Syracuse University and University of Minnesota researchers have come up with two new ideas to enhance efficiency of wind turbines.

With funding support from the U.S. Department of Energy through the University of Minnesota Wind Energy Consortium, the Syracuse University’s L.C. Smith College of Engineering and Computer Science (LCS) research team is testing new intelligent-systems-based active flow control methods.

The situation now is the aerodynamic performance of a wind turbine is best under steady wind flow, while the efficiency of the blades degrade when exposed to conditions such as wind gusts, turbulent flow, upstream turbine wakes and wind shear.  Variability of wind offers considerable challenges.

The new Syracuse approach estimates the flow conditions over the blade surfaces from on blade surface measurements, and then uses this information in an intelligent controller to implement real-time actuation on the blades to control the airflow and increase the overall efficiency of the wind turbine system. The work may also reduce excessive noise and vibration due to flow separation.

The Syracuse researchers, Guannan Wang, Basman El Hadidi, Jakub Walczak, Mark Glauser and Hiroshi Higuchi designed and operated a lab simulation.  The initial lab work shows that flow control applied on the outboard side of the blade beyond the half radius could significantly enlarge the overall operational range of the wind turbine with the same rated power output, or considerably increase the rated output power for the same level of operational range.

The measured improvements are significant, suggesting that either the overall operational range of the wind turbine could be effectively enlarged by 80 percent with the same rated power output, or the rated output power could be increased by 20 percent while maintaining the same level of operational range when the control is on. One might envision even smarter software in the controller that could choose which optimization would pay off best in real time. The lab work also shows the optimal location for the actuator is found to be on the outboard of the blade beyond half of the radius.

The Syracuse team has an advantage with a new anechoic wind tunnel facility at SU to determine the airfoil lift and drag characteristics with appropriate flow control while exposed to large-scale flow unsteadiness.  That’s quite a change from a wind tunnel set up to drive airflow at high speed for airplane aerodynamic tests.  The chamber also allows study of the effects of flow control on the noise spectrum of the wind turbine.

Mark Glauser, Professor of Mechanical and Aerospace Engineering at Syracuse said, “This is a wonderful opportunity to transition our expertise in intelligent systems for flow control, developed largely through support from the aerospace sector, to this important and growing area of the renewable energy sector.’’

Scientists at the University of Minnesota, Roger Arndt, Leonardo P. Chamorro and Fotis Sotiropoulos, are looking at another inefficiency with wind energy – the drag, which is the resistance felt by the turbine blades as they beat the air. The team, at the University of Minnesota’s Saint Anthony Falls Lab (SAFL), looked at drag reduction from effect of placing tiny grooves on turbine blades.

The grooves are in the form of triangular ‘riblets’ scored into a coating on the blade surface. They are so shallow (between 40 and 225 microns) that can’t be seen by the human eye – thus the blades look perfectly smooth. Through wind-tunnel tests of 2.5-megawatt turbine airfoil surfaces (becoming one of the popular industry standards) and computer simulations, they have looked at the grooves’ efficacy for various groove geometries and angles of attack (how the blades are positioned relative to the air stream).

The ‘riblets’ suggest a wind turbine efficiency increase of about 3 percent from the surfacing technique.  At these depths, is seems a kind of etching effect on a coating or paint would be the practical technique if the optimal designs can be built with the optimum geometry.

The two new ideas were recently presented at the American Physical Society Division of Fluid Dynamics meeting in Long Beach, Calif. On Nov. 21, the SU research team presented “Benefits of Active Flow Control for Wind Turbine Blades,” and researchers at the University of Minnesota presented “On the skin friction drag reduction in large wind turbines using sharp V-grooved riblets.”

One’s impression from such developing research suggests that the field of moving air or fluid dynamics is getting going on wind turbine research in sophisticated ways.  While 3% efficiency gains doesn’t sound like much, if a cheap application solution comes out, a serious amount of air drive as well as air driven tools could get a worthwhile refit.

But for retrofitting, the Syracuse team’s controller system seems likely to get development and market legs quickly.  The numbers noted above, an operational range increase of 80% would make an enormous difference on wind turbine production.  An assumption for many is that operating time loss is from light or no wind, when in reality highly variable or gusty winds take operating times down in a very significant way as well.

The numbers will vary on geographic location, but that 30% general operating time assumption could quickly become obsolete.  We’ll see if 30% can get to 30 + 24 for an uptime of 54%.  But even getting half, to 42%, would be a massive improvement.


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