Thermochemical Nonequilibrium Research Articles

HCN Production via Impact Ejecta Reentry During the Late Heavy Bombardment

AbstractMajor impact events have shaped the Earth as we know it. The Late Heavy Bombardment is of particular interest because it immediately precedes the first evidence of life. The reentry of impact ejecta creates numerous chemical by‐products, including biotic precursors such as HCN. This work examines the production of HCN during the Late Heavy Bombardment in more detail. We stochastically simulate the range of impacts on the early Earth and use models developed from existing studies to predict the corresponding ejecta properties. Using multiphase flow methods and finite‐rate equilibrium chemistry, we then find the HCN production due to the resulting atmospheric heating. We use Direct Simulation Monte Carlo to develop a correction factor to account for increased yields due to thermochemical nonequilibrium. We then model 1‐D atmospheric turbulent diffusion to find the time accurate transport of HCN to lower altitudes and ultimately surface water. Existing works estimate the necessary HCN molarity threshold to promote polymerization that is 0.01 M. For a mixing depth of 100 m, we find that the Late Heavy Bombardment will produce at least one impact event above this threshold with probability 24.1% for an oxidized atmosphere and 56.3% for a partially reduced atmosphere. For a mixing depth of 10 m, the probability is 79.5% for an oxidized atmosphere and 96.9% for a partially reduced atmosphere. Therefore, Late Heavy Bombardment impact ejecta is likely an HCN source sufficient for polymerization in shallow bodies of water, particularly if the atmosphere were in a partially reduced state.

Influence of surface catalysis on coupled aerodynamic heating for Mars entries

The integral simulation of aerodynamic heating for Mars entries encounters great challenges due to exceptional and complex high-temperature real-gas effect and gas-solid thermochemistry effect. Coupling computation strategy for hypersonic nonequilibrium aerodynamic heating and in-depth heat transfer was established in order to accurately predict the thermal environment of Mars entry vehicles. Coupling analysis for the heatshield of Mars entry vehicle was then performed to reveal the mechanism how the nonequilibrium thermochemistry affects the coupled aerodynamic heating. Computation results show that both the convection and diffusion heatflux from non-equilibrium flow field have large influences on the total aerodynamic heating rate; the diffusion component contributes the foremost to the overall aerodynamic heating, especially for that originating from CO2; the current thermal protection structure can effectively prevent the severe thermal load from transferring into the cabin, and the aerodynamic heating and the surface radiation can rapidly get close to thermal equilibrium, accounting for the validation of the radiation equilibrium assumption for uncoupled aerodynamic heating prediction; the heatflux decreases for non- and fully catalytic walls while the finite-rate catalytic heating rises and then drops due to the gas-solid interface thermochemistry effect; the linearity between the surface heatflux and temperature will get weak due to the introduction of diffusion heating induced by the gas-solid interface thermochemistry.

Assessment of Classical Impulsive Models of Dissociation in Thermochemical Nonequilibrium

In strong shock waves in rarefied gases, chemical processes such as dissociation and exchange reactions occur in conditions of thermodynamic nonequilibrium, and the rate coefficients are functions of both translational–rotational and vibrational temperatures. In this work, we reexamine and validate the physical model for nonequilibrium dissociation rates proposed earlier by Macheret et al. The model is based on the classical impulsive approximation and enables analytical formulas for reaction thresholds, probabilities, and multitemperature rate coefficients. The recent quasi-classical trajectory calculations for , , , , and are used to evaluate the Macheret–Fridman dissociation model. The full version of the model that incorporates the reduction of dissociation energy due to rotation of the dissociating molecule as well as the appearance of the centrifugal barrier is found to be in good agreement with quasi-classical trajectory data, whereas the simplified version of the model that ignores the rotational effect significantly underpredicts the dissociation rates in vibrationally cold conditions. The good agreement with quasi-classical trajectory data validates the classical impulsive approximation and implies that details of the potential energy surface are not important for dissociation at high temperatures. Preliminary one-dimensional computational fluid dynamics calculations with the validated dissociation model were conducted for conditions of the shock-tube experiments in pure oxygen by Ibraguimova et al. Generally reasonable agreement was found between the calculations and the experimental data; however, some underprediction of the peak vibrational temperature suggests that some improvement in the model would be desirable.

Thermochemical nonequilibrium parameter modification of oxygen for a two-temperature model

Thermochemical nonequilibrium parameters of oxygen, O2, for a two-temperature model are proposed in the present work. The rovibrational nonequilibrium and chemical reactions of three low-lying electronic states of O2(X3Σg−, a1Δg, and b1Σg+) are investigated in one-dimensional post-shock flow environments, including the rovibrational state-to-state kinetics and electronic excitations due to heavy-particle collisions. Based on the results of rigorous state-resolved calculations and state-of-the-art shock-tube experimental data, the nonequilibrium parameters of O2 are proposed to improve the two-temperature model accuracy. For shock wave velocities above 3 km/s, the proposed nonequilibrium parameters of the two-temperature model better reproduce the results of the rigorous state-resolved calculations and shock-tube experimental data than do the previous parameters.

Plasma flow modeling for Huels-type arc heater with turbulent diffusion

In this study, we developed an analytical model for the flow field in the Huels-type arc-heated wind tunnel (L2K) of the German Aerospace Center. This flow-field model can be used to accurately reproduce the discharge behavior in the heating section and expansion in the nozzle section of L2K. It includes the radiation transport and turbulent flow as well as thermochemical nonequilibrium models, which are tightly coupled with electric field calculations. In addition, we considered the turbulent diffusion model for the mass conservation of the species and performed numerical simulations for several cases with and without the turbulent diffusion model. Computations were conducted to obtain the general characteristics of an arc-heated flow containing an arc discharge and supersonic expansion. We verified that radiation and turbulence play important roles in the transfer of heat from the high-temperature core flow to the outer cold gas in the heating section of L2K. In addition, we performed parametric studies that involved varying the degree of turbulent diffusion. The results showed that turbulent diffusion has a large influence on the formation of the arc discharge in the heating section and on the enthalpy distribution at the nozzle exit.

Effect of thermochemical non-equilibrium on the aerodynamics of an osculating-cone waverider under different angles of attack

In order to research the effect of thermochemical non-equilibrium on the aerodynamics of an osculating-cone waverider, thermochemical non-equilibrium flow and perfect gas model are employed to study the aerodynamics of an osculating-cone waverider under different angles of attack. The obtained results show that the slope of the oblique shock wave has little difference when considering the thermochemical non-equilibrium effect under the condition of zero angle of attack. However, under the condition of other attack angles, the slope of the oblique shock wave diminishes when considering the thermochemical non-equilibrium effect. Furthermore, the non-equilibrium effect moves the pressure center of the osculating-cone waverider forward by as much as 1.53% of the whole craft's length, which must be taken into consideration in the balance design of aircraft.

Disturbance Development in an Obstacle Wake in a Reacting Hypersonic Boundary Layer

The presented work is a continuation of the investigation of the influence of an isolated roughness on the laminar-turbulent transition for hypersonic boundary-layer flows. The first part of the investigation describing the steady flow around a cuboid obstacle as it was flown in the Hypersonic Boundary-Layer Transition experiment was described by Stemmer et al. [“Hypersonic Boundary-Layer Flow with an Obstacle in Thermochemical Equilibrium and Nonequilibrium,” Journal of Spacecraft and Rockets (in print)]. In the second part, stability investigations reveal odd and even instability modes being unstable in the wake. Direct numerical simulations are used to investigate the disturbance development of high-frequency velocity disturbances. The unsteady, fully three-dimensional direct numerical simulations under consideration of chemical equilibrium and nonequilibrium effects shed light on the role of the chemical models on the disturbance development. The chemical equilibrium case shows less damping of the disturbances in the integration domain compared to the perfect gas case. For the chemical nonequilibrium simulations, the disturbances are initially damped but experience amplification further downstream. Detailed investigations of the disturbance development in the wake flow are presented. The current results underline the necessity of the consideration of chemical nonequilibrium effects in direct numerical simulations of high-temperature boundary-layer transition from laminar to turbulent, even for moderate temperature and dissociation levels.

Hypersonic Boundary-Layer Flow with an Obstacle in Thermochemical Equilibrium and Nonequilibrium

The hypersonic flow around a tip of a rocket-mounted Hypersonic Boundary-Layer Transition experiment has been simulated with direct numerical simulations. The numerical results reveal the local flow conditions at the location of a surface-mounted cuboid on the wedge-shaped geometry roughly 50 cm downstream of the leading edge for ideal-gas, chemical-equilibrium, and nonequilibrium conditions. The flow is subject to an oblique shock to deliver about at the boundary-layer edge at the cuboid depending on the gas model used. The flow around the object of about one-third of the boundary-layer thickness in height is influenced by the chemical modeling of the air, and reveals different wakes downstream of the cuboid. The details of the flow depending on the chemical model employed underline the necessity for nonequilibrium simulations under the conditions investigated. The laminar wake shows hot fluid being transported close to the surface through the trailing longitudinal vortices, increasing the heat flux at the wall for the chemically reacting cases, most notably for the nonequilibrium case, compared to an ideal-gas comparative case. Although the maximum temperature in the wake decreases for the chemically reacting flows, the location of the maximum moves closer to the wall amounting to a net increase in heat transfer.

Modeling of high pressure arc-discharge with a fully-implicit Navier–Stokes stabilized finite element flow solver

This work addresses the modeling of high pressure electric discharge in an arc-heated wind tunnel. The combined numerical solution of Poisson’s equation, radiative transfer equations, and the set of Favre-averaged thermochemical nonequilibrium Navier–Stokes equations allows for the determination of the electric, radiation, and flow fields, accounting for their mutual interaction. Semi-classical statistical thermodynamics is used to determine the plasma thermodynamic properties, while transport properties are obtained from kinetic principles with the Chapman–Enskog method. A multi-temperature formulation is used to account for thermal non-equilibrium. Finally, the turbulence closure of the flow equations is obtained by means of the Spalart–Allmaras model, which requires the solution of an additional scalar transport equation. A Streamline upwind Petrov–Galerkin stabilized finite element formulation is employed to solve the Navier–Stokes equation. The electric field equation is solved using the standard Galerkin formulation. A stable formulation for the radiative transfer equations is obtained using the least-squares finite element method. The developed simulation framework has been applied to investigate turbulent plasma flows in the 20 MW Aerodynamic Heating Facility at NASA Ames Research Center. The current model is able to predict the process of energy addition and re-distribution due to Joule heating and thermal radiation, resulting in a hot central core surrounded by colder flow. The use of an unsteady three-dimensional treatment also allows the asymmetry due to a dynamic electric arc attachment point in the cathode chamber to be captured accurately. The current work paves the way for detailed estimation of operating characteristics for arc-heated wind tunnels which are critical in testing thermal protection systems.

Turbulent spots in hypervelocity flow

The turbulent spot propagation process in boundary layer flows of air, nitrogen, carbon dioxide, and air/carbon dioxide mixtures in thermochemical nonequilibrium at high enthalpy is investigated. Experiments are performed in a hypervelocity reflected shock tunnel with a 5-degree half-angle axisymmetric cone instrumented with flush-mounted fast-response coaxial thermocouples. Time-resolved and spatially demarcated heat transfer traces are used to track the propagation of turbulent bursts within the mean flow, and convection rates at approximately 91, 74, and 63% of the boundary layer edge velocity, respectively, are observed for the leading edge, peak, and trailing edge of the spots. A simple model constructed with these spot propagation parameters is used to infer spot generation rates from observed transition onset to completion distance. Spot generation rates in air and nitrogen are estimated to be approximately twice the spot generation rates in air/carbon dioxide mixtures.

Thermal protection performance of magnetohydrodynamic heat shield system based on multipolar magnetic field

In order to cover the shortage of dipole magnetic field in the magnetohydrodynamic(MHD) heat shield system, physical model of a multipolar magnetic field with central and peripheral solenoids is constructed. By employing the governing equations of three dimensional thermochemical nonequilibrium flow with electromagnetic source terms based on the low magneto-Reynolds assumption, the flow control performance of the dipole and multipolar magnetic fields are numerically simulated. To make the results comparable, two groups of cases are designed by first assuming equal stagnation magnetic induction strength and secondly assuming equal ampere-turns. Results show that, the five-magnet system, whose central polar orientation is the same with the peripheral ones, have stronger work capability and better shock control and thermal protection performance. Moreover, the five-solenoid systems are the best when the ampere-turns of the central solenoid are twice and fourth of the peripheral ones under those two circumstances respectively. Compared with the dipole magnetic field, the stagnation non-catalytic heat fluxes are decreased by a factor of 47.5% and 34.0% respectively.

Numerical solution procedure for Hall electric field of the hypersonic magnetohydrodynamic heat shield system

Magnetohydrodynamic (MHD) heat shield system is a novel-concept thermal protection technique for hypersonic vehicles, which has been proved by lots of researchers with both numerical and experimental methods. Most of researchers neglect the Hall effect in their researches. However, in the hypersonic reentry process, the Hall effect is sometimes so significant that the electric current distribution in the shock layer can be changed by the induced electric field. Consequently, the Lorentz force as well as the Joule heat is varied, and thus the efficiency of the MHD heat shield system is affected.In order to analyze the influence of Hall effect, the induced electric field must be taken into consideration. According to the weakly-ionized characteristics of hypersonic flow post bow shock, the magneto-Reynolds number is assumed to be small. Therefore, the Maxwell equations are simplified with the generalized Ohm's law, and the induced electric field is governed by the potential Possion equation. Numerical methods are hence established to solve the Hall electric field equations in the thermochemical nonequilibrium flow field. The electric potential Poisson equation is of significant rigidity and difficult to solve for two reasons. One is that the coefficient matrix may not be diagonally dominant when the Hall parameter is large in the shock layer, and the other is that this matrix including the electric conductivity is discontinuous across the shock. In this paper, a virtual stepping factor is included to strengthen the diagonal dominance and improve the computational stability. Moreover, approximate factor and alternating direction implicit method are employed for further improving the stability. With these methods, a FORTRAN code is written and validated by comparing the numerical results with the analytical ones as well as results available from previous references. After that, relation between the convergence property and the virtual stepping factor is revealed by theoretical analysis and numerical simulations. Based on these work, a local variable stepping factor method is proposed to accelerate the iterating process. Results show that the convergence property is closely related to the mesh density and Hall parameter, and there exists a best stepping factor for a particular mesh as well as a particular Hall parameter. Since the best stepping factor varies a lot for different meshes and different Hall parameter, its appropriate value is hard to choose. The best value of stepping factor coefficient still exists in the local step factor method, but its value range is relatively smaller. More importantly, the local stepping factor method yields better convergence property than the regular constant one when employing a locally refined mesh.

Investigation of Hall effect on the performance of magnetohydrodynamic heat shield system based on variable uniform Hall parameter model

There has been a resurgence in the field of magnetohydrodynamic (MHD) flow control in the past 20 years. An increasing demand for sustained hypersonic flight and rapid access to space, along with numerous mechanical and material advances in flight-weight MHD technologies, has aroused renewed interest in this subject area. As a novel application of MHD flow control in the thermal protection field, MHD heat shield system has been proved to be of great intrinsic value by lots of researchers in recent years. Although its theoretical feasibility has been validated, there are many problems that remain to be further investigated. Among those problems, the Hall effect is a remarkable one that may affect the effectiveness of MHD flow control. Considering the fact that it is not sufficient to evaluate the Hall effect by merely using the chemical reaction model implemented in the nonequilibrium flow simulation to calculate the Hall parameter, a parametric study is conducted under the assumption of simplified uniform Hall parameter. First, coupling numerical methods are constructed and validated to solve the thermochemical nonequilibrium flow field and the electro-magnetic field. Second, a series of numerical simulations of the MHD head shield system is conducted with different magnitudes of Hall parameter under two magnetic induction intensities (B0=0.2 T, 0.5 T). Finally, the influence of Hall effect on the performance of MHD heat shield system is analyzed. Results indicate that Hall effect is closely related to the wall conductivity. If the vehicle surface is regarded as an insulating wall, the heat flux variation is co-determined by varying the Lorentz forces within the boundary layer and the shock-control effect. Compared with the one neglecting the Hall effect, the heat flux with Hall effect is slightly mitigated as the increase of Lorentz forces in the boundary layer dominates when the stagnation magnetic induction intensity B0 equals 0.2 T. However, the heat flux is increased when B0 equals 0.5 T, because the decrease of shock stand-off distance dominates which increases the gas temperature outside the boundary layer. Moreover, in this case the larger the Hall parameter, the higher the heat flux will be. As for the conductive wall, the performance of MHD heat shield system becomes worse with the increase of Hall parameter, and while it is equal to or higher than 5.0, this system loses its effectiveness.

Flow-field differences and electromagnetic-field properties of air and N2 inductively coupled plasmas

A numerical model for simulating air and nitrogen inductively coupled plasmas (ICPs) was developed considering thermochemical nonequilibrium and the third-order electron transport properties. A modified far-field electromagnetic model was introduced and tightly coupled with the flow field equations to describe the Joule heating and inductive discharge phenomena. In total, 11 species and 49 chemical reactions of air, which include 5 species and 8 chemical reactions of nitrogen, were employed to model the chemical reaction process. The internal energy transfers among translational, vibrational, rotational, and electronic energy modes of chemical species were taken into account to study thermal nonequilibrium effects. The low-Reynolds number Abe-Kondoh-Nagano k-ε turbulence model was employed to consider the turbulent heat transfer. In this study, the fundamental characteristics of an ICP flow, such as the weak ionization, high temperature but low velocity in the torch, and wide area of the plasma plume, were reproduced by the developed numerical model. The flow field differences between the air and nitrogen ICP flows inside the 10-kW ICP wind tunnel were made clear. The interactions between the electromagnetic and flow fields were also revealed for an inductive discharge.

Numerical analysis of Hall effect on the performance of magnetohydrodynamic heat shield system based on nonequilibrium Hall parameter model

Magnetohydrodynamic (MHD) heat shield system, a novel thermal protection technique in the hypersonic field, has been paid much attention in recent years. In the real flight condition, not only the Lorentz force but also the Hall electric field is induced by the interaction between ionized air post shock and magnetic field. In order to analyze the action mechanisms of the Hall effect, numerical methods of coupling thermochemical nonequilibrium flow field with externally applied magnetic field as well as the induced electric field are constructed and validated. Based on the nonequilibrium model of Hall parameter, numerical simulations of the MHD heat shield system is conducted under two different magnetic induction strengths (B0=0.2T, 0.5T) on a reentry capsule forebody. Results show that, the Hall effect is the same under the two magnetic induction strengths when the wall is assumed to be conductive. For this case, with the Hall effect taken into account, the Lorentz force counter stream diminishes a lot and the circumferential component dominates, resulting that the heat flux and shock-off distance approach the case without MHD control. However, for the insulating wall, the Hall effect acts in different ways under these two magnetic induction strengths. For this case, with the Hall effect taken into account, the performance of MHD heat shield system approaches the case neglecting the Hall effect when B0 equals 0.2T. Such performance becomes worse when B0 equals 0.5T and the aerothermal environment on the capsule shoulder is even worse than the case without MHD control.

Numerical Simulation of Weakly Ionized Dynamic Plasma for Reentry Vehicles

Past studies of plasma sheaths enveloping vehicles have shown that the distribution of plasma is time-varying and results in communication and navigation problems. This paper aims to investigate the dynamic characteristics of the plasma sheath through the simulations of the Radio Attenuation Measurements-C II vehicle and the Apollo command module flowfields. The numerical methodology is based on the unsteady Reynolds-averaged Navier–Stokes model and the detached-eddy simulation model, and the thermochemical nonequilibrium effect is considered. The stable flows of both vehicles with a steady plasma sheath widely distributed in the shock-wave layer are first obtained. For the Radio Attenuation Measurements-C II vehicle, the dynamic plasma arising from the vehicle pitching oscillation has the same frequency as the vehicle oscillation, and the magnitude of the disturbance to plasma is related to the oscillation velocity. For the Apollo command module, the oscillation period of the electron density is the same as the evolution period of the vortex structures in the leeward regions. The time-varying surface electron density and pressure reveal a similar variation trend with the phase difference. In addition, the periodicity of the dynamic plasma disappears as the flow instability intensifies in the Apollo command module flowfields, whereas periodic plasma exists for a long time in the Radio Attenuation Measurements-C II vehicle oscillation flowfields.

Laminar and turbulent heating predictions for mars entry vehicles

Laminar and turbulent heating rates play an important role in the design of Mars entry vehicles. Two distinct gas models, thermochemical non-equilibrium (real gas) model and perfect gas model with specified effective specific heat ratio, are utilized to investigate the aerothermodynamics of Mars entry vehicle named Mars Science Laboratory (MSL). Menter shear stress transport (SST) turbulent model with compressible correction is implemented to take account of the turbulent effect. The laminar and turbulent heating rates of the two gas models are compared and analyzed in detail. The laminar heating rates predicted by the two gas models are nearly the same at forebody of the vehicle, while the turbulent heating environments predicted by the real gas model are severer than the perfect gas model. The difference of specific heat ratio between the two gas models not only induces the flow structure's discrepancy but also increases the heating rates at afterbody of the vehicle obviously. Simple correlations for turbulent heating augmentation in terms of laminar momentum thickness Reynolds number, which can be employed as engineering level design and analysis tools, are also developed from numerical results. At the time of peak heat flux on the +3σ heat load trajectory, the maximum value of momentum thickness Reynolds number at the MSL's forebody is about 500, and the maximum value of turbulent augmentation factor (turbulent heating rates divided by laminar heating rates) is 5 for perfect gas model and 8 for real gas model.

Analysis of non-equilibrium phenomena in inductively coupled plasma generators

This work addresses the modeling of non-equilibrium phenomena in inductively coupled plasma discharges. In the proposed computational model, the electromagnetic induction equation is solved together with the set of Navier-Stokes equations in order to compute the electromagnetic and flow fields, accounting for their mutual interaction. Semi-classical statistical thermodynamics is used to determine the plasma thermodynamic properties, while transport properties are obtained from kinetic principles, with the method of Chapman and Enskog. Particle ambipolar diffusive fluxes are found by solving the Stefan-Maxwell equations with a simple iterative method. Two physico-mathematical formulations are used to model the chemical reaction processes: (1) A Local Thermodynamics Equilibrium (LTE) formulation and (2) a thermo-chemical non-equilibrium (TCNEQ) formulation. In the TCNEQ model, thermal non-equilibrium between the translational energy mode of the gas and the vibrational energy mode of individual molecules is accounted for. The electronic states of the chemical species are assumed in equilibrium with the vibrational temperature, whereas the rotational energy mode is assumed to be equilibrated with translation. Three different physical models are used to account for the coupling of chemistry and energy transfer processes. Numerical simulations obtained with the LTE and TCNEQ formulations are used to characterize the extent of non-equilibrium of the flow inside the Plasmatron facility at the von Karman Institute. Each model was tested using different kinetic mechanisms to assess the sensitivity of the results to variations in the reaction parameters. A comparison of temperatures and composition profiles at the outlet of the torch demonstrates that the flow is in non-equilibrium for operating conditions characterized by pressures below 30 000 Pa, frequency 0.37 MHz, input power 80 kW, and mass flow 8 g/s.

Numerical analysis on the effect of angle of attack on evaluating radio-frequency blackout in atmospheric reentry

A three-dimensional numerical simulation model that considers the effect of the angle of attack was developed to evaluate plasma flows around reentry vehicles. In this simulation model, thermochemical nonequilibrium of flowfields is considered by using a four-temperature model for high-accuracy simulations. Numerical simulations were performed for the orbital reentry experiment of the Japan Aerospace Exploration Agency, and the results were compared with experimental data to validate the simulation model. A comparison of measured and predicted results showed good agreement. Moreover, to evaluate the effect of the angle of attack, we performed numerical simulations around the Atmospheric Reentry Demonstrator of the European Space Agency by using an axisymmetric model and a three-dimensional model. Although there were no differences in the flowfields in the shock layer between the results of the axisymmetric and the three-dimensional models, the formation of the electron number density, which is an important parameter in evaluating radio-frequency blackout, was greatly changed in the wake region when a non-zero angle of attack was considered. Additionally, the number of altitudes at which radio-frequency blackout was predicted in the numerical simulations declined when using the three-dimensional model for considering the angle of attack.

Investigation of Unsteady Edney Type IV and VII Shock–Shock Interactions

Edney type IV and type VII shock–shock interactions are complex hypersonic flow phenomena. They are characterized by a supersonic jet that reaches far into the flowfield. An experimental investigation of the inner jet structure is difficult, especially in cases where the jet is subject to high-frequency unsteady movements. The present paper provides insight into the jet structure and its movement by means of a highly resolved computational fluid dynamics analysis in thermochemical nonequilibrium that significantly exceeds the resolution of existing publications. Simulations of an Edney type IV interaction in nitrogen flow are presented. Advanced adaptation strategies allow for the identification and analysis of the mechanisms of the jet unsteadiness, resulting in a new classification of the unsteady flowfield behavior with respect to the periodic jet movement. This classification is based not only on wall quantities, but also on the core flowfield. The computations are supplemented by a grid sensitivity study. The second configuration is an Edney type VII interaction. This shock–shock interaction type was observed and defined in nitrogen flow by Yamamoto et al (Numerical Investigation of Shock/Vortex Interaction in Hypersonic Thermochemical Nonequilibrium Flow, Journal of Spacecraft and Rockets, Vol. 36, No. 2, 1999, pp. 240–246. The present results demonstrate that this interaction may also be observed in carbon-dioxide-dominated flow with a gas composition similar to the Martian atmosphere. The results provide insight into the jet structure of this less known interaction.