Experimental And Numerical Study On Flow Characteristics In Micro Shock Tubes

Recently micro shock tubes have been widely used in many engineering and industrialapplications, but detailed flow characteristics are not well known to date. Compared to macroshock tubes, unsteady flows related to the moving shock waves are highly complicated due tomore active viscous dissipation and rarefaction effects in micro shock tubes. This makes shockwave dynamics significantly different from theoretical predictions. Due to effects of the scale,shock wave experiences more attenuation in micro shock tubes.This paper aims at shock wave and contact surface propagation, shock wave attenuation andboundary layer formation by performing different diaphragm pressure ratios and different shocktube diameters in micro shock tube models. In addition, no-slip and slip wall boundaryconditions will be also operated. Firstly, a pressure measurement has been performed to studyshock wave propagation in a contoured shock tube device. High sensitive pressure transducerswill be used to record pressure change as shock wave moves through the test section. Thenschlieren visualization was conducted to observe the dynamic behavior of shock wave atdifferent diaphragm pressure ratios. Finally, a Computational Fluid Dynamics (CFD) approachhas been also used to understand the flow characteristics in micro shock tube models. A fullyimplicit finite volume scheme and density-based solver will be employed to solve the unsteadycompressible Navier-Stokes equations.Results showed that shock wave and contact surface velocity increase with the increase of thediaphragm pressure ratio. As shock wave moves in micro shock tube, shock wave strengthgradually decreases. A thicker boundary layer is observed at the lower driven pressure, whichindicates that low pressure effect makes shock wave and flow more energy loss. As shock waveand contact surface propagate in micro shock tube, pressure gradient of flow in the front andafter shock wave gradually decreases and contact surface velocity increases. In addition, S valuecan indicate effects of low pressure and small scale in micro shock tube. The utilization of slipwall boundary condition reduces the boundary layer effects and promotes shock wavepropagation. For experimental study, the primary normal shock and oblique shock systemdominating the starting process existed as a result of the expanded nozzle operation wereobtained. As the oblique shock waves are reflected, the shock strength gradually decreases. Inthe future time, Particle Image Velocimetry (PIV) and CFD study will be performed in presentneedle-free drug delivery device. The results will be compared with the obtained experimentalresults.