Implementation of the WICS wall Interference Correction System at the National Transonic Facility

Venkit Iyer', Lockheed MartinJoel L. Everhart*, NASA Langley Research CenterPamela J. Bir*, ViGYAN, Inc.andNorbert Ulbrich _, Sverdrup Technology, Inc.ABSTRACTThe Wall Interference Correction System (WICS) isoperational at the National Transonic Facility (NTF) ofNASA Langley Research Center (NASA LaRC) forsemispan and full span tests in the solid wall (slotscovered) configuration. The method is based on thewall pressure signature method for computingcorrections to the measured parameters. It is anadaptation of the WICS code operational at the 12 ftpressure wind tunnel (12ft PWT) of NASA AmesResearch Center (NASA ARC). This paper discussesthe details of implementation of WlCS at the NTFincluding tunnel calibration, code modifications fortunnel and support geometry, changes made for theNTF wall orifices layout, details of interfacing with thetunnel data processing system, and post-processing ofresults. Example results of applying WlCS to a semi-span test and a full span test are presented. Comparisonwith classical correction results and an analysis ofuncertainty in the corrections are also given. As aspecial application of the code, the Mach numbercalibration data from a centerline pipe test wascomputed by WICS. Finally, future work forexpanding the applicability of the code including on-line implementation is discussed.INTRODUCTIONThe National Transonic Facility (NTF) was designedfor high Reynolds number testing in a cryogenic,pressurized environment with slotted tunnel walls toalleviate transonic wall interference effects. Recently,the facility has developed the capability to run tests onlarge high-lift models at subsonic speeds with thetunnel wall slots covered. The need for an accurate andreliable method to compute wall interferencecorrections for full span and semispan testing undersolid wall conditions became apparent. Stringentaccuracy requirements on corrected equivalent free-airvalues of measured parameters limit the use ofclassical corrections except at low lift conditions.The wall interference code WICS _is based on the wallsignature method of Hackett 2 to compute corrections forsolid-walled tunnels. It has been operational at theAmes 12 ft pressurized wind tunnel for several years. Inthis method, the aerodynamic test article is representedby a discrete number of singularities whose strengthsare computed by a global fit of the tunnel wall pressuresand the measured forces and moments. Subsequently,the code computes the averaged blockage and AOAcorrections based on interpolation from databases ofperturbation velocities or influence coefficients. Thesecorrections are then applied to the tunnel parameters toapproximate the equivalent free-air flow field. Inaddition, the code provides the wall interferencevariation in the vicinity of the model (which is notobtainable from simpler classical methods). Theadvantage of the method is that it is fast, robust andsuited for real-time application; therefore, it wasselected for implementation at the NTF.The method is currently operational at NTF and hasbeen successfully applied to recent semispan and fullspan tests. This paper presents a summary of tunnelcalibration activities, WICS implementation for semi-span and full span tests, and a sample of resultsobtained. Work reported here falls under one of the• Aeronautical Engineer, Senior Member AIAA.t Research Engineer, Senior Member AIAA.Research Engineer. Member AIAA.Senior Aerodynamicist.Copyright © 2000 by the American Institute of Aeronautics and Astronautics, Inc. No copyright is asserted in the United States under Title 17,U.S Code. The U.S. Government has a royalty-freelicense to exercise all rights under the copyright claimed herein for Government Purposes.All other rights are reserved by the copyright owner.