Search Results (826)

Boundary-layer atmospheric stability, wind-shear variability, and thermodynamic forcing are all important factors for the initiation, intensification, and transport of dust storms. But there is limited knowledge of the quantitative evaluation of bulk-layer atmospheric stability and the relation between wind-driven dust dynamics and atmospheric stability in arid and semi-arid regions. In this research, a hybrid AI–meteorology framework, HyMet-Fusion, is presented that combines visual information derived from satellite observations with physics-based indicators of atmospheric stability to evaluate atmospheric stability during dust storm events over Iraq. The proposed framework is based on the use of deep features extracted from the satellite imagery through a frozen EfficientNetB0 backbone, combined with indicators derived from the ERA5 pressure level data for the atmosphere, such as the Bulk Richardson Number (Bulk Ri), the Wind Shear (WS) and the Dry Air Index (DAI). The two branches were merged using a late fusion (0.75 physics/0.25 image) and each hour was classified into three atmospheric stability conditions: Relatively Stable, Moderately Unstable and Unstable. The overall hourly accuracy using a Leave-One-Event-Out (LOEO) cross-validation scheme, where each dust event was used for independent testing and no dust event was used for training, was 72.4%, with 81.2% accuracy for the dominant stability state and 92.2% correct assessment of the unstable condition time for the severe dust events. Inaccuracies were mainly (66%) in the conservative direction (more instability). Unstable atmospheric conditions were also found to be associated with all severe dust storms and coincided with higher wind shear, lower Bulk Ri values and higher thermodynamic variability. Moderate and light dust events were primarily associated with transitional and relatively stable atmospheric conditions, and differed between the various regions, primarily in Kirkuk and Nasiriyah. Correlation analysis showed that wind shear had the highest correlation with atmospheric instability (r = 0.92), followed by DAI (r = 0.90) and Bulk Ri (r = −0.75). In addition, the wind shear also increased significantly from light to severe dust events at all stations investigated, showing that wind shear is a critical factor for turbulent mixing, vertical momentum exchange and dust uplift processes. The results suggest wind shear is the leading dynamics mechanism for bulk-layer instability in Iraqi dust storms. The findings highlight the complementary benefit of using physics-based atmospheric indicators embedded with deep learning satellite image analysis. The HyMet-Fusion system can be used as a transferable method for observing wind-driven instability of the atmosphere and related dust hazards, which could be employed in boundary-layer meteorology, air-quality forecasting, aviation safety and environmental risk assessment in arid and semi-arid areas. Full article

High-speed turbulent boundary layers govern the transport of momentum, mass, and energy in compressible flows and play a central role in determining aerodynamic performance, skin-friction drag, aerodynamic heating, flow stability, and thermal protection requirements of advanced aerospace vehicles. Over the past three decades, direct numerical simulation (DNS) has revolutionized the study of compressible wall-bounded turbulence by resolving all dynamically relevant turbulent scales without turbulence-model assumptions, providing benchmark-quality databases and unprecedented physical insight into flow phenomena that remain difficult or impossible to measure experimentally. Together with complementary high-fidelity approaches, DNS has substantially advanced the understanding of turbulence dynamics across a broad range of supersonic and hypersonic flow conditions. This review presents a critical assessment of advances in the high-fidelity simulation of compressible turbulent boundary layers under non-reacting conditions. Particular emphasis is placed on the flow physics of canonical zero-pressure-gradient boundary layers, shock-wave/turbulent-boundary-layer interactions (SWTBLIs), pressure-gradient-driven flows, streamline-curvature effects, and thermochemical non-equilibrium phenomena. Recent developments in numerical methodologies are also briefly examined, including high-order discretization techniques, turbulence inflow generation methods, hybrid continuum-kinetic formulations, and advances in high-performance computing that have enabled DNS at increasingly high Reynolds and Mach numbers. The review highlights the major physical insights emerging from DNS studies, demonstrating that many fundamental characteristics of compressible wall turbulence remain closely related to their incompressible counterparts when appropriate compressibility transformations are employed. At the same time, DNS has revealed the critical influence of wall temperature, pressure gradients, streamline curvature, shock interactions, and finite-rate thermochemistry on turbulence structure, coherent motions, interscale energy transfer, boundary-layer separation, and aerodynamic heating. Full article

In engineering fields such as aviation, shipping, and high-speed rail, system operational efficiency and energy consumption are largely determined by turbulent drag. The drag reduction design of shark skin-inspired micro-groove structures have opened up new avenues for improving aerodynamic efficiency, optimizing flow field characteristics, and saving energy, representing a highly promising research hotspot in the field of functional micro-structured surfaces. Addressing the issue of drag reduction for V-shaped grooves (frictional Reynolds number 85–695), this paper employs Design of Experiments (DOE) combined with high-precision numerical simulation to clarify the influence of groove height (h), groove width (s), and inflow velocity (U) on the drag reduction rate for bionic microgroove surfaces. The drag reduction mechanism is further revealed through the analysis of vorticity distribution, vortex core position, boundary layer velocity distributions, pulsating velocity fields, and Reynolds stress distributions. When the dimensionless height h⁺ and width s⁺ range from 8.50 to 29.75, these grooves can effectively reduce resistance. A maximum drag reduction rate of 12.33% is achieved at h⁺ = s⁺ = 25.29 and a flow velocity of 80.7 m/s (frictional Reynolds number 599). At low flow velocities, larger groove dimensions are favorable for drag reduction. In contrast, smaller groove dimensions are required under medium-to-high flow velocity conditions. The optimal microstructural dimensions of V-shaped grooves decrease as the inflow velocity increases. V-shaped grooves can lift turbulent vortex coherent structures, reduce pulsating velocities in the streamwise, normal, and spanwise directions, and decrease the peak values of Reynolds stress in the near-wall region. The results can provide a quantitative basis for the design and engineering applications of biomimetic riblet drag-reducing surfaces. Full article

Urban air mobility depends on small aerial vehicles threading through dense, wind-swept cities, yet most sampling-based planners treat the urban wind field as noise to reject rather than structure to exploit—and pay for it in flight energy. We take the opposite view. Behind every building lies a sheltered wake where the air slows and aerodynamic drag drops, and this work turns that physical fact into a planning principle. We present an energy-aware, wind-shadow-aware framework that routes a single quadrotor, at the planning level, through these low-wind corridors. The wind model couples a power-law shear profile with Ekman directional veer and a frozen-turbulence gust component, grounding the planner in realistic boundary-layer physics. A feed-forward neural energy surrogate, trained to approximate a cost field that aggregates wind exposure and obstacle clearance, then guides a two-stage refinement—energy-aware, collision-checked shortcutting followed by Laplacian and energy-guided smoothing—so that every accepted change stays collision-free. Against classical sampling-based baselines (RRT, goal-biased RRT, Informed RRT*, and BIT*) over a 50-run Monte-Carlo study, evaluated with multi-criteria metrics and Pareto-dominance analysis, the framework characterizes how wind-shadow-aware routing balances route energy against smoothness and clearance, offering a reproducible, wind-informed basis for flying robots navigation. Full article

Conventional particle image velocimetry (PIV) techniques face an inherent trade-off between temporal resolution and single-pulse laser energy, limiting their performance in shock wave measurements. This study develops a multi-channel parallel PIV system with programmable timing control to address this constraint. By distributing laser pulses across eight independent optical channels, the system decouples single-pulse energy from the repetition rate, enabling continuous velocity field measurements at microsecond temporal resolution with high signal-to-noise ratio. Experiments were conducted on a planar shock wave propagating over a trapezoidal step in a shock tube facility. The system captured velocity fields at seven consecutive time instants with a 1 μs pulse interval, revealing the curved evolution of diffracted shock fronts and transient flow separation induced by shock–boundary-layer interaction. Comparison with unsteady Reynolds-averaged Navier–Stokes simulations demonstrated that the PIV system resolves fine-scale post-shock perturbations and turbulent fluctuations that were numerically dissipated in computational fluid dynamics. The results verify that the parallel-channel architecture accurately captures unsteady flow structures during shock reflection and diffraction, offering a reliable diagnostic technique for investigations of shock wave dynamics. Full article

We explore the analogy between the asymptotic (high Reynolds number) scaling of two canonical wall-bounded turbulent flows, namely zero-pressure-gradient (ZPG) and pipe flows. We find that the two flows can be characterised using similar scaling laws that relate the streamwise turbulence intensity to friction: the product of the dimensionless drag and the square root of a dimensionless boundary-layer thickness for ZPG flow plays the role of the streamwise turbulence intensity for pipe flow, and the two flows are linked through a Reynolds-number-dependent correction term derived from the logarithmic mean-velocity profile. As a consequence, the squared product scales as the friction factor. Establishing a common, friction-based turbulence intensity scaling for ZPG and pipe flows is of interest both for fundamental studies of canonical wall-bounded flows and for the specification of the turbulence intensity in computational fluid dynamics simulations. Full article

Engine high-altitude simulation tests require establishing a stable low test-chamber pressure across a wide range of operating conditions. Existing studies focus predominantly on the local starting mechanisms—namely, shock-wave swallowing, aerodynamic choking, and boundary-layer separation—of individual ejector or diffuser components, with limited investigation of the coupling among shock evolution, chamber pressure response, starting hysteresis, and diffuser starting thresholds during continuous ejection pressure regulation. To address this gap, a two-dimensional axisymmetric Reynolds-averaged Navier–Stokes model with the standard k-ε turbulence model is employed, encompassing the test chamber, engine nozzle, supersonic diffuser, and annular ejector of a large-scale active-ejection test stand (where an annular ejector actively evacuates the test chamber to simulate high-altitude backpressure). The formation, migration, and stabilization of the shock system are revealed under increasing ejection pressure. Hysteresis characteristics are elucidated by comparing pressure-increasing and pressure-decreasing paths. The non-monotonic relationship between chamber pressure and ejector total pressure ratio under zero-secondary-flow conditions is established. The mechanism governing diffuser starting threshold variation under coupled engine gas and ejection flows is identified. Quantitatively, the ejector starting pressure ratio is found to be approximately 16.78 with a hysteresis width of ~13.6% between the starting and unstarting thresholds, and the diffuser starting threshold scales linearly with the ejector total pressure ratio (R² = 0.976). The results reveal the coupling among shock evolution, hysteresis, chamber pressure response, and diffuser starting thresholds and clarify the dual influence of ejection pressure on both chamber pressure regulation and diffuser starting thresholds. These findings provide a theoretical basis for parameter matching and operational control of high-altitude simulation facilities. Full article

Low-altitude aviation requires spatially resolved turbulence information, but routine observing networks do not directly measure dense three-dimensional eddy dissipation rate (EDR) fields. We formulate EDR retrieval as physics-constrained probabilistic tomography of EDR (PCT-EDR) and construct an author-curated private multi-source low-altitude observation dataset designated SORA2025 to support the retrieval and benchmark evaluation. The observation operator partitions Doppler spectral-width variance into turbulent, beam, within-volume shear, hydrometeor, instrument, and residual components, then converts the corrected turbulent contribution into posterior distributions of ${log}_{10}ϵ$ and EDR on a 0–2 km grid. Wind-profiling and S/X-band Doppler radars supply vertical and horizontal constraints, while microwave radiometers and automatic weather stations provide stability and near-surface context. Twelve cases from four campaign dates characterize the retrieved posterior fields. A separate frozen processed benchmark contains 240 tower-sonic and unmanned aerial vehicle (UAV) windows from four later dates. Recalculation from the supplied processed package gives a root mean square error (RMSE) of 0.238 in ${log}_{10}ϵ$, a Spearman correlation of 0.812, and an area under the receiver operating characteristic curve (AUC) of 0.913 for the stored prefit-calibrated product at $\mathrm{EDR}>0.10{\mathrm{m}}^{2/3}{\mathrm{s}}^{-1}$. The nominal 90% interval covers 84.2% of the processed targets, indicating mild under-dispersion. Full article

This study investigates heat transfer enhancement in the cooling channels of gas turbine blade turbulators using modified transverse baffles with isosceles triangular sawtooth perforations. The proposed baffle design aims to improve convective heat transfer by promoting flow mixing and disrupting the thermal boundary layer. Experiments were conducted in a rectangular channel with an aspect ratio of 3.75 under constant heat flux conditions using air (Pr = 0.7) as the working fluid. The effects of Reynolds number (Re = 6000–24,000), sawtooth width ratio (a/W = 0.0, 0.0625, 0.125, 0.25, and 0.5), and sawtooth height ratio (b/e = 0.0, 0.25, 0.5, 0.75, and 1.0) were systematically investigated. The blockage ratio (e/H) and pitch ratio (P/H) were maintained at 0.3 and 1.5, respectively. Heat transfer characteristics were evaluated using the thermochromic liquid crystal (TLC) technique, while thermal–hydraulic performance was assessed in terms of the Nusselt number (Nu), friction factor (f), and thermal performance factor (TPF). The results demonstrate that introducing sawtooth perforations significantly enhances heat transfer compared with a smooth channel, yielding Nusselt number ratios (Nu/Nu_s) between 1.6 and 2.6. The highest heat transfer enhancement was achieved at a/W = 0.0625 and b/e = 0.25, where the relatively small sawtooth openings generated stronger jet impingement, enhanced flow mixing, and more effective disruption of the thermal boundary layer. However, these geometric modifications also increased the pressure loss due to intensified flow blockage and recirculation, resulting in friction factor ratios (f/f_s) ranging from 8.9 to 14.9. The maximum pressure-drop penalty occurred at b/e = 0.25 because the smaller openings produced stronger turbulence and increased flow resistance. Despite the increased friction loss, the optimum configuration (a/W = 0.0625 and b/e = 0.25) achieved the highest thermal performance factor of 1.2 at Re = 6000. Full article

Boundary Layer Ingestion (BLI) is a propulsion integration concept that improves aircraft efficiency by recovering wake momentum deficit and reducing propulsive power requirements. In this study, a numerical methodology is created to study electrified aft-fuselage BLI on a simplified A320 aircraft model across multiple operating conditions. Three configurations were developed: a baseline aircraft, a cruciform-tail configuration in OpenVSP and CFD simulations performed in ANSYS Fluent 2025 R2 using the Spalart–Allmaras turbulence model. The results demonstrate reduced drag, improved lift-to-drag ratio, and a Power Saving Coefficient (PSC) of approximately 5–14%, highest during cruise, climb, and descent conditions at higher altitudes. Full article

Pin-fins are widely used to enhance heat transfer in compact heat exchangers, turbine cooling passages, and electronic devices, but their complex geometries make accurate thermal–fluid prediction computationally expensive. This paper presents a geometry-aware multiscale (GAMS) graph neural network (GNN) for predicting steady turbulent flow and heat transfer in a two-dimensional channel containing arbitrarily shaped pin-fin geometries. An automated framework integrating geometry generation, meshing, and ANSYS Fluent simulations was developed to construct the training dataset. Pin-fin geometries were parameterized using piecewise cubic splines, generating 1000 unique configurations through Latin Hypercube Sampling. Each simulation was converted into a graph representation, where nodes contained spatial coordinates, normalized streamwise position, one-hot boundary indicators, and signed distance to the nearest wall. These graph-based features were used to train the GNN to predict the temperature, velocity magnitude, and pressure fields directly from geometry. The network achieved excellent predictive accuracy, successfully capturing boundary layers, recirculation zones, and upstream stagnation regions while reducing computational wall time by 2–3 orders of magnitude compared to conventional CFD simulations. Overall, the proposed GNN provides a fast, reliable surrogate modeling framework for complex thermal–fluid flow configurations. Full article

The shock wave/boundary layer interaction (SWBLI) is a common flow phenomenon in high-speed aircraft flow fields. It is important to control the separation caused by SWBLI. This paper investigates the influence of spanwise periodic-motion micro-vortex generators (MVGs) on SWBLI. A combination of particle image velocimetry (PIV), high-frequency Schlieren and fluorescent oil-film visualization was employed to analyze the interaction region of a flat plate compression ramp model. The incoming flow Mach number was 6, and the MVGs oscillation frequencies were 10 Hz, 30 Hz and 50 Hz, respectively. The results reveal that neither the presence nor the spanwise oscillation in the MVGs fundamentally altered the separation–reattachment flow structure. Nonetheless, both factors contributed to an increase in boundary layer thickness and an expansion of the absolute size of the separation region. The trailing vortices generated by the MVGs exerted a stabilizing influence on near-wall turbulent structures, resulting in a reduction in surface friction drag. However, the drag reduction effect diminished as the oscillation frequency increased, corresponding to a weakening of the trailing vortex strength. Additionally, the MVGs and their spanwise oscillation modulated the low-frequency energy distribution of the flow, amplifying the low-frequency oscillation peak associated with the separation shock and raising the time-averaged oscillation position. Full article

The increasing power density of modern electronics demands more efficient thermal management. Heat sinks with sinusoidal fins remain understudied, and the combined effect of perforations and variable fin spacing on transient performance has not been systematically quantified. This numerical study, conducted using ANSYS Fluent 2025 R2, analyzes three sinusoidal fin configurations under forced convection (3–5 m/s): solid fins (Case A), perforated fins (Case B), and perforated fins with alternating spacing of 2 mm and 4.5 mm (Case C). The base was maintained at 60 °C during a 20 s transient period. A mesh with an average skewness of less than 0.25 ensured numerical convergence. Case B showed remarkable uniformity in the base temperature (variations < 1 °C), in contrast to Case A (variations of up to 14.17 °C), due to a thermal boundary layer restart effect induced by the perforations. Case C reached the highest heat dissipation temperatures (up to 54.64 °C at 3 m/s), representing a 47.2% increase compared to Case A, indicating more effective heat extraction with this type of separate fin. The critical transient window occurs within the first 5 s (>85% of the total temperature rise). A vertical temperature gradient of 1.19 °C/mm was observed near the base. Although the perforations reduced the heat transfer area by 5.94%, the induced turbulence compensated for this loss. Sinusoidal fins with perforations and variable spacing significantly improve convective heat removal. Full article

This paper presents internal flow measurements in two shape-transitioning nozzle ducts using planar Particle Image Velocimetry (PIV). Nozzle 1 is a converging nozzle transitioning from a square cross-section to a rectangular exit with an equivalent diameter ($D_e$) of 2.2 in, an exit aspect ratio of 6.68, and a length-to-diameter ratio ($L/D_e$) of 7.8. Nozzle 2 also converges globally but incorporates a diverging sidewall that introduces localized adverse pressure gradients. Both nozzles are tested at an exit Mach number of 0.2, corresponding to $R{e}_{D_e}\approx 2.50\times {10}^5$. Wall-normal velocity profiles reveal boundary layer thinning under favorable pressure gradients followed by thickening in regions of streamwise curvature and local adverse pressure gradients. In nozzle 2, the adverse streamwise pressure gradient along the diverging wall produces thicker boundary layers than in nozzle 1, while a cross-stream pressure imbalance shifts the velocity peak toward the diverging wall. Complementary steady RANS simulations using the k–$\omega$ SST turbulence model yield wall-normal velocity profile agreement within 2% mean absolute error for both nozzles in the upstream and mid-duct regions, with errors increasing toward the exit. Discharge coefficients from CFD and experiment agree within approximately 1%, with nozzle 1 exhibiting greater integrated losses than nozzle 2 despite thinner boundary layers at the measured plane, indicating a three-dimensional loss distribution. Independent pitot probe measurements at the nozzle exit confirm the PIV trends over the CFD predictions in the near-exit region. Full article

Accurate characterization of wind-speed distributions is essential for preliminary wind-resource assessment, vertical wind-profile evaluation, and energy-yield estimation. This study presents a CFD-assisted reconstruction and validation framework that integrates two-parameter Weibull statistics with class-conditioned OpenFOAM v13 simulations to reconstruct wind-speed distributions at different measurement heights. Hourly wind-speed records measured at 10 m and 30 m at the Sakarya–Esentepe station during the period of 2009–2010 were used. The 2009 dataset was employed to estimate the Weibull shape and scale parameters by maximum likelihood estimation, while the 2010 dataset was reserved for independent validation. To ensure methodological consistency between statistical wind characterization and steady CFD modeling, the fitted Weibull distribution was discretized into representative wind-speed classes. For each class, a steady Reynolds-averaged Navier–Stokes simulation was performed in OpenFOAM under neutral atmospheric boundary-layer assumptions using the standard k–ε turbulence model, a logarithmic inlet velocity profile, and rough-wall boundary treatment. The class-wise CFD velocity responses extracted at 10 m and 30 m were then weighted by the corresponding Weibull class probabilities to reconstruct height-specific wind-speed probability distributions. The reconstructed distributions showed good agreement with the measured and fitted Weibull references. The RMSE values obtained by CFD for measurements at heights of 10 m and 30 m on the measurement mast were 0.45 m s⁻¹ and 0.52 m s⁻¹, respectively, and the Pearson correlation coefficients were 0.97 and 0.96, respectively; these values indicate that the CFD analyses are reliable. For the Lilliefors-adjusted Kolmogorov–Smirnov statistics, there is no value higher than 0.06. The differences between the reference and CFD-reconstructed AEP estimates were +0.40% at 10 m and −1.97% at 30 m. These findings indicate that the proposed Weibull–OpenFOAM framework provides a reproducible engineering approach for CFD-assisted wind-speed distribution reconstruction and height-specific consistency assessment. However, the method should be interpreted as a class-conditioned reconstruction framework rather than a stand-alone transient atmospheric wind prediction model. Full article