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Key research themes
1. How is the critical Richardson number and turbulence persistence characterized in stably stratified turbulence?
This research area focuses on understanding the threshold conditions under which turbulence transitions to laminar flow in stably stratified shear flows, specifically characterizing the critical Richardson number (Ri_c). It revisits classical stability criteria, evaluates turbulence survival at high Richardson numbers, and integrates the effects of waves, anisotropy, and internal mixing mechanisms. The theme is fundamental for improving turbulence closure models in atmospheres, oceans, and stellar convection zones.
Key finding: This study challenges the classical critical Richardson number range (0.2-1), presenting extensive theoretical and simulation evidence that turbulence persists for Ri > 1. The authors propose that anisotropization driven by... Read more
Key finding: Using direct numerical simulations of Holmboe wave instabilities under strong stratification, this work demonstrates self-organized criticality with the gradient Richardson number continuously attracted to a value near Ri_g ≈... Read more
Key finding: Laboratory experiments delineate two distinct regimes in thermally stratified turbulent boundary layers—a weakly stable regime where turbulent stresses scale with wall shear stress, and a strongly stable regime characterised... Read more
Key finding: Through hydrodynamical simulations of subsonic turbulence with varying stratification, this paper quantifies how the Richardson number modifies kinetic, density, and pressure fluctuations in astrophysical intracluster media... Read more
2. What are the wave-eddy interactions and energy partitioning mechanisms in rotating and stratified turbulence?
This theme investigates the complex dynamics between internal gravity waves and vortical eddies in rotating stratified turbulence. By leveraging direct numerical simulations with varying ratios of Brunt-Väisälä to inertial frequencies and rotation rates, researchers explore the energy cascades, spectral transitions, and scale-dependent partitioning between kinetic and potential energy. Understanding this wave-eddy interplay is essential for characterizing mesoscale and sub-mesoscale atmospheric and oceanic turbulence, improving predictive models for geophysical flows.
Key finding: The study reveals that energy in stratified turbulence predominantly resides in slow quasi-geostrophic vortical modes undergoing an inverse cascade to larger scales, even as the ratio of stratification to rotation frequency... Read more
Key finding: High-resolution simulations demonstrate that the wavenumber k_R marking transition from vortex-dominated to wave-dominated dynamics is independent of Reynolds number and scales inversely with Froude number. This transition... Read more
Key finding: The authors use space-and time-resolved energy spectra from nonlinear stratified turbulence simulations to demonstrate that internal gravity waves experience Doppler shifts from vertically sheared horizontal winds (VSHW).... Read more
Key finding: Direct numerical simulations of rotating stratified turbulence at moderate buoyancy Reynolds numbers display large-scale kinetic energy spectra consistent with Bolgiano-Obukhov scaling (E(k) ~ k^(-11/5)), confirming the... Read more
3. How are density and velocity fluctuations related in stratified astrophysical and geophysical turbulence, and what implications does this have for observational inferences?
This theme addresses the quantitative relationships between turbulent velocity fields and corresponding density, pressure, and entropy fluctuations in stratified turbulent media, with emphasis on astrophysical systems like the intracluster medium (ICM). It combines large-scale simulations and theoretical modeling to derive scaling laws that connect observable scalar perturbations (e.g., from X-ray or Sunyaev-Zeldovich measurements) to underlying turbulent motions, accounting for stratification, anisotropy, and thermodynamics, thus refining indirect turbulence diagnostics in complex stratified environments.
Key finding: Numerical simulations scanning a wide parameter range demonstrate that in the stratified intracluster medium, density and pressure fluctuations scale with the rms Mach number and perpendicular Froude number (Fr_⊥), capturing... Read more
Key finding: This study conducts high-resolution simulations under controlled stratification to analyze how the Richardson number modifies density, pressure, and velocity statistics in the ICM. The paper confirms that moderate... Read more
Key finding: The authors rigorously derive the equations for mean entropy and internal energy in low-Mach-number temperature-stratified turbulence, clarifying that the turbulent flux of entropy (F_s = ρ〈u s〉) differs fundamentally from... Read more
Key finding: Direct numerical simulations of decaying shearless turbulent layers with superimposed stable and unstable thermal stratification reveal that stratification intensity alters turbulent mixing dynamics significantly. In the... Read more