Inspection of structures interaction in laminar separation bubbles with extended proper orthogonal decomposition applied to multi-plane particle image velocimetry data

Verdoya, Jacopo; Dellacasagrande, Matteo; Lengani, Davide; Simoni, Daniele; Ubaldi, Marina

doi:10.1063/5.0047347

Cited by 17 publications

(8 citation statements)

References 59 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These observations made in figures 18 and 19( f – j , non-modal) implies the co-existence of both modal and non-modal instability mechanisms, confirming the observations in DNS (Hosseinverdi & Fasel 2019) and experimental investigations (Istvan & Yarusevych 2018; Verdoya et al. 2021) on LSBs subjected to FST, along with the experimental results of Veerasamy et al. (2021) for an attached boundary layer developing over a flat plate.…”

Section: Resultssupporting

confidence: 84%

“…The slight downwards shift of the profile at the most advanced chordwise positions is due to the flow finishing the transition process. These observations made in figures 18 and 19( fj, non-modal) implies the co-existence of both modal and non-modal instability mechanisms, confirming the observations in DNS (Hosseinverdi & Fasel 2019) and experimental investigations (Istvan & Yarusevych 2018;Verdoya et al 2021) on LSBs subjected to FST, along with the experimental results of Veerasamy et al (2021) for an attached boundary layer developing over a flat plate. In contrast, in configurations where Tu < 1 % (refer to figure 19(a-e), modal), wall-normal disturbance profiles do not agree with theoretical predictions and do not exhibit the same behaviour as for configurations with Tu > 1 %, with the maxima of the peaks being in the range y/δ 1 = 0.3-0.5, implying that there is no formation of streaks and that only a modal transition mechanism is present.…”

Section: Co-existence Of a Modal And A Non-modal Instabilitiessupporting

confidence: 83%

“…Additionally, Verdoya et al. (2021) conducted a novel proper orthogonal decomposition analysis of PIV data and found structures resembling streaks in the – plane. A recent large eddy simulation LES investigation by Li & Yang (2019) on a low-pressure turbine blade subjected to a leading edge turbulence intensity level of , suggested that the secondary instability breaking down into 3-D structures is ‘bypassed’ due to the high levels of FST.…”

Section: Introductionmentioning

confidence: 99%

“…Experimentally, Istvan & Yarusevych (2018) found that at FST levels of 1.99 %, streamwise streaks were inferred through the reduction of the spanwise wavelength of the shear layer roller, signifying the passage to non-modal instability. Additionally, Verdoya et al (2021) conducted a novel proper orthogonal decomposition analysis of PIV data and found structures resembling streaks in the x-z plane. A recent large eddy simulation LES investigation by Li & Yang (2019) on a low-pressure turbine blade subjected to a leading edge turbulence intensity level of Tu = 2.9 %, suggested that the secondary instability breaking down into 3-D structures is 'bypassed' due to the high levels of FST.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Disturbance growth in a laminar separation bubble subjected to free-stream turbulence

et al. 2023

View full text Add to dashboard Cite

Experiments were conducted to study the transition and flow development in a laminar separation bubble (LSB) formed on an aerofoil. The effects of a wide range of free-stream turbulence intensity ( $0.15\,\%< Tu<6.26\,\%$ ) and streamwise integral length scale ( $4.6\ {\rm mm}<\varLambda _{u}<17.2\ {\rm mm}$ ) are considered. The co-existence of modal instability due to the LSB and non-modal instability caused by streaks generated by free-stream turbulence is observed. The flow field is measured using hot-wire anemometry, which showed that the presence of streaks in the boundary layer modifies the mean-flow topology of the bubble. These changes in the mean flow field result in the modification of the convective disturbance growth, where an increase in turbulence intensity is found to dampen the growth of the modal instability. For a relatively fixed level of $Tu$ , the variation of $\varLambda _{u}$ has modest effects. However, a slight advancement of the nonlinear growth of disturbances and eventual breakdown with the decrease in $\varLambda _{u}$ is observed. The data show that the streamwise growth of the disturbance energy is exponential for the lowest levels of free-stream turbulence and gradually becomes algebraic as the level of free-stream turbulence increases. Once a critical turbulence intensity is reached, there is enough energy in the boundary layer to suppress the laminar separation bubble, resulting in the non-modal instability taking over the transition process. Linear stability analysis is conducted in the fore position of the LSB. It accurately models incipient disturbance growth, unstable frequencies and eigenfunctions for configurations subjected to turbulence intensity levels up to 3 %, showing that the mean-flow modification due to the non-modal instability dampens the modal instability.

show abstract

Section: Resultssupporting

confidence: 84%

Section: Co-existence Of a Modal And A Non-modal Instabilitiessupporting

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Disturbance growth in a laminar separation bubble subjected to free-stream turbulence

et al. 2023

View full text Add to dashboard Cite

show abstract

“…For each condition, eight independent sets of 2000 instantaneous velocity fields were acquired at a sampling rate of 1596 Hz. The detailed description of the experimental data and measuring techniques adopted in this work can be found in the authors' previous works Dellacasagrande et al (2021b), Verdoya et al (2021). For each flow condition, an LDV traverse was performed downstream of the channel throat (i.e., at x∕L = 0.3 ) for the characterization of the velocity profile at the inlet section of the PIV measuring plane.…”

Section: Measuring Techniquesmentioning

confidence: 99%

A procedure for computing the spot production rate in transitional boundary layers

et al. 2022

Self Cite

View full text Add to dashboard Cite

The present work describes a method for the computation of the nucleation rate of turbulent spots in transitional boundary layers from particle image velocimetry (PIV) measurements. Different detection functions for turbulent events recognition were first tested and validated using data from direct numerical simulation, and this latter describes a flat-plate boundary layer under zero pressure gradient. The comparison with a previously defined function adopted in the literature, which is based on the local spanwise wall-shear stress, clearly highlights the possibility of accurately predicting the statistical evolution of transition even when the near-wall velocity field is not directly available from the measurements. The present procedure was systematically applied to PIV data collected in a wall-parallel measuring plane located inside a flat plate boundary layer evolving under variable Reynolds number, adverse pressure gradient (APG) and free-stream turbulence. The results presented in this work show that the present method allows capturing the statistical response of the transition process to the modification of the inlet flow conditions. The location of the maximum spot nucleation is shown to move upstream when increasing all the main flow parameters. Additionally, the transition region becomes shorter for higher Re and APG, whereas the turbulence level variation gives the opposite trend. The effects of the main flow parameters on the coefficients defining the analytic distribution of the nucleation rate and their link to the momentum thickness Reynolds number at the point of transition are discussed in the paper. Graphical abstract

show abstract

Influence of roughness-generated streaks on laminar separation bubbles

Jaroslawski,

Forte,

Vermeersch

et al. 2024

Exp Fluids

View full text Add to dashboard Cite

This experimental investigation studies the impact of streaks on two-dimensional laminar separation bubbles forming over an aerofoil. Streaks are introduced into the boundary layer using cylindrical roughness elements, and the resulting mean and unsteady flow fields are measured using hot-wire anemometry. The observed streaks generated by roughness exhibit analogous behavior to those generated by freestream turbulence, significantly altering the mean-flow characteristics of the bubble, including reductions in its length, height, and the introduction of spanwise velocity gradients. These mean flow modifications have a damping effect on convective disturbance growth. The experiments suggest the coexistence of modal instability due to the laminar separation bubble and non-modal instability due to streaks. We perform linear stability analysis at the fore position of the laminar separation bubble and find that by incorporating a spanwise wavenumber into the calculations, the experimental findings are reasonably modeled, indicating an oblique modal instability. To investigate the combined effect of roughness and the presence of freestream turbulence, we increase the turbulence level from the baseline in the presence of a roughness forcing configuration. We find that increasing the turbulence intensity leads to an enhancement of non-modal instability, accompanied by distinctive chordwise disturbance growth compared to lower freestream turbulence intensity levels. Moreover, increasing the turbulence intensity level in the presence of roughness not only bypasses the modal instability observed without the addition of turbulence but also suppresses laminar separation.

show abstract

Inspection of structures interaction in laminar separation bubbles with extended proper orthogonal decomposition applied to multi-plane particle image velocimetry data

Cited by 17 publications

References 59 publications

Disturbance growth in a laminar separation bubble subjected to free-stream turbulence

Disturbance growth in a laminar separation bubble subjected to free-stream turbulence

A procedure for computing the spot production rate in transitional boundary layers

Influence of roughness-generated streaks on laminar separation bubbles

Contact Info

Product

Resources

About