Improving the understanding and control of tip leakage noise is increasingly important for meeting future aviation noise-reductions targets. This study experimentally investigates porous tip treatments on a single stationary aerofoil, focusing on their effect on the two tip leakage noise sources, vortex-shedding and shear layer roll-up, both arising from the tip flow separation at the pressure side tip. Porous tip effectively reduces the roll-up noise source, with even a thin treatment of 1.6 mm providing reductions of almost 10 dB, whereas vortex-shedding noise radiation shifts toward lower frequencies and achieves almost full suppression for the thickness treatment of 10 mm. Localising the porous section to the mid-chord yields comparable noise reductions to full-chord treatments. Aerodynamic measurements indicate a modest lift reduction with the porous treatment compared to the hard-wall case, whereas drag remains largely unaffected for larger gaps.

The physical mechanism of oscillatory instability in spiked-body flow at a freestream Mach number of 6 and a Reynolds number of 0.13 million, based on the cylinder diameter, is investigated using high-fidelity delayed detached-eddy simulation (DDES). The simulation successfully captures the unsteady shock structures and global flow features, enabling a detailed analysis of the underlying dynamics. A dominant low-frequency mode governing the large-scale oscillation is identified and shown to be intrinsically linked to the evolution of the complex coupled interaction among shock waves, shear layers, and separation regions. The oscillation cycle is characterized by the periodic advance and retreat of the separation zone, accompanied by the flapping motion of the separation shock and the shear layer. The bidirectional propagation of inner compression waves and their convection velocities are identified, revealing their key role in sustaining the feedback loop among the separation shock, shear layer, and recirculation region. These findings provide a new physical understanding of the origin and sustaining mechanism of large-scale oscillations in hypersonic spiked-body flows.

Experimental data-driven calibration of the SST turbulence model: Validating physical interpretability via large Eddy simulation

Density fluctuations in the shear layer locally alter the effective index of refraction of the atmosphere, causing bore-sight errors that are characterized by an apparent shift in the target location. To address the lack of viable correction methods for supersonic and hypersonic aero-optical distortions, we perform a large-eddy simulation using the JENRE Multiphysics Framework to approximate the boundary-layer and shear-layer flow over a cavity operating at a free-stream Mach number of 2.3 and an altitude of 16km. The optical path difference (OPD) is calculated from the high-frequency density sampling over a 0.0254m×0.0254m aperture located at the center of the cavity. Spectral proper orthogonal decomposition of the OPD reveals dominant flow structures contributing to wavefront aberrations. Using the simulated OPD data, we train an artificial neural network to process the Shack-Hartmann wavefront sensor outputs and reconstruct the original wavefront. This data-driven approach demonstrates potential for faster and more accurate correction of imaging errors compared to traditional methods, particularly when tailored to specific operational conditions.

Be stars are currently viewed as B-type stars surrounded by a disc fuelled by the star itself during episodic excretion events. The origin of these events is poorly understood. This study aims to determine whether surface equatorial Kelvin waves can be unstable and therefore can play a role in triggering the Be phenomenon. We first derived an analytical expression for gravito-inertial modes in the shallow water framework. We then numerically investigated the evolution of equatorial Kelvin modes as the system parameters varied. We extended the study to thick-layer configurations with a constant-density fluid. We then analysed the stability of these modes under differential rotation and viscous effects. We show that equatorial Kelvin waves still exist in a spherical shell of finite thickness, but their equatorial confinement is weaker. At low azimuthal wave numbers, Kelvin waves lie in the inertial-wave frequency band and therefore exhibit specificities of inertial waves, such as shear layers associated with singularities of the Poincaré equation. These shear layers constitute new dissipative structures for Kelvin waves. When a radial (shellular) differential rotation is imposed, we show that equatorial Kelvin waves can be destabilised, provided that differential rotation and viscosity are in an appropriate range. We trace back the non-monotonic behaviour of the instability growth rate to the rise of a critical layer where the fluid azimuthal velocity equals the phase speed of the surface waves. This study provides new insights into the behaviour of equatorial Kelvin waves in astrophysics, particularly in rapidly rotating stars. The results reinforce the idea that gravito-inertial waves, and more specifically the equatorial Kelvin waves, can be unstable and thus constitute key components in the mechanisms leading to the Be phenomenon.

SynopsisBird wings contain several feather groups, some of which contribute to their aerodynamic performance during flight. One of these groups is the emarginated primary feathers, which exhibit slots, bending, and twisting in flight. Slotted wingtips vary in morphology across the avian clade, raising questions about the relationship between their form and function, particularly with regard to their aerodynamic role. This study expands the current understanding of the functional morphology of slotted wingtips by systematically studying slots, bending, and twist using various engineered wingtip configurations: one that captures the slotting only, another that has both slotting and bending, and a third that combines slots, bending, and twist. Force, moment, and PIV data acquired during wind tunnel testing reveal that the bioinspired wingtips have both global and local aerodynamic effects. The wingtips’ global aerodynamic effect is to delay spanwise stall propagation, thereby altering the lift distribution over the wing. Local aerodynamic effects include the reduction of aerodynamic load over the wingtips as well as changes to the separated shear layer location and the breakdown of tip vorticity. The results show that while global aerodynamic effects are universal across all configurations, local effects are sensitive to wingtip design. Nonetheless, both the global and local effects enable structural resilience and effective roll and yaw control authority. These results demonstrate that the emarginated primary feathers may have multiple aerodynamic functions, offering new insights into their role in bird flight and showcasing their potential as flow- and flight-control devices for engineered aerial vehicles.

• A rigorous two-stage DNS framework is developed to provide high-quality reference data for shock-turbulence-flame interactions in supersonic reacting shear layers using a moderately complex hydrocarbon fuel. • The flow is shown to be remarkably robust to variations in mean scalar dissipation rate, with reaction rates governed by localized regions of high scalar dissipation, implying accurate modelling is possible at lower grid resolutions than traditionally expected. This study examines critical aspects of Direct Numerical Simulations (DNS) of ethylene-air combustion for hypersonic propulsion applications. A combustion mechanism was selected based on a comparative analysis of multiple models, balancing chemical fidelity and computational cost. Detailed configurations of two DNS cases are presented, focusing on high-speed reacting turbulent shear layers including interactions with an oblique shock wave ( M s = 1.3 , inflow angle 5 ∘ ). A lower and standard Reynolds number case are employed to ensure mesh convergence while maintaining computational feasibility. Although most statistical quantities exhibit strong convergence trends, full convergence was not achieved for the scalar dissipation rate. This study investigates the underlying physical mechanisms responsible for this behaviour and demonstrates their limited impact on all other key variables. These results advance the understanding of turbulence-combustion interactions and will be used to guide new developments in numerical modelling for next-generation air-breathing hypersonic propulsion systems.

Modulation of a ramp-induced shock wave/boundary layer interaction through extended frequency range pulsed discharge

This study numerically investigates the flow-induced vibration characteristics of two tandem and side-by-side cylinders at Reynolds number of 100. The finite element method combined with the Arbitrary Lagrangian–Eulerian formulation is adopted to capture fluid–structure interaction behaviors. Numerical results reveal distinct flow regime transitions governed by spacing ratios. For tandem cylinders, the flow evolves sequentially from the extended-body regime and shear layer reattachment regime to the co-shedding regime as spacing increases. For side-by-side configurations, the flow transits from a single bluff-body pattern to a biased mode, eventually forming synchronized parallel vortex streets. For oscillating cylinders, strong near-field coupling dominates at small spacings, which weakens with increasing distance. When spacing exceeds critical thresholds (L/D≥4,H/D≥3), cylinder oscillation governs flow features, evolving into a weakly coupled state. Two mean phase differences based on the Hilbert transform are introduced to quantitatively characterize coupling strength, energy transfer, and vortex synchronization. Both spacing ratio and oscillation frequency (f0) jointly determine vortex patterns and lock-in phenomena. At the medium oscillation frequency (f0=0.160), stable lock-in behavior is well-established for small-spacing configurations. In contrast, at the low frequency (f0=0.080), tandem cylinders exhibit incomplete lock-in, whereas no lock-in phenomenon is observed for side-by-side counterparts. At the high frequency (f0=0.192), the lock-in effect fails for large-spacing configurations. These findings provide fundamental references for fatigue-resistant optimization of engineering structures.

• Simulations and experiments on aeroacoustically driven thermoacoustic phenomena. • Three-dimensional interactions between cavity flow and honeycomb stack. • Contributions to aerodynamic noise suppression and energy harvesting. • Significant influence of stack position on cavity flow and heat pump behavior. To control and utilize aerodynamic sound energy through thermoacoustic effects, this study investigates the effects of a multi-channel stack on fluid-resonant oscillations in a cavity flow. Compressible flow simulations were conducted for a cavity containing a honeycomb stack with an incoming turbulent boundary layer, and the results were validated through wind tunnel experiments. The effects of the vertical position of the stack relative to the cavity depth on the self-sustained oscillations and heat-pumping effects were examined. The placement of the stack significantly affected the acoustic resonance within the cavity, with mode shifts observed in shear layer oscillations at specific stack positions. When the stack was positioned near the cavity bottom, an effective heat flow was induced through the stack due to thermoacoustic heat pumping, resulting in a temperature gradient between the stack ends. These findings demonstrate the possibility for controlling self-sustained oscillations in cavity flows using a honeycomb stack, highlighting energy conversion mechanisms between sound and heat.

The next generations of gas turbines are expected to be ‘fuel-flexible’, i.e. to reliably operate with variable fuel mixtures ranging from pure carbon-free fuels such as ammonia and hydrogen to natural gas and blends thereof. These fuel mixtures pose challenges, however, due to variations in combustion dynamics that are primarily caused by the fuels' reactivities and their molecular transport properties. Multiple Mapping Conditioning (MMC) offers a cost-effective simulation approach that can account for realistic species transport and detailed chemical kinetics. Here, an improved mass-based particle mixing method is introduced that can capture differential diffusion by adapting the spatial displacement of the particles and effectuate mixing in different steps. This approach allows accurate modelling with a single particle cloud while maintaining a model-free closure for the chemical source term. The model is tested in a shear layer configuration with various fuel blends. The findings reveal that the new MMC mixing method improves the accuracy of species predictions when compared to standard MMC mixing approaches, and it offers an acceptable estimation of differential diffusion effects for a wide range of fuel blends.

Velocity measurement techniques, such as particle image velocimetry (PIV), face a trade-off between field of view, spatial resolution and sampling rate, so that small-scale vortices, shear layers and high-frequency turbulent motions are often under-resolved. Most physics-informed reconstructions use a velocity–pressure formulation, even though pressure is not measured in typical PIV experiments, so the Navier–Stokes constraints are only weakly enforced. We address this issue by formulating a vorticity–velocity physics-informed network (VVPINN), in which pressure is eliminated and incompressibility is enforced together with a vorticity transport equation, thereby directly constraining the velocity field and its derivatives. We then compare this formulation with a conventional velocity–pressure PINN (VPPINN) for spatio-temporal super-resolution of planar PIV data in three cases: a laminar multi-cylinder wake, a two-dimensional Taylor–Green vortex and an experimental two-cylinder wake. In the Taylor–Green vortex case, with identical architectures and training strategies, the VVPINN yields smaller velocity errors, reduces the $L_2$ errors in vorticity and shear by approximately $10\,\%$ , and the pressure gradient errors by up to approximately $30\,\%$ at moderate super-resolution factors, and produces instantaneous fields with more physically plausible vorticity, shear and fine-scale pressure gradient patterns. Spectral analysis shows that the temporal energy spectrum is recovered accurately, whereas the wavenumber spectra, particularly beyond the Nyquist wavenumber, remain more difficult to match because the training data strongly constrain the time histories at sampled locations, but only indirectly inform the smallest spatial scales. Overall, the results indicate that vorticity-based constraints provide a more effective route to physics-consistent super-resolution of sub-sampled PIV data than the conventional velocity–pressure formulation.

Abstract The entrainment zone (EZ) governs the exchange of heat, momentum, and mass between the mixed layer and free atmosphere, shaping dry convective boundary layer (CBL) evolution. Although dry CBL depth ( z i ) is a fundamental dynamical scale, how it regulates entrainment under different geostrophic winds ( U g ) and stratification has not been systematically examined. A series of large‐eddy simulations (LES) is employed to address this gap. The main findings are as follows. (a) Regardless of z i , wind shear plays a dual role in entrainment dynamics: reducing heat transport and entrainment efficiency, suppressing entrainment, limiting CBL growth, and lowering entrainment heat flux ( δQ ) under weak winds. Once wind shear exceeds a threshold, substantially enhanced turbulent kinetic energy (TKE) above the mid‐entrainment layer strengthens entrainment, promoting the growth of δQ and z i . (b) The deepening of the z i weakens shear within the EZ, suppressing entrainment under strong U g . Consequently, differences between strong‐wind and calm conditions in δQ , z i , and other key parameters diminish. (c) The discrepancy between LES and the shear‐free zero‐order model grows with z i ; however, for shallow CBL with moderate shear, the model remains valid. (d) The increase in δQ and entrainment heat flux ratio with z i under strong surface heating and moderate U g likely arises from more vigorous free convection in a deeper CBL. (e) The nondimensional EZ thickness decreases with z i , as the lower EZ portion ratio remains nearly constant and the upper part ratio shrinks. These findings clarify the dependence of entrainment on z i in a sheared dry CBL.

This study investigates the hydraulic influence of localized vegetation introduced upstream of a spur dike in a rectangular channel using a validated computational fluid dynamics (CFD) model. Two scenarios were simulated: one without vegetation and another with a rigid vegetative patch positioned upstream of the spur dike. Analysis focused on flow distributions to assess the impact of vegetation. Results showed that the vegetation considered resulted to a consistent reduction in flow velocity and wall shear stress along both channel banks. The vegetative resistance weakened recirculation zones, attenuated shear layers, and redistributed momentum across the flow domain. Additionally, the presence of vegetation modified the flow structure by promoting more uniform velocity gradients and dampening turbulence intensity near the bed and banks, especially around the spur dike nose. This altered hydrodynamic behavior contributed to a noticeable decline in erosive forces, particularly in zones vulnerable to scour. The simulation outcomes underscore the potential of strategically placed vegetation in reducing local scour and improving bank protection. These findings demonstrate that even limited vegetation placement can effectively reduce erosive forces and enhance flow stability around spur dikes. The study supports the use of targeted vegetation as a nature-based solution in hybrid river training strategies, contributing to sustainable river engineering and flood management practices.

Abstract Using time–distance helioseismology applied to 14 yr of Solar Dynamics Observatory/Helioseismic and Magnetic Imager observations spanning solar cycle 24 and the rising phase of cycle 25, we present evidence that meridional flows in the lower half of the near-surface shear layer (NSSL), modulated by active-region magnetic fields, play a central role in the episodic global transport of magnetic flux. In particular, polar-field buildup is tightly linked to plasma outflows diverging from active latitudes within the deeper NSSL. The magnitude and timing of hemispheric polar-field evolution are regulated by depth-dependent meridional flow, including its cross-equatorial component, responding to active-region flux asymmetries. During cycle 24 maximum, stronger southern outflows accelerated flux transport, causing the southern polar field to peak nearly 4 yr before the northern. Global magnetic flux transport patterns in the previous three solar cycles (21, 22, and 23) show broad consistency with the deeper meridional flow modulation inferred in cycles 24 and 25. These results identify activity-dependent flow variations in deeper layers of the NSSL as a dynamically significant component of the Babcock–Leighton process that governs the generation and hemispheric asymmetry of the global dipole field.

Comparison of Shack–Hartmann and digital holographic measurements of the optical effect of a subsonic compressible shear layer

The scattering of acoustic waves by the turbulent shear layer that develops from the side walls of an open jet wind tunnel is investigated experimentally. A microphone array measures the acoustic field, while particle image velocimetry (PIV) characterizes the shear layer. Microphone measurements reveal a broadening of the power spectral density and two sidelobes around the source tone (haystacking). The bicoherence spectrum computed from the microphone signals confirms a nonlinear interaction between the source tone and low-frequency shear-layer dynamics. These low-frequency fluctuations correspond to the passage of large coherent structures in the turbulent shear layer, with a Strouhal number of approximately 0.2 based on vorticity thickness. Synchronized microphone array and PIV measurements demonstrate a direct correlation between the transverse velocity component of the shear layer and coherence loss between microphones. This suggests that transverse velocity fluctuations primarily drive the interaction with acoustic waves, modifying acoustic transmission. The findings have implications for improving acoustic imaging techniques in industrial settings. A compensation technique is proposed, leveraging velocity field data to mitigate coherence loss. This method can be applied even with a single microphone array if positioned close enough to the shear layer to capture hydrodynamic pressure fluctuations.

As offshore wind power expands into deeper waters, the hydrodynamic interference between large-scale wind turbine foundations and transmission cables has become increasingly prominent. This study employs the shear-stress transport k–ω turbulence model to numerically simulate the three-dimensional flow field and structural loading characteristics of a monopile foundation and its adjacent cables. Unlike previous studies focused on subcritical flow, this research investigates transcritical flow conditions (Re ≈ 6 × 106) representative of realistic offshore environments. The study systematically analyzes how different cable spatial layouts (θ = 0°, 45°, 90°, 135°, and 180°, where θ denotes the angle between the incoming flow direction and the cable orientation) affect the wake vortex structure, vortex shedding characteristics, and hydrodynamic forces. Results indicate that the cable orientation significantly alters wake symmetry and stability. Specifically, the 135° arrangement triggers a “shear layer locking” effect, leading to the strongest flow field asymmetry with a root-mean-square lift coefficient (CLRMS) of 0.195 and a mean drag coefficient (CDM) of 0.519. Furthermore, the cable experiences dramatic force fluctuations at 45° due to gap flow acceleration (Venturi effect), with the root-mean-square lift coefficient (CLRMS) reaching 0.458. These findings provide critical reference data for the fatigue design of cable protection systems in high-energy tidal environments.

This study employs wall-resolved large-eddy simulations to investigate the effectiveness of unsteady suction actuation applied near the upper edge of the slant surface of a 25° Ahmed body at a Reynolds number of 7.6 × 105. A key approach to this work is the validation of the baseline flow, which achieves a drag coefficient of 0.31, closely matching the benchmark experimental from Ahmed et al. [“Some salient features of the time-averaged ground vehicle wake,” SAE Trans. 93, 473–503 (1984)]. From this validated baseline case, the application of an unsteady suction jet with an optimal momentum coefficient Cμ=2.6×10−3 leads in a drag value of 0.274 and reduction of approximately 12%. This study establishes a clear connection between targeted momentum injection and drag reduction through detailed analysis of modifications to the separation bubble, shear layer development, and wake topology. It is found that the suction jet effectively delays flow separation while promoting earlier reattachment and suppressing large-scale coherent structures. Quantitative evaluations confirm a 28% shortening of the recirculation bubble length. The analysis of first- and second-order statistics reveals that turbulence intensifies locally near the actuation location. However, the controlled wake exhibits a shortened recirculation region in both instantaneous and mean resolved velocity fields, and the so-called C-pillar vortices display reduced structural coherence. Additional insight is provided through the energy spectra, and the resolved turbulent kinetic energy budget evaluated at downstream locations. We observed that the suction effect significantly alters the flow characteristics over the slant surface and in the near wake of the vehicle model, leading to a reduced drag coefficient and controlled lift, which are essential for improving overall energy efficiency.

The main objective of this article is to investigate the stochastic dynamic response of functionally graded sandwich (FGSW) plates composed of a hard core and two functionally graded (FG) face sheets, resting on a Pasternak foundation (PF) and subjected to a moving mass (MM), while explicitly accounting for uncertainties in material properties and moving mass density. The uncertain parameters are modeled as random variables following normal probability distributions. A finite element formulation based on four-node (Q4) elements is developed within the framework of the refined first-order shear deformation theory (RFSDT), ensuring an accurate representation of transverse shear effects with high computational efficiency. The Pasternak foundation is incorporated through both spring and shear layer stiffness components. The accuracy and validity of the proposed formulation are rigorously verified through comparisons with available benchmark solutions, demonstrating excellent agreement. A comprehensive parametric investigation is then conducted to examine the effects of geometric dimensions, material properties, and foundation stiffness on the dynamic response. The results indicate that both geometric parameters and material properties have a significant influence on the dynamic behavior of the plate under deterministic as well as stochastic conditions. These findings provide valuable theoretical guidance and practical insights for the robust design and reliability assessment of advanced sandwich structures in transportation, aerospace, and defense engineering.