Journal of Aerospace Engineering

The dynamic mode-I energy release rate of cracks propagating along elastic interfaces in double cantilever beams under high loading rates is derived analytically for the first time by accounting for structural vibration, wave propagation, and the Doppler effect along with the assumption of crack tip energy conservation. The developed theory can be used to study the “stick-slip” crack propagation behavior commonly observed in experiments, a progression of crack initiation, propagation, arrest, and reinitiation. In addition, the developed theory can be applied to measure crack initiation toughness as well as crack arrest toughness. The developed theory is verified against results from finite-element-method simulations of two experimental cases under high loading rates, demonstrating the excellent ability of the developed theory in capturing the crack propagation behavior as well as the ability in assessing dynamic mode-I energy release rate.

A quasi-three-dimensional (3D) theory considering transverse shear and normal deformation effects is presented for the static flexure of simply supported symmetric sandwich plates. The theory was developed based on the third- and fifth-order shear strain functions in terms of thickness coordinate. The displacement field accounts for nonlinear variation of in-plane displacements and transverse displacement through the plate thickness and enforces satisfying conditions of zero transverse shear stresses on the upper and lower surfaces of the plate. The present theory does not require the shear correction factor associated with the first-order shear deformation theory. Governing equations and boundary conditions were obtained using the principle of virtual work. The transverse shear and normal stresses were obtained from the stress equilibrium equations of theory of elasticity satisfying the continuity conditions at the layer interfaces and the stress-free boundary conditions at the top and bottom surfaces of the plate. The closed-form solutions for simply supported sandwich plates subjected to sinusoidal, uniform, and uniformly varying loads were obtained for various side to thickness ratios. The results of the present quasi-3D theory were compared with those of the exact theory, first- and third-order shear deformation theories, and the classical plate theory. Results showed that the present quasi-three-dimensional (3D) theory is in excellent agreement with the exact theory.

As a common engineering material, wood has been widely used and researched for a long time. The dynamic characteristic of green wood in living trees is very critical in the impact analysis; however, the research on it is limited. This work aims to characterize a material model for green birch wood with strain rate effect, so it can be implemented in the finite-element code LS-DYNA. Several static and impact tests, along with the corresponding numerical simulations, were conducted. The damage mode and the energy absorption ability during the impact process were analyzed and compared. Good agreement is demonstrated between the simulations and the experiments over a wide range of impact velocities with errors of energy absorption less than 8%, indicating good reliability and robustness of the model. This material model can be applied to crashworthiness analysis of aircraft and air crash reconstruction involving birch trees.

Hybrid-electric civil airliners (HECAs) are considered the forerunner of the solution of relieving aviation emissions. This paper presents a multidisciplinary design analysis and optimization (MDAO) framework named GENUS, which has been extended to design HECAs. GENUS is a modular, expandable, and flexible design environment with 10 integrated modules for HECA design. Key extensions included hybrid-electric propulsion architectures (HEPAs), the corresponding powertrains, and power management strategies (PMS). In addition, a cost module and an aviation emission tracking function were developed and integrated into GENUS. GENUS was validated for investigating the design of HECAs by evaluating existing HECA concepts. Furthermore, three conventional turbofans were hybridized within GENUS to analyze the sensitivity of the performance of engines to the degree of hybridization (DoH) of power. The effects of hybridized engines on aircraft design were evaluated based on Boeing 737, demonstrating that at least 27.18% fuel saving, 9.97% energy saving, 12.40% cost saving, and 43.56% aviation emissions migration can be achieved. Finally, the potential directions of applying GENUS to explore the design space of HECA was discussed, which is useful to maximize the benefits of HECA.

2A16 aluminum alloys possess outstanding mechanical characteristics such as high specific strength and remarkable heat-resistance capacity. Figuring out the dynamic mechanical performance of 2A16 aluminum alloy over a large range of strain rates is beneficial to further broaden its application as crucial civil and military structures under extreme loading. This paper mainly focused on the mechanical properties and ballistic impact capacity of 2A16 aluminum alloy under different strain rates. Firstly, the quasi-static, intermediate strain rates and high strain rate mechanical experiments of 2A16 aluminum alloy specimens were conducted using an electronic universal testing machine, a high velocity hydraulic servotesting machine, and a split Hopkinson pressure bar (SHPB) at room temperature, which aims to acquire its dynamic mechanical properties at different strain rates and the fracture behaviors under different stress conditions. Then, the modified Johnson-Cook constitutive model and the Johnson-Cook fracture model were fitted based on the stress-strain relationships obtained from the tests. Finally, the ballistic impact experiments were carried out by a spherical nosed projectile striking on square 2A16 aluminum plates with the incident velocities ranging from $150–190\mathrm{m}/\mathrm{s}$. Numerical simulations based the nonlinear explicit finite-element (FE) code Ls-dyna were conducted to reproduce the ballistic impact tests. The ballistic limit velocity of 2A16 aluminum was obtained through the Recht-Ipson empirical model and the predicted results agreed well with the numerical results. The results obtained from this study can contribute to the design and optimization of 2A16 aluminum aerospace engineering structures with better impact protection capacity.

A detailed ultrasonic cycle fatigue study has been presented for aluminum alloy 7075-T6 (AA7075-T6) under fully reversed tension-compression loading to investigate the geometric sensitivity, frequency effects, size effects, surface roughness effects, and the corresponding failure mechanisms across different fatigue regimes. The dominating sources of life variability were identified using sensitivity studies conducted using finite-element analysis (FEA)–based modal and harmonic analyses and probability studies for typical ultrasonic fatigue specimens. In contrast to some studies of crack initiation for aluminum alloys under fatigue, subsurface crack initiations were observed for low stress amplitudes. The presence of both surface and subsurface crack initiations was strongly correlated to the surface conditions and loading conditions. Fatigue-fracture behavior was evaluated via detailed scanning electron microscopy (SEM) analysis of fracture surfaces, exhibiting unique features that are not observed under conventional fatigue testing of aluminum alloys.

The non-unique relationship between the density and quasi-static strength of Miura-ori metamaterials was explored for graded materials with respect to quasi-static and dynamic in-plane compression. A lower bound estimate of quasi-static strength and energy absorption was obtained using an analytical method by only considering the deformation mechanism of the rigid origami motion. Graded origami metamaterials were achieved by applying either a variation of the initial folding angle or a variation of the thicknesses of cell walls in the loading direction. It was shown that grading by a moderate increase of the initial folding angle does not notably contribute to the overall material strength and consequently to an improvement of the energy absorption efficiency of the metamaterial under quasi-static compression. Grading by wall thickness variation leads to a notable strength increase and moderately enhanced energy absorption. It is shown that the significant strength gradient leads to a violation of the rigid motion rule and the cells collapse sequentially, which has been validated by test results published in the literature. Different from quasi-static behavior, the response of the Miura-ori metamaterial to relatively high velocity impact is governed by the density gradient values, regardless of the grading technique. Furthermore, the differently graded profiles (positive or negative) affect the force-displacement histories but not the energy absorption efficiency of the examined metamaterials.

The cable-net structure is an important part of the mesh reflector antenna, and it determines the accuracy of the reflector. Traditional approaches for designing mesh reflector antennas usually treat the supporting truss as rigid. However, with an increase in the antenna aperture, the flexibility of the supporting truss becomes more obvious, and thus, its deformation is not negligible. Although many form-finding approaches that consider the elastic deformation of the supporting truss have been proposed to date, their purpose is to adapt to the deformation rather than to reduce the deformation from the perspective of the cable-net design. Therefore, by analyzing the stiffness characteristics of the supporting truss, this study first proposes a new cable-net form-finding method that ensures that the deformation of the supporting truss is uniform and minimal under the action forces of the cable-net structure. Then, by considering the incremental equilibrium equation of the cable-net structure, the stiffness equation of the mesh reflector antenna is established. Subsequently, a novel form-finding strategy is presented, which is embedded into an iterative approach for exactly designing the mesh reflector antenna that considers the flexibility of the supporting truss. Finally, by making a comparison with the existing approaches, it is shown that the method proposed in this study can find a set of relatively uniform tensions and high surface accuracy under the premise of having only a small deformation of the supporting truss.

Metal materials still dominate the separation shell of pyrotechnic separation devices in space launch vehicles. Moreover, research on carbon-fiber–reinforced polymer (CFRP) composites as a separation shell material has mainly focused on the exploration and test stages. Based on safety and environmental adaptability, the buffer substance in separation devices has a great influence on the cutting results of laminates. In this study, compared with the traditional separation device, a new separation device with a shaped charge and buffer substance was designed by finite-element analysis (FEA), and a test was carried out. The predesigned cutting strategies were divided into three categories: no buffer, expansion–deformation energy-absorbing (EDEA) material buffer, and low-density energy-absorbing (LDEA) material buffer as the control group. Based on the separation time of the laminate, delamination of the laminate, deformation of the protective cover, and environmental applicability of the device, the results show that the proposed separation device with LDEA as a buffer is the best, and the trend of delamination is consistent in FEA and the test. The LDEA buffer can effectively reduce the secondary damage of detonation products to the laminate by crushing and absorbing energy to improve the separation effect of the separation shell, providing guidance for the design of CFRP-based separation devices with shaped charges.

Aircrafts with high Mach speeds are exposed to severe thermal load, which affect the performance of aircraft components. Although several experimental studies have been performed on the mechanical behavior of aircraft structures subjected to high temperatures, the experimental research on dynamic characteristics of structures under thermal load is limited. In this work, a series of laboratory modal tests have been carried out on carbon fiber reinforced silicon carbide matrix (C/SiC) composite plates under various radiant-heating conditions. High temperatures are achieved using quartz lamps, and their dynamic responses are measured using a scanning laser vibrometer. The modal parameters are evaluated by PolyMAX at several static temperature distributions. The temperatures are acquired by both full-field noncontacting infrared thermography and contacting thermocouples. The flat plates are with both free and constrained boundary conditions and the high temperature modal survey are performed for two kinds of thickness. The stiffened plate with free boundary condition is further studied as a more practical structure. Both the changes of the modal frequency and modal shape as temperature rises are presented. The effects of the thermal loads on the modal characteristics are investigated by test. The results show that the thermal stresses have a much greater effect on the modal characteristics than the change of the material properties due to heating. The test results could provide technical material for the limited database of high-temperature modal testing results.

Parameters of the honeycomb core, such as cell size and foil thickness, as well as the material of the core, influence the ballistic performance of honeycomb-core sandwich panels (HCSPs) in the case of hypervelocity impact (HVI) by orbital debris. Two predictive models that account for this influence have been developed in this study: a dedicated ballistic limit equation (BLE) and an artificial neural network (ANN) trained to predict the outcomes of HVI on HCSP. BLE fitting and ANN training was conducted using a database composed of entries resulting from physical and numerical experiments. The new ballistic limit equation was based on the Whipple shield BLE, in which the standoff distance between the facesheets was replaced by a function of the honeycomb cell size, foil thickness, and yield strength of the HC material. The BLE demonstrated excellent accuracy in predicting the ballistic limits of HCSP when tested against a new set of simulation data, with the discrepancy ranging from 1.13% to 5.58% only. The ANN was developed using MATLAB’s version 2018b Deep Learning Toolbox framework and was trained utilizing the same HCSP HVI database as that employed for the BLE fitting. A comprehensive parametric study was conducted to optimize the ANN architecture, including such parameters as the activation function, the number of hidden layers, and the number of nodes per layer. The resulting ANN demonstrated a very good predictive accuracy when tested against a set of simulation data not previously used in the training of the network, with the discrepancy ranging from 0.67% to 7.27%. Both of the developed predictive models—the BLE and the ANN—can be recommended for use in the design of spacecraft orbital debris shielding involving honeycomb-core sandwich panels.

This paper proposes a fault-tolerant control allocation (FTCA) scheme for a flexible satellite. A novel control strategy is implemented, which fulfills the satellite mission and also decreases vibrations, saturation time of the actuators, and required energy. Avoiding spillover instability, an infinite-dimensional model of the flexible satellite is considered, which is one of the important benefits of the proposed control scheme over the previously presented FTCA methods. External disturbances, the uncertainty of moment of inertia, actuator fault and failure, imprecision in fault estimation, and control constraints are considered. The designed control system is comprised of two modules: the virtual control module that designs the virtual control law to stabilize the satellite and control vibrations without any in-domain actuators on panels, and a distribution control module that distributes the virtual control law among actuators based on their fault information and distance of bound of the control limit. The proposed virtual control law consists of an observer-based PD-like nominal control and adaptive control parts, and the internal reaction torque is estimated using a nonlinear observer. The closed-loop uniformly ultimately bounded (UUB) stability is achieved using Lyapunov criteria. A numerical example illustrates the effectiveness of the proposed approach regarding attitude stabilization and vibration control objectives.

Thermal modelling and analysis of CubeSats is needed to have control over its final platform performance. In this paper, we present the method and the thermal analysis results applied to an infrared spectrometer for a geostationary transfer orbit (GTO) mission, on board the 6U CubeSat named SpectroCube, developed and funded by the European Space Agency. Three challenges have been addressed: first, to maintain the correct temperature range for the spectrometer in a high-density platform with different surrounding thermal requirements; second, external radiation flux intensity from the Earth changes considerably along the orbit; and third, internal dissipation and external heat loads are significant with respect to the heat evacuation available area. Thermal analysis made in ESATAN-TMS 2019 has been used to improve and modify the layout of the payload mechanical design and to achieve the thermal control system requirements. Main mission parameters, orbit thermal characteristics, power dissipated and thermal requirements are presented. The results show that both active and passive thermal control are needed to maintain the payload’s components within their temperature ranges.

Structural parameters and inlet preswirl have great influences on the static and dynamic characteristics of honeycomb seals. In this paper, a multifrequency elliptical vortex dynamic model of a honeycomb seal was established by an unsteady dynamic grid technique. Based on verification of the numerical model, the effects of honeycomb cell size, axial length, and inlet preswirl on seal performance were investigated. Rotor–bearing–seal stability experiments were carried out to measure the logarithmic decrement rate of the rotor system under different rotational speeds, and the stability of the rotor system was further analyzed. The results showed that with increasing hole depth, leakage of the honeycomb seal increased initially due to the increasing airflow rate in response to vortex formation, and thereafter decreased, caused by the intense dissipation effect of turbulence. With increasing opposite-edge distance of core cell and decreasing axial length, the decreasing number of honeycomb cores on stator surfaces weakened the dissipation capacity of the turbulence, resulting in increases of leakage. Inlet preswirl had little effect on the leakage. However, it had a lower absolute value of tangential airflow excitation force and a lower effective damping coefficient under a higher inlet preswirl, indicating a lower dynamic characteristic of the honeycomb seal. Compared with other seals with different parameters, the honeycomb seal with structural parameters of B3H3L96 showed a higher effective damping coefficient under different inlet/outlet pressure ratios and different vortex frequencies and a higher logarithmic decrement rate under different rotational speeds, indicating a better stability of the rotor system.

The reconfiguration of a constellation with several faulty satellites concerns performance improvements in multiple fields, which can be regarded as a multiobjective optimization (MOO) problem. In the optimization design, it is inevitable to evaluate the constellation performance and providing the reconfiguration strategy thousands of times is time-consuming. To decrease the high computational expense, this paper proposes an accurate and efficient MOO method based on the kriging surrogate model, termed as the surrogate-based MOO (SBMOO) algorithm. A new hybrid refinement method is presented to select infilling samples for updating the surrogate model. Different from the orbital phasing maneuver, the low-thrust reconfiguration strategy is implemented to optimize the transfer trajectory with low fuel consumption, by changing the orbital inclination and right ascension of the ascending node. With the tradeoff between the constellation performance and the uniformity of fuel consumption, the MOO problem of constellation reconfiguration can be investigated and settled by the proposed SBMOO algorithm. The simulations confirm that the preferable constellation reconfigurations are achieved with a low computational expense for optimization and a low fuel cost for orbital transfer.

In comparison with conventional thin-cylindrical tethers, tape-shaped tethers have obvious advantages in orbital applications such as electron collection, satellite deorbit, and reliability. There are many differences between them not only in appearance but also in dynamics. Hence, this paper studies the dynamics of a tape-shaped flexible tethered satellite during free deployment. First, an approximate model for the system, in which the tape-shaped tether is divided into a series of rigid elements connected by massless spherical joints, was structured. The bending stiffness of the tether was analyzed, and the tension force along the tether length direction was ignored. In particular, three types of constraint equations for rigid elements were built to help identify tether deployment. Then, the kinetic friction force between the tape-shaped tether and deployment device, as well as the atmospheric drag/lift on the system, were discussed. Finally, numerical simulations demonstrated that the deployment dynamics of the tape-shaped tethered system are sensitive to the bending stiffness, friction force, and orbital altitude.

Visualization experiments are conducted in a water channel to investigate the wake vortex characteristics of a flat plate and convex and concave curved plates. Three parameters—vortex size ($S_v$), vortex length ($L_v$), and Strouhal number ($St$)—are investigated in this study to deduce the effect of plate curvature and orientation. These parameters are estimated for both the upper and lower vortices by keeping the chord length ($L_c$) fixed and changing the plate diameter (D). Various plate configurations are demonstrated by altering the $L_c/\mathrm{D}$ ratio from 0 to 1; $L_c/\mathrm{D}=0$, 6/13, 3/4, and 1. The Reynolds number (Re) based on chord length remains unchanged at 5,878 throughout the analysis. For each case of the $L_c/\mathrm{D}$ ratio, the angle of flow incidence of the plate ($\alpha$) is varied from 0° to 30° in steps of 5°. For the convex plate, the combined effect of curvature and orientation is found to enhance the vortex shedding frequency by 70.7%, whereas vortices shrink by 26.71%, and the vortex length is reduced by 25.38%. The manipulations achieved for concave plates reveal comparatively lesser enhancement in shedding frequency; however, concave surfaces are observed to be more suitable for stretching the vortices toward the downstream. The modifications thus achieved have significant practical relevance in various applications. A shedding mechanism that partially interrupts Gerrard’s mechanism is also found to operate with concave plate configurations.

A nonlinear progressive damage model was adopted to study the energy absorption mechanism of fabric composite channel section structures under axial quasi-static crushing loading. Based on continuous damage mechanics (CDM), intralayer and interlayer failure were initiated by the maximum stress and quadratic nominal stress criteria, respectively. The damage process of the material is described using the progressive damage evolution law based on the stiffness degradation method. The different failure modes exhibited by the composite channel section structure under different crushing displacements are analyzed in detail. The effects of geometric sizes and stacking sequences on the initial peak value, specific energy absorption (SEA), mean load, and failure mode are analyzed and discussed. The results show that thickness has a positive effect on the specific energy absorption and induces progressive failure of the structure. The initial peak force is a positive correlation function with respect to thickness and flange length. The flange length and stacking sequence have a significant effect on the crushing load response of the structure, and a reasonable stacking sequence can improve the crushing behavior of the structure.

Aeroengine noise, which is the main noise source of modern aircraft, has an inevitable negative effect on the health and life of people. There is a growing need to reduce aeroengine noise. Acoustic liners are crucial components of nacelles to damp aeroengine noise. However, the wide range of engine operating frequencies and narrow installation space of the aeroengine make the design of the traditional acoustic liner with large size and narrow absorption not meet demands. Therefore, the design of a broadband acoustic liner with a compact size is a hot issue to date. In this work, a new broadband metasurface acoustic liner design method is proposed based on the quadratic residual sequence (QRS) that is a typical sequence of Schroeder diffuser sequences. Single-degree-of-freedom (SDOF) liners are permutated by QRS to prove the feasibility of it for broadband sound absorption. In addition, the technique of metasurface is introduced to minimize the thickness of the acoustic liner. Numerical results show that the 50% absorption bandwidth of the QRS liner can be over 10 times than those with linear sequences (LS) in the range of 200 to 1,200 Hz. The thickness of acoustic liner reduces by 87.2% with the application of metasurface. The ratio of the new broadband metasurface acoustic liner thickness to the wavelength at the lowest absorption peak is less than 1.75%, confirming its operation in the deep subwavelength regime. The Fourier transform of the QRS sequence value has the property of constant amplitude, so it can be used to broaden the sound absorption of coupled liners. This work provides a new broadband acoustic liner and, more importantly, may motivate the application of digital sequences to solve broadband sound absorption problems.

Cable-network structures are an important part of mesh reflector antennas. The performance of antennas depends greatly on the surface accuracy and tension distribution. However, there are periodic temperature changes in the space environment where the mesh antenna is located. The traditional form-finding and optimization design methods can only guarantee good performance at room temperature, while active adjustment technology is limited by on-orbit measurement technology and control technology. Therefore, it is critical to carefully design the cable-network configuration to reduce the influence of space thermal loads. In this study, a thermal design optimization method for mesh reflector antennas was proposed by considering the deformation compatibility conditions. The length variation of the cable element under thermal loads was analyzed accurately. With the combination of the force density sensitivity matrix and temperature deformation equation, the force density increment equation of the whole cable net was established. By constraining the reflector nodes to the paraboloid and selecting the quadratic sum of the node thermal deformation as the objective function, we obtained a cable-network configuration with better surface shape stability than traditional design methods. Finally, a numerical example is presented to illustrate the effectiveness of the proposed method.

To improve the crashworthiness of the landing gear buffer, an oleo-pneumatic buffer combined with an expansion tube is proposed in this paper. A numerical analytical model based on deformation theory was used to acquire the buffer force of the combined-type buffer during crushing. A finite-element model (FEM) was established to simulate the crushing process of the landing gear expanding buffer at the crash speed. The buffer force–displacement curve was exported from the analysis results, and the buffer force in the stable period was compared with that obtained from the theoretical analytical model. The deviation, 10.99%, verified the effectiveness of the expansion tube FEM model. Buffer performance analysis models of oleo-pneumatic and metal expansion tube oleo-pneumatic combing buffers with high- and low-pressure chambers were established. A parametric model of the landing gear was established. The crashworthiness response of different landing gear buffers at crash speed was studied. The results proved the high buffer efficiency of the combined-type buffer and its superiority and feasibility.

An experimental study was conducted to investigate and compare the effects of beveled and double-beveled circular nozzles on supersonic jet screech at a nozzle pressure ratio of 5. In particular, near- and far-field microphone measurements and schlieren visualizations were utilized to look into selected acoustic and flow features associated with jet screech radiation. Results show that beveled nozzles eliminate jet screech by producing asymmetric shock structures and instability waves that are mismatched in phase and amplitude. In contrast, double-beveled nozzles produce symmetric shock structures and amplify screech intensity, even when jet mixing effects have been significantly enhanced. It is further observed that amplified jet screeches produced by double-beveled nozzles are highly unsteady and undergo nonperiodic and stochastic temporal variations. Last but not least, double-beveled nozzles also significantly impact screech peak noise locations and confer different changes along different measurement planes. The present study demonstrates that not all beveled-type nozzles are able to mitigate jet screech, with nonoptimal designs amplifying it instead.

Dual-aircraft platform (DAP) is a novel atmospheric satellite concept that features two gliderlike unmanned aircraft connected by a long, ultrathin cable, which uses the persistent levels of vertical wind shear in the lower stratosphere to sail without propulsion. This article presents a comparative design and analysis of three control strategies applied to a simplified analog of the DAP concept, which involves one aircraft connected by a thin cable to a steadily moving ground vehicle (GV). Similar to the DAP, the goal is to sustain flight without thrust (“sail”), and without being towed by the GV, using a sufficient persistent crosswind, despite uncertainties in the cable aerodynamics and disturbances associated with turbulence and changes in mean wind velocity. These control strategies, which include a linear nonadaptive architecture, a nonlinear dynamic inversion, and a ${\mathrm{L}}_1$ output feedback adaptation, are designed following an unorthodox control allocation. The robustness and performance of these control strategies are characterized using a set of metrics designed to capture control actuation energy and thrust impulse used to maintain sailing flight conditions. The results show that including an adaptive layer prevents instability of the vehicle under unforeseen extreme flight conditions and enables sailing with minimum use of propulsion.

Platelet injectors are quite different from other injectors because of the specificity of the manufacturing technology and spray characteristics. In this study, a splash platelet injector was designed to obtain its combustion characteristics. Gaseous oxygen and methane were used as the propellants. A three-dimensional (3D) model was used with a reduced mechanism involving 16 species and 41 reactions. The influence of the structural parameters of the splash platelet injector, that is, the nondimensional parameter ($\mathrm{\Delta }$), nozzle space ($D$), and scale factor ($\xi$), on combustion characteristics were analyzed. Results indicate that the temperature was nonuniform near the injector faceplate in all cases, and large corner recirculation zones were formed at the head of the combustion chamber. Combustion length ($L_{\mathrm{C}}$) decreased as $\mathrm{\Delta }$ increased, and the shortest combustion length was obtained when $\mathrm{\Delta }=3.5$. The combustion characteristics at $D=2.4\mathrm{mm}$ slightly differed from those at $D=3.6\mathrm{mm}$, and the combustion characteristics in the front part of the combustor at $D=4.8\mathrm{mm}$ were worse. The scale factor had little effect on component and temperature distribution.

A unique electrostatic precipitator combined with an ionic fan is proposed for air purification in a lunar module, and its feasibility was investigated. Dust contaminating the air in the habitat module is circulated by the ionic wind generated by the ionic fan, which comprises coaxial cylinder electrodes. A positive direct current (DC) voltage exceeding the corona discharge onset voltage is applied to the inner electrode, where the sharpened edge faces the outer cylinder electrode. The migration of charged molecules generated by the corona discharge forms an air stream, and simultaneously, dust particles are charged. Charged particles are introduced into the electrostatic precipitator, which comprises parallel-plate electrodes. A high DC voltage less than the onset voltage of the spark discharge is applied to the electrodes, and the introduced charged dust particles are trapped in the collection electrodes owing to the Coulomb force. It appears that dust is effectively cleaned by a compact system. An ozone filter is installed to decompose the ozone synthesized in the corona discharge field. Because the proposed system affords simplicity, a small configuration without mechanical moving components, lightweight, low power consumption, and silence, it is suitable for use in the lunar habitat module and pressurized rover. The proposed air-purification system would contribute to reduce the load on the mechanical filtration system.

The wind disturbance in flight induces measuring error of air data, including the true airspeed, angle of attack, and sideslip angle. To obtain the air data with better accuracy, a synthetic filtering system integrated with a customized wind model and an adaptive square root Kalman smoother (ASR-UKS) were proposed based on the flight data of civil aviation aircraft. The Gaussian process (GP) regression was first used to extract the random and rapid-changing turbulence that deteriorated the air-data measurements, and a parameterized turbulence model was built by autoregressive (AR) modeling. After this, a synthetic filtering system integrated with the recursive turbulence model was developed based on the inertial measurements in flight data. Finally, the ASR-UKS was designed to estimate the airspeed, angle of attack, and sideslip angle within the finite time span of flight data. Simulation results indicate that the customized wind model is able to recover in situ wind series experienced by the aircraft, and the synthetic filtering system is able to track the true value of air data and wind series well. Furthermore, the ASR-UKS, characterized by fully using the finite-length flight data and updating the noise covariance matrices adaptively, is able to reduce the estimation error and counteract the adverse effects of uncertain noise in flight data as well. A further test with real flight data indicates that the proposed method gives the refined estimation of airspeed, angle of attack, and sideslip angle in wind disturbance.

The ground effect influences the flow structure on a delta wing during landing and take-off processes. In this regard, comprehensive instantaneous velocity measurements and flow visualizations were carried out by particle image velocimetry and dye flow visualization techniques to reveal the ground effect on leading-edge vortex characteristics of a 40° swept delta wing. The flow behaviors on the delta wing under the impact of the ground were analyzed at two angles of attack, 8° and 11°, and the space between the ground and lower surface of the wing was nondimensionalized with the wing’s chord length. It was found that the presence of the ground caused premature leading-edge vortex breakdown due to the increasing adverse pressure gradient on the wing’s suction side along the chord direction. The ground effect caused an increase in peak value and distributions of turbulent kinetic energy on the wing surface that depended on the earlier leading-edge vortex bursting and complex and disorganized flow structures. The value of time-averaged vertical velocity was lower when the delta wing descended from the free-stream flow zone into the ground effect zone because of the blocking of fluid flow in the gap between the ground and pressure surface of the wing. Thus, it can be concluded that the ground effect is very influential on the change of vortical flow characteristics of nonslender delta wings.