Wind Energy

Power fluctuation of a single turbine/wind farm

Our current work has established a solid framework for predicting the power and wake characteristics of both single wind turbines and wind farms based on the space-time correlations of incoming turbulence.

Figure 1. Top: experiments of single turbine performance with various scales; bottom: wind tunnel experiments of wind farm performance.

Offshore wind energy

We use modeled wind turbines in wind tunnel with active/passive control mechanisms to simulate the offshore floating wind turbines and focus on the coupling between multi-degree structure dynamics and wake characterizations.

Snow       Forest

Figure 2. Left: a) Experimental set-up of an actively controlled wind turbine under b) pitch and c) roll motions. Right: time-averaged streamwise velocity with the turbine a) fixed, b) under pitch and c) roll motions.

Fluid structure interactions

Flow over flexible bodies

We are interested in studying the effect of structure geometry, layout and inclination on the bending and oscillations of wall-mounted, flexible structures. We apply theoretical analysis as well as experimental measurements on structure deformation and wake evolution to explore the behaviors of both single and multiple bodies.

Figure 3. Flow over flexible plates with various tip geometries. Top: experimental set-up. Bottom: turbulence kinetic energy for flow over a) rectangular plate; b) elliptic-tip plate; c) arist-tip plate.

Figure 4. Dynamics of two flexible plates in tandem. a) mean tip deformations; structure deformation and mean streamwise velocity distributions under low (b) and high (c) incoming flow.

a)                                             b)                                               c)

  

Video 1. Fluttering (a), twisting (b), and orbital oscillations (c) of flexible plates inclined to incoming flow.

Dynamics of slung prisms

We study the distinctive pendulum-like oscillation and pitching patterns of cubic and rectangular slung prisms for various aspect ratios, Reynolds numbers and free-stream turbulence levels.

Figure 5. Experimental set up for the dynamics of slung prisms.

Tracing of free-falling objects

We explore the dynamics of falling objects and flow with various geometries and densities. 2D and 3D high-speed particle image velocimetry were applied to measure the wake characteristics.

Figure 6. Left: 2D instantaneous flow field induced by a free-falling cone. Right: 3D vortex of free-falling cones with (a) high (b) medium and (c) low densities.

Dynamic control

Hydrodynamic control in complex flows
Using laboratory experiments and simplified theoretical arguments, we show that the level of turbulence may reverse the direction of the mean lift on two- and three-dimensional structures with relatively short, deflected splitters. The distinctive role of turbulence in structures with splitters provides insight to control hydrodynamic force in various environments.

Snow       Forest
Figure 7. Left: Sample of instantaneous lift coefficient for 3D body-tail assembly under a) low and b) high incoming turbulence. Right: Time-averaged streamwise velocity for flow over 2D body-tail system.

 

Bio-inspired assemblies for locomotion

With state-of-art flow diagnostics, we investigate the bio-inspired locomotion including jellyfish, active pitching of plates under complex flow, among others.

Figure 8. a) raw image of jellyfish swimming; b) corresponding 3D flow field measured via particle tracking velocimetry.

Figure 9. Instantaneous flow field induced by active pitching of a splitter in the wake of a circular cylinder under a) static splitter, b) low pitching intensity, c) medium pitching intensity, d) high pitching intensity.

 

Video 2: Instantaneous flow induced by active pitching of a flexible plate with a) low and b) high stiffness.