Compressibility Effects on Boundary-Layer Transition Induced by an Isolated Roughness Element

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

doi:10.2514/1.j050186

Cited by 58 publications

(53 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Although transition in supersonic and hypersonic flow regimes is further influenced by compressibility and temperature effects, many features of the transition mechanisms are similar to those of low-speed incompressible flows (Redford et al 2010;Bernardini et al 2012). These include the formation of unsteady hairpin structures after the roughness and lift-up process, and the influence of the hairpin structures on destabilising the shear layer over the roughness element.…”

mentioning

confidence: 99%

Turbulence in a transient channel flow with a wall of pyramid roughness

Seddighi

Pokrajac

et al. 2015

J. Fluid Mech.

View full text Add to dashboard Cite

A direct numerical simulation investigation of a transient flow in a channel with a smooth top wall and a roughened bottom wall made of close-packed pyramids is presented. An initially stationary turbulent flow is accelerated rapidly to a new flow rate and the transient flow behaviour after the acceleration is studied. The equivalent roughness heights of the initial and final flows are k + s = 14.5 and 41.5, respectively. Immediately after the acceleration ends, the induced change behaves in a 'plug-flow' manner. Above the roughness crests, the additional velocity due to the perturbation flow is uniform; below the crest, it reduces approximately linearly to zero at the bottom of the roughness elements. The interaction of the perturbation flow with the rough wall is characterised by a series of events that resemble those observed in roughness-induced laminar-turbulent transitions. The process has two broad stages. In the first of these, large-scale vortices, comparable in extent to the roughness wavelength, develop around each roughness element and high-speed streaks form along the ridge lines of the elements. After a short time, each vortex splits into two, namely (i) a standing vortex in front of the element and (ii) a counter-rotating hairpin vortex behind it. The former is largely inactive, but the latter advects downstream with increasing strength, and later lifts away from the wall. These hairpin vortices wrap around strong low-speed streaks. The second stage of the overall process is the breakdown of the hairpin vortices into many smaller multi-scale vortices distributed randomly in space, leading eventually to a state of conventional turbulence. Shortly after the beginning of the first stage, the three components of the r.m.s of the velocity fluctuation all increase significantly in the near-wall region as a result of the vortical structures, and their spectra bear strong signatures of the surface topology. During the second stage, the overall turbulence energy in this region varies only slightly, but the spectrum evolves significantly, eventually approaching that of conventional turbulence. The direct effect of roughness on the flow is confined to a region up to approximately three element heights above the roughness crests. Turbulence in the core region does not begin to increase until after the transition near the wall is largely complete. The processes of transition over the smooth and rough walls of † Email addresses for correspondence: m.seddighi@ljmu.ac.uk, s.he@sheffield.ac.uk Turbulence in a transient channel flow with a rough wall 227 the channel are practically independent of each other. The flow over the smooth wall follows a laminar-turbulent transition and, as known from previous work, resembles a free-stream turbulence-induced boundary layer bypass transition.

show abstract

mentioning

confidence: 99%

Turbulence in a transient channel flow with a wall of pyramid roughness

Seddighi

Pokrajac

et al. 2015

J. Fluid Mech.

View full text Add to dashboard Cite

show abstract

“…Choudhari et al [6] found that, for lower roughness height, the sinuous modes were dominant, whereas the varicose modes became dominant for a roughness element with larger height. Wall cooling at Mach 3 and 6 was found to have a stabilizing influence [7,9], which was explained in work by De Tullio and Sandham [10] as a stabilization of the wake modes. The experimental measurement of roughness wake instability at hypersonic speed is difficult, due to the high structural loads on measurement probes, and not many studies have been published that cross validate experimental and numerical results of hypersonic wake instability.…”

mentioning

confidence: 71%

“…Direct numerical simulations (DNSs) can also be used to study the roughness-induced transition process and make it possible to obtain data and measurements that would not be possible using wind-tunnel experiments. Due to the high computational cost, however, DNSs of high-speed roughness-induced transition have only been performed recently, e.g., Marxen and Iaccarino [5], Choudhari et al [6], Redford et al [7], Groskopf et al [8], Bernardini et al [9], and De Tullio and Sandham [10], among others. DNS has its own set of limitations (e.g., the potential dependency on grid quality and numerical dissipation, and the need to prescribe an external forcing or noise source).…”

mentioning

confidence: 99%

“…Originally developed for incompressible roughness-induced transition, the performance of Re kk as a transition criterion diminishes for high-speed flow; and laminar cases have been reported with a Reynolds number Re kk well above the critical values often quoted in literature [9]. Redford et al [7] investigated compressibility effects on roughness-induced transition at Mach 3 and Mach 6 and found they could separate the subcritical and transitional cases using a critical Reynolds number Re kk dependent on the Mach number in the surrounding boundary layer at the roughness height M k and wall temperature T w . They proposed a map of M k T ∞ ∕T w against Re kk , for which the dividing line between laminar and transitional simulations was given by…”

mentioning

confidence: 99%

“…Bernardini et al [9] modified Redford et al's [7] transition map and used a modified transition Reynolds number Re kw (sometimes denoted by Re k ), for which the reference viscosity was taken at the wall instead of at the roughness height. In the modified transition map, the critical line would be independent of M k T ∞ ∕T w , and thus a constant value.…”

mentioning

confidence: 99%

See 2 more Smart Citations

Numerical Simulations of Transition due to Isolated Roughness Elements at Mach 6

Eynde

Sandham

2016

AIAA Journal

Self Cite

View full text Add to dashboard Cite

An accurate prediction of transition onset behind an isolated roughness element has not yet been established. This is particularly important in hypersonic flow, where transition is accompanied by increased surface heating. In the present contribution, a number of direct numerical simulations have been performed of a Mach 6 boundary layer over a flat plate with isolated roughness elements. The effects of roughness shape, planform, ramps, and freestream disturbance levels on instability growth and transition onset are investigated. It is found that the frontal shape has a large effect on the transition onset, which is in agreement with previous studies, whereas the roughness element planform has a marginal influence. A new result is that the roughness shape in the streamwise direction (in particular, the aft section) is also an important characteristic, since an element with a ramped-down aft section allows the detached shear layer to spread out and weaken, leading to a lower instability growth rate. Above a critical value, the instability growth rate is found to be correlated with the amplitude of the low-speed streak formed by the roughness element, suggesting that a more physically based transition criterion should take account of the local liftup effect of the particular roughness shape.

show abstract

WP-2 Basic Investigation of Transition Effect

Babinsky

Dupont

Polivanov

et al. 2020

Notes on Numerical Fluid Mechanics and Multidisciplinary Design

View full text Add to dashboard Cite

An important goal of the TFAST project was to study the effect of the location of transition in relation to the shock wave on the separation size, shock structure and unsteadiness of the interaction area. Boundary layer tripping (by wire or roughness) and flow control devices (Vortex Generators and cold plasma) were used for boundary layer transition induction. As flow control devices were used here in the laminar boundary layer for the first time, their effectiveness in transition induction was an important outcome. It was intended to determine in what way the application of these techniques induces transition. These methods should have a significantly different effect on boundary layer receptivity, i.e. the transition location. Apart from an improved understanding of operation control methods, the main objective was to localize the transition as far downstream as possible while ensuring a turbulent character of interaction. The final objective, involving all the partners, was to build a physical model of transition control devices. Establishing of such model would

show abstract

Compressibility Effects on Boundary-Layer Transition Induced by an Isolated Roughness Element

Cited by 58 publications

References 20 publications

Turbulence in a transient channel flow with a wall of pyramid roughness

Turbulence in a transient channel flow with a wall of pyramid roughness

Numerical Simulations of Transition due to Isolated Roughness Elements at Mach 6

WP-2 Basic Investigation of Transition Effect

Contact Info

Product

Resources

About