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ATO #98 - February 25, 2000

PART 1: Upcoming Chats
PART 2: Black History Month Chats
PART 3: Project News
PART 4: In the Beginning ...


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
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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

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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

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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


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

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/

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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 


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/

- - - - - - -

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

- - - - - -

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

[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 ]


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 ?

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