Numerical investigation of the development of three-dimensional wavepackets in a sharp cone boundary layer at Mach 6

Jayahar Sivasubramanian, Hermann F Fasel

Research output: Contribution to journalArticle

38 Citations (Scopus)

Abstract

Direct numerical simulations were performed to investigate wavepackets in a sharp cone boundary layer at Mach 6. In order to understand the natural transition process in hypersonic cone boundary layers, the flow was forced by a short-duration (localized) pulse. The pulse disturbance developed into a three-dimensional wavepacket, which consisted of a wide range of disturbance frequencies and wavenumbers. First, the linear development of the wavepacket was studied by forcing the flow with a low-amplitude pulse (0.001 % of the free-stream velocity). The dominant waves within the resulting wavepacket were identified as the second-mode axisymmetric disturbance waves. In addition, weaker first-mode oblique disturbance waves were also observed on the lateral sides of the wavepacket. In order to investigate the nonlinear transition regime, large-amplitude pulse disturbances (0.5 % of the free-stream velocity) were introduced. The response of the flow to the large-amplitude pulse disturbances indicated the presence of a fundamental resonance mechanism. Lower secondary peaks in the disturbance wave spectrum were identified at approximately half the frequency of the high-amplitude frequency band, suggesting the possibility of a subharmonic resonance mechanism. However, the spectrum also indicated that the fundamental resonance was much stronger than the subharmonic resonance. A secondary stability investigation using controlled disturbances confirmed that fundamental resonance is indeed a dominant mechanism compared to subharmonic resonance. Furthermore, strong peaks in the disturbance wave spectrum were also observed for low-azimuthal-wavenumber second-mode oblique waves, hinting at a possible oblique breakdown mechanism. Thus, the wavepacket simulations indicate that the second-mode fundamental resonance and oblique breakdown mechanisms are the strongest for the investigated flow. Hence, both mechanisms are likely to be relevant in the natural transition process for a cone boundary layer at Mach 6.

Original languageEnglish (US)
Pages (from-to)600-649
Number of pages50
JournalJournal of Fluid Mechanics
Volume756
DOIs
StatePublished - Oct 10 2014

Fingerprint

Mach number
Cones
boundary layers
cones
Boundary layers
disturbances
pulse amplitude
free flow
breakdown
Hypersonic aerodynamics
Direct numerical simulation
Frequency bands
hypersonics
direct numerical simulation
pulse duration
pulses

Keywords

  • boundary layer stability
  • compressible boundary layers
  • high-speed flow

ASJC Scopus subject areas

  • Mechanical Engineering
  • Mechanics of Materials
  • Condensed Matter Physics

Cite this

Numerical investigation of the development of three-dimensional wavepackets in a sharp cone boundary layer at Mach 6. / Sivasubramanian, Jayahar; Fasel, Hermann F.

In: Journal of Fluid Mechanics, Vol. 756, 10.10.2014, p. 600-649.

Research output: Contribution to journalArticle

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