Skip to content

Computational Fluid Dynamics

The Role of Computational Fluids Dynamics

flume_CFD_force_traces
Force measurements comparing the small-scale flume model and the CFD results showing excellent agreement in Lift and Drag Forces, and also Torque. From these measurements the mechanical efficiency can be computed.

Computational Fluid Dynamics (CFD) is utilized in conjunction with scaled-down laboratory experiments to learn more about the flow physics of the oscillating foil technology.  The flume measurements and CFD serve as validation of one another’s prediction capabilities in order to provide accurate kinematics and configurations to the prototype design team.   The figure below has one example of the measurements from both the flume and CFD, demonstrating the excellent agreement and accuracy of the forces and moments on the foil throughout a complete stroke.

 

 

Computational Methods

NSEqns
Incompressible Navier-Stokes Equations used for the computational fluid dynamics (CFD) simulations. They are recast into a non-inertial form to handle the heaving and pitching motion of the body.

The low Reynolds number two-dimensional simulations (Re=1000) utilize a direct numerical simulation (DNS) code that provides complete spatial and time resolution of the Navier-Stokes equations. Single foil simulations are computed in a non-inertial reference frame on a fixed mesh that includes body forces for the translation and rotational motion of the foil.   Such low Reynolds number simulations have a fast turn-around time suitable for more extensive kinematic sweeps.  From the CFD we can compute forces, torques, and thus power from both the pressure and viscous forces the foil, and visualize the flow field throughout the cycle

 

High Reynolds Number Simulations

low_high_Re_power
The power over a single cycle of the low Reynolds number simulation compared with the high Reynolds number simulation. This shows the insensitive of a single foil simulation to size of foil (Reynolds number).

Large-Eddy Simulations (LES) in a non-intertial reference frame are utilized for high Reynolds number simulations.  At a Reynolds number comparable to the flume measurements (50,000) there is little difference between the vortex dynamics of the high and low Reynolds number results.  Although transition to turbulence and turbulence often affects aero/hydrodynamics at this Reynolds number, it is not as important to the vortex dynamics as the high level of flow separation at the leading edge.

Multiple Foil Interactions

In order to investigate how foils interact with one another, a moving mesh technique is developed for multiple foil simulations.  This enables Leading Edge to project the efficiency and power of oscillating foils as they work in tandem, and also how they can optimally arranged in arrays.

For more information contact Dr. Jennifer Franck.