AEDC-managed NFAC site of unique future generation test

  • Published
  • By Philip Lorenz III
  • AEDC/PA
ARNOLD AIR FORCE BASE, Tenn. --  AEDC's National Full-Scale Aerodynamics Complex's (NFAC) 40-by-80-foot wind tunnel at Moffett Field, Calif., is the chosen location for a unique wind tunnel test on a 10-foot span model of a NASA's cruise efficient short take-off and landing (CESTOL) concept aircraft.

According to Chris Hartley, NFAC's Jacobs Technology engineer on the project, CESTOL-type aircraft have the potential to reduce required take-off and landing distances and noise footprints of passenger aircraft through the use of steep descent profiles and slow landing speeds. He said the sponsor for the test is NASA's Subsonic Fixed Wing Aero Group, and the customer is California Polytechnic State University.

"NASA subsonic fixed wing has a lot of interest in short take off and landing technologies," he said. "CESTOL technologies, which are blown slots and flaps, improve the high-lift [aircraft's flight] characteristics at slow speeds. They've been advancing that technology for some time and so this [test] is a milestone on that road.

"There are a number of technologies on this plane, characterized as N+2 technologies - that designation means that it's [at least] two generations away from current airplane technology. We're assessing that vehicle for its acoustic properties and we will be base-lining this wind tunnel test to CFD (computational fluid dynamics) predictions."

Dave Duesterhaus, NFAC's site director, said the test entry "will have several unique aspects requiring high pressure air and a sting balance model with a flow-through balance system."

Eric Paciano, a graduate student working on a master's degree from California Polytechnic State University in San Luis Obispo, is one of two graduate students still working on the project since its inception three years ago. He spoke about the goals and challenges the project presents.

"The CESTOL model incorporates circulation control (CC), more broadly considered leading and trailing edge blowing. When this blowing is coupled with a large flap deflection - in our case 80 degrees - the downwash is significant. Our predictions indicate that downwash from the trailing edge blowing could be in excess of 10 feet below the CESTOL model.

"The overall goal of the test is to create an open source of data for CFD validation, which means we wanted to get away from the complexity of jet impingement on the tunnel floor.

"Another priority of this test is acquiring acoustic data throughout the experiment. The NFAC's 40-by-80 acoustically-treated tunnel allows the aerodynamic and acoustic data to be acquired simultaneously which allows us to avoid trying to match an acoustic dataset to an aerodynamic dataset. The downwash of the CC jets - requiring a large test section - and the acoustically treated walls were the two primary reasons we chose this test facility."

Paciano added, "The overall goal of the test is to provide a large, high fidelity, dataset that can be used to validate CFD models. The dataset will be open to the public - most likely via a website - along with the CAD (computer aided design) geometry and other information."

Ultimately, the database will be tailored to CFD analysis of the complex flows associated with a circulation controlled wing, a blended wing body and over-the-wing engine locations. The database will be comprised of pressure, skin friction, aero-acoustic and boundary layer interaction measurements.

Craig Hange, NASA's contracting officer's technical representative on the project, said it is important to have the big picture regarding the challenges facing the future of aviation.

"NASA's goal is to improve aeronautics technology and the airspace system," he said. "So, if we can increase the capacity of the airport or get you to airports that aren't being used and do it quieter and more efficiently, all those things are NASA's goals."

Hange said the NFAC has features that are necessary for the CESTOL test.

"The 40-by-80 has a nice speed range - basically all the way up from 20 miles an hour, up through 250 knots which is 275 miles an hour," he said. "At that speed range, there's a lot of room. This is a 10-foot span model, which you'd think is kind of small for that tunnel, [until] you realize that we're using high pressure air to represent the vectoring thrust. When you start doing that you start using up a lot of space in the tunnel. You don't want to hit the walls or your measurements may not be valid. So you need a lot of space in order to do that and the 40-by-80 suits that quite well."