Destabilisation of Stationary and Travelling Crossflow Disturbances Due to Steps over a Swept Wing

Cooke, Emma E.; Mughal, Shahid; Sherwin, Spencer J.; Ashworth, Richard; Rolston, Stephen

doi:10.2514/6.2019-3533

Cited by 9 publications

(5 citation statements)

References 16 publications

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“…Nonetheless, recent numerical (e.g. Tufts et al 2017;Cooke et al 2019;Casacuberta, Hickel & Kotsonis 2021) and experimental (e.g. Duncan et al 2014b;Eppink 2018Eppink , 2020bRius-Vidales & Kotsonis 2020Groot & Eppink 2021) studies revealed numerous unresolved aspects essential to the understanding of the FFS-CFI interaction.…”

Section: Introductionmentioning

confidence: 99%

Unsteady interaction of crossflow instability with a forward-facing step

Rius-Vidales

Kotsonis

2022

J. Fluid Mech.

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Experiments have been conducted on a swept wing model in a low-turbulence wind tunnel at chord Reynolds number of $2.17 \times 10^{6}$ to investigate the unsteady interaction of a forward-facing step (FFS) with incoming stationary crossflow (CF) vortices. The impact of varying the FFS height on the development and growth of primary and secondary CF disturbances and the ensuing laminar–turbulent transition is quantified through detailed hot-wire anemometry and infrared thermography measurements. The presence of the FFS results in either a critical (i.e. moderate transition advancement) or a supercritical behaviour (i.e. transition advancing abruptly to the FFS location). The arrival of the forced stationary CF vortices at the step is accompanied by their amplification. Unsteady analysis for the critical cases indicates temporal velocity fluctuations following closely the development of the baseline configuration (i.e. agreeing with the development of secondary instabilities). Consequently, laminar breakdown originates from the outer side of the upwelling region of the CF vortices. In contrast, for the supercritical FFS, the laminar breakdown unexpectedly originates from the inner side of the upwelling region. Evidence points to an unsteady mechanism possibly supported by locally enhanced spanwise-modulated shears and the recirculation region downstream of the FFS edge. This mechanism appears to govern the abrupt tripping of the flow in supercritical step cases. The findings in this work provide insight into the unsteady FFS–CF vortex interaction, which is pivotal to understanding the influence of an FFS on the laminar–turbulent boundary-layer transition in swept aerodynamic surfaces.

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Section: Introductionmentioning

confidence: 99%

Unsteady interaction of crossflow instability with a forward-facing step

Rius-Vidales

Kotsonis

2022

J. Fluid Mech.

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“…The crossflow perturbation lifts up as it approaches the step, and the perturbation profile, i.e. the perturbation shape in the wall-normal direction, develops a distinctive secondary peak close to the wall (Tufts et al 2017;Eppink 2018Eppink , 2020Cooke et al 2019;Casacuberta, Hickel & Kotsonis 2021). A new set of secondary vortices induced locally at the step has been identified by Eppink (2018Eppink ( , 2020, Rius-Vidales & Kotsonis (2021) and Casacuberta et al (2021).…”

Section: Effect Of Two-dimensional Roughness On Boundary-layer Stabil...mentioning

confidence: 99%

“…On the other hand, the present problem serves as an ideal platform to assess the limitations of a classic stability method such as the PSE when they are applied in the presence of a sharp geometrical discontinuity. Cooke et al (2019) report that the PSE method suffers from lack of numerical convergence when it is marched over the step due to the restriction concerning the minimum marching step size.…”

Section: Perturbation Amplification Upstream Of the Stepmentioning

confidence: 99%

Direct numerical simulation of interaction between a stationary crossflow instability and forward-facing steps

et al. 2022

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The interaction between forward-facing steps of several heights and a pre-existing critical stationary crossflow instability of a swept-wing boundary layer is analysed. Direct numerical simulations (DNS) are performed of the incompressible three-dimensional laminar base flow and the stationary distorted flow that arise from the interaction between an imposed primary stationary crossflow perturbation and the steps. These DNS are complemented with solutions of the linear and the nonlinear parabolised stability equations, used towards identifying the influence of linearity and non-parallelism near the step. A fully stationary solution of the Navier–Stokes equations is enforced numerically, in order to isolate the mechanisms pertaining to the interaction of the stationary disturbance with the step. Results provide insight into the salient modifications of the base laminar boundary layer due to the step, and the response of the incoming crossflow instability to these changes. The fundamental spanwise Fourier mode of the disturbance field gradually lifts up as it approaches the step and passes over it. The flow environment around the step is characterised by a sudden spanwise modulation of the base-flow streamlines. Additional stationary perturbation structures are induced at the step, which manifest in the form of spanwise-aligned velocity streaks near the wall. Shortly downstream of the step, the fundamental component of the crossflow perturbation maintains a rather constant amplification for the smallest steps studied. For the largest step, however, the fundamental crossflow perturbation is stabilised significantly shortly downstream of the largest step. This surprising result is ascribed to a modulation of the kinetic energy transfer between the base flow and the fundamental perturbation field, which is brought forward as a new step interaction mechanism. Possible non-modal growth effects at the step are discussed. Furthermore, the results from DNS indicate significant amplification of the high-order harmonic crossflow components downstream of the step.

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“…As a result, current efforts into simulating transitional mechanisms often use high fidelity simulation in a near-body, reduced domain which is embedded in a outer domain encompassing the whole geometry where a lower fidelity model is applied. (See [2] [3,4] [5,6] [7] [8].) Unlike in a large domain where the inflow and outflow boundaries are far away from the geometry of interest so that uniform freestream values can be enforced for the boundary conditions, simple boundary conditions are not available on the reduced domain.…”

Section: Introductionmentioning

confidence: 99%

Stable, entropy-pressure compatible subsonic Riemann boundary condition for embedded DG compressible flow simulations

Lyu¹,

Chen²,

Du³

et al. 2022

Preprint

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One approach to reducing the computational cost of simulating transitional compressible boundary layer flow is to adopt a near body reduced domain with boundary conditions enforced to be compatible with a computationally cheaper three-dimensional RANS simulation. In such an approach it is desirable to enforce a consistent pressure distribution which is not typically the case when using the standard Riemann inflow boundary conditions. We therefore revisit

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Destabilisation of Stationary and Travelling Crossflow Disturbances Due to Steps over a Swept Wing

Cited by 9 publications

References 16 publications

Unsteady interaction of crossflow instability with a forward-facing step

Unsteady interaction of crossflow instability with a forward-facing step

Direct numerical simulation of interaction between a stationary crossflow instability and forward-facing steps

Stable, entropy-pressure compatible subsonic Riemann boundary condition for embedded DG compressible flow simulations

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