Numerical simulations of turbulent spots in supersonic boundary layers: Effects of Mach number and wall temperature

Redford, J.A.; Sandham, Neil D.; Roberts, G.T.

doi:10.1016/j.paerosci.2011.08.002

Cited by 40 publications

(26 citation statements)

References 25 publications

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“…• , which lies within the interval derived by Fischer (1972) from experimental data reporting the spreading half-angle of compressible turbulent spots, and is in agreement with more recent DNS and experimental results (Fiala et al 2006;Krishnan & Sandham 2006;Redford, Sandham & Roberts 2012). Assuming that the turbulence spreads laterally starting from a point source, it is also possible to obtain an estimate of the virtual origin of the turbulent boundary layer.…”

Section: Nonlinear Breakdown To Turbulencesupporting

confidence: 88%

Laminar–turbulent transition induced by a discrete roughness element in a supersonic boundary layer

et al. 2013

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The linear instability and breakdown to turbulence induced by an isolated roughness element in a boundary layer at Mach 2.5, over an isothermal flat plate with laminar adiabatic wall temperature, have been analysed by means of direct numerical simulations, aided by spatial BiGlobal and three-dimensional parabolized (PSE-3D) stability analyses. It is important to understand transition in this flow regime since the process can be slower than in incompressible flow and is crucial to prediction of local heat loads on next-generation flight vehicles. The results show that the roughness element, with a height of the order of the boundary layer displacement thickness, generates a highly unstable wake, which is composed of a low-velocity streak surrounded by a three-dimensional high-shear layer and is able to sustain the rapid growth of a number of instability modes. The most unstable of these modes are associated with varicose or sinuous deformations of the low-velocity streak; they are a consequence of the instability developing in the three-dimensional shear layer as a whole (the varicose mode) or in the lateral shear layers (the sinuous mode). The most unstable wake mode is of the varicose type and grows on average ∼17 % faster than the most unstable sinuous mode and ∼30 times faster than the most unstable boundary layer mode occurring in the absence of a roughness element. Due to the high growthrates registered in the presence of the roughness element, an amplification factor of N = 9 is reached within ∼50 roughness heights from the roughness trailing edge. The independently performed Navier-Stokes, spatial BiGlobal and PSE-3D stability results are in excellent agreement with each other, validating the use of simplified theories for roughness-induced transition involving wake instabilities. Following the linear stages of the laminar-turbulent transition process, the roll-up of the three-dimensional shear layer leads to the formation of a wedge of turbulence, which spreads laterally at a rate similar to that observed in the case of compressible turbulent spots for the same Mach number.

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Section: Nonlinear Breakdown To Turbulencesupporting

confidence: 88%

Laminar–turbulent transition induced by a discrete roughness element in a supersonic boundary layer

et al. 2013

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“…DNS of bypass transition at low speed have been shown, for example by Jacobs & Durbin (2001), to include turbulent spots. Similar spots have been observed previously in high-speed flows (Fiala et al 2006) and their growth rates measured in DNS (Redford, Sandham & Roberts 2012). For transitional flows, particularly those with higher background disturbances, the range of phenomena between fully laminar and fully turbulent interactions may be described using the idea of boundary-layer intermittency, introduced by Narasimha (1985), based on the idea of the transition process being dominated by the growth and merging of turbulent spots.…”

supporting

confidence: 69%

“…It is interesting that even the HEG experiments show the same values, implying, for the same spot creation rate n, that the spot growth rate σ is not strongly affected by the cold wall temperature. In a DNS study of isolated turbulent spots Redford et al (2012) showed a small reduction in spot growth rate with decreasing wall temperature, but this was a secondary effect to that of Mach number. It is also worth noting that the relation Re λ = 10Re x T given in Narasimha (1985) does not hold for the cases shown here.…”

Section: −2mentioning

confidence: 96%

Transitional shock-wave/boundary-layer interactions in hypersonic flow

et al. 2014

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Strong interactions of shock waves with boundary layers lead to flow separations and enhanced heat transfer rates. When the approaching boundary layer is hypersonic and transitional the problem is particularly challenging and more reliable data is required in order to assess changes in the flow and the surface heat transfer, and to develop simplified models. The present contribution compares results for transitional interactions on a flat plate at Mach 6 from three different experimental facilities using the same instrumented plate insert. The facilities consist of a Ludwieg tube (RWG), an open-jet wind tunnel (H2K) and a high-enthalpy free-piston-driven reflected shock tunnel (HEG). The experimental measurements include shadowgraph and infrared thermography as well as heat transfer and pressure sensors. Direct numerical simulations (DNS) are carried out to compare with selected experimental flow conditions. The combined approach allows an assessment of the effects of unit Reynolds number, disturbance amplitude, shock impingement location and wall cooling. Measures of intermittency are proposed based on wall heat flux, allowing the peak Stanton number in the reattachment regime to be mapped over a range of intermittency states of the approaching boundary layer, with higher overshoots found for transitional interactions compared with fully turbulent interactions. The transition process is found to develop from second (Mack) mode instabilities superimposed on streamwise streaks.

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“…Note that in the present research, where small-amplitude disturbances are introduced, the growth of primary instability waves starts the transition process. Whereas, in the studies by Krishnan & Sandham (2006a,c), Jocksch & Kleiser (2008) and Redford et al (2011) …”

Section: Scope Of Present Researchmentioning

confidence: 89%

“…Even more recently, Jocksch & Kleiser (2008) performed DNS to investigate the growth of isolated turbulent spots in laminar zero-pressuregradient boundary layers on a flat-plate at Mach 1.1 and 5. Redford et al (2011) investigated the effect of the Mach number and wall temperature on the lateral growth of turbulent spots in supersonic boundary layers with free-stream Mach numbers of 3 and 6. Note that in the present research, where small-amplitude disturbances are introduced, the growth of primary instability waves starts the transition process.…”

Section: Scope Of Present Researchmentioning

confidence: 99%

Numerical Investigation of Laminar-Turbulent Transition in a Cone Boundary Layer at Mach 6

Sivasubramanian

2011

41st AIAA Fluid Dynamics Conference and Exhibit

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Numerical simulations of turbulent spots in supersonic boundary layers: Effects of Mach number and wall temperature

Cited by 40 publications

References 25 publications

Laminar–turbulent transition induced by a discrete roughness element in a supersonic boundary layer

Laminar–turbulent transition induced by a discrete roughness element in a supersonic boundary layer

Transitional shock-wave/boundary-layer interactions in hypersonic flow

Numerical Investigation of Laminar-Turbulent Transition in a Cone Boundary Layer at Mach 6

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