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A series of tests has been conducted in the variable-density wind tunnel on several airfoils of different sizes and sections to determine the effect of tunnel-wall interference and to determine the effect of tunnel-wall interference and to determine a correction which can be applied to reduce the error caused thereby. The use of several empirical corrections was attempted with little success. The Prandtl theoretical correction gives the best results and its use is recommended for correcting closed wind tunnel results to conditions of free air.
Linearized compressible-flow analysis is applied to the study of wind-tunnel-wall interference for subsonic flow in either two-dimensional or circular test sections having slotted or porous walls. Expressions are developed for evaluating blockage and lift interference.
This report was compiled by an international team of wind tunnel wall correction experts. It presents the present state of the art in wind tunnel wall corrections with a special emphasis given to the description of modern wall correction methods based on Computational Fluid Dynamics. This AGARDograph was planned by the AGARD Fluid Dynamics Panel to be a modern sequel of the successful AGARDograph 109 "Subsonic Wind Tunnel Wall Corrections", which was published in 1966. AGARDogaph 109 is still valid and continues to be used to provide wall corrections in many wind tunnels. Nevertheless, in the thirty two years since the publication of AGARDograph 109, much work has been done on the subject, and the influence of the new tool of numerical fluid dynamics was so strong, that a sequel to AGARDograph 109 was considered to be necessary.
A problem associated with the wind tunnel testing of very slow flying aircraft is the correction of observed pitching moments to free air conditions. The most significant effects of such corrections are to be found at moderate downwash angles typical of the landing approach. The wind tunnel walls induce interference velocities at the tail different from those induced at the wing, and these induced velocities also alter the trajectory of the trailing vortex system. The relocated vortex system induces different velocities at the tail from those experienced in free air. The effect of the relocated vortex and the walls is to cause important changes in the measured pitching moments in the wind tunnel.
Numerous aspects of transonic aerodynamics include wall interference corrections in conventional wind tunnels, subsonic flow in a variety of wind tunnels, and test results from transonic wind tunnels. 1961 edition.