Strut-based Scramjet Combustor Research Articles

Shock waves affected turbulent mixing region development in a strut-based scramjet combustor

The mixing of fuel and air is an important issue in the development of current scramjet engines. Defining the mixing region thickness using the fuel mole fraction is one of the widely accepted methods, but a consensus on the specific value of the fuel mole fraction to be used has not yet reached. In order to solve this problem, this paper conducts a detailed numerical study on a hydrogen-fueled strut-based scramjet combustor utilizing the two-dimensional Reynolds-Averaged Navier-Stokes (RANS) equation coupled with the SST k-ω turbulence model. The thickness of the mixing zone formed by the hydrogen jet at the end of the combustor strut and the incoming air is defined by the region with hydrogen molar fraction greater than a certain threshold, and the effects of the incident shock waves on the thickness of the mixing zone are investigated at eight different locations in the mixing zone for the thresholds of 0.05, 0.02, 0.01 and 0.005. The study shows that in order to make the thickness profiles of the mixing zone reflect both the overall law of thickness change and the influence of the shock waves on the thickness of the mixing zone, the threshold value of 0.01 is a better choice. The growth rate of the thickness of the mixing zone decreases and then increases when the shock wave is incident on the mixing zone, and the decrement and the subsequent increment of the growth rate both increase with the intensity of the shock wave.

Effect of crossflow impinging type throttling mechanism on combustion characteristics of a strut-based scramjet combustor

Efficient mixing of fuel-air, improved combustion performance, and flame stabilization are the critical events for the successful operation of scramjets that must be realized within the short residence time. One of the significant concerns is flame blow-off during the start-up stage even with the presence of the flame holders. To counter it, an innovative mechanism of air-throttle injection has been proposed and investigated through computational fluid dynamics in the present study. In the proposed mechanisms, a strut is used as a base flame holder, and a provision is made to inject the air in the transverse direction behind the strut's base. Two- and three-dimensional Reynolds-averaged Navier-Stokes (RANS) equations have been solved using the k-ω SST turbulence model for reacting and non-reacting flows. A finite-rate/eddy-dissipation combustion model is selected to include the effects of turbulence-chemistry interaction. It was observed from the simulations that the impingement of hydrogen jet and the transverse throttled jet generates the vortices and recirculation zones. Improved fluid-dynamics associated with the impinging action of the air-throttle has been studied by considering argon as a surrogate for air; also, the enriched oxygen (due to air throttling) around the hydrogen jet makes fuel-air mixture more flammable. These fluid dynamics and chemistry aspects are responsible for the superior performance of air-throttling mechanisms. The proposed mechanism showed 46 % reduction in combustor length to reach the combustion efficiency of more than 95 %. The maximum improvement of mixing efficiency is 48 % observed at downstream of the throttle base over the non-throttled condition. Further the effectiveness of the proposed throttling mechanism is demonstrated to show a promise for holding the flame even at a higher Mach number, i.e., M=4.5. The ignition is achieved at a shorter distance in the air-throttling case, resulting in 28 % reduction in ignition length. The air throttling within the two-shear layer may reduce the ignition delay associated, and the flame can be held immediately downstream of the injector. Additionally, a three-dimensional flow field was also analysed to study the flow characteristics around the transverse jet. In the 3-D flow field, the circulation profiles indicated that the stronger vorticity was generated during the air-throttling than without air-throttling.

Large Eddy Simulation and Dynamic Mode Decomposition of Supersonic Combustion Instability in a Strut-Based Scramjet Combustor

Supersonic combustion instability studies are crucial for the future maturation of scramjet engines. In the present paper, the supersonic combustion instability in a strut-based scramjet combustor is investigated through large eddy simulation and dynamic mode decomposition. The results show significant pressure oscillation in the strut-based scramjet combustor when the air parameters at the combustor inlet and the fuel parameters at the injector outlet are under certain conditions, and these pressure oscillation situations correspond to supersonic combustion instability. The oscillations have multiple dominant frequencies, including relatively low frequency of 2984 Hz, high frequency of 62,180 Hz, and very high frequency of 110,562 Hz. Large pressure oscillations in the strut-based scramjet combustor are closely related to wake instability, shear layer instability, shear layer and wave interactions, and combustion. Reducing the air total temperature at the combustor inlet can attenuate the pressure oscillations, and reducing the fuel flow rate at the injector outlet can also attenuate the pressure oscillations.

Impact of cavity and ramp configuration on the combustion performance of a strut-based scramjet combustor

Abstract The flow performance of a dual wall-mounted cavity in a strut-injector scramjet combustor in steady reacting flow conditions is computationally analyzed. A baseline configuration corresponding to DLR experiments and two proposed configurations with varying bottom wall cavity depth and fixed top wall ramp is considered. Steady-flow computations are performed using the 2-D Reynolds Averaged Navier–Stokes method with k-ω SST turbulence closure coupled and single-step reaction chemistry. The calculated flow patterns, density, pressure, and temperature fields are compared with shadowgraph and wall pressure measurements from DLR experiments. The cavity and strut are mounted downstream of the strut to analyze the shock patterns and their interference with the shear layer mixing features. The estimated flow patterns, density, pressure, and temperature fields are compared with shadowgraph and wall pressure measurements from DLR experiments. Incorporating cavity and ramp configuration provides earlier complete combustion compared to the baseline model, with a marginal rise in the total pressure caused by additional shock wave formation that emanates from the corners of the cavity and ramp. The combustion zone widens in the lateral direction as the cavity shifts the shock train downstream of the strut injector owing to intense shock shear layer interactions.

Numerical Exploration of Staged Hydrogen Combustion in A Strut Based Scramjet Combustor

Scramjet combustor with fuel injection from strut and wall is numerically simulated using three-dimensional Navier Stokes equations along with k - ε turbulence model. Turbulence - chemistry interaction is modeled through Eddy Dissipation Concept (EDC) based on infinitely fast rate kinetics. The simulations captured all the essential features of flow field for various combinations of fuel injections from the strut and the wall. The computed surface pressures match very well with the experimental values for both reacting and non-reacting cases. Performance parameters are evaluated from the computed flow variables. It was found that more fuel could be injected in the scramjet combustor through staged injection without inlet - combustor interaction.

Numerical investigations on the influence of double ramps in a strut based scramjet combustor

This numerical study addresses the performance of double ramps in a strut injection scramjet combustor. Reynolds Averaged Navier Stokes (RANS) equations with the Shear Stress Transport SST k-[Formula: see text] turbulence model are used for numerical analysis. The dual ramps are located symmetrically at the top and bottom wall of a scramjet combustor downstream of the strut injector. The influence of the location of ramps in the scramjet combustor is analyzed based on the key parameters such as shock waves, static pressures, and temperature distribution across the combustor, which are verified with available DLR scramjet experimental data that show similar acceptable values within the range. Simulation is extended for the investigation of other configurations. The performance of the scramjet configurations has been analyzed using the variables such as shock patterns, Mach number contours, wall static pressures, mass fractions of the reactants and products, combustion efficiency, and stagnation pressure loss of combustor. Numerical shadowgraph indicates that numerous shock reflections occur for the dual ramp cases that decelerate the combustor’s flow downstream. In addition, the recirculation regions are created for the dual ramp cases, which help in anchoring the flame. The static pressure distributions show the variation of peaks due to shock patterns and their interactions. The combustion efficiency increases as the ramps are positioned downstream of the strut injector. The mass fractions of reactants and products indicate complete combustion of the hydrogen issued from the combustor in the vicinity of the cavities. The total pressure loss for the DLR strut model is comparatively lower than dual ramp cases due to the multiple shocks from the ramp decelerating the flow downstream of the combustor.

NUMERICAL INVESTIGATION OF COMBUSTION PERFORMANCE OF VARIOUS FUELS IN WEDGE-SHAPED STRUT-BASED SCRAMJET COMBUSTOR

NUMERICAL INVESTIGATION OF COMBUSTION PERFORMANCE OF VARIOUS FUELS IN WEDGE-SHAPED STRUT-BASED SCRAMJET COMBUSTOR

Numerical investigation on geometric sensitivity and flame stabilisation mechanism in H2 fueled two-strut based scramjet combustor

The layout of the strut fuel injector has a significant impact on the flame stabilization process of the strut-based scramjet combustor. That’s why a two-strut-based scramjet model has been developed in recent researches. As several recent studies have shown that the two-strut model performs better than a single-strut model in terms of performance parameters, the current research thus focuses on the effect of geometric sensitivity to the combustion flow-field as well as flame stabilization mechanism of the two-strut scramjet engine. To begin with, the adopted computational approaches are validated using experimental data from the existing literature for a single strut. Following that, multiple ramp positions are imported onto the existing two-strut geometry and then divergence angles on both the walls of the two-strut combustor are also varied to explore the combustion performance. The present investigation reveals that geometric variation has a significant influence on the performance study of a supersonic combustor. Increasing the ramp position from the combustor entrance leads to a slight improvement in combustion efficiency but at the cost of a corresponding increase in total pressure loss. Moreover, increasing the divergence angle on both walls weakens the combustion performance to some extent. Finally, a flame stabilization analysis is carried out in a two-strut model, which identifies two stable modes of combustion in the same way as single strut geometry does, suggesting that two-strut geometry can be adopted as an effective flame holder in future works.

Implication of self-throttling on combustion performance in a strut-based scramjet combustor

The present work describes the numerical investigation on the implication of self-throttling on combustion performance of a strut-based scramjet combustor. Firstly, the mixing characteristics of a strut with and without self-throttling are compared and evaluated to portray the effect of self-throttling in a DLR based scramjet combustor. Later, a separate study is performed to investigate the influence of location of self-throttling on the combustion performance of a strut-based scramjet combustor. Our study reveals that the self-throttling increases the enthalpy of formation and the generates the strong shock waves which improves the mixing rate of fuel and air. Further, the mixing commences relatively earlier with reduced pressure losses when the self-throttling is employed. It is observed that the volume of core flame region and the thickness of a flame depends on the distance between the reflected shock and the self-throttling injection slot.Also, the combustion performance deteriorates with the increase in distance between the reflected shock and the injection slot of self-throttling. Further, the combustion and mixing efficiency is found to be optimalwhen self-throttling is employed at the distance of100 mm from the inlet of the combustor.

Numerical investigations on the hydrogen jet pressure variations in a strut based scramjet combustor

PurposeThis paper aims to study the influences of hydrogen jet pressure on flow features of a strut-based injector in a scramjet combustor under-reacting cases are numerically investigated in this study.Design/methodology/approachThe numerical analysis is carried out using Reynolds Averaged Navier Stokes (RANS) equations with the Shear Stress Transport k-ω turbulence model in contention to comprehend the flow physics during scramjet combustion. The three major parameters such as the shock wave pattern, wall pressures and static temperature across the combustor are validated with the reported experiments. The results comply with the range, indicating the adopted simulation method can be extended for other investigations as well. The supersonic flow characteristics are determined based on the flow properties, combustion efficiency and total pressure loss.FindingsThe results revealed that the augmentation of hydrogen jet pressure via variation in flame features increases the static pressure in the vicinity of the strut and destabilize the normal shock wave position. Indeed, the pressure of the mainstream flow drives the shock wave toward the upstream direction. The study perceived that once the hydrogen jet pressure is reached 4 bar, the incoming flow attains a subsonic state due to the movement of normal shock wave ahead of the strut. It is noticed that the increase in hydrogen jet pressure in the supersonic flow field improves the jet penetration rate in the lateral direction of the flow and also increases the total pressure loss as compared with the baseline injection pressure condition.Practical implicationsThe outcome of this research provides the influence of fuel injection pressure variations in the supersonic combustion phenomenon of hypersonic vehicles.Originality/valueThis paper substantiates the effect of increasing hydrogen jet pressure in the reacting supersonic airstream on the performance of a scramjet combustor.

The Effect of Ramp Location in a Strut Based Scramjet Combustor under non reacting flow field

The scramjet engine is considered to be the high-speed propulsive system for hypersonic air-breathing vehicles. Researchers focus on various geometries of strut injectors to enhance the mixing and combustion efficiencies of the scramjet combustor. This paper reveals the non-reacting flow characteristics of various ramp locations in a scramjet combustor with strut injection. The ramps are symmetrically placed at three different locations upstream of the strut within the combustor. Air enters into the combustor inlet with Mach number 2, and the fuel is injected at the sonic velocity from the strut. The 2D supersonic flow characteristics are numerically investigated using ANSYS 18.0 software. The steady-state flow simulations are performed in this study. The flow field is modelled using RANS equations, and the k-ω SST turbulence model and default constants are chosen to investigate the flow characteristics within the combustor. The flow characteristics of the ramp based DLR scramjet combustors are compared with the baseline DLR scramjet model. The computational results are validated with the experimental data. The shock wave interaction from the ramps enhances the distribution of hydrogen in the lateral direction of the flow than the baseline strut configuration. The ramps create recirculation regions that could enhance fuel-air mixing. The ramp induced strut based DLR scramjet engine provides increased total pressure loss of the baseline DLR scramjet.

The Combustion Characteristics of Double Ramps in a Strut-Based Scramjet Combustor

This paper focuses on the influence of ramp locations upstream of a strut-based scramjet combustor under reacting flow conditions that are numerically investigated. In contrast, a computational study is adopted using Reynolds Averaged Navier Stokes (RANS) equations with the Shear Stress Transport (SST) k-ω turbulence model. The numerical results of the Deutsches Zentrum für Luft- und Raumfahrt or German Aerospace Centre (DLR) scramjet model are validated with the reported experimental values that show compliance within the range, indicating that the adopted simulation method can be extended for other investigations as well. The performance of the ramps in the strut-based scramjet combustor is analyzed based on parameters such as wall pressures, combustion efficiency and total pressure loss at various axial locations of the combustor. From the numerical shadowgraph, more shock interactions are observed upstream of the strut injection region for the ramp cases, which decelerates the flow downstream, and additional shock reflections with less intensity are also noticed when compared with the DLR scramjet model. The shock reflection due to the ramps enhances the hydrogen distribution in the spatial direction. The ignition delay is noticed for ramp combustors due to the deceleration of flow compared to the baseline strut only scramjet combustor. However, a higher flame temperature is observed with the ramp combustor. Because more shock interactions arise from the ramps, a marginal increase in the total pressure loss is observed for ramp combustors when compared to the baseline model.

Computational investigation of an ethylene-fueled supersonic combustor assisted by a porous cylindrical burner

To facilitate burning of ethylene fuel in a scramjet combustor, as a relevant route to hydrocarbon combustion, we propose an alternative design of configuration. Three-dimensional flow field in a strut-based scramjet combustor has been investigated computationally. The Large Eddy Simulation (LES) turbulence model and Partially Stirred Reactor (PaSR) combustion model are used. Validations have been performed against published literature to ensure the numerical settings and accuracy. It is shown that, while hydrogen can be successfully ignited and lead to stabilized flame, ethylene combustion cannot be sustained in the same way. By adding a porous cylindrical burner at downstream of the strut injector, consequently, continuous ignition and flame sustainment of ethylene in the primitive combustor can be achieved. To understand the essential difference, the key factors such as net thrust, momentum and pressure variations, flame extinction, and flame stabilization mechanisms have been studied. Specifically, while the porous cylinder may provide a re-ignition source for the hot flow quenched upstream, it expectably introduces a bow shock and extra drag when being placed at the downstream supersonic region. When the porous burner is inserted right behind the strut where the flow is locally subsonic, however, no shock is formed additionally and the total drag is not significantly increased while flames can be stabilized downstream of the porous burner. As a consequence, a positive net thrust and specific impulse at the same flow rate of fuel mass can be obtained, in contrast to the decelerating state in the primitive configuration that yields a negative thrust. Furthermore, the auxiliary device renders a larger penetrating depth of the injected fuel and flame spreading area as well as higher consumption ratio of oxygen, leading to a more favorable condition of design for a supersonic nozzle to produce effective propulsion.

P.598 Role of microRNAs in the mechanisms underlying stress vulnerability and resilience

To facilitate burning of ethylene fuel in a scramjet combustor, as a relevant route to hydrocarbon combustion, we propose an alternative design of configuration. Three-dimensional flow field in a strut-based scramjet combustor has been investigated computationally. The Large Eddy Simulation (LES) turbulence model and Partially Stirred Reactor (PaSR) combustion model are used. Validations have been performed against published literature to ensure the numerical settings and accuracy. It is shown that, while hydrogen can be successfully ignited and lead to stabilized flame, ethylene combustion cannot be sustained in the same way. By adding a porous cylindrical burner at downstream of the strut injector, consequently, continuous ignition and flame sustainment of ethylene in the primitive combustor can be achieved. To understand the essential difference, the key factors such as net thrust, momentum and pressure variations, flame extinction, and flame stabilization mechanisms have been studied. Specifically, while the porous cylinder may provide a re-ignition source for the hot flow quenched upstream, it expectably introduces a bow shock and extra drag when being placed at the downstream supersonic region. When the porous burner is inserted right behind the strut where the flow is locally subsonic, however, no shock is formed additionally and the total drag is not significantly increased while flames can be stabilized downstream of the porous burner. As a consequence, a positive net thrust and specific impulse at the same flow rate of fuel mass can be obtained, in contrast to the decelerating state in the primitive configuration that yields a negative thrust. Furthermore, the auxiliary device renders a larger penetrating depth of the injected fuel and flame spreading area as well as higher consumption ratio of oxygen, leading to a more favorable condition of design for a supersonic nozzle to produce effective propulsion.

Implication of geometrical configuration of cavity on combustion performance in a strut-based scramjet combustor

The present work describes the numerical investigation on the implication of the geometrical configuration of a cavity with a strut-based scramjet combustor. Firstly, the combustion characteristics of a combustor with a cavity and the combustor without a cavity are compared and evaluated to portray the effect of a cavity. On the other hand, a separate study is performed to investigate the interplay of cavity parameters namely, length to depth (L/D) ratio of a cavity and angle of a cavity (α) on the performance of a strut-based scramjet combustor. Our study reveals the formation of a strong recirculation zone in the cavity region which improves the mixing and combustion efficiency in the case of a cavity-based combustor. It is observed that the combustion commences relatively earlier in the case of a cavity-based combustor and reaches to its peak value of around 80%. Further, the size of a recirculation region depends on the distance between the strut injector and the length of a cavity. Moreover, the shear layer is observed in the cavity region inducing a weak shock at the trailing edge of a cavity which deteriorates the performance of a scramjet combustor particularly for a higher angle of a cavity(α) and lowers L/D ratio of a cavity. Also, the combustion efficiency is found to be optimal with moderate pressure losses at L/D = 4 and α = 300.

The numerical analysis of combustion performance of a wedge shaped strut-based scramjet combustor

The combustion performance of hydrogen fueled supersonic ramjet combustor has been computationally analysed. For the need of comparison, DLR Scramjet model of German Aerospace Center (DLR) has been taken into consideration. Off design analysis has also been conducted through the same model to see the appropriate changes. Ansys 14.0 fluent solver has been used to solve the two dimensional DLR Scramjet model with the help of Reynolds Averaged Navier-Stokes (RANS) equation. To have the reasonable accurateness of turbulent flow, RNG k-ε two equation model has been chosen. The good agreement can be seen between present computation and the experiment data in open literature. Shock incident point follows the same pattern as previous experimentations and this can also be recognised in contour plots. To explore the variation behind the combustion performance by means of two selected parameters i.e. Mach number and temperature of incoming free stream air. This variation in the supersonic combustor is found helpful in terms of mixing length, shock wave behavioural strength, mixing efficiency and combustion efficiency. The changes in air speed lead to alter the incident location points of the shock waves. As the free stream air speed is getting higher, the appearance of fuel from the strut face became parallel in nature with air. Smallest mixing length of 26 mm is accomplished. Ignition delay between fuel entrainment and start of combustion did not take place in cases with Mach number 2.6, 2.8 and 3.0. However the superior combustion performance among all the selected cases is seen at the free stream air Mach number 3.0.

Impact of parametric variation on combustion characteristics of hydrogen‐fueled strut based scramjet combustor at supersonic speed

Impact of parametric variation on combustion characteristics of hydrogen‐fueled strut based scramjet combustor at supersonic speed

Numerical investigation on implication of dual cavity on combustion characteristics in strut based scramjet combustor

The present study investigates the implication of a dual cavity on combustion and mixing characteristics of strut based combustor numerically. A scramjet combustor with and without cavity are considered to evaluate the influence of cavity on combustion characteristics. Moreover, the effect of spacing between the cavities on combustion performance is also discussed. A separate study is carried out to understand the interplay of the Mach number and the spacing between the cavities on combustion characteristics. Our study reveals that the introduction of a dual cavity in scramjet combustor enhances the mixing and improves combustion performance. Further, it is found that the mixing length is lesser and the penetration height is more when a dual cavity is employed in a combustor. It can also be observed that the size of the recirculation region is found to be larger for the combustor with dual cavity among all configurations at the spacing S2 = 12.7 mm. Further, the combustion efficiency and fuel penetration height are found to be maximum at Mach 2.5 with a spacing S2 = 12.7 mm.

A novel method for flame stabilization in a strut-based scramjet combustor

For successful operation of propulsion system of an air-breathing hypersonic aircraft, flame stabilization in its scramjet combustor is very critical. In this paper, a novel strut is proposed for flame stabilization in a scramjet combustor. The novel strut is a modification of the traditional strut with the angles of its rear part enlarged. Employing the two-dimensional compressible multi-species Navier–Stokes equations and a one-step hydrogen–air reaction model, six simulation cases are performed. An analysis of the simulations is conducted to explain the stabilization of the flame by the proposed novel strut. The shock waves induced by the rear part of the novel strut cause a high-temperature and high-pressure region for combustion and an effective total pressure loss. The strong shock waves affect only the nearby region of the strut for the reason that only a small part of the wedge is wedge angle enlarged. The novel strut is thus able to stabilize the flame behind it and can be used as a flame holder in a scramjet combustor.

Numerical investigation on the performance of scramjet combustor with a novel strut configuration

The design of the strut fuel injector plays an important role in the performance of the strut-based scramjet combustor. The current study numerically investigates the flow and combustion characteristics of a scramjet combustor. An in-house code was developed to compute the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the SST k-ω turbulence model and the one-step reaction finite-rate/eddy-dissipation model. In order to enhance the mixing and combustion efficiency, we develop a novel double-strut concept with backward-facing steps in the scramjet combustor. Firstly, the numerical methods are validated by the available experimental data in open literature. Then we compare the mixing and combustion performance between the single strut and the double-strut. Finally, the effects of the perpendicular distance between the two struts on the mixing and combustion efficiency are also reported. The numerical results show an acceptable agreement with the experimental results. The presence of the double-strut with backward facing steps has a remarkable enhancement on the mixing degree and combustion efficiency in the scramjet combustor when compared with the original single-strut. Further, the combustion efficiency for the perpendicular distance of 4 mm is the highest one among the six cases, and the total pressure loss is relatively low. Therefore, the new configuration with the perpendicular distance of 4 mm is the optimal one within the range considered in this study.