Transonic Dynamics Tunnel
NASA Langley Research Center
The TDT is specifically dedicated to investigating flutter problems of fixed-wing aircraft. However, the tunnel is also used to investigate other aeroelastic phenomena such as fixed-wing buffet and divergence and to conduct rotary-wing tests that investigate the performance, loads, and stability characteristics of both helicopter and tiltrotor configurations. The tunnel is used by aircraft industry, NASA, Department of Defense, and university researchers for a multitude of purposes such as clearing new designs from flutter, studying the use of active controls technologies for both fixed-wing and rotary-wing configurations, determining the effects of ground-wind loads on launch vehicles, and providing steady and unsteady aerodynamic pressure data to support computational aeroelasticity and computational fluid dynamics code development and validation.
Cutaway drawing of the TDT.
The tunnel is specially configured for flutter tests of fixed-wing models. There is excellent model visibility from the tunnel control room and safety screens protect the tunnel fan blades from debris in case of a model failure. One feature of the TDT which is particularly useful for flutter tests is a group of four bypass valves that connect the test section area to the opposite leg of the wind-tunnel circuit downstream of the fan motor. In the event of model instability, these quick actuating valves are opened, which causes a rapid reduction in the test section Mach number and dynamic pressure that serves to stabilize the model. The TDT also offers an airstream oscillation system for studies of the effects of gusts on fixed-wing and rotary-wing aircraft.
TDT boundary for air and R-134a test mediums.
The DAS can handle typical model instrumentation arrangements such as strain-gage balances, potentiometers for position indication, and electronically scanned pressure (ESP) transducers. Additionally, most aeroelastic models are highly instrumented with dynamic signal instrumentation such as strain gages and accelerometers. Individual in situ unsteady pressure measurements are often made for well over 100 orifice locations on a model.
The TDT open-architecture dynamic data acquisition system (DAS) allows real-time acquisition and display of measured static and dynamic data as well as online analysis of the acquired data.
The DAS hardware is comprised of three subsystems, each switch connectable to a subset of four NEFF "front ends". Each NEFF provides signal conditioning, filtering, and sample-and-hold analog-to- digital conversion for 64 channels for a total capability of 256 channels. Data can be sampled at an aggregate rate approaching 300,000 samples per sec, which typically provides data acquisition at a rate of at least 1000 samples per sec for all available model instrumentation. The computer systems supporting the DAS perform basic data acquisition, archiving, and continuous buffering that is necessary to provide high quality dynamic data during tests. The facility also has the capability to provide on-line frequency analysis, postpoint time- and frequency-domain data analysis, and controller performance evaluations. All computers and terminals are connected, via networks, to work-stations at the TDT or at remote sites, which provides a distributed real-time data display capability.
Langley?s LHB 1710.15 Wind Tunnel Model System Criteria is the guideline for model design and fabrication. Model installation and any exceptions to this document must have the approval of the TDT Safety Head on a case-by-case basis to assure personnel and tunnel hardware are not exposed to risk.
