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Title: Pressure fluctuations beneath instability wavepackets and turbulent spots in a hypersonic boundary layer

To investigate the pressure-fluctuation field beneath turbulent spots in a hypersonic boundary layer, a study was conducted on the nozzle wall of the Boeing/AFOSR Mach-6 Quiet Tunnel. Controlled disturbances were created by pulsed-glow perturbations based on the electrical breakdown of air. Under quiet-flow conditions, the nozzle-wall boundary layer remains laminar and grows very thick over the long nozzle length. This allows the development of large disturbances that can be well-resolved with high-frequency pressure transducers. A disturbance first grows into a second-mode instability wavepacket that is concentrated near its own centreline. Weaker disturbances are seen spreading from the centre. The waves grow and become nonlinear before breaking down to turbulence. The breakdown begins in the core of the packets where the wave amplitudes are largest. Second-mode waves are still evident in front of and behind the breakdown point and can be seen propagating in the spanwise direction. The turbulent core grows downstream, resulting in a spot with a classical arrowhead shape. Behind the spot, a low-pressure calmed region develops. However, the spot is not merely a localized patch of turbulence; instability waves remain an integral part. Limited measurements of naturally occurring disturbances show many similar characteristics. From the controlled disturbance measurements,more » the convection velocity, spanwise spreading angle, and typical pressure-fluctuation field were obtained.« less
Authors:
 [1] ;  [2] ;  [3]
  1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Purdue Univ., West Lafayette, IN (United States)
  2. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
  3. Purdue Univ., West Lafayette, IN (United States)
Publication Date:
OSTI Identifier:
1111311
Report Number(s):
SAND--2013-7947J
Journal ID: ISSN 0022-1120; PII: S0022112014004753
Grant/Contract Number:
AC04-94AL85000
Type:
Accepted Manuscript
Journal Name:
Journal of Fluid Mechanics
Additional Journal Information:
Journal Volume: 756; Journal ID: ISSN 0022-1120
Publisher:
Cambridge University Press
Research Org:
Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA)
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING high-speed flow; instability; transition to turbulence