Transitional Flow Dynamics Behind a Micro-Ramp

Casacuberta, J.; Groot, Koen J.; Ye, Q.; Hickel, Stefan

doi:10.1007/s10494-019-00085-1

Cited by 12 publications

(7 citation statements)

References 36 publications

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“…The DNS are carried out with INCA, a conservative finite-volume-based flow solver (Hickel and Adams, 2008, Hickel et al, 2014, Casacuberta et al, 2020. The free-stream evolution and the DNS setup considered in this work are identical to the ones presented in a recent article (Casacuberta et al, 2021).…”

Section: A Steady Dnsmentioning

confidence: 99%

Secondary instabilities in swept-wing boundary layers: Direct Numerical Simulations and BiGlobal stability analysis

Casacuberta

Groot

Hickel

et al. 2022

AIAA SCITECH 2022 Forum

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The evolution of secondary instabilities in a three-dimensional stationary-crossflow-dominated boundary layer is investigated by means of Direct Numerical Simulations (DNS) and linear spanwise BiGlobal stability analysis. Single-frequency unsteady disturbances and a critical stationary crossflow mode are considered. Unsteady perturbation content at 1 kHz manifests in the form of the type-III instability mechanism in the lower portion of the boundary layer in both the DNS and the stability approach. Considering disturbances at 6 kHz, the results from the stability analysis reveal the existence of largely amplified type-I and type-II secondary instability mechanisms. Strong growth displayed by the former is measured in the DNS, which potentially overshadows manifestations of the type-II mechanism. Laminar-turbulent transition primarily induced by the growth of type-I disturbances is captured in the 6 kHz case. Overall, we report good agreement between DNS and stability analysis in terms of perturbation organization and growth rate for all cases studied.

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Section: A Steady Dnsmentioning

confidence: 99%

Secondary instabilities in swept-wing boundary layers: Direct Numerical Simulations and BiGlobal stability analysis

Casacuberta

Groot

Hickel

et al. 2022

AIAA SCITECH 2022 Forum

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“…Relevant previous applications of this flow solver include perturbation growth flow mechanisms in incompressible and compressible boundary layers. See for instance Hu et al [18], who model the dynamics of a supersonic transitional flow over a backward-facing step, or Casacuberta et al [19], who studied the transitional wake of a micro-ramp immersed in a quasi incompressible boundary layer. The incompressible Navier-Stokes equations are marched in time with a third-order Runge-Kutta method.…”

Section: Computational Setupmentioning

confidence: 99%

Mechanisms of interaction between stationary crossflow instabilities and forward-facing steps

Casacuberta

Hickel

Kotsonis

2021

AIAA Scitech 2021 Forum

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We study the interaction between a stationary crossflow instability and forward-facing steps in a swept-wing boundary layer using Direct Numerical Simulations (DNS). The stationary primary crossflow mode is imposed at the inflow. Steps of several heights are modeled. Particular emphasis is placed on ensuring a fully stationary solution, in order to isolate the modulation of the primary instability at the step and the generation of stationary secondary perturbations. The main features of the base flow are step-induced flow reversal and secondary inflection points. When approaching the step, the incoming crossflow instability lifts up and passes over it. Additional perturbation streaks arise, which are accompanied by secondary stationary vortices that have the same spanwise wavenumber as the fundamental crossflow disturbance. For sufficiently high steps, secondary perturbation structures attain amplitude values comparable in magnitude to primary instability in the vicinity of the step. We propose metrics to quantify the impact of the step on the development of the crossflow disturbance upon interaction. Considering energy-based criteria, we find that the crossflow perturbation is amplified upstream of the step. Interestingly, the incoming primary crossflow instability undergoes strong stabilization immediately downstream of the largest step. The mechanisms revealed in this work provide a first insight into the possible causes of transition on swept wings due to forward-facing steps.

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“…The present solver is well established in studies of flow instability and perturbation dynamics; see, for instance, the transitional-flow mechanisms behind a micro-ramp immersed in a quasi-incompressible boundary layer (Casacuberta et al. 2020).…”

Section: Methodsmentioning

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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Transitional Flow Dynamics Behind a Micro-Ramp

Cited by 12 publications

References 36 publications

Secondary instabilities in swept-wing boundary layers: Direct Numerical Simulations and BiGlobal stability analysis

Secondary instabilities in swept-wing boundary layers: Direct Numerical Simulations and BiGlobal stability analysis

Mechanisms of interaction between stationary crossflow instabilities and forward-facing steps

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

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