Slat Track Research Articles

Effects of slat track on the flow and acoustic field of high-lift devices

Most of the published works related to noise generation in high-lift devices only consider clean idealized geometries, whereas real aircraft wings contain important parts called the slat tracks that connect the slat and the main wing. To investigate the effects of slat tracks on the ambient flow and noise, simulations are performed for wings based on the 30P30N airfoil. Two configurations are considered, i.e., the 30P30N wing with and without a slat track. Improved detached-eddy simulation is carried out to compute the unsteady near-field flow. The far-field noise propagation is calculated using the Ffowcs Williams-Hawkings equation. The results show that the installation of the slat track has observable effects on the aerodynamic and aeroacoustic performances of the high-lift devices. The maximum lift coefficient of the high-lift device and the stall angle of attack is reduced. Low-frequency broadband noise radiated from the main wing is significantly increased and the directivity of the overall sound pressure level is changed due to the slat track. The far-field noise from the configuration with the slat track displays noticeable sensitivity to the angle of attack. The slat track has an amplification effect on the high-pressure fluctuation on the main wing, especially at a small angle of attack. This leads to nearly 10 dB in the far-field noise based on the discussed wing section. To reveal the relative noise mechanism, vortical structures near the slat track, large-scale spanwise flows above the main wing, and the vortex dynamics are investigated. A spiral vortex pair is captured as the most important flow structure. It is generated in the spanwise direction by the interaction of slat wakes with the boundary layer on the upper surface of the main wing. The pressure fluctuations on the main wing are highly correlated with this flow structure, which cannot be ignored for the study of noise in a real aircraft.

On three-dimensional printing of 17-4 precipitation-hardenable stainless steel with direct metal laser sintering in aircraft structural applications

The martensitic 17-4 precipitation-hardenable stainless steel is one of the commercially established materials for structural engineering applications in aircrafts due to its superior mechanical and corrosion resistance properties. The mechanical processing of this alloy through a conventional manufacturing route is critical from the dimensional accuracy (Δ d) viewpoint for development of innovative structural components such as: slat tracks, wing flap tracks, etc. In past two decades, a number of studies have been reported on challenges being faced while conventional processing of 17-4 precipitation-hardenable stainless steel for maintaining uniform thickness of aircraft structural components. However, hitherto little has been reported on direct metal laser sintering of 17-4 precipitation-hardenable stainless steel for development of innovative functional prototypes with uniform surface hardness (HV), Δ d, and surface roughness ( Ra) in aircraft structural engineering. This paper reports the effect of direct metal laser sintering process parameters on HV, Δ d, and Ra for structural components. The results of study suggest that optimized settings of direct metal laser sintering from multifactor optimization viewpoint are laser power 100 W, scanning speed 1400 mm/s, and layer thickness 0.02 mm. The results have been supported with scanning electron microscopy analysis (for metallurgical changes such as porosity (%), HV, grain size, etc.) and international tolerance grades for ensuring assembly fitment.

High Strength Corrosion Resistant Steel for Aircraft Landing Gears and Structures

<div class="section abstract"><div class="htmlview paragraph">High stressed aircraft landing gear and structural components are subjected to severe loading, corrosion and adverse environmental conditions. Materials such as high strength steels and high-strength titanium alloys are widely used for those critical components. The main criterions for choosing the materials are their strength and fatigue strength, toughness and ductility.</div><div class="htmlview paragraph">300M steel is widely used for high stress aircraft landing gears and structures; however, this steel is not corrosion-resistant and requires protective coatings.</div><div class="htmlview paragraph">Cobalt-free, quenched and tempered high strength corrosion resistant steel alloy (“HSCR steel”) provides the same strength, ductility, and toughness as the 300M steel and while it possesses corrosion resistance in salt spray test. HSCR steel has showed no rust after the standard salt spray test in accordance with ASTM B117 using a 5% NaCl concentration, natural pH, at 95°F, for 200 hours test duration.</div><div class="htmlview paragraph">Aircraft applications of the wrought HSCR steel include landing gear components, rotatable shafts, actuators, flap tracks, slat tracks, fasteners, and others.</div><div class="htmlview paragraph">Besides forging, the aircraft components can be manufactured from HSCR steel powders by:<ul class="list disc"><li class="list-item"><div class="htmlview paragraph">Powder metallurgical-based hot isostatic pressing (PM HIP) to the near net shapes</div></li></ul></div><div class="htmlview paragraph">(NNS) followed by finish machining/surface finishing and heat treatment<ul class="list disc"><li class="list-item"><div class="htmlview paragraph">Additive manufacturing (AM) followed by surface finishing and heat treatment.</div></li></ul></div><div class="htmlview paragraph">Modification of the HSCR steel is applicable for vacuum and investment casting of aircraft hydraulic fluid system, motion control and actuation system, cargo system, and flight safety components.</div><div class="htmlview paragraph">HSCR steel is a low cost alternative of Ti-6Al-4V alloy. The components made from Ti- 6Al-4V alloy can be substituted by the same weight components made from HSCR steel due to HSCR steel possesses slightly higher specific stiffness and specific strength (ratio of modulus elasticity and ultimate tensile strength to density) and slightly lower ductility and toughness compared to Ti-6Al-4V alloy.</div><div class="htmlview paragraph">Industrial production of HSCR steel is underway.</div></div>

Japan Aerospace Exploration Agency Studies for the Second High-Lift Prediction Workshop

This paper summarizes Japan Aerospace Exploration Agency studies using a structured grid solver UPACS and an unstructured grid solver TAS-code for the second AIAA CFD High-Lift Prediction Workshop test cases and follow-on problems. Computations are performed for the grid convergence study using the configuration without any slat tracks and flap track fairings on a series of multi-block structured grids and a series of unstructured grids provided by the High Lift Prediction Workshop committee. In this paper, the following are mainly discussed: 1) grid convergence verification study of the turbulence models using a two-dimensional bump case, 2) grid convergence studies for Spalart–Allmaras and shear stress transport turbulence models using UPACS, 3) change of grid convergence and predicted flow fields with and without a nonlinear quadratic constitutive relation model for Spalart–Allmaras and shear stress transport turbulence models using UPACS including evaluation at higher angles of attack, and 4) comparison studies using different solvers UPACS and TAS on different grid systems with and without the quadratic constitutive relation model for the Spalart–Allmaras model.

Lattice Boltzmann Method Contribution to the Second High-Lift Prediction Workshop

This paper presents the results of the computational-fluid-dynamics code XFlow for the test case proposed in the 2nd High-Lift Prediction Workshop. The target of this international workshop is to assess the accuracy of numerical predictions provided by a wide selection of computational-fluid-dynamics codes and applied to the aeronautical industry. It deals with a full aircraft in high-lift configuration with unstowed flap and slat, including slat tracks, flap track fairings, and slat pressure tube bundles. XFlow is a particle-based kinetic solver, based on the lattice Boltzmann method. It is well suited for such low-speed flows because the standard lattice Boltzmann method is limited to low Mach number. It employs large-eddy simulation turbulence modeling with the wall-adapting local eddy model, coupled with a generalized law of the wall to model the boundary-layer prediction. Traditional computational-fluid-dynamics software requires a time-consuming meshing process that is prone to errors, which significantly affects the mesh quality and thus the outcome of a simulation. Furthermore, the complex geometries such as elements in small gaps add an extra complication to generate the mesh. In contrast, the method employed by XFlow avoids the traditional meshing process using an octree structure, with spatial refinement related by a factor of 2 based on the input geometry. The discretization stage is strongly accelerated, thus reducing engineering costs and complex geometry computations are affordable in a straightforward way. The research presented in this paper starts with a grid validation study (case 1) with the DLR F11 geometry in configuration 2. Because the lattice Boltzmann method approach used by XFlow simplifies the integration of geometrical details, the full polar characteristic is directly investigated with configuration 5 (case 3) that includes the actual model configuration on the aerodynamic performances. The configuration 5 geometry includes slat tracks and flap track fairings, as well as slat pressure tube bundles. This is the highest-fidelity geometry in comparison with wind-tunnel testing. This study is conducted for both low- and high-Reynolds-number conditions, 1.35 and 15.1 million, respectively. In addition, the study focuses on the poststall region and the influence of geometrical details on turbulence and flow patterns. The interest for the poststall region is justified by the lack of consistency in the stall prediction found during the 2nd AIAA High-Lift Prediction Workshop by all the participants.

Aeroacoustic Effects of High-Lift Wing Slat Track and Cut-Out System

Effects of the slat track and cut-out on noise propagation were investigated using compact source models for a high-lift wing. Two different geometries of the high-lift devices, with and without the slat track and cut-out, were investigated. Convection effects were also considered with the mean flows obtained from precursor simulations of corresponding high-lift configurations. Major noise sources in the slat cove region were modelled with equivalent compact dipoles placed along the slat trailing edge and cusp. Results show that sound propagation is modified by the add-on components. The acoustic waves are amplified significantly and radiate more energy towards the ground due to the interaction between propagating waves and the slat track and cut-out. Although the cancellation caused by interference of the radiated and reflected waves happens in both of these configurations especially in the downwards direction, it is more prominent once sound waves pass the slat track and cut-out. Wave cancellation is also significant when the wavelength is comparable to the size of the barrier such as the gap between the slat and the main element. It is also noticed that higher frequencies radiate large proportion of energy towards ground for the sources at slat cusp.

A method for crack sizing using Laser Doppler Vibrometer measurements of Surface Acoustic Waves

The goal of non-destructive testing (NDT) is to determine the position and size of structural defects, in order to measure the quality and evaluate the safety of building materials. Most NDT techniques are rather complex, however, requiring specialized knowledge. In this article, we introduce an experimental method for crack detection that uses Surface Acoustic Waves (SAWs) and optical measurements. The method is tested on a steel beam engraved with slots of known depth. A simple model to determine the cracks size is also proposed. At the end of the article, we describe a possible application: fatigue crack sizing on a damaged slat track. This technique represents a first step toward a better understanding of the crack growth, especially in its early stages (preferably when the cracks can still be repaired) and when it is possible to assume a linear propagation of the crack front. The ultimate goal of this research program is to develop a useful method of monitoring aircraft components during fatigue testing.

Reliability-Based Fatigue Optimization of an Air Plane Slat Track with Respect to Manufacturing Tolerances*

Abstract Especially for the design with respect to fatigue the scattering in load conditions and durability performance has a significant influence. In the case studied in this paper we concentrate on the durability performance, and here especially on manufacturing tolerance influences. For the original design all specimen of the component have been measured, such that reliable data on the manufacturing process are available. This data now enables to estimate which tolerances are necessary for a safe durability performance but also shows that there is significant potential for reducing the weight of the component. The development from optimization methods with respect to durability to reliability based optimization methods is an important step to better and safer designs.

Effect of ion nitriding on the microstructure and properties of Maraging steel (250 Grade)

In the present investigation, ion nitriding of Maraging steel (250 grade) has been carried out at three different temperatures i.e., at 435 °C, 450 °C and 465 °C for 10 h duration in order to achieve good wear resistance along with high strength required for the slat track component of aircraft. The microstructure of the base material and the nitrided layer was examined by optical and scanning electron microscope, and various phases present were determined by X-ray diffraction. Various properties, such as, hardness, case depth, tensile, impact, fatigue properties and corrosion resistance were investigated for both un-nitrided and ion-nitrided materials. It is observed that the microstructure of the core material remains unaltered and Fe 4N is formed in the hardened surface layer after ion nitriding at all the three temperatures employed. Surface hardness increases substantially after ion nitriding. Surface hardness remains almost the same but case depth increases with the increase in ion nitriding temperature due to greater diffusivity at higher temperatures. Tensile strength, fatigue strength and corrosion resistance are improved but ductility and energy absorbed in impact test decrease on ion nitriding. These results are explained on the basis of microstructural observations. The properties obtained after ion nitriding at 450 °C for 10 h are found to be optimum when compared to the other two ion nitriding temperatures.

Robust optimization of an airplane component taking into account the uncertainty of the design parameters

AbstractA slat track, structural component of an aircraft wing that transfers the aerodynamical loads, excited by operational forces can result in excessive displacement levels if not properly designed. The design parameter values are not always precisely known but can contain a level of uncertainty to some extent due to, for example dimensional variation. During the different optimization approaches, the slat track geometry is optimized in order to limit the maximum vertical displacement, taking into account the variability of the design parameters. Application and comparison of different optimal, robust and generalized optimization approaches is presented and applied on the slat track finite element model, making use of mean and variance response functions to model the uncertainty on the finite element displacement values. Next to validating different objective function statements, a comparison is also made on the level of accuracy and practicability concerning the different response function models, based on regression techniques and Monte Carlo simulations, optimization and transmissibilities and regressive techniques and vibration reduction over a frequency range. Copyright © 2008 John Wiley & Sons, Ltd.

Reliability-Based Design of a Slat-Track Fatigue LifeUsing Mesh Morphing Technology

Although the aerospace production process is much better controlled than in other industries, it remains true that very small manufacturing tolerances exist in the geometrical parameters such as flange thickness and hole diameters. In the current design process, the effect of this manufacturing variability on the structural durability and safety cannot be accurately assessed and is hence compensated for by applying safety factors. This is not an ideal situation, because it may lead to slightly overdesigned structures. A much more promising approach is to include probabilistic models of design variables into the mechanical simulation process. With a new methodology based on reliability analysis, engineers can obtain a better understanding of the actual effect of the manufacturing tolerances and of variability in material properties. Based on the analysis results, the robustness and reliability of the design can be assessed and improved if needed. In this paper, the aforementioned probabilistic approach is demonstrated on a slat-track structure. Measurements of different geometrical properties were collected during the manufacturing process and their variability was characterized probabilistically with statistical models. Then a reliability analysis was carried out using mesh morphing technology and fatigue life predictions with an industrial-sized finite element model of the slat track to assess the reliability of the structure in terms of fatigue life. The outcome of the analysis consists of a probabilistic model of the structural performance (e.g., fatigue life for the slat track), given the variability in the geometrical parameters. Then a reliability-based design optimization procedure was carried out to improve the design of the slat track while maintaining the same reliability of the nominal design.

JAXA高揚力形態半裁模型の空力特性について

This paper presents basic aerodynamics and stall characteristics of the high-lift configuration aircraft model JSM (JAXA Standard Model). During research process of developing high-lift system design method, wind tunnel testing at JAXA 6.5m by 5.5m low-speed wind tunnel and Navier-Stokes computation on unstructured hybrid mesh were performed for a realistic configuration aircraft model equipped with high-lift devices, fuselage, nacelle-pylon, slat tracks and Flap Track Fairings (FTF), which was assumed 100 passenger class modern commercial transport aircraft. The testing and the computation aimed to understand flow physics and then to obtain some guidelines for designing a high performance high-lift system. As a result of the testing, Reynolds number effects within linear region and stall region were observed. Analysis of static pressure distribution and flow visualization gave the knowledge to understand the aerodynamic performance. CFD could capture the whole characteristics of basic aerodynamics and clarify flow mechanism which governs stall characteristics even for complicated geometry and its flow field. This collaborative work between wind tunnel testing and CFD is advantageous for improving or has improved the aerodynamic performance.

Laser vibrometer measures surface acoustic waves for nondestructive testing

In assessing the safety of a structure, a nondestructive testing (NDT) technique should be able to detect the position of any defects and calculate their size. Most NDT techniques are thus necessarily complex, require qualified staff, and are unsuited to automation. In this article, we describe an experimental NDT methodology for crack detection using surface acoustic waves (SAWs) and optical laser Doppler vibrometer measurements. We evaluate whether ultrasonic laser measurements appropriately detect damage and imperfections in structural components. SAWs are elastic waves that are confined to the surface of a material. They travel along, penetrating about one wavelength into the surface (where the depth of penetration is defined by the depth at which 95% of the wave energy is transmitted). 4 We chose an ultrasonic optical technique instead of other currentlyavailable methods (e.g., ultrasonic scanning, magnetic particle inspection, x-ray imaging, and imaging techniques in general5) for two reasons. First, using the laser as a receiving ultrasound transducer enables remote access to the structure being tested. Second, laser scanning a region of interest makes it possible to obtain many measurements regarding the incident, transmitted, and reflected waves. These measurements, in turn, elucidate the behavior of the SAWs and of the crack itself. In the presence of surface discontinuities such as surface roughness and cracks, part of an incident wave is reflected. The rest is transmitted. Hence, gauging SAWs in the vicinity of a discontinuity allows one to infer information about the state of the surface. The material we tested was the slat track of an Airbus A320. This part of the plane is the movable support structure connecting the wing with the leading-edge slats (see Figure 1). A hydraulic test rig was used to induce in the structure the kind Figure 1. Shown is an Airbus A320 and the slat track used for testing.

Improved total least squares estimators for modal analysis

Nowadays, modal analysis has become a common tool for studying the dynamical behaviour of complex mechanical structures. However, the analysis of extensive data sets, that are obtained during high channel-count modal testing, requires additional efforts for the development of dedicated modal parameter estimation methods. The present paper discusses an efficient formulation of a frequency-domain total least squares identification approach for the field of experimental modal analysis. In particular the performance for high model orders and efficient computational properties are discussed and illustrated using experimental data. The evaluation is based on a practical case study, discussing the dynamical modelling of slat tracks of an Airbus A320 commercial aircraft. This safety critical component is characterized by a complex modal behaviour requiring both high model orders and a high spatial resolution in order to achieve an accurate model.

A comparison of frequency-domain transfer function model estimator formulations for structural dynamics modelling

The purpose of this paper is to present the results of a comparative study of various formulations of a frequency-domain least-squares (LS) estimator. This study was the basis for the optimization of the LS algorithm for modal parameter estimation. Nowadays, modal analysis studies the dynamical behaviour of very complex structures, which requires both robustness for high model orders and efficient numerical properties to analyse extensive data sets that are obtained during high channel-count modal testing. This paper focuses on the optimal choice between various transfer function models and a weighted formulation of the LS problem by taking also a measure for the noise on the data into account. The evaluation is based on a practical case study, discussing the dynamical modelling of slat tracks of an Airbus A320 commercial aircraft. This safety critical component is characterized by a complex modal behaviour requiring both high model orders and a high spatial resolution in order to achieve an accurate model.

Multisine load cycle design for fatigue testing

To experimentally quantify the fatigue life of critical airplane components (such as, for instance, the slat tracks), extensive tests must be performed on a test rig. In this paper, a method is proposed to design the load signal which has to be applied in order to exactly obtain a certain damage content. The method presented uses a (band-limited) perturbed multisine (MS) excitation signal. Therefore, the load can be easily controlled. In addition, because the designed multisine is periodic, the health of the structure can easily be monitored on-line. The proposed method will be validated both on simulations and on (low cycle) fatigue measurements of a steel beam.

AUTONOMOUS STRUCTURAL HEALTH MONITORING—PART I: MODAL PARAMETER ESTIMATION AND TRACKING

A growing interest for techniques and systems allowing the early detection and monitoring of damage based on vibration analysis is clearly present in different research and application areas, such as civil constructions, mechanical systems, and aircraft and aerospace industry. However, an important element for the applicability of modal-based damage assessment techniques in practice is the automation of the identification and tracking procedure. In this contribution it is shown that, by using a frequency-domain maximum likelihood estimator, features such as high accuracy and confidence bounds for the estimated parameters and robustness for high measurement noise levels create the possibility to automate the modal identification process. For the validation of the model, criteria based on a statistical approach were developed in addition to the well-known criteria such as modal phase colinearity and mode complexity, while the final mode selection is done by means of a fuzzy clustering algorithm. At the same time, an accurate mode-tracking algorithm is presented. It is shown that the problem of coinciding poles, due to shifting or crossing modes under changing structural dynamics, can hamper the mode tracking and a robust solution is proposed. The possibilities and limitations of the automated approach are investigated and tested for a slat track of an Airbus A320 commercial airplane, providing a preliminary study for future monitoring practices during life cycle tests on slat tracks.

AUTONOMOUS STRUCTURAL HEALTH MONITORING—PART II: VIBRATION-BASED IN-OPERATION DAMAGE ASSESSMENT

Monitoring structural health of civil and industrial structures, based on in-operation modal testing, has become an important issue. Recently, a sensitivity-based damage assessment technique was presented and successfully tested on both civil and more academic structures. As shown in literature, these sensitivities can be experimentally calculated (without the use of a finite element model) on a basis of the estimated natural frequencies and mass-normalised mode shapes of the test structure in its reference condition. Since a driving point measurement is required for an easy scaling (e.g. mass-normalisation) of the mode shapes, the applicability of the method was restricted to forced-vibration tests only. In this contribution, the applicability of the sensitivity-based method is extended to the domain of operational modal analysis (output-only measurements). In a first step, a new method is used for the correct re-scaling of operational mode shape estimates that neither requires forced vibration testing nor finite element modelling. Secondly, two innovative sensitivity-based in-operation damage assessment schemes are introduced. Both methods were experimentally tested on an academic frame structure as well as a slat track of an Airbus A320 commercial aeroplane.

Structural Design

THE Trident has been designed with the objective of achieving freedom from fatigue cracks on the primary structure, during the operational life of the aircraft. Additionally, in areas where the fail safe concept can be applied, the design aim has been to provide multiple load paths and/or crack stoppers so that, in the event of any one member failing, the remaining structure can sustain at least limit loads for a longer period than the interval specified between major inspections of the structure. In the places where it is not possible to apply the fail safe concept, that is on flap and slat tracks, tailplane hinge fitting, engine mountings and landing gear, a substantial margin of safe life is provided.