CFD mesh

Iso-surfaces of vorticity magnitude

Downwind configuration

Iso-surfaces of vorticity magnitude

Upwind configuration

ABSTRACT

Large wind turbines are typically designed to operate in the upwind configuration, wherein the

rotor is located upwind of the tower. However, as blades get larger there is increased possibility

of blade-tower interference, and the use of robust and heavy blades that resist deformation

could be expensive. A downwind rotor may offer a simple, cost-effective solution. A downwind

rotor shows promise, but the optimal use of the concept will require an investigation into the

impact of the tower shadow on the wind turbine loads and power. A Computational Fluid

Dynamics tool solving for full Navier-Stokes equations is used to determine the detailed flow

field developing around two-blade horizontal axis wind turbines (HAWT) in downwind and

upwind configurations. The resulting flow field around the wind turbine is used to evaluate the

noise radiating to the farfield using an acoustic analogy method. The influence of the variation

of wind velocity and rotational speed of the rotor on the sound pressure level is analyzed.

TOOL

The numerical tool used to carry out the simulations of fluid flow around the wind

turbine is an advanced Computational Fluid Dynamics commercial solver ( ANSYS

Fluent). The propagation of sound to the far field is predicted using an acoustic analogy

method (Ffowcs Williams and Hawkings).

COMMENTS AND CONCLUSIONS

Acoustic pressure

Sound pressure level

Sound pressure level

Pressure force in x-direction

Torque

References

[1] Jonkman, J., “NREL Offshore Baseline 5MW,” NREL / NWTC publication, Feb. 2007.

[2] Jonkman, J. M., Butterfield, S., Musial, W., and Scott, G., “Definition of a 5 MW reference wind turbine

for offshore system development,” NREL/TP-500-38060, Golden, CO, Feb. 2009.

[3] ANSYS, Inc., www.ansys.com, Canonsburg, PA.

[4] Hubbard, H.H. and Shepherd, K.P. (1990), Wind Turbine Acoustics, NASA TM DOE/NASA 20320-77.

• The overall effect of the tower wake on the torque seems to be negligible.

• Larger spikes would raise concerns related to structural analysis because they generate

larger deflections of the blades, although, these spikes are not so large.

• The acoustic pressure generated by the downwind configurations is larger compared to

upwind configuration by about 12%.

• The low frequency noise radiating from downwind configurations is higher by about

7db.

• Higher level noise is radiating from systems operating under larger wind velocities.

• However, even if the downwind configurations generate more noise, off-shore designs

are possible because the wind turbines are far from residential areas.

MOTIVATION: Install a 2-blade downwind configuration wind turbine in Lake Erie

Analysis of Tower Shadow Effects and Noise Radiation from Downwind HAWT’s Using a CFD Tool

Adrian Sescu Abdollah A. Afjeh Brett Andersen

Univ. of Toledo, MIME Department Univ. of Toledo, MIME Department Univ. of Toledo, MIME Department

Current affiliation: Johns Hopkins University

Research conducted with support from the US Department of Energy (Grant DE-FOA-0000090) which is gratefully acknowledged.