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Key research themes
1. How do adverse pressure gradients modify the turbulence structure and velocity profile in turbulent boundary layers?
This research theme investigates the effects of pressure gradients opposing the flow direction (adverse pressure gradients, APG) on turbulent boundary layers (TBLs). Understanding APGs is crucial because such conditions commonly arise in engineering (e.g. around bluff bodies, diffusers, airfoil trailing edges) and influence flow separation risks and turbulence dynamics. The focus is on how pressure gradients affect velocity profiles, turbulence intensities, Reynolds stresses, and large-scale coherent structures. Experimental, numerical, and modeling studies analyze parameters like pressure gradient parameter (β), Reynolds number, and acceleration parameter (K) to clarify their roles. Identifying altered flow features such as the absence of traditional logarithmic velocity regions and energization of outer-layer large scales informs better prediction and control of APG flows.
Key finding: This study isolates the influence of pressure gradient parameter β, Reynolds number, and acceleration parameter K on APG turbulent boundary layers. Key specific findings include the absence of a classical logarithmic velocity... Read more
Key finding: By comparing Reynolds-averaged Navier-Stokes (RANS) and hybrid RANS/LES approaches against high-Reynolds-number experimental data with APG from Cuvier et al., this paper shows difficulties in accurately predicting Reynolds... Read more
Key finding: This work develops analytic and numerical methods to generate fully turbulent boundary layers under both zero and adverse pressure gradients at Reynolds numbers up to 31000. Validations against wind tunnel and DNS data show... Read more
Key finding: This DNS study provides high-fidelity turbulence statistics for spatially developing TBLs at Reynolds numbers up to 2500, essential for understanding turbulence structure under variable conditions including APG. Results... Read more
2. What mechanisms govern secondary flows induced by spanwise heterogeneous roughness in turbulent boundary layers, especially under stable thermal stratification?
This theme explores how spanwise variations in surface roughness generate streamwise vortical secondary flows in turbulent boundary layers due to turbulence-induced Reynolds stress gradients. Such flows are significant in environmental and engineering applications involving complex terrains or structured surfaces. Recent work addresses how stable thermal stratification modulates these secondary motions, their strength, vertical extent, and the formation of vortex stacks. Both experimental and numerical studies identify turbulence gradients as drivers of Prandtl's secondary flows of the second kind and provide insights into stratification-induced reorganization of turbulent structures near rough surfaces.
Key finding: By combining numerical simulations and experiments, this paper uncovers that mean secondary flows over spanwise heterogeneous roughness are Prandtl's secondary flows of the second kind, driven by spatial gradients in... Read more
Key finding: This research demonstrates experimentally and numerically that stable thermal stratification suppresses vertical motions and reduces the vertical size and strength of the primary off-wall secondary vortex induced by spanwise... Read more
Key finding: Utilizing particle image velocimetry over a herringbone riblet surface, this study identifies large-scale coherent low-momentum streaks organized by the spanwise heterogeneity. It reveals that turbulence structures adapt... Read more
Key finding: Through experiments, this work characterizes the turbulent/non-turbulent interface and internal layers of high shear within turbulent boundary layers. It finds that internal shear layers of similar properties to the outer... Read more
3. How do stable thermal stratification and buoyancy forces influence turbulence statistics and mixing processes in turbulent boundary layers?
This research area investigates turbulent boundary layers subjected to stable thermal stratification, which significantly affects turbulent mixing, Reynolds stresses, and fluxes within the atmospheric surface layer and laboratory flows. Key questions include the delineation of different stratification regimes distinguished by changes in scaling of turbulence with wall shear stress and critical Richardson numbers. Studies combine laboratory experiments, numerical simulations, and theoretical analyses to elucidate turbulence suppression, the formation of energetic sublayers or pits, and transitions from weakly to strongly stable states, improving models for atmospheric and environmental turbulence that is often stratified.
Key finding: Laboratory measurements show that at low to moderate stable stratification, turbulent stresses scale with wall shear stress, indicating little change in turbulence structure. Beyond a critical stratification, this scaling... Read more
Key finding: By controlling inlet temperature profiles in a wind tunnel, this study shapes the vertical gradient Richardson number profile in the developed stable boundary layer. Findings indicate that Reynolds stresses and turbulent heat... Read more
Key finding: Direct numerical simulations of shearless turbulent layers with step changes in temperature lapse rate reveal that intense stratification alters turbulent mixing dynamics, forming kinetic energy pits (sublayers) under stable... Read more
Key finding: Using a one-dimensional turbulence model, this study captures features of time-dependent atmospheric Ekman-Stokes boundary layers driven by oscillatory forcing. The model reproduces parametric enhancement of bulk-surface... Read more