Oblique shock interaction with a laminar cylindrical jet (original) (raw)

Oblique shock interaction with a cylindrical density interface

WIT transactions on engineering sciences, 2015

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.

Numerical Simulation of Laser-Induced Fluorescence Imaging in Shock-Layer Flows

AIAA Journal, 1999

Planar laser-induced fluorescence (PLIF) images of nitric oxide (NO) in hypersonic flow over a wedge and a hemisphere are compared with a theoretical PLIF model. The theoretical PLIF images are based on computational fluid dynamics (CFD) models including a perfect-gas model and a nonequilibrium chemistry model. Two dimensional maps of the flow parameters generated by the CFD are used to predict the theoretical PLIF images, including the effects of collisional quenching. We find good agreement between the model and the experimental measurements. We explain how this method of computational flow imaging (CFI) can be useful for designing experiments.

Shock-driven mixing: Experimental design and initial conditions

2012

A new Vertical Shock Tube (VST) has been designed to study shock-induced mixing due to the Richtmyer-Meshkov Instability (RMI) developing on a 3-D multi-mode interface between two gases. These studies characterize how interface contours, gas density difference, and Mach No. affect the ensuing mixing by using simultaneous measurements of velocity/density fields. The VST allows for the formation of a single stably-stratified interface, removing complexities of the dual interface used in prior RMI work. The VST also features a new diaphragmless driver, making feasible larger ensembles of data by reducing intra-shot time, and a larger viewing window allowing new observations of late-time mixing. The initial condition (IC) is formed by a co-flow system, chosen to minimize diffusion at the gas interface. To ensure statistically stationary ICs, a contoured nozzle has been manufactured to form repeatable co-flowing jets that are manipulated by a flapping splitter plate to generate perturbations that span the VST. This talk focuses on the design of the IC flow system and shows initial results characterizing the interface.

Symmetric and asymmetric shocked gas jets for laser-plasma experiments

The Review of scientific instruments, 2021

Shocks in supersonic flows offer both high density and sharp density gradients that are used, for instance, for gradient injection in laser-plasma accelerators. We report on a parametric study of oblique shocks created by inserting a straight axisymmetric section at the end of a supersonic "de Laval" nozzle. The effect of different parameters, such as the throat diameter and straight section length on the shock position and density, is studied through computational fluid dynamics (CFD) simulations. Experimental characterizations of a shocked nozzle are compared to CFD simulations and found to be in good agreement. We then introduce a newly designed asymmetric shocked gas jet, where the straight section is only present on one lateral side of the nozzle, thus providing a gas profile well adapted for density transition injection. In this case, full-3D fluid simulations and experimental measurements are compared and show excellent agreement.

Effects of Axisymmetric Square-Wave Excitation on Transverse Jet Structure and Mixing

AIAA Journal, 2019

The influence of temporal square-wave excitation on structural and mixing characteristics of an equidensity, gaseous jet in crossflow (JICF) was explored in the present study. As in separate unforced and sinusoidally excited JICF experiments, acetone planar laser-induced fluorescence imaging enabled this detailed quantification for the JICF for mean jet-to-crossflow momentum flux ratios J ranging from J 41 (with a convective unstable upstream shear layer, or USL, in the absence of forcing) to J 5 (with a globally unstable USL). Such square-wave excitation of the jet fluid required adaptive feedforward control, not only to create more accurate temporal square waveforms but to enable more accurate comparison among alternative forcing conditions. Square-wave excitation of the JICF demonstrated a significant influence on the naturally globally unstable JICF, where specific nondimensional stroke ratios within J-dependent ranges could produce deeply penetrating, periodic vortices with improved jet penetration and spread. Enhanced jet penetration did not always correlate with better molecular mixing, however; there was a stronger correlation of improved mixing at higher J values with creation of a more symmetric jet cross section via square-wave excitation, especially one with a clear counter-rotating vortex pair structure.

The Time Evolution of the Flow Fields and Mixing Characteristics of Non-Reactive Jets

2010

Numerical simulations are used to study an under-expanded sonic jet injected into a supersonic crossflow and an over-expanded supersonic jet injected into a subsonic crossflow. A finite volume compressible Navier–Stokes solver developed by Park & Mahesh (2007) for unstructured grids is used. The flow conditions are based on Santiago et al.’s (1997) and Beresh et al.’s (2005) experiments for sonic and supersonic injection, respectively. The simulations successfully reproduce experimentally observed flow vortical structures and shock systems such as the barrel shock, Mach disk, horseshoe vortices that wrap up in front of the jet and the counter rotating vortex pair (CVP) downstream of the jet. The time averaged flow fields are compared to the experimental results, and reasonable agreement is observed.

Momentum and scalar transport at the turbulent/non-turbulent interface of a jet

Journal of Fluid Mechanics, 2009

Conditionally sampled measurements with particle image velocimetry (PIV) of a turbulent round submerged liquid jet in a laboratory have been taken at Re = 2 × 103 between 60 and 100 nozzle diameters from the nozzle in order to investigate the dynamics and transport processes at the continuous and well-defined bounding interface between the turbulent and non-turbulent regions of flow. The jet carries a fluorescent dye measured with planar laser-induced fluorescence (LIF), and the surface discontinuity in the scalar concentration is identified as the fluctuating turbulent jet interface. Thence the mean outward ‘boundary entrainment’ velocity is derived and shown to be a constant fraction (about 0.07) of the the mean jet velocity on the centreline. Profiles of the conditional mean velocity, mean scalar and momentum flux show that at the interface there are clear discontinuities in the mean axial velocity and mean scalar and a tendency towards a singularity in mean vorticity. These actu...

Transverse jet mixing characteristics

This experimental study explores and quantifies mixing characteristics associated with a gaseous round jet injected perpendicularly into cross-flow for a range of flow and injection conditions. The study utilizes acetone planar laser-induced fluorescence imaging to determine mixing metrics in both centreplane and cross-sectional planes of the jet, for a range of jet-to-cross-flow momentum flux ratios (2 J 41), density ratios (0.35 S 1.0) and injector configurations (flush nozzle, flush pipe and elevated nozzle), all at a fixed jet Reynolds number of 1900. For the majority of conditions explored, there is a direct correspondence between the nature of the jet's upstream shear layer instabilities and structure, as documented in detail in Getsinger et al. (J. Fluid Mech., vol. 760, 2014, pp. 342–367), and the jet's mixing characteristics, consistent with diffusion-dominated processes, but with a few notable exceptions. When quantified as a function of distance along the jet trajectory, mixing metrics for jets in cross-flow with an absolutely unstable upstream shear layer and relatively symmetric counter-rotating vortex pair cross-sectional structure tend to show better local molecular mixing than for jets with convectively unstable upstream shear layers and generally asymmetric cross-sectional structures. Yet the spatial evolution of mixing with downstream distance can be greater for a few specific convectively unstable conditions, apparently associated with the initiation and nature of shear layer rollup as a trigger for improved mixing. A notable exception to these trends concerns conditions where the equidensity jet in cross-flow has an upstream shear layer that is already absolutely unstable, and the jet density is then reduced in comparison with that of the cross-flow. Here, density ratios below unity tend to mix less well than for equidensity conditions, demonstrated to result from differences in the nature of higher-density cross-flow entrainment into lower-density shear layer vortices.