Disk wakes in nonlinear stratification

Gola, Divyanshu; Nidhan, Sheel; Ortiz-Tarin, Jose Luis; Sarkar, Sutanu

doi:10.1017/jfm.2022.1084

Cited by 2 publications

(1 citation statement)

References 57 publications

(121 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Moreover, the influence of the angle of attack and surface properties (roughness, porosity) on the development of these structures could be explored. Also, it is worth investigating how density stratification (Nidhan, Schmidt & Sarkar 2022;Gola et al 2023), often found in the natural environment, affects the lift-up mechanism and formation of streaks in turbulent disk wakes. Finally, a direct comparison of the characteristics of streaks in wakes, such as length scales, intermittency and life cycle, with those in other turbulent flows, such as channel flows and jets, can inform about potentially universal behaviour of streaks in turbulent flows.…”

Section: Discussionmentioning

confidence: 99%

Large-scale streaks in a turbulent bluff body wake

Nekkanti,

Nidhan,

Schmidt

et al. 2023

J. Fluid Mech.

View full text Add to dashboard Cite

A turbulent circular disk wake database (Chongsiripinyo & Sarkar, J. Fluid Mech., vol. 885, 2020) at Reynolds number $Re = U_\infty D/\nu = 5 \times 10^{4}$ is interrogated to identify the presence of large-scale streaks – coherent elongated regions of streamwise velocity. The unprecedented streamwise length – until $x/D \approx 120$ – of the simulation enables investigation of the near and far wakes. The near wake is dominated by the vortex shedding (VS) mode residing at azimuthal wavenumber $m=1$ and Strouhal number $St = 0.135$ . After filtering out the VS structure, conclusive evidence of large-scale streaks with frequency $St \rightarrow 0$ , equivalently streamwise wavenumber $k_x \rightarrow 0$ in the wake, becomes apparent in visualizations and spectra. These streaky structures are found throughout the simulation domain beyond $x/D \approx 10$ . Conditionally averaged streamwise vorticity fields reveal that the lift-up mechanism is active in the near as well as the far wake, and that ejections contribute more than sweeps to events of intense $-u'_xu'_r$ . Spectral proper orthogonal decomposition is employed to extract the energy and the spatiotemporal features of the large-scale streaks. The streak energy is concentrated in the $m=2$ azimuthal mode over the entire domain. Finally, bispectral mode decomposition is conducted to reveal strong interaction between $m=1$ and $St = \pm 0.135$ modes to give the $m=2$ , $St \rightarrow 0$ streak mode. Our results indicate that the self-interaction of the VS mode generates the $m=2$ , $St \rightarrow 0$ streamwise vortices, which leads to streak formation through the lift-up process. To the authors’ knowledge, this is the first study that reports and characterizes large-scale low-frequency streaks and the associated lift-up mechanism in a turbulent wake.

show abstract

Section: Discussionmentioning

confidence: 99%

Large-scale streaks in a turbulent bluff body wake

Nekkanti,

Nidhan,

Schmidt

et al. 2023

J. Fluid Mech.

View full text Add to dashboard Cite

show abstract

Modulation of the wake of a horizontal cylinder by pycnocline thickness in stratified flow

Zheng,

Liu,

Liu

et al. 2024

Physics of Fluids

View full text Add to dashboard Cite

This study investigates the modulating effect of the pycnocline thickness in two-dimensional stratified flow on a cylinder. It encompasses three typical flow regimes identified by Boyer in experiments conducted within the Reynolds number range of Re = 260–2000. Quantitative control of the modulation effect of internal interface waves on the cylinder wake is achieved by varying the thickness of the pycnocline. Under appropriate thickness of the pycnocline, a multiple-centerline-structure can transition to isolated-mixed-structure flow regimes and Double-Eddy-Wavy-Wake flow regimes. Similar modulation patterns are also observed in isolated-mixed flow regimes. Normalized pressure distribution and velocity fields indicate that in low Reynolds number flow regimes (Re < 600), downstream isolated mixed regions generate dynamic pressure that periodically cascades upstream. This periodic reverse energy transfer provides favorable adverse pressure gradients, cyclically reducing the drag force on the cylinder. The cyclic period is, for the first time, classified into four stages: dynamic pressure storage stage, dynamic pressure transfer stage, dynamic pressure consumption stage, and dynamic pressure exhaustion stage. Despite the highly nonlinear modulation effect of internal interface waves in low Reynolds number conditions, the linear predictive theory of lee waves based on streamline equations remains instructive in predicting the trend of lee waves wavelength variation with pycnocline thickness. Drawing upon the modulation study results concerning the pycnocline thickness on lee waves, a regime map is constructed, illustrating the directional evolution of lee waves flow patterns based on variations in pycnocline thickness.

show abstract

Disk wakes in nonlinear stratification

Cited by 2 publications

References 57 publications

Large-scale streaks in a turbulent bluff body wake

Large-scale streaks in a turbulent bluff body wake

Modulation of the wake of a horizontal cylinder by pycnocline thickness in stratified flow

Contact Info

Product

Resources

About