Scramjet Nozzle Research Articles

Numerical investigation of thermochemical non-equilibrium effects in Mach 10 scramjet nozzle

Abstract High-temperature non-equilibrium effects are prominent in scramjet nozzle flows at high Mach numbers. Hence, the thermochemical non-equilibrium gas model incorporating the vibrational relaxation process of molecules in the hydrocarbon-air reaction is developed to numerically simulate the flow of a hydrocarbon fuel scramjet nozzle at Mach 10. Besides, the results computed by the models of the thermally perfect gas, chemically non-equilibrium gas, and thermally non-equilibrium chemically frozen gas are applied for comparative studies. Results indicate that chemical non-equilibrium effects are more significant for the flow-field structure and parameters compared to thermal non-equilibrium effects. Meanwhile, vibrational relaxation and chemical reactions interact in the flow-field. The heat released from the chemical reactions in the flow-field of the thermochemical non-equilibrium gas model makes the thermal non-equilibrium effects weaker compared to the thermally non-equilibrium chemically frozen gas model; the chemical reactions in the thermochemical non-equilibrium gas model are more intense than in the chemically non-equilibrium gas model. Due to the slow relaxation of vibrational energy, the thermal non-equilibrium models predicted nozzle thrust lower than the thermal equilibrium models by approximately 1.11% to 1.33%; when considering the chemical reactions, the chemical non-equilibrium models predicted nozzle thrust higher than the chemical frozen models by approximately 7.30% to 7.54%. Hence, the structural design and performance study of the high Mach numbers scramjet nozzle must consider thermochemical non-equilibrium effects.

Influence of thermochemical non-equilibrium effects on non-uniform entrance scramjet nozzle

The high Mach number scramjet nozzle flow has prominent non-uniform characteristics and high-temperature non-equilibrium effects. Thus, the thermochemical non-equilibrium gas model was developed for simulating flows in the non-uniform and uniform entrance of a Mach 10 hydrocarbon fuel scramjet nozzle. The results show that the non-uniform entrance has a higher non-uniform degree in the flow-field compared to the uniform entrance. Additionally, the expansion degree inside the nozzle is greater and the thermal non-equilibrium effects downstream of the nozzle exit are stronger. The non-uniform entrance condition has a more intense chemical reaction near the nozzle exit but has less impact on the flow parameters. For the nozzle performance, under the influence of the non-uniform entrance, the greater gas expansion degree inside the nozzle results in a lower pressure acting on the upper wall, and then the nozzle thrust decreases by 1.68%. Hence, the structural design and performance optimization of the high Mach number scramjet nozzle must consider entrance non-uniform characteristics and thermochemical non-equilibrium effects.

Multi-objective optimization design of scramjet nozzle based on grey wolf optimization algorithm and kernel extreme learning machine surrogate model

This study delves into the parametric design of the scramjet nozzles, utilizing the Catmull–Rom curve, to meet the high-performance design requirements. It establishes a high-dimensional, multi-objective optimization design method based on a surrogate model for the nozzle. In addition, this research proposes a surrogate model for nozzle performance to enhance the accuracy of the traditional surrogate model and prevent the multi-objective optimization design method from optimizing in an incorrect direction. This model incorporates the grey wolf optimization (GWO) algorithm and kernel extreme learning machine (KELM). Various machine learning algorithms are compared and analyzed, demonstrating that the performance parameters predicted by the GWO-KELM model are the most accurate, and the generalization of GWO-KELM is verified. Utilizing the particle swarm optimization algorithm assisted by GWO-KELM, the multi-objective optimization of the nozzle is further investigated. This study obtains the optimal Pareto front, analyzes the distribution of design variables in the Pareto solution set, and reveals the impact of geometric parameters on nozzle performance. Comparing the representative nozzle from the Pareto front with the truncated maximum thrust nozzle, it is found that the thrust, lift, and outlet Mach number increase by 3.3%, 12.2%, and 0.5%, respectively, while the outlet height decreases by 5.3%. This research contributes to overcoming the limitations of traditional design methods, which are typically time-consuming. The proposed GWO-KELM surrogate model effectively tackles the issue of low prediction accuracy.

Combined effects of inlet airflow temperature and upper expansion angle on the performance of scramjet nozzle

PurposeThe purpose of this paper is to study the combined effects of inlet airflow temperature and the expansion angle of the upper expansion surface (upper expansion angle) on the performance of the scramjet nozzle.Design/methodology/approachThe Spalart-Allmaras turbulence two-dimensional model of the nozzle is established for the study. The influence of inlet airflow temperature on the performance of the nozzle is analyzed by detecting the change of the wall pressure of the nozzle. The three angles are chosen for the upper expansion angle (βb) in the model: 8°, 12° and 16°. The temperature of inlet airflow is 600–1,800 K.FindingsThe study results show that when the βb is 8° and 16°, the wall pressure of the nozzle has a complicated and large fluctuation with the inlet airflow temperature, while the wall pressure has little change as βb is 12°; the thrust coefficient, pitching moment coefficient and lift coefficient of the nozzle fluctuate greatly with the increase of the inlet airflow temperature when βb is 8° and 16°, while the thrust coefficient, pitching moment coefficient and lift coefficient have little fluctuation as βb is 12°.Originality/valueThe study of the combined effects of the inlet airflow temperature and upper expansion angle on the performance of the scramjet nozzle can provide guidance for the design of scramjet nozzles.

Design Method of Scramjet Nozzles within Predetermined Geometrical Space and Experimental Verification

AbstractA new design method of scramjet nozzles within predetermined geometrical space is proposed to optimize the nozzle aerodynamic performance. The main characteristic of the proposed method is ...

Design Method for Scramjet Nozzles Under Geometric Constraints

This paper presents a novel design method for scramjet nozzles under geometric constraints. Performance optimization theory is incorporated in both the expansion flows along the ramp and the cowl. Method of characteristics is implemented to determine the nozzle configuration, and numerical methods are adopted to obtain the performance parameters and flowfield of the designed nozzle. The results denote that both the initial expansion angles of the ramp and the cowl have significant influence on nozzle performance, and there is an optimal value in the initial expansion angle of the cowl for maximum thrust. The changing tendency of axial thrust coefficient is opposite to that of lift and pitching moment, as the initial expansion angle of the ramp increases. The designed nozzle obtains significant increases of 11.14 and 917.20% in axial thrust coefficient and lift, respectively, as compared with the common nozzle designed by the truncation method. It also enhances the pitching moment by 3.90% for the trimming of the vehicle. Compared with the previous method, the scramjet nozzle obtained by the present design method can realize higher efficiencies for scramjets under geometric constraints.

A Design Method for Three-Dimensional Scramjet Nozzles with Shape Transition

A design method for three-dimensional shape transition scramjet nozzles is introduced. The method employs streamline tracing to capture the properties of an axisymmetric thrust nozzle in a complex three-dimensional shape that allows for airframe integration and side-by-side mounting of scramjet engine modules. A contoured centerbody is added to an established maximum thrust nozzle and used as the axisymmetric parent flowfield. This allows for tailoring the shape of the nozzle to a variety of vehicle geometries while at the same time eliminating drag producing surfaces traditionally encountered in this type of nozzle. The design procedure is described and applied to the design of a nozzle for a Mach 12 scramjet engine at an off-design condition. An inviscid computational fluid dynamics analysis of the nozzle is used to analyze the accuracy of the capture of the parent flowfield’s properties. It is found that despite the shape transition the nozzle is able to reproduce the interior flow of the axisymmetric flowfield.

Design of Thrust-Optimized Scramjet Nozzle and Its Concise Estimation Method

This Paper is a computational investigation of a scramjet nozzle design based on maximum thrust theory and its feasibility analysis. A new design method for a two-dimensional complete thrust-optimized single expansion ramp nozzle under aerodynamic constraints by applying the method of characteristics is proposed. The carefully chosen verification and validation benchmarks confirm the accuracy, effectiveness, and superiority of the current method. Results indicate that the introduced design method has comprehensive advantages over the traditional approach under design/off-design conditions. Specifically, the maximum increase in axial thrust reaches 6.38%, and the maximum increase in lift exceeds 180%. Necessary conditions of the thrust-optimized nozzle design are deduced combining Prandtl–Meyer relation and corner conditions, which provides a direct judgment criterion for the rationality of initial design conditions, and leads to a concise dimension estimation method. Relative errors of no more than 5% demonstrate the credibility of this approach through a comparison with the theoretical solutions. The refined structure topology of the thrust-optimized single expansion ramp nozzle further reveals the equivalent relations between the aerodynamic and geometric design conditions based on the estimation results.

Design and analysis of the scramjet nozzle with contact discontinuity

A scramjet nozzle design method that utilizes Rao's maximum thrust theory and the slip-line unit process is proposed to reduce the negative effect of the internal contact discontinuity on the aerodynamic performance. The proposed method divides the nozzle flowfield into a lower region and an upper region. The compatibility between the two regions with different aerothermal properties is achieved by the constraints of the flow deflection angles and the static pressure along an inviscid slip line. Due to the high computational expense allied with finite rate reactions, particularly for heavy hydrocarbon fuels, the basic studies of scramjet nozzles in this paper are conducted with the chemically frozen flow assumption. It underestimates the influence of the dissociated species of combustion product or unburned fuels to some extent, but still reveals nozzle performance trends efficiently, and serves as a helpful reference. The initial expansion arc radius influences the evolution of the inviscid slip line, thereby changing the expansion processes of the upper and lower regions. However, the position deviation between the nozzle entrance and the exit cannot change the shape of the inviscid slip line except retreating of the terminal point. Notably, a critical position deviation maximizes the axial thrust coefficient and minimizes the lift. Compared with the nozzle designed by the truncated method, the nozzle designed by the proposed method shows increases in the axial thrust coefficient, lift, and pitching moment of 6.22%, 166.3%, and 164.8%, respectively, at the design point. Numerical results also show that only a minor decrease in the nozzle performance appears when 3D effects are considered, further revealing the reliability of the proposed method.

Inverse Design Method on Scramjet Nozzle with Full Geometrical Constraints for Nozzle–Afterbody Integration

AbstractA design method on scramjet nozzles is proposed to satisfy the requirements of nozzle positions and geometrical constraints. The proposed method adopts the inverse design concept and maximu...

3-D printing and computational fluid analysis of single expansion ramp nozzle

To develop a scram jet nozzle by altering the existing supersonic nozzle design. A SCRAM jet nozzle alias, Supersonic combustion RAM nozzle is typically a derived structure of supersonic nozzle, in which the exit of the nozzle is truncated for minimizing the losses. The speed at the inlet should be greater than five Mach (>5), to give the full characteristics of a SCRAM jet. That means the exit will be greater than five Mach (>5), it attains a hypersonic condition. The SCRAM jet is not used in any of the voyages because it is said to less efficient than other nozzles. This SCRAM jet is a developing stage conceptual design in the flight era. The future will rely on these technologies. Our modification in this technology is to attain a hypersonic condition our modified supersonic nozzle. To attain this there are certain controlling parameters to be considered before designing a nozzle, they are thrust required, lift, drag, friction on sidewalls. These are minimized by swirling the air in the divergent section of the nozzle. The swirling action is attained by having internal helical grooves on the divergent section of the nozzle.

Optimization and analysis of inverse design method of maximum thrust scramjet nozzles

With the development of scramjet engines and hypersonic vehicles, the importance of the scramjet nozzle has become increasingly prominent. Many studies have attempted to increase the aerodynamic performance of nozzles. Under this circumstance, an inverse design method on the scramjet nozzle has been proposed on the basis of maximum thrust theory. The effectiveness and flexibility of the proposed method have been verified. As an inverse method, the target (i.e., the flow conditions on the key point) is a primary factor in the design process that significantly affects the performance and geometry of the nozzle. The present study investigates the influence of the key point on the shapes and performance of the nozzles. It aims to obtain a relative universal design principle in the inverse design process. First, the inverse design method is introduced briefly to facilitate understanding of the background. Second, the design of experiment (DOE) technique is presented, which can be used to study the effect of factors on the responses. Third, the effects of flow conditions, including Mach number, flow deflection angle, and ratio of mass flow rate, are investigated. The major factors on the thrust, lift, and nozzle length are distinguished successively. The thrust is mainly affected by the Mach number and flow deflection angle. The lift and nozzle length are dominated by the Mach number and ratio of mass flow rate. The influence of the flow deflection angle on the lift and length is negligible. Finally, the conclusion obtained from the DOE study is utilized to optimize an actual nozzle design process. The aerodynamic performance and geometrical configuration of the nozzles can be adjusted quickly. Combined with the inverse design concept, a fast and comparatively accurate design method on scramjet nozzle is formed.

Experimental and numerical investigations of a scramjet nozzle at various operations

The present paper focuses on the study of a scramjet asymmetric nozzle at various operations by applying both experimental and numerical methods, which confirms the reliability of the single expansion ramp nozzle (SERN) design method under geometric constraints based on maximum thrust theory as well. The pitot pressure measurement is used to calibrate the exit Mach number of the facility nozzle. The combination of schlieren photograph, static pressure measurement and strain-gauge balance is employed to obtain the flowfield feature, pressure distribution along the SERN wall and forces acting on the experimental model. Besides, the numerical method is also applied to achieve the more detailed flowfield and performance of the SERN. The results show that the flowfield structure is obviously different between at the experimental conditions and at the actual flight operations. As the interaction of the nozzle plume with the external flow, the shock waves following the expansion waves at the trailing edge of the SERN are all presented at both overexpanded and underexpanded conditions; however, the SERN core flow is independent of the external flow. The existing of two platforms with high-pressure at the front areas of the ramp and cowl are beneficial for improving the thrust performance, verifying the superiority of the new SERN design method. The error of the force between the numerical and experimental results is relatively small, denoting the capability of the numerical method. Furthermore, along with the increase in the flight Mach number, the axial thrust coefficient is decreased, while the lift and pitching moment coefficients are increased. Compared with the cases at the overexpanded operations, the axial thrust loss arising from the underexpanded flow is more serious at certain operations.

Inverse design method on scramjet nozzles based on maximum thrust theory

An inverse nozzle design method based on maximum thrust theory and method of characteristics (MOC) is proposed to increase the aerodynamic performance and practicality of scramjet nozzles. In comparison with the general maximum thrust nozzle design method, the proposed method not only utilizes maximum thrust theory but also demonstrates additional flexibility under geometrical constraints. The main characteristic of the proposed method is that the key point in the maximum thrust nozzle can become the target and be manually determined in advance in accordance with the actual requirements, rather than through an iteration method based on the flow conditions of the nozzle inlet and flight in the general design method. The proposed method is implemented using MOC, which is a universal mathematical method in solving partial differential equations. First, a brief introduction of maximum thrust theory and MOC are provided to comprehend the background. Second, the application of maximum thrust theory in the inverse design method is discussed, including the specific design procedure. Third, the feasibility and effectiveness of the proposed method are verified in an actual design case using computational fluid dynamic approaches. Then, the influence of cowl lengths on the aerodynamic performance of the nozzle is analyzed. Results show that the proposed method can provide different solutions to obtain high thrust coefficient or high lift and pitching moments, which offers flexibility and operability for the engineers. Finally, a nozzle named nozzle B is designed using the traditional forward method. In terms of aerodynamic performance, the nozzle A designed by the proposed method shows evident advantages. The thrust coefficient of nozzle A obtains approximately 31.8% increment, and the lift and pitching moments improve with 201.0% and 56.6% increments, respectively. In conclusion, this study proposes a new inverse nozzle design method that utilizes maximum thrust theory and MOC, which can not only increase the aerodynamic performance but also provide further flexibility and operability in the scramjet nozzle design.

Ramjet Compression System for a Hypersonic Air Transportation Vehicle Combined Cycle Engine

This report assesses the performance characteristics of a ramjet compression system in the application of a hypersonic vehicle. The vehicle is required to be self-powered and perform a complete flight profile using a combination of turbojet, ramjet and scramjet propulsion systems. The ramjet has been designed to operate between Mach 2.5 to Mach 5 conditions, allowing for start-up of the scramjet engine. Multiple designs, including varying ramp configurations and turbo-ramjet combinations, were investigated to evaluate their merits and limitations. Challenges arose with attempting to maintain sufficient pressure recoveries and favourable flow characteristics into the ramjet combustor. The results provide an engine inlet design capable of propelling the vehicle between the turbojet and scramjet phase of flight, allowing for the completion of its mission profile. Compromises in the design, however, had to be made in order to allow for optimisation of other propulsion systems including the scramjet nozzle and aerodynamics of the vehicle; it was concluded that these compromises were justified as the vehicle uses the ramjet engine for a minority of the flight profile as it transitions between low supersonic to hypersonic conditions.

Numerical analysis and design optimization of supersonic after-burning with strut fuel injectors for scramjet engines

Scramjets are a class of hypersonic airbreathing engine that offer promise for economical, reliable and high-speed access-to-space and atmospheric transport. The expanding flow in the scramjet nozzle comprises of unburned hydrogen. An after-burning scheme can be used to effectively utilize the remaining hydrogen by supplying additional oxygen into the nozzle, aiming to augment the thrust. This paper presents the results of a single-objective design optimization for a strut fuel injection scheme considering four design variables with the objective of maximizing thrust augmentation. Thrust is found to be augmented significantly owing to a combination of contributions from aerodynamic and combustion effects. Further understanding and physical insights have been gained by performing variance-based global sensitivity analysis, scrutinizing the nozzle flowfields, analyzing the distributions and contributions of the forces acting on the nozzle wall, and examining the combustion efficiency.

Design of a three-dimensional scramjet nozzle considering lateral expansion and geometric constraints

A new method based on quasi two-dimensional supersonic flow and maximum thrust theory to design a three-dimensional nozzle while considering lateral expansion and geometric constraints is presented in this paper. To generate the configuration of the three-dimensional nozzle, the inviscid flowfield is calculated through the method of characteristics, and the reference temperature method is applied to correct the boundary layer thickness. The computational fluid dynamics approach is used to obtain the aerodynamic performance of the nozzle. Results show that the initial arc radius slightly influences the axial thrust coefficient, whereas the variations in the lateral expansion contour, the length and initial expansion angle of the lower cowl significantly affect the axial thrust coefficient. The three-dimensional nozzle designed by streamline tracing technique is also investigated for comparison to verify the superiority of the new method. The proposed nozzle shows increases in the axial thrust coefficient, lift, and pitching moment of 6.86%, 203.15%, and 642.86%, respectively, at the design point, compared with the nozzle designed by streamline tracing approach. In addition, the lateral expansion accounts for 22.46% of the entire axial thrust, while it has no contribution to the lift and pitching moment in the proposed nozzle.

Design and analysis on three-dimensional scramjet nozzles with shape transition

A trimming method to optimize the configuration of a three-dimensional asymmetric nozzle with shape transition, which aims to obtain good aerodynamic performance and to save weight at the same time, is presented in this paper. Then the effects of the entry shape on the performance of the three-dimensional nozzle are investigated. The streamline tracing involved in an axisymmetric flowfield with optimal thrust is employed to obtain the inviscid contour of the three-dimensional nozzle with shape transition, and the reference temperature method is applied to correct the thickness of the boundary layer. The performance of the designed nozzle is obtained by using computational fluid dynamics. The calculated results show that the trimmed nozzle gains increases in the lift and pitching moment by 427.00% and 10.80%, respectively, with only a 0.76% decrease in the axial thrust coefficient, while the weight can be reduced by as much as 37.51%. For the nozzles with elliptical entrances, as the axial ratio ranges from 1.0 to 2.0, the axial thrust coefficient is increased by 5.38%, while the lift is decreased by 67.74%. When considering the nozzles with rectangular entrances, as the aspect ratio ranges 1.0 to 2.0, the axial thrust coefficient is increased by 3.58%, while the lift and pitching moment are decreased by 82.09% and 16.43%, respectively. Most of the axial thrust is produced on the upper-wall and side-walls in all nozzles, and the contribution of the expansion flow along the side-walls on the thrust generation is pronounced in the nozzle with a relatively smaller entry ratio. However, the majority of the lift and pitching moment are generated on the upper-wall and lower-wall. Besides, the viscosity loss and weight can be reduced by applying the elliptical cross-section in the propulsion system.

Optimization design of energy deposition on single expansion ramp nozzle

Optimization design has been widely used in the aerodynamic design process of scramjets. The single expansion ramp nozzle is an important component for scramjets to produces most of thrust force. A new concept of increasing the aerodynamics of the scramjet nozzle with energy deposition is presented. The essence of the method is to create a heated region in the inner flow field of the scramjet nozzle. In the current study, the two-dimensional coupled implicit compressible Reynolds Averaged Navier–Stokes and Menter's shear stress transport turbulence model have been applied to numerically simulate the flow fields of the single expansion ramp nozzle with and without energy deposition. The numerical results show that the proposal of energy deposition can be an effective method to increase force characteristics of the scramjet nozzle, the thrust coefficient CT increase by 6.94% and lift coefficient CN decrease by 26.89%. Further, the non-dominated sorting genetic algorithm coupled with the Radial Basis Function neural network surrogate model has been employed to determine optimum location and density of the energy deposition. The thrust coefficient CT and lift coefficient CN are selected as objective functions, and the sampling points are obtained numerically by using a Latin hypercube design method. The optimized thrust coefficient CT further increase by 1.94%, meanwhile, the optimized lift coefficient CN further decrease by 15.02% respectively. At the same time, the optimized performances are in good and reasonable agreement with the numerical predictions. The findings suggest that scramjet nozzle design and performance can benefit from the application of energy deposition.

Effect of energy addition parameters upon scramjet nozzle performances based on the variance analysis method

As an important component, the nozzle produces most of thrust in scramjets. A new concept of increasing the aerodynamics of the scramjet nozzle with energy addition is presented. The essence of the method is to create a heated region in the inner flow field of the scramjet nozzle. In this paper, the two-dimensional coupled implicit compressible Reynolds Averaged Navier–Stokes (RANS) and Menter's shear stress transport (SST) turbulence model have been applied to numerically simulate the flow fields of the single expansion ramp nozzle (SERN) with and without energy addition. The variance analysis method coupled orthogonal experimental design has been introduced to investigate the effects of the energy addition parameters on the aerodynamics (i.e. thrust coefficient CT, lift coefficient CN and pitching moment coefficient CM) of the scramjet nozzle. The numerical results show that the proposal of energy addition can be an effective method of increasing force characteristics of the scramjet nozzle, the thrust coefficient CT, lift coefficient CN and pitching moment coefficient CM increase by 1.55%, 47.27% and 2.53% respectively. The effect of the energy addition density on the aerodynamics of the scramjet nozzle is substantial, and it must be foremost when considering the design of the scramjet nozzle. The findings suggest that scramjet nozzle design and performance can be benefitted from the application of energy addition.