We report a novel experimental technique that measures simultaneously in three dimensions the trajectories, the translation and the rotation of finite-size inertial particles together with the turbulent flow. The flow field is analyzed by tracking the temporal evolution of small fluorescent tracer particles. The inertial particles consist of a super-absorbent polymer that renders them index and density matched with water and thus invisible. The particles are marked by inserting at various locations tracer particles into the polymer. Translation and rotation, as well as the flow field around the particle are recovered dynamically from the analysis of the marker and tracer particle trajectories. We apply this technique to study the dynamics of inertial particles much larger in size (Rp/η ≈ 100) than the Kolmogorov length scale η in a von Kármán swirling water flow (Rλ ≈ 400). We show, using the mixed (particle/fluid) Eulerian second-order velocity structure function, that the interaction zone between the particle and the flow develops in a spherical shell of width 2Rp around the particle of radius Rp. This we interpret as an indication of a wake induced by the particle. This measurement technique has many additional advantages that will make it useful to address other problems such as particle collisions, dynamics of non-spherical solid objects, or even of wet granular matter.
Simulation capabilities for low-speed aircraft stall prediction are important for determining the limits of safe aircraft operations during design processes. The simulations are extremely demanding in terms of physical models involved, overall computation effort, and the needed efforts for validation. The present paper describes coordinated, fundamental research into new simulation methodologies for wing stall that also include the effects of atmospheric gusts. The research is carried out by the DFG funded Research Unit FOR 1066 composed of German Universities and the German Aerospace Center, DLR. The research Unit investigates advanced models of turbulence, advanced physics-based gust models, and new numerical approaches for gust simulation. These modeling and computational activities are supplemented by an unique validation experiment, that aims at providing stall data on a high-lift wing with well defined, generic distortions of the onset flow.
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