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Chapter 15 - Characterization of Freestream Disturbances in Conventional Hypersonic Wind Tunnels

Casper, Katya M.; Duan, Lian; Choudhari, Meelan M.; Chou, Amanda; Munoz, Federic; Radespiel, Rolf; Schilden, Thomas; Schroder, Wolfgang; Marineau, Eric C.; Chaudhry, Ross S.; Candler, Graham V.; Gray, Kathryn A.; Schneider, Steven P.

Prediction of boundary-layer transition is a critical part of the design of hypersonic vehicles because of the large increase in skin-friction drag and surface heating associated with the onset of transition. Testing in conventional (noisy) wind tunnels has been an important means of characterizing and understanding the boundary-layer transition (BLT) behavior of hypersonic vehicles. Because the existing low disturbance, i.e., quiet, facilities operate only at Mach 6, moderate Reynolds numbers, fairly small sizes, and low freestream enthalpy, conventional facilities will continue to be employed for testing and evaluation of hypersonic vehicles, especially for ground testing involving other Mach numbers, higher freestream enthalpies, and larger models. To enable better use of transition data from conventional facilities and more accurate extrapolation of wind-tunnel results to flight, one needs an in-depth knowledge of the broadband disturbance environment in those facilities as well as of the interaction between the freestream disturbances with laminar boundary layers.