Hauke Ehlers

High-Speed PIV Applied to Wake of NASA CRM Model in ETW Under High Re-Number Stall Conditions for Sub- and Transonic Speeds

Particle Image Velocimetry (PIV) using high-speed camera and laser has been applied to turbulent flow regions in the wake of a stalled aircraft wing. The measurements took place on the Common Research Model (CRM) of NASA in the pressurized cryogenic European Transsonic Wind tunnel (ETW) within the framework of the EU project ESWIRP. The employed high-speed PIV setup is described and preliminary results are presented comprising sub- (M = 0.17) and transsonic (M = 0.85) stall conditions at flight Reynolds numbers of 7 and 30 million, respectively.

Tracking the Nacelle Vortex Above Aircraft Wing in the ETW at Real Mach- and Reynolds Numbers by Means of PIV

Stereo PIV measurements have been performed in multiple planes of the flow above the wing of a high-lift aircraft configuration in order to investigate the performance of strake vortex generators attached to the nacelle with regard to the evolution of flow separations on the main wing at high angles of attack. The measurements have been carried out in the cryogenic pressurized transonic wind tunnel facility of ETW that allows to perform the measurements at real flight Mach and Reynolds numbers by using total gas temperatures and pressures down to 110 K and up to 450 kPa, respectively. Because of this extreme wind tunnel conditions a specific cryo-PIV measurement system has been used. To provide insights into the streamwise development of the vortical flow a light-sheet, oriented perpendicular to the direction of free stream velocity, has been positioned to different chord stations of the wing. This paper focuses on a description of the employed PIV setup in the ETW showing first results for a standard configuration obtained at flight Reynolds numbers.

3D Flow Field Investigations on Flapping Wing Aerodynamics

Three-dimensional, unsteady flow fields of a flapping low aspect ratio wing are investigated by means of tomographic PIV (Tomo-PIV) measurements and computational fluid dynamics (CFD). Furthermore force measurements have been done. Tomo-PIV was applied to the flow above the flat-plate-wing during the down-stroke. A high spatial resolution and a large volume thickness could be achieved by using sensitive sCMOS cameras and a traversable set-up. The CFD calculations cover the complete period of motion. Analyzing the vortex dominated flow fields provides a deeper understanding of vortex interaction and three-dimensionality of low Reynolds number (Re = 18,000 and Re = 36,000) flows. Two different Strouhal numbers (St = 0.06 and St = 0.13) are considered and their effects on the development of a leading edge and tip vortex are discussed.

Experimental and numerical investigations of pitch-plunging wing aerodynamics at low Reynolds number

In the present paper, the first results of a broad study of static and moving flat plate wings for micro air vehicles (MAVs) are presented. Wind tunnel experiments with force measurements and particle image velocimetry (PIV) were performed in a specially designed wind tunnel environment for low Reynolds number investigations. Corresponding numerical flow simulations were also carried out. Effects of the wing shape (elliptical and rectangular), the Reynolds number (18,000, 36,000 and 108,000) and the kinematics using different motion forms of pure plunge and combined pitch/plunge with a reduced frequency of k = 0.2 are discussed.

Three-Dimensional Flow Field Investigations of Flapping Wing Aerodynamics

Three-dimensional unsteady flow fields of a flapping, low-aspect-ratio wing have been investigated by means of highly resolved tomographic particle image velocimetry (Tomo-PIV) measurements and computational fluid dynamics (CFD). Furthermore, force measurements have been carried out. Tomo-PIV was applied to the flow above a flat plate wing during the downstroke. High spatial resolution and large volume thickness could be achieved by using sensitive sCMOS cameras and a traversing setup. The CFD calculations covered the complete period of motion. The analysis of the vortex-dominated flow fields provides a deeper understanding of vortex interaction and three-dimensionality of low Reynolds number (Re=18,000 and Re=36,000) flows. Two different Strouhal numbers (St=0.06 and St=0.13) are considered and their effects on the development of a leading edge and tip vortex are discussed. The PIV results show instantaneous flow fields after a leading edge separation that are dominated by small-scale turbulent vortex st...

Combined Time-Resolved PIV and Structure Deformation Measurements for Aeroelastic Investigations

The aeroelastic behaviour of a thin plate has been investigated by applying two different optical measuring techniques: velocity field (PIV) and structure deformation (IPCT) measurements. The aim of the experiment is to solve Collar’s triangle of forces. The focus of the present chapter is on describing the wind tunnel experiment and the measuring techniques in detail. A second key aspect is on the calculation of instantaneous pressure fields and aerodynamic forces from PIV data.

Time Resolved Flow Field Investigations of Low Reynolds number Transient Maneuvers

Transient pitch and plunge maneuvers of low aspect ratio wings in a special low Reynolds number wind tunnel have been investigated by means of high speed Particle Image Velocimetry to analyze the leading edge vortex dynamics quantitatively. A specific requirement of the measurement was to design and apply an optical arrangement for the laser light sheet which moves with the wing so as to keep the light sheet in fixed position on the upper side of the model. This became necessary because of the low pulse energy of high speed lasers and the large amplitudes of motion. This paper shows the principle and the implementation of this particular set-up. The evaluation procedure shows some specific steps concerning the preprocessing, for example, mask generation and disparity correction. The temporally-resolved data sets enable a tracking of vortices and a detailed analysis of the leading edge vortex dynamics in terms of circulation build-up and convection velocity.