Hypersonic Plasma Flow Research Articles

Influence analysis of uncertainty of chemical reaction rate under different reentry heights on the plasma sheath and terahertz transmission characteristics

Plasma sheath prediction of hypersonic vehicle is critical to radio frequency (RF) blackout solutions as well as vehicle design and development. In this paper, an optimized chemical reaction (OCR) model by considering the difference in reaction rate coefficient under different re-entry heights is proposed to obtain more accurate plasma sheath distribution. In the OCR model, the correction coefficient of chemical reaction rate at different heights is obtained by deriving the relationship between vehicle surface temperature and reaction rate. Further, through the coupling with hypersonic plasma flow model and co-simulation with terahertz transmission model, the influence of reaction rate uncertainty on the plasma sheath and terahertz transmission characteristics under different heights is studied. The reaction rate uncertainty has little effect on the collision frequency and sheath thickness, but has a significant effect on the electron density. Numerical simulations and comparisons with flight data validate the electron density prediction accuracy of OCR model was improved by more than 13.1% compared with the traditional chemical reaction (TCR) model, which causes prediction accuracy of signal attenuation at 0.05 THz improves about 25%, and it gradually decreases with the increasing terahertz frequency. The above conclusions are of great significance for the communication attenuation prediction and RF blackout schemes.

Numerical simulation of hypersonic plasma flow field disturbed by pulsed discharge

A plasma sheath will be generated around the hypersonic vehicle during reentry, and a large number of electrons in the plasma sheath will seriously affect the communication between the vehicle and the ground station. In order to reduce the electron number density of the hypersonic vehicle plasma sheath, a method of using pulsed discharge active actuation to regulate the plasma sheath is proposed. Based on the air dissociation and ionization model including 11 components and 32 chemical reactions, the reduction effect of pulsed discharge actuation on the electron density of plasma sheath is studied by numerical simulation. A first test is performed in which the pulsed discharge is compared with the plasma jets' experimental data. Then, a second test compared the plasma flow field around the RAMC-II vehicle with the flight test and NASA data. In these two tests, the simulation results are basically consistent with the experimental results. Finally, the effect of pulsed discharge with different energy density on the plasma sheath electron density is studied. The numerical results show that the interaction between the high-pressure aerodynamic actuation generated by the actuator and the plasma sheath produces an obvious shock wave, which blocks electrons from flowing downstream, reduces the velocity and pressure of the flow field behind the shock wave, and, finally, makes the electron density downstream of the actuator attenuate significantly, with the maximum attenuation amplitude of about 35%. Compared with the traditional method, the method proposed in this paper requires less space, load, and source power and has certain engineering feasibility.

The Post-Shock Nonequilibrium Relaxation in a Hypersonic Plasma Flow Involving Reflection off a Thermal Discontinuity

The evolution in the post-shock nonequilibrium relaxation in a hypersonic plasma flow was investigated during a shock’s reflection off a thermal discontinuity. It was found that within a transitional period, the relaxation zone parameters past both the reflected and transmitted waves evolve differently compared to that in the incident wave. In a numerical example for the non-dissociating N2 gas heated to 5000 K/10,000 K across the interface and M = 3.5, the relaxation time determined for the transmitted wave is up to 50% shorter and the relaxation depth for both waves is significantly reduced, thus resulting in a weakened wave structure. The results of the extension into larger values of heating strength and the shock Mach numbers are discussed. The findings can be useful in the areas of research involving strong shocks interacting with optical discharges or other heated media on the scale where the shock structure becomes important.

High resolved Optical Emission Spectroscopy as accurate physics methodology for plasma freestream temperature characterization

In this work the hypersonic plasma flow generated by SCIROCCO hypersonic facility has been experimentally characterized as test case, using a high resolved Optical Emission Spectroscopy (OES) during a high enthalpy test campaign. The CIRA methodology to measure roto-translational and NO vibrational temperatures of a free jet via analyses performed in the Ultra Violet spectral range has been improved and a comparison between experimental data and Computational Fluid Dynamics (CFD) simulations has been carried out. The revised methodology estimates the roto-translational and vibrational temperatures using high definition spectroscopy carried out at conditions of high values of pressure and enthalpy.In particular, attention is mainly focused on the NO emission band at Non-Local Thermal Equilibrium (NLTE) conditions in the hypersonic flight regime which means equilibrium between the molecular rotational and translational degrees of freedom but not between the roto-translational and vibrational degrees of freedom. Three tests at high enthalpy hypersonic conditions (23.8, 24.0 and 26.0 MJ/kg at a total pressure of about 2.5 bars) have been investigated and experimental data have been compared with numerical simulations in order to verify sensitivity of the method in estimating the small variation in NO roto-translational and vibrational temperatures by changing slightly the total enthalpy fluid-dynamic conditions. The current work presents a high definition spectral method which can be used to determine the temperature of NLTE hypersonic free jets, and may serve as a benchmark in determining the accuracy of various numerical models dedicated to these flow regimes.

Experimental Investigation on the Dynamic Propagation Characteristics of Low-Frequency Electromagnetic Waves in Cylindrical Time-Varying Enveloping Plasma Generated by a Shock Tube

A feasible solution for mitigating radio blackout has been proposed using the magnetic field component of low-frequency (LF) electromagnetic waves (referred to as the LF magnetic field) to transmit critical low-rate data because of the low attenuation of the LF magnetic field in the electrically small plasma. Previous works have modeled the hypersonic plasma flow field as spherical or cylindrical steady-state plasma, ignoring the time-varying properties of the plasma. This article presents the dynamic propagation of the LF magnetic field in a hypersonic plasma flow field generated by a shock tube, introducing a colored-Gaussian time-varying electron density model. Analytical expressions for the propagation characteristics of the LF magnetic field in cylindrical time-varying plasma are derived using an equivalent circuit. Meanwhile, a frequency-division-multiplex experimental method for a shock tube is presented to quantitatively measure the propagation characteristics of a multifrequency LF magnetic field. The experimental results are in good agreement with the theoretical results. As the fluctuation intensity of the electron density increases, the fluctuation intensities of the time-varying envelope and phase shift increase, and the power spectral density broadens. As the frequency of the LF magnetic field increases, the effects of the time-varying plasma on the propagation characteristics strengthen. These results are important to the design of LF communication systems and modulation algorithms in the scenario of shock-tube-generated plasma.

Mechanism analysis of magnetohydrodynamic shock control in hypersonic flow

The effects of external magnetic fields on the shock-wave configuration at hypersonic plasma flow field are investigated in this paper. A series of numerical simulations over various geometry configurations, namely, a blunt body and a fixed-geometry inlet forebody, have been conducted by varying the applied magnetic field under different freestream conditions. Results show that magnetohydrodynamic shock control capabilities under three types of magnetic field are ranked from weak to strong as dipole magnet, solenoid magnet, and uniform magnet field. Under the same applied magnetic field, it is easier to deflect the shock at a relatively high altitude condition, compared with the low altitude case. The bow shock standoff distance is dependent on the distribution of counter-flow Lorentz force right after shock in the stagnation region. For the oblique shock control, the function of two components of Lorentz force is different that the counter-flow one decelerates the flow and increases the shock-wave angle, while the normal one squeezes the oblique shock and deflects the streamlines.

Моделювання взаємодії космічних апаратів з іоносферною розрідженою плазмою

Principles of simulation of the physical-chemical and electromagnetic interaction of a spacecraft with the near-satellite environment and principles of probe diagnostics of rarefied plasma flows onboard a spacecraft are stated. Equivalence criteria are formulated for the interaction of a spacecraft with the near-satellite environment and hypersonic rarefied plasma flows on dedicated setups, in particular on the plasmaelectrodynamic setup of the Institute of Technical Mechanics of the National Academy of Sciences of Ukraine and the State Space Agency of Ukraine, which has the status of the National Patrimony of Ukraine. The features of spacecraft interaction with the near-satellite environment were studied along the following three lines: - degradation of the materials and performance characteristics of spacecraft components in a long-term orbital service: - magnetohydrodynamic interaction of a spacecraft with hypersonic rarefied plasma flows; - probe diagnostic of rarefied plasma flows onboard a spacecraft. Along the first line, a calculation-and-experiment procedure was developed to evaluate the power decrease of spacecraft silicon solar batteries under long-term (~ 10 years) exposure to the space factors and the near-satellite environment in circular orbits. Principles of accelerated life tests for the resistance of spacecraft polymer materials to long-term exposure to atomic oxygen flows and vacuum ultraviolet radiation were developed. Simultaneous exposure of polymers to atomic oxygen and vacuum ultraviolet radiation results in the synergic effect of mass loss by materials that contain a monomer of the (CH)n group. Along the second line, models were formulated for magnetohydrodynamic interaction in the magnetized spacecraft – ionospheric plasma system. It was shown that the interaction of a ?0,8 – 1.5 T magnetic field of a space debris object (in particular, a spent spacecraft) with the ionospheric plasma produces an electromagnetic drag force sufficient for removing it to a low orbit followed by its burn-up in the dense atmosphere. Along the third line, procedures were developed for ionospheric plasma probe diagnostics using onboard instrumentation that includes mutually orthogonal cylindrical electrical probes and a two-channel neutral-particle detector. It was shown that this instrumentation with the use of proprietary output signal interpretation algorithms and procedures allows one to locate sources of space-time disturbances in inospheric plasma parameters caused by natural and technogeneous catastrophic phenomena on the subsatellite track.

Acceleration of Boltzmann Collision Integral Calculation Using Machine Learning

The Boltzmann equation is essential to the accurate modeling of rarefied gases. Unfortunately, traditional numerical solvers for this equation are too computationally expensive for many practical applications. With modern interest in hypersonic flight and plasma flows, to which the Boltzmann equation is relevant, there would be immediate value in an efficient simulation method. The collision integral component of the equation is the main contributor of the large complexity. A plethora of new mathematical and numerical approaches have been proposed in an effort to reduce the computational cost of solving the Boltzmann collision integral, yet it still remains prohibitively expensive for large problems. This paper aims to accelerate the computation of this integral via machine learning methods. In particular, we build a deep convolutional neural network to encode/decode the solution vector, and enforce conservation laws during post-processing of the collision integral before each time-step. Our preliminary results for the spatially homogeneous Boltzmann equation show a drastic reduction of computational cost. Specifically, our algorithm requires O(n3) operations, while asymptotically converging direct discretization algorithms require O(n6), where n is the number of discrete velocity points in one velocity dimension. Our method demonstrated a speed up of 270 times compared to these methods while still maintaining reasonable accuracy.

Hypersonic plasma flows created by a pulse capillary discharge

The possibility of producing by a pulsed capillary discharge the quasi-stationary high-speed plasma flows in a wide range of Mach numbers (M=3-20), electron number densities (ne∼1011-1015 cm-3) and temperatures (Te∼3-10 eV), rotational and vibrational temperatures (Tr=3800-6000 K and Tv=9000-15000 K), which can be used for setting up plasma aerodynamic experiments on small laboratory facilities, is shown. The most suitable for this purpose is a mode close to supersonic outflow into a vacuum, the transition to which occurs when the total pressure ratio exceeds N = p0/p∞ >5·103. This mode permits to obtain wide-aperture flows (D >10 cm) with spatially extended weakly inhomogeneous segments sufficient to accommodate tested bodies of a centimeter scale.

Drag on a spacecraft produced by the interaction of its magnetic field with the Earth's ionosphere. Physical modelling

The dynamic interaction of a “magnetized” sphere (a sphere with a magnetic field source) with a hypersonic rarefied plasma flow was studied experimentally to model the interaction of a “magnetized” spacecraft with the ionospheric plasma. The experiments were conducted at the plasma flow velocity parallel and normal to the sphere's magnetic field. The electromagnetic drag coefficient was determined as a function of the ratio of the magnetic pressure to the dynamic pressure and the ratio of the mini-magnetosphere dimension to the spacecraft dimension (sphere radius). It was shown that a spacecraft's magnetic field of about 0.8–1.5 T produces an electromagnetic drag comparable with the drag produced using ion beam technologies of space debris removal, which require dedicated spacecraft with plasma accelerators. Energy-efficient compact sources of a 0.8–1.5 Т magnetic field for space debris objects may be made using special arrangements of small-size permanent magnets – Halbach arrays.

Two-Photon Laser-Induced Fluorescence Measurements of Atomic Oxygen Density in Hypersonic Plasma Flow

An experimental investigation of high-enthalpy air flow generated by L2K arc-jet facility of DLR is carried out by means of two-photon absorption laser-induced fluorescence (TALIF) measurements of atomic oxygen at transition. The experiment has been conducted with an arc current of 600 A, a mass flow rate of , and a total pressure of , resulting in both mass-specific enthalpy of and a reservoir temperature of 4200 K. Atomic oxygen has been characterized in terms of translational temperature and absolute number density either in the freestream or behind a shock wave upstream a blunt body. A calibration method based on TALIF measurements of xenon at transition has been used. The results highlight that in the freestream the fluorescence signal exhibits a peak activity lower with respect to that inspected in the shock layer. The measured lifetimes of and indicate that, in the shock layer, the depletion of the atomic oxygen excited state occurs mainly via quenching. The analysis of the line broadening of the spectral profile of atomic oxygen reveals an increment of the translational temperature in the shock layer with respect to that measured in the freestream, resulting in and , respectively. It is found that in the freestream the absolute number density attains and the presence of the shock wave induces an increment of the number density of , that is, 4.85 times higher than that detected in the freestream.

Inhibition of the "magnetized" sphere in a hypersonic rarefied plasma flow

Inhibition of the "magnetized" sphere in a hypersonic rarefied plasma flow

Braking of a “Magnetized” Sphere in a Hypersonic Rarefied Plasma Flow

The dependence of the drag coefficient of a “magnetized” (with a self-generated magnetic field) sphere on the ratio of the magnetic pressure to the gas dynamic pressure in a hypersonic rarefied plasma flow is determined experimentally. The dependences are obtained for a wide range of angles between the vectors of the incident flow velocity and the magnetic field, as well as between the velocity vectors of the incident hypersonic plasma flow and a subsonic plasma jet injected from the surface of the sphere. It is shown that the injection of a subsonic plasma jet from the surface of a “magnetized” sphere in a hypersonic rarefied plasma flow increases its drag coefficient by several times in comparison with an “unmagnetized” sphere.

Control of the drag on a spacecraft in the earth’s ionosphere using the spacecraft’s magnetic field

This paper shows the possibility of active control of the drag on a spacecraft in the Earth's ionosphere using the electromagnetic force produced by the interaction of the spacecraft's magnetic field with the incident plasma flow. As a result of experimental simulation of the dynamic interaction of the magnetic field of a sphere with a hypersonic flow of the rarefied ionospheric plasma, the sphere drag coefficient is determined as a function of the ratio of the magnetic pressure to the dynamic pressure in a wide range of the angle between the incident flow velocity and the magnetic field and the angle between the incident hypersonic plasma flow and the velocity of a subsonic plasma jet injected from the sphere surface. It is shown that injecting a subsonic plasma jet into the mini-magnetosphere cavity provides a several-fold increase in the drag coefficient of a “magnetized” sphere (a sphere with its own magnetic field) in a hypersonic rarefied plasma flow in comparison with a “nonmagnetized” sphere. A 0.6 … 0.8 T magnetic field of a “magnetized” body may be an efficient means for its deorbiting through increasing the drag on the body in the Earth's ionosphere, which provides a way for removing space debris objects to lower orbits.

Experimental Research of Dynamics and Macrostructure of Light Erosion Radiative Plasmodynamic Discharges

The investigations of dynamics and macrostructure (spatial and temporal distributions of charged particles) of optic-plasmadynamic discharges with light erosion mechanism of plasma formation and generation of accelerated gas–plasma flows of various chemical composition in the wide range of dynamic and energy & power characteristics are presented. The plasma was heated as a result of the thermalization due to shock interaction of high kinetic energy plasma flows with a gas medium, which works as a stopping barrier for such discharges. It was shown that the deceleration of the radially inhomogeneous flow at a deformable gas barrier has an essentially two-dimensional nature: a complex system of conical shock wave forms in a hypersonic plasma flow.

Dynamic interaction of a magnetized solid body with a rarefied plasma flow

Dependences of the drag and lift coefficients of a magnetized sphere in a hypersonic rarefied plasma flow on the angle between the plasma flow velocity and the self-magnetic field induction vector of the body are obtained in a wide range of the ratio of the magnetic pressure to the plasma flow pressure. It is shown that changing the orientation of the magnetic field vector of the body and the incoming flow velocity can be used to control the dynamic interaction in the plasma–body system, namely, to decelerate and accelerate the magnetized sphere in a rarefied hypersonic plasma flow.

An unstructured shock-fitting solver for hypersonic plasma flows in chemical non-equilibrium

A CFD solver, using Residual Distribution Schemes on unstructured grids, has been extended to deal with inviscid chemical non-equilibrium flows. The conservative equations have been coupled with a kinetic model for argon plasma which includes the argon metastable state as independent species, taking into account electron–atom and atom–atom processes. Results in the case of an hypersonic flow around an infinite cylinder, obtained by using both shock-capturing and shock-fitting approaches, show higher accuracy of the shock-fitting approach.

Consistent multi-internal-temperature models for vibrational and electronic nonequilibrium in hypersonic nitrogen plasma flows

In this work, a state-to-state vibrational and electronic collisional model is developed to investigate nonequilibrium phenomena behind a shock wave in an ionized nitrogen flow. In the ionization dynamics behind the shock wave, the electron energy budget is of key importance and it is found that the main depletion term corresponds to the electronic excitation of N atoms, and conversely the major creation terms are the electron-vibration term at the beginning, then replaced by the electron ions elastic exchange term. Based on these results, a macroscopic multi-internal-temperature model for the vibration of N2 and the electronic levels of N atoms is derived with several groups of vibrational levels of N2 and electronic levels of N with their own internal temperatures to model the shape of the vibrational distribution of N2 and of the electronic excitation of N, respectively. In this model, energy and chemistry source terms are calculated self-consistently from the rate coefficients of the state-to-state database. For the shock wave condition studied, a good agreement is observed on the ionization dynamics as well as on the atomic bound-bound radiation between the state-to-state model and the macroscopic multi-internal temperature model with only one group of vibrational levels of N2 and two groups of electronic levels of N.

315 極超音速プラズマ気流に対する複数磁場印加による効果

315 極超音速プラズマ気流に対する複数磁場印加による効果

テーパー・コーン型プラズマフォーカス装置によって生成された極超音速プラズマ流による実験室宇宙物理

We investigated a hypersonic plasma flow generated by a taper-cone-shaped plasma focus device toward astrophysical phenomena. The effects of applied magnetic field on shock velocity were observed with a streak camera. From the dependence of shock deceleration on the magnetic field distribution with comparable plasma beta, the gradient of magnetic field affects the shock deceleration. To compare the shock behavior from the numerical simulation with the experimental results, we developed a one-dimensional hybrid particle-in-cell code. The results indicated that the magnetic field distribution affected the deceleration of the shock velocity. It means that the shock behaviors generated by the taper-cone-shaped plasma focus device are comparable to the numerical simulation.