed to reduction in uncertainty.