German Institute of Aerodynamics and Flow Technology

Braunschweig, Germany

German Institute of Aerodynamics and Flow Technology

Braunschweig, Germany
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Schutte A.,German Aerospace Center | Schutte A.,German Institute of Aerodynamics and Flow Technology
Journal of Aircraft | Year: 2017

The present work is investigating the vortex-dominated flow physics as well as the aerodynamic behavior of swept wing configurations with round leading edges. The research is based on numerical simulations using the computational fluid dynamics method DLR TAU. The target configurations are swept wings of constant aspect ratio, variable leading-edge contours, and leading-edge sweep angles. The work deals with the onset of the vortical flow at the leading edge for constant and variable leading-edge nose radii, the influence of the angle of attack, the leading-edge sweep, and the onflow Mach number. Furthermore, the aerodynamic behavior is analyzed and assessed, as well as the specific flow physics in the vicinity of the vortical flow separation at round leading edges. The objective of the present work is to provide a contribution for the design and assessment of the physical characteristics of swept wing configurations. Furthermore, sensitivities will be given for the design process. In addition, the current investigation provides a deeper understanding of the separation onset process and the flow physics of swept wing configurations with round leading edges. Copyright © 2016 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Alder M.,German Aerospace Center | Alder M.,German Institute of Aerodynamics and Flow Technology
23rd AIAA Computational Fluid Dynamics Conference, 2017 | Year: 2017

The aeroelastic stability of circular cylindrical shells is investigated in axial supersonic flow. Although some experimental and numerous numerical results on cylindrical shell flutter are published, the in uence of a turbulent boundary layer on the aerodynamic damping at low supersonic Mach numbers is quite controversially discussed in the literature. Therefore, the present study employs a previously developed fluid-structure solver which couples the finite-element solver MSC Nastran with the Navier-Stokes solver DLR-Tau in order to account for viscous flow effects. Aerodynamic damping coefficients are deducted from time domain solutions, comparing the dynamic response of a cylindrical shell at Mach 1.2 and Mach 2.0 in inviscid and viscous flow. It is found that a fluid boundary layer slightly decreases the aerodynamic damping on real cylinder modes, but attenuates the excitation of critical complex modes, i.e. traveling wave flutter. Results from experimental studies are qualitatively reproduced in the present numerical study and discussed with respect to the boundary layer. © 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

Wolf T.,German Institute of Aerodynamics and Flow Technology
DLR Deutsches Zentrum fur Luft- und Raumfahrt e.V. - Forschungsberichte | Year: 2017

This paper presents the results of surface measurements performed on two free-flying birds of the Tyto alba (barn owl) species. Apart from high-resolution surface data from the gliding and flapping flight, wing shape parameters are specified under consideration of the flight phase of individual flapping cycles. Furthermore, the animals' motion parameters and the resulting effective angles of attack are determined and compared for the measured flap flights. Besides the presentation and discussion of the measurement results, the measurement procedure, which was designed especially for this purpose, and the implemented measurement system are covered in detail. New sample projectors and image processing algorithms were developed for the visual measurement of feathered surfaces with major curvatures and motion changes. A moving measurement system that could be maneuvered almost in sync with the free-flying animals was implemented for the test flights. In this way, the animals can be tracked over several meters or flapping cycles while flying without any external influence, and the complex movements of their wings and bodies can be captured three-dimensionally. The surface data gained and the extracted motion and shape parameters of the barn owls' wings deliver a level of resolution and precision not reached in previous measurements and will be used for further examinations. The stroke, pitch and pan movements of a wing action, which are presented in parameterised form in Fourier series based on their wingspan, demonstrate a number of characteristics that have not been described in literature so far. For example, the stroke movement follows an almost sinus-shaped pattern, while the pitch movement takes place almost exclusively in the flap-up phase. An almost steady, effective angle of attack can be observed in the direction of the wingspan.

Gruhn P.,German Aerospace Center | Gruhn P.,German Institute of Aerodynamics and Flow Technology | Gulhan A.,German Aerospace Center | Gulhan A.,German Institute of Aerodynamics and Flow Technology
Journal of Propulsion and Power | Year: 2011

The inlet of a Mach 8 cruise vehicle has been experimentally investigated in a hypersonic blowdown wind tunnel with test times of up to 30 s. Two test series have been carried out: The first one with a two-dimensional inlet configuration and the second one with the inlet featuring additional sidewall compression. The objective of the tests was to determine the performance of the inlet at ondesign and offdesign conditions, i.e., at angle of attack and angle of yaw. Additionally, the starting behavior of the inlet has been determined, i.e., the contraction ratio at which the inlet starts. Results were interpreted from schlieren visualizations, infrared thermography, static and pitot pressure readings, and mass flow measurements. The offdesign investigation of both inlet configurations revealed the sensitivity of the inlet toward a cowl-shock-induced separation on the second compression ramp. If the cowl shock was not ensured to fall into the bleed duct behind the second ramp, no inlet flow could be established. The comparison of starting contraction ratios showed the advantage of the inlet with sidewall compression; that is, the inlet with sidewall compression starts at higher contraction ratios. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc.

Hepperle M.,German Aerospace Center | Hepperle M.,German Institute of Aerodynamics and Flow Technology
Journal of Aircraft | Year: 2010

Inverse design methods are elegant and efficient tools for the design of aerodynamic shapes like airfoils, wings, and propellers. In the case of propeller design, only a few general parameters have to be prescribed and the design procedure returns the propeller geometry in terms of chord-length and blade-angle distributions along the radius. The common design procedures require the prescription of the lift coefficient over the blade radiusin orderto obtain the unknown chord length. In this paper, a modified design method is presented that allows for designing optimum propellers having a prescribed chord-length distribution. Now the radial distribution of the lift coefficient becomes the unknown, which is determined by the design procedure. Copyright © 2010.

Dobrzynski W.,German Aerospace Center | Dobrzynski W.,German Institute of Aerodynamics and Flow Technology
Journal of Aircraft | Year: 2010

The most important findings from experimental and applied research in airframe noise worldwide are discussed. Efforts were undertaken to first quantify airframe noise through dedicated flyover noise measurements when airframe noise was identified as the potential lower aircraft noise barrier in approach. Fink developed the first semi-empirical airframe noise prediction method based on this approach. There are still other types of noise sources, which were detected lately when the first full-scale original airframe component tests were possible with the availability of large acoustic wind tunnels. Such noise tests were performed on original landing gears and an aircraft wing in high-lift configuration. When airframe noise was identified as a major aircraft noise component in approach scale model wind-tunnel experiments were conducted to quantify landing gear noise characteristics. The model of Smith and Chow computed sound intensities according to the components' dimensions and orientation with respect to an observer location.

Wild J.,German Aerospace Center | Wild J.,German Institute of Aerodynamics and Flow Technology
Journal of Aircraft | Year: 2013

Experimental investigations have been carried out with the two-dimensional DLR-F15 high-lift wing-section model in the Cryogenic Wind-tunnel Cologne DNW-KKK to differentiate between the influence of Mach and Reynolds numbers on the stall behavior. Because of the cryogenic environment, Mach and Reynolds numbers have been varied independently between M = 0.1-0.25 and Re = 1.4 × 106 - 15.6 × 106. The investigation covers two- and threeelement configurations at various slat and flap settings and two different slat shapes. The focus of the investigation is to identify conditions of turbulent leading-edge stall, shock-related lift limitations, and flap separations and their influence on achievable maximum lift coefficient. Copyright © 2013 by Jochen Wild, DLR Institute of Aerodynamics and Flow Technology.

Cummings R.M.,United States Air Force Academy | Schutte A.,German Aerospace Center | Schutte A.,German Institute of Aerodynamics and Flow Technology
Aerospace Science and Technology | Year: 2013

The numerical simulation of the flow for the VFE-2 delta wing configuration with rounded leading edges is presented using the Cobalt Navier-Stokes solver. Cobalt uses a cell-centered unstructured hybrid mesh approach, and several numerical results are presented for the steady RANS equations as well as for the unsteady DES and DDES hybrid approaches. Within this paper the focus is related to the dual primary vortex flow topology, especially the sensitivity of the flow to angle of attack and Reynolds number effects. Reasonable results are obtained with both steady RANS and SA-DDES simulations. The results are compared and verified by experimental data, including surface pressure and pressure sensitive paint results, and recommendations for improving future simulations are made. © 2011 Elsevier Masson SAS. All rights reserved.

Riehmer J.,German Institute of Aerodynamics and Flow Technology
DLR Deutsches Zentrum fur Luft- und Raumfahrt e.V. - Forschungsberichte | Year: 2015

The aim of this work was the design of a scramjet configuration with inlet, combustor and nozzle for a flight experiment on a sounding rocket and test of this configuration in the hypersonic wind tunnel (H2K) of the German Aerospace Center in Cologne. Therefore semi-empirical design methods, based on previous studies were used to define an optimized scramjet geometry. The performance parameters and the off-design behavior were determined in advance with extensive numerical simulations and were subsequently verified in the wind tunnel experiments. The experiments were carried out for the entire scramjet configuration under flight-related conditions, in which the combustion was simulated by the injection of high pressure air. In order to study the scramjet configuration's behavior at different flight conditions, the flow was varied in relation to Reynolds number, stagnation temperature, and angle of attack. Here, a stable supersonic flow was observed with Pitot measurements, wall pressure measurements, and infrared thermography, which confirmed the design methods.

Ewert R.,German Institute of Aerodynamics and Flow Technology
22nd AIAA/CEAS Aeroacoustics Conference, 2016 | Year: 2016

Stochastic sound sources derived from Reynolds Averaged Navier-Stokes (RANS) solution are recognized in Computational Aeroacoustics as one possible way to efficiently predict broadband sound. In this paper a stochastically forced linear advection-diffusion- dissipation equation is introduced. The model provides spectra and anisotropic two-point correlations that otherwise have to be incorporated in datum stochastic methods as additional model assumptions. The output are uctuating velocity components, from which vortex sound sources derive. The forcing is white (delta-correlated) in time and possess a finite correlation length scale in space. The well-posedness is demonstrated in the paper. A solenoidal forcing term is shown to realize the correlation tensor of homogeneous isotropic turbulence together with a longitudinal turbulence spectrum that exhibits a plateau for lower frequencies followed by a characteristic power law roll-off and final cut-off. Exponent of decay and cut-off are adjustable. The stochastic partial differential equation involves a diffusion parameter, a time-scale, a re-distribution tensor, and a forcing variance. Transport equations for Reynolds stresses and turbulence kinetic energy derive from it that have the canonical form of major RANS transport equations. In particular, all parameters needed can be assigned to corresponding RANS parameters so that an accurate reproduction of RANS one-point statistics becomes feasible. For the generation of two-point statistics the hypothesis from turbulence modeling is adopted that the present model calibrated for homogeneous isotropic turbulence is also applicable for more general flows. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

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