Characterization of Freestream Disturbances in Conventional Hypersonic Wind Tunnels

TLDR

Low‑disturbance hypersonic wind tunnels are limited to Mach 6, moderate Reynolds numbers, low enthalpy, and subscale models, so conventional noisy tunnels are required to reproduce the high‑Mach, high‑enthalpy, large‑model conditions needed for flight‑vehicle testing. This paper reports progress in characterizing tunnel noise from the AVT‑240 specialists group to support hypersonic boundary‑layer transition prediction. Experimental measurements in conventional tunnels from Mach 6 to 14 and direct numerical simulations of turbulent nozzle wall boundary layers were used to map freestream fluctuations and model their propagation to Pitot sensors.

Abstract

Although low-disturbance ("quiet") hypersonic wind tunnels are believed to provide more reliable extrapolation of boundary-layer transition behavior from ground to flight, the presently available quiet facilities are limited to Mach 6, moderate Reynolds numbers, low freestream enthalpy, and subscale models. As a result, only conventional ("noisy") wind tunnels can reproduce both Reynolds numbers and enthalpies of hypersonic flight configurations and must therefore be used for flight vehicle test and evaluation involving high Mach number, high enthalpy, and larger models. This paper outlines the recent progress and achievements in the characterization of tunnel noise that have resulted from the coordinated effort within the AVT-240 specialists group on hypersonic boundary-layer transition prediction. The new experimental measurements cover a range of conventional wind tunnels with different sizes and Mach numbers from 6 to 14 and extend the database of freestream fluctuations within the spectral range of boundary-layer instability waves over commonly tested models. New direct numerical simulation datasets elucidate the physics of noise generation inside the turbulent nozzle wall boundary layer, characterize the spatiotemporal structure of the freestream noise, and account for the propagation and transfer of the freestream disturbances to a Pitot-mounted sensor.