ATO #98 - February 25, 2000
QuestChats require pre-registration. Unless otherwise noted, registration is at: http://quest.arc.nasa.gov/aero/chats/#chatting To be Rescheduled Regimes of Flight Chat with Steve Smith Steve Smith is an aerospace research engineer who studies how airplanes will perform at different speeds. Right now he's researching supersonic flight and he uses computers, wind tunnels and is build his own plane. Read his bio at http://quest.nasa.gov/aero/team/smith.html - - - - - - Thursday, March 2, 2000 10 AM - 11 AM Pacific Aerospace Team Online QuestChat with Earl Duque Earl Duque studies how air flows around, through, and under objects such as wings, propellers and aircraft vehicles. Read his biography at http://quest.nasa.gov/aero/team/duque.html - - - - - - - Tuesday, March 7, 2000, 10-11AM Pacific Aerospace Team Online QuestChat with Brent Nowlin Brent Nowlin is responsible for making sure medium and large-scale gas turbine engines function Properly Read his biography at http://quest.nasa.gov/aero/team/nowlin.html - - - - - - - Tuesday, March 14, 2000, 10 AM - 11 AM Pacific Regimes of Flight QuestChat with Roxana Greenman Roxana Greenman is currently designing applications for aviation. She is developing computerized feedback systems which use artificial intelligence. The feedback systems will be used to provide information for aircraft autopilot systems. Read her bio at http://quest.nasa.gov/aero/team/greenman.html
BLACK HISTORY MONTH CHAT SERIES
February is Black History Month. To celebrate, NASA Quest will host a series of QuestChats and forums with African American scientists and engineers who contribute their work in support of NASA's mission and goals. The schedule which may be added to over time can be found at http://quest.nasa.gov/qchats/special/mlk00/ Of special interest to Aerospace Team Online participants! Tuesday, February 29, 2000, 9 AM Pacific Chat with Oran Cox, Chat Moderator Oran moderates lots of NASA Questchats. He has chatted with astronauts, engineers, pilots, scientists. He also helps teachers who have questions about chats. Read his bio at http://quest.nasa.gov/qchats/ocox/ - - - - - - - Tuesday February 29, 2000 Donald James, Education Branch Director/Chief As education director, Donald is responsible for the center's education programs, including K-12, college and graduate. Read his bio at http://quest.arc.nasa.gov/qchats/special/mlk00/bios/james.html
AIRFOIL STUDY PUBLISHED ON ATO Earl Duque has published some of his research on Air Foil Stalls. His pages are still evolving. Visit: http://quest.nasa.gov/aero/team/fjournals/duque/ - - - - - - - NEW CONTENT Sneak preview the "Regimes of Flight" a new resource for teachers and students about flight at different speeds. This will be targeted for grades 4-8. You will find background material, lesson plans, chats and contests!! For more information see http://quest.nasa.gov/aero/events/regimes - - - - - - CONTEST Entries due soon!!! Regimes of Flight Class Mural Contest, Grades 4-8 January 25 - March 2,2000 Choose one regime of flight: low, medium, high, supersonic, or hypersonic. Classes submit a mural that visually depicts not only the definition and description of the category, but also visually depicts aircraft from that category (Note: Key word "visually" means no words). For more information: go to http://quest.nasa.gov/aero/events/regimes/contest.html
[Editors note: Earl Duque is a Research Scientist for the US Army at NASA Ames. He studies how the air around objects such as wings, propellers, and vehicles acts, how the air flows around, through and under them and how they are affected. Read his biography at http://quest.nasa.gov/aero/team/duque.html ]
IN THE BEGINNING ....
by Earl Duque
February 2, 2 000 For the past 2 years I've been working on the application of computational fluid dynamics, CFD, to studying and understanding the aerodynamics of wind turbines. I published the first paper on this topic 1 year ago at the 1999 AIAA Aerospace Sciences Conference at Reno. This paper presented the first Navier-Stokes computation of a wind turbine rotor, tower and nacelle. However, the computations were very expensive and really not too practical. In addition, we wanted to evaluate the ability to compute the power predicted by a wind turbine across its entire wind speed. At the 2000 AIAA Aerospace Sciences Conference at Reno, I presented a paper that began to look in more detail the aerodynamic forces predicted by the computations. This paper compared the ability to predict the aerodynamic forces that result in power production. The CFD predictions were obtained using, as before, the OVERFLOW code. These predicted power and aerodynamic loads were compared against the CAMRAD II, lifting-line vortex-l attice code. [To see the graphs of Earls research visit http://quest.nasa.gov/aero/team/fjournals/duque/ ] The OVERFLOW calculations does a good job of predicting the power at the lower wind speeds, but does not do as good of a job at the higher speeds. The CAMRAD code shows the correct trends but predicts too much power particularly at the higher wind speeds. We wanted to find out why we weren't correctly predicting the power. The force coefficient acts just like the lift force on an airplane wing. For a wind turbine, this turns the rotor blades, which turn the electrical generator that produces the electrical power. However, at the inboard, radius less than 0.4, the computations begin to vary from one another. As the wind speed increases, the differences between the OVERFLOW and CAMRAD computations increase. As shown in the picture above, the two methods show vastly different trends. In addition, the CAMRAD code tends to underpredict the forces on the inboard. The CAMRAD shows a nearly constant force coefficient of about 1.0 from radius of 0.4 to 0.8. The experiment shows the same trend. This trend indicates that at this wind speed, the wind turbine blade stalls. When stall occurs, the boundary layer on the airfoil separates, and fails to increase the lifting force as angle of attack increases. As the angle of attack increases, the lift increases with it up to about 8 degrees. It's interesting to note that the slope of the line in the lower angle of attack range is approximately equal to 2p. At certain angle of attack, the lift curves approach a maximum value and stops increasing with angle of attack. For the airfoil in question, the S809, the maximum lift coefficient is approximately equal t o 1.0. The force coefficients for the turbine rotor increase are greater than 1.0 on the inboard radial locations. This phenomenon is called stall delay. These computed and experiment observations lead to three questions that I must now try to answer. 1. Why is it that the OVERFLOW code doesn't correctly predict the stall on the rotor blade. 2. Why does the experiment show force coefficients greater than 1.0 on the inboard radial sections ? 3. How do I improve the computational method so that I can accurately predict the power of a wind turbine ?