The mixing characteristics of an underexpanded sonic jet injected into a Mach 1.6 crosse ow are studied experimentally. Shadowgraph photography and planar laser-induced e uorescence from acetone are used to obtain temporally resolved e owe eld visualizations of a side viewof the barrel shock region, a side view of the downstream plume, and an end view cross section of the plume. Instantaneous images, mean and standard deviation images, and image-intensity probability density functions (PDFs) are used to study the mixing produced by large-scale turbulent structures. PDFs show that time-averaged mixture fraction measurements greatly overestimate the actual level of instantaneous mixing in the e owe eld. Comparisons of the instantaneous images and PDFs show the role of large-scale rolling structures and jetlike plumes in transporting coherent packets of e uid across the threedimensional shear layer formed between the jet and crosse ow. Signie cant instantaneous mixing in this e owe eld occursin the wakeregiondownstream ofthebarrel shock region and below thejetcenterline.Thecounter-rotating streamwisevortex pairin thejetplumeplaysan importantrole in the scalarmixing processes becauseit transports jet e uid down toward the wake and entrains crosse ow e uid from below up into the jet.

Mixing of a Sonic Transverse Jet Injected into a Supersonic Flow

The flowfields created by transverse injection of sonic gaseous jets through a circular nozzle into a supersonic crossflow have been experimentally investigated using planar Rayleigh/Mie scattering from silicon dioxide particles seeded into the crossflow stream. Helium and air were used as injectant gases allowing an examination of the effects of compressibility on the large-scale structural development and near-field mixing characteristics present within the flowfield. Instantaneous images from end and side view image planes show a highly three-dimensional interaction dominated by both large- and small-scale vortices. Analyses of these image ensembles provide jet spreading and penetration characteristics, standard deviation statistics, large-scale mixing information, and two-dimensional spatial correlation fields. Results indicate that injectant molecular weight variations do not strongly affect the jet’s transverse penetration into the crossflow, although they lead to substantially different compressibi...

Compressibility effects in supersonic transverse injection flowfields

New supersonic combustion research facility

Computational predictions of transverse injection of air, helium, and ethylene into a Mach 1.98 crossflow of air are presented. A hybrid large-eddy simulation/Reynolds-averaged Navier―Stokes turbulence model is used. A blending function, dependent on modeled turbulence variables, is used to shift the turbulence closure from the Menter t-ω model near solid surfaces to a Smagorinsky subgrid model in the outer part of the incoming boundary layer and in the jet mixing zone. The results show reasonably good agreement with time-averaged Mie-scattering images of the plume structure for both helium and air injection and with experimental surface pressure distributions, even though the penetration of the jet into the crossflow is slightly overpredicted. Predictions of ethylene mole fraction at several transverse stations within the plume are in good agreement with time-averaged Raman-scattering mole-fraction data. The model results are used to examine the validity of the commonly used assumption of the constant turbulent Schmidt number in the intense mixing zone downstream of the injection location. The assumption of a constant turbulent Schmidt is shown to be inadequate for jet mixing dominated by large-scale entrainment.

Large-Eddy/Reynolds-Averaged Navier-Stokes Simulations of Sonic Injection into Mach 2 Crossflow

In flowfields created by transverse injection into supersonic cross-flows, the bow and separation shocks formed upstream of the injectant plume are dominant features. In the present investigation, the interaction between these features and the large-scale eddies that develop at the jet/freestream interface has been examined.

Bow shock/jet interaction in compressible transverse injection flowfields

: Transverse injection of helium and air through circular and elliptical nozzles into a supersonic cross flow was investigated using optical diagnostics and probe-based measurement techniques. Shadowgraph visualizations documented the global characteristics of the jet/freestream interaction. Rayleigh/Mie scattering allowed ensembles of digital images from several measurement planes in each case to be collected. Pitot and concentration probes were used in the helium injection cases. The images provide mean and standard deviation statistics, spreading and penetration characteristics, large-scale mixing and convective velocity information, bow and separation shock features, and two-dimensional spatial correlation fields. Results indicate that the elliptical nozzle produces jets with greater lateral spread and suppressed transverse penetration compared to the jets from the circular nozzle. Injectant molecular weight does not strongly affect the jet's penetration, although it leads to substantial compressibility differences that dramatically influence the characteristics of the large-scale shear layer structures and the entrainment and mixing occurring between the injectant and crossflow. Probe measurements provide quantitative comparisons of total pressure losses and mixing characteristics. Results suggest better near field mixing and lower total pressure losses in the elliptical injection flowfield.

An Experimental Investigation of Transverse Injection from Circular and Elliptical Nozzles into a Supersonic Crossflow.

: The Experimental Research Branch of the Advanced Propulsion Division at Wright-Patterson Air Force Base began taking steps toward the development and installation of a supersonic combustion research facility during FY90. A large- scale in-house research facility devoted to the study of supersonic fuel air mixing and combustion has been designed, fabricated, and installed. The purpose of the report that follows is to present documentation of the features of the air supply system, the design details and the characteristics of the actual supersonic combustion tunnel, and a description of the control system and instrumentation. Supersonic flow, Supersonic tunnel, Instrumentation nozzle, Laser diagnostics.

Abdollah S. Nejad

Papers

An Experimental Investigation of Transverse Injection from Circular and Elliptical Nozzles into a Supersonic Crossflow.

Supersonic Combustion Research Laboratory. Volume 1. Design and Fabrication