Effect Of The Reynolds Number On The Freestream Disturbance Environment In A Mach 6 Nozzle


To understand the impact of Reynolds number on the acoustic disturbance field inside a high-speed wind tunnel, we use Direct Numerical Simulations (DNS) to model the turbulent boundary layers along the walls of a quasi-two-dimensional nozzle configuration. Intended as a stepping stone to fully three-dimensional simulations of freestream noise inside the NASA 20-Inch Mach 6 Wind Tunnel, the present simulations are based on periodic boundary conditions across the spanwise width of the computational domain that corresponds to about one third of the actual tunnel width. These simulations are performed at four different unit Reynolds numbers, ranging from 3.56 x 106 m−1 to 14.0 x 106 m−1 . The predominantly hydrodynamic fluctuations inside the boundary layer are shown to be nearly unaffected by the presence of freestream forcing associated with the impinging acoustic radiation from the opposite wall. Thus, the Reynolds number trends associated with boundary-layer quantities are consistent with previously published DNS of flat-plate boundary layers at similar Mach numbers and wall temperature ratios. Within the nozzle core region, the unstable disturbance environment is found to be spatially uniform and solely acoustic in character. Comparisons with tunnel noise measurements are made using the numerical data. For the first time, direct comparisons of fluctuations in the same physical quantity, namely, the streamwise mass flux, have been published, as opposed to earlier comparisons involving static-pressure fluctuations based on the DNS and pitot-pressure fluctuations recorded in the wind tunnel. The NASA 20-Inch Mach 6 Wind Tunnel observations corroborate the predicted trend of decreased root-mean-square variations in pressure and mass flux as the Reynolds number rises. Additional details of the acoustic radiation field are quantified and should be useful toward a digital synthesis of the tunnel disturbance environment that would enable realistic simulations of the natural transition process.


Mechanical and Aerospace Engineering


Office of Naval Research, Grant N00014-17-1-2347

International Standard Book Number (ISBN)


Document Type

Article - Conference proceedings

Document Version


File Type





© 2023 American Institute of Aeronautics and Astronautics, All rights reserved.

Publication Date

01 Jan 2022