Next-generation Aircraft Research Articles

Comparison of the Aircraft Noise Calculation Programs sonAIR, FLULA2 and AEDT with Noise Measurements of Single Flights

As aircraft noise affects large areas around airports, noise exposure calculations need to be highly accurate. In this study, we compare noise exposure measurements with calculations of several thousand single flights at Zurich and Geneva airports, Switzerland, of three aircraft noise calculation programs: sonAIR, a next-generation aircraft noise calculation program, and the two current best-practice programs FLULA2 and AEDT. For one part of the flights, we had access to flight data recorder (FDR) data, which contain flight configuration information that sonAIR can account for. For the other part, only radar data without flight configuration information were available. Overall, all three programs show good results, with mean differences between calculations and measurements smaller than ±0.5 dB in the close range of the airports. sonAIR performs clearly better than the two best-practice programs if FDR data are available. However, in situations without FDR data (reduced set of input data), sonAIR cannot exploit its full potential and performs similarly well as FLULA2 and AEDT. In conclusion, all three programs are well suited to determine averaged noise metrics resulting from complex scenarios consisting of many flights (e.g., yearly air operations), while sonAIR is additionally capable to highly accurately reproduce single flights in greater detail.

Fiber optic pressure measurement on a complex outer winglet model with active flow control actuators

The next generation of aircraft requires novel approaches on lift increase and drag reduction technologies as active flow control to counter local flow separations. Testing and monitoring its effectiveness in flight require precise pressure evaluation as a possible control input. Pressure-based measurements of local flow separation are challenging utilizing conventional electrical pressure sensors. These sensors might show degradation of their long-term performance in harsh environments, e. g., in real aircraft applications, due to their low overload protection, susceptibility to electromagnetic influences, and corrosion. Fiber optic measurements overcome those challenges and promise to be a robust sensing solution. We investigate the potential application of a novel fiber optic measurement system that monitors the active flow control system's effectiveness. Furthermore, the results are compared to conventional static pressure measurements. Due to the high-frequency capabilities of the fiber optic sensors, the dynamic behavior of the boundary layer separation and vortex generation was captured in the frequency domain. An industry-relevant outer wing was equipped with 25 fiber optic pressure sensors positioned at one wingspan section for this experiment. The experiments were conducted at a Reynolds number Re=1.1⋅106and a Mach number Ma=0.12. Wind tunnel testing results show that fiber optic pressure sensors can measure aerodynamic characteristics and, furthermore, even allow a detailed look at the dynamic behavior.

Physical and chemical imaging of adhesive interfaces with soft X-rays

Adhesion is an interfacial phenomenon that is critical for assembling carbon structural composites for next-generation aircraft and automobiles. However, there is limited understanding of adhesion on the molecular level because of the difficulty in revealing the individual bonding factors. Here, using soft X-ray spectromicroscopy we show the physical and chemical states of an adhesive interface composed of a thermosetting polymer of 4,4’-diaminodiphenylsulfone-cured bisphenol A diglycidyl ether adhered to a thermoplastic polymer of plasma-treated polyetheretherketone. We observe multiscale phenomena in the adhesion mechanisms, including sub-mm complex interface structure, sub-μm distribution of the functional groups, and molecular-level covalent-bond formation. These results provide a benchmark for further research to examine how physical and chemical states correlate with adhesion, and demonstrate that soft X-ray imaging is a promising approach for visualizing the physical and chemical states at adhesive interfaces from the sub-mm level to the molecular level.

Spark Safe

Test engineers are adapting to the high-voltage environments of the next generation of aircraft with vital safety measures

Jet direction control using secondary flows

In recent years, studies on the fundamental principle of thrust vectoring using jets have been conducted with the aim of application to next-generation aircraft. Consequently, the improvement of aircraft motion performance is expected. Previously, a method using secondary flow with a Coanda surface was proposed for the direction control of the primary jet, and some valuable results were reported. The effect of ejection or suction on the traveling direction of the primary jet was examined. However, as many physical quantities dominate the phenomenon in this complicated situation, parametric studies are insufficient. The present study is a fundamental study of fluidic thrust vectoring. The effect of secondary injection or suction flow near the Coanda surface on the travel direction of primary jets was investigated parametrically using the momentum ratio, nozzle width ratio, etc. without changing the nozzle geometry. A larger deflection of the primary jet was observed because of the suction rather than ejection at the same momentum ratio. Furthermore, the effect of the slot width ratio on the dead zone where the traveling direction of the second jet does not depend on the momentum of the secondary flow was studied.

Observed impact of meso-scale vertical motion on cloudiness

AbstractWe use estimates of meso-scale vertical velocity and co-located cloud measurements from the second Next-Generation Aircraft Remote Sensing for Validation campaign (NARVAL2) in the tropical North Atlantic to show the observed impact of meso-scale vertical motion on tropical clouds. Our results not only confirm previously untested hypotheses about the role of dynamics being non-negligible in determining cloudiness, but go further to show that at the meso-scale, the dynamics has a more dominant control on cloudiness variability than thermodynamics. A simple mass-flux estimate reveals that meso-scale vertical velocity at the sub-cloud layer top explains much of the variations in peak shallow cumulus cloud fraction. In contrast, we find that thermodynamic cloud-controlling factors, such as humidity and stability, are unable to explain the variations in cloudiness at the meso-scale. Thus, capturing the observed variability of cloudiness may require not only a consideration of thermodynamic factors, but also dynamic ones such as the meso-scale vertical velocity.

Effect of Radiation on Heat Transfer Inside Aeroengine Compressor Rotors

AbstractThe blade clearance in aero-engine compressors is mainly controlled by the radial growth of the compressor discs, to which the blades are attached. This growth depends on the radial distribution of the disc temperature, which in turn is determined by the heat transfer inside the internal rotating cavity between adjacent discs. The buoyancy-induced convection inside the cavity is significantly weaker than that associated with the forced convection in the external mainstream flow, and consequently radiation between the cavity surfaces cannot be ignored in the calculation of the disc temperatures. In this paper, both the Monte Carlo Ray-Trace (MCRT) method and the view factor (VF) method are used to calculate the radiative flux when the temperatures of the discs, shroud, and inner shaft of the compressor vary radially and axially. The Monte Carlo Ray-Trace method is computationally expensive, but it is able to incorporate the effect of complex geometries on radiation. The view factor method is quick to compute and, although the derivation becomes complicated when geometrical details are considered, it can be used as a first check of the effect of radiation in compressor cavities. Given distributions of surface temperatures, the blackbody and gray body heat fluxes were calculated for the discs, shroud, and inner shaft in two experimental compressor rigs and in a simulated compressor stage. For the experimental rigs, although the effect of radiation was relatively small for the case of large Grashof numbers, the relative effect of radiation increases as Gr (and consequently the convective heat transfer) decreases. For the simulated compressor, with a pressure ratio of 50:1 for state-of-the-art aircraft engines, radiation could have a significant effect on the disc temperature and consequently on the blade clearance; the effect is predicted to be more prominent for the next generation of aircraft engines with pressure ratios up to 70:1.

Robust design of an adaptive cycle engine performance under component performance uncertainty

The adaptive cycle engine can vary the cycle in wider range and meet the requirement of mixed missions. It is expected to be the propulsion system for the next generation of aircraft and has therefore attracted a lot of attention. The uncertainty in component performance can offset the performance benefits of adaptive cycle engine. Therefore, the robust design should be applied at the engine performance design stage to reduce the effect of component performance uncertainty. Compared with conventional engines, the adaptive cycle engine has more variable geometry components. It causes two major difficulties for the robust design: one is the high computation cost and the other is the complex control law design. In this paper, a robust design method based on a two-level surrogate model and a two-stage design process is presented to overcome these difficulties. In this method, the probabilistic method is applied to quantify uncertainty and the selection principle of optimization target is studied. The cycle parameters and control law are optimized through a two-stage design process. The optimization is developed based on a two-level surrogate model to reduce the computational cost. This robust design method is validated by the Monte Carlo method. According to this study, performance under confidence probability is a better optimization target than the signal-to-noise ratio of performance. Using this method, the probability of engine performance meeting demand can be improved from about 50% to over 96%. The computational cost of uncertainty quantification is only 0.5% of the Monte Carlo method and the computational cost of whole optimization design process is less than the cost of once uncertainty quantification through Monte Carlo method. This method can improve the robustness of adaptive cycle engine performance and reduce the computational cost significantly. It can also be applied to the robust design of other complex gas turbine engines performance.

High Temperature Insulation Materials for DC Cable Insulation—Part II: Partial Discharge Behavior at Elevated Altitudes

Utilizing hybrid electric propulsion systems in the next generation of aircrafts with elevated DC voltage level has raised the concern about the degradation of insulation subjected to partial discharge at high altitude and harsh environment. In this work, the surface discharge behavior of commonly used high-temperature insulation materials in aviation systems (FEP, ETFE, and PEEK) under positive and negative DC and ramp voltage was studied, including the pulse waveform, frequency spectrum, PD count and magnitude. Pressure changes as a significant factor influencing surface discharge phenomenon was thoroughly studied. Dust figure technique was employed after voltage ramping tests for both positive and negative polarities at low pressure to investigate the surface charge accumulation and surface discharge traces, and unveil the involved physical mechanisms at different stages of streamer propagation. The content of this paper provides a reference for surface discharge studies and evaluation of high temperature materials for medium voltage direct current power distribution in the future aviation systems.

New Demands of Aircraft Components and Responding Behaviour to Next-generation Aircraft in Peripheral Regions

New Demands of Aircraft Components and Responding Behaviour to Next-generation Aircraft in Peripheral Regions

On trailing edge noise from propellers with interactions to shear layers

In underwater and next-generation aircraft propulsion systems, the propellers could interact with shear layers that develop from leading edge aerodynamic components (e.g., rudders and guiding vanes). Observations suggest that random pulsations inside shear layers would suppress large-scale separations from the downstream propellers, which could benefit aeroacoustic designs by reducing tip vortex that is otherwise one of the dominant aerodynamic noise sources. To understand the inherent fluid mechanics, we apply a phase-averaged beamforming method to conduct time-frequency analysis on acoustic images measured from a demonstrative experimental set-up, where the shear layer is simply developed from an open-jet nozzle inside an anechoic wind tunnel. The results confirm that the interaction between the shear layer and the propeller could suppress the trailing edge noise (and tip noise) from the propellers. Furthermore, our results show that the proposed phase-averaged beamforming method enables us to conduct powerful time-frequency analysis in acoustic imaging tests and, consequently, possibly leads to deep physical insights of various transient fluid mechanics in underwater and aerospace systems.

Power to air transportation via hydrogen

This study proposes a framework to analyse the concept of power to hydrogen (P2H) for fuelling the next generation of aircraft. The impact of introducing new P2H loads is investigated from different aspects namely, cost, carbon emission, and wind curtailment. The newly introduced electric load is calculated based on the idea of replacing the busiest international flight route in the Europe, Dublin-London Heathrow, by hydrogen fuel-powered aircraft as a high potential candidate for the next generation of air travel systems to cope with the ambitious targets set in Europe Flight Path 2050 by the Advisory Council for Aeronautics Research in Europe. The simulation is performed on a representative Irish transmission network to demonstrate the effectiveness of the proposed solution.

A proposal for a lightweight, large current superconducting cable for aviation

More Electric Aircraft (MEA) is one of the most important subjects for designing the next generation of aircraft. Since we cannot ground the electric power systems of a flying aircraft and the air insulation voltage is lower at high altitude, a low voltage, direct current (DC) aircraft electrical system is preferable for a MEA. Since the current must be high to supply high power, we consider high temperature superconducting (HTS) technology because it handles large currents well. We propose a new HTS cable in this paper. The cable uses a stacked conductor, with oppositely directed current in each HTS tape, a structure that has already been shown to be feasible for low voltage cables. It enhances the critical current compared to a single tape conductor, especially for Bi2223 tape. In order to avoid a current imbalance in the stacked conductor, we use the current lead resistance rather than a Roebel conductor design. Then the critical current remains high, and this is confirmed by measurements. The cryogenic pipe will be made of magnesium-lithium alloy, one of the lightest metals available at the present time. We estimate the weight-to-current ratio per unit length to be less than 0.5 kg/A/km at the liquid nitrogen operational temperature of 77 K, lighter than conventional copper cable. If instead we use liquid hydrogen at 20 K, we expect a value less than 0.1 kg/A/km, which is one of the lowest presently achievable values and satisfies the requirements for MEA.

The airplane trim system – new functionalities

PurposeA standard automatic flight control system – autopilot – will become required equipment of the future aircraft, operating in the common sky. For a specific group of aircraft, they are too expensive and too energy-consuming solutions. This paper aims to present the concept of an automatic flight control system that overcomes those limitations.Design/methodology/approachThe proposed automatic flight control system uses the trim tabs in all prime flight controlling surfaces: elevator, ailerons and rudder, for stabilizing and controlling the steady flights of an aircraft.FindingsThe results of an aeroplane flight controlled with the use of trim tabs simulation tests and remarks have been presented and discussed. The simulation was conducted in real-time hardware in the loop environment. The stabilization of the flight was achieved in performed test scenarios.Originality/valueThe possibility to control an aircraft with coordinated deflections of the trimming surfaces is a beneficial alternate to those currently used and can be recommended for use in the next-generation aircraft.

Ensemble daily simulations for elucidating cloud–aerosol interactions under a large spread of realistic environmental conditions

Abstract. Aerosol effects on cloud properties and the atmospheric energy and radiation budgets are studied through ensemble simulations over two month-long periods during the NARVAL campaigns (Next-generation Aircraft Remote-Sensing for Validation Studies, December 2013 and August 2016). For each day, two simulations are conducted with low and high cloud droplet number concentrations (CDNCs), representing low and high aerosol concentrations, respectively. This large data set, which is based on a large spread of co-varying realistic initial conditions, enables robust identification of the effect of CDNC changes on cloud properties. We show that increases in CDNC drive a reduction in the top-of-atmosphere (TOA) net shortwave flux (more reflection) and a decrease in the lower-tropospheric stability for all cases examined, while the TOA longwave flux and the liquid and ice water path changes are generally positive. However, changes in cloud fraction or precipitation, that could appear significant for a given day, are not as robustly affected, and, at least for the summer month, are not statistically distinguishable from zero. These results highlight the need for using a large sample of initial conditions for cloud–aerosol studies for identifying the significance of the response. In addition, we demonstrate the dependence of the aerosol effects on the season, as it is shown that the TOA net radiative effect is doubled during the winter month as compared to the summer month. By separating the simulations into different dominant cloud regimes, we show that the difference between the different months emerges due to the compensation of the longwave effect induced by an increase in ice content as compared to the shortwave effect of the liquid clouds. The CDNC effect on the longwave flux is stronger in the summer as the clouds are deeper and the atmosphere is more unstable.

Healable, memorizable, and transformable lattice structures made of stiff polymers

Emerging transformable lattice structures provide promising paradigms to reversibly switch lattice configurations, thereby enabling their properties to be tuned on demand. The existing transformation mechanisms are limited to nonfracture deformation, such as origami, instability, shape memory, and liquid crystallinity. In this study, we present a class of transformable lattice structures enabled by fracture and shape-memory-assisted healing. The lattice structures are additively manufactured with a molecularly designed photopolymer capable of both fracture healing and shape memory. We show that 3D-architected lattice structures with various volume fractions can heal fractures and fully restore stiffness and strength over two to ten healing cycles. In addition, coupled with the shape-memory effect, the lattice structures can recover fracture-associated distortion and then heal fracture interfaces, thereby enabling healing of lattice wing damages, mode-I fractures, dent-induced crashes, and foreign-object impacts. Moreover, by harnessing the coupling of fracture and shape-memory-assisted healing, we demonstrate reversible configuration transformations of lattice structures to enable switching among property states of different stiffnesses, vibration transmittances, and acoustic absorptions. These healable, memorizable, and transformable lattice structures may find broad applications in next-generation aircraft panels, automobile frames, body armor, impact mitigators, vibration dampers, and acoustic modulators.

Thermal Mismatch Effect and High-Temperature Tensile Performance Simulation of Hybrid CMC and Superalloy Bolted Joint by Progressive Damage Analysis

The hybrid CMC and superalloy bolted joints have exhibited great potential to be used as thermostructural components of reusable space transportation systems, given the respective strengths of these two materials. In the high temperature excursion of the hybrid joints with the aircrafts and space vehicles, the substantial difference in thermal expansion coefficients of CMC and superalloy materials will induce complex superposition of initial assembly stress, thermal stress, and tensile stress around fastening area, which might lead to unknown failure behavior of joint structure. To address this concern, a finite element model embedded with progressive damage analysis was established to simulate the thermostructural behavior and high-temperature tensile performance of single-lap, single-bolt C/SiC composite and superalloy joint, by using the ABAQUS software. It was found that the initial stiffness of the CMC/superalloy hybrid bolted joints decreases with the rise of applied temperature under all bolt-hole clearance levels. However, the load-bearing capacity varies significantly with the initial clearance level and exposed temperature for the studied joint. The thermal expansion mismatch generated between the CMC and superalloy materials led to significant changes in the assembly preload and bolt-hole clearance as the high-temperature load is applied to the joint. The evolution in the thermostructural behavior upon temperature was then correlated with the variations in stiffness and failure load of the joints. The provided new findings are valuable for structural design and practical application of the hybrid CMC/superalloy bolted joints at high temperatures in next-generation aircrafts.

Configuring LES Based on Dropsonde Data in Sparsely Sampled Areas in the Subtropical Atlantic

AbstractThis study explores the question of how field campaign data, gathered over a large area that is poorly sampled, can be used to make large-eddy simulation (LES) realizations more representative of the local conditions. To this purpose, dropsonde data recorded during the first Next-Generation Aircraft Remote Sensing for Validation Studies (NARVAL)-South campaign, in the marine subtropical North Atlantic, are blended into the forcing data. Control simulations are driven by time-dependent forcings derived from a combination of analyses and short-range weather forecasts, using weak nudging to prevent excessive model drift. A second set of simulations is driven by forcing data with dropsonde profiles included at the time points of their release. Metrics are designed to (i) quantify the impact on the boundary layer vertical profiles as a result of nudging toward the dropsondes and (ii) use a probabilistic method to allow a fair comparison of the inversion strengths in the simulations and observations. The simulations show strong time variation in the cloud-layer depth on relatively short time scales, which is commensurate with recent observational studies in the area. Nudging toward dropsondes improves the representation of the atmospheric profiles throughout the depth of the boundary layer in all simulations. However, the impact on the inversion strength is less pronounced. All impacts persist for some time after the dropsonde time point, depending on the intensity of the nudging and the nudging time window. The sensitivity of the results to nudging details and vertical resolution is assessed.

Unified Solver Based Real-Time Multi-Domain Simulation of Aircraft Electro-Mechanical-Actuator

Electro-mechanical-actuator (EMA) is the key component to convert electrical power into mechanical power for flight control in next-generation aircrafts. Multi-domain simulation of EMA can benefit its on-going evolution process. This paper presents the real-time multi-domain modeling and simulation of an EMA as elevator for flight control by utilization of a unified solver. Several key issues concerning the computational efficiency and successful implementation of this solver are provided and its relationship with state-variable model is also elaborated. Analysis shows that this solver could be a competitive candidate for multi-domain simulation because of its high computational efficiency and relatively less modeling effort. Electrical, mechanical, and thermal parts of the EMA are modeled and simulated interactively based on the proposed solver. The multi-domain model is implemented on FPGA board and executes in real time. Simulation results from FPGA board and commercial softwares under several test scenarios coincide with each other in very high degree, which showcases the efficacy of the proposed solver with respect to computational efficiency and ability to accommodate multi-domain models. The proposed model and solver are useful for hardware-in-the-loop design and testing of EMA.

Roar Aboard: Protecting Service Members' Ears on Aircraft Carriers

Roar Aboard: Protecting Service Members' Ears on Aircraft Carriers