Impact of Forward-Facing Steps on Laminar-Turbulent Transition in Subsonic Flows

Edelmann, Christopher A.; Rist, Ulrich

doi:10.1007/978-3-319-03158-3_16

Cited by 12 publications

(8 citation statements)

References 2 publications

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“…5(b), the adoption of sponge region effectively removes the wave reflection and the TS wave packet is clearly resolved. In addition to the sponge region, mesh coarsening [8] and lower order polynomials can be used for the spectral elements outside the boundary layer region to reduce the resolution and therefore smear the waves as they travel across this region, further damping the reflected waves.…”

Section: Methods To Reduce Wave Contaminationmentioning

confidence: 99%

“…However, it can be expected that acoustic modelling at the surface irregularities is more difficult than that for the freestream acoustics. Moreover, in the TS wave study by Edelmann [8] the reflected waves were considered as acoustics whereas the profile of the reflected waves of the same case (see section VII) in Fig. 7 indicates a more complicated condition.…”

Section: Methods To Reduce Wave Contaminationmentioning

confidence: 99%

“…To obtain the clean TS wave packet signal Edelmann used a "Moving Tukey Window" for Fourier transform to obtained the amplitude [8]. However, the moving speed needs to be known in advance to apply the window, which restricts the application of this method.…”

Section: Methods To Reduce Wave Contaminationmentioning

confidence: 99%

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Open-source Framework for Transonic Boundary Layer Natural Transition Analysis over Complex Geometries in Nektar++

Lyu¹,

Chen²,

Du³

et al. 2022

Preprint

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We introduce an open-source and unified framework for transition analysis for laminar boundary layer natural transition at transonic conditions and over complex geometries, where surface irregularities may be present. Different computational tools are integrated in the framework, and therefore overcomes the difficulties of two separate and usually quite disparate processes when using 𝑒 𝑁 method for transition analysis. To generate a baseflow with desired pressure distribution, appropriate pressure compatible inflow boundary condition needs to be developed and enforced. We first derive the system for 1D numerical stability analysis for boundary conditions, and construct three types of pressure compatible inflow. We demonstrate that the entropy-pressure compatible inflow is stable unlike other choices. Compared with the steady baseflow computation, the unsteady simulation for the disturbance field is more challenging for compressible flows because of complex wave reflections, which can easily contaminate the results. We therefore introduce the two main sources of wave decontamination and corresponding methods to obtain clean signal. The workflow within the framework is then verified by computing the disturbance development in 2D flat plate boundary layer flows at Mach 0.8. The 𝑁-factors over a clean flat plate and a flat plate with a forward-facing step are generated, and agree well with the results from the reference. Following the verified workflow, We then analyze the disturbance growth on a wing section of the CRM-NLF model. The 𝑁-factor on a 2D simulation is generated and studied.

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Section: Methods To Reduce Wave Contaminationmentioning

confidence: 99%

Section: Methods To Reduce Wave Contaminationmentioning

confidence: 99%

See 1 more Smart Citation

Open-source Framework for Transonic Boundary Layer Natural Transition Analysis over Complex Geometries in Nektar++

Lyu¹,

Chen²,

Du³

et al. 2022

Preprint

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show abstract

“…Following the work of Perraud et al. (2004) and Crouch, Kosorygin & Ng (2006), Edelmann & Rist (2014) characterise the effect of the step by quantifying the correspondingly modified perturbation amplification factor, relative to the reference no-step case. The transitional-flow features downstream of a forward-facing step in unswept conditions have been examined further by Rizzetta & Visbal (2014) using numerical simulations.…”

Section: Introductionmentioning

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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“…Crouch [13] applied the approach to capture the superposition of a forward-facing and a backward-facing step in the form of a rectangular protrusion or a wide gap to assess the applicability of this approach for more general step arrangements. The influence of the FFS on laminar to turbulent transition was studied with both DNS and the method by Edelmann and Rist [14] for a compressible subsonic flow with = 0.15 − 0.8 at varying step locations and step heights. Perraud et al [15][16][17] performed numerical and experimental investigations in the ONERA F2 low speed wind-tunnel in 2D and 3D mean flows to assess the tolerable heights of surface imperfections (steps, gaps and humps) in various types of laminar flows.…”

Section: Introductionmentioning

confidence: 99%

Effect of Step Surface Imperfections on Boundary Layer Transition

Lin¹,

Wang²

2021

14th WCCM-ECCOMAS Congress

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Surface imperfections due to manufacturing tolerance, such as steps, gaps, and waviness, can cause early boundary layer transition, thus reduce the practicability of the natural laminar flow (NLF) technology for aircraft drag reduction. In this study, a new numerical methodology is proposed and implemented to predict the effect of backward-facing step (BFS) and forward-facing step (BFS) on boundary layer transition over NLF aircraft body. The method is based on a hypothesis that the effect of surface imperfections on boundary layer flow can be mimicked as that of surface roughness due to the relevant small size of the imperfection compared to the local boundary layer thickness. The predicted transition location on BFS/FFS surface agrees very well with the experimental validation data. It implies the applicability and capability of this approach for transition location prediction over more general surface imperfection arrangements. The study thus provides an efficient, practical prediction tool to determine the manufacturing allowance on surface imperfection dimension on NLF body for aerodynamic engineers.

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Impact of Forward-Facing Steps on Laminar-Turbulent Transition in Subsonic Flows

Cited by 12 publications

References 2 publications

Open-source Framework for Transonic Boundary Layer Natural Transition Analysis over Complex Geometries in Nektar++

Open-source Framework for Transonic Boundary Layer Natural Transition Analysis over Complex Geometries in Nektar++

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

Effect of Step Surface Imperfections on Boundary Layer Transition

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