Reentry Research Articles

Adjoint-based shape optimization for compressible flow based on volume penalization method

AbstractReducing the resistance of compressible flow around a blunt body is of great interest in engineering applications, while an efficient shape optimization method for compressible flows remains far from well established, especially for high Mach numbers. To this end, a volume penalization method for simulating compressible flows past a no-slip and isothermal solid is established by introducing an artificial body force and a heat sink into the governing equations. The level-set functions are introduced as design variables, and the cost functional is defined as the total drag acting on the solid. Then, a continuous adjoint-based shape optimization algorithm for drag reduction is developed by deriving the adjoint equations, the adjoint boundary conditions, and the shape update formula. Both the forward and adjoint simulations are verified by existing studies. The results show that the relative deviations of the drag coefficients obtained in the present study from those reported in the reference studies are around 5% at most, and also a comparable drag reduction rate and also optimal shapes can be reproduced by the present optimization scheme for benchmark problems at relatively low Mach numbers considered in previous studies. Finally, the present method is applied to shape optimization of an initially two-dimensional cylinder and also a three-dimensional sphere in the transonic regime of Ma∞ = 1.2. The drag reduction of over 20% is achieved for both two-dimensional and three-dimensional cases.

Drag reduction mechanism based on the aerospike-jet composite approach under different incoming dynamic pressures

The drag experienced by the nose of an aircraft varies significantly under different incoming flow conditions. In order to reduce the aerodynamic force on the nose of the (hypersonic) supersonic vehicle, the numerical simulation approach has been used to analyze the drag reduction laws and mechanisms of a blunt-body vehicle with the aerospike-counterflowing jet composite approach under different incoming flow dynamic pressures. The effects of two environments with H = 0.1 km and H = 30 km, as well as the influence of different incoming Mach numbers on the drag reduction at H = 0.1 km were investigated. The research has shown that there exists a minimum overall drag value for the vehicle under different dynamic pressures, while the variation in the wall pressure is related to the actual operating conditions. The recirculation zones at the aerospike and in front of the blunt body are important flow structures that affect the drag reduction. When the jet total pressure ratio increases, the position of the recirculation zone at the head of the drag reduction rod moves away from the central axis of the model. When the incoming flow dynamic pressure is higher, the separation point of the recirculation zone in front of the blunt body is located further downstream, and the reattachment point is related to the incoming flow and jet conditions, aligning with the trend of variation of the position of the maximum pressure on the blunt body wall. As it can effectively push away the shock wave, the enhanced drag reduction effect of the jet is significant when the incoming flow dynamic pressure is higher. However, the high jet pressure resulting from high dynamic pressure needs to be considered in the actual design. Furthermore, the complex turbulent flow field formed by the high dynamic pressure incoming flow and the jet is worthy of further study by means of the large eddy simulation.

Molecular dynamics simulations of thermomechanical properties of silicone-modified phenolic polymer

The silicone-phenolic multicomponent polymers are typically employed as the matrix of fiber-reinforced nanocomposites developed for reentry vehicles due to their excellent thermal and mechanical properties. The thermomechanical properties of the silicone-phenolic multicomponent polymer system, which are greatly related to the processing and microstructures, were studied using molecular dynamics (MD) simulations combined with experiments. A multistep dynamic polymerization approach was utilized to form the crosslinked polymer model, which was also validated in terms of both microstructures and properties. The thermomechanical properties of the crosslinked polymer system were established as a function of crosslinking degree, component ratio, temperature, strain rate, and cooling rate, and the influence mechanisms of the processing parameters were revealed. The crosslinking degree can greatly influence the glass transition temperature and volumetric coefficient of thermal expansion, which is attributed to the constrained chain mobility. The crosslinking degree and the component ratio have a significant effect on the morphologies and vibrational density of states of the polymer system, respectively, which in turn affects the thermal conductivity. The failure mode during uniaxial tensile was investigated in terms of the atomic energy distribution through MD simulations. The elastic and plastic deformation stages are dominated by intermolecular non-bonding interactions, but less contributed by the bonding interactions. This work can guide the design of polymeric nanocomposites by establishing the relationship of processing-microstructure-thermomechanical properties.

Aerodynamic/control coupling optimization of reentry vehicle under wide speed range

Aerodynamic/control coupling optimization of reentry vehicle under wide speed range

Perturbation amplification near the stagnation point of blunt bodies

Perturbation amplification near the stagnation point of blunt bodies

Aerodynamic Drag Coefficient Prediction of a Spike Blunt Body Based on K-Nearest Neighbors

Spike blunt bodies are a method to reduce drag when a body moves at speeds above sound. Several numerical works based on computational fluid dynamics (CFD) have deeply studied fluid performance and highlighted its advantages. However, most documentation focuses on modifying spike physical properties while keeping constant supersonic or hypersonic flow conditions. In recent years, machine learning models have emerged as viable tools to predict values in almost any field, including aerodynamics. In the case of CFD, many models have been explored, such as support vector regression, ensemble methods, and artificial neural networks. However, a simple and easy-to-implement method such as k-Nearest Neighbors has not been extensively explored. This work extrapoled k-Nearest Neighbors to predict the drag coefficient of a spike blunt body for a range of supersonic and hypersonic speeds based on drag data obtained from CFD analysis. The parametric study of the spike blunt body was performed considering body diameter, spike length, and freestream Mach number as input variables. The algorithm presents proper predictions, with errors less than 5% for the drag coefficient and considering a minimum of three neighbor nodes. The k-NN was compared again Kriging model and k-NN presents a better accuracy. The above validates the flexibility of the method and shows a new area of opportunity for the calculation of aerodynamic properties.

Cosmogenic radionuclides in meteorites from the Otway Massif blue ice area, Antarctica: An unusual, well‐preserved H5 chondrite strewn field

AbstractThe US Antarctic Search for Meteorites (ANSMET) discovered a dense cluster of 88 ordinary chondrites with a total mass of more than 100 kg on a blue ice area (BIA) of 1.6 × 0.3 km2 near the Otway Massif, Grosvenor Mountains, Antarctica. The larger masses (weighing up to 29 kg) were found at one end of an oval‐shaped pattern and the smaller masses (50–200 g) at the other end. We measured concentrations of the cosmogenic radionuclides 10Be (half‐life—1.36 × 106 year) and 36Cl (3.01 × 105 year) in the metal fraction of 17 H chondrites, including 14 fragments of this cluster, to verify the hypothesis that this meteorite cluster on the Otway Massif BIA represents a meteorite strewn field produced by the atmospheric breakup of a single meteoroid. The 10Be and 36Cl concentrations confirm that 10 out of 14 H chondrites from different locations within this small area are paired fragments of the same meteorite fall, while the four other H chondrites represent two additional—smaller—falls. The radionuclides suggest a pre‐atmospheric mass of 200–400 kg for the large pairing group, suggesting that 25%–50% of the meteoroid survived atmospheric entry. Based on the distribution of the paired H chondrites and evidence of their common cosmic‐ray exposure history in space, we conclude that most of the 88 meteorites within this small area represent a meteorite strewn field. The small size of the strewn field suggests that the meteoroid entered at a steep angle (>60°), while the low amount of fusion crust on most meteorite surfaces most likely indicates atmospheric break up at low altitude, while additional fragmentation of a large surviving fragment may have occurred during impact on the ice. This well‐documented strewn field provides a good opportunity to apply model simulations of the atmospheric fragmentation of this object as a function of entry angle, velocity, and meteoroid strength. Cosmogenic 14C analyses in two members of the Otway Massif pairing group yield a terrestrial age of 15.5 ± 1.5 kyr, which represents the time elapsed since this meteorite fell on Earth. The excellent preservation of an Antarctic meteorite strewn field suggests that the Otway Massif BIA represents a relatively stagnant blue ice field.

Design and characterization of a wind-adaptable piezoelectric energy harvester utilizing a rigid-flexible compound blunt body

In response to the challenges posed by uncontrolled amplitude during galloping and narrow effective bandwidth during vortex-induced vibrations in current energy harvesters, a novel wind-adaptable piezoelectric energy harvester utilizing a rigid-flexible compound blunt body (W-APEH) is proposed. The rigid-flexible compound blunt body improves environmental adaptability and power generation capacity. During the transformation process of the rigid-flexible compound blunt body from a Y-shape to an r-shape, a vibration pattern changes from galloping to coupled vibration, then to vortex-induced vibration. The feasibility of the structure and principle of the W-APEH were proved through a series of simulations and experiments. The higher proportion of rigid wings within a blunt body increases the susceptibility to galloping. A larger windward angle will delay the occurrence of galloping in the W-APEH, shorten the time of coupled vibration, and reduce the output voltage. In the case of the flexible wing thickness remains below 0.3 mm, an increase in thickness leads to an extended galloping time, with vortex-induced vibrations occurring later. Specifically, the onset wind speed is only 3.5 m/s, and the working wind speed range is 5–21 m/s with appropriate structural dimensions. Furthermore, the W-APEH provides a maximum output power of 3.78 mW at an optimal load resistance of 250 kΩ.

Optimal Gliding Trajectories for Descent on Mars

In this paper, optimal gliding trajectories are analyzed, formulating an optimal control problem to be solved computationally via nonlinear programming. A multi-objective terminal cost function that minimizes the velocity, altitude, horizontal flight path angle, and the error of a desired terminal point is formulated. The results are validated via Monte Carlo simulations, analyzing the influence of the variations in the lift-to-drag ratios in the atmospheric entry. The results show feasible solutions for minimizing the distance to the desired final point, which have significant practical implications for the controlled gliding entry of a spaceplane on Mars. In this sense, the results also show that the longitudes of the landing points do not change too much for almost all trajectories, while the latitude of these points is in the interval of about 4 degrees for the majority of the trajectories. This suggests that it is possible to implement an optimal control approach with reasonable accuracy for the controlled gliding entry of a spaceplane on Mars, even in the presence of some uncertainties regarding the aerodynamic performance of the spacecraft, such as the lift-to-drag ratio.

Weight-adaptive augmented Lagrange multiplier sequential convex programming for nonlinear trajectory optimization

Sequential convex programming has become a prominent research focus in aerospace trajectory optimization due to its high computational efficiency. One critical challenge in sequential convex programming is the infeasibility of subproblems, which significantly impacts its stability. To address this issue, certain constraints must be relaxed using relaxation variables, which are then incorporated into the objective function as a penalty term. However, the choice of penalty weight greatly influences the optimality and convergence of sequential convex programming. Therefore, this paper proposes a weight-adaptive augmented Lagrange multiplier sequential convex programming algorithm to tackle the challenge. First, this paper analyzes the difficulty of determining an appropriate penalty weight from the perspective of its penalty effect. Based on this analysis, an augmented penalty term is introduced, and the update rule for the augmented Lagrange multiplier is formulated using the Karush-Kuhn-Tucker conditions. Subsequently, a method with adaptive weight adjustment is designed based on the change in the penalty term to further improve the algorithm's solving speed. Finally, the proposed method is validated through numerical simulations in a Mars-powered landing problem and a small glide vehicle reentry problem. The results show that the proposed method is 20.59 % and 25.16 % faster compared to the general sequential convex programming algorithm, respectively. Furthermore, the proposed method is demonstrated to be robust to the initial choice of penalty weight.

Thermo-mechanical coupling failure mechanisms of reusable SiCf/SiC composites with PyC interphase

The extreme and repeated aerothermal environments working on reusable launch vehicles bring challenges for the design of hot structure. Due to the outstanding high-temperature resistant, SiCf/SiC composite is an excellent candidate material for hot structures in re-entry vehicles. In this paper, the thermo-mechanical coupling failure mechanisms of SiCf/SiC composite are investigated comprehensively. Experimental results reveal different failure mechanisms of SiCf/SiC composites subjected to monotonic quasi-static tension at room temperature and high temperature, cyclic thermal fatigue and thermo-mechanical coupling fatigue. Cyclic thermal environment causing oxidation of interphase layer and embrittlement of fiber plays a significant role in decrease of load bearing capacity of SiCf/SiC composites. The long-term periodic fatigue load that is superimposed on the cyclic thermal condition would further deteriorate the performance of materials. To better understand the damage evolution process, a thermo-mechanical coupling fatigue model is proposed to describe the degradation of SiCf/SiC composites for different stress levels. The service life of SiCf/SiC composites is obtained, which could be used to evaluate the reusable performance of SiCf/SiC hot structure. The results of this study provide novel insights into the design of SiCf/SiC composites for reusable launch vehicles under prolonged and repeated service environment.

Mechanism-specific chemical energy accommodation with finite-rate surface chemistry in non-equilibrium flow

During atmospheric reentry, the vehicle surface is exposed to highly non-equilibrium flow. The vehicle surface can experience heterogeneous recombination of reactive atoms, which contributes to its aerothermodynamic heating. This process is followed by chemical energy accommodation (CEA), where the released energy is either transferred to the surface or the internal energy modes of the recombined molecule. Heterogeneous recombination can be categorized into Eley–Rideal (ER) and Langmuir–Hinshelwood mechanisms, which differ in their methods of molecule formation and degrees of CEA. The complete CEA assumption may not consider the dependency of CEA on the mechanisms of heterogeneous recombination. This study aims to consider the mechanism-specific CEA for a more accurate prediction of surface heat flux. The authors implement mechanism-specific CEA within the direct simulation Monte Carlo framework using the finite-rate surface chemistry model, resolving elementary surface reactions and assigning a CEA coefficient, β, to each mechanism. The model is verified through comparisons with analytical solutions of surface coverage and validated against benchmark references. A parametric investigation of rarefied hypersonic flow over a two-dimensional cylinder is conducted under different freestream Mach and Knudsen numbers. Results show a reduction in total heat flux of up to 14.44% using mechanism-specific CEA compared to the complete CEA assumption. The reduction is attributed to the relative contribution of the ER mechanism, which can be a function of atomic partial pressure at the boundary layer.

Iterated rational quadratic kernel - High-order unscented Kalman filtering algorithm for spacecraft tracking

The high-speed development of space defense technology demands a high state estimation capacity for spacecraft tracking methods. However, reentry flight is accompanied by complex flight environments, which brings to the uncertain, complex, and strongly coupled non-Gaussian detection noise. As a result, there are several intractable considerations on the problem of state estimation tasks corrupted by complex non-Gaussian outliers for non-linear dynamics systems in practical application. To address these issues, a new iterated rational quadratic (RQ) kernel high-order unscented Kalman filtering (IRQ-HUKF) algorithm via capturing the statistics to break through the limitations of the Gaussian assumption is proposed. Firstly, the characteristic analysis of the RQ kernel is investigated in detail, which is the first attempt to carry out an exploration of the heavy-tailed characteristic and the ability on capturing high-order moments of the RQ kernel. Subsequently, the RQ kernel method is first introduced into the UKF algorithm as an error optimization criterion, termed the iterated RQ kernel-UKF (RQ-UKF) algorithm by derived analytically, which not only retains the high-order moments propagation process but also enhances the approximation capacity in the non-Gaussian noise problem for its ability in capturing high-order moments and heavy-tailed characteristics. Meanwhile, to tackle the limitations of the Gaussian distribution assumption in the linearization process of the non-linear systems, the high-order Sigma Points (SP) as a subsidiary role in propagating the state high-order statistics is devised by the moments matching method to improve the RQ-UKF. Finally, to further improve the flexibility of the IRQ-HUKF algorithm in practical application, an adaptive kernel parameter is derived analytically grounded in the Kullback-Leibler divergence (KLD) method and parametric sensitivity analysis of the RQ kernel. The simulation results demonstrate that the novel IRQ-HUKF algorithm is more robust and outperforms the existing advanced UKF with respect to the kernel method in reentry vehicle tracking scenarios under various noise environments.

Drag and Thermal Reduction of Spiked Hypersonic Vehicle in Thermochemical Nonequilibrium

This study utilizes the in-house parallel direct simulation Monte Carlo–quantum dynamics method to model the aerodynamic flowfield of a spiked reentry vehicle within a rarefied high-altitude atmosphere. Investigating the flight of spiked aircraft under various flight conditions and spike sizes and considering both the real gas effect and the rarefied gas effect, the aerodynamic characteristic of the aircraft is evaluated. Performance evaluation for effectiveness in drag reduction and thermal protection is based on drag and the maximum stagnation heat flux coefficient at the vehicle’s shoulder. Findings indicate that, in the rarefied atmosphere, the distinction between the characteristic shock intensities of spiked and unspiked vehicles is not pronounced, which results in a drag reduction of approximately 5%, accompanied by a more than 100% increase in thermal effect on the vehicle’s shoulder, obviously poor in effectiveness. Subsequently, this study examines the spiked vehicle equipped with a lateral jet, and this augmented approach achieves a marked reduction in the intensity of the shock wave impacting the vehicle’s shoulder with a drag reduction exceeding 10% and attenuates the thermal impact by over 50% in comparison to the implementation of spiking alone, thereby demonstrating superior performance in terms of effectiveness.

Ground experimental study of the electron density of plasma sheath reduced by pulsed discharge

Abstract A plasma sheath will be generated around the hypersonic vehicle during reentry, where a large number of electrons will significantly affect the propagation of EM waves, resulting in the phenomenon of communication blackout. This paper proposes a method of reducing the electron density of reentry vehicle plasma sheath by pulsed discharge. Experiments were conducted in a high-speed plasma wind tunnel to study the effects and scope of pulsed discharge on the plasma sheath electron density using an ultrahigh-speed camera and microwave diagnostic system. The experimental results show that the application of pulsed discharge resulted in the formation of a light intensity attenuation region measuring 14 × 19 × 4 cm around the discharge area, with an attenuation degree ranging from 30% to 58%. The microwave diagnostic results indicate that after the actuator discharge, the electron density of the plasma sheath within a 4 cm height above the vehicle wall is significantly reduced compared to before the actuator discharge, with a maximum reduction of approximately 86%. These results demonstrate that this method has significant effects on reducing plasma sheath electron density. Furthermore, the low power consumption, load, and space requirements suggest that it has potential for practical applications.

The first results of the hydrogen cyanide (HCN) interferometer measuring experimental research apparatus for electromagnetic science (ERAES) for hypersonic vehicle plasma in near space.

The formation of a plasma sheath on the surface of spacecraft or satellites during high-speed atmospheric entry is a significant factor that affects communication and radar detection. Experimental research apparatus for electromagnetic science can simulate this plasma sheath and study the interaction mechanisms between electromagnetic waves and plasma sheaths. Electron density is a crucial parameter for this research. Therefore, in this paper, a HCN heterodyne interferometer has been designed to measure the electron densities of the device, which range from 1 × 109 to 3 × 1013cm-3 and the pressure ranges from 50 to 1500Pa. The light source is a HCN laser with a wavelength of 337 µm, which exhibits higher spatial resolution compared to microwave interferometers. The interferometer is configured as a Mach-Zehnder interferometer, which generates an intermediate frequency through the Doppler shift achieved by a rotating grating. The spatial and temporal resolution of the HCN interferometry reach ∼14mm and 100 µs, respectively. Antenna-coupled ALGaN/GaN-HEMT detectors have been utilized, as they possess higher sensitivity-with a typical reduction factor responsivity of around 900 V/W-than VDI planar-diode Integrated Conical Horn Fundamental Mixers in HCN interferometry. Recently, the initial results of the HCN interferometer designed for ERAES have been obtained during an experimental campaign, demonstrating a phase resolution of up to 0.04π.

Intelligent calculation of reachable domain under No-fly zone influence based on tangent flight trajectories

Rapid and accurate calculation of reachable domain, especially under the no-fly zone influence, is important in the reentry mission of reentry vehicles. The basic problem is the complex boundary of the reachable domain. Aiming to solve this problem, the intelligent reachable domain calculation approach with unfixed no-fly zone location based on tangent flight trajectory is presented. First, the algorithm of reachable domain calculation under no-fly zone influence is proposed. After finding the tangent flight trajectories, the tangency point states are determined and the subdomains are generated. To obtain a closed domain, the new algorithm for limiting boundary calculation is given. The no-fly zones are classified and the solution ideas of different categories are given separately to ensure that the algorithm can apply to different kinds of no-fly zones. Back Propagation neural networks are introduced and trained for different types of no-fly zones to solve reachable domains rapidly. Finally, the simulations of the proposed algorithm are presented, including each category of a single no-fly zone and different categories of multiple no-fly zones. Comparisons are also made between the general solution method and the method using neural networks. The results illustrate the effectiveness of the proposed method and the calculation time reduced by a factor of 103 through neural networks.

Modular Chip-Based nanoSFC-MS for Ultrafast Separations.

This study presents the development of a miniaturized device for supercritical fluid chromatography coupled with mass spectrometry. The chip-based, modular nanoSFC approach utilizes a particle-packed nanobore column embedded between two monolithically structured glass chips. A microtee in the pre-column section ensures picoliter sample loads onto the column, while a microcross chip structure fluidically controls the column backpressure. The restrictive emitter and the minimal post-column volume of 16 nL prevent mobile phase decompression and analyte dilution, maintaining chromatographic integrity during transfer to the atmospheric pressure MS interface. This facilitates high-speed chiral separations in less than 80 s with high reproducibility.

Probability-oriented disturbance estimation-triggered control via collaborative and adaptive Bayesian optimization for reentry vehicles

The paper investigates the performance improvement issue for reentry vehicles under uncertainties from the perspective of probability. The disturbance estimation-triggered control (DETC) proves to achieve transient performance increase compared with the standard disturbance-observer control methods, and the presented approach further exploits the probability-oriented transient performance improvement based on the collaborative and adaptive Bayesian optimization (CABO) technique, which constructs the main contribution of the paper. Based on the attitude dynamics of reentry vehicles, the DETC method is first introduced to guarantee the tracking stability and robustness against the uncertainties including the aerodynamic perturbation and wind effects. Meanwhile, the performance improvement is analyzed theoretically. Then, by virtue of the CABO algorithm, the CABO-based DETC is presented by combining the performance and probability indexes. Finally, the simulation results verify the effectiveness of the proposed control scheme and parameters influence is also discussed.

Multidisciplinary design analysis and optimization of the aerodynamic shape of the SpaceLiner passenger stage

The SpaceLiner is a futuristic concept of a suborbital space plane intended to provide ultra-fast intercontinental passenger transport, currently in pre-development at DLR-SART. Vehicles traveling at hypersonic speeds inevitably produce shock waves that are perceived at ground level as sonic booms, with associated disturbance of the overflown populations. The reduction of this disturbance, together with the decrease of the noise associated to the launch and ascent phase, is critical for a viable future operation of the SpaceLiner. The objective of this work is the redesign of the passenger stage aerodynamic shape in order to improve its atmospheric re-entry performance, in terms of a reduction of both the heat flux and the disturbance of the overflown populations. For this purpose, a MDAO methodology was developed with the tasks of (1) computing vehicle performance from a wing shape parametrization using fast estimation methods, (2) exploring the design space and (3) finding a new promising aerodynamic shape. First, a Python tool-chain was developed to compute vehicles performances from a wing shape parametrization using fast estimation methods. The tool-chain was then systematically exploited to explore the design space by means of parametric studies, whose results informed the implementation of the forthcoming optimization. Afterwards, the wing shape was optimized using a three-objective evolutionary algorithm that minimized the vehicle mass and maximized its lift-to-drag ratio and lift coefficient. Simplified trajectory optimizations were then run on the set of non-dominated solutions in order to identify the most performing configurations. Finally, multi-objective evolutionary trajectory optimizations were run for the most promising candidate along intercontinental point-to-point routes of interest. Comparisons with the previous design iteration showed a significant improvement in terms of a reduction of both reentry heat flux and population disturbance.