Supersonic Crossflow Research Articles

Research on diffusion characteristics of liquid jet effected by shock wave in supersonic high-enthalpy crossflow

The diffusion characteristics of liquid jets with phase transition under the action of shock waves in supersonic high-enthalpy crossflow were discussed in this paper. Numerous numerical simulations were carried out in high enthalpy inflow (Tt = 1680 K) under different shock wave intensity and injection parameter conditions. The Euler-Lagrangian method was employed to solve the gas-liquid two-phase flow coupling, and the evaporation, diffusion and mixing processes of kerosene were obtained. By analyzing simulation results, the influence and the mechanism of shock waves on enhanced kerosene mixing were revealed. The results show that increasing the shock wave intensity effectively improves the penetration and mixing of kerosene in general by changing the flow state and evaporation process. The penetration depth can be increased by up to 63.54 % in this paper. To balance the contradiction between total pressure loss and mixing efficiency, it is necessary to select an appropriate shock wave intensity. The enhanced diffusion and mixing process of kerosene by shock waves are related to the injection momentum ratio, evaporation momentum ratio and streamwise vortex intensity. Weakening mainstream momentum while boosting evaporation and vortex intensity effectively strengthens kerosene diffusion and mixing. This research significantly contributes to enhancing the diffusion and mixing of liquid kerosene and improving combustor performance.

Quantitative Definition of Spray Edge With Extinction Diagnostics and Evaluation of Attenuation Coefficient for Liquid Jets in Supersonic Crossflow

Abstract A quantifiable, reproducible, and repeatable definition of the three-dimensional spray width and depth for a canonical jet in an open-source supersonic crossflow is presented. An expanding Mach 2 dry-air crossflow is generated through a converging-diverging nozzle with a 25.4 mm by 230 mm wide throat area. A one-millimeter injector with ethanol seeding provides the liquid injection. Injector characteristics and losses are quantified through a calibrated cavitating venturi. Momentum flux ratios ranged from 0.1 to 20, and Reynolds number scaled by the injector diameter ranged from 5000 to 40,000. A shadowgraph setup with a telecentric lens provides uniform magnification for precise and repeatable measurements from injection to 150 mm downstream of the jet. A Phantom v2012 camera with a frame rate of 20 kHz and shutter time of 285 ns was employed. Light transmittance is defined and calculated for each image pixel with a ratio method paired with no-spray images collected immediately before injection. These values are then related to an attenuation coefficient by incorporating spray width profiles collected with cross-sectional Mie-scatter imaging at multiple axial locations with a burst mode laser.

On the double-sided shock diffractions in quiescent and supersonic crossflows

Shock diffraction is a widespread phenomenon in aerospace applications, such as shock tunnel nozzle and jet exciter exit, impacting their performance significantly. This paper focuses on the transient evolution of double-sided shock diffraction in both quiescent and supersonic crossflows by unsteady numerical simulations. The characteristics of the shock wave and the vortex are revealed. In the quiescent flow, the double-sided shock diffraction exhibits remarkable symmetry. The diffracted shock retains a self-similar nature, but its intensity distribution displays non-uniform characteristics, which gradually weakens from the center to both sides. The vortices on both sides also exhibit symmetrical behavior, with their trajectory behaving in linear tendency. When the supersonic crossflow interacts with the diffracted shock, an upward-moving separation shock and an asymmetric diffracted shock are generated. The vortices remain confined beneath the boundary layer and exhibit different shapes. Moreover, due to the rapid motion of the separation shock, the relative Mach number is introduced into the free-interaction theory (FIT) to predict the shock angle of the separation shock. The F(x¯) values corresponding to the separation point and pressure plateau are determined to be 3.04 and 4.68, respectively. The results evaluated by modified FIT show a good agreement with the values of simulation and experiment.

FUNDAMENTAL INVESTIGATION OF LIQUID INJECTION IN SUPERSONIC CROSSFLOW: AN EXPERIMENTAL STUDY

Experimental investigation of the liquid injection into a Mach 2.2 supersonic crossflow through a transverse single circular injector has been carried out in the present study. High-speed visualization techniques such as back-lit imaging, shadowgraphy, and schlieren imaging have been employed to investigate the flow and the liquid jet features. The present study provides a detailed analysis of the breakup behavior of a liquid jet introduced into a crossflow with a Mach number of 2.2 by categorizing it into distinct zones. The liquid jet breakup was induced by surface instabilities, leading to the formation of a protrusion structure that traveled downstream along the jet. The schlieren photographs captured the essential flow dynamics resulting from the liquid injection, such as the bow shock wave and the separation shock wave. Observations indicated that the location where the bow shock wave interacts with the upper wall shifts in the upstream direction as the liquid injection pressure is increased. Furthermore, a parametric analysis was conducted to assess the penetration height of the injected liquid and its variation relative to the injection pressure. The analysis revealed that the penetration of the jet was greatest at an injection pressure of 7 bar, succeeded by 5 bar and 3 bar, respectively. The minimal penetration height was recorded at an injection pressure of 1 bar. In a quantitative analysis, the penetration of a liquid jet was measured at various injection pressures at a normalized axial distance of 5. It was found that the penetration of the liquid jet with an injection pressure of 7 bar was 3.67 times greater than the liquid injection with an injection pressure of 1 bar.

Numerical investigate on flow process and mixing characteristics of hydrogen/aluminum powder two-phase fuel under different inlet and injection conditions

The flow and mixing process of a hydrogen/aluminum powder two-phase fuel transverse jet in a supersonic cross flow are simulated in this work using the Euler-Lagrangian scheme. The effects of the inlet Mach numbers (Ma) and jet-to-crossflow momentum flux ratios (J) on the mixing process and flow characteristics of the gas-solid two-phase fuel are investigated. The results show that there are substantial differences in the flow and mixing properties of the two-phase fuel consisting of hydrogen and aluminum powder. While the powder fuel has a minimal impact on the flow field, the interaction of the hydrogen jet with the supersonic cross flow creates complex wave structures in the flow field. Hydrogen is influenced by the large-scale structures of the counter-rotating vortex pair (CVPs) and surface-trailing counter-rotating vortex pairs (TCVPs) in the flow field. In contrast, the powder fuel is influenced by various initial conditions, including the momentum of the hydrogen jet, the momentum of the supersonic mainstream, and the size of the combustor. The mixing efficiency of hydrogen is 7.381%–33.933 % higher than that of the powdered fuel under the same inlet and injection conditions. The comparison showed that the mixing efficiency of hydrogen decreases with the increase of injection momentum and inlet Mach number, while the mixing efficiency of powder fuel increases with increase of injection momentum and inlet Mach number. Among them, the mixing efficiency of hydrogen and powder fuel under the conditions of Ma = 1.6 and J = 0.86 are 0.63 and 0.29, respectively. The mixing efficiency of hydrogen and powder fuel under the conditions of Ma = 3.0 and J = 1.72 are 0.48 and 0.41, respectively.

Flow fields around asymmetrical micro vortex generators in supersonic flow

Motivated by the favorable effects of asymmetrical vortical structures on shock-wave boundary layer interactions, we performed implicit large-eddy simulations to analyze the ability of micro mechanical vortex generators (VGs) to generate such structures. For this purpose, we studied modified VG geometries, by skewing and varying the orientation of a microramp and introducing pairs of unevenly sized ramped-vanes. The modified VGs allow to study the effectiveness of these devices when operating in off-design conditions. The flow physics of all devices were investigated in a supersonic crossflow at Mach 2.5 and a momentum-thickness Reynolds number of 7000. The flow topology around each VG is very similar: the VG acts as an obstacle to the incoming flow and induces a complex system of shocks, recirculation regions, and vortical structures. We present a detailed study of the evolution of the dominant major counter-rotating vortex pair (CVP) to estimate the VGs' flow-control effectiveness. All modified configurations introduce asymmetry into the flow, yet to varying degree for different device types. The modifications made to the microramp have minimal impact on the boundary layer, while the uneven ramped-vane configurations have significant effect. Lateral spread of mechanical VG induced major CVP is not larger than the spanwise dimension of the VG. Consequently, the favorable effect of interactions between VGs arranged in arrays on flow-control effectiveness observed for air-jet VG arrays cannot be reproduced with mechanical VGs. Considering the large design offsets we introduced to the microramp and ramped-vane configurations, both device types are robust to off-design flight conditions.

Investigations of the Atomization Characteristics and Mechanisms of Liquid Jets in Supersonic Crossflow

In the combustion chamber of scramjets, fuel jets interact with supersonic airflow in the form of a liquid jet in crossflow (LJIC). It is difficult to achieve adequate jet–crossflow mixing and the efficient combustion of fuel in an instant. Large eddy simulation (LES), the coupled level-set and volume of fluid (CLSVOF) method, and an adaptive mesh refinement (AMR) framework are used to simulate supersonic LJICs in this article. This way, LJIC atomization characteristics and mechanisms can be further explored and analyzed in detail. It is found that the surface waves of the liquid column exist in a two-dimensional form, including vertical and spanwise directions. Column breakup occurs when all the spanwise surface waves between adjacent vertical surface waves break up. Bow shock waves, composed of multiple connected arcuate shock waves, are dynamic and will change with the evolution of the liquid column. The vortex ring movement of supersonic LJICs, whose trends in the vertical and spanwise directions are different, is relatively complex, which is due to the complex and time-dependent shape of liquid columns.

Using extruded circular multi-injectors to improve fuel jet mixing and distribution in combustion chambers of scramjet

An extensive investigation of multi-nozzle with various heights is done for enhancing the fuel mixing and distribution in supersonic combustion chambers of scramjets by using Computational Fluid Dynamics. Fuel injection and mixing play a crucial role in many industries, including automotive. This study examines the mechanism of hydrogen fuel jet mixing when injected through a multi-nozzle with varying heights in the combustion chamber of a scramjet. The impact of different injector height configurations on supersonic cross-flow is analyzed through computational fluid dynamics, and the flow and fuel mixing are evaluated to determine the most efficient fuel injection setup. A comparison is made between the proposed multi-jet configurations and simple multijet configurations to identify the primary hydrodynamic and mixing benefits of multi-jet configuration with different heights. The findings indicate that the use of multi-jet injectors with different heights decreases the circulation factor and improves fuel mixing downstream of four jets by 40 %.

Effects of jet-injection-pipe length on the flow-control effectiveness of spanwise-inclined jets in supersonic crossflow

Effects of jet-injection-pipe length on the flow-control effectiveness of spanwise-inclined jets in supersonic crossflow

Application of multi-extruded fuel injectors for mixing enhancement of hydrogen gas at scramjet engine: computational study.

Scramjet engines are considered a highly promising technology for improving high-speed flight. In this study, we investigate the effects of using multi-extruded nozzles on fuel mixing and distribution inside the combustion chamber at supersonic flow. Additionally, we explore the impact of an inner air jet on fuel mixing in annular nozzles. To model fuel penetration in the combustor, we employ a computational technique. Our study compares the roles of three different extruded injectors on fuel diffusion and distribution at supersonic cross-flow. Our findings reveal that the use of an inner air jet increases fuel mixing in the annular jet, while the use of extruded nozzles improves fuel distribution by enhancing the vortices between injectors. These results demonstrate the potential benefits of incorporating multi-extruded nozzles and inner air jets in the design of scramjet engines.

Improvement of fuel mixing of single ejected 2-lobe fuel injector using shock generator at supersonic flow

In present paper, computational fluid dynamic is applied to evaluate hydrogen mixing impacts of the single extruded lobe injector at supersonic cross flow. The aim of this investigation is to introduce efficient injection system by elongation of the extruded nozzle at high-velocity air flow. The shock waves and temperature contour for the two nozzle heights are compared. The importance of vortex produced inside the domain on the fuel diffusion is also explained. The usage of annular and coaxial air and fuel jet for the improvement of the proposed configurations are also investigated. Obtained results shows that elongation of extruded nozzle form 2 mm to 4 mm improves the fuel mixing about 50%. However, the injection of the inner air jet results in 85% higher fuel mixing in combustion chamber of the scramjet engine.

Numerical investigation on spray and flow field characteristics of elliptical nozzle in supersonic crossflow

ABSTRACT It has been suggested that using an elliptical nozzle could enhance the atomization and mixture quality. In order to explore the elliptical liquid jet on spray and flow field characteristics in supersonic airflow, the VOF-Spray one-way coupling model was adopted to study the nozzle exit patterns, size, and velocity distribution of droplets. The research also compared the flow field characteristics in Mach 2.85 air crossflow under the application of different orifices. The numerical results showed that elliptical 4 nozzle (Aspect ratio of 4) had better flow performance than circular nozzle. The cavitation area and turbulent disturbance of elliptical 4 nozzle were mainly concentrated in the major axis direction. The elliptical 4 jet always had a lower penetration depth than circular jet. At the flow range of 0 ~ 50 mm, the penetration depth of elliptical 4 jet is roughly 12% less than that of circular jet. Another finding was that the spanwise extension range of elliptical 4 spray was larger than the circular spray. The spanwise extension range of elliptical 4 spray increased by about 19.4% at most in the flow range of 0 ~ 50 mm. Additionally, the elliptical 4 spray had the smallest Santer Mean Diameter (SMD). The elliptical 4 jet had a 2.9% smaller Santer Mean Diameter than the circular jet. Due to the greater windward surface area of the elliptical 4 orifice, the gas streamwise velocity near the bottom wall was reduced. A reverse vortex pair with distinct characteristics could be observed under the application of elliptical 4 orifice. Furthermore, compared with the circular orifice, the shock wave angle generated by elliptical 4 orifice reduced by 9.7%, and the total pressure recovery coefficient rose by 2.3%.

Forced Injection of a Spanwise-Inclined Jet in Supersonic Crossflow

Beneficial effects of forced air-jet vortex generators in controlling shock-induced flow separation motivated us to study forced jet injection in detail to understand the advantageous control effects. We performed implicit large-eddy simulations to examine the influence of sinusoidally forced injection of a spanwise-inclined jet in supersonic crossflow. Two forcing frequencies were considered (with and 0.0062) in a crossflow at Mach 2.5 and momentum-thickness Reynolds number of 7000. The underexpansion of the jet has a near-linear dependence on the injection pressure. Consequently, in the near field, the major vortices pulsate with the injection pressure. Statistical analysis using triple decomposition revealed that periodic oscillations of the major counter-rotating vortex pair (CVP) result in momentum transfer by major CVPs, also on their lateral sides, leading to enhanced mixing and lateral spreading, which is beneficial for separation control. Three-dimensional dynamic mode decomposition revealed that forced injection induces a large-scale clockwise rotation of the major vortex. These effects are weak at low forcing frequency. High-frequency jet forcing thus leads to more efficient control of flow separation. On the other hand, periodic oscillations cause these vortical structures to dissipate and breakdown faster in the midfield region than for steady jets. The placement of forced jets is therefore an important parameter when used for separation-control purposes.

Numerical simulation of angled-injected liquid jet breakup in supersonic crossflow by a hybrid VOF-LPT method

The breakup of angled-injected liquid jets in supersonic airflow is investigated numerically by a hybrid Volume of Fluid and Lagrangian Particle Tracking (VOF-LPT) method. A Multi-criterion adaptive mesh refinement (AMR) procedure and dynamic load balancing (DLB) algorithm are applied to improve the accuracy of interface and shock wave characteristics and reduce the use of computational resources and liquid mass loss. The flow characteristics of the spray field and penetration depth of the angled-injected liquid jet from the simulations agreed well with the experimental results. Under the supersonic crossflow conditions, the jet has momentum in the counter-flow direction that improves gas-liquid interactions. The penetration depth of the liquid jet increase with the increase of the injection angle. In particular, the penetration depth of the angled-injected liquid jet is given in the: y/d=0.12·sin(2θ/3)·(esin(2θ/3))3.185·q0.389(x/d)0.309. Moreover, the liquid jet at a larger injection angle has a larger spray spread angle and wider wake region due to the larger windward area. Furthermore, the total pressure loss of airflow increases with the injection angle increasing. Considering the total pressure loss for all injection conditions is lower than 14%, the total pressure loss caused by the injection angle increase can be negligible.

Numerical Simulation of a Sonic Jet Injected into a Supersonic Crossflow With K.(l) Turbulence Model

Numerical simulation of normal injection of a sonic jet into supersonic crossflows were performed with a k-ul turbulence model. Favre-averaged Navier-Stokes equations along with k-6p equations were solved in a coupled manner by calculating inviscidfluxes with Roe's flux-dffirence splitting, central dffirencing of derivatives in the viscous terms, and by performing Runge-Kutta time integration in a finite volume formuLation. Experiments of sLot injection at several freestream Mach numbers and injection pressure ratios were simulated. It was observed that simulations agreed well at low pressure ratios but departed with increasing pressure ratio as had been observed in other simulations. A qualitative difference in the structure of the jet was observed when explicit compressibility fficts were included. In turn, the agreement with experiment improves significantly. It was also observed that imposing a lower ReynoLds number in the caLculations than the value determined from reported experimental conditions resulted in solutions expected of transitional separation and vvhich then agreed more closely with experiment.

Numerical study on spray characteristics of liquid jets in supersonic crossflow

The spray characteristics of liquid jets in supersonic crossflow at different injection jet-gas momentum ratios are investigated numerically. The compressible two-phase flow large eddy simulation (LES) method is based on the Eulerian-Lagrangian scheme. The average droplet volume fraction is defined to quantify spray concentration distribution, which can also reflect the oscillation boundary of the spray. The LES predicted the spray boundaries at different injection jet-gas momentum ratios in the central and cross-sectional planes, which agree reasonably well with the experiment. Two sets of counter-rotating vortex pair (CVP) are in the gas-liquid mixing region. As injection momentum ratio q increases, the upper CVP increases. Still, the absolute size of the wall CVP remains almost unchanged, which means that the relative size of the wall CVP to the upper CVP becomes smaller. As q increases, the spray's overall distribution position is generally upward, and the number of droplets entering the near-wall region becomes small. Thus, droplet-wall interactions are weakened. The spray body increases with the increase of q, while the spray foot decreases gradually. In the central plane, the coherent structures near the wall are mainly composed of splashed droplets, and this phenomenon gradually weakens as q increases. Although the increase of q can increase the total droplet mass flow rate, the proportion of the droplet mass flow rate in the near-wall region to the total mass flow rate decreases, and the droplet mass flow rate in the near-wall region decreases.

Influence of extruded injector nozzle on fuel mixing and mass diffusion of multi fuel jets in the supersonic cross flow: computational study

The efficient injection system has a great role on the overall enactment of air breathing propulsion systems at supersonic flow. In this work, the usage of extruded multi-injectors in the fuel distribution and mixing through the combustor is fully investigated. The usage of the extruded nozzles considerably intensifies the formation of the vortices nearby the injectors and this research has tried to visualize the role of these vortices on the diffusion of the fuel jet through the combustor of the scramjet. The influences of the jet space on the strength of produced circulations are fully discussed. The simulation of the high-speed air stream moving the combustion chamber with extruded nozzles is done via Computational Fluid dynamics. Based on our computational data, the use of extruded multi-jets enhances the penetration and diffusion of the hydrogen cross jet in supersonic airflow. Increasing the gap between injectors improves fuel mixing performance by up to 27% downstream of the jets, primarily by enhancing the lateral penetration of the fuel jet.

Numerical study on coupled flow characteristics of a gas-solid two-phase jet in a supersonic crossflow

In this study, the Eulerian-Lagrangian scheme coupled with the gas-solid two-phase Reynolds-average Navier-Stokes (RANS) method was used to study the airflow and particles flow characteristics of particles of different diameters injected into a supersonic flow field by a sonic jet. The results show that introducing small particles has little effect on the flow field. When the particle diameter is 1e-6 m, most particles are mainly distributed in the shear layer, and some parts of the particles are sucked into the surface trailing counter-rotating vortex pairs (TCVP) and the wall boundary layers by the airflow. The introduction of large diameter particles hinders the jet's development, reduces the Mach disk's height, and makes the counter-rotating vortex pair (CVP) closer to the wall. This leads to a decrease in the streamwise velocity and an increase in the wall-normal velocity near the wall downstream of the jet. The streamwise velocity increases and the wall-normal velocity decreases at the far wall downstream of the jet. At the same time, it exacerbates the Kelvin-Helmholtz (K-H) instability in the shear layer on the windward side of the jet, forming a large-scale coherent structure between the shear layer and crossflow. The penetration depth and diffusion range of particles increase with particle diameter and density, and the velocity decreases with particle diameter increase by comparing the trajectories of particles with different diameters and densities.

Spray characteristics of a liquid fuel jet in a tandem backward-facing step cavity in supersonic flow

The influences of the backward-facing step and injection schemes on the spray characteristics of a liquid jet in a tandem backward-facing step cavity were investigated experimentally using high-speed photography and Schlieren techniques under a Mach 2.0 supersonic crossflow for the first time. The instantaneous structures of the spray and wave structures of the air-flow field were accurately captured by the high temporal resolution experimental technology. It is found that exist complex wave structures in the tandem backward-facing step cavity. A dimensionless spray factor was defined to describe the concentration of spray inside the cavity qualitatively. As a result, it is revealed that for the short backward-facing step cavity, the injection scheme near the upstream inlet has a higher penetration depth but a lower spray distribution, while the injection scheme near the cavity has a more spray distribution. For the long backward-facing step cavity, the injection scheme near the upstream inlet also has a higher penetration depth and the injection scheme near the sharp corner of the backward-facing step has a more sufficient spray distribution. The long backward-facing step cavity-based combustor with the upstream wall transverse injection is an optimized injection scheme to both improve penetration and spray distribution inside the cavity. Finally, a penetration depth formula is proposed to explain the spray distribution behaviors in a tandem backward-facing step cavity.

Mathematical representation of liquid jet diffusion characteristics effected with evaporation process in supersonic crossflow

The liquid jet diffusion characteristics effected with evaporation process and the mathematical representation of penetration depth in supersonic crossflow were discussed in this paper. A series of numerical simulations were carried out in both cold inflow (Tt = 300 K) and high enthalpy inflow (Tt = 1680 K). Based on the Euler-Lagrange method, the evaporation and diffusion process of liquid kerosene under different inflow conditions were studied. The mathematical representation of kerosene vapor penetration depth was obtained by convolution method. By analyzing the influence of different evaporation processes on the penetration depth of kerosene vapor, the penetration law of kerosene vapor with evaporation was revealed. The results show that the penetration process of kerosene is not only affected by the injection momentum ratio, but also the evaporation momentum ratio is an important factor affecting the penetration depth. The total penetration depth of kerosene vapor is composed of liquid kerosene penetration and penetration gain due to kerosene evaporation. And the mathematical expression of quantitative analysis was obtained by derivation. Making the local evaporation momentum of kerosene evenly distributed, extending the action distance and expanding the evaporation range are important ways to increase the penetration depth. The investigation in this paper plays an important role in explaining the diffusion mechanism and quantitative analysis of kerosene vapor with evaporation.