Capturing Unsteady Flow Phenomena at High Speed Stall Conditions by Adaptation and Application of cryogenic PIV

Abstract

We measured and characterized the flow around a full-span, generic passenger aircraft model under buffet conditions at Mach numbers up to Ma=0.9, Reynolds numbers up to Ra=25 Mio and angles of attack up to about 7° by adapting and employing the cryogenic Particle Image Velocimetry technique in the European Transonic Windtunnel (ETW). Three different scenarios, involving buffet on the main wing, interaction of the buffet-wake with the horizontal tail plane and buffet-phenomena in the vicinity of the engine nacelle were addressed in three dedicated wind-tunnel entries incorporating a variety of fields of view. To enable these measurements and to improve performance, reliability and data quality under the harsh experimental conditions at ETW, we carried out a comprehensive extension and upgrade of the cryoPIV measurement system. As a result, three different stereo PIV systems, involving one state of the art high-speed and two novel multi-pulse PIV systems, were installed into the test section and operated during the tests. The captured flow fields clearly reflect the large- and small-scale flow structures involved in the highly three-dimensional flow. Beside the position and shape of the shock waves the turbulent wake of the wing and its interaction with the horizontal tail plane is revealed by both, instantaneous and mean velocity and fluctuation fields. The overlapping measurement fields show a very good agreement among different measurement positions and systems.