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UPDATE #23 - May 14, 1998

PART 1: Space Day Chat
PART 2: Survey Coming
PART 3: Navier Stokes computations
PART 4: Subscribing & Unsubscribing: How to do it


The goal of Space Day is to advance science, math and technology
education and inspire future generations to realize the vision of our
space pioneers. Space Day '98 takes place on Thursday, May 21. In
anticipation of that day, Quest is hosting a two full days of
QuestChats on May 19 and May 20. During these days, classrooms
will be able to interact with NASA experts from our various
projects in real time. Besides Space Shuttle and International Space
Station folks, experts on Mars and aeronautics and other NASA
activities will be represented.

See all of the details and register to participate at:

Tuesday May 19, 1998 9:00 a.m.- 10:00 a.m. Pacific Time:
Dale Satran, Aerospace Engineer,

Dale is involved in high lift research. Currently he is studying lift on
the Boeing 777.

Registration information is at
Read his biography prior to joining this chat.

Wednesday May 20, 1998 8:00 a.m.- 9:00 a.m. Pacific Time:
Larry Bisbee, Mechanical Design Engineer

Larry designs the models that go into the wind tunnels. He gets paid to
design model planes.

Registration information is at
Read his biography prior to joining this chat.

Wednesday May 20, 1998 12:00 p.m.- 1:00 p.m. Pacific Time:
Mina Cappuccio, Aerospace Research Engineer

Mina is working in the area of propulsion airframe integration, or how to
fit the engine on the plane. Currently she is working on the High Speed
Civil Transport.

Registration information is at
Read her biography prior to joining this chat.

Wednesday May 20, 1998 1:00 p.m.- 2:00 p.m. Pacific Time:
Liza Alderete, Education Technology and Multimedia Manager

Liza Alderete has worked in wind tunnels, simulations and now is in the
Education Department at NASA Ames Research Center. She recently produced a
CD called Exploring Aeronautics which will be available in June.

Registration information is at
Liza's bio will be at http://quest.arc.nasa.gov/aero/team/alderete.html


Since we are spending US taxpayer dollars on Space Team Online,
we have to demonstrate to NASA management that the project is
having an outreach impact. To assess the impact, we will be
conducting a survey of the Space Team Online audience in a week or
two. Please help us by taking the time to respond to this survey at
that time. It should only take a few minutes.

A significant response rate to the survey will best help us make
a case to NASA management that Space Team Online is worth
continuing into the future. In addition, this survey will be the
only way we can assess the demographics of the audience we serve.
Though we reach many more people then a traditional NASA outreach
program, if we cannot present information about that large audience,
we don't get much credit.

So please, when the time comes, take a few moments to help us
in this small way.

[Editor's note: Steve Smith is an Aerospace Research Engineer. He uses computational fluid dynamics (computer programs) to predict the performance of new concepts. Sometimes he does research in wind tunnels. Read his biography at http://quest.arc.nasa.gov/aero/team/smith.html ]


by Steve Smith

February 18, 1998

Meanwhile, I've also been working on Navier Stokes computations, the
most advanced flow simulation we can do, on a new business jet design
from Raytheon Aircraft, to see how well these simulations can predict the
''edge of the envelope'' of transonicon jetliners and business jets.My
goal is not to compute the performance at the normal cruising
conditions, which are about Mach 0.83 and angle of attack of 2 degrees,
but rather to compute the flow at Mach 0.86 or so.  This higher speed
causes a transonic flow problem called buffet.

Usually buffet conditions are identified in the wind tunnel, and then
during flight tests of the real airplane.  In the wind tunnel, we measure
the overall lift and drag, but its hard to measure all the distributed
lift loads all over the airplane. The structural design people need to
know this, so they can be sure that all the individual pieces of the
airplane are strong enough.  Usually they can't be really sure about the
structural strength and the loads until they start flight testing.  If
something isn't strong enough and they need to re-design it, thats very
expensive.  So what I want to do is give the structural designers good
predictions of these localized structural loads caused by buffet, much
sooner in the design process, so there is less need for re-design later.

The challenge is that the buffet flow conditions are very complicated.
The formation of turbulence and separated flow has a big effect.  The
shock waves that form on the wings get so strong that they start to
disrupt the smooth flow in the boundary layers where the flow touches the
airplane.  Eventually, the boundary layer is so disrupted that it lifts
off the surface and forms turbulence.

Turbulence and separated flow are two areas of fluid mechanics that still
are not very well understood, and the computer simulations don't work very
well. Recently, there have been some real improvements in these turbulence
models, and my project will put these new methods to the test to see if
they can predict the buffet characteristics.


Once again, the first step is getting the surface shape represented in the
computer. For Navier Stokes methods, this surface definition must be much
more precise than I usually need for my panel methods.  Not only that, but
the Navier Stokes methods require that the whole region around the outside
the airplane be divided up into a very fine three-dimensional mesh of
little cubes.  The solution method used for these codes is called a
''finite difference'' method.  It approximates the smooth change in flow
properties in the real flow by little jumps in the flow properties from
one cube to another.  If the mesh is very fine, these jumps are very small
and approximate the smooth flow changes pretty well.  So, the grid
generation process to create these little cubes throughout the flow takes
a long time.

This project was my first experience at making a fine mesh for a Navier
Stokes code. It took me more than a month to go from the basic surface
geometry of the whole business jet to the three-dimensional mesh around
it.  My mesh has over 9,000,000 grid-points.

Running the Navier Stokes code

These methods used to take hundreds of hours of computer time on the Cray
supercomputer to run.  But a new version of the code runs on parallel
machines like the IBM SP-2 and the SGI Origin 2000.  I got my first
results back in about 7 hours of computer time on the Origin 2000.
For the first cases, I ran flight conditions pretty close to the cruise
conditions, just to compare and make sure everything is working.  The next
step is to run higher and higher Mach numbers approaching the buffet
condition.  To start with, I'm using an older turbulence model, then I
must incorporate the new turbulence model that is supposed to work much
better.  We'll see!


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