Flow-structure Interaction/feedback

Our group puts special attention on the turbulent interaction (and feedback) between flow and structures to: i) understand the flow-induced mechanisms that modulates the rotations and translations of compact objects, and ii) the flow-induced oscillations in flexible structures. We are performing coupled characterization of the motion of objects with surrounding flow at high temporal resolution.

Rotation and pitching of flat plates

Systematic wind tunnel experiments are underway to characterize and quantify the rotation and free pitching of flat plates as a function of thickness ratio, location of the axis of rotation and Reynolds number. High-resolution telemetry, laser tachometer, and hotwire were used to get time series of the plates motions and the signature of the wake flow at a specific location (Figure 1). Figure 2 illustrates the behavior of free pitching plates under various wind speed.

Figure 1: a) Schematic of the experimental setup; b) photograph of the plates and test section; c) characterization of scales.

Figure 2: Characterization of free pitching plates under various wind speed.

Rotation and pitching of plates under turbulent flow

We are particularly interested on studying the influence of turbulence in the motion of plates. We use active grids and cylinders with different diameters to induce specified turbulence. PIV, hotwire, high-resolution telemetry and laser tachometer are used to track the motions of the structures and flow. Figure 3 shows a case with a cylinder and Figure 4 illustrates an example of the dominating frequency of plate oscillations and wake fluctuations, while Figure 5 shows the flow and vertical motions around a plate.

Figure 3: Schematic of the experimental setup.

Figure 4: a) Frequency of the dominating plate pitching and oscillations; b) velocity spectra downstream of the plate.

Figure 5: a, b) Mean velocity in streamwise direction around a plate; c) Instantaneous signed swirling strength Λci.

Falling and rising objects

Laboratory experiments are under way to study the dynamics of falling objects and flow. Figure 6 shows the case of free-falling cone in a quiescent water tank. Telemetry is used to track the 3D translations and rotations. Flow field is captured via planar and 3D PIV (Fig. 7).

Figure 6: Basic setup of the falling cone, trajectory and Lagrangian features of a 30o cone durng the free fall.

Figure 7: Example of the flow field around a falling cone in stable (left) and unstable (middle) stages from planar PIV. Right: 3D field in the stable fall showing the rollup vortex formation.

 

Our research group aims at providing fundamental insights on the role of turbulence in basic and applied problems of high interest, which can be divided in the following sub-areas:

i) structure of the boundary layer over complex topographies;

ii) wind & hydrokinetic energy technologies,

iii) scalar transport over urban and natural environments,

iv) flow-structure interaction; and

v) instrumentation for turbulence measurements.

We have developed a comprehensive research on these topics that are going to be sustained and expanded in the future. Our versatile experimental approach combines a set of state-of-the-art experimental techniques, including particle image velocimetry (PIV), computer vision, and our recently developed 3D particle tracking velocimetry (PTV). This framework allows us to study fluid dynamics from Eulerian and Lagrangian frame of references

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