Hypersonic Reactive Flow Research Articles

Dynamic interaction patterns of oblique detonation waves with boundary layers in hypersonic reactive flows

Due to their high thermal cycle efficiency and compact combustor, oblique detonation engines hold great promise for hypersonic propulsion. Previous numerical simulations of oblique detonation waves have predominantly solved the Euler equations, disregarding the influence of viscosity and boundary layers. This work aims to study how the interaction between the oblique detonation wave and the boundary layer influences the detonation wave structures in confined spaces. Two-dimensional numerical simulations considering detailed chemistry are performed in a stoichiometric H2/air mixture. The results indicate that the wedge-induced oblique detonation wave generates a strong adverse pressure gradient upon impacting the upper wall, leading to boundary layer separation. The separation zone subsequently induces an oblique shock wave near the upper wall, and an increase in separation angle will cause the transition from an oblique shock wave to an oblique detonation wave. The formation of the separation zone reduces the actual flow area and may even lead to flow choking; its obstructive effect is similar to that of the Mach stem in inviscid flow. To establish a connection between the viscous recirculation zone and the inviscid Mach stem, we introduce a dimensionless parameter, η, based on the inviscid assumption. It is defined as the ratio of the inviscid Mach stem height to the channel entrance height. This parameter can be used to identify three wave systems in a viscous flow field: separation shock-dominated wave systems, separation detonation-dominated wave systems, and unstable Mach stem-dominated wave systems. Among these, the appearance of detonation Mach stems leads to flow choking, and the shock-detonation wave system continually moves upstream, ultimately causing the failure of the oblique detonation combustion. The findings of this study provide new insights into the investigation of the influence of viscosity on the flow structure of oblique detonation waves.

Effects of thermal stratification on detonation development in hypersonic reactive flows

Effects of thermal stratification on detonation development in hypersonic reactive flows

Eulerian discrete kinetic framework in comoving reference frame for hypersonic flows

Flow physics vary in different regimes across the full Mach number range, with our knowledge being particularly poor about the hypersonic regime. An Eulerian realization of the particles on demand method, a kinetic model formulated in the comoving reference frame, is proposed to simulate hypersonic compressible flows. The present model allows for flux evaluation in different reference frames, in this case rescaled and shifted by local macroscopic quantities, i.e. fluid speed and temperature. The resulting system of coupled hyperbolic equations is discretized in physical space with a finite volume scheme ensuring exact conservation properties. Regularization via Grad expansion is introduced to implement distribution function and flux transformation between different reference frames. It is shown that the proposed method possesses Galilean invariance at a Mach number up to $100$ . Different benchmarks including both inviscid and viscous flows are reproduced with the Mach number up to $198$ and pressure ratio up to $10^5$ . Finally, the new model is demonstrated to be capable of simulating hypersonic reactive flows, including one-dimensional and two-dimensional detonations. The developed methodology opens up possibilities for the simulation of the full range of compressible flows, without or with chemical reactions, from the subsonic to hypersonic regimes, leading to enhanced understanding of flow behaviours across the full Mach number range.

Developlment of a Thermo-Chemical Non-Equilibrium Solver for Weakly Ionized Hypersonic Flowfields

A three dimensional solver for numerical simulation of weakly ionized hypersonic reactive air flows past high speed flight vehicles had been indigenously developed. The two-temperature, seven species, eighteen reactions, thermo-chemical non equilibrium, ionizing, air-chemistry model of Park is implemented in a compressible viscous code CERANS and solved in the finite volume framework. The energy relaxation is addressed by a conservation equation for the vibrational-electron-electronic energy of the gas mixture resulting in the evaluation of its vibrational temperature. The contribution of vibrational-electron-electronic energy of the reactive mixture is accounted in total energy equation as well as in the source terms of the relaxation model. The AUSM-PW+ numerical flux function has been used for modeling the convective fluxes and a central differencing approximation is used for modeling the diffusive fluxes. The code has been characterized for standard test cases involving weakly ionized hypersonic reactive thermo-chemical non equilibrium flows and results obtained are in good qualitative agreement with results available in open literature.

Thermal analysis of hypersonic reactive flows on the SARA Brazilian satellite reentry trajectory

Thermal analysis of hypersonic reactive flows on the SARA Brazilian satellite reentry trajectory

A quasi-one-dimensional model for hypersonic reactive flow along the stagnation streamline

This study proposes a quasi-one-dimensional model to predict the chemical non-equilibrium flow along the stagnation streamline of hypersonic flow past a blunt body. The model solves reduced equations along the stagnation streamline and predicts nearly identical results as the numerical solution of the full-field Navier-Stokes equations. The high efficiency of this model makes it useful to investigate the overall quantitative behavior of related physical-chemical phenomena. In this paper two important properties of hypersonic flow, shock stand-off distance and oxygen dissociation, are studied using the quasi-one-dimensional model with the ideal dissociating gas model. It is found that the shock stand-off distance is affected by both chemical and thermal non-equilibrium. The shock stand-off distance will increase when the flow conditions are changed from equilibrium to non-equilibrium, because the average density of the shock-compressed gas will decrease as a result of the increase in translational energy. For oxygen dissociation, the maximum value of its dissociation degree along the stagnation line varies with the flight altitude. It is increased at first and decreased thereafter with the altitude, which is due to the combination effect of the equilibrium shift and chemical non-equilibrium relaxation. The overall variation of the maximum dissociation is then plotted in the speed and altitude coordinates as a reference for engineering application.

Modelling Rarefied Hypersonic Reactive Flows Using the Direct Simulation Monte Carlo Method

AbstractThis paper presents the implementation, validation and application of TCE (total collision energy) model for simulating hypersonic reactive flows in a parallel direct simulation Monte Carlo code, named PDSC++, using an unstructured grid. A series of benchmarking test cases, which include reproduction of theoretical rate constants in a single cell, 2D hypersonic flow past a cylinder and 2D-axisymmetric hypersonic flow past a sphere, were performed to validate the implementation. Finally, detailed aerothermodynamics of the flown reentry Apollo 6 Command Module at 105 km is simulated to demonstrate the powerful capability of the PDSC++in treating realistic hypersonic reactive flow at high altitude.

A theoretical model for the shock stand-off distance in frozen and equilibrium flows

In the literature it was recently reported that for hypersonic reactive flow the shock stand-off distance depends not only on a reaction rate parameter, but also on the density ratio between shock and body. This is confirmed in this paper by a theoretical approach which is based on the governing conservation equations. Reasonable simplifications are introduced which for the frozen and equilibrium case allow an analytical solution for the stand-off distance on spheres. The solution method is restricted to this area since only the stand-off distance at the stagnation point is of interest. The excellent agreement achieved for the frozen or non-reactive case with well-known solutions gives evidence for the correctness of the solution method. For the equilibrium case the solution obtained shows the same behaviour as a recent study which agrees with experimental results and numerical simulations.

Numerical Simulations and Planar Laser-Induced Fluorescence Imaging Results of Hypersonic Reactive Flows

This paper shows comparisons between computational e uid dynamics (CFD) calculations and planar laserinduced e uorescence and schlieren measurements of inert and reactive hypersonic e ows around two-dimensional and axisymmetric bodies. In particular, both hydrogen ‐oxygen and methane ‐oxygen chemical reactions are considered for the shock-induced combustion in hypersonic e ows. The hydrogen ‐oxidation mechanism consists of an existing mechanism of 8 reacting species and 19 elementary reactions. The reduced model of the methane ‐ oxidation mechanism is newly derived from the GRI-Mech 1.2 optimized detailed chemical reaction mechanism, and consists of 14 species and 19 chemical reaction steps. Both chemical reaction mechanisms are combined with a point-implicit Euler CFD code. The OH species density distributions of the present numerical calculations and imaging experiments for both mixtures are found to be in qualitative agreement.

Plif imaging of hypersonic reactive flow around blunt bodies

Qualitative OH planar laser-induced fluorescence (PLIF) imaging experiments of supersonic reactive flows over a 40° wedge and a 19-mm-diameter blunted cylinder are reported. Hydrogen-, ethylene-, and methane-based mixtures have been used in this work. Three different free stream conditions. M∞=6.7, 5.2 and 4.2, were used to study the combustion modes around the wedge and blunted cylinder. Separate schlieren imaging results were also obtained for several of the test cases, providing complementary shock wave visualization. In several cases for the wedge, shock-induced combustion was observed a finite distance behind the nonreacting oblique shock wave. For the most sensitive hydrogen mixture, an oblique detonation occurred in which the shock wave and combustion front were fully coupled. In the experiments with the blunted cylinder, two different regimes of combustion were observed. When the velocity of the flow was larger than the CJ velocity of the mixture, the mode was that of an adiabatic shock followed by a smooth combustion front. For cases of flow velocity similar to the CJ velocity or less, regular oscillations were observed on the image and in the stagnation pressure history. These observations are qualitatively consistent with previous work.

REDUCED CHEMISTRY MODELING IN REACTING FLOWS

This paper reviews the need for reduced chemistry modeling for hypersonic reactive flows, and describes the method of computational singular perturbation which can computationally derive reduced chemistry models for a massively complex reaction system.

Hypersonic reactive flow computations

Abstract Finite-volume and finite-element solutions to the Euler equations are presented for the computation of hypersonic reactive flows around blunt bodies. The basic numerical method is explicit for the time integration. Robust spatial approximations are constructed from either first-order or M.U.S.C.L.-type quasi second-order upwind schemes in which the flux-vector splitting accounts for a mixture of 5 perfect gases (N2, O2, NO, N and O) in the equation of state and for a local value of the parameter γ, here defined as the ratio of enthalpy to internal energy. Equilibrium flow solutions are found by combining the basic method with a classicial algebraic model, solved by Newton's method. Solutions to recently proposed non-quilibrium chemistry models are found by integrating forward in time additional transport equations. Treating the convection term explicitly, and the source term implicitly, the timestep is only moderately reduced. The effects on the equilibrium/non-equilibrium flow of the freestreatm Mach numver, Mχ, and the nose radius,Rb, are evaluated. In particular, it is verified that as Rb → ∞ (Mχ being fixed), the non-equilibrium flow solver does produce the equilibrium solution.