Dr. S. Balakrishna at the NASA Langley Research Center

One could say that Dr. Balakrishna had something to do with all major facilities at NASA Langley, as well as many of the smaller ones. Advancing the state of the art through technical innovation is key to maintaining facilities capabilities to support NASA’s mission. He was an important innovator for that mission.

National Transonic Facility

His major accomplishments occurred at Langley’s premier wind tunnel, the National Transonic Facility (NTF). Dr. Sundareswara Balakrishna’s many engineering contributions to NTF has improved the technical capabilities, efficiency, and safety of the facility. The NTF is an extremely complex facility that uses gas at cryogenic temperatures to conduct transonic aerodynamic experiments at high Reynolds numbers. This complexity requires considerable technical and operational expertise in order to guarantee and understand the accuracy and quality of the results, produce the results efficiently despite the operational complexities, and ensure the safety of personnel who work in the tunnel’s dangerous environment. The facility is unique in the nation and was a first of its kind, and is still one of only two tunnels world-wide with this class of experimental capabilities. Because of its uniqueness, overcoming engineering and operational challenges is particularly difficult, and Dr. Balakrishna has been a cornerstone of the tunnel’s success.

Dr. Balakrishna’s engineering achievements to improve NTF are numerous. He developed and implemented an Active Balance Damper system, capable of reducing
wind tunnel model aerodynamic-induced vibrations. While the system is operational across a wide range of tunnel conditions, it was especially challenging to ensure that the active system was effective at cryogenic conditions. This system allows customers to acquire data at a significant larger angle of attack range than would be possible (safe) without the damper active.

A number of other NTF systems have been designed and/or improved by Dr. Balakrishna. These include:

  • Dr. Balakrishna was the PI and Co-PI (with W. Allen Kilgore) of Small Business Innovation Research (SBIRs) studies that formed the foundation of control laws for NTF.

  • To ensure the continued safety of the personnel, strain gauge balance systems, and models tested in the NTF, Dr. Balakrishna also developed and upgraded the Balance Limit Alarm Measurement System.

  • NTF model test article wakes at high Reynolds numbers are very strong and can damage many tunnel components. Dr Balakrishna has designed a wake strength monitoring system to ensure safety of tunnel and model components. This system monitors the loads experienced on a wind tunnel model and will alarm tunnel operators that testing is nearing critical limits. If these alarms are ignored, he designed the system to take control of the facility to reduce test conditions to a safe point.

  • To improve the tunnel temperature spatial and temporal uniformity, critically related to data quality, Dr. Balakrishna developed a new set of control algorithms that, in conjunction with new proportion control valves, allow for finer control of the LN2 system to realize uniform temperatures. This enables optimization of LN2 usage, thereby saving customers’ cost. This system has the added benefit of increasing system reliability of the LN2 pumps by reducing shock loads on the system.

  • NTF uses a hot sidewall balance at 100 degrees F while the tunnel is at -250 degrees F. Dr Balakrishna designed the “Balance Cavity Recirculation System”
    to maintain balance accuracy that has resulted in excellent data quality in critical tests in recent a Hybrid Wing body evaluation test.

  • Initial studies on all electric propeller drive system for NTF and other tunnels driving 12 inch propellers up to 20000 rpm as a part of acoustic and airframe engine integration at subsonic and transonic speeds

Dr. Balakrishna’s innovation and rapid response to a challenge is unmatched, and NASA relied on him to ensure the successful operation and continuous improvement of the NTF. Because of his contributions, the NTF team produced significant contributions to NASA and the nation, including: the ARMD Fixed Wing Common Research Model test, Lockheed/AFRL/NASA-sponsored Speed Agile test to develop the next generation transport for DoD, and consulting to ARC 11-Foot for an Ares I test made possible only by Dr. Balakrishna’s techniques. Dr. Balakrishna significantly increased the technical capabilities of the NTF while also making it safer and more efficient.

Other NASA and ViGYAN facilities.

In addition to his NTF support, he has had technical leadership roles in the design, implementation, and support for other facilities and facility systems at LaRC and elsewhere. These include:

  • Balance monitoring systems at LaRC 14×22

  • Design of a new Flight Dynamics Research Facility (FDRF) for the LaRC Flight Dynamics Branch

  • Design of a Compressible Aerodynamics Research Tunnel (CART) for LaRC

  • Co-PI for the original active damper system in the ViGYAN Wind Tunnel for under an AEDC SBIR

  • Co-PI for the early SBIR Phase I design of the ViGYAN Digital Bridge thermal anemometer system

  • Developer and inventor of an extended capability damper system (based on the original active damper mentioned earlier) to address roll vibrations for AEDC

  • Design and commissioning of a Propeller Test Stand for the LaRC Low Speed Aeroacoustics Wind Tunnel

  • Developed and implemented a new control system for the ViGYAN Low Speed Wind Tunnel.