Experimental and finite element analyses of multifunctional skins for morphing wing applications

As a consequence of operational efficiency because of rising energy costs, future transport systems need to be mission-adaptive. Especially in aircraft design the limits of lightweight construction, reduced aerodynamic drag and optimized propulsion are pushed further and further. The first two aspects can be addressed by using a morphing leading edge. Great economic advantages can be expected as a result of gapless surfaces which feature longer areas of laminar flow. Instead of focusing on the kinematics, which are already published in a great number of varieties, this paper emphasizes as major challenge, the qualification of a multi-material layup which meets the compromise of needed stiffness, flexibility and essential functions to match the flight worthiness requirements, such as erosion shielding, impact safety, lighting protection and de-icing. It is the aim to develop an gapless leading edge device and to prepare the path for higher technology readiness levels resulting in an airborne application. During several national and European projects the DLR developed a gapless smart droop nose concept, which functionality was successfully demonstrated using a two-dimensional 5 m in span prototype in low speed (up to 50 m/s) wind tunnel tests. The basic structure is made of commercially available and certified glass-fiber reinforced plastics (GFRP, Hexcel Hexply 913). This paper presents 4-point bending tests to characterize the composite with its integrated functions. The integrity and aging/fatigue issues of different material combinations are analyzed by experiments. It can be demonstrated that only by adding functional layers the mentioned requirements such as erosion-shielding or de-icing can be satisfied. The total thickness of the composite skin increases by more than 100 % when required functions are integrated as additional layers. This fact has a tremendous impact on the maximum strain of the outer surface if it features a complete monolithic build-up. Based on experimental results a numerical model can be set up for further structural optimizaton of the multi-functional laminate. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Investigation towards an active barrier for structure borne sound using structural intensity

Vibrations of aircraft or vehicle engines, for instance, are often transmitted by structure borne sound, leading to a significant radiation of noise inside passenger cabins. Current active vibration control concepts use either velocity or acceleration as a control source. However, these only lead to a local reduction in vibration and not necessarily to the reduction of the vibration energy flow. This study presents the implementation of current methods for structural intensity measurement with a real-time control. The work investigates one and two-dimensional structures. A reduction of energy flow in a beam structure is shown experimentally, as well as numerically for plates. The measurements are strongly influenced by theoretical simplifications concerning the composition of the structure borne waves and the quality of the sensor arrays used, i.e. the sensor spacing and the positioning accuracy. Though, sufficient accordance between numerically and experimentally estimated structural intensity can be found using methods with smaller sensor arrays. A barrier effect is shown by numerical investigations and is measured on a beam. Therefore, the control of vibration energy flow is a more effective method for a global reduction if vibration downstream the control area

Transmission loss variation of mass constant sandwich plates using geometric honeycomb core variation

Pollutant emissions like CO2 or NOX increased in the last decades. One reason is the increased av-erage distance covered by each person which has grown in a similar proportion. This again leads to the use of vehicles with combustion process more frequently. In order to counteract this trend, the government restricts the pollutant emission of new vehicles. One approach for efficient vehicles is the reduction of the transported mass. Lightweight structures such as sandwich composites offer the possibility of mass reduction with similar stiffness. Unfortunately, this leads to an increased sound radiation at lower frequencies. Therefore, insulating elements are necessary to reduce the sound transmission in the vehicle cabin, but this increases the mass and counteract the benefit of the light-weight structures. The example of sandwich plates will be used to show that the geometrical variation of a honeycomb core can increase the transmission loss. The core mass stays constant during this variation. The cell diameter of these cores varies between 5 cm and 13 cm, while commercially available cores have often diameters in millimeter range. The core variation is done with finite element analysis in the frequency range up to 2000 Hz. The transmission loss of selected sandwich plates is measured in order to confirm the simulation results. If the cell diameter size increases, the transmission loss in-crease can be shifted to lower frequencies. With a cell diameter of 13 cm the averaged increase of the transmission loss is by 3 dB and it starts by approximately 500 Hz. Thus, the design of a mass constant core improves the acoustic properties of a sandwich and it can address critical frequencies. Such acoustically adapted lightweight structures will reduce the number of insulating elements in vehicles. This design approach can contribute to lower the pollutant emissions of future vehicles

DESIGN OF AN ACTIVE NOISE CONTROL SYSTEM FOR A BUSINESS JET WITH TURBOFAN ENGINES

An active noise vibration control (ANVC) system is designed for a Dassault Falcon 2000LX business jet. Measurement data from ground tests and recordings from cruise flight reveal narrowband and tonal cabin noise in the bandwidth from 50 Hz to 500 Hz. In both conditions the sound pressure level (SPL) of the tonal components is up to 10 dB above the cabin noise floor. The designed ANVC system is expected to reduce the tonal components to the noise floor. The system is realized on the ceiling panel in the aft of the cabin. A frequency domain filtered-x least mean squares algorithm (FxLMS) is used for control. The main design task is the definition of actuator (inertial exciter) and error sensor (microphone) locations on the ceiling panel and in the cabin fluid. measurement data from a ground vibration test of DLR test aircraft iSTAR is used for the identification of suitable actuator and sensor locations. The system performance is predicted with numerical simulations using sampled sound pressures and identified frequency response functions (FRF). The sound pressures are recorded at 312 locations in the volume of the aft cabin. FRF from 48 actuator locations to 312 microphone locations are available for optimization. The system will be realized in the iSTAR in July 2023. Ground tests will be performed with engine excitation up to 80% N1 (rotational speed of low the pressure compressor shaft)

Aerostructural investigation of shape adaptive rotor blading for the reduction of BLI induced losses in the distorted flow regimes of a transonic fan rotor

Within the Cluster of Excellence for Sustainable and Energy-Efficient Aviation SE2A, a blended wing body aircraft is investigated to improve efficiency and carbon emissions of future air transport. By embedding the aircraft engines on the top rear fuselage, parts of the aircraft’s wing boundary layer are ingested, which has the potential to further improve the engine’s propulsion efficiency. Through the ingestion of low momentum fluid however, inflow distortion is induced and the fan rotor operates under increased flow incidence in the distorted flow regimes. To reduce the thereby arising efficiency and pressure ratio penalties in the aircraft engine, alternative design strategies for the fan stage are required. Within this investigation, an active shape morphing mechanism is introduced, which allows to temporarily adjust the fan blading when the fan rotor is exposed to distorted inflow conditions. By integrating piezoceramic actuators into the rotor blading, the blade staggering and turning can be adjusted with the goal to reduce flow incidence and deviation in the distorted flow regimes. For this investigation the NASA rotor 67 is chosen as a reference test case and its performance under boundary layer ingestion (BLI) conditions is evaluated. For the shape morphing assessment, FEA morphing simulations are tightly coupled with a geometry re-engineering methodology and stationary CFD simulations of the actuated fan rotor geometries under distorted inflow. For the chosen test case, the achievable deformations are however too small to compensate for the strong distortion effects of a blended wing body’s boundary layer. Therefore, the blade reference design needs to be adapted in order to increase the achievable deformations. This includes the investigation of typical compressor design parameter variations, such as blade hub-to-tip ratio, chord length as well as lean and sweep and their impact on the deformability of a shape-adaptive fan stage

A review of modelling and analysis of morphing wings

Morphing wings have a large potential to improve the overall aircraft performances, in a way like natural flyers do. By adapting or optimising dynamically the shape to various flight conditions, there are yet many unexplored opportunities beyond current proof-of-concept demonstrations. This review discusses the most prominent examples of morphing concepts with applications to two and three-dimensional wing models. Methods and tools commonly deployed for the design and analysis of these concepts are discussed, ranging from structural to aerodynamic analyses, and from control to optimisation aspects. Throughout the review process, it became apparent that the adoption of morphing concepts for routine use on aerial vehicles is still scarce, and some reasons holding back their integration for industrial use are given. Finally, promising concepts for future use are identified

3D Design of a Large-Displacement Droop-Nose Wing Device

The 3D structural design of a morphing droop-nose device for a new high-lift system is presented in this paper. This new type of high-lift system is anticipated to reduce airframe noise, takeoff and landing speeds and thus runway length, and be capable of actively producing a range of lift coefficients as per demand. A structural design process using optimization tools was further developed and applied to the case of large target deflections required for this high-lift system. The results of the 3D optimization of thickness distribution, stringer position, and force introduction points on a hybrid fiberglass-elastomeric composite skin showed close agreement to the target shapes under different aerodynamic load cases. The design of a kinematic system of linkages was also performed and upon input actuation the outer surface conformed to the target aerodynamic shapes. Required actuator torque in this design was shown to be high in the order of 3600 Nm thought actuators are available which meet the internal space requirements. Reported strains were within design limits in the order of 1.5%. The design is set to be refined in the near future with manufacturing and ground tests to follow.