The formation of a gravity-driven falling particle curtain is important for many problems, including solar tower particle receivers and setting the correct initial conditions for modeling shock interaction with multiphase media. One important characteristic of the curtain is the time history of its fractal dimension that characterizes the evolutionary growth of perturbations along the curtain's extent. For multiphase flows, fractal dimension can be used to help predict the types of instabilities that will occur within the flow. Our experiment aimed to establish the transient and stationary-value fractal dimension of a dense particle curtain with varying thickness containing particles with a density of 1.44 gm/cm(3) and nominal diameter of 40 mu m. High-speed video of the curtain was captured and analyzed. This data from this experiment, besides providing insights into the relevant physical processes, will be used to validate numerical models for multiphase flows.

Daltons and Amagats laws (also known as the law of partial pressures and the law of partial volumes respectively) are two well-known thermodynamic models describing gas mixtures.Our current research is focused on determining the suitability of these models in predicting effects of shock propagation through gas mixtures.Experiments are conducted at the Shock Tube Facility at the University of New Mexico (UNM).The gas mixture used in these experiments consists of approximately 50% sulfur hexafluoride (SF6) and 50% helium (He) by moles.Fast response pressure transducers are used to obtain pressure readings both before and after the shock wave; these data are then used to determine the velocity of the shock wave.Temperature readings are obtained using an ultra-fast mercury cadmium telluride (MCT) infrared (IR) detector, with a response time on the order of nanoseconds.Coupled with a stabilized broadband infrared light source (operating at 1500 K), the detector provides pre-and postshock line-of-sight readings of average temperature within the shock tube, which are used to determine the speed of sound in the gas mixture.Paired with the velocity of the shock wave, this information allows us to determine the Mach number.These experimental results are compared with theoretical predictions of Daltons and Amagats laws to determine which one is more suitable.

We present an experimental study of planar shock interaction with an initially cylindrical, diffuse density interface, where the angle a between the plane of the shock and the axis of the cylinder can be zero (planar normal interaction) or non-zero (oblique interaction). The interface is formed by injecting a laminar jet of a heavy gas mixture (sulfur hexafluoride, acetone, nitrogen) into quiescent air. The jet is stabilized by an annular co-flow of air to minimize diffusion. Interaction between the pressure gradient (shock front) and density gradient leads to vorticity deposition, and during the subsequent evolution, the flow undergoes mixing (injected material - air) and eventually transitions to turbulence. Several parameters affect this evolution, including the angle a, the Atwood number (density ratio), and the Mach number of the shock. For quantitative and qualitative characterization of the influence of these parameters, we use flow visualization in two planes that relies on planar laser-induced fluorescence (PLIF) in acetone, which forms part of the injected material.

We consider two cases of interaction between a planar shock and a cylindrical density interface. In the first case (planar normal shock), the axis of the gas cylinder is parallel to the shock front, and baroclinic vorticity deposited by the shock is predominantly two-dimensional (directed along the axis of the cylinder). In the second case, the cylinder is tilted, resulting in an oblique shock interaction, and a fully three-dimensional shock-induced vorticity field. The statistical properties of the flow for both cases are analyzed based on images from two orthogonal visualization planes, using structure functions of the intensity maps of fluorescent tracer pre-mixed with the heavy gas. At later times, these structure functions exhibit power-law-like behavior over a considerable range of scales. Manifestation of this behavior is remarkably consistent in terms of dimensionless time defined based on Richtmyer's linear theory within the range of Mach numbers from 1.1 to 2.0 and the range of gas cylinder tilt angles with respect to the plane of the shock front (0 to 30 degrees).

Amagat and Dalton mixing-models were analyzed to compare their thermodynamic prediction of shock states. Numerical simulations utilized the Sandra National Laboratories (SNL) shock hydrodynamic code CTH [1]. Simulations modeled the University of New Mexico (UNM) shock tube laboratory experimental series shocking a 1:1 molar mixture of helium (He) and sulfur hexafluoride (SF6). Five input parameters were varied for sensitivity analysis: driver section pressure; driver section density; test section pressure; test section density; and mixture ratio (mole fraction). We show via incremental Latin hypercube sampling (LHS) analysis that significant differences exist between Amagat and Dalton mixing-model predictions. The differences observed in predicted shock speeds, temperatures, and pressures grow more pronounced with higher shock speeds.

An experimental study examines shock acceleration with an initially diffuse cylindrical column of sulfur hexafluoride surrounded by air and inclined with respect to the shock front. Three-dimensional vorticity deposition produces flow patterns whose evolution is captured with planar laser-induced fluorescence in two planes. Both planes are parallel to the direction of the shock propagation. The first plane is vertical and passes through the axis of the column. The second visualization plane is normal to the first plane and passes through the centerline of the shock tube. Vortex formation in the vertical and centerline planes is initially characterized by different rates and morphologies due to differences in initial vorticity deposition. In the vertical plane, the vortex structure manifests a periodicity that varies with Mach number. The dominant wavelength in the vertical plane can be related to the geometry and compressibility of the initial conditions. At later times, the vortex interaction produces a complex and irregular three-dimensional pattern suggesting transition to turbulence. Highly repeatable experimental data are presented for Mach numbers 1.13, 1.4, 1.7, and 2.0 at column incline angles of 0\(^{\circ }\), 20\(^{\circ }\), and 30\(^{\circ }\) for about 50 nominal cylinder diameters (30 cm) of downstream travel.

A cylindrical, initially diffuse density interface is formed by injecting a laminar jet of heavy gas into the test section of a shock tube. The injected gas is mixed with a fluorescent gaseous tracer, small liquid droplets, or smoke particles. The shock tube is tilted with respect to the horizontal. Thus the axis of the gravitystabilized heavy gas jet is at an oblique angle with the plane of the arriving shock front. The flow structure forming after the oblique shock wave interaction with the column of heavy gas is revealed by visualization in multiple planes. We observe the formation of the well-known counter-rotating vortex columns (same as caused by normal shock waves). However, along with them, periodic co-rotating vortices form in the vertical plane in the flow downstream of the oblique shock. The size of these vortices varies both with the Mach number and with the initial angle between the column and the shock front.

When a shock encounters a multiphase interface at an oblique angle, threedimensional (3D) flow effects are produced.Experiments using advanced optical diagnostics seek to elucidate the 3D nature of the flow as it transitions to turbulence.Planar laser-induced fluorescence (PLIF) images capture the development of flow instabilities in a shock-accelerated heavy gas column.Early time images show the counter-rotating vortex pair (CRVP) associated with the Richtmyer-Meshkov instability (RMI) both for normal planar and for oblique shocks, with the cores of the vortex pair parallel to the axis of the original gas column.For the oblique case, a shear-driven Kelvin-Helmholtz instability (KHI) also develops along the axis of the column due to 3D vorticity deposition.The influence of inclination angle of the column with respect to the shock direction on this secondary instability and thus upon the fully 3D flow, is assessed.The 3D data collected in these experiments is essential to the validation of numerical codes predicting a range of problems from scramjets to supernovae.

Both Rayleigh-Taylor instability (RTI [1, 2]) and Richtmyer-Meshkov instability (RMI [3, 4]) develop on a fluid (or gaseous) density interface undergoing sustained (RTI) or impulsive (RMI) acceleration. Misalignment between pressure and density gradients (baroclinicity) leads to vorticity production, and thus to interface perturbation, vortex formation, onset of secondary instabilities, and ultimately to turbulence

Richtmyer–Meshkov instability (RMI) has long been the subject of interest for analytical, numerical, and experimental studies. In comparing results of experiment with numerics, it is important to understand the limitations of experimental techniques inherent in the chosen method(s) of data acquisition. We discuss results of an experiment where a laminar, gravity-driven column of heavy gas is injected into surrounding light gas and accelerated by a planar shock. A popular and well-studied method of flow visualization (using glycol droplet tracers) does not produce a flow pattern that matches the numerical model of the same conditions, while revealing the primary feature of the flow developing after shock acceleration: the pair of counter-rotating vortex columns. However, visualization using fluorescent gaseous tracer confirms the presence of features suggested by the numerics; in particular, a central spike formed due to shock focusing in the heavy-gas column. Moreover, the streamwise growth rate of the spike appears to exhibit the same scaling with Mach number as that of the counter-rotating vortex pair (CRVP).

This work presents an experimental and numerical consideration of the flow developing after a planar shock wave accelerates a cylindrical column of heavy gas seeded with glycol droplets and surrounded by lighter unseeded gas. Special consideration is given to the formation of the gas column, and it is shown that careful modeling of the initial conditions and the tracer behavior is required to accurately match experimental results. Numerical analysis of the instability formation was performed using the Eulerian hydrodynamics code SHAMRC (second-order hydrodynamic automatic mesh refinement code), while the commercial CFD code FLUENT was used to model the formation of the initial conditions used in experiments. Experimental images and numerical results are presented for Mach numbers ranging from 1.2 to 2.1.