Guoqiang He

Numerical Study of a Boundary Layer Bleedfor a Rocket-Based Combined-Cycle Inlet in Ejector Mode

Abstract Fully integrated numerical simulations were performed for a ready-made central strut-based rocket-based combined-cycle (RBCC) engine operating in ejector mode, and the applicability of using a boundary layer bleed in the RBCC inlet designed for supersonic speeds was investigated in detail. The operational mechanism of the boundary layer bleed and its effects on the RBCC inlet and the engine under different off-design conditions in ejector mode were determined. The boundary layer bleed played different roles in the RBCC inlet for different flight regimes. When the RBCC engine took off, some air was entrained into the inlet through the bleed block, thereby inducing significant flow separation and a low-speed vortex, which deteriorated the inner flow and reduced the entraining air mass flow rate: thus, the total pressure loss increased and extra drag was exerted on the inlet. In the low subsonic regime, the bleed block had almost no impact on the RBCC engine and its inlet. However, as the RBCC engine accelerated into a high subsonic flight regime, the boundary layer bleed had a clearly positive effect, comprehensively improving the performance of the RBCC inlet. A boundary layer bleed operation strategy for the RBCC inlet in ejector mode was also developed in this study.

Numerical Investigation of Effects of Boundary Layer Bleed on a RBCC inlet in Ejector Mode

Nomenclature H∞ = flight height Ma∞ = Mach number of the incoming flow Mastart = starting Mach number Maout = Mach number of the outlet of RBCC inlet σ = total pressure recovery coefficient of RBCC inlet φ = entraining ratio of secondary flow (air) mrocket = mass flow rate of rocket engine mbleed = mass flow rate of bleed block Dinlet = drag of RBCC inlet FRBCC = overall inner thrust of RBCC engine

Numerical Investigation of Cowl Lip Adjustments for a Rocket-Based Combined-Cycle Inlet in Takeoff Regime

Abstract Numerical integration simulations were performed on a ready-made central strut-based rocket-based combined-cycle (RBCC) engine operating in the ejector mode during the takeoff regime. The effective principles of various cowl lip positions and shapes on the inlet operation and the overall performance of the entire engine were investigated in detail. Under the static condition, reverse cowl lip rotation in a certain range was found to contribute comprehensive improvement to the RBCC inlet and the entire engine. However, the reverse rotation of the cowl lip contributed very little enhancement of the RBCC inlet under the low subsonic flight regime and induced extremely negative impacts in the high subsonic flight regime, especially in terms of a significant increase in the drag of the inlet. Changes to the cowl lip shape provided little improvement to the overall performance of the RBCC engine, merely shifting the location of the leeward area inside the RBCC inlet, as well as the flow separation and eddy, but not relieving or eliminating those phenomena. The results of this study indicate that proper cowl lip rotation offers an efficient variable geometry scheme for a RBCC inlet in the takeoff regime.

Large Eddy Simulation of Effects of Primary Rocket jet on Low Frequency Combustion Instability in a RBCC Combustor

This paper reports on effects of primary rocket jet parameters, which are among the most probable sources of combustion instability in a Rocket-Based Combined-Cycle (RBCC) engine, on combustion characteristics of a RBCC combustor numerically. Compressible Large Eddy Simulation (LES) with kerosene sprayed and vaporized is performed on an experimental RBCC combustor. Coupling with a reduced three-step chemical kinetics of kerosene, the LES is used to investigate the large amplitude and low frequency longitudinal oscillations in the engine. LES results are compared with experimental observations in pressure oscillation amplitude and frequency in the low components, all show good agreement. Influence of the primary rocket jet on pressure oscillations of the combustor is analyzed and the relation of its high speed jet oscillation characteristics with that of the combustor is recognized. Results reveal that the unsteady high temperature jet comes out of the rocket, which is always rich in fuel, has a significant influence on the vaporization and combustion features of the fuel downstream of the secondary fuel struts, and consequently on combustion features of the combustor. LES solver is validated with experimental data for a model scramjet located in the Institute for Chemical Propulsion of the German Aerospace Centre (DLR) and shows good predictions.

A new framework of global sensitivity analysis for the chemical kinetic model using PSO-BPNN

Abstract Global sensitivity analysis is a tool that primarily focuses on identifying the effects of uncertain input variables on the output and has been investigated widely in chemical kinetic studies. Conventional variance-based methods, such as Sobol’ sensitivity estimation and high dimensional model representation (HDMR) methods, are computationally expensive. To accelerate global sensitivity analysis, a new framework that combines a variance-based (Wus method) and two ANN-based sensitivity analysis methods (Weights and PaD) was proposed. In this framework, a back-propagation neural network (BPNN) methodology was applied, which was optimized by a particle swarm optimization (PSO) algorithm and trained with original samples. The Wus method and Weights and PaD methods were employed to calculate sensitivity indices based on a well-trained PSO-BPNN. The convergence and accuracy of the new framework were compared with previous methods using a standard test case (Sobol’ g-function) and a methane reaction kinetic model. The results showed that the new framework can greatly reduce the computational cost by two orders of magnitude, as well as guaranteeing accuracy. To take maximum advantage of the new framework, a four-step process combining the advantages of each method was proposed and applied to estimate the sensitivity indices of a C2H4 ignition model. The sensitivity indices of the more complex model could be implemented easily with good accuracy when the four-step process is followed

Influence of Structural Parameters on the Performance of Vortex Valve Variable-Thrust Solid Rocket Motor

Abstract The vortex valve solid variable thrust motor is a new solid motor which can achieve Vehicle system trajectory optimization and motor energy management. Numerical calculation was performed to investigate the influence of vortex chamber diameter, vortex chamber shape, and vortex chamber height of the vortex valve solid variable thrust motor on modulation performance. The test results verified that the calculation results are consistent with laboratory results with a maximum error of 9.5%. The research drew the following major conclusions: the optimal modulation performance was achieved in a cylindrical vortex chamber, increasing the vortex chamber diameter improved the modulation performance of the vortex valve solid variable thrust motor, optimal modulation performance could be achieved when the height of the vortex chamber is half of the vortex chamber outlet diameter, and the hot gas control flow could result in an enhancement of modulation performance. The results can provide the basis for establishing the design method of the vortex valve solid variable thrust motor.

Design and Numerical Investigations on a Dual-Duct Variable Geometry RBCC Inlet

Abstract A widely applicable and variable geometry 2-D rocket based combined cycle (RBCC) inlet characterized by the dual-duct design is conceptually put forward. The inlet operates as dual-duct status in the low Mach range (0~4), and transits to single-flowpath status in the following high Mach range (4~7). It accomplishes operational status transition through an 8.0-degree ramp rotation and a 4.0-degree cowl rotation at Mach 4. Through numerical simulations on typical flight Mach numbers, the observed starting Mach number is 2.2, which provides a sufficient operational window for a smooth ejector-to-ramjet mode transition. The RBCC inlet achieves comprehensive high mass capture coefficients in the overall wide flight range, especially in the low speed regimes. Suitable Mach numbers satisfying various combustion requirements in different modes together with high total pressure recovery coefficients are also obtained since the physical throat areas, compression angles, and the corresponding contraction ratios can be adjusted by a large margin through very limited rotations. The variable geometry scheme is not only feasible for practical realizations, but is also simple to arrange the dynamic sealing issues in a low-temperature environment in the RBCC engine.

Numerical Simulations of Multiscale Ablation of Carbon/Carbon Throat with Morphology Effects

A multiscale thermochemical ablation model for the multidirection carbon/carbon composite throat was established in solid rocket motors. The model was established based on the reactivity of differe...

LES of Turbulent Reacting Flow in a Rocket Based Combined Cycle Combustor

Large Eddy Simulation (LES) has been used to examine the turbulent reacting flow in a model Rocket Based Combined Cycle (RBCC) combustor with a focus on the underlying flow-mixing-combustion physics in the combustor with supersonic fuel-rich rocket jet. For the purpose of validation for the numerical methods and combustion mechanisms, a laboratory scramjet is used as the test-computational configuration. The LES results are compared with shadow-pictures and measurements of velocity and temperature at different cross-sections. In addition, a simplified RBCC combustor is designed with a strut rocket in the middle of the flow path. LES of the hydrogen-fueled RBCC combustor is carried out to investigate the nature of mixing and combustion of the rocket’s supersonic exhaust flow and the air stream. The interaction of the rocket jet and the air flow are studied with a particular focus on the supersonic shear layer that forms at the interface between them. Flow features are examined and a particular emphasis is placed upon the role of the strut rocket in the high-speed reacting flow since its fuel-rich hot gas acts as the ignition source and pilot flame, which is conducive to efficient combustion in the engine.

Numerical Investigation of the Shear Layer Growth Influenced by Shock Waves in a Model Scramjet Engine

A numerical study has been conducted to investigate the effect of shock waves on the boundary layer growth and the mixing layer development in a model scramjet where a hydrogen jet is injected at 2.3 Ma into a Mach 2.0 surrouding air flow. The qualitative and quantitative agreements are found between the experimental data and the simulation results validating calculations are reasonable. The boundary layer thickness is carefullyed examined, which offers a renewed schematic of shock-wave/boundary-layer interaction featured with separation and reattachement. The thickness of the mixing layer is also calculated and plotted over the channel length to assess the impact of shock waves on its development. The mixing layer thickness increases wave-likely over the channel length as shock waves travel downstream and are reflected by the channel wall and the mixing layer. The mixing layer thickness decreases a little at the very location where the shock wave interacts with the mixing layer due to compression. Meanwhile, the induced vorticity makes contributions to the development of coherent structures in the mixing layer and leads to an increase of the mixing layer thickness.