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Numerical investigation of turbulent supersonic axisymmetric wakes

Numerical investigation of turbulent supersonic axisymmetric wakes
Numerical investigation of turbulent supersonic axisymmetric wakes
Numerical experiments are conducted of turbulent supersonic axisymmetric wakes at Mach number M= 2.46 and Reynolds number, based on free-stream velocity and base diameter, ReD = 1 x 10(5). Direct numerical simulations (DNS) are used to study the effect of approach flow conditions, and of specific azimuthal modes, on the near-wake behaviour. To that end, DNS are performed with laminar and turbulent approach boundary layers, and additional turbulent approach flow DNS with reduced circumferential size are conducted to deliberately eliminate certain azimuthal/helical modes. DNS with turbulent approach flow show an increased turning angle and increased growth of the separating shear layer, leading to a shorter recirculation region, a stronger recompression shock system, and ultimately good agreement with experimental data at considerably higher Reynolds number. A similar wake structure is found for laminar and turbulent inflow conditions, giving further evidence of the wake structure being a consequence of the global near-wake instabilities and not a result of upstream conditions. Stability analyses of two-dimensional basic states are carried out by computing the temporal pulse response using forced Navier–Stokes simulations to investigate which azimuthal modes are dominant for fully turbulent wakes and how the stability behaviour is influenced by the choice of basic state. Using the time- and azimuthally averaged data from three-dimensional DNS with turbulent inflow as basic state, an absolute instability of the axisymmetric mode was found and helical modes m= 4, 5, 6 were found to be linearly most unstable, in contrast to results obtained earlier using an axisymmetric flow solution as the basic state. The addition of a turbulence viscosity in the forced DNS retains most of the stability characteristics but reduces the wavenumber of the linearly most-amplified modes.
absolute/convective instability, turbulent transition, wakes
0022-1120
488-520
Sandberg, R.D.
41d03f60-5d12-4f2d-a40a-8ff89ef01cfa
Sandberg, R.D.
41d03f60-5d12-4f2d-a40a-8ff89ef01cfa

Sandberg, R.D. (2012) Numerical investigation of turbulent supersonic axisymmetric wakes. Journal of Fluid Mechanics, 702, 488-520. (doi:10.1017/jfm.2012.201).

Record type: Article

Abstract

Numerical experiments are conducted of turbulent supersonic axisymmetric wakes at Mach number M= 2.46 and Reynolds number, based on free-stream velocity and base diameter, ReD = 1 x 10(5). Direct numerical simulations (DNS) are used to study the effect of approach flow conditions, and of specific azimuthal modes, on the near-wake behaviour. To that end, DNS are performed with laminar and turbulent approach boundary layers, and additional turbulent approach flow DNS with reduced circumferential size are conducted to deliberately eliminate certain azimuthal/helical modes. DNS with turbulent approach flow show an increased turning angle and increased growth of the separating shear layer, leading to a shorter recirculation region, a stronger recompression shock system, and ultimately good agreement with experimental data at considerably higher Reynolds number. A similar wake structure is found for laminar and turbulent inflow conditions, giving further evidence of the wake structure being a consequence of the global near-wake instabilities and not a result of upstream conditions. Stability analyses of two-dimensional basic states are carried out by computing the temporal pulse response using forced Navier–Stokes simulations to investigate which azimuthal modes are dominant for fully turbulent wakes and how the stability behaviour is influenced by the choice of basic state. Using the time- and azimuthally averaged data from three-dimensional DNS with turbulent inflow as basic state, an absolute instability of the axisymmetric mode was found and helical modes m= 4, 5, 6 were found to be linearly most unstable, in contrast to results obtained earlier using an axisymmetric flow solution as the basic state. The addition of a turbulence viscosity in the forced DNS retains most of the stability characteristics but reduces the wavenumber of the linearly most-amplified modes.

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e-pub ahead of print date: 7 June 2012
Published date: July 2012
Keywords: absolute/convective instability, turbulent transition, wakes
Organisations: Aerodynamics & Flight Mechanics Group

Identifiers

Local EPrints ID: 300802
URI: http://eprints.soton.ac.uk/id/eprint/300802
ISSN: 0022-1120
PURE UUID: c9a0a6cb-7a68-46a6-9250-64a4740edac0
ORCID for R.D. Sandberg: ORCID iD orcid.org/0000-0001-5199-3944

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Date deposited: 29 Feb 2012 12:51
Last modified: 14 Mar 2024 10:26

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Author: R.D. Sandberg ORCID iD

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