B61 undergoes testing in AEDC wind tunnel
By Deidre Ortiz, AEDC/PA
/ Published July 18, 2014
ARNOLD AIR FORCE BASE, TENN --
A test conducted in Arnold Engineering Development Complex's (AEDC) 16-foot transonic wind tunnel (16T) supports the design of the newest version of the B61 nuclear bomb.
As part of the B61-12 Life Extension Program (LEP), AEDC engineers partnered with researchers from Sandia National Laboratories to perform a wind tunnel test on a full-scale mock-up B61 to determine the configuration that would deliver the necessary spin motion of the bomb during freefall.
It was noted by the customer that the decision to test at AEDC was made in large part because it has the nation's largest wind tunnel capable of the required air speeds but also due to AEDC personnel's experience in testing jet interactions similar to those on the B61.
Aerospace Testing Alliance (ATA) Project Engineer Melissa Minter stated during the eight-days of recent testing, the test team's primary objective was to characterize the aerodynamic counter torque effect produced by the interaction between the B61 Spin Rocket Motor (SRM) plumes and the weapon's aft fins. Counter torque occurs when plumes from the rocket motors work against the fin performance, thwarting the torque from the motors and reducing the vehicle spin rate.
Sandia's team analyzed the counter torque produced by the jet-fin interaction as a function of the jet-to-free stream dynamic pressure ratio.
"Background-Oriented Schlieren (BOS) images of the airflow around the model were acquired for all runs during the test and provided visualization of the flow disturbances caused by the jet plumes," Minter said. "The images show that the counter torque is caused by a vortex/fin interaction, and the vortex is caused by the jets and begins downstream of the jets."
Air Force Project Manager Tyler Neale explained a legacy version of the B61 gravity bomb had undergone a full-scale wind tunnel test at AEDC in 2002, but that data is no longer applicable since the bomb now uses a significantly different tail design than earlier versions.
While the legacy test had previously confirmed that counter torque was a result of vortex/fin interaction, the BOS images from this most recent test provided additional insight into the vortex trajectories and the shock structure at the jet nozzle exits.
ATA Analysis engineer Scott Keen stated this "was a very non-standard type of testing for AEDC."
Sandia researchers have stated they're extremely pleased with the data received from the recent test.
The new data gained from this test will be used in the development of a model of the B61 flight performance characteristics.