Benjamin Heine

Dynamic Stall Control by Passive Disturbance Generators

Passive cylindrical disturbance generators mounted near the leading edge of an airfoil significantly improved its performance under dynamic stall conditions. Time-resolved particle image velocimetry and simultaneous pressure measurements were conducted at the midchord of a pitching airfoil equipped with passive disturbance generators. The disturbance generators were effective in reducing the strength of the dynamic stall vortex and therefore the negative pitching moment peak and hysteresis effects. When the disturbance generators were applied, the flow separation type was altered from leading- to trailing-edge stall. In contrast to the clean case, reattachment was initiated immediately after the separation reached the leading-edge region. In addition to the circular shape, also backward- and forward-wedge-shaped disturbance generators were investigated. Although the backward wedge also showed favorable results, the forward wedge was less successful. The shape of the disturbance generators appears to have ...

Deployable Vortex Generator Dynamic Stall Alleviation through Experimental and Numerical Investigations

The flow over an OA209 airfoil subjected to a sinusoidal pitching motion under dynamic stall conditions and equipped with an innovative Deployable Vortex Generator actuator inducing stall control is experimentally and numerically investigated. Pressure and TR-PIV measurements allow a detailed comparison to be performed between clean and controlled cases, including separation point detection and Proper Orthogonal Decomposition analysis. Along with wind tunnel testing, numerical simulations are performed by solving the Unsteady RANS equations with the ONERA elsA code. Computations are successfully compared to the experimental reference and bring further understanding of the Deployable Vortex Generator actuation.

Investigation of Transitional Flow Structures Downstream of a Backward-Facing-Step by Using 2D-2C- and High Resolution 3D-3C- Tomo- PIV

Transitional flow structures in the shear layer of a laminar separation bubble downstream of a backward facing step (BFS) have been investigated by means of 2D-2C- und highly resolved 3D-3C- tomographic Particle Image Velocimetry (PIV) for Reynolds numbers between Reh = 1420 and 3000 based on free-stream velocity U and step height h. By using an external acoustic excitation of the shear layer it was possible to arrange phase locked measurements of the wavy flow structures which emanate from instabilities according to Kelvin-Helmholtz [1] (KH). Snapshots of fully 3D-3C velocity vector volumes show complex flow topologies of the non-linear part of the laminar-turbulent transition scenario. This part seems to be governed by hairpin-like, streamwise elongated vortices on top of the classical spanwise oriented 2-D waves. These vortices organize a rapid fluid exchange normal to the shear layer leading to turbulent reattachment of the flow and subsequent development of a turbulent boundary layer.

Visualization and Computation of Quantified Density Data of the Rotor Blade Tip Vortex

In this paper, flow visualization of the blade vortices of four-bladed Mach-scaled rotor, as used in the ONERA-DLR ABC project (Active Blade Concept) in hover flight condition, were investigated experimentally by means of Background Oriented Schlieren method (BOS). For BOS setup, a high-speed camera with a resolution of 4 Mpx was used with pulsed LED-illumination in order to illuminate a reflective background. The ABC rotor blades include a trailing edge flap of 15% chord mounted from 80% to 90% blade radius. In this project, the influence of several flap angles of deflections on the density field of the blade tip vortices was studied. In order to compute the density field of the compressible vortex, a tomographic reconstruction algorithm was applied to the BOS data.