It is common for jets of fluid to interact with crossflow. This article reviews our understanding of the physical behavior of this important class of flow in the incompressible and compressible regimes. Experiments have significantly increased in sophistication over the past few decades, and recent experiments provide data on turbulence quantities and scalar mixing. Quantitative data at high speeds are less common, and visualization still forms an important component in estimating penetration and mixing. Simulations have progressed from the Reynolds-averaged methodology to large-eddy and hybrid methodologies. There is a general consensus on the qualitative structure of the flow at low speeds; however, the flow structure at low-velocity ratios (jet speed/crossflow speed) might be fundamentally different from the common notion of shear-layer vortices, counter-rotating vortex pairs, wakes, and horseshoe vortices. Fluid in the near field is strongly accelerated, which affects the jet trajectory, entrainment, ...

The Interaction of Jets with Crossflow

We report an experimental investigation that reveals significant differences in the near-flowfield properties of hydrogen and ethylene jets injected into a supersonic crossflow at a similar jet-to-freestream momentum flux ratio. Previously, the momentum flux ratio was found to be the main controlling parameter of the jet’s penetration. Current experiments, however, demonstrate that the transverse penetration of the ethylene jet was altered, penetrating deeper into the freestream than the hydrogen jet even for similar jet-to-freestream momentum flux ratios. Increased penetration depths of ethylene jets were attributed to the significant differences in the development of large-scale coherent structures present in the jet shear layer. In the hydrogen case, the periodically formed eddies persist long distances downstream, while for ethylene injection, these eddies lose their coherence as the jet bends downstream. The large velocity difference between the ethylene jet and the freestream induces enhanced mixing at the jet shear layer as a result of the velocity induced stretching-tilting-tearing mechanism. These new observations became possible by the realization of high velocity and high temperature freestream conditions which could not be achieved in conventional facilities as have been widely used in previous studies. The freestream flow replicates a realistic supersonic combustor environment associated with a hypersonic airbreathing engine flying at Mach 10. The temporal evolution, the penetration, and the convection characteristics of both jets were observed using a fast-framing-rate (up to 100 MHz) camera acquiring eight consecutive schlieren images, while OH planar laser-induced fluorescence was performed to verify the molecular mixing.

Time evolution and mixing characteristics of hydrogen and ethylene transverse jets in supersonic crossflows

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

An experimental investigation was conducted to compare the supersonic mixing performance of a novel e ush-wall aerodynamic ramp injector with that of a physical ramp injector. The aerodynamic ramp injector consists of nine e ush-wall jets arranged to produce fuel‐ vortex interactions for mixing enhancement in a supersonic crosse ow. Test conditions included a Mach 2.0 crosse ow of air with a Reynolds number of 3.63 10 7 per meter and helium injection with jet-to-freestream momentum e ux ratios of 1.0 and 2.0. Conventional probing techniques, including species composition sampling, were employed to interrogate the e owe eld at several downstream locations. Results show that with increasing jet momentum the aeroramp exhibited a signie cant increase in fuel penetration, whereas the physical ramp showed no discernible change. The near-e eld mixing of the aeroramp was superior to that of the physical ramp; however, the physical ramp reaches a fully mixed condition at approximately half the distance of the aeroramp. As the jet momentum was increased, the far-e eld mixing performance of the aeroramp approached that of the physical ramp. In all cases the total pressure loss incurred with the aeroramp was less than that caused by the physical ramp. For both injectors the total pressure loss decreased with increasing jet momentum. It was concluded that, although physical ramps may provide better far-e eld mixing, properly designed e ush-wall injection can provide comparable mixing performance while avoiding the practical problems associated with an intrusive geometry in a scramjet combustor.

Comparison of Physical and Aerodynamic Ramps as Fuel Injectors in Supersonic Flow

Pre-test computational fluid dynamics (CFD) data have been generated for an experimental scramjet combustor concept. These calculations represent the first step of a research initiative at Wright-Patterson Air Force Base that combines state-of-the-art experimental facilities with CFD towards the development of scramjet propulsion technologies. Both cold flow and reacting simulations have been performed for a baseline combustor pilot concept that consists of a wall mounted fuel injection system combined with a cavity flameholder. Results show reasonable mixing levels with minimal total pressure losses. Reacting simulations have shown that further refinements are needed to the combustor geometry to prevent thermal choking under certain conditions. Data obtained from CFD have proven beneficial to the experimental program by directing tests towards evaluating potential problems revealed by the calculations. Preliminary comparisons with measurements were favorable.

A numerical and experimental investigation of a scramjet combustor for hypersonic missile applications

Temporally correlated Rayleigh/Mie scattering images were used to examine the convection characteristics of the large-scale vortex structures developing in flowfields created by sonic transverse injection through circular and elliptical nozzles into a Mach 1.98 crossflow. Both compressibility and injector geometry were found to have significant influences on the convection characteristics of the large eddies. High compressibility injection cases produce eddies having dramatically larger near-field convection velocities than those in low compressibility cases. Farther downstream, the large-scale vortices tend to travel at velocities nearer the freestream veocity. Injector geometry primarily affects the near-field behavior.

A. S. Nejad

Papers

Large structure convection velocity measurements in compressible transverse injection flowfields

Large structure convection velocity measurements in compressible transverse injection flowfields

Circular and elliptical transverse injection into a supersonic crossflow-- the role of large-scale structures