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

Casacuberta, J.; Groot, Koen J.; Hickel, Stefan; Kotsonis, Marios

doi:10.2514/6.2022-2330

Cited by 6 publications

(3 citation statements)

References 37 publications

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“…For consistency with established experimental and numerical studies, the double-spectral notation (h, k) is adopted to refer to generalized CF instability modes featuring integer multiples of the reference frequency f 0 and spanwise wavenumber c 0 , namely, h ¼ f =f 0 , where f 0 ¼ 200 Hz and k ¼ c=c 0 , where c 0 ¼ 1=k 0 ; k 0 ¼ 8 mm. U HW i z , showing that the wallnormal distribution of traveling modes strongly depends on the frequency, as observed by Casacuberta et al 44 Compared with the negative traveling modes ðh; ÀkÞ, positive traveling modes ðh; þkÞ are evidently more amplified by the PA forcing. The dominance of positive traveling modes is also experimentally observed by Borodulin et al 45,46 and agrees well with previous LST predictions.…”

Section: Spanwise-wavenumber Spectrasupporting

confidence: 58%

Unsteady disturbances in a swept wing boundary layer due to plasma forcing

2022

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This work investigates the response of a transitional boundary layer to spanwise-invariant dielectric barrier discharge plasma actuator (PA) forcing on a [Formula: see text] swept wing at a chord Reynolds number of [Formula: see text]. Two important parameters of the PA operation are scrutinized, namely, the forcing frequency and the streamwise location of forcing. An array of passive discrete roughness elements is installed near the leading edge to promote and condition a set of critical stationary crossflow (CF) instability modes. Numerical solutions of the boundary layer equations and linear stability theory are used in combination with the experimental pressure distribution to provide predictions of critical stationary and traveling CF instabilities. The laminar–turbulent transition front is visualized and quantified by means of infrared thermography. Measurements of velocity fields are performed using hotwire anemometry scans at specific chordwise locations. The results demonstrate the inherent introduction of unsteady velocity disturbances by the plasma forcing. It is shown that, depending on actuator frequency and location, these disturbances can evolve into typical CF instabilities. Positive traveling low-frequency type III modes are generally amplified by PA in all tested cases, while the occurrence of negative traveling high-frequency type I secondary modes is favored when PA is operating at high frequency and at relatively downstream locations, with respect to the leading edge.

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Section: Spanwise-wavenumber Spectrasupporting

confidence: 58%

Unsteady disturbances in a swept wing boundary layer due to plasma forcing

2022

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“…The finger vortex acts as a Type-2 SI by being distributed to cover the CFV (Nakagawa et al, 2023a,b). In general, Type-1 SI and Type-2 SI can be distinguished by their generating location and frequency band (Malik et al, 1999;Högberg and Henningson, 1998;Serpieri and Kotsonis, 2016;Casacuberta et al, 2022;Chen et al, 2022), and in addition, we suggested that they are also distinguishable in terms of the turbulent energy production (Nakagawa et al, 2023a). However, in this paper, we do not make a strict distinction because they are high frequencies that play a common role in finally collapsing CFVs.…”

Section: Process Change From Path a To Path Bmentioning

confidence: 79%

Changes in the Transition Process of Roughness-Induced Crossflow Vortices due to Freestream Turbulence

Nakagawa,

Ishida,

Tsukahara

2024

Preprint

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Laminar-turbulent transitions in boundary layers are one of the major research topics in fluid dynamics.In this study, we focused on a three-dimensional boundary layer formed on a swept flat plate.In this boundary layer, the crossflow instability is dominant, and the instability induces crossflow vortices (CFVs).Many studies have focused on the dependency of the transition process on the intensities of steady or unsteady disturbances, which correspond to a roughness element and freestream turbulence (FST), respectively.On the other hand, the effects of the FST wavelength are still unclear.Moreover, there is a lack of knowledge about the transition processes caused by both steady and unsteady disturbances.We investigated how the transition process of a stationary structure caused by cylindrical roughness changes depending on the FST wavelength using direct numerical simulations.We classified transition processes into two types: processes in which stationary structures grow into CFVs and processes in which hairpin vortices are generated on the stationary structures.The former is further classified into four types depending on the presence or absence of FST and on the FST wavelength.We revealed the contributions of different FST wavelengths to the transition process changes.The short-wavelength FST provides hairpin vortices to the stationary structure at low roughness height conditions because of its high-frequency components.The long-wavelength FST changes the process due to unsteady fluctuations influencing the stationary structure.In summary, depending on the FST wavelength, the transition process is changed by a completely different mechanism.

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“…However, few research works have paid close attention to the suction effects on the initial amplitude of dominant unstable waves in real transonic swept wings compared to experimental data. According to Saric's experimental and theoretical research [25][26][27][28][29], stationary crossflow waves, that is, when the wave frequency is equal to zero, usually dominate the crossflow instabilities in low turbulence disturbance environments. So, here, the stationary crossflow instabilities are only focused on due to their common role in aeronautical flow transitions.…”

Section: Introductionmentioning

confidence: 99%

Receptivity and Stability Theory Analysis of a Transonic Swept Wing Experiment

Liu,

et al. 2023

Aerospace

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Surface suction provides an efficient way to delay boundary layer transitions. In order to verify the suction effects and determine the mechanism of suction control in transonic swept wing boundary layers, wind tunnel transition measurements in a hybrid laminar flow control (HLFC) wind tunnel model uses an infrared thermography technique in the Aircraft Research Association (ARA) 2.74 m × 2.44 m low turbulence level transonic wind tunnel. Based on the experimental data of stationary crossflow dominant transitions without and with surface suction in transonic swept wing boundary layers, in this paper, the effects on the receptivity and linear and nonlinear evolution of stationary crossflow vortices have been analyzed with the consideration of curvature. Theoretical analysis agreed with the experimental observations in regard to the transition delay caused by boundary layer suction near the leading-edge region.

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

Cited by 6 publications

References 37 publications

Unsteady disturbances in a swept wing boundary layer due to plasma forcing

Unsteady disturbances in a swept wing boundary layer due to plasma forcing

Changes in the Transition Process of Roughness-Induced Crossflow Vortices due to Freestream Turbulence

Receptivity and Stability Theory Analysis of a Transonic Swept Wing Experiment

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