Composite Fan Research Articles

Effects of Surface Waviness on Fan Blade Boundary Layer Transition and Profile Loss—Part II: Experimental Assessments and Applications

AbstractPart II describes the experimental assessment and the application of the ideas in Part I concerning the mechanisms that determine the role of blade surface waviness on laminar-turbulent transition and their consequent effect on civil aircraft fan performance. A natural transition wind tunnel was designed and constructed to characterize the impact of surface waviness on transition, using both hotwire anemometry and infrared thermography. The experimental results support the new hypothesis presented in Part I, concerning the way in which blade surface waviness affects fan performance through motion of the transition onset location due to interaction between surface waviness and Tollmien–Schlichting (TS) boundary layer instability. In particular, the theoretical amplification of the TS waves, and the corresponding transition onset location movement due to surface waviness, was borne out over a range of variations in Reynolds number, nondimensional surface wavelength, nondimensional surface wave height, and location of surface wave initiation, relevant to composite fan blade parameters. Further, the increase of receptivity coefficient, and thus, the initial amplitude of disturbances due to geometric resonance between surface wavelength and TS wavelength was also confirmed by the experiments. Surface waviness was estimated, in some cases, to result in a nearly 1% decrease in fan efficiency compared to a nonwavy blade. Suggestions are given for mitigation of the effects of waviness, including the idea of blade curvature rescheduling as a method to delay transition and thus decrease loss.

Effects of Surface Waviness on Fan Blade Boundary Layer Transition and Profile Loss—Part I: Methodology and Computational Results

AbstractThis two-part paper describes a new approach to determine the effect of surface waviness, arising from manufacture of composite fan blades, on transition onset location movement and hence fan profile losses. The approach includes analysis and computations of unsteady disturbances in boundary layers over a wavy surface, assessed and supported by wind tunnel measurements of these disturbances and the transition location. An integrated framework is developed for analysis of surface waviness effects on natural transition. The framework, referred to as the extended eN method, traces the evolution of disturbance energy transfer in flow over a wavy surface, from external acoustic noise through exponential growth of Tollmien–Schlichting (TS) waves, to the start and end of the transition process. The computational results show that surface waviness affects the transition onset location due to the interaction between the surface waviness and the TS boundary layer instability and that the interaction is strongest when the geometric and TS wavelengths match. The condition at which this occurs, and the initial amplitude of the boundary layer disturbances that grow to create the transition onset is maximized, is called receptivity amplification. The results provide first-of-a-kind descriptions of the mechanism for the changes in transition onset location as well as quantitative calculations for the effects of surface waviness on fan performance due to changes in surface wavelength, surface wave amplitude, and the location at which the waviness is initiated on the fan blade.

Interpretation of Stall Precursor Signatures

Abstract Unsteady aerodynamic phenomena appearing close to the stall boundary in axial fans and compressors have been the subject of extensive investigations. A particular phenomenon known as “rotating instabilities” typically occurs in the tip region at highly loaded conditions and is often linked to blade vibrations. During rig and engine testing, it is usually identified by the characteristic shape of its pressure spectra. In the 1990s, this shape has been explained as the result of a circumferentially propagating disturbance, which is unsteady in a frame of reference rotating with the disturbance. In this analysis, conclusions regarding its propagation speed and frequency have been made based on the analysis of spectral peaks, and this method is still often used to classify unsteady aerodynamic phenomena. However, in high subsonic and transonic machines, where aeroacoustic and aeroelastic phenomena interact with aerodynamic disturbances, the interpretation of measurements using spectra alone is challenging. The present article aims to demonstrate the difficulties and subtleties associated with the analysis of measurement signals, which need to be overcome to correctly interpret stall precursor signatures. At the example of a recent investigation on a composite fan, the consequences of sensor placement and postprocessing techniques are discussed with a focus on spectral averaging, isolation of non-synchronous phenomena, and multisensor cross correlation methods. It is seen that the interpretation of phenomena based solely on spectral peaks and their spacing can be misleading and that the characteristic features of a rotating instability spectrum do not require an unstable pulsating disturbance.

Application of genetic algorithm to optimize the impact resistance of composite laminates

The impact resistance of composite fan hood is of great significance to improve the safety of engine. Taking the fiber reinforced resin matrix composite laminate for Aeroengine fan case as the research object, the maximum loss kinetic energy of impact body as the objective function, and the fiber ply angle as the design variable, the impact resistance of the fiber reinforced composite laminate was optimized. ABAQUS finite element software is used to simulate the high velocity impact of composite laminates, and genetic algorithm is used to optimize the design, and the optimal stacking method is obtained. Through the optimization design, the impact resistance of fiber reinforced composite laminates has been greatly improved.

Aerodynamic Investigation of a Composite Low-Speed Fan for UHBR Application

Abstract A composite fan stage representative of a modern Ultra High Bypass Ratio (UHBR) architecture has been investigated experimentally on a novel test facility at Ecole Centrale de Lyon. These measurements show indications for strong overloading of the tip region resulting in extensive blockage of the blade passage. The performance of the fan is analyzed with extensive instrumentation including radial profiles upstream and downstream of the rotor. Unsteady pressure measurements help to interpret the flow structure in the tip region. The results are presented across a range of operating points on the design speedline. At the stability limit, the machine suffers from non-synchronous vibrations, which result from small-scale aerodynamic disturbances propagating between the leading edges. Detailed analysis of the occurring waveforms is presented for two operating speeds. In order to further analyze the observed phenomena, a numerical study has been conducted using the Reynolds-averaged Navier–Stokes (RANS) solver elsA. The results of steady calculations are discussed in comparison with the detailed experiments. Unsteady simulations near the stability limit accurately predict the aerodynamic disturbances observed during non-synchronous vibrations (NSV). The obtained results are unusual for typical state-of-the-art transonic fans, as they show the same behavior as high-pressure compressor front stages, dominated by a blockage caused by tip-leakage flow. Even though flutter is not observed, the observed non-synchronous vibration mechanism is a critical aeroelastic phenomenon which is of great interest for future designs of low-speed fans.

Collaborative optimization of conical cutter sequence for efficient multi-axis machining of deep curved cavities

As an essential part of the composite fan blade, the leading edge protection cap (LPC) has a very narrow and deep cavity which, in order to avoid the interference, requires the conical ball-end cutter to be long and thin. It calls to improve the cutter’s stiffness so to increase the roughing efficiency of the whole cavity. Targeting this important problem, this paper proposes a novel method to collaboratively optimize a conical cutter sequence, the machining ranges, and the cutting parameters for achieving the highest material removal efficiency. The main difficulty is that all the relevant entities – i.e., the LPC cavity geometry, tool size, tool axis, machining ranges, minimum tool length, tool stiffness, and cutting performance – collaboratively affect the total cutting efficiency. To facilitate decoupling them, the 3D LPC cavity is characterized by its medial surface. To identify all the geometrically accessible conical tools of each medial point, an efficient algorithm is proposed, which is featured by searching characteristic points on the cavity surface. By considering both the geometric and physical accessibilities, the tool sequence domain is constructed. To obtain the appropriate cutting parameters, the best cutting performance of a weak conical cutter is modeled under the constraint of deflection due to the cutting force. Finally, the complicated collaborative optimization model aiming for the minimum cutting time is established and solved by a PSO-based algorithm. The experimental results confirm that the proposed model and algorithm are practicable for improving the roughing efficiency of LPC cavity.

Design and Optimization of Hybrid Interface Joint in a Composite Fan Blade of Aircraft Engine

Fan blades are one of the most important components of an aircraft engine. Bird strikes on fan blades have always been a cause of worry and it can cause slices of birds hitting other parts of the engine which may lead to greater damages. Bird strikes cannot be completely avoided. However, reduction of the impact of a bird on jet engines can be achieved by suitable design and manufacturing, through the simulation analysis. Although current composite blades can withstand the bird strike impact, some delamination failures are still observed on the trailing edge side of the blade, possibly due to vibration bending modes This paper talks about using two fibers in composite blade instead of the current single fiber one. For this to be feasible, two fiber joints at various locations on the blade have to be properly designed. The design criteria used here is the lowest inter-laminar shear strain level at critical joint locations. Suitable size coupon models in FEA with hybrid joints inside are used to simulate the blade bending with appropriate boundary conditions. The coupon models were developed by using the ANSYS APDL and linear static analysis was performed for different repetitive layups and varying layer by layer joint locations. The coupon joint designs with minimum inter-laminar shear strains are shortlisted to be recommended for use in sub-element and blade models.

Hybrid textile composite fan with smart and fractal structure

It is a key issue to embed sensing components in a smart material. A fractal-like distribution of sensing components is considered in this paper to collect data for smart-type fan test blades with hybrid textile composite, which is proved to have self-monitoring property. A fluid-solid coupling model is proposed to analyze the functional relationship among the hybrid fiber arrangement and morphology and the mechanical properties of blade in each force point. It is concluded that the deformation and the self-adaptability of flexible fan blades are two main factors affecting power efficiency.

Developing a sport fan equity index

PurposeThe primary purpose of this study was to generate a composite sport fan equity index (SFEI) for use in estimating the asset value of an individual fan to a sport organization. The index was developed by applying a simple additive weighting (SAW) method.Design/methodology/approachA cross-sectional survey-based research was carried out to validate key components of sport fan equity (SFE) and formulate the SFEI on the basis of the NCAA Division I collegiate sport context. These objectives were satisfied through a twofold process involving first-order confirmatory factor analysis intended to assess the validity of SFE measurement scales and SAW designed to produce the composite SFEI.FindingsThe developed index indicated that the average SFE of focal sport fans of Division I collegiate sport was 54.8 and that the overall SFE of such contributors ranged from 20.4 (the lowest score) to 94.6 (the highest score). The SFEI serves as a single, summary score and an essential gauge for sport marketers to use when assessing profitable fans and tracking/comparing them over time.Originality/valueThis research contributes to the sport marketing literature through its application of SAW in an initial effort to produce an easily understandable index that determines the asset value of sport fans and serves as an imperative criterion for overall sport team valuation from the sport consumer side. Specifically, the SFEI can function as a standard numeric measure that enables sport marketers to identify fans from whom sport organizations can generate considerable profits, segment these devotees systematically, and tailor marketing strategies to each fan base.

A Study on Stacking Sequence Design of Composite Fan Blades Using Multi-level Optimization

In this paper, the multi-level optimization method is proposed to design the optimal stacking sequence of composite fan blade more efficiently. The fan blade model used is a laminate with inconsistent stiffness because the thickness is not uniform throughout the model. This feature complicates the optimization problem and makes it difficult to apply optimal design algorithms that use only continuous or discrete variables. For this reason, we conducted the literature survey about combining the optimal design algorithm with continuous and discontinuous variables and developed optimization algorithm for the composite fan blade. Moreover, the design space of discrete variables is reduced through the optimal design of continuous variables. In the first-level, response surface method is used, with the design variables being the volume fraction of plies of the predefined angles of [0°/±45°/90°]. The optimization problem in the first-level aims at minimizing the tip displacement of the fan blade and constraints on other structural responses are imposed. At the second-level, the permutation genetic algorithm is used with the fiber orientation of each ply as design variables. In this level, we perform the optimal design of the stacking sequence using the results determined by prior level, while the composite design rule and compliance constraints are applied.

Application of 3D Projection Profilometry in the High Speed Impaction Surface Deformation Measurement Research

In order to study the strength of the composite material plate problems, need to adopt a nondestructive testing method to obtain the specimen surface under the effect of high-speed impact regularity of shape. The projection profilometry was used to measure the surface profile or the full field deformation. Furtherly, by using the Fourier transform algorithm, there is only one frame of captured image which is needed in the measurement, so that it can be introduced into the high speed impaction procedure measurement. An experimental system, which was contained with an impact setup and the projection profilometry measurement part, was constructed for the impaction action characteristic research. The metallic impact object can be launched by a gas gun or a spin fan, respectively. The detected object is manufactured by composite materials. In order to increase the surface deformation measurement accuracy, the calibration method and the error was discussed with different calibration specimen. And then, the proposed profilometry measurement method is proved by the gas gun and spin fan projectile test. The surface deformation of the manufactured composite plates and fan case are measured in the impaction procedure. So that the impact action details can be described much more clearly than the traditional video monitoring method.

Innovative designs of embedded foam inserts in aerospace composite structures

Abstract There have been many attempts to redesign the aerospace composite structures in recent times to further improve their performance and reduce the weight. As part of these efforts, it has been proposed here that lightweight polymeric foam can be used as an embedded insert inside the fiber reinforced composite structure to further reduce its weight. The target application here is composite fan blade of aircraft engine This paper describes the analysis led design (FEA) and experimental efforts to optimize the shape of this embedded foam insert inside the composite structure under both representative static and dynamic loading so that weight reduction is achieved without affecting the structural performance of the aerospace composite structure. Different geometrical parameters like taper of foam tip, blunting level of the foam tip, use of dual or multiple foam inserts, use of continuous ply layer and other parameters like use of softer material like glass near foam tip, thickness of adhesive (which is used to bond foam with carbon composite) are investigated and their effect on the level of shear stress near the foam tip has been observed. The level of shear stress near the foam insert tip is found to be the major indicator of the possible crack initiation near tip. This study helped optimize the shape of the foam insert inside the composite structure to avoid the initiation of cracks, which is validated by manufacturing the lab level carbon fiber epoxy composite specimens with optimized foam insert geometry and testing them under representative staggered four point bend boundary conditions.

Creation and verification of computational models for analysis of the mechanical behaviour of jet engines composite components under high-velocity impact: main problems and basic recommendations

Currently, modern CAE programs like ANSYS, LS-DYNA, ABAQUS, Simcenter 3D etc. are widely used to develop each engineering product. CAE reduces development costs and speeds up product launches. Computer modelling allows eliminating unsuccessful design options at early design stages and minimising or eliminating critical design changes at the prototype testing stage. Computer simulations are especially needed for the development of high-performance perfection designs like jet engines. The use of composites in the engines requires the availability of appropriate design tools to assess the mechanical behaviour of structural elements made of such materials under operational loads and in an emergency. Predictive modelling of the deformation and fracture of the composite fan blades and fan case subjected to dynamic loading cause considerable interest of engineers. As in the case of simulation of shock loading of metals, a model of a composite material must be verified. However, the problem is that the fibrous composite material itself is already a structure and can be modelled in various ways: without considering the layered structure (homogeneous approach) taking the mesostructure into account (at the ply-level or at the yarn-level) taking the microstructure into account (at the filament level). The requirements for the initial data, the number of parameters determined during the verification process, the complexity of creating geometric models will differ in each case. This paper briefly describes the main approaches to the numerical simulation of composite elements under high-velocity impact loading. The main advantages and disadvantages of these approaches are also considered. On the example of the meso-scale approach, the main parameters of the computational models that affect the results of calculations are shown. Based on the obtained data, the main recommendations were formulated on the validation of meso-scale models of composites.

Numerical investigation of rub-induced composite fan blade vibrations and abradable coating removals

Composite blade vibrations, removal of abradable coating, and blade stress resulting from blade/casing rubs are investigated. Composite fan blade models with different stacking sequences and a metal blade are created and calculated through a three-dimensional finite element method. Centrifugal stiffness, damping of composite structures, B-spline surfaces, and abradable coating are included in the calculations. The results show that the maximum vibration amplitudes of composite blades at different rotational speeds could be affected by stacking sequences. The responses of metal blade are more sensitive to the natural frequencies of the second to the fifth blade modes than those of the composite blades. Abradable coating removals are highly related to blade vibration amplitudes. Considerably more coatings are removed by the metal blade than by the composite blades at the design speed, particularly in the axial direction. Moreover, according to the stress results, the metal blade is more vulnerable to rub-induced vibrations than the composite blades at the design speed. Larger vibration amplitudes in the composite blades do not necessarily lead to lower failure margins because of the complexity of composite structures. The strategy established can be utilized to aid in the initial designs of state-of-the-art composite blades and reduce potential rub-induced problems.

Strength Assessment of Fan Blade with Different Materials

Weight reduction of turbofan engines is one of the main concerns of aero engine manufacturers in order to cut fuel burn. To achieve higher fuel efficiency, aero engine manufacturers develop turbofans with higher bypass ratio, which can only be achieved with larger (and heavier) fan sections. This makes weight reduction in fan components a major consideration and becomes a key driver for the use of composite materials in future engines. The objective of this project is to design, perform structural analysis and optimization of a Composite fan blade. Development of a fan blade is comparable to a future large aircraft engine fan blade. This thesis is about the structural analysis of a composite fan blade with a honeycomb sandwich construction with a polymer matrix composite and honeycomb Aluminium core compared with baseline solid basic fan blade made of titanium. The focus of this work is to design the sandwich composite blade with honeycomb core and conduct static and dynamic analysis.

Dynamic Behavior and Damage Mechanism of 3D Braided Composite Fan Blade under Bird Impact

The three-dimensional braided composites, with intertwined fiber bundles in the through-thickness direction, have advantages of high interlaminar shear strength, fracture toughness, and excellent impact resistance, making them a promising material for applications in the field of aeroengine fan blades. As the bird impact behavior of the fan blade directly affects the safety of the aeroengines, it is of great significance to study the dynamic response and damage mechanism of 3D braided composites under bird strike load. In this paper, the bird impact tests on the 3D four-step braided composite targets were carried out using the gas gun system. The effects of impact velocity, impact location, and braiding angle on the bird impact behavior were studied. It is concluded that the damage and failure become more severe with the increasing impact velocity. The whole impact event could be divided into 3 stages, i.e., local deformation stage, postflow impact stage, and bending deflection stage. The braided composite presents flexible characteristics and could bear extraordinary deformation during the bird impact. One distinguishing feature of bird impact damage is the destruction of the clamping root due to bending load caused by cantilever construction. The internal damage form at the impact area was mainly the separation of the fiber bundles from the matrix while the breakage of the fiber bundles and the crushing of the matrix play the primary role at the root part. The target plate impacted at the 70% height had the largest bending angle and most serious damage, followed by those impacted at the 90% and 50% heights. Both the appearance damage and internal damage extent are smallest for 45° braiding composites.

Estimating Hydraulic Conductivity Fields in Composite Fan Delta Using Vertical Electrical Sounding

Hydraulic conductivity (K) is crucial for groundwater studies and is conventionally obtained through pumping tests, which are costly due to well installation, resulting in a limited amount of data. Recent studies have addressed this limitation by estimating K through the integration of a pumping-test K and electrical resistivity measurements. While this approach is suitable for local areas, it cannot readily be applied to determine K fields for the composite fan delta. This study proposes and demonstrates an advanced method to estimate the K’s spatial distribution of a composite fan delta. The proposed method included data classification, linear regression, and kriging interpolation. Data classification was conducted using a physical-based zonation method. The K and formation factor (F) data pairs were classified into several groups. Linear regression was used to develop K-F mapping for each group. The regression results showed a good correlation between K and F in each group. These K-F mappings were verified by additional pumping tests. These results indicate that estimation errors were between 7 m/day and 58 m/day, and the correlation coefficient of each data group was greater than 0.8. Based on these regression equations and ordinary kriging method, the detailed K spatial distribution of the study area was derived. According to these results, the proposed method is efficient and economical to delineate K’s spatial features for regional groundwater systems and can benefit groundwater-related studies.

Non-destructive evaluation of through-thickness permeability in 3D woven fabrics for composite fan blade applications

In this study, we propose a non-destructive modeling framework, with an ability to obtain computational models for numerical prediction of resin flow through 3D fabrics (commonly used in engine fan blade applications) at multiple fiber volume fractions using a single experiment. The work involves extracting real-time geometrical features of two types of 3D reinforcements during an in-situ compaction experiment using micro CT. The 3D image slices obtained at four different thicknesses were converted to computational models. The fiber tows and inter-tow gaps were modeled as distinct phases. The gap analysis and geometrical measurements revealed significant differences in the preform microstructure investigated at different thicknesses. This was followed by a detailed flow analysis using two different commercial software packages. The exported mesh was analyzed in GeoDict® and Ansys Fluent® for through-thickness permeability computations. The governing fluid dynamics equations were solved to obtain the flow field within the inter-tow gaps for representative volume elements. The predicted through-thickness permeability values were in very good agreement with the experimental data.

Numerical Investigation on Aeroelastic Behavior of Composite Material Plate Excited by Pulsed Air Jet

Nowadays, carbon fiber composite material is becoming more and more popular in aero engine industry due to its high specific strength and stiffness. Laminate carbon fiber composite material is widely used to manufacture the high load wide chord fan blade, containment casing, etc. The aeroelastic behavior of composite product is critical for the optimization of the product design and manufacturing. In order to explore its aeroelastic property, this paper discusses the coupled simulation of aerodynamic excitation applied on laminate composite material plate. Mechanical behavior of composite material plate is different from that of isotropic material plate such as metal plate, because it is anisotropy and has relative high mechanical damping due to resin between plies. These plates to be studied are designed using 4 different layup configurations which follow the design methods for composite fan blade. The numerical simulation of force response analysis mainly uses single frequency mechanical force input to simulate the electromagnetic shakers or other actuators, which could transmit mechanical force to the test parts. Meanwhile, pulsed air excitation is another way to “shake” the test parts. This excitation method induces aero damping into the test part and simulates the unsteady flow in aero engine, which could cause aeroelastic problems, such as flutter, forced response and non-synchronous vibration (NSV). In this study, numerical simulation using coupled method is conducted to explore the characteristics of laminate composite plates and the property of aerodynamic excitation force generated by pulsed air jet device. Modal analysis of composite plate shows that different ply stacking sequences have a significant impact on the plate vibration characteristics. Air pulse frequency and amplitude in flow field analysis are calibrated by hot wire anemometer results. As the air pulse frequency and amplitude are varied, incident angle of flow and layup configurations of plate can be analyzed in details by the simulations. Through the comparisons of all these factors, air pulse excitation property and the aeroelastic behavior of composite material plate are estimated. It would provide a possible way to guide the next-step experimental work with the pulsed air rig. The new composite fan blade design can be evaluated through the process.

Estimation of the temperature field on a composite fan cowl using the static capacity of surface-mounted piezoceramic transducers.

The influence of temperature on SHM (Structural Health Monitoring) systems using guided waves is a major problem for their industrial deployment. One of the cheapest SHM process developed in aeronautical context is based on piezoelectric transducers mounted on the monitored structure. Several methods are used to assess the presence of damage. A popular one is based on tracking changes in the electromechanical impedance of the transducers: it is an efficient damage indicator around the device and can also be used as a fault diagnosis indicator for the transducer itself. However, monitoring decisions need to be robustified with temperature sensors also mounted on the structure. In this article, the electromechanical impedance is used to determine the temperature on each lead zirconate titanate transducer (PZT). This avoids supplementary instrumentation and the entire temperature field of the structure is estimated. The proposed approach is tested experimentally on a on a small composite plate and then on a real part of an A3 80 composite nacelle. Results show that the temperature field on the structure can be estimated with a precision of ±5 °C using a linear regression between static capacity and temperature.