Entwicklung, Umsetzung und Flugerprobung von Minderungstechnologien bei Schallquellen am Flugversuchsträger ATRA des DLR

Der Vortrag gibt einen Überblick über Minderungstechnologien für Außengeräuschquellen an einem aktuellen Mittelstreckenverkehrsflugzeug, die ihm Rahmen des Projekts ''Low Noise ATR'' am Deutschen Zentrum für Luft- und Raumfahrt e.V. (DLR) in Braunschweig entwickelt, umgesetzt und flugerprobt wurden. Ziel dieses Forschungsprojekts war es, die mit heute aus vorangegangenen Forschungsprojekten bekannten Technologien erreichbare Minderung des Überfluggeräuschs zu quantifizieren. Nach einer Vorauswahl solcher nachrüstbaren Technologien waren diese auf die einschränkenden Randbedingungen eines realen Flugzeugs prototypisch umzusetzen und zu implementieren. Wenngleich auch eine Maßnahme zur Minderung von Strahlgeräusch implementiert wurde, lag das Hauptaugenmerk auf der Reduzierung des Umströmungsgeräuschs, das beim Landeanflug von größter Bedeutung ist und sowohl Fahrwerk wie Klappensysteme betrifft. Hintergrund dieser Schwerpunktsetzung war der Umstand, dass Aktualisierungen von Verkehrsflugzeugen i.d.R. über neue Triebwerksgenerationen erfolgen, womit typischerweise Pegel des Triebwerksgeräuschs reduziert werden, während das Umströmungsgeräusch an der Flugzeugzelle unverändert bleibt. Hiermit wächst dessen Anteil und damit Bedeutung am Gesamtgeräusch. Anwendung fanden speziell konfigurierte aerodynamische Verkleidungen wie poröse Materialien, die an den bekannten Hauptschallquellen appliziert wurden. Als Ergebnis der Überflugmessungen konnten signifikante Absenkungen des Überflugschalldruckpegels nachgewiesen werden

An Approach towards semi-empirical Slat Track Noise Prediction

High lift wing leading edge noise is often attributed to the slats or more generally speaking to the leading edge high lift device. Except for droop noses, flow exposed mechanical systems are necessary to mount and actuate such devices. For mechanical reasons these so called tracks are typically oriented perpendicular to the wing leading edge and accordingly inclined towards the mean flow or flight direction. Mainly from wind tunnel studies and in rare cases also from flight tests these tracks are known as strong noise sources, which locally exceed slat noise levels and show up as intense noise sources in noise maps originating from phased array beamforming. This finally means that track noise cannot be omitted for the noise prediction of high lift systems and in particular not in view of new systems like Krueger flaps. Against this background track noise was investigated in the German national funded research project INTONE (Minderung von Triebwerksinstallations- und Hochauftriebslaerm). Based on parametric studies with the small scale DLR F16 high lift system in DLR s Acoustic Wind Tunnel Braunschweig track noise was isolated and characterized. In a second step a first prediction scheme was established. The scheme allows now for the prediction of slat noise and track noise and the summation of both components which contributes to the overall leading edge noise. The application of this model showed the impact and importance of track noise compared to slat noise. Furthermore, the noise generation at the D-nose cut-outs was assessed. Both results together reveal that track noise is a major contributor to the overall high lift system noise and track noise reduction is essential in order to reduce the high lift system related airframe noise contribution. The current development is meant as first step towards a more sophisticate tool chain for wing leading edge noise prediction

Installation Effects of a Propeller Mounted on a High-Lift Wing with a Coanda Flap. Part I: Aeroacoustic Experiments

In this contribution, we present aeroacoustic experiments concerning installation effects of propellers. Such installation effects are important as they can significantly alter the sound radiation as compared to an isolated propeller. For this purpose, detailed experiments have been conducted in the NWB aeroacoustic wind tunnel in Braunschweig, Germany. The considered geometry is a nine-bladed propeller installed in front of a high-lift wing (employing a Coanda flap). The results illustrate the influence of propeller rotational speed, blade pitch angle, wind tunnel velocity, and angle of attack variations on the sound radiation. Furthermore, with a source localisation technique insight is gained in the dominant sound sources, and reveals the importance of periodic as well as broadband noise for the considered geometry

The Challenge of Tonal Fan Noise Prediction for an Aircraft Engine in Flight

Expensive fly-over tests are needed to verify that noise certification standards are fulfilled. Currently, no numerical alternative exists to perform a holistic virtual fly-over test. As a step towards enabling such evaluations in the future, the authors focus on an isolated noise source - the tonal rotor-stator-interaction (RSI) of the fan stage. A high-fidelity simulation relying on a state-of-the-art yet computationally efficient method is performed for a V2527 aircraft engine in approach conditions. The computational domain includes the noise generation in the fan stage, its propagation in the engine inlet and bypass duct, as well as its radiation into the far field. Installation effects due to bifurcations and struts in the duct, ESS (engine section stator), liners, and inflow distortions are not considered. Post-processing methods are introduced and applied to the numerical data to allow for a meaningful comparison of the results to microphone data recorded during fly-over experiments. In particular, great care is taken to quantify the numerical dissipation of the simulation inside the nacelle and to enable a suitable correction of the numerical data. The numerical simulation cannot fully reproduce the experimental data indicating that its level of complexity is not yet sufficient. As there is no obvious cause for the mismatch, it would be necessary to incrementally increase the complexity of the simulation in order to pinpoint the most significant sources and effects

Noise reduction potential of flow permeable materials for jet-flap interaction noise

Jet-flap interaction (JFI) noise plays a particularly important role during take-offs and landings, i.e. when the aircraft is in the immediate vicinity of inhabited areas. The interaction of the jet with the deployed flaps causes a substantial increase of low-frequent aircraft noise. Noise reduction technologies (NRTs) were studied for their potential to diminish the JFI effect: The wing was equipped with various permeable or porous (flap) trailing edges which cover the last 10% of the clean chord length. The first test was conducted at the Aeroacoustic Wind tunnel in Braunschweig (AWB) on a cruise wing model, i.e. the engine was not installed. Beneath the testing of various materials and concepts, a design parameter study was conducted about the minimally needed treated chord length. The four most promising materials were down-selected for an installed engine test at the jet noise test facility JExTRA in Berlin: Two NRTs are designed as hollow flaps: perforated or slotted metal sheets are fixed onto a rib structure. The other two NRTs are porous materials (fine/coarse size). The tests were conducted for static operations between Mj=0.45 and 0.75. The engine integration was mainly defined by a height of H=0.6Dj (close integration) and a length of L=2Dj. Remarkable noise reduction was measured especially for low jet Mach numbers and up to Mj=0.7. At high Mach number, some NRTs produce tones which follow a Helmholtz analogy. The only tested NRT which is immune to this, uses a cover mesh which introduces another trailing edge. The tests with flow permable flap trailing edges show the great potential of reducing jet-flap interaction noise. Open questions regard (1) the deepening of the physical understanding of noise reduction mechanisms, (2) a proof of performance under flight conditions and (3) a design optimization which balances a small aerodynamic lift penalty vs. the acoustic benefit

A Novel Test Bed for the Aeroacoustic Investigation of UCAV Configurations with Highly Integrated Propulsion Systems

In this contribution, a novel test bed designed for the experimental investigation of the acoustic signature of unmanned combat air vehicle with highly integrated propulsion systems is presented. The model integrates a curved intake duct design as well as a curved, high aspect ratio, rectangular nozzle design. Operation of the model in suction mode or pressurized mode allow investigations of the intake and nozzle acoustics independently and in a realistic Mach number range, e.g. Ma=0.4 in the intake duct and Ma=0.75 in the jet. Intake sound emissions are found to have a directivity peaking in the forward arc which is strongly dependent on the suction mass flow rate and almost independent of the free-stream Mach number. The jet is found to radiate sound with a rear arc directivity for model scale frequencies above 3.15 kHz. The acoustic is also a strong function of the nozzle mass flow rate only. The overall shape of the jet acoustic directivity suggests the existence of two source component aligned at 90° and 140° to the upstream direction, respectively

Large-Scale Slat Noise Studies within the Project OPENAIR

The present contribution summarizes the slat noise research activity within work package WP4.2 (Wing Systems) of the EC co-financed project OPENAIR (Optimisation for low environmental noise impact aircraft) conducted by the partners Airbus and DLR. It involves both experimental and numerical studies at the large-scale (1:3.3) swept high-lift wing model F15-LS. Experiments were performed in the Large Low-speed Facility DNW-LLF • to extend current slat noise validation data bases towards more realistic test conditions than in precursor projects to support the further development of DLR’s numerical slat noise prediction capability and • to verify the documented noise reduction benefit of established slat noise reduction concepts from precursor projects for these extended test conditions. Slat noise reduction concepts that have been revisited and further developed were • optimized slat gap and overlap settings as well as • an adaptive slat concept that actively reduces the gap width to reduce noise under typical approach conditions but restores the original gap width / maximum lift if necessary. OPENAIR slat noise studies build upon the outcome of the forerunner project TIMPAN, where the noise differences attributed to slat setting variations were numerically predicted and experimentally validated at a fourfold smaller 1:13.2-scaled 2D high-lift system (F16 model). FEM analysis served to specify technically feasible adaptive slat profile bending, accounting for conventional actuator specifications, feasible skin materials and critical aerodynamic loads determined by the flight envelope. Two selected adaptive slat shapes were finally realized as solid model parts that were tested in the DNW-LLF (fully closed gap, intermediate gap width). Main results were: The adaptive slat with closed gap provides a noise reduction of order 5 dB at wing level, equivalent to a full elimination of the slat noise source. Modified slat settings or an adaptive slat with intermediate gap width are suited to reduce slat noise by about 2─3 dB at wing level while producing negligible aerodynamic impact at the operative test angles of attack. Comparisons of CAA (Computational Aeroacoustics) prediction results with the DNW-LLF measurement data revealed a generally good reproduction of the observed trends with the restriction that measured differences to be resolved were relatively small for most of the tested slat setting variants. Overall, major results from the TIMPAN project were reproduced within OPENAIR. Particularly, the expectation of a relatively broad optimum for aeroacoustically optimized slat settings, as deduced from the former TIMPAN results, is supported by both the measurement and CAA results

An integrated design approach for low noise exposing high-lift devices

The DLR project LEISA combines and focuses activities in the research areas of high lift system design, flow control and aero-acoustic design methods, which have been carried out rather independently up to now. Furthermore, the competence in the fields of aerodynamics, aero-acoustics, structures and flight systems will be integrated to provide an interdisciplinary assessment of high lift system design for transport aircraft configurations. The project LEISA started at the beginning of 2005, so up to now only few results are available. This paper addresses the integrated design approach and first results for a noise reduced slat device and combined wind tunnel testing results for aerodynamics and aero-acoustics

Vermessung und Simulation strömungsakustischer Quellen

Studien an Fluglärmquellen im WIndkanal, Herleitung halb-empirischer Quellmodelle, Skalierungsproblematik bei kleinen WIndkanalmodelle