Aerodynamics is the way that most of us thing about fluid mechanics (planes flying), but it is broadly related to anything that moves through air.  In this context, there are many open problems related to wind energy and wind engineering that are the primary focus at NTNU.

Focus of our work

Our two main focus areas are wind energy and how turbulence influences relevant aerodynamic problems.  In wind energy we have investigated how icing influences the aerodynamics of wind turbine blades, the comparison of static “actuator” disks and spinning turbines, and wind farm dynamics.  

Wind energy also overlaps into how turbulence influences aerodynamic problems, in that we investigate how different incoming turbulence conditions change the flow field and forces on both horizontal-axis wind turbines and urban vertical axis wind turbines. We also look more fundamentally at how turbulence influences the loads and flow around other bodies, such as circular and square cylinders and airfoils.

Another area of interest is how turbulence changes the dynamics of wing-tip vortices.

Methods

We primarily use our large wind tunnel (2.7 m x 1.8 m in cross-section) that is equipped with an active grid to generate the flows of interest.  The size of the facility allows us to put in full-scale urban vertical axis wind turbines, and scaled-models of other problems, e.g. airfoils, wind turbines.  We then use an array of hot-wires, particle image velocimetry, and pressure measurement systems to capture the physics of the problems.

For more information, please contact Jason Hearst or Tania Bracchi.
 

Nobel-laureate Richard Feynman famously said “Turbulence is the most important unsolved problem in classical physics,” likely because it is omnipresent in our experience with fluids.  

At NTNU, we focus on a broad range of topics within turbulent flows, from the fundamentals of energy transfer at the small scales to how turbulence interacts with other fluid mechanics problems (for instance, an air-water interface, a turbulent boundary layer, or a wind turbine). The challenge in these investigations is on generating turbulence that is representative of that experienced outside of the laboratory, thus allowing for some general conclusions to be drawn. 

Focus of our work

We focus on understanding the fundamental motion of turbulent fluids, and understanding how those motions influence problems of engineering interest.  For the former, previous investigations have focussed on the motion of the small scales and the decay of energy in turbulent systems. We have also investigated turbulent wall-bounded flows and the naturally occurring interfaces therein.  

When it comes to the interaction of turbulence with other problems, it is important to create turbulence with properties similar to those that occur outside of the laboratory. For instance, we replicate the turbulence intensities that a field wind turbine would experience in the lab and then see how the wake and power output of the wind turbine is influenced.  

We also manipulate the turbulence upstream of canonical turbulent flows, like channels and jets, and see how the properties of these textbook example flows are altered by the variation to the initial condition.

Methods

We exploit the facilities and measurement equipment at NTNU to perform cutting-edge experiments in turbulence. The large wind tunnel is home to the second largest active grid in the world—this is a device that allows us to tailor the velocity profile as well as the turbulence intensity and length scales in the wind tunnel. Using this device we can measure the decay of high-Reyolds number turbulence using hot-wire anemometry or particle image velocimetry.  We can also place objects into these flows, e.g., wind turbines, allowing us to see the interactions of turbulence with other bodies.  

Using our large water facilities, we are also able to slow down turbulent processes. Here we can perform time-resolved volumetric particle image velocimetry and laser-induce fluorescence to see the flows in 4-D and understand scalar transport processes.

For more information, please contact Jason Hearst or James Dawson.