Transverse Injection Research Articles

Significance of fluid flow characteristics in the hydrogen-fuelled scramjet combustor using flame stabilisation analysis

ABSTRACT A supersonic combustion ramjet engine is an air breathing propulsive systems aimed for futuristic hypersonic vehicles. The profound advantages observed in the area of defence applications grabbed the researcher’s attention towards improvising the fluid flow dynamics of scramjet engines. To analyse the fluid flow dynamics of the scramjet combustor, research has been carried out to study the influence of cold flow and ignited conditions, the standard k-Ɛ turbulence model, 2D Navier–Stokes equations with eddy dissipation model is chosen. In the present analysis, significance of injection temperature, wall pressure and the formation of the compressed wave train are studied using the simulations. Additionally the impact of horizontal and transverse modes of fuel injection over the fluid flow of the computational domain was examined. It was observed that transition mode could be achieved through enhancement of injection pressure and reduction of the temperature. However, at higher injection pressure, the shock-wave train got shifted towards the outer periphery of the isolator resulting in inlet-flow un-start. Compared to injection pressure, injection temperature exhibited lower significance over mode transition. Transverse injection of fuel drastically reduced the combustion efficiency. This made it difficult to achieve the expected mode transition during the horizontal injection of fuel into the airflow. Abbreviations: M: Mach Number; K: Turbulence Kinetic Energy: H: Hydrogen

Characteristics of hydrogen jet combustion in a high-enthalpy supersonic crossflow

The facilitation of a stable combustion process is of utmost importance for the realizability and performance of hypersonic propulsion systems. To elucidate the turbulent combustion characteristics, wall-modeled large eddy simulations of a transverse jet injection into a heated supersonic flow are conducted employing a detailed reaction mechanism. The computation framework utilizes an adaptive central-upwind weighted essentially nonoscillatory (WENO-CU) scheme to achieve the sixth-order accuracy in smooth flowfields, while keeping a good shock-capturing ability. The reacting zones agree well with experimental measurements in terms of the instantaneous distribution of OH radicals. And the flame penetration height has been predicted with an error of less than 17%. It is found that the turbulent reacting flow is dominated by nonpremixed combustion mainly taking place in the near-wall region and jet windward shear-layer. Moreover, the autoignition process, which plays a critical role in stabilizing supersonic combustion, shows to favor a fuel-lean or not very fuel-rich environment of a high enthalpy. Local scalar dissipation induced by turbulence gives rise to a rapid fuel mixing with the surrounding air. However, this effect may also lead to the decrease in local temperature.

Characterisation of the eddy dissipation model for the analysis of hydrogen-fuelled scramjets

ABSTRACTThe eddy dissipation model (EDM) is analysed with respect to the ability to address the turbulence–combustion interaction process inside hydrogen-fuelled scramjet engines designed to operate at high Mach numbers (≈7–12). The aim is to identify the most appropriate strategy for the use of the model and the calibration of the modelling constants for future design purposes. To this end, three hydrogen-fuelled experimental scramjet configurations with different fuel injection approaches are studied numerically. The first case consists of parallel fuel injection and it is shown that relying on estimates of ignition delay from a 1D kinetics program can greatly improve the effectiveness of the EDM. This was achieved through a proposed zonal approach. The second case considers fuel injection behind a strut. Here the EDM predicts two reacting layers along the domain which is in agreement with experimental temperature profiles close to the point of injection but not the case any more at the downstream end of the test section. The first two scramjet test cases demonstrated that the kinetic limit, which can be applied to the EDM, does not improve the predictions in comparison to experimental data. The last case considered a transverse injection of hydrogen and the EDM approach provided overall good agreement with experimental pressure traces except in the vicinity of the injection location. The EDM appears to be a suitable tool for scramjet combustor analysis incorporating different fuel injection mechanisms with hydrogen. More specifically, the considered test cases demonstrate that the model provides reasonable predictions of pressure, velocity, temperature and composition.

Flow Structure and Thrust Change at Gas Jet Injection into the Supersonic Part of a Nozzle

The numerical simulation of gas-dynamic processes accompanying the transverse injection of a gas jet into the supersonic part of a nozzle is considered in the context of creating steering forces in rocket engines. Numerical calculations are conducted based on various turbulence models at different mass flow rates of the injected gas. The calculation results obtained for the non-viscous, laminar, and turbulent formulation of the problem are compared with each other and with the physical experiment data. The formation of a shock wave and vortex flow pattern is discussed. Conclusions about the effect of problem input parameters on the thrust gain coefficient are made.

Flameholding characteristics of ethylene-fueled model scramjet in shock tunnel

The flameholding characteristics of a model scramjet were investigated experimentally. Experiments were performed in a shock tunnel at a nominal freestream Mach number of 4. The considered total enthalpy was approximately 1.7 MJ/kg. The test model consisted of a double- ramp inlet, combustor with cavity, and cowl. The investigated fuel was ethylene, with a fuel–air equivalence ratio ranging from 0.05 to 0.21. Shadowgraph and flame luminescence images were obtained. The effects of injection location, angle, and equivalence ratio on flameholding were investigated. As the equivalence ratio was increased, the flame signals in the cavity shear layer strengthened with a near-constant spreading angle for inlet injection. The flame was maintained at the shear layer above the cavity. Unlike in the inlet case, the cavity upstream injection indicated that the flame was quite unstable during steady flow, and in general, the flame height downstream of the cavity increased as the equivalence ratio increased. In line with the literature, the flame stabilization mode for inlet injection was categorized as a “cavity shear layer-stabilized flame,” while the cavity upstream injection was a “combined cavity shear layer/recirculation zone-stabilized flame.” The effect of the injection angle on flameholding indicated that transverse injection exhibited superior fuel–air mixing compared to angled injection for the inlet case. With the cavity upstream injection, the flame was effectively maintained for both the transverse and angled injections, with approximately equivalent flame spreading angles downstream of the cavity.

Investigation of the mixing characteristics in a transverse hydrogen injection combustor with an inlet compression ramp

A shock-enhanced mixing in a transverse hydrogen injection combustor with an inlet compression ramp is carried out by using Large-eddy simulation (LES). Effects of a shock train induced by the inlet compression ramp on the mixing process have been investigated at three jet to cross-flow momentum flux ratios, J. The counter-rotating vortex pairs (CVP), promoting the mixing process of the fuel jet plume and mainstream air, is significantly affected by the reflected shock. The vorticity analysis is constructed to further understand the turbulent mixing mechanism. The shock-induced baroclinic torque is found to play an important role on the generation of the vorticity in the near field of the fuel jet, and the place where the reflected shock interacts with the jet plume. In addition, the probability density function (PDF) of mixture fraction is also investigated.

Effects of an accompanied gas jet on transverse liquid injection in a supersonic crossflow

A liquid injection scheme in a supersonic crossflow, namely transverse liquid injection accompanied with a gas jet, is proposed and investigated experimentally and numerically. High-speed photography was adopted to capture the jet spray in the experimental work; while a discrete phase model was utilized to simulate the liquid jet penetration and gas-liquid interaction in the numerical study. The differences between transverse liquid injection with and without an accompanied gas jet were analyzed. The effects of an accompanied gas jet were determined. Both the experimental and computational results indicate that an accompanied gas jet can significantly enhance liquid jet penetration. Simulation results also indicate that gas injection would cause additional total pressure losses.

Структура течения и изменение тяги при вдуве струи газа в сверхзвуковую часть сопла

AbstractThe numerical simulation of gas-dynamic processes accompanying the transverse injection of a gas jet into the supersonic part of a nozzle is considered in the context of creating steering forces in rocket engines. Numerical calculations are conducted based on various turbulence models at different mass flow rates of the injected gas. The calculation results obtained for the non-viscous, laminar, and turbulent formulation of the problem are compared with each other and with the physical experiment data. The formation of a shock wave and vortex flow pattern is discussed. Conclusions about the effect of problem input parameters on the thrust gain coefficient are made.

Investigation on three mixing enhancement strategies in transverse gaseous injection flow fields: A numerical study

Numerical investigation of some mixing enhancement strategies based on the traditional transverse injection technique proposed in recent years was carried out by means of the three-dimensional Reynolds-average Navier–Stokes (RANS) equations coupled with the two equation k-ω shear stress transport (SST) turbulence model. The numerical approaches employed in the current study were validated against the available two- and three-dimensional data in the open literature, and they can be used with confidence to achieve a better understanding of mixing augmentation mechanisms in transverse injection flow fields with various mixing enhancement strategies, namely the pulsed jet, the air jet and the ramp. Results obtained in this study provide important insight into complex flow phenomena. Various fundamental mechanisms dictating the intricate flow characteristics for the transverse injection flow field with various mixing enhancement strategies, including the circulation, vertical structures, velocity vectors and shock wave systems, have been analyzed systematically. The performance parameters of the transverse injection flow fields, such as the mixing length, the fuel penetration depth and the stagnation pressure loss have been compared. Different mixing enhancement strategies have their advantages and disadvantages, and the combination of various mixing enhancement strategies may be a promising injection strategy for better mixing performance of the transverse injection flow field. A stronger streamwise vorticity is the main reason for the mixing enhancement. However, the mixing length and the stagnation pressure loss of the transverse injection flow field show opposite trends from each other with a variance in the intensity of streamwise vorticity.

Mixing augmentation mechanism induced by the dual injection concept in shcramjet engines

As one of the key techniques, achieving adequate fuel/air mixing before combustion is a task that must be addressed seriously for shock-induced combustion ramjet (shcramjet) engines. In this paper, dual injectors which have been combined by a front hydrogen jet and a rear air jet with different aspect ratios are placed on the second ramp of a shcramjet inlet to promote mixing process between fuel and hypersonic crossflow. At the same time, dual injectors with pure hydrogen injection and the single hydrogen injection with the same injection area are studied as well for comparison. Flow field properties are investigated numerically based on grid independency analysis and code validation. Obtained results predicted by the three-dimensional Reynolds-average Navier-Stokes (RANS) equations coupled with the two equation SST κ-ω turbulence model show that the grid scale makes only a slight difference to wall pressure profiles for all cases studied in this article. The dual transverse injection system with a front hydrogen jet and a rear air jet is beneficial for improvement of the mixing efficiency between hydrogen and air. Mixing efficiency in the near field increases with increase of aspect ratio of the air porthole. The air porthole in dual transverse injections would accelerate mixing process when compared with the single injection strategy irrespective of aspect ratio of the air porthole.

Numerical investigation and optimization on the micro-ramp vortex generator within scramjet combustors with the transverse hydrogen jet

An effective fuel supply strategy with high mixing efficiency, large penetration depth and low stagnation pressure losses determines the overall performance of the scramjet (supersonic combustion ramjet) engine. In this paper, the transverse hydrogen injection flow field with a micro-ramp located upstream of the wall orifice has been investigated numerically based on the code validation. There are four design variables considered in the current study, namely the width, length, and height of the micro-ramp and the distance between the center of the wall orifice and the trailing point of the micro-ramp. Nine cases predicted by the three-dimensional Reynolds-averaged Navier–Stokes (RANS) equations coupled with the two equation k–ω shear stress transport (SST) turbulence model are used for parametric analysis, and the parametric analysis has been carried out by the extreme difference analysis approach. Three optimization cases are obtained, and they have different objectives, namely the minimization of the mixing length, the maximization of the penetration depth and the minimization of the stagnation pressure losses. The flow structures of all cases have been discussed and compared. The quantitative evaluation results of three optimization cases show that the extreme difference analysis approach is an efficient parametric analysis method, and it can obtain the optimal strategy for the micro-ramp within scramjet combustors with the transverse hydrogen jet.

Numerical investigation on the mechanism of the effects of plate vibration on mixing and combustion of transverse hydrogen injection

This study numerically investigates the effects of plate vibration and deformation on the combustion performance, the shock wave structure, the mixing characteristics and the flame structure for transverse hydrogen injection. The finite-rate method is used to simulate combustion. Results show that plate vibration causes the combustion performance to oscillate both temporally and spatially, while plate deformation can only change the static characteristics of the flow. Plate vibration and deformation increase the intensity and number of shock wave reflections in different ways. In addition, both plate vibration and deformation increase the momentum flux ratio and the jet penetration depth, which enhances mixing. Finally, plate vibration widens the flame and moves it upward to a greater extent than plate deformation.

분사구 형상에 따른 초음속 유동장 내 수직 분사된 연료-공기 혼합 및 반응 특성 연구

A computational simulations were performed to investigate the effect of injector shapes on fuel-air mixing and reacting characteristics for a transverse injection into a supersonic flow. Five different injector geometries are considered and all injectors have the same cross-sectional area and mass flow rate. The simulation results of the circular injector performed for verification were well consistent with those of the experiment. For other injectors, mixing efficiency, streamwise vorticity, combustion efficiency, and spatial distribution of the reaction product are compared with each other. Results show that mixing and combustion efficiencies differ with injector geometries as flow structures are varied. It was found that the mixing and combustion efficiencies of diamond injector are the best among the shapes considered in this study.

Effects of operational parameters on liquid nitrogen spray cooling

To determine the influence of design parameters on droplet evaporation and distribution of liquid nitrogen (LN2) spray cooling, experimental and numerical studies are performed by varying the mass flow rate, flow velocity, droplet diameter, injection orientation, and droplet velocity. The results demonstrate that backward injection yields the highest droplet evaporation ratio, which is 40% and 10% higher than the evaporation ratios obtained through forward and transverse injections, respectively. Counter-rotating vortex pairs are observed in the transverse injection, which improves the temperature distribution via convective mixing. Reducing the droplet diameter provides a more effective means of enhancing the evaporation than increasing the droplet velocity, and a linear increase in the droplet evaporation is observed by reducing the droplet diameter from 0.6 to 0.2 mm. The results and findings provide guidelines for the design of LN2 spray cooling systems for cryogenic wind tunnels.

Large-eddy simulation and linear acoustic modeling of entropy mode oscillations in a model combustor with coolant injection

Lean-burn combustor is particularly susceptible to combustion instability and the unsteady heat release is usually considered as the excitation of the self-maintained thermo-acoustic oscillations. The transverse coolant injection is widely used to reduce the temperature of burnt gas, but on the other hand, it will introduce temperature fluctuation inside the combustor. Therefore, it is necessary to consider the influence of the coolant injection on combustion instability, and evaluate its dynamic feature. In this paper, Large-Eddy Simulation (LES) of the self-excited pressure oscillations in a model combustor with coolant injection is carried out. The analysis of transient flow characteristics and the identification of the pressure modes confirm that one of the low frequency pressure oscillations is related to entropy fluctuations, which is known as rumble combustion instability. The LES results show that transient coolant injection is another excitation of temperature fluctuation other than unsteady combustion. The amplitude of the entropy mode oscillation increases with increasing coolant air mass whereas the change of its frequency is insignificant. According to the major feature of entropy wave oscillation caused by coolant injection, a compact coolant injection model is proposed and applied in the One Dimensional (1D) Acoustic Network Method (ANM). Key correlations used in the model match well with LES data in low frequency range. This means that the coolant injection model is a complex one reflecting the interaction of the fluctuating coolant mass, pressure and temperature. Finally, the combustion instability frequencies and modes predicted by acoustic network method are also in good agreement with LES results.

Characteristics and mixing enhancement of a self-throttling system in a supersonic flow with transverse injections

A three-dimensional self-throttling system is proposed in a scramjet combustor with transverse fuel jet, and investigated by Reynolds-averaged Navier-Stokes (RANS) simulations with the k-ω SST turbulence model. Numerical validation has been carried out against experiment and LES results. The effects of the jet-to-cross-flow momentum flux ratio and the throttling angle on mixing performance, fuel jet penetration depth and total pressure losses are all addressed. Through the proposed throttling system, the higher pressure upstream of the transverse fuel injection can drive part of the low momentum mainstream air into the downstream lower pressure region. The flow structures and the interactions between the shock waves and boundary layer are significantly changed to improve the mixing performance. The enhancement of mixing efficiency in the self-throttling system is closely related to the magnitude of the jet to crossflow momentum flux ratio, and a smaller throttling angle is found to further improve the mixing. On the other hand, the self-throttling system has a good performance in reducing the total pressure losses.

분사구 형상에 따른 초음속 유동장 내 수직 연료 분사 특성

분사구 형상에 따른 초음속 유동장 내 수직 연료 분사 특성

Three-dimensional couette flow of dusty fluid with heat transfer in the presence of magnetic field

This paper is focused on the mathematical modelling of three-dimensional couette flow and heat transfer of a dusty fluid between two infinite horizontal parallel porous flat plates in the presence of an induced magnetic field. The problem is formulated using a continuum two-phase model and the resulting equations are solved analytically. The lower plate is stationary while the upper plate is undergoing uniform motion in its plane. These plates are, respectively subjected to transverse exponential injection and its corresponding removal by constant suction. Due to this type of injection velocity, the flow becomes three dimensional. The closed-form expressions for velocity and temperature fields of both the fluid and dust phase are obtained by solving the governing partial differentiation equations using the perturbation method. A selective set of graphical results is presented and discussed to show interesting features of the problem. It is found that the velocity profiles of both fluid and dust particles decrease due to the increase of (magnetic parameter) Hartmann number.

Couette flow of an incompressible fluid in a porous channel with mass transfer

The present discussion deals with the study of couette flow through a porous medium of a viscous incompressible fluid between two infinite horizontal parallel porous flat plates with heat and mass transfer. The stationary plate and the plate in uniform motion are subjected to transverse sinusoidal injection and uniform suction of the fluid. Due to this type of injection velocity, the flow becomes three dimensional. The analytical solutions of the nonlinear partial differential equations of this problem are obtained by using perturbation technique. Expressions for the velocity, temperature fields and the rate of heat and mass transfers are obtained. Effects of the following parameters Schmidt number (Sc), Modified Grashof number (Gm) on the velocity, temperature and concentration fields are obtained numerically and depicted through graphs. The rate of heat and mass transfer are also analyzed.

Mixing improvement induced by the combination of a micro-ramp with an air porthole in the transverse gaseous injection flow field

A new injection strategy combined with a micro-ramp and an air porthole is proposed in this paper, and the properties of the transverse gaseous injection flow field with such injection strategy have been investigated simultaneously. The numerical approach employed in the current study has been validated against the two-dimensional and three-dimensional experimental data in the open literature, and it can be used with confidence to investigate the influence of the air porthole aspect ratio and the distance between the air porthole and the fuel orifice on the transverse injection flow field with the combination of a micro-ramp and an air porthole. The obtained results predicted by the three-dimensional Reynolds-average Navier–Stokes (RANS) equations coupled with the two equation k-ω shear stress transport (SST) turbulence model show that the mixing performances of the transverse gaseous injection flow fields vary under different conditions, and a transverse injection flow field with short mixing length, low stagnation pressure loss and ideal fuel penetration depth has been achieved by adding the combination of an optimized micro-ramp with a proper air porthole, i.e. Case 6–8, and its mixing length decreases considerably by 14.26 mm on the basis of Case c, even shorter than the mixing length of Case a by 2.86 mm. However, its total pressure loss increases when compared with Case c, and its stagnation pressure loss is 2.7 percent smaller than Case a. Further, the hydrogen distribution on the flat plate of Case 6–8 is much less than that of Case a and Case b. Additionally, it is found that the mixing enhancement mechanism of the air jet is different from that of the micro-ramp. The micro-ramp enhances the mixing process between the fuel and air by inducing large-scale vortices, while the air porthole enhances the mixing process by seeding lots of air into the fuel boundary layer, as well as fuel plume.