This paper describes ongoing research efforts in the scramjet community on cavity e ame holders, a concept for e ame holding and stabilization in supersonic combustors. During the last few years, cavities have gained the attention of the scramjet community as a promising e ame-holding device, owing to results obtained in e ight tests and to feasibility demonstrations in laboratory-scale supersonic combustors. However, comprehensive studies are needed to determine the optimal cone guration that will yield the most effective e ame-holding capability with minimum losses. The e owe eld characteristics of cavities and research efforts related to cavities employed in lowand high-speed e ows are summarized. Open questions impacting the effectiveness of the cavities as e ame holders in supersonic combustors are discussed.

https://research.engr.utexas.edu/benyakar/images/stories/pdfs/Ben-Yakar_lab_Ben-Yakar_et_al_JPP_2001.pdf

Cavity Flame-Holders for Ignition and Flame Stabilization in Scramjets: An Overview

Acoustic perturbation equations based on flow decomposition via source filtering

High-order compact finite-difference methods on general overset grids

Within a parametric study on brush-type trailing-edge extensions, the noise reduction potential of several design concepts was determined. The obtained database represents the first phase of an ongoing project with the long-term objective to develop scaling laws for a future application of such devices as add-on solutions for today's aircraft components. The experiments comprised both acoustic and aerodynamic measurements on a zero-lift generic plate model (Re = 2.1 x 10 6 to 7.9 × 10 6 ) in DLR's open jet Aeroacoustic Wind Tunnel Braunschweig. Noise data were taken by means of a directional microphone system. Measurement results indicate a significant source noise reduction potential in excess of 10 dB, depending on the configuration. Two relevant noise reduction mechanisms were identified: 1) the suppression of narrowband bluntness noise, as well as 2) the reduction of broadband turbulent boundary-layer trailing-edge noise.

Experimental investigations in low-noise trailing-edge design

A review of cavity-based trapped vortex, ultra-compact, high-g, inter-turbine combustors

Systematic testing of the microstructural and aeroacoustic properties of porous metals applicable as low-noise trailing-edge (TE) treatments has been initiated within the Col-
laborative Research Center SFB 880|Fundamentals of High-Lift for Future Civil Aircraft. Generic TE noise experiments were performed at Re = 0.8x10^6 to 1.2x10^6 in DLR's
open-jet AWB facility. Complementary flow measurements in the closed test section MUB wind-tunnel of the TU Braunschweig served to quantify the induced aerodynamic effects. The presented database forms part of an ongoing cumulative effort, combining experimental and numerical methods, to gain a deeper understanding of the prevalent TE noise reduction mechanisms. For the large variety of porous materials tested herein a clear dependence of the achieved broadband noise reduction (reaching 2-6 dB at maximum) on the flow resistivity was identified. Basic design recommendations for material resistivity and
pore sizes, the latter to minimize high-frequency self-noise contributions, were deduced for low-noise TE applications. An acoustic nearfield pressure release across the porous region, adversely coupled with a loss in lift performance for porous TE replacements, appears as the major noise-reduction requirement.

/pdf/specifcation-of-porous-materials-for-low-noise-trailing-edge-2ovl4td5tq.pdf

Specifcation of Porous Materials for Low-Noise Trailing-Edge Applications

A high order/high resolution grid communication algorithm was developed for use in combination with the high resolution DRP scheme of Tarn and Webb. In order to establish this grid communication a special high order, though straight forward interpolation scheme is employed at the interfaces between two curvilinear grids of arbitrary shape. The interpolation procedure is local and shows excellent spectral characteristics such that for a given resolution the application range of the DRP-scheme is not narrowed. Twodimensional tests have been done of which may be concluded that the method is robust since additional time step limitations or numerical instabilities have not been observed. A reliable grid overlap detector algorithm for high order metric representation was developed and tested, which is capable of identifying points inside and outside arbitrarily curved domains and subdomains. Geometric information is needed only on the surface of the domains such that their interior does not need to be meshed. Benchmark examples are presented to show the validity of the approach.

An overlapped grid technique for high resolution CAA schemes for complex geometries

Research at DLR towards airframe noise prediction and reduction

Motivation for the presented activities is the integration of noise as an additional objective in conceptual aircraft design. Therefore, the Parametric Aircraft Noise Analysis Module (PANAM) is developed to account for individual noise sources depending on their geometry and operating conditions. Each major noise source is modeled with an individual semi-empirical noise source model. These models capture the major relevant correlations, can still be executed on a standard desktop PC, and provide comprehensive simulation results. All models and approximations are based on physics, thus PANAM can be classified as a scientific prediction method. Dedicated validation with experimental data confirms feasible overall aircraft noise prediction. The noise tool is integrated into an existing aircraft design framework in order to realize an overall design process with integrated noise prediction capabilities. A multiple criteria design evaluation is introduced, to quickly assess the environmental and economical performance of different vehicles under various scenarios. The process is applied to identify promising low-noise aircraft concepts with the focus on realizable, medium term solutions. It is demonstrated, that the aircraft designer’s influence on the environmental vehicle performance is significant at the conceptual design phase. Extensive engine noise shielding is achieved for over-the-fuselage mounted engines resulting in a 10 EPNdB overall noise reduction. In conclusion, PANAM can be ranked as well suitable to assess all four measures of ICAO’s balanced approach. / 
Die Motivation der Arbeit ist die Einbindung von Larm als zusatzlichem Entscheidungskriterium innerhalb des Flugzeugvorentwurfs. Daher wird ein Programm PANAM zur Fluglarmvorhersage entwickelt, das den Beitrag ausgewahlter Larmquellen anhand deren Geometrie und Betriebsbedingungen berucksichtigt. Dabei kommen fur jede Einzelquelle individuelle und semi-empirische Rechenmodellen zum Einsatz. Die ausgewahlten Modelle berucksichtigen die wesentlichen Zusammenhange, stellen geringe Rechneranforderungen und generieren dabei nachvollziehbare Ergebnisse. PANAM kann als wissenschaftliches Berechnungsverfahren klassifiziert werden, da alle implementierten Modelle und Naherungsverfahren auf physikalischen Grundlagen basieren. Ein direkter Vergleich von Simulationsergebnissen mit experimentellen Daten bekraftigt die Richtigkeit der berechneten Ergebnisse. Durch die Integration von PANAM in eine existierende Flugzeugentwurfsumgebung wird der konventionelle Entwurfsprozess um die Fahigkeit zur Larmvorhersage erweitert. Eine neu eingefuhrte Bewertungsmetrik erlaubt den direkten Vergleich von Wirtschaftlichkeit und erzeugtem Fluglarm fur unterschiedlichste Flugzeugkonzepte. Der erweiterte Prozess wird schlieslich angewendet, um vielversprechende, larmarme Entwurfe zu identifizieren. Dabei liegt der Schwerpunkt auf mittelfristig realisierbaren Konzepten und Technologien. Es kann gezeigt werden, dass durch Entscheidungen im Flugzeugvorentwurf ein signifikanter Einfluss auf die okologische Flugleistung des finalen Entwurfes genommen wird. Dabei konnen durch geeignete Abschattung des Triebwerklarms lokal bis zu 10 EPNdB Larmreduktion erreicht werden. Grundsatzlich kann PANAM dazu eingesetzt werden, alle von der ICAO als "balanced approach" vorgeschlagenen Masnahmen zur Larmreduktion zu untersuchen.

Noise Prediction within Conceptual Aircraft Design

The code PIANO, developed at the Institute of Aerodynamics and Flow Technology (Dept.
Technical Acoustics), is designed to simulate aeroacoustic noise generation and acoustic wave
propagation in non-uniform flows. It is based on the equations governing the inviscid dynamics
of perturbations to a given time-averaged mean flow field. PIANO simulates the noise generation
process, when vorticity interacts with solid structures or gradients in the flow field. PIANO is
not designed to calculate wave propagation over very large distances in uniform flows, like from
aircraft to ground. In that case methods based on wave equations are more appropriate.
Currently, PIANO is based on structured, curvilinear multi-block grids. The coding structure is
designed for high performance on workstations, vector machines, PCs or PC clusters as well.
PIANO is a research code.

Jan Werner Delfs

Papers

Specifcation of Porous Materials for Low-Noise Trailing-Edge Applications

An overlapped grid technique for high resolution CAA schemes for complex geometries

Research at DLR towards airframe noise prediction and reduction

Noise Prediction within Conceptual Aircraft Design

Numerical Simulation of Aerodynamic Noise with DLR's aeroacoustic code PIANO