Hypersonic Aircraft Research Articles

Discussion on the static-thermal test technology of aircraft

During the high-speed flight of the aircraft, the cabin body will bear aerodynamic loads, engine thrust loads, structural and equipment component mass inertial loads. At the same time, aerodynamic thermal loads will be generated due to high speed flight. With the development of hypersonic aircraft technology, the demand for multi-field coupling test is more and more common. Therefore, it is necessary to carry out the technical verification of the mechanics and thermal composite test on the ground to obtain the structural characteristics. In this paper, a certain type of aircraft cabin as the research object, carried out the research on the combined mechanical and thermal test technology. The results of this paper show that the displacement response of the cabin under the combined action of force and thermal load is consistent with the change trend of the force loading curve, and the force load has obvious influence on the displacement response of the cabin. The strain response is consistent with the trend of temperature curve, and thermal load has obvious influence on cabin deformation. Through this study, we can obtain the static-thermal test technology method, and provide the technical basis for the development of similar test technology.

Radar absorption characteristics of ceramic oxide fiber/aluminosilicate-sendust composite structure at ultrahigh temperatures

This study proposes a novel radar-absorption structure (RAS) composed of Nextel 601 fiber and a geopolymer-based aluminosilicate matrix for withstanding high temperatures and providing effective electromagnetic (EM) absorption performance. To measure its complex permittivity and permeability in the X-band frequency range, we dispersed flake-type sendust particles with different sizes and contents in the matrix. The complex permittivity increased with increasing size and content of the sendust particles, which was attributed to the increase in dielectric polarizations and electrical conductivity of the composites. Furthermore, the simulation studies of the designed RAS showed excellent EM absorption performance, with a thickness of 4.25 mm, revealed a maximum return loss (RLmax) of −24 dB with a broad absorption bandwidth (BW @ −10 dB) of 8.3 GHz at room temperature (RT). Similarly, the measurement of fabricated RAS exhibited a RLmax of −19.2 dB and a broad absorption BW of 5.45 GHz at RT in the S- and X-band frequency range (6.95–12.4 GHz). However, in X-band measurements conducted at elevated temperatures, the RLmax values declined, reaching −8.04 dB at 9.87 GHz and −10.97 dB at 9.45 GHz observed at 900 °C and 1200 °C, respectively. This decrease in EM absorption performance can be ascribed to variations in impedance matching conditions arising from factors such as dielectric and magnetic losses, as well as shifts in frequency. In addition, the significant RCS reduction of the proposed RAS indicates its applicability to hypersonic aircraft.

Analysis of electromagnetic waves reflected by re-entry plasma sheath based on CSO-FDTD

A transmission model of terahertz waves in the plasma sheath is established based on a cascaded finite time domain difference method and analyzed the transmission characteristics of electromagnetic waves under the action of an external magnetic field and collision frequency. The flow field around the hypersonic aircraft is simulated and the characteristics of the flow field as the altitude changes of the aircraft are analyzed based on the flow field distribution of the RAM-C (Rapid Attenuation Measurement) vehicle. The results show the transmission characteristics of terahertz waves in plasma that will be affected by flight height, plasma parameters, external magnetic field, and collision frequency. In addition, under the action of an external magnetic field and the different collision frequency, the transmission characteristics of the left-handed terahertz wave will be improved. The application of the magnetic field will introduce an absorption peak in the right-handed terahertz wave, and it will move to the high frequency direction with the increase of the magnetic induction intensity.

Advanced Hypersonic Transportation Perspectives

High-speed transportation design concepts are examined for advanced civil aviation and space transportation applications. The design concept of transatmospheric vehicles, flying directly from earth to orbit, will enable launching and recovery of small telecommunication and remote sensing satellites, harvesting solar energy from space, and space tourism.Commonality of flight regimes in atmospheric flight, the similarity of fuels, propulsion technology, aerodynamic configuration design, and airframe structure materials used in these high-speed flight regimes for air and space transportation are discussed in detail.A single, Integrated Hypersonic Transport Programme, is recommended, based on small size, low risk, and low cost vehicles. A dual fuel, kerosene-hydrogen system meets the needs of such an Integrated Hypersonic Transportation Programme, with kerosene for take-off, powered landing and low speed ascent/descent flight. Hydrogen is used for high-speed cruise flight. India would greatly benefit by an Integrated Hypersonics Transportation Programme, with leading institutions like ISRO, NAL and ADA working together to jointly study, design and build a strong technology base for small, unmanned hypersonic flight demonstrators. This project could then lead on, safely and economically, to hypersonic Executive Jet aircraft, and small fully Reusable Trans-Atmospheric Vehicles for direct ascent of the hypersonic aerospacecraft to earth orbit.

Deep-Learning Strategy Based on Convolutional Neural Network for Wall Heat Flux Prediction

Aerodynamic thermal prediction plays an important role in the design of hypersonic aircraft, especially in the design of the aircraft’s thermal protection system. The main challenges of the aerothermal prediction lie in the slow converging speed and the strict requirements of the computational grid. In this paper, a convolutional-neural-network-based hybrid-features deep-learning strategy is constructed to efficiently predict aerodynamic heating, which is named the convolutional neural network/hybrid-feature method. The hybrid features of this strategy consist of the normal distribution of physical quantities from the wall and the flow parameters at the extreme temperature point. The strategy, which extends through the multilayer perceptron regression layer method, constructs the relationship between the hybrid features and the wall heat flux to obtain a high-precision model trained by the flowfield data without gradient convergence. It is demonstrated that the model has a better inflow generalization ability to predict wall heat flux with different inflow conditions and angles of attack by zero-angle-of-attack training data, which has great potential in aircraft thermal protection system design and shape optimization.

Thermal insulation characteristics of high-temperature heat seals for hypersonic aero-engines

The high-temperature baseline sealing thermal protection technology is of great significance to realizing hypersonic aero-engines and aircraft. Based on the fact that there are few studies on the high-temperature baseline heat sealing in the ultra-high temperature environment (above 1000 °C), the paper establishes a simulation model to analyze the influence of different characteristic parameters on the thermal protection performance of the heat seal at ultra-high temperature and carried out experiments. Verification, simulation, and experiment error are less than 6%. The research results show that the aluminum silicate fiber has the best thermal insulation effect in the material of the inner thermal insulation layer, and the temperature can be lowered by more than 900 °C under an environment of 1200 °C. It is used to prepare heat seals. In addition, the filling density and thickness of the inner thermal insulation layer have little influence on the thermal insulation effect, and the influence coefficient does not exceed 5%. In the test of the degree of degradation of the thermal insulation performance of the heat seal, it is found that it does not exceed 5%, which meets the requirements for use. This paper further promotes the development of high-temperature thermal protection technology. It can also provide a corresponding technical basis for developing supersonic aero-engines.

Fabrication of high aspect ratio boron nitride nanotube–ZrB₂ composites and the effect of dispersion

AbstractUltrahigh‐temperature ceramics (UHTCs) exhibit remarkable hardness and resistance to oxidative ablation, making them suitable for use in hypersonic environments, such as hypersonic aircraft and space shuttles. However, their low fracture toughness limits their applications as engineering materials. In this study, zirconium diboride, an extremely hard and oxidation‐resistant UHTC, was sintered with high aspect ratio boron nitride nanotubes (BNNTs) to improve the fracture toughness of UHTC. Although the high aspect ratio BNNTs tend to become entangled and are inefficient in improving the fracture toughness of the composite, the use of plasma functionalization can effectively disperse the BNNTs in UHTC, resulting in the increase in the fracture toughness of the UHTC composite.

Dynamic responses of a conceptual two-dimensional airfoil in hypersonic flows with random perturbations

This paper investigates a conceptual pitch–plunge airfoil in hypersonic flows with both structural and aerodynamic nonlinearity, meanwhile the effects of irregular fluctuations in the flow and external random loads modeled as a Gaussian white noise are considered. The dynamic responses of the airfoil model especially the bifurcation behaviors are analyzed via the harmonic balance method for the deterministic case. We found the airfoil system undergo both subcritical and supercritical Hopf bifurcations. Subsequently, the effects of stochasticity on the dynamical behaviors of the hypersonic airfoil system are explored in the regimes of subcritical and supercritical Hopf bifurcations depending on the system parameters. Several interesting phenomena are triggered under random perturbations such as intermittency and stochastic transition between the low-amplitude oscillation state and the undesirable high-amplitude oscillation state. These dynamics are further characterized via the probability density function and time history. This work will provide new insights into the safety and reliability design of hypersonic aircraft.

Conditions for simulation of transonic flutter of aerodynamic control surfaces of supersonic aircraft in wind tunnels

The transonic flutter of the aerodynamic control surfaces of supersonic and hypersonic aircraft refers to those phenomena of dynamic aeroelasticity, the assessment of whichin a flight experiment is dangerous. Since there is still no universally accepted mathematical model of the occurrence of this phenomenon, tests of dynamic-like models in wind tunnels can be classified as basic and safe methods for evaluating the characteristics of transonic flutter. Therefore, the substantiation of the conditions for modeling transonic flutter, which allow the transfer of the results of blowing of dynamic-like models in wind tunnels to full-scale aircraft designs, remains an actual scientific problem.The article proposes one of the possible approaches to justifying the conditions for modeling transonic flutter of aerodynamic control surfaces in wind tunnels, which is based on the analysis of a nonlinear mathematical model of the occurrence of this phenomenon.Based on the analysis of this mathematical model, it was determined that, in addition to the conditions for modeling transonic flutter in wind tunnels, which are due to the geometric similarity of the system "carrying aerodynamic surface – aerodynamic control surface", additional conditions for modeling this phenomenon should be the following dimensionless quantities of nature and model:- amplitudes of oscillations of nature and model;- numbers M at which transonic flutter occurs;- logarithmic decrements of oscillations of aerodynamic control surfaces;- Strouhal numbers;- ratio of gas density to material density of aerodynamic control surfaces;- the adiabatic index k=1.405, that is, the working body in the wind tunnel should be air.Blowing of dynamically similar models must be carried out in wind tunnels of a continuous type, subject to conditions (s-1).

Green hydrogen as an environmentally-friendly power source

Hydrogen is the most plentiful chemical element in the visible universe. The mass composition of the visible universe is approximately 74% hydrogen, 24% helium, 1% oxygen, and the rest of all other chemical elements is about 1%. Hydrogen has the symbol H and the atomic number 1. It is placed in the first position in Mendeleev's periodic table of elements, in the upper left corner. It is an easily flammable, colorless, tasteless, odorless gas, and in nature, it is found mainly in the form of the diatomic molecule, H 2. With an atomic mass unit of 1.00794, hydrogen is the lightest chemical element. Etymologically, the word hydrogen is a combination of two Greek words hydor and gennan meaning: water producer. Hydrogen (H 2) has a very good calorific value per mass unit 143 MJ/kg which is 3.33 times more than the calorific value of kerosene or diesel fuel. Green hydrogen (clean hydrogen or renewable hydrogen) is produced by electrolysis of water (splitting of water into hydrogen and oxygen) using electricity from renewable sources such as solar energy, wind energy, seawater waves energy, or tidal power. Green hydrogen is an environmentally-friendly power source (no harmful gases). This paper presents recent documentary research by the authors on green hydrogen as an environmentally-friendly power source: for space rocket launches and for hydrogen fuel cells used in the space shuttle as electrical power generators and drinking water generators from launch to return from the space mission; as fuel for a modified turboprop engine (Rolls-Royce and easyJet); as fuel for the European Destinus aircraft using the Jungfrau technology system for a planned hypersonic aircraft using a modified commercial afterburning engine; as fuel for modified gas turbine engines and hydrogen fuel cells to supply electrical power to supplement the gas turbine for the Airbus ZEROe aircraft, etc.

Decentralized Adaptive Quantized Dynamic Surface Control for a Class of Flexible Hypersonic Flight Vehicles with Input Quantization

A control strategy for a certain class of hypersonic flight aircraft dynamic models with unknown parameters is proposed in this article. The strategy is adaptive dynamic surface input quantization control. To address the issues in conventional inversion control, a first-order low-pass filter and an adaptive parameter minimum learning law are introduced in the control system design process. This method has the following features: (1) it solves the problem of repeated differentiation of the virtual control law in the conventional back-stepping method, greatly simplifying the control law structure; (2) by using the norm of the neural network weight vector as the adaptive adjustment parameter instead of updating each element online, the number of adaptive adjustment parameters is significantly reduced, improving the execution efficiency of the controller; (3) the introduced hysteresis quantizer overcomes the disadvantage of the quantization accuracy deterioration when the input value is too low in the logarithm quantizer, improving the accuracy of the quantizer. Stability analysis has shown that all signals in the closed-loop system are semi-globally uniformly bounded, and simulation results have verified the effectiveness of the proposed adaptive quantized control scheme.

Working state map of hydrocarbon fuels for regenerative cooling

Regenerative cooling by endothermic hydrocarbon fuel (EHF) is one of the most promising techniques for thermal management of supersonic or hypersonic aircraft. How to maintain the fuel working in proper states is an important issue to maximize the cooling potential of EHT. This work proposes a novel working state map, including risking zone (RZ), thermal cracking zone (TCZ), supercritical zone (SupZ) and subcritical zone (SubZ), to differentiate possible working states of an EHF during regenerative cooling. Using n-decane flowing in a circular tube as an example, the boundaries of four zones are determined by numerical simulation covering different heat fluxes (0.2–4.0 MW·m−2) and mass flow rates (0.5–10.5 g·s−1) under two operating pressures (3.45 and 5.00 MPa). Empirical correlations for three boundary lines are obtained and the maximum cooling capacity is identified, as well as the identification of the pressure effect. The revelation of such new perspective of regenerative cooling is of great implication to the design and optimization of cooling system for future thermal management.

Morphological and Compositional Analysis on Thermal Deposition of Supercritical Aviation Kerosene in Micro Channels.

The integration of active cooling systems in super or hypersonic aircraft using endothermic hydrocarbon fuels is considered an effective way to relieve the thermal management issues caused by overheating. When the temperature of aviation kerosene exceeds 150 °C, the oxidation reaction of fuel is accelerated, forming insoluble deposits that could cause safety hazards. This work investigates the deposition characteristic as well as the morphology of the deposits formed by thermal-stressed Chinese RP-3 aviation kerosene. A microchannel heat transfer simulation device is used to simulate the heat transfer process of aviation kerosene under various conditions. The temperature distribution of the reaction tube was monitored by an infrared thermal camera. The properties and morphology of the deposition were analyzed by scanning electron microscopy and Raman spectroscopy. The mass of the deposits was measured using the temperature-programmed oxidation method. It is observed that the deposition of RP-3 is highly related to dissolved oxygen content (DOC) and temperature. When the outlet temperature increased to 527 °C, the fuel underwent violent cracking reactions, and the structure and morphology of deposition were significantly different from those caused by oxidation. Specifically, this study reveals that the structure of the deposits caused by short-to-medium term oxidation are dense, which is different from long-term oxidative deposits.

HALO3D: An All-Mach Approach to Hypersonic Flows Simulation, Part II

ABSTRACT This paper is Part II of the two-paper series ‘HALO3D: An All-Mach Approach to Hypersonic Flows Simulation’ presenting advances in a monolithic flow simulation software for the design of high-speed aircraft. Part II highlights the methodology behind the continuum regime finite-rate surface chemistry, weak-ionisation, and rarefied regime Direct Simulation Monte Carlo modules. Validation and benchmark simulations of flows over a 2D cylinder, the 3D RAM-C II geometry, and the 3D Lockheed Martin X-33 geometry are provided. Within HALO3D, a Hessian-based multiphysics automatic mesh adaptation methodology yields optimal solutions that ought to provide valuable benchmarks for verifying other hypersonic flow simulation tools. Such mesh optimisation automatically generates a common truly mesh-independent solution across the continuum and rarefied regimes, taking into account various thermo-chemical models. These developments establish HALO3D as a mature, readily extendible software package for hypersonic aircraft analysis.

Integrated Flight Control System Characterization Approach for Civil High-Speed Vehicles in Conceptual Design

Recent studies have revealed that control surface deflection can cause a reduction in the aerodynamic efficiency of a hypersonic aircraft of up to 30%. In fact, the characterization of the Flight Control System is essential for the estimation of the consistent aerodynamic characteristics of the vehicle in different phases, considering the contribution of control surfaces to stability and trim. In terms of the sizing process, traditional methodologies have been demonstrated to be no longer applicable to estimations of the actuation power required for the control surfaces of a high-speed aircraft, due to their peculiar working conditions and to the characteristics of the flow to which they are exposed. In turn, numerical simulation approaches based on computational fluid dynamics or panel methods may require considerable time resources, which do not fit with the needs of the quick and reliable estimates that are typical of the early design phases. Therefore, this paper is aimed at describing a methodology to show how to anticipate the Flight Control System design for high-speed vehicles at the conceptual design stage, properly considering the interactions at vehicle level and predicting the behavior of the system throughout an entire mission. It is also a core part of the work to provide designers with an example of how neglecting the effect of trim drag can be detrimental to a reliable estimation of overall aircraft performance. The analysis, mainly focused on the longitudinal plane of the vehicle, is presented step-by-step on a specific case study, namely the STRATOFLY MR3 vehicle, a Mach 8 waverider concept for civil antipodal flights. The application of the methodology, conceived as an initial step towards an iterative Flight Control System design process, also shows that the most power-demanding phases are take-off, low supersonic acceleration, and approach, where peaks of over 130 kW are reached, while an average of 20 kW is sufficient to support deflections in a hypersonic cruise.

Experimental study of tensile and flexural performances and failure mechanism of none-felt needled composites

None-felt needled composite material is a novel type of composite with excellent interlayer connection performance. Nonetheless, the tensile and flexural properties and failure mechanism have not been clarified. In this work, none-felt needled fabrics and reinforced composites were manufactured, which were then characterized structurally using Micro-CT. Moreover, the tensile and flexural performances were researched with digital image correlation (DIC) technology, and the fracture morphology was observed employing SEM. The results showed that more needled fiber bundles were implanted along the thickness direction, and the fiber diameter and length were increased by 127.2% and 148.2% respectively. The tensile strengths and modulus also enhanced by 31.5% and 32.8%, and the flexural strengths and modulus improved by 13.1% and 26.7%. The tensile and flexural failure modes of none-felt needled composites and conventional felt needled composites consisted of matrix fracture, in-plane fiber pull-out and brittle fracture. Besides, the flexural specimens of none-felt needled composites had a shorter delamination length. The none-felt needled composites with high tensile and flexural performances are expected to be used in key core components such as radome, cabin and skin of hypersonic aircraft.

Fixed-time Disturbance Observer-Based Finite-Time Backstepping Control for Hypersonic Vehicle

Due to the severe flight environment, hypersonic vehicles are susceptible to external disturbances and aerodynamic parameter uncertainties, dramatically challenging the precise control and stable tracking. This paper presented a fixed-time disturbance observer (FTDO) to obtain better tracking performance for hypersonic vehicles. The FTDO can improve the tracking performance under external disturbances and aerodynamic parameter perturbations, whose observation time is bounded and does not depend on the initial errors. The backstepping control can guarantee finite-time convergence with the finite-time control technique. A second-order filter is designed to process the complexity explosion problem in the traditional backstepping control and ensure the tracking system’s finite-time stability. Then with Lyapunov theory, it is proved that the control system is stable and convergent in finite time. Finally, three numerical simulation results based on typical conditions are given to show the effectiveness and advantage of the developed control scheme, and external disturbances can be estimated accurately within two seconds. These results have reference value for flight controller design of hypersonic and other aircraft in complex disturbance environments.

Relativistic Bistatic Scattering of a High-Speed Moving Plasma Coated Object

Accurate modeling of relativistic electromagnetic scattering characteristics from high-speed motion of plasma coated objects is crucial for the development of hypersonic aircraft and their applications in the identification and surveillance of moving stealth targets. Nevertheless, a solution for bistatic polarized radar cross sections (RCSs) from a 3-D object with plasma coated layer in motion has yet to be obtained. This manuscript proposes a solution to this problem by employing a combination of the auxiliary differential equation (ADE) method with Lorentz finite-difference time-domain (FDTD) method. Utilizing the Lorentz transformation, this paper presents the transformation of parameters of the incident plane wave and dimensions of the object between the laboratory system that remains static and the rest system that remains stationary relative to the object in high-speed motion. The near-zone electromagnetic fields near the object are computed using the ADE method in the rest system, after which the near-field to far-field (NF-FF) transformation is employed to obtain the far-zone polarized scattered field. By applying Lorentz transformation to the coordinates, this paper presents a solution for the polarized scattering from moving plasma coated objects. Especially, radial components of the polarized scatterings are analyzed. The proposed method is validated through several numerical experiments, demonstrating its efficiency and accuracy.

CoolPINNs: A physics-informed neural network modeling of active cooling in vascular systems

Emerging technologies like hypersonic aircraft, space exploration vehicles, and batteries avail fluid circulation in embedded microvasculatures for efficient thermal regulation. Modeling is vital during the design and operational phases of these engineered systems. However, many challenges exist in developing a modeling framework. What is lacking is an accurate framework that (i) captures sharp jumps in the thermal flux across complex vasculature layouts, (ii) deals with oblique derivatives (involving tangential and normal components), (iii) handles nonlinearity because of radiative heat transfer, (iv) provides a high-speed forecast for real-time monitoring, and (v) facilitates robust inverse modeling. This paper addresses these challenges by availing the power of physics-informed neural networks (PINNs). We develop a fast, reliable, and accurate Scientific Machine Learning (SciML) framework for vascular-based thermal regulation—called CoolPINNs: a PINNs-based modeling framework for active cooling. The proposed mesh-less framework elegantly overcomes all the mentioned challenges. The significance of the reported research is multi-fold. First, the framework is valuable for real-time monitoring of thermal regulatory systems because of rapid forecasting. Second, researchers can address complex thermoregulation designs since the approach is meshless. Finally, the framework facilitates systematic parameter identification and inverse modeling studies, perhaps the most significant utility of the current framework.

Flow and heat transfer characteristics of intake-precooler system for hypersonic precooled aero-engine

Precooled aero-engines are promising hypersonic propulsion mechanisms for hypersonic aircraft that are capable of taking off and landing horizontally. The performance of the intake-precooler system has a significant impact on the performance of the engine. In this study, a coupled simulation of a hypersonic intake with a precooler was performed using computational fluid dynamics. The pressure drop and heat transfer through the precooler are evaluated using porous media and dual cell heat exchanger models, respectively, without modeling the detailed structure of the heat exchanger. Coupled axisymmetric variable-geometry hypersonic intake-precooler simulations were conducted at typical operating conditions (i.e., at Mach numbers = 5.0, 3.5, and 2.0). The coupled flow and heat transfer characteristics and the effects of the working pressure ratio on the intake-precooler system were analyzed. It was found that the total temperature distortion of the airflow through the precooler at the cruising velocity (Ma = 5.0) reached 0.337. Besides, the loss of the airflow through the precooler at lower velocity (Ma = 2.0) accounted for 48.4% of the overall total pressure loss. These results indicate that the coupled simulation method is capable of simulating the behavior of hypersonic intake-precooler systems and provides some guidance on the design of precooled engines.