Acoustic conditions in the vicinity of an orifice that depends on grazing flow boundary layers. An experimental investigation

The reflection factor at a tube which ends at a plate over which a flow is forming was determined as a function of the Strouhal number, formed from the flow velocity, the aperture radius, and the acoustic frequency. Several adjacent openings were investigated to determine the interactions between several openings

Analytical and experimental investigations of dual-plane PIV

In its 'classical' form particle image velocimetry (PIV) extracts two components of the flow velocity vector by measuring the displacement of tracer particles within a double-pulsed laser light sheet. The method described in this paper is based on the additional recording of a third exposure of the tracer particles in a parallel light sheet, which is slightly displaced with respect to the first one. The particle images resulting from these three exposures are stored on separate frames. The locations of the correlation peaks, as obtained by cross-correlation methods, are used to determine the projections of the velocity vectors onto the plane between both light sheets. In the manner described below, the amplitudes of these peaks are used to obtain information about the velocity component perpendicular to the light sheet planes. The mathematical background of this method is described in the paper. Numerical simulations show the influence of the main parameters (e.g. light sheet thickness, light sheet displacement and out-of-plane component) on the resolution and reliability of the new method. Two different recording procedures and their results will be shown to demonstrate the ease of operation when applying this technique to liquid flows

Measuring structure deformations of a composite glider by optical means with on-ground and in-flight testing

© 2016 IOP Publishing Ltd. In aeronautical research experimental data sets of high quality are essential to verify and improve simulation algorithms. For this reason the experimental techniques need to be constantly refined. The shape, movement or deformation of structural aircraft elements can be measured implicitly in multiple ways; however, only optical, correlation-based techniques are able to deliver direct high-order and spatial results. In this paper two different optical metrologies are used for on-ground preparation and the actual execution of in-flight wing deformation measurements on a PW-6U glider. Firstly, the commercial PONTOS system is used for static tests on the ground and for wind tunnel investigations to successfully certify an experimental sensor pod mounted on top of the test bed fuselage. Secondly, a modification of the glider is necessary to implement the optical method named image pattern correlation technique (IPCT), which has been developed by the German Aerospace Center DLR. This scientific technology uses a stereoscopic camera set-up placed inside the experimental pod and a stochastic dot matrix applied to the area of interest on the glider wing to measure the deformation of the upper wing surface in-flight. The flight test installation, including the preparation, is described and results are presented briefly. Focussing on the compensation for typical error sources, the paper concludes with a recommended procedure to enhance the data processing for better results. Within the presented project IPCT has been developed and optimized for a new type of test bed. Adapted to the special requirements of the glider, the IPCT measurements were able to deliver a valuable wing deformation data base which now can be used to improve corresponding numerical models and simulations

Investigation of Unsteady Flow Fields in Wind Tunnels at High Flow Velocities by Means of Particle Image Velocimetry (Invited Lecture)

Particle Image Velocimetry (PIV) is already a well established tool in many areas of fluid mechanics. For the first time the PIV technique allows the recording of a complete velocity field in a plane of the flow within microseconds. This does not only give information about unsteady flow fields otherwise not obtainable but also helps to save operational time when working in a wind tunnel. Special requirements have to be fulfilled, when applying the PIV technique in large wind tunnels or at high flow velocities. Typical problems are: tracer particles (concentration, velocity lag, scattered light), use of pulse lasers (energy, repetition rate of pulses), technique for ambiguity removal (image shifting, cross correlation), flexible and reliable installation of the recording system in the wind tunnel, automatic control of the whole measuring sequence, evaluation and post processing of PIV recordings etc. After having explained the basic principles of PIV very briefly, different possibilities to realize a PIV system for application at aerodynamic investigations will be presented and discussed in the frame of the experience gained at DLR

Investigation of Instantaneous Flow Fields in Wind Tunnels by Means of Particle Image Velocimetry

Particle Image Velocimetry (PIV) is already a well estabilished tool in many areas of fluid mechanics. For the first time the PIV technique allows the recording of a complete velocity field in a plane of the flow within microseconds. Special requirements have to be fulfilled, when applying the PIV technique in wind tunnels. Typical problems are: tracer particles, use of pulse lasers,technique for ambiguity removal,flexible and reliable installation of the recording system in the wind tunnel, automatic control of the whole measuring sequence, evaluation and post processing of PIV recordings etc. After having explained the basic principles of PIV very briefly, the experimental setup of DLR, which has been developed with the aim to be able to operate a PIV system even under the rough environmental conditions of a large wind tunnel, will be described in some detail. This PIV-system has been successfully applied to flow field measurements in the velocity range from U &#61 10 to 500 m/s. The evaluation and the post processing of the PIV recordings run fully automatical on a workstation. Finally, applications of the PIV technique at the investigation of unsteady flow fields in different wind tunnels will be presented. These examples show, that the PIV technique is a useful tool for aerodynamic investigations - in low speed flows as well as in transonic flows - in the field of grid turbulence, boundary layer instabilities, wake flow behind 2-d models, and for the investigationof transonic flows above pitching airfoils

PIV - Anwendungen

Es wurden die Anwendungen der PIV Methode in der Aerodynamik erläuter