Erosion resistance of basalt fiber-aeolian sand concrete under wind-sand erosion: Experimental analysis and mechanisms

Influence of front airfoil leading-edge serrations on turbulence interaction noise characteristics of tandem airfoils at different angles of attack

The efficacy of compliant surfaces for load alleviation during aircraft manoeuvres or in turbulent gusts was investigated. A rectangular wing with a NACA0012 profile and a semi aspect-ratio of sAR = 5 was tested in a wind tunnel at a chord Reynolds number of 300,000 by means of lift, drag, wing root bending moment, flow fields, and compliant surface deformation measurements. The compliant surfaces with both ends fixed on the suction surface near the leading edge formed a hump which acted like rigid spoilers for separation control and led to substantial lift reduction. Similar lift reduction performance was also observed with leading-edge inverted compliant surfaces that exhibit steady large deflection to induce massive flow separations, thus led to a maximum lift reduction of 44% at the angle of attack of α = 10°. The trailing-edge inverted compliant surfaces with both steady deflections and limit-cycle flapping motions demonstrated a nearly constant lift reduction of up to Δ C L ≈ -0.28 by deflecting its wake flows upwards and reducing the circulation of the wing. When α increased beyond a critical value, both self-activated compliant spoilers and rigid spoilers with compliant hinges flipped over towards the upper surface, created massive flow separations over the wing and led to a maximum lift reduction of 32% at α = 10°. However, hysteresis loops in lift and drag appear when decreasing the angle of attack as both compliant and rigid spoilers remained on the upper surface of the wing and this requires future investigations. Nevertheless, to the best of our knowledge, this was the first time that compliant surfaces were employed for loads alleviation, and it provided a very cost-effective mechanism that can potentially eliminate the need for heavy mechanical surfaces such as trailing edge flaps or fluidic actuators.

This paper presents an experimental investigation into gust load alleviation using an actively controlled folding wingtip concept. The system employs a proportional–integral–derivative controller driven by real-time feedback from the wing root bending moment (WRBM) to dynamically adjust the wingtip deflection during gust encounters. Experiments were conducted in a closed-circuit wind tunnel under both 1−cosine and harmonic gust excitations, covering a range of gust frequencies and angles of attack. Time-domain measurements of WRBM and wingtip angle were used to evaluate performance based on two metrics: i) peak load reduction relative to a fixed-tip baseline and ii) cycle work, quantifying control effort and hysteresis. The active folding wingtip achieved consistent load mitigation across the test envelope, with maximum reductions of approximately 44% in positive peaks and 31% in negative peaks near the first bending resonance. A clear correlation was observed between enhanced load relief and increased actuation work, providing guidance for gain scheduling and actuator sizing. Overall, the results demonstrate the effectiveness of feedback-controlled folding wingtips as a practical, broadband approach for gust load alleviation in high-aspect-ratio wings.

The AIAA workshop series supports the computational fluid dynamics (CFD) community through impartial evaluation of publicly available test case submissions to establish and improve the state-of-the-art in applied CFD. The Fifth AIAA CFD High Lift Prediction Workshop (HLPW-5) is organized to assess the numerical prediction and physical modeling capabilities of CFD technology for swept wings in landing and takeoff high-lift configurations. Multiple Common Research Model High-Lift variants are assessed, and the Mesh Adaptation Technical Focus Group submissions are summarized. Test Case 1 focuses on turbulence model verification. Variation between methods is low for a fuselage with a single-element wing, which allowed for convincing verification of two Spalart–Allmaras turbulence model variants. Test Case 2 provides an incremental high-lift component buildup to isolate the influence of geometry. Variation between methods increases slightly with a deployed leading-edge slat and increases dramatically with the addition of trailing-edge flaps. Comparisons to experiment and between submissions are favorable for the configuration without trailing-edge flaps at low and moderate angles of attack, which roughly defines the validation and validity threshold of existing methods using steady Reynolds-averaged Navier–Stokes (RANS) turbulence models. Documenting this validity threshold sets the stage for developing RANS modeling improvements.

This study investigates the aerodynamic forces and moments acting on a women's discus as functions of angle of attack, freestream velocity, and spin rate about its axis of symmetry. Wind tunnel experiments were conducted to measure these aerodynamic forces and moments and to visualize the flow field using oil-flow visualization and particle image velocimetry (PIV). The results show that no significant dependence of the aerodynamic coefficients on the spin parameter was observed within the tested ranges (20-30m/s; 0-7 rev/s). The drag, lift, and pitching moment coefficients depend strongly on the angle of attack, whereas the side force and the rolling and yawing moment coefficients remain approximately zero. The drag, lift, and pitching moment coefficients increase with angle of attack until stall occurs at approximately 28-30°, after which the lift and pitching moment decrease sharply. Stall recovery occurs at a lower angle of attack, around 25°, corresponding to a hysteresis window of approximately 4-5°. Surface static pressure measurements and flow visualizations suggest that this hysteresis is associated with the history-dependent formation and collapse of a leading-edge laminar separation bubble, which appears during increasing-angle-of-attack process with flow reattachment and disappears during the decreasing-angle-of-attack process.

This study investigates the aerodynamic characteristics of crescent-shaped iced conductors through combined wind tunnel experiments and numerical analysis. Wind tunnel tests were conducted to obtain both steady and unsteady aerodynamic coefficients, the latter measured using an oscillating conductor model. The steady coefficients were acquired under various wind velocities ranging from 10 to 18m/s and ice thicknesses of 14, 24 and 33mm, covering trans-critical and super-critical Reynolds number regimes. Analytical expressions relating steady coefficients to the angle of attack were derived via polynomial fitting. A BP neural network model was subsequently developed and trained on this experimental data to predict aerodynamic coefficients for untested conditions. Furthermore, a MATLAB-based quasi-static model was established to convert steady coefficients into unsteady equivalents, enabling a direct comparison with the unsteady oscillation test data to validate the quasi-static assumption. The results confirm that the quasi-static assumption retains reasonable applicability in the studied regime. More importantly, the developed BP neural network demonstrates robust predictive capability, with its outputs showing close agreement with wind tunnel measurements, achieving determination coefficients exceeding 0.95. This work provides enhanced analytical tools and validated data for improving the prediction of conductor galloping-a critical wind-induced vibration-thereby contributing to the safety assessment and structural design of overhead transmission lines.

Envenomation is a complex process involving multi-physics interactions between the fang, the liquid venom, and the tissue of the target. Direct measurements of how fang shape modulates in-wound venom transport are scarce, as most studies isolate puncture performance or conduit hydrodynamics. It is widely assumed that tubular anterior fangs enable the most rapid, high-pressure delivery, but rigorous cross-type, standardized comparisons of delivery efficiency are limited. Here, we present the design and validation of Bite-Bot, a robotic platform designed to facilitate highly controlled experiments that intend to reveal the constituent and combined effects of evolutionary variation in the envenomer and the target tissue. First, we obtained uCT scans of snake fangs that varied in overall shape and venom delivery mechanism and 3D printed them in titanium. Our robot controls the angle of attack, speed, and force of the bite. The robot also injects our bespoke venom phantom, which matches the rheological properties of specific snake species, at a given pressure. By leveraging robotics, we can now more holistically and empirically study the complex physical interactions and the coevolution between the envenomer and the target tissue.

The aerodynamic efficiency of conventional lifting-wing quadrotors is severely constrained by the rigid coupling between fuselage pitch attitude and wing angle of attack (AoA), which prevents the vehicle from maintaining optimal lift-to-drag performance across varying flight speeds. This study presents a novel variable-incidence lifting-wing quadrotor that effectively decouples fuselage attitude from wing aerodynamics. The proposed mechanism incorporates a 143g lightweight lifting wing and a dual-actuator drive system, with a total structural mass penalty of only 209g. High-fidelity Computational Fluid Dynamics (CFD) simulations, reveal that the variable-incidence strategy alleviates detrimental rotor-wing interference. Specifically, a fuselage pitch of - 20° combined with a wing AoA of 10°-12° reestablishes a strong suction peak on the wing's upper surface, maximizing passive lift. Systematic flight experiments validate the decoupling control strategy, demonstrating that the prototype achieves a maximum normalized power-saving ratio of 42.98% at 10m/s relative to hover. Furthermore, even when accounting for the 209g structural weight penalty, the design provides a net 13.22% efficiency improvement over the fixed-incidence concept of the original RflyLW. Leveraging these aerodynamic enhancements, predictive analyses indicate that the UAV can achieve an extended maximum flight endurance of 46.8min and a practical range of 28.1km. These results, showing high consistency between numerical predictions and experimental data, offer a robust and highly efficient solution for extending the endurance of UAVs in energy-constrained environments.

To address the limited understanding of the aerodynamic characteristics of bird-inspired flapping-wing aircraft across different flight phases and the unclear flow field interaction mechanisms between the wings and tail, this study performs three-dimensional numerical simulations based on a self-developed prototype using ANSYS Fluent and the overset mesh method. The aerodynamic effects of key tail parameters under different flight conditions are quantitatively evaluated, and the mechanisms of bidirectional wing-tail aerodynamic coupling are investigated. The results show that tail twist has a negligible influence on instantaneous lift and thrust during level flight, with a maximum variation of only 0.2 N, but significantly affects the overall aerodynamic moments of the aircraft. When the tail twist angle increases from 15° to 20°, the pitching moment increases by 6%. In contrast, during climbing flight, the tail pitch angle has a pronounced effect on lift and thrust, and its aerodynamic influence depends strongly on the aircraft angle of attack. At an aircraft angle of attack of 15°, the difference between the maximum and minimum cycle-averaged pitching moments reaches 0.2 N·m. Further analysis of vorticity fields and pressure distributions confirms the existence of distinct wing-tail aerodynamic coupling. The tail not only directly modifies the aerodynamic forces and moments acting on the aircraft but also alters the wing-generated flow structures, while the wing wake simultaneously influences the aerodynamic effectiveness of the tail. This bidirectional wing-tail aerodynamic coupling plays a critical role in shaping the aerodynamic response of the aircraft under different flight conditions. These findings clarify the aerodynamic roles of key tail parameters and reveal the underlying flow field interaction mechanisms across different flight phases, providing a theoretical basis for motion-parameter optimization and precise attitude control of bird-inspired flapping-wing aircraft.

Accurate and rapid aerodynamic prediction is essential for projectile trajectory simulation and digital twin driven exterior ballistic systems, where conventional CFD methods are computationally expensive and difficult to deploy in real-time applications. To address this challenge, this paper proposes a primary-residual dual-stage surrogate modeling method based on a multilayer perceptron (MLP). A primary prediction model for aerodynamic parameters is constructed using CFD simulation data, where Mach number and angle of attack are used as input variables to establish the global nonlinear aerodynamic mapping. By introducing a residual learning mechanism, a compensation model is established to address fitting deviations in highly nonlinear regions, thereby correcting the nonlinear biases of the primary model predictions. The residual network further captures localized nonlinear discrepancies not fully resolved by the primary model, significantly improving prediction accuracy in high-Mach-number and large-angle-of-attack regions. Comparative validation against polynomial fitting, RBF, and single-stage MLP models shows that the proposed method achieves the best overall performance. For example, the RMSE is reduced from 2.91 to 0.87 for lift prediction and from 0.634 to 0.086 for pitching moment prediction. Overall, the proposed model reduces the average RMSE by approximately 50% across all aerodynamic parameters, demonstrating stronger robustness, improved generalization capability, and practical engineering applicability for digital twin based projectile exterior ballistic prediction.

The present study investigates the entropy-generation and irreversibility characteristics of air flow across a fin-and-tube heat exchanger fitted with rectangular winglet pairs (RWPs). A three-dimensional computational fluid dynamics analysis was carried out for Reynolds numbers between 2000 and 4000 and angles of attack of 15°–60°, considering RWP locations at upstream, adjacent, and downstream positions relative to the tube centerline. The total, thermal, and viscous entropy-generation rates were evaluated using second-law formulations, and exergy-based parameters such as the entropy-generation ratio (EGR), irreversibility distribution ratio, Bejan number, and thermal efficiency index were employed to assess overall performance. Results show that an upstream RWP at 30° angle of attack and Reynolds number of 3000 provides the best thermodynamic performance, reducing the total entropy-generation rate by approximately 17% (EGR = 0.83) and increasing the heat-transfer improvement number by about 18%. The Bejan number remains above 0.95 for all cases, confirming that heat-transfer-related irreversibility dominates over viscous effects. Exergy analysis further indicates that the total irreversibility decreases while the thermal improvement factor increases with optimized RWP placement. The findings offer practical guidance for the design of energy-efficient fin-tube heat exchangers using vortex generators.

This paper presents a computational investigation of aero-optic aberrations that arise when multiple lateral jets are used to control a supersonic interceptor. Reynolds-averaged Navier–Stokes simulations are employed to examine the flow structure and evaluate the effects of various parameters, including altitudes ranging from 30–50 km, angles of attack (AOAs) from −15 to 25 deg, and four distinct jet configurations. the flow structure are analyzed by calculating the optical path difference (OPD) and normalizing it through scale analysis. When the jet flow does not interfere with the seeker’s field of view (FOV), the normalized OPD is predominantly governed by the bow shock and the conical expansion region in front of the vehicle head and exhibits similar profiles along the beam path for all altitudes. When the jet flow is introduced, the separation shock and bubble induced by jet interaction interfere with the seeker’s FOV at altitudes over 35 km and AOAs over 15 deg. Multijet cases at 35 km show that the separation bubble blocks a larger portion of the seeker’s FOV and increases the normalized OPD at higher AOA as the per-jet strength increases. For the most severe degradation case, unsteady delayed detached eddy simulation results predict a time-averaged normalized OPD that is about 20% larger than the steady-state counterpart.

Recent studies have revealed exceptionally low transition N-factors (below 2) based on modal instabilities for the leeward ray of yawed cones in the wind tunnels, suggesting that nonmodal growth mechanisms could potentially play a significant role. In light of these findings, the present work employs optimal growth theory to examine linear evolution of optimal disturbances on the leeward side of cones at 2° and 4° angles of attack in high-speed flows. Three distinct types of optimal disturbances are identified: low-frequency disturbance, Mack-mode-like disturbance, and entropy-layer disturbance. Among these, low-frequency disturbances exhibit the highest N-factors of approximately 5.5 near experimentally observed transition locations. Aside from the entropy-layer disturbance which relies solely on the Orr mechanism, the other optimal disturbances initially leverage the lift-up or Orr mechanism and progressively transition to growth driven by the modal instability mechanism downstream. The dominant energy production for all three types of disturbances mainly comes from the wall-normal shear of the base flow. Specifically, the low-frequency and Mack-mode-like disturbances gain energy inside the boundary layer, whereas the entropy-layer disturbance obtains its energy within the entropy layer region outside the boundary layer.

This paper investigates entry guidance for the second stage of super heavy-lift launch vehicles, which are lifting-body vehicles equipped with aerodynamic control surfaces. The vehicle performs a gliding entry, demanding very high targeting accuracy. Existing methods relying solely on bank-angle control typically achieve only kilometer-level targeting accuracy. This paper proposes a predictor–feedback entry guidance method realizing meter-level targeting accuracy. The high accuracy necessitates the use of both angle of attack and bank angle as controls. However, this leads to a difficulty in that the controls have a strong coupled effect on the downrange and cross-range errors. To address this, the proposed method first applies reference control profiles to predict the terminal position error, then introduces an appropriate transformation to obtain a transformed terminal position error. This error serves as feedback to the designed guidance laws for computing the control commands. A unique property is the near decoupling of the controls’ influence on the transformed error, enabling significant improvement in targeting accuracy. Path constraints on heating rate, dynamic pressure, and load factor are also incorporated via reference control refinement. Notably, the proposed entry guidance’s stability is theoretically established. Numerical results clearly demonstrate the effectiveness, strong robustness, and high targeting accuracy of the proposed method.

Symmetry breaking and wake reorganization of flow past a square cylinder at small angles of attack

We present an adaptive flow control strategy for a turbulent separated flow using online dynamic mode decomposition. The system dynamics are identified in real time, and a linear quadratic tracking controller regulates the separation location along a predefined target. Controller gains are updated continuously based on the new system updates, allowing for an adaptive formulation of real-time feedback control that can adjust to both variations in the freestream flow due to external disturbances and actuation-induced changes of the flow dynamics. The approach is demonstrated on a NACA4412 wing at Re=50,000 using direct numerical simulation at 0 and 10 deg angles of attack, outperforming steady blowing in moving the separation point downstream. At 10 deg, adaptive control increases lift to drag by approximately 60%. The framework is further extended to directly regulate the lift-to-drag ratio, illustrating its potential for real-time control of aerodynamic forces in unsteady, separated flows.

Active flow control of high-lift multielement swept wings remains a critical yet underexplored field in aerodynamics. This study investigates the effects of the duty cycle (DC) and the jet-to-freestream velocity ratio (VR) on pulsed jet flow control (PJFC) actuators near the leading edge of a multielement swept wing with three major innovations. First, a threshold effect is identified at VR≈7.30. Below this threshold, a low DC actuation achieves comparable or superior maximum lift enhancement relative to a high DC operation. Second, mechanistic analysis reveals that at a high DC, the initial jet-induced vortex fails to merge with the dominant shear-layer vortex, leading to the emergence of an additional high-frequency shedding mode. In contrast, a low DC actuation increases the maximum lift coefficient by expanding the favorable suction pressure region, particularly at a lower VR. Third, PJFC delays the stall angle by approximately 4–6 degrees and achieves significant drag reduction at moderate angles of attack. These findings provide novel insights into the underlying mechanisms and enable a physics-informed selection of the VR and DC in effective active flow control on swept high-lift wings.

The effect of pitch angle on blade loading and in-rotor wake dynamics in an H-type vertical axis wind turbine

The key to improving ship wind energy utilization efficiency lies in optimizing the aerodynamic performance of suction-type turbosails, yet the coupling mechanism of suction port position (α) and suction intensity (γ) remains unrevealed. Focusing on the attack angle of β = −15°, this study established a two-dimensional numerical simulation using the renormalization group k–ε turbulence model and semi-implicit method for pressure-linked equations algorithm to explore the coupling effect of α (5°–85°) and γ (0.2–2.0). Results show a significant synergistic regulation with three distinct regimes of aerodynamic performance. The optimal parameter range was identified as α = 35°–55° coupled with γ = 1.2–2.0, achieving high lift coefficient (CL = 5.168–6.217), low drag coefficient (CD = 0.290–0.556), and high lift-drag ratio (R = 10.652–21.241). Flow field analysis confirms favorable pressure gradient, over 85% airflow attachment rate, and a uniform and well-organized time-averaged wake structure. A three-level parameter zoning system was proposed. This study quantifies the α–γ coupling regulation law, fills the theoretical gap of multi-parameter collaborative optimization for turbosails, and provides directly applicable design criteria for full-scale ships, contributing to shipping decarbonization.