Protection System Of Hypersonic Vehicles Research Articles

Mechanical properties and fracture behavior of ultrahigh temperature ceramics at ultrahigh temperatures

The mechanical properties of an ultrahigh temperature ceramic (UHTC) made up of ZrB2, SiC and graphite flake (ZrB2-SiC-G) are explored by ultrahigh-temperature uniaxial tension, combined with in-situ monitoring of the fracture behavior. The results suggest an inconsistent property degradation of ZrB2-SiC-G at 1200–2000 °C. Significant degradation in tensile modulus is observed at 1400 °C, which differs from the strength degradation that mainly occurs at 1800 °C. Moreover, ZrB2-SiC-G is elastically fractured at 1200 °C, 1400 °C and 1600 °C, which is interrupted at 1800 °C and 2000 °C. At the temperature range, severe plasticity takes place, which reduces the bearing capacity of this material. The brittle-to-ductile transition is well ascertained by in-situ observation of the fracture behavior at 1200–2000 °C. Finally, the constitutive relation of modulus and strength is built by coupling the effect of temperature. It can be integrated in finite element models and is useful for structural design of UHTC based thermal protection systems of hypersonic vehicles.

Thermal Protection Mechanism of a Novel Adjustable Non-Ablative Thermal Protection System for Hypersonic Vehicles

In order to improve the thermal protection performance of the active thermal protection system (TPS) based on the spike and jet, an adjustable non-ablative thermal protection system, of which the spike can be rotated in the direction of the free stream, is proposed in this paper. The thermal protection mechanism and the optimal installation angle are analyzed by adopting the numerical method. The results show that the angle of attack has great influence on the peak heat flux of hypersonic vehicles, the dangerous point is on the windward side of the vehicles at the non-zero angle of attack. With the increase in angle of attack, the heat flux of the windward side of the vehicles rises rapidly, leading to the decrease in the global thermal protection efficiency. The adjustable non-ablative TPS in this paper greatly reduces the aeroheating of the windward side through the installation angle between the spike and nose cone, thus improving the global thermal protection efficiency. The optimal installation angle can be obtained by numerical or experimental methods in engineering design, and the difference between the angle of attack and the optimal installation angle is about 2.4° for the proposed model. Therefore, the installation angle can be automatically adjusted based on the angle of attack to achieve the highest thermal protection efficiency.

In-situ formed intergranular TiB2 into lightweight SiC(rGO) composite PDCs enable elevated temperature resistance for aerospace components

Strengthening interface bonding for superior mechanical/ablation performances of SiC-based aerospace vehicle components remains a major challenge. Attractively, polycarbosilane-vinyltriethoxysilane-graphene oxide with addition of TiN/B (PVG(TiN, B)) were successfully synthesized for the first time. An ingenious route via re-pyrolyzing ball-milling-induced SiC(rGO, TiB2)p fillers/PVG(TiN, B) precursors blends was introduced to prepare lightweight SiC(rGO, TiB2) composite polymer-derived ceramics (PDCs). Interestingly, both SiC(rGO, TiB2)p and PVG(TiN, B) pyrolysis products, composed of β-SiC/SiOxCy/Cfree(rGO, TiB2), are tightly coupled by each other owing to plentiful Si-dangling bonds. In-situ formed intergranular TiB2/B4C, well compatible with amorphous ceramic network, can prevent β-SiC grain growth, strengthen interface bonding, and even hinder further crack propagation along the grain boundaries. Particularly, samples re-pyrolyzed at 1300 °C possess unique combination of good hardness (5.44 GPa), excellent fracture toughness (4.70 MPa·m1/2), high flexural strength (41.90 MPa) and outstanding compressive strength (126.33 MPa). Improved high-temperature and ablation resistance gives them distinct advantages of interlocked microstructure under exposure of butane flame. As demonstrated, SiC(rGO, TiB2) composite PDCs were developed into porous ceramics with good thermal insulation, focusing on manufacturing large-size bulk PDCs for thermal protection system of hypersonic vehicles.

Transient Heat Transfer Analysis on Composite Solids for Hypersonic Flow Applications

Surface heating rates have the importance in high speed flow due to viscous or aerodynamic heating which leads to enormous rise in surface temperature. Prediction of exact heat transfer rates is essential for design of protection systems for aerodynamic bodies aimed. For the thermal protection system, the aerodynamic Surfaces are generally configured with multiple solids. Hence present study is planned to develop the conjugate heat transfer (CHT) solver for composite solids. A CHT solver is in hypersonic flow environment. Finite volume framework and explicit time stepping have been implemented for both the compressible Navier-Stokes solver and conduction solver. Loose coupling has been established between the above mentioned fluid and solid domain solvers. The following observations were made in the CHT simulations. In the case of hypersonic flows over finite thickness flat plate, considerable difference in surface heat transfer rate has been noticed along the stream wise direction at the solid-fluid interface and also the Effect of wall material on heat diffusion for hypersonic application has been analyzed using loosely coupled CHT solver. The CHT solver has also been implemented for hypersonic flow over composite cylinder. Necessity of insulating material in the region of stagnation point has been realized as the outcome of these studies.
 HIGHLIGHTS
 
 Accurate prediction of Convective heating rates is essential for the design of thermal protection system for hypersonic vehicles
 In The thermal protection system, the aerodynamic surfaces are generally configured with multiple solids. Hence the present study is planned to develop the conjugate heat transfer (CHT) solver for composite solids
 The CHT solver has been implemented for hypersonic flow over composite flat plate and cylinder. It has been observed flows over finite thickness flat plate, a considerable difference in surface heat transfer rate has been noticed along the stream wise direction at the solid-fluid interface and the necessity of insulating material in the region of stagnation point has been realized as the outcome of these studies
 
 GRAPHICAL ABSTRACT

Transitional wave configurations between Type III and Type IV oblique-shock/bow-shock interactions

The interactions of oblique/bow shock waves are the key flow phenomena restricting the design and aerothermodynamic performance of high-speed vehicles. Type III and Type IV Shock/Shock Interactions(SSIs) have been extensively investigated, as such interactions can induce abnormal aerodynamic heating problems in hypersonic flows of vehicles. The transition process between these two distinct types of shock/shock interactions remains unclear. In the present study, a subclass of shock/shock interaction configuration is revealed and defined as Type IIIa. Type IIIa interaction can induce much more severe aerodynamic heating than a Type IV interaction which was ever reported to be the most serious in literature. The intense aerodynamic heating observed in this configuration highlights a new design point for the thermal protection system of hypersonic vehicles. A secondary Mach interaction between shock waves in the supersonic flow path of a Type III configuration is demonstrated to be the primary mechanism for such a subclass of shock/shock interaction configuration.

Double Peak-Heating in Hypersonic Transitional Shock-Wave/Boundary-Layer Interactions

Estimating heat-flux peak location and magnitude is important to efficiently design thermal protection systems of hypersonic vehicles, which are characterized by strict low-weight requirements. This work is a numerical study of hypersonic shock-wave/boundary-layer interaction experiments on flat plates and compression corners. In all the cases presented herein, shock-induced transition resulted in unusual heat-flux levels and distributions. Fully laminar and Reynolds-averaged Navier–Stokes simulations failed in predicting the heat-flux trends; however, by artificially triggering transition at specific location it was possible to enhance the agreement with the experiment and isolate the beginning of transition with reasonable precision.

Numerical Comparison of Transpiration Cooling Designs Using Real Gas Effects and Approximate Gas Model

In the severe high-temperature environment caused by aerodynamic heating, the vibrational excitation, dissociation and ionization of gas may successively occur, which are known as real gas effects. Under the real gas effects, the thermodynamic properties of gas vary drastically and significantly influence the performances of the active thermal protection system of hypersonic vehicles, especially in the case with coolant outflow, for example transpiration cooling. This paper numerically investigates the transpiration cooling performance with the consideration of the interaction between coolant outflow and hypersonic flow under the real gas effects. The mathematical models and coupled numerical strategy are firstly validated by experimental data, then the influences of real gas effects on the transpiration cooling of a wedged leading edge (WLE) are studied under a flight Mach number range from 8 to 12 and a flight height of 40 km. The analysis and discussions of the numerical results reveal some important phenomena and demonstrate the need to consider real gas effects.

Insights into adsorption, diffusion, and reactions of atomic nitrogen on a highly oriented pyrolytic graphite surface

To gain insight into the nitrogen-related gas-surface reaction dynamics on carbon-based thermal protection systems of hypersonic vehicles, we have investigated the adsorption, diffusion, and reactions of atomic nitrogen, N(4S), on the (0001) face of graphite using periodic density functional theory with a dispersion corrected functional. The atomic nitrogen is found to bind with pristine graphite at a bridge site, with a barrier of 0.88 eV for diffusing to an adjacent bridge site. Its adsorption energy at defect sites is significantly higher, while that between graphene layers is lower. The formation of N2 via Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms was also investigated. In the LH pathway, the recombinative desorption of N2 proceeds via a transition state with a relatively low barrier (0.53 eV). In addition, there is a metastable surface species, which is capable of trapping the nascent N2 at low surface temperatures as a result of the large energy disposal into the N-N vibration. The desorbed N2 is highly excited in both of its translational and vibrational degrees of freedom. The ER reaction is direct and fast, and it also leads to translationally and internally excited N2. Finally, the formation of CN from a defect site is calculated to be endoergic by 2.75 eV. These results are used to rationalize the results of recent molecular beam experiments.

Influence of mass ratios between SiC particles and chopped carbon fibers on properties of C/SiC/SiO2 porous ceramics

Transpiration cooling in the thermal protection system of hypersonic vehicles still remains a challenge due to the lack of lightweight porous ceramic with excellent permeability. C/SiC/SiO2 porous ceramics with low density and good permeability are fabricated by optimized grinding-mould pressing-sintering process. The influences of different mass ratios between SiC particles and chopped carbon fibers on the microscopic structure, mechanical performance, pore-size distribution and permeability of the porous ceramics are studied systematically. C/SiC/SiO2 porous ceramics with density of 1.092～1.327 g/cm3, compressive strength of 1.55～15.7 MPa, permeability of 5.903 × 10–8～13.434 × 10-8 mm2, as well as uniform microstructure and pore-size distribution have been obtained with the increasing of the mass ratios. Notably, the densities and compressive strengths of C/SiC/SiO2 porous ceramics improve gradually but their permeabilities decrease with the increasing of mass ratio between SiC particles and chopped carbon fibers from 0.3:1 to 1:1. The porous ceramics fabricated by optimized processing method can have a potential application in the transpiration cooling.

Numerical Investigation of the Transient Nature of a Laminar Separation Bubble in Hypersonic Flow

Shock-wave/boundary-layer interaction is a prime research topic in the design of hypersonic vehicles. For the proper designing of hypersonic vehicles, especially, their thermal protection systems, it is necessary to understand the time-dependent behavior of the wall properties and the corresponding pressure and thermal loads. Hence investigation is carried out to understand the unsteady nature of shock-induced laminar boundary layer separation for a simple canonical configuration of a two-dimensional ramp. A density-based non-reactive Navier-Stokes solver named rhoCentralFoam in openFOAM is employed in the present investigation. The detailed physics of laminar boundary layer separation in hypersonic flow is investigated through timewise behavior of the streamline patterns and the surface properties, such as the pressure, heat flux, and friction coefficients. It is found that at the onset of fluid flow it is its inviscid characteristics that are predominant and there is occurrence of very small separation bubble. The separation bubble grows, as the involvement of viscous characteristics increases gradually, and ultimately it attains a steady state. Because of separated boundary layer the heat flux and skin friction coefficients are found to follow the diffused V and deformed W shapes, respectively. The peaks of pressure and thermal loads are found to exist in the vicinity of the reattachment region. These peaks are higher in the initial stage of the process and attain steady state eventually. The high pressure and thermal loads may cause structural damage to the vehicle and hence their correct prediction is necessary. Thus, the current investigation is helpful in the design of thermal protection systems of hypersonic vehicles.

Bending behavior of lightweight C/SiC pyramidal lattice core sandwich panels

Due to the excellent mechanical and chemical properties at ultra-high temperature, ceramic matrix composite structures have potential applications for thermal protection systems of hypersonic vehicles. This paper presented a PIP method to fabricate C/SiC pyramidal lattice core sandwich panels (LCSPs). Their bending behaviors with different core angles were experimentally studied firstly. Then the critical failure loads of different failure modes, including facesheet crushing or wrinkling, core member crushing, core shear failure and interlayer delamination, were theoretically established to construct the failure mechanism maps. The influence of geometric parameters, such as the length and the core angle of the core strut, and the thickness of the facesheet, on the failure mode was also analyzed. In addition, further failure process under bending load was investigated by finite element analysis (FEA) method. Elastic-damage constitutive model and cohesive element were applied to modeling the behavior of C/SiC composite and interlayer delamination between the sheet of the core and the facesheet. Theoretical and FEA results agreed well with experimental data. This work is believed to be helpful to understand the bending mechanism C/SiC pyramidal LCSPs.

Protective effect of pyrolysis gases combustion against surface ablation under different Mach numbers

Whether pyrolysis gases combustion has effect on surface ablation of charring material is a key issue in the optimization design of thermal protection system for hypersonic vehicles. The coupled method considering combustion of pyrolysis gases in shock layer is presented, realized in MATLAB and validated by comparison with the arcjet experiments. Relationship between surface ablation and mole fraction of oxygen, mass injection rate of pyrolysis gases and surface temperature of charring material under different Mach numbers are predicted by this coupled method. Numerical results indicate that the protective effect of pyrolysis gases combustion on surface ablation is more and more obvious with increase of Mach number. This study is helpful to the optimization of thermal protection system for hypersonic vehicles.

Six sigma robust design optimization for thermal protection system of hypersonic vehicles based on successive response surface method

Lightweight design is important for the Thermal Protection System (TPS) of hypersonic vehicles in that it protects the inner structure from severe heating environment. However, due to the existence of uncertainties in material properties and geometry, it is imperative to incorporate uncertainty analysis into the design optimization to obtain reliable results. In this paper, a six sigma robust design optimization based on Successive Response Surface Method (SRSM) is established for the TPS to improve the reliability and robustness with considering the uncertainties. The uncertain parameters related to material properties and thicknesses of insulation layers are considered and characterized by random variables following normal distributions. By employing SRSM, the values of objective function and constraints are approximated by the response surfaces to reduce computational cost. The optimization is an iterative process with response surfaces updating to find the true optimal solution. The optimization of the nose cone of hypersonic vehicle cabin is provided as an example to illustrate the feasibility and effectiveness of the proposed method.

Experimental investigation of liquid film cooling in hypersonic flow

Film cooling is generally considered as a promising active cooling technology for developing thermal protection systems of hypersonic vehicles; however, most of experimental and numerical studies of film cooling mainly concentrated on gaseous film cooling. Since the phase change of liquid coolants can absorb a large amount of latent heat, liquid film cooling should have more potential advantages, especially for severe environments accompanied by hypersonic flight. To address this issue, the film cooling using water as a coolant was experimentally investigated in hypersonic flow. Experiments were carried out in a detonation tunnel, at a hypersonic Mach number of 6 using a 25° apex-angle wedge. Characteristic physical quantities, such as surface temperature rise, shock wave structure, film thickness, and cover area, are measured by thermocouples, schlieren, and a specially devised liquid film measurement system. The experimental results verify that the liquid film cooling is feasible in hypersonic flow and also indicate that it is featured with maintaining aerodynamic performances due to the weak effect on the main flow caused by coolant injection. Inspired by these results, liquid film flow characteristics and its influencing factors including mass flow rate, dynamic pressure, coolant injection direction, and surface tension are investigated to guide the design of a thermal protection system.

Aerothermoelastic Load Calculation for Hypersonic Vehicles Based on Multiphysics Coupled Analysis

To fulfill the design objective of a structure and thermal protection system, accurate load environment prediction is very important, so we present a high-fidelity aerothermoelastic load calculation method based on a partitioned computational fluid dynamics/computational structural dynamics/computational thermal dynamics (CFD/CSD/CTD) coupling analysis. For the data transformation between the CFD/CSD/CTD systems, finite element interpolation (FEI) is explored, and a shape-preserving grid deformation strategy is achieved via radical basis functions (RBFs). Numerical results are presented for validation of the proposed CFD/CSD/CTD coupling analysis. First, a simply supported panel in hypersonic flow is investigated for results comparison of the proposed coupling method and previous work. Second, a hypersonic forebody is investigated to explore the aerothermoelastic effects while considering the feedback between deformation and aerodynamic heating. The results show that the CFD/CSD/CTD coupling method is accurate for analysis of aerothermoelasticity. In addition, considering the aerothermoelastic effect, the shear force and bending movement increase with time before 900s and decrease after 900s, and at 900s increased percentages of 5.7% and 4.1% are observed, respectively. Therefore, it is necessary to adopt high-fidelity CFD/CSD/CTD coupling in the design of a structure and thermal protection system for hypersonic vehicles.

Large-eddy simulation of transpiration cooling in turbulent channel with porous wall

Transpiration cooling is an excellent and effective cooling technology and is one of the optional technologies for thermal protection systems of hypersonic vehicles. This paper presents a numerical investigation on transpiration cooling of a turbulence channel, the behaviors of vorticities in hot mainstream are investigated by using large-eddy simulation (LES) that incorporate the Darcy-Forchheimer model and the local non-equilibrium thermal model. The instability of the boundary layer obtained in the experiment is simulated and analyzed by numerical simulation. Both experiments and simulations can observe that the coolant and the mainstreams form the jelly roll when the coolant is injected into the hot mainstream, and this phenomenon is inferred to be Kelvin-Helmholtz instability. Periodic vortex behavior was observed experimentally and numerically, each cycle is 1.25 ms when the injection rate is 1%, and there are three processes of vortex generation, development and fragmentation in a complete cycle.

Numerical investigation of heat flux distribution in a deep gap based on chemical equilibrium

PurposeThe purpose of this paper is to perform the simulation to explore the gap flow field under a hypersonic air flow. Thermal protection systems of hypersonic vehicles generally consist of thermal insulation tiles, and gaps between these tiles probably cause a severe local aerodynamic thermal effect.Design/methodology/approachThe discretizations of convection flux term and temporal term in the governing equation with chemical equilibrium, respectively, take AUSM+-up flux-vector splitting scheme and the implicit lower-upper symmetric Gauss–Seidel method. Based on these, the flow field in a deep gap is simulated by means of the computer codes that the authors have written.FindingsThe numerical results show that the heat flux distribution in a gap has a good agreement with experimental results. Importantly, the distribution of heat flux is “U” shaped and the maximum of the heat flux occurs at the windward corner of a gap.Originality/valueTo explore the gap flow field under a hypersonic air flow, which is a chemically reacting, all speed and viscous flow, a novel model with an equivalent ratio of specific heats is presented. The investigation in this paper has a guide for the design of the thermal protection system in hypersonic vehicles.

Reactive Spark Plasma Sintering and Mechanical Properties of Zirconium Diboride–Titanium Diboride Ultrahigh Temperature Ceramic Solid Solutions

Ultrahigh temperature ceramics (UHTCs) such as diborides of zirconium, hafnium tantalum and their composites are considered to be the candidate materials for thermal protection systems of hypersonic vehicles due to their exceptional combination of physical, chemical and mechanical properties. A composite of ZrB2-TiB2 is expected to have better properties. In this study, an attempt has been made to fabricate ZrB2-TiB2 ceramics using mechanically activated elemental powders followed by reactive spark plasma sintering (RSPS) at 1400 °C. Microstructure and phase analysis was carried out using X-ray diffractometer (XRD) and electron microscopy to understand microstructure evolution. Fracture toughness and hardness were evaluated using indentation methods. Nanoindentation was used to measure elastic modulus. Compressive strength of the composites has been reported.

Dynamic response of acoustically excited plates resting on elastic foundations in thermal environments

In order to ensure integrity of thermal protection system for hypersonic vehicles, the random dynamic response induced by the combination of the thermal and acoustic loadings has been investigated for a composite thin skin panel resting on a two-parameter elastic foundation. A theoretical model is developed based on the first four symmetric plate modes through Galerkin method. The solutions of a set of the high-order coupled ODEs have been validated by comparison of the postbuckling deflection with the results obtained from FEM postbuckling analysis. A dynamic response evolution parameter deduced from the primary-mode modal equation is used to characterize a transition from linear vibration to fully nonlinear dynamic snap-through. The study demonstrates the combination of acoustic excitation, thermal effect and structural stiffness governs the dynamic response evolution. As the elastic foundation stiffness increases, the buckling temperature increases and the postbuckling deflection decreases, which promote the nonlinear dynamic snap-through response remarkably with reducing snap-through amplitude.

A new surface catalytic model for silica-based thermal protection material for hypersonic vehicles

Silica-based materials are widely employed in the thermal protection system for hypersonic vehicles, and the investigation of their catalytic characteristics is crucially important for accurate aerothermal heating prediction. By analyzing the disadvantages of Norman’s high and low temperature models, this paper combines the two models and proposes an eight-reaction combined surface catalytic model to describe the catalysis between oxygen and silica surface. Given proper evaluation of the parameters according to many references, the recombination coefficient obtained shows good agreement with experimental data. The catalytic mechanisms between oxygen and silica surface are then analyzed. Results show that with the increase of the wall temperature, the dominant reaction contributing to catalytic coefficient varies from Langmuir–Hinshelwood (LH) recombination (TW<620K) to Eley–Rideal (ER) replacement (620K<TW<1350K), and then to O2 desorption (TW>1350K). The surface coverage of chemisorption areas varies evidently with the dominant reactions in the high temperature (HT) range, while the surface coverage of physisorption areas varies within quite low temperature (LT) range (TW<250K). Recommended evaluation of partial parameters is also given.