NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Automatic control of cryogenic wind tunnelsInadequate Reynolds number similarity in testing of scaled models affects the quality of aerodynamic data from wind tunnels. This is due to scale effects of boundary-layer shock wave interaction which is likely to be severe at transonic speeds. The idea of operation of wind tunnels using test gas cooled to cryogenic temperatures has yielded a quantrum jump in the ability to realize full scale Reynolds number flow similarity in small transonic tunnels. In such tunnels, the basic flow control problem consists of obtaining and maintaining the desired test section flow parameters. Mach number, Reynolds number, and dynamic pressure are the three flow parameters that are usually required to be kept constant during the period of model aerodynamic data acquisition. The series of activity involved in modeling, control law development, mechanization of the control laws on a microcomputer, and the performance of a globally stable automatic control system for the 0.3-m Transonic Cryogenic Tunnel (TCT) are discussed. A lumped multi-variable nonlinear dynamic model of the cryogenic tunnel, generation of a set of linear control laws for small perturbation, and nonlinear control strategy for large set point changes including tunnel trajectory control are described. The details of mechanization of the control laws on a 16 bit microcomputer system, the software features, operator interface, the display and safety are discussed. The controller is shown to provide globally stable and reliable temperature control to + or - 0.2 K, pressure to + or - 0.07 psi and Mach number to + or - 0.002 of the set point value. This performance is obtained both during large set point commands as for a tunnel cooldown, and during aerodynamic data acquisition with intrusive activity like geometrical changes in the test section such as angle of attack changes, drag rake movements, wall adaptation and sidewall boundary-layer removal. Feasibility of the use of an automatic Reynolds number control mode with fixed Mach number control is demonstrated.
Document ID
19900006641
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Balakrishna, S.
(NASA Langley Research Center Hampton, VA, United States)
Date Acquired
September 6, 2013
Publication Date
November 1, 1989
Publication Information
Publication: AGARD, Special Course on Advances in Cryogenic Wind Tunnel Technology
Subject Category
Research And Support Facilities (Air)
Accession Number
90N15957
Distribution Limits
Public
Copyright
Other
Document Inquiry

Available Downloads

There are no available downloads for this record.
No Preview Available