Jet In Supersonic Crossflow Research Articles

Simulating schlieren and shadowgraph images from LES data

Geometrical optics ray-tracing is used to derive schlieren and shadowgraph images from large-eddy simulation (LES) data of a jet in supersonic crossflow and to compare with experimental data. Including the components of the optical system that forms the image in the simulation is found to be important. The technique produces images that replicate flow physics more faithfully than straight-line path integration and other techniques, and more efficiently than physical-optics techniques. Applications of these simulated images are demonstrated in supersonic flows. Time-correlated pairs of shadowgraph images taken from the LES using this technique are used in conjunction with an image-correlation velocimetry technique to compare the estimated convection velocity field in the LES to that of experiments of the same flow. Agreement between the two is good with a maximum variance of 5% by some metrics. This technique can aid in the validation of LES results, allowing quantitative comparison between experiment and simulation, and to extract information unattainable by experiment alone. Comparisons of simulated and experimental jet penetration into the supersonic freestream are also made.Graphic abstract

Fuel injection location studies on pylon-cavity aided jet in supersonic crossflow

The current study numerically investigates the effect of fuel injection locations within a pylon-cavity aided Supersonic Combustion Ramjet (SCRAMJET) combustor on mixing enhancement, flame holding, fuel jet penetration and total pressure loss. RANS equations for compressed real gas are solved by coupled, implicit, second-order upwind solver. Two-equation SST model is used for turbulence modelling. The computational model is validated using experimental steady wall pressure data and 2D velocity field. The study uses seven distinct sonic fuel injection location cases of hydrogen fuel through a 1 mm diameter hole along the axis of the test section floor. All cases maintain crossflow of Mach number 2.2. The simulations show that the counter rotating vortex pair within the cavity plays a vital role in fuel dispersion and fuel jet penetration capability. The presence of pylon resulted in an increase of pressure loss by 7%, whereas the influence on total pressure loss due to transverse fuel injection is found to be insignificant. The injection locations within the cavity give around 55% (max) increase in fuel dispersion compared to location upstream of the pylon. Also the cavity floor locations give about 55% - 90% more flammable plume area than the injection from other locations.

URANS study of pulsed hydrogen jet characteristics and mixing enhancement in supersonic crossflow

In this paper, three-dimensional pulsed hydrogen jet in supersonic crossflow (PJISC) is investigated by the unsteady Reynolds Averaged Navier-Stokes (URANS) simulations with the k-ω shear stress transport (SST) turbulence model. The numerical validation and mesh resolution have been carried out against experiment firstly. The effects of the pulsed frequency and amplitude on the jet flow field and mixing performance in supersonic cross-flow are all addressed. It significantly changes the distribution of the hydrogen jet flow by comparing with the steady jet in supersonic crossflow. The fuel jet penetration, mixing efficiency, decay rate of the maximum hydrogen mass fraction and total pressure losses are used to quantitatively analyze the mixing performance. The mixing of fuel and incoming air flow is enhanced by the pulsed jet, especially for the case of 50 kHz, which is the optimal pulsed frequency while considering the effects of jet excitation frequency in the present simulations. The decay rate of the maximum mass fraction of hydrogen in the far field downstream is related to the frequency of the pulse jet. Moreover, the pulsed frequency and amplitude have little effects on the total pressure recovery coefficient for the cases studied in the present simulations.

Three-dimensional flow structures and droplet-gas mixing process of a liquid jet in supersonic crossflow

The mixing process of a liquid jet in supersonic crossflow with a Mach number of 2.1 was investigated numerically using large eddy simulation (LES) based on the Eulerian-Lagrangian method. The gas phase was described using the Navier-Stokes equations and the liquid phase was represented using discrete droplets, which were injected and tracked in the computational domain individually according to Newton's second law of motion. The KH (Kelvin-Helmholtz) breakup model was used to calculate the droplet stripping process, and the secondary breakup process was simulated by coupling the RT (Rayleigh-Taylor) breakup model and the TAB (Taylor Analogy Breakup) model. Two-way coupling was enforced to consider the momentum and energy exchange between the gas and the droplets. It was found that the LES predicted spray characteristics, including spray penetration and cross-sectional distribution, agree reasonably well with the experiment. The major gas flow structures such as the bow shock, the large-scale vortices, and the recirculation zones were replicated successfully in the simulations. It was found that the gas flow structures have a significant effect on the mixing process of the droplets. The simulation results revealed that two sets of counter-rotating vortex pair (CVP) exist in the gas-liquid mixing region. Under the influence of CVP, part droplets were transported to the near wall region and subsequently to both sides of the core spray region. The formation mechanism of the CVP was analyzed by comparing the pressure gradient and the source term of droplets in the Navier-Stokes equations. Differences of the mixing process of liquid jet in supersonic crossflow, gas jet in supersonic crossflow and liquid jet in incompressible crossflow were identified.

LES of primary breakup of pulsed liquid jet in supersonic crossflow

The injection of a pulsed liquid jet into supersonic air flow is a promising approach to improving the fuel atomization performance in a Scramjet engine. Therefore, the primary breakup of a pulsed liquid jet in supersonic crossflow is numerically investigated in the present paper. A two-phase flow Large Eddy Simulation (LES) algorithm is developed for simulations of liquid jet atomization in supersonic gas flow. A coupled Level Set and Volume of Fluid (VOF) method is used to track the interface deformation and disintegration. The supersonic gas flow is solved using a compressible flow solver while the liquid phase is solved by an incompressible flow solver. Appropriate boundary conditions are specified at the interface for both solvers to correctly capture the interaction between the gas and liquid phases. The primary atomization of a steady liquid jet with the same average mass flow rate as the pulsed jet is also simulated as a benchmark test case. The liquid velocity pulsation produces a very different primary atomization morphology in comparison with the steady liquid jet, which significantly enhances the primary breakup process. It is observed that Rayleigh-Taylor instability dominates the development of surface waves for the steady liquid jet. For the pulsed liquid jet, the liquid column deformation induced by the liquid velocity pulsation determines the wavelength of the surface waves and thus the liquid jet breakup location. In comparison with the steady liquid jet, the penetration of the pulsed liquid jet increases by 20%, and the width of the wake zone expands by 25%, resulting in improved atomization and mixing performance.

Effect of boundary layer thickness on transverse sonic jet mixing in a supersonic turbulent crossflow

The surface boundary through which a sonic jet in supersonic cross flow is injected is shown to have a significant effect on the size, penetration, and mixing characteristics of the jet plume. A circular, high-pressure, sonic jet is injected into a M = 3.4 supersonic crossflow through a well-characterized turbulent boundary layer of two different thicknesses (δ/d = 0.6 and 6.1), with variable momentum ratios (J = 1.2, 2.6, and 5). Planar laser Mie scattering of condensed ethanol droplets is used to quantitatively image the injected fluid concentration in both side and end-views at multiple downstream locations. Jet penetration, plume area, and characteristic size and location of regions of intense mixing are compared. The jets injected through the thicker boundary layer are shown to have significantly enhanced jet penetration (∼50%), spread (∼100%), and mixing intensity (∼100%, especially in the near-field) over a wider area of the jet plume. Additionally, characterization of mixing is examined using the variance in the concentration field as well as probability density functions of concentration determined along contours of constant jet fluid concentration. From these results, the jet injections associated with the thicker boundary layer transition from shear dominated mixing zones on the windward side to more distributed mixing zones throughout the plume at earlier downstream locations and show influence of interactions between boundary layer vorticity and vortical structures within the jet leading to larger lateral expansion.

Numerical investigation of transverse jet in supersonic crossflow using a high-order nonlinear filter scheme

We carried out a numerical study of a sonic transverse jet into a Ma = 2.0 crossflow based on a hybrid Reynolds-averaged Navier-Stokes (RANS)/large eddy simulation (LES) method. In order to enhance the calculation accuracy, an improved high-order finite-difference scheme is introduced. This scheme consists of an eighth-order central scheme and a nonlinear dissipation filter. The filter is derived from the explicit seventh-order weighted compact nonlinear scheme (WCNS-E−7). By incorporating a local smoothness indicator and a discontinuity sensor into the nonlinear filter, we further decrease the unnecessary dissipation and increase the resolution. With the proposed scheme, the key flow features, including shock structures, large-scale vortical structures and jet-crossflow shear/mixing layers, are well captured. The simulation shows a good agreement with the experiment data in jet penetration and diffusion.

Numerical study on lateral jet interaction in supersonic crossflows

This paper presents numerical analyses of lateral jets in supersonic cross flows on a flat plate and on a generic missile. The freestream Mach number is 4 for the flat plate and 3 for the missile, and the jets are sonic for both cases. The numerical results are validated with wind tunnel data such as Schlieren images and surface pressure distributions. The flow structure due to the jet interaction with the supersonic free-stream is examined in terms of the vortex structure. A 3-dimensional compressible RANS solver is used for the study. To describe the effects of high temperature, a thermally perfect gas is assumed. When high temperature is applied, the shock structure changes, which affects the separation region and recirculation zone. Next, the effects of turbulence models on the jet interaction flow are investigated. The Spalart–Allmaras, Menter's shear-stress transport k–ω, Huang and Coakley's k–ε, and Coakley's q–ω models are used to analyze the flows. The differences in pressure distribution among the turbulence models are larger in the case of the flat plate than the missile. In addition, several numerical flux functions are compared to investigate their effects on the jet interaction: the Roe scheme with Sanders's H-correction, RoeM scheme, and the HLLE scheme. Although the HLLE scheme shows a little difference at the indent of the barrel shock, the three numerical flux schemes give similar CP distributions on the wall.

Mixing of Fuel Jet in Supersonic Crossflow: Estimation of Subgrid-Scale Scalar Fluctuations

Non-reactive large-eddy simulations (LES) of a hydrogen jet injected into a transverse supersonic flow of vitiated air at Mach 2 are conducted. The present investigation is focused on the intertwinement of first- and second-order subgrid-scale (SGS) moments, such as the filtered value of a normalized reference scalar and its associated SGS variance level. Such a reference scalar is often settled to follow the mixing between the jet of hydrogen and the vitiated airflow. The discussion covers the influence of numerical errors, including commutation and discretization errors, as well as the possible effects of the closures retained to represent the unresolved SGS scalar dynamics. The sensitivity of the SGS scalar description, on the former, i.e., numerical errors, is enlightened with a special focus placed on the SGS variance evaluation, which is of practical importance for applications to turbulent reactive flow simulations. The SGS scalar variance is presently calculated by using three distinct procedures, which are at least formally, i.e., mathematically, equivalent. However, the results obtained by using the various procedures display some remarkable differences, which are the subject of the present analysis and discussion. It is finally demonstrated that the different results can be reconcilied together. The present results may thus provide some useful guidance for SGS variance estimation in the context of LES of turbulent scalar mixing and combustion.

Mixing augmentation of transverse hydrogen jet by injection of micro air jets in supersonic crossflow

In this study, the influences of the micro air jet on the mixing of the sonic transverse hydrogen through micro-jets subjected to a supersonic crossflow are investigated. A three-dimensional numerical study has been performed to reveal the affects of micro air jet on mixing of the hydrogen jet in a Mach 4.0 crossflow with a global equivalence ratio of 0.5. Parametric studies were conducted on the various air jet conditions by using the Reynolds-averaged Navier–Stokes equations with Menter's Shear Stress Transport (SST) turbulence model. Complex jet interactions were found in the downstream region with a variety of flow features depending upon the angle of micro air jet. These flow features were found to have subtle effects on the mixing of hydrogen jets. Results indicate a different flow structure as air jet is presented in the downstream of the fuel jet. According to the results, without air, mixing occurs at a low rate. When the air jet is presented in the downstream of fuel jet, significant increase (up to 300%) occurs in the mixing performance of the hydrogen jet at downstream. In multi fuel jets, the mixing performance of the fuel jet is increased more than 200% when the micro air jet is injected. Consequently, an enhanced mixing zone occurs downstream of the injection slots which leads to flame-holding.

Wall-Modeled Large-Eddy Simulation of Autoignition-Dominated Supersonic Combustion

Simulations of combustion in high-speed and supersonic flows need to account for autoignition phenomena, compressibility, and the effects of intense turbulence. In the present work, the evolution-variable manifold framework of Cymbalist and Dimotakis (“On Autoignition-Dominated Supersonic Combustion,” AIAA Paper 2015-2315, June 2015) is implemented in a computational fluid dynamics method, and Reynolds-averaged Navier–Stokes and wall-modeled large-eddy simulations are performed for a hydrogen–air combustion test case. As implemented here, the evolution-variable manifold approach solves a scalar conservation equation for a reaction-evolution variable that represents both the induction and subsequent oxidation phases of combustion. The detailed thermochemical state of the reacting fluid is tabulated as a low-dimensional manifold as a function of density, energy, mixture fraction, and the evolution variable. A numerical flux function consistent with local thermodynamic processes is developed, and the approach for coupling the computational fluid dynamics to the evolution-variable manifold table is discussed. Wall-modeled large-eddy simulations incorporating the evolution-variable manifold framework are found to be in good agreement with full chemical kinetics model simulations and the jet in supersonic crossflow hydrogen–air experiments of Gamba and Mungal (“Ignition, Flame Structure and Near-Wall Burning in Transverse Hydrogen Jets in Supersonic Crossflow,” Journal of Fluid Mechanics, Vol. 780, Oct. 2015, pp. 226–273). In particular, the evolution-variable manifold approach captures both thin reaction fronts and distributed reaction-zone combustion that dominate high-speed turbulent combustion flows.

Dynamics and mixing mechanism of transverse jet injection into a supersonic combustor with cavity flameholder

The interaction between sonic transverse jet and supersonic crossflow coupled with a cavity flameholder is investigated using large eddy simulation (LES), where the compressible flow dynamics and fuel mixing mechanism are analyzed emphatically. An adaptive central-upwind 6th-order weighted essentially non-oscillatory (WENO-CU6) scheme along with multi-threaded and multi-process MPI/OpenMP parallel is adopted to improve the accuracy and parallel efficiency of the solver. This simulation aims to reproduce the flow conditions in the experiment, and the results show fairly good agreement with the experimental data for distributions of streamwise and normal velocity components. Instantaneous structures such as the shock, large scale vortices and recirculation zone are identified, and their spatial deformation and temporal evolution are presented to reveal the effect on the subsequent mixing. Then some time-averaged and statistical results are obtained to explain the interesting phenomenon observed in the experiment, that there are two pairs of counter-rotating streamwise vortices existing in and above the cavity with the same rotation direction. The above pair is induced by the transverse momentum of jet in supersonic crossflow, which is so-called counter-rotating vortices (CRVs) in the flat-plate injection. On account of the entrainment, the reflux in the cavity transports to the core of jet wakes, and then another pair of counter-rotating streamwise vortices is formed below with the effect of cavity. A pair of trailing CRVs is generated at the trailing edge of cavity, and the turbulent kinetic energy (TKE) here is obviously higher than that in other regions. To some extent, the cavity can enhance the mixing, but will not bring excess total pressure loss.

Numerical simulation of the gas-liquid interaction of a liquid jet in supersonic crossflow

The gas-liquid interaction process of a liquid jet in supersonic crossflow with a Mach number of 1.94 was investigated numerically using the Eulerian-Lagrangian method. The KH (Kelvin-Helmholtz) breakup model was used to calculate the droplet stripping process, and the secondary breakup process was simulated by the competition of RT (Rayleigh-Taylor) breakup model and TAB (Taylor Analogy Breakup) model. A correction of drag coefficient was proposed by considering the compressible effects and the deformation of droplets. The location and velocity models of child droplets after breakup were improved according to droplet deformation. It was found that the calculated spray features, including spray penetration, droplet size distribution and droplet velocity profile agree reasonably well with the experiment. Numerical results revealed that the streamlines of air flow could intersect with the trajectory of droplets and are deflected towards the near-wall region after they enter into spray zone around the central plane. The analysis of gas-liquid relative velocity and droplet deformation suggested that the breakup of droplets mainly occurs around the front region of the spray where gathered a large number of droplets with different sizes. The liquid trailing phenomenon of jet spray which has been discovered by the previous experiment was successfully captured, and a reasonable explanation was given based on the analysis of gas-liquid interaction process.

Combustion effects of a staged transverse jet and pulsed detonation in supersonic crossflow

The combustion effects of a H2/O2 pulsed detonation (PD) staged downstream of a primary transverse H2 jet in supersonic crossflow (JICF) was investigated. A Mach 2.35 crossflow representative of Mach 7 flight combustor entry conditions (T∞=1330K, P∞=40kPa) was considered. The jet-to-crossflow momentum flux ratio (Jj) of the primary jet was varied between 0.5 and 5.0 to span different stabilization modes. The PD provides a short-duration, high temperature and momentum, radical-rich plume of gas to the wake of the primary transverse jet. The temporal evolution of the interaction between the two plumes was studied using high-speed schlieren and OH* chemiluminescence imaging. Phase-locked OH planar laser-induced fluorescence imaging was used to identify the instantaneous reaction zone along the center-plane at various times of the blowdown process. It was found that the interaction of the two plumes promotes earlier ignition and release of heat. The presence of a high momentum flux ratio transverse jet increases the effective blowdown period (EBP) over which OH* is exhausted; thus increasing the duration of the effects of the PD on the JICF. Lastly, the penetration of the reacting layer into the crossflow was observed to increase with the staged PD present as compared to cases without it.

Vortex structure and breakup mechanism of gaseous jet in supersonic crossflow with laminar boundary layer

Employing nano-particle planar laser scattering and particle image velocimetry technology, underexpanded jet in supersonic crossflow with laminar boundary layer is experimental investigated in a low noise wind tunnel. Instantaneous flow structures and average velocity distribution of jet plume are captured in experimental images. Horseshoe vortex system is dominated by oscillating and coalescing regime, contributing to vortex generation of jet shear layer. The “tilting-stretching-tearing” mechanism dominating in near field raises average fractal dimension. But vortex structures generated on the windward side of jet plume scatter in jet plume and dissipate gradually, which makes the vortexes break up from outside in near field and break down into small turbulence completely in far field.

Effects of micro-ramp on transverse jet in supersonic crossflow

The effects of micro-ramp on the characteristics of transverse jet were investigated by the LES simulation at Mach 2.7, with recycling-rescaling method applied to reproduce the turbulent boundary layer. The transverse nitrogen jet in front of micro-ramp and behind micro-ramp were studied by comparison with plate jet. It is found that the micro-ramp can improve the penetration height obviously, while placing jet orifice behind micro-ramp, due to the low freestream momentum in ramp wake. On the other hand, when placing the jet orifice in front of micro-ramp, the improvement in penetration is quite slight, because most injection is above the boundary layer and micro-ramp has little influence on the main flow. It is also observed that unlike the periodic Kevin Helmholtz (K–H) vortices appeared in ramp wake, the periodic K–H vortices are not achieved in jet cases.

Aerothermal exploration of reaction control jet in supersonic crossflow at high altitude

Multiple reaction control jets injected normal to free-stream is used to manoeuvre aerospace vehicle at high altitudes. Detailed aerothermal analysis of a high speed aerospace vehicle with multiple lateral jets is carried out in its full trajectory covering wide range of Mach numbers and altitudes. Three dimensional RANS simulations with laminar-turbulent transition models are performed at several instances in the flight trajectory using commercial CFD solver. Numerical simulations captured all complex flow phenomena of free stream & multi-jet interaction at high altitudes and its influence on vehicle airframe temperature. Heat flux data base obtained from CFD analysis is used for transient thermal analysis of flight vehicle. High temperature local hot spots in jet wake regions and detailed thermal analysis of total vehicle provided important inputs to the system design.

Investigations on the droplet distributions in the atomization of kerosene jets in supersonic crossflows

Phase Doppler anemometry was applied to investigate the atomization processes of a kerosene jet injected into Ma = 1.86 crossflow. Physical behaviors, such as breakup and coalescence, are reproduced through the analysis of the spatial distribution of kerosene droplets' size. It is concluded that Sauter mean diameter distribution shape transforms into “I” type from “C” type as the atomization development. Simultaneously, the breakup of large droplets and the coalescence of small droplets can be observed throughout the whole atomization process.

Ignition, flame structure and near-wall burning in transverse hydrogen jets in supersonic crossflow

We have investigated the properties of transverse sonic hydrogen jets in high-temperature supersonic crossflow at jet-to-crossflow momentum flux ratios$J$between 0.3 and 5.0. The crossflow was held fixed at a Mach number of 2.4, 1400 K and 40 kPa. Schlieren and$\text{OH}^{\ast }$chemiluminescence imaging were used to investigate the global flame structure, penetration and ignition points;$\text{OH}$planar laser-induced fluorescence imaging over several planes was used to investigate the instantaneous reaction zone. It is found that$J$indirectly controls many of the combustion processes. Two regimes for low (${<}1$) and high (${>}3$)$J$are identified. At low$J$, the flame is lifted and stabilizes in the wake close to the wall possibly by autoignition after some partial premixing occurs; most of the heat release occurs at the wall in regions where$\text{OH}$occurs over broad regions. At high$J$, the flame is anchored at the upstream recirculation region and remains attached to the wall within the boundary layer where$\text{OH}$remains distributed over broad regions; a strong reacting shear layer exists where the flame is organized in thin layers. Stabilization occurs in the upstream recirculation region that forms as a consequence of the strong interaction between the bow shock, the jet and the boundary layer. In general, this interaction – which indirectly depends on$J$because it controls the jet penetration – dominates the fluid dynamic processes and thus stabilization. As a result, the flow field may be characterized by a flame structure characteristic of multiple interacting combustion regimes, from (non-premixed) flamelets to (partially premixed) distributed reaction zones, thus requiring a description based on a multi-regime combustion formulation.

Effects of oblique and transverse injection on the characteristics of jet in supersonic crossflow

The effect of oblique and transverse injection on the transverse jet was investigated by the hybrid RANS/LES simulation with recycling–rescaling procedure. The streamwise velocity distribution and instantaneous fine turbulent structures of transverse jet obtained by the particle image velocimetry (PIV) and nanoparticle-based planar laser-scattering (NPLS) are applied to validate the accuracy of simulation approach. Statistics obtained from the hybrid RANS/LES simulation with fine mesh shown good agreement with the experimental results. Four kinds of vortex structures are observed in the flow field, namely leading edge vortices, hanging vortices, counter-rotating vortex pairs (CVPs) and horseshoes vortex. The instantaneous results and spatial correlation analysis show that the size and interval of large-scale structures in windward shear layer of 45o jet are smaller and shorter than that of 90o jet, respectively. Compared with the 45o jet, the stronger shear between injectant and crossflow leads to the early breakup of CVPs in 90o jet, so the length of CVPs in 90o jet is shorter than that of 45o jet in time-averaged results. The simulation also shows that the rotating number of CVPs in 45o jet is more than in 90o jet, but the mixing of 45o jet is worse than that of 90o jet, which indicates that the large-scale structures in the shear layer between the crossflow and injectant make more contribution to the mixing process.