Supersonic Crossflow Research Articles

Effects of the penetration height of ethylene transverse jets on flame stabilization behavior in a Mach 2 supersonic crossflow

Effects of fuel jet penetration height on supersonic combustion behaviors were investigated experimentally in a supersonic combustion ramjet model combustor at a Mach speed of 2 and at a stagnation temperature of 1900 K. The jet-to-crossflow momentum flux ratio was varied to control the fuel-jet penetration height, using several injectors with different orifice diameters: 2, 3, and 4 mm. First, transverse nitrogen jets were observed to identify a relationship between the fuel jet penetration height and the momentum flux ratio by focusing Schlieren photography. Then, supersonic combustion behaviors of ethylene were investigated through combustion pressure measurements. Simultaneously, time-resolved images of CH* chemiluminescence and shadowgraphs were recorded with high-speed video cameras. Furthermore, a morphology of supersonic combustion modes was investigated for various equivalence ratios and fuel penetration heights in a two-dimensional latent space trained by the shared Gaussian process latent variable models (SGPLVM), considering CH* chemiluminescence images and the shock parameters. The results indicated that the penetration height of nitrogen jets was a function of the jet momentum flux ratio; this function was expressed by a fitting curve. Five typical combustion modes were identified based on time-resolved CH* chemiluminescence images, shadowgraphs, and pressure profiles. Even for a given equivalence ratio, different combustion modes were observed depending on the fuel penetration height. For an injection diameter of 3 and 4 mm, cavity shear-layer and jet-wake stabilized combustions were observed as the scram modes. On the other hand, although the cavity shear-layer and lifted-shear-layer stabilized combustions were observed, no jet-wake stabilized combustion was observed for an orifice diameter of 2 mm. Fuel penetration heights above the cavity aft wall were expected to affect the combustion behavior. Finally, a morphology of the supersonic combustion modes was clearly shown in the two-dimensional latent space of the SGPVLM.

Liquid jet injection in supersonic crossflow: Self-induced jet oscillations and its effects

Liquid jet injection into supersonic crossflow is one of the conceptually simple ways of fuel atomization in Scramjet engines. In the present work, we experimentally investigate the flow and spray formed due to the injection of a liquid jet in supersonic crossflow with free stream Mach number of M∞ = 2.5. The main focus of the work is on the unsteady aspects of the flow and spray, which are found to be self-induced and occur naturally in the flow. High speed shadowgraphy shows large variations in the windward spray edge and penetration with time. Unsteady pressure measurements in the liquid injection line show that in the presence of a supersonic crossflow, there exist significant self-generated mass flow fluctuations that occur in the injection line. The frequency of these oscillations is seen to be close to a Strouhal number, St = fδ /U∞ ≈ 0.007, close to the typical low frequencies seen in Shock-Wave Boundary Layer Interaction studies (δ = boundary layer thickness). The variations in mass flow rate within the injection line leads to significant fluctuations of the spray penetration and shocks. In particular, the variations in spray penetration with time is observed to lead to significant variations in both the droplet numbers and size at a given location in the generated spray, which can have significant implications for applications where such configurations are used.

Influence of downstream ramp on mass diffusion of various coaxial hydrogen and air injectors at supersonic combustion chamber

The mixing efficiency of injection system inside combustion chamber of the scramjet significantly influence on the total performance of the hypersonic vehicles. In this study, the existence of the downstream ramp on the flow structure of hydrogen cross jet at supersonic air stream is comprehensively investigated. Computational fluid dynamic method is used to simulate flow structure of sonic hydrogen jet at supersonic air cross flow in existence of ramp positioned downstream of annular injectors. Effects of different annular injectors on mixing and penetration of fuel jet are also disclosed. Besides, effects of ramp angles on the distribution of hydrogen jet are also explored. Comparison of the 3-lobe injector in two different downstream angles of 10 and 30 deg indicates that the mixing efficiency increase about 30% when the angle of the downstream ramp is increased from 10 deg to 30 deg. Moreover, our results show that fuel mixing of the 3-lobe injector with ramp angle of 30 deg is about 55% more than circular jet at the same condition.

Numerical investigation on mixing process of a sonic fuel jet into a supersonic crossflow

The mixing process of a fuel jet in a supersonic crossflow is one of the significant issues for the design of the scramjet combustor. In this paper, the orthogonal analysis was employed to investigate the influences of the parameters of the supersonic mainstream and the fuel jet on the mixing process. Eight variables were considered and 27 cases were performed by the three-dimensional Reynolds-averaged Navier-Stokes (RANS) coupled with the shear stress transport (SST) turbulence model. The results show that the jet patterns can be divided into three categories by calculating the velocity ratio, named attachment pattern, transition pattern, and separation pattern, respectively. The extreme difference analysis indicates that the total pressure and Mach number of the mainstream, the total pressure of the fuel jet, and the diameter of the jet hole have a remarkable impact on the penetration depth and total pressure recovery. Additionally, a new dimensionless number named BS was proposed. And the penetration depth and total pressure recovery can be fitted to different functions of the BS. The fitted curves show that the larger penetration depth and smaller total pressure loss are generated as the BS increases. Finally, another new dimensionless number named LJ was proposed. And a positive correlation between the LJ and mixing efficiency has been elaborated based on analyzing the influence mechanism of the streamwise vortexes and the shockwaves on the mixing process. These correlations can provide help for primary optimization of supersonic combustor.

Penetration of a kerosene liquid jet injected in a high temperature Mach 2 supersonic crossflow

Penetration of a kerosene liquid jet injected in a high temperature Mach 2 supersonic crossflow

Numerical Study of the Induced Shock on the Mixing Augmentation of Hydrogen Counter-Flow Jet in the Supersonic Flow

In the scramjet engine, the injection and mixing of fuel are the basis for organizing efficient combustion. The shock wave/jet shear layer interaction is one of the methods used to enhance fuel mixing in supersonic flow. In this research, the effect of the induced shock wave on the mixing augmentation of fuel counter-flow jet is studied in the supersonic crossflow. The results show that the symmetrical setting of the shock wave generators (SWGs) has the highest mixing efficiency but brings a greater total pressure loss. In the specific range, the mixing efficiency increases with the increase in the angle of the SWG, while the total pressure recovery coefficient is the opposite. The induced oblique shock wave acting on the front of the fuel jet has an obvious influence on the flow field, resulting in the highest mixing efficiency. In the end, the analytic hierarchy process (AHP) is used to evaluate the extent of mixing augmentation by mixing parameters, which provides a decision-making idea for the scheme decision of mixing augmentation.

Dual Injection in Supersonic Crossflow: Analysis Jet Shear Layer from Schlieren Images

In supersonic-combustion ramjets (scramjets), fuel is injected, which should mix rapidly with the supersonic crossflow to minimize the length of the scramjet. Tandem dual-jet injection has shown improved mixing performance over single-jet injection. However, experiments on tandem dual-jet injection have not addressed the jet shear layer, in which the mixing occurs, yet. The present study investigates the jet shear layer, as well as the bow shocks in front of the jets, in a continuous air-indraft supersonic wind tunnel at Mach number 1.55. A schlieren setup has been used for visualizing the flow features. A largely automated algorithm for processing schlieren images has been developed to determine the location of the upper boundary of the jet shear layer. The penetration of the jet is studied as a function of 1) , the ratio of the momentum of the jet and that of the crossflow, and 2) the dimensionless distance between the dual-jets. An empirical similarity relation has been established for the time-averaged location of the jet upper shear layer as function of and , covering the investigated conditions (, ). This empirical similarity relation provides , the spacing for maximal penetration of the jets as function of .

Shock wave boundary layer interactions in sonic gas jet injection into supersonic crossflow

Shock wave boundary layer interactions in sonic gas jet injection into supersonic crossflow

The presence of downstream ramp on fuel mixing of the multi micro jets at supersonic cross flow

Development of the fuel injection system in combustion chamber is greatly important for the overall thrust efficiency of the high-speed vehicles. Current article developed a three-dimensional model to discover the reality of downstream ramp on fuel mixing of the multi-jet at Ma>1. FVM is hired to scrutinize the impact of injector types (3-lobe, circular and rectangular shape) on the mixing productivity of downstream ramp in combustion chamber. Besides, the effects of ramp angle on fuel mixing are also analysed. Fuel mixing mechanisms in the selected models are investigated by comparing the Ma contour and mixing zone. Comparisons of the circulation strength downstream of these models confirm that the 3-lobe nozzles is more efficient than other styles. Our comparison indicates that overall mixing productivity of the circular jet is more than other cases.

Influence of jet spacing in spanwise-inclined jet injection in supersonic crossflow

In separation control with air-jet vortex generators in supersonic flow, the spacing of the jets in a row array has a crucial effect on the control effectiveness. Previous experimental studies have revealed the overall influence of jet spacing on air-jet vortex generator controlled shock-induced separation zones, focusing mostly on the separation regions. There is, however, a gap in knowledge regarding the mechanisms leading to these changes in control effectiveness, particularly on the interaction between multiple jets and the details of downstream flow evolution. Therefore, the objective of the current study is to provide detailed information on the underlying flow dynamics associated with the injection of a row of spanwise-inclined jets into a supersonic turbulent boundary layer – and in particular the effects of different jet spacings. Four different spacings were studied with large-eddy simulations. In addition, we performed oil-flow and schlieren visualizations of separation control in a 24$^\circ$compression–ramp interaction with different jet-spacing configurations to validate and discuss our conclusions regarding the effects of jet/jet interactions on the separation-control effectiveness. We analyse the influence of jet spacing on the flow topology, induced vortical structures, and boundary-layer statistics. The jet-induced major vortex pair is the dominant flow structure energizing the near-wall boundary layer. The paper details how interactions amongst adjacent vortex pairs differ for varying jet spacings, thus influencing the momentum transfer and eventually the control efficiency. The dynamic behaviour of the flow was analysed using a three-dimensional dynamic mode decomposition. The resulting insights are key to the development of efficient control set-ups.

Control mechanism of the three-dimensional shock wave/boundary layer interaction with the steady and pulsed micro-jets in a supersonic crossflow

The separation induced by shock wave/boundary layer interactions (SWBLI) is detrimental to the performance of the flow field, and thus, needs to be reduced by using passive or active approaches. In this study, the authors numerically evaluate flow control induced by steady and pulsed micro-jets to capture the mechanism of control of three-dimensional (3D) SWBLIs. The volume of the separation zone is accurately calculated to assess the control effect. The results predicted by the 3D Reynolds-averaged Navier–Stokes equations coupled with the two-equation κ-ω turbulence model of shear stress transport show that the proposed method of using steady or pulsed micro-jets can significantly reduce the volume of the separation zone induced by shock wave/boundary layer interactions. The best comprehensive effect of control over the flow field was obtained by using a high frequency angled jet—namely, case P5—as it reduced the volume of the separation zone by 19.43% with only a small loss in the total pressure. The upwash and downwash motions induced by the streamwise counter-rotating vortex pairs of the jet constituted a key factor influencing the control of the separation zone.

Comparison between sonic jets with one jet orifice and two opposite orifices into a Ma-3.0 supersonic crossflow through circular ducts

Large-eddy simulations and nanoparticle-based planar laser scattering experiments are conducted to investigate various physical aspects of transverse sonic jets injected into a Ma-3.0 supersonic crossflow through a circular pipe. Configurations with one jet and two opposite jets are compared. For the single jet, a separation shock is generated by the recirculation zone on the opposite wall, and this intersects with the jet shear layer to push several jet plumes into the near-wall region. For the two jets, the bow shocks interact with each other, forming an oblique shock train. All of the shocks promote vortex breakage in jet wakes. A counter-rotating vortex pair is generated in the jet near-field region, enhancing the local mixing. A near-wall region in the jet lee between the counter-rotating vortex pair branches exhibits a low fuel mass fraction. The jet fluid in the downstream near-wall region is entrained by the crossflow upstream of the jet. The interaction between the bow shocks and shear layers of the two jets induces recirculation zones in the lee of the jet, which enhance the fuel mixing. This explains the phenomenon whereby the total pressure recovery coefficient and mixing efficiency of two jets are higher than those of the single jet.

Numerical study on the transverse jet flow and mixing characteristics of hydrogen/metal powder fuel in powder fuel scramjet

The powder fuel scramjet is one of the most promising propulsion systems for future hypersonic vehicles. To study the flow mechanism and mixing characteristics of gas-particle two-phase fuel in a supersonic crossflow. In this study, the porosity was introduced into the Navier-Stokes equation, and a program suitable for solving gas-particle two-phase flow in the supersonic flow field was developed. The evolution process of vortex structure, hydrogen/metal powder fuel distribution, jet penetration depth, and mixing efficiency in the single-hole and the double-hole jet flow fields were analyzed. The results show that the particle disturbance reduces the center position of the Mach disk, the height of the barrel shock and jet shear layer, intensifies the Kelvin-Helmholtz instability in the flow field and forms a large number of large-scale coherent structures downstream of the jet. The jet and supersonic crossflow interaction form a large-scale CVP structure for hydrogen fuel. Among them, three pairs of CVP structures (including CVP-B, CVP-C, and CVP-D) appear before and after the downstream of the double-hole jet. CVP-C is the main factor affecting the shape and area of the hydrogen fuel reaction zone. For powder fuel, the penetration depth of fuel is mainly affected by the height of the Mach disk and the shear layer. The higher Mach disk and shear layer position, the greater the velocaity obtained by particles and the higher the penetration kinetic energy. The double-hole injection system has a higher fuel penetration depth and higher mixing efficiency of hydrogen and powder fuel. The mixing efficiency of hydrogen fuel at the outlet of the double-hole jet is 0.728, which is 10% higher than that of the single-hole jet; The mixing efficiency of powder fuel is 0.342, which is 2% higher than that of the single-hole jet. However, the complex flow field structure of the double-hole jet leads to a large total pressure loss, about 0.74% higher than that of the single-hole jet.

Numerical study of multi-jet with upstream divergent ramp at supersonic cross flow

The efficiency of supersonic air-breathing propulsion is highly associated with fuel mixing enhancement in a tank. Current study performed all-inclusive simulations to scrutinize the impacts of the upstream inclined ramp on the fuel mixing mechanism of four multi-jet configurations at supersonic crossflow. The presence of divergent ramp in two jet spaces of 3 Dj and 10 Dj is fully analyzed via three-dimensional modeling of supersonic flow with four cross jets. Circulation factor and mixing performance are studied to obtain an efficient configuration for the injection system. Our results show that the fluctuation and strength of the circulation factor are more in low jet space. The assessment of fuel mixing productivity indicates that fuel mixing of low jet space is approximately 15% more than high jet space far downstream. Our findings show that a strong unite vortex produced in low jet space is more effective on fuel mixing than low multi vortices.

Mixing and Evolution of Laterally Injected Liquid Fuel in Mach 2 Air Channel with Cavity

ABSTRACT The present study deals with the flow structure and mixing characteristics of liquid fuel injected laterally into a supersonic crossflow. The geometry, with a cavity downstream of the injector, mimics a supersonic combustor with a cavity flame holder. A variety of injection schemes and cavity configurations were investigated by means of high-speed schlieren photography. A reflected shock tunnel was employed to generate a Mach 2 air flow and to simulate the high-temperature environment in the combustor. JP-4 liquid fuel was injected at different jet-to-crossflow momentum flux ratios upstream of and from the front wall of the cavity. Results showed that in direct injection into the cavity adjusting the injection angle has significant effect on the local fuel-air ratio. Upstream injection far from the leading edge of the cavity yielded more effective fuel mixing and shorter dissipation length (Ld) than closer injection, due to the development of a vortex on the lee side of the jet core. These results suggest that a combination of upstream injection far from the leading edge of the cavity and inclined direct injection into the cavity may be beneficial for effective mixing in a supersonic combustor cavity flame holder.

The spray distribution of a liquid jet in supersonic crossflow in the near-wall region

The gas–liquid mixing process of a liquid jet in supersonic crossflow with a gas–liquid momentum ratio of 7.67 in the near-wall region is investigated numerically. The two-phase flow large eddy simulation is based on the Eulerian–Lagrangian approach and considers the droplet–wall interaction. The results indicate the penetration depth and the lateral extension width, which are in good agreement with the experimental data. The Ω shape, especially the spray foot structure of spray in the cross-sectional plane, is captured well. The transport process of spray toward the wall and the formation of spray foot are systematically studied. Under the influence of the upper CVP (counter-rotating vortex pair), partial droplets in the center region of the spray are transported to the near-wall region and move toward both sides when encountering the wall CVP. Under the current gas–liquid momentum ratio, droplets collide with the wall mainly in the central region at the bottom, which will produce splashed droplets. Affected by the horseshoe vortex, the instantaneous distribution of droplets on both sides near the wall shows stripes shape. The spray foot structure forms the shape that is narrow on the top and wide on the bottom and is mainly formed by splashed droplets. Some splashed droplets in the low-speed boundary layer constitute the lower half of the spray foot; meanwhile, some splashed droplets enter mainstream and constitute the upper half of the spray foot. Moreover, the spray is mainly distributed in the core region, and the spray concentration is very sparse in the spray foot region.

The influence of annular lobe-injector on the fuel mixing of hydrogen jet at supersonic combustion chamber

The performance of the engine highly depends on the fuel mixing process as a significant process to achieve efficient supersonic flight. Current article has attempted to release the effects of different annular lobe-injectors on fuel mixing when Ma>1. Three various annular jet nozzles are expansively investigated for injection of the sonic hydrogen jet at supersonic air crossflow with Mach-4. Comprehensive comparison of the jet structure of these models are performed through the evaluation of Mach and fuel concentration downstream of these lobe-injectors. Comparison of mixing efficiency also indicates that the nozzle with 3-lobe configuration has 25% more fuel mixing performance than other configurations. Our findings also show that mixing performance of annular lobe-injector is about 15% more than simple one for cases with 2-lobe and 4-lobe injectors.

Hydrogen mixing augmentation mechanism induced by the vortex generator and oblique shock wave in a scramjet engine

The mixing process between the fuel and the incoming air is extremely important for the engineering implementation of the scramjet engine. In the current study, the vortex generator coupled with the oblique shock wave is utilized to promote the hydrogen mixing process in a supersonic crossflow. The configurations of the vortex generator are put into investigation, namely typical ramp, split ramp and ramp vane. Some parameters are provided to evaluate the flow field properties quantitatively. The obtained results predicted by the three-dimensional Reynolds-average Navier-Stokes (RANS) equations show that the method of shock wave/jet shear layer interaction coupled with the vortex generator can effectively improve the mixing efficiency. Different vortex generator structures all have great effect, especially for Case SR (split ramp), with the mixing efficiency raised by 36.27%. The streamwise vorticity plays an important role in the mixing process.

Effects of confinement and curvature on a jet in a supersonic cross-flow

To reveal the effects of confinement and curvature on the jet mixing in a supersonic cross-flow, large eddy simulations were conducted to study the jet in supersonic cross-flow in a channel and a pipe at a Mach number of 2.7. The comparison was based on an equal friction Mach number, friction Reynolds number, and Prandtl number. The synthetic eddy model was utilized to generate the inflow turbulent boundary layer. Our study shows the major counter-rotating vortex pair (CVP) was higher in the pipe than in the channel, while the trailing CVP was larger and appeared within the recirculating flow. The pipe had a stronger shock train than the channel due to the confinement and curvature of the pipe. The jet penetration of the pipe is 18.4% larger than that of the channel at x/ D = 10, and the stream velocity of the pipe is much more reduced behind the jet than in the channel. Three reasons for the higher mixing efficiency of the pipe are revealed according to our findings, including the larger and higher major CVP, the higher penetration, the stronger shock. The mixing efficiency of the pipe is 4.68% higher than that of the channel due to the above reasons at x/ D = 10.

Flow fields around spanwise-inclined elliptical jets in supersonic crossflow

Motivated by favorable effects in separation control with air-jet vortex generators in aerospace applications, we performed implicit large-eddy simulations to analyze the flow physics of spanwise-inclined elliptical jets in supersonic crossflow and reveal the influence of aspect ratio. Orifices with similar hydraulic diameters and aspect ratios of 0.5, 1.0, and 2.0 were studied at Mach number M=2.5 and momentum-thickness Reynolds number Reθ=7000. The jet injection results in the formation of asymmetric flow features (bow and barrel shocks, upstream and downstream separation regions, and vortical structures), which are qualitatively similar for all cases. Compared with the more commonly-studied wall-normal injection, the axis-switching phenomenon and its effects are very mild for spanwise-inclined injection. For the low-aspect-ratio orifice, the clockwise-rotating major vortex strengthens and vice versa for the high-aspect-ratio orifice. Flow penetration increases with aspect ratio; however, the influence of the injection is limited within the boundary layer and the outer layer is undisturbed. In the far field, the enhanced momentum transfer makes the boundary layer more resistant to separation for all orifices. Combined with the amplified vorticity for elliptical cases, elliptical jet orifices become more effective for separation control purposes than circular orifices.