Search Results (62)

This review critically analyzes the evolution of passive heat transfer enhancement in internal flows, charting a paradigm shift from momentum-based flow perturbation to the precise engineering of vortex structures. The central thesis is that the highest-performance, next-generation thermal systems will be realized through ‘flow field programming’—a unified design paradigm that intelligently architects vortex-topology and surface architecture across scales using smart materials, additive manufacturing, and artificial intelligence. This progression is traced from classical devices such as twisted tapes, which generate global swirl, to bio-inspired aerofoil inserts that efficiently produce discrete longitudinal vortices. The synergy achieved in compound systems—through the integration of geometries or the combination of inserts with advanced fluids—is identified as a key mechanism for surpassing traditional performance limits. Furthermore, applications in microscale and phase-change heat transfer, where surface engineering dominates, are explored. The novelty of this work lies in its synthesis of the underlying vortex-generation physics across diverse techniques and scales, introducing ‘flow field programming’ as a forward-looking framework for adaptive thermal management. This evolution—from static geometries to intelligent, responsive designs—is positioned to dramatically improve energy sustainability by enabling more compact, efficient, and adaptive thermal management across power generation, advanced electronics, and renewable energy systems. Full article

Corrugated insect wings inspire biomimetic aerodynamic design, yet their behaviour at low and transitional Reynolds numbers remains not fully understood. This study presents a three-dimensional computational analysis of flow over an infinite corrugated wing across Reynolds numbers from 10 to 10,000 and angles of attack from −5 to 20°, with emphasis on spanwise effects. An expanded verification and validation procedure ensured numerical reliability. At the lowest Reynolds numbers, the flow is steady and largely two-dimensional, with localised recirculation zones. As Reynolds numbers or angles of attack increase, the flow transitions to periodic vortex shedding, and three-dimensional structures appear. At a Reynolds number of ten thousand, periodic shedding occurs at zero degrees incidence, indicating a shift toward turbulent or bluff body-like behaviour. The examined corrugated profile does not exhibit a lift-to-drag benefit over smooth aerofoils in steady gliding, although root section corrugation helps delay separation in transitional regimes. This behaviour reflects mechanisms used by dragonflies to maintain stable gliding despite textured wings. By extending flow regime classification, the study identifies conditions where two-dimensional assumptions fail and highlights the influence of spanwise flow structures. These findings deepen understanding of insect wing aerodynamics and support biomimetic design of future wings. Full article

Nickel-based single-crystal superalloy turbine blades are typically manufactured via investment casting followed by a well-established heat treatment process, resulting in a uniform microstructure composed of thin γ channels and cubic-shaped γ’. However, the region near the corner of the aerofoil/platform of the blade exhibits a distinct contrast compared to the surrounding area. High-resolution scanning electron microscopy (SEM) reveals significant degradation of the γ and γ’ phases in the dark contrast region. In this area, the γ’ phase no longer maintains its characteristic cubic morphology and appears partially dissolved or even melted. Although the regularity of the γ/γ’ microstructure is disrupted, the region is still composed of irregular-shaped γ and γ’ phases. Based on these microstructural observations, a possible formation mechanism of the abnormal microstructure is discussed. Although the blades are not exposed to conventional creep conditions during casting and heat treatment, residual stress accumulated during casting may be relieved at elevated temperatures during the heat treatment process. The synergistic effect of stress, temperature, and time may contribute to the formation of the observed abnormal microstructure. Full article

Electrothermal anti-/de-icing systems are widely used in aircraft, and the structures of these systems generally consist of multiple layers laminated together. In service, laminated structures are prone to structural deformation and delamination, which can significantly affect heat conduction. Therefore, it is essential to study the temperature field of these electrically heated anti-icing structures during operation and analyse the impact of delamination damage on the temperature distribution. In this thesis, a dynamic multiphysical field study of an electric heating anti-icing structure is conducted using a thermal expansion layer-by-layer/3D solid element method. By studying the electric heating process of composite plates experiencing pre-positioned delamination, the thermal expansion layer-by-layer/3D solid element method considers the thermal convection boundary conditions as well as a constant heat source. In addition, to considering the influences of the geometric shape and delamination damage, we apply the thermal expansion layer-by-layer/3D solid element method to the electric heating anti-icing process of aerofoil structures using a coordinate transformation matrix. The calculations show that when delamination damage is located above the heating layer, the maximum temperature of the structure reaches 450 °C at 50 s, which severely affects the normal functioning of the structure. Additionally, the surface temperature of the anti-icing system decreases to the ambient temperature at the delamination. In contrast, delamination damage located below the heating layer has a minimal effect on the surface temperature distribution. Moreover, the damage caused by multiple types of damage is greater than that caused by a single type of damage. Full article

A computational fluid dynamics-based study of a corrugated wing section inspired by the dragonfly wing was performed for a low Reynolds number (10’000), focusing on gliding flight. The aerodynamic characteristics are compared to those of a typical technical aerofoil (NACA 0009). The objective of this study is to develop a simulation tool for the design and development of corrugated wings for aerospace applications and to gain a better understanding of the flow over corrugated wing sections. The simulation results were verified using a convergence study and validated by an angle of attack study and comparison with experimental results. The results demonstrated the simulations capability of predicting key flow features but there were some discrepancies from the experimental observations, mainly the prediction of the critical angle of attack. Overall, the simulation results demonstrated a comparable, if not better, aerodynamic performance compared to the technical aerofoil. Full article

This research focuses on addressing a significant concern in the aviation industry, which is drag. The primary objective of this project is to achieve drag reduction through the implementation of riblets on a wing featuring the NACA 2412 aerofoil, operating at subsonic speeds. Riblets, with the flow direction on wing surfaces, have demonstrated the potential to effectively decrease drag in diverse applications. This investigation includes computational analysis within the ANSYS Workbench framework, employing a polyhedral mesh model. The scope of this research encompasses the analysis of both a conventional wing and a modified wing with riblets. A comparative analysis is conducted to assess variations in drag values between the two configurations. Parameters, including geometry, dimensions, and riblet placement at varying angles of attack, are explored to comprehend their impact on drag reduction. Notably, 15.6% and 23% reductions in drag were identified at a 16-degree angle of attack with midspan and three-riblet models, separately. The computational mesh and method were validated using appropriate techniques. Full article

Anti-icing/de-icing is of fundamental importance in practical applications such as power transmission, wind turbines, and aerofoils. Despite recent efforts in developing engineering surfaces to delay ice accumulation or reduce ice adhesion, it remains challenging to design robust photothermal icephobic surfaces in a durable, low-cost, easy-fabrication manner. Here, we report an intelligent candle soot-based photothermal surface (PDMS/CS60@PDMS/Al) that can utilize sunlight illumination to achieve the multi-abilities of anti-icing, de-icing, and self-cleaning. Our method lies in the construction of hierarchical micro/nanostructures by depositing photothermal candle soot nanoparticles, which endow the surface with superior superhydrophobicity and excellent photothermal performance. The underlying mechanism is exploited by establishing the heat transfer model between the droplets and the cooled surface. We believe that the smart PDMS/CS60@PDMS/Al developed in this work could provide a feasible strategy to design intelligent engineering surfaces for enhanced anti-icing/de-icing. Full article

The manufacturing geometrical variability in axial compressors is a stochastic source of uncertainty, implying that the real geometry differs from the nominal design. This causes the real geometry to lose the ideal axial symmetry. Considering the aerofoils of a stator vane, the geometrical variability affects the flow traversing it. This impacts the downstream rotor, especially when considering the aeroelastic excitation forces. Optical surface scans coupled with a parametrisation method allow for acquiring the information relative to the real aerofoils geometries. The measured data are included in a multi-passage and multi-stage CFD setup to represent the mistuned flow. In particular, low excitation harmonics on the rotor vane are introduced due to the geometrical deviations of the upstream stator. The introduced low engine orders, as well as their amplitude, depend on the stator geometries and their order. A method is proposed to represent the phenomena in a reduced CFD domain, limiting the size and number of solutions required to probabilistically describe the rotor excitation forces. The resulting rotor excitation forces are reconstructed as a superposition of disturbances due to individual stator aerofoils geometries. This indicates that the problem is linear in the combination of disturbances from single passages. Full article

Bio-inspired flexible pillar-like wind-hairs show promise for the future of flying by feel by detecting critical flow events on an aerofoil during flight. To be able to characterise specific flow disturbances from the response of such sensors, quantitative PIV measurements of such flow-disturbance patterns were compared with sensor outputs under controlled conditions. Experiments were performed in a flow channel with an aerofoil equipped with a 2D array of such sensors when in uniform inflow conditions compared to when a well-defined gust was introduced upstream and was passing by. The gust was generated through the sudden deployment of a row of flaps on the suction side of a symmetric wing that was placed upstream of the aerofoil with the sensors. The resulting flow disturbance generated a starting vortex with two legs, which resembled a horseshoe-type vortex shed into the wake. Under the same tunnel conditions, PIV measurements were taken downstream of the gust generator to characterise the starting vortex, while further measurements were taken with the sensing pillars on the aerofoil in the same location. The disturbance pattern was compared to the pillar response to demonstrate the potential of flow-sensing pillars. It was found that the pillars could detect the arrival time and structural pattern of the flow disturbance, showing the characteristics of the induced flow field of the starting vortex when passing by. Therefore, such sensor arrays can detect the “footprint” of disturbances as temporal and spatial signatures, allowing us to distinguish those from others or noise. Full article

The main purpose of this investigation was to explore the heat transfer and flow characteristics of aero-foil-shaped fins combined with extended jet holes, specifically focusing on their feasibility in cooling turbine blades. In this study, a comprehensive investigation was carried out by applying impinging jet array cooling (IJAC) on a semi-circular curved surface, which was roughened using aerofoil-shaped fins. Numerical computations were conducted under three different Reynolds numbers (Re) ranging from 5000 to 25,000, while nozzle-to-target surface spacings (S/d) ranged from 0.5 to 8.0. Furthermore, an assessment was made of the impact of different fin arrangements, single-row (L₁), double-row (L₂), and triple-row (L₃), on convective heat transfer. Detailed examinations were performed on area-averaged and local Nusselt (Nu) numbers, flow properties, and the thermal performance criterion (TPC) on finned and smooth target surfaces. The study’s results revealed that the use of aerofoil-shaped fins and the reduction in S/d, along with surface roughening, led to significant increases in the local and area-averaged Nu numbers compared to the conventional IJAC scheme. The most notable heat transfer enhancement was observed at S/d = 0.5 utilizing extended jets and the surface design incorporating aerofoil-shaped fins. Under these specific conditions, the maximum heat transfer enhancement reached 52.81%. Moreover, the investigation also demonstrated that the highest TPC on the finned surface was achieved when S/d = 2.0 for L₂ at Re = 25,000, resulting in a TPC value of 1.12. Furthermore, reducing S/d and mounting aerofoil-shaped fins on the surface yielded a more uniform heat transfer distribution on the relevant surface than IJAC with a smooth surface, ensuring a relatively more uniform heat transfer distribution to minimize the risk of localized overheating. Full article

With the increasing popularity of yachting sports and races comes the need to develop a more advanced and efficient propulsion device. Significant improvement can be made when using a mainly lift-driven propulsion source, known as a wing sail. This idea, dating back as far as the mid-70s, is nowadays regaining interest as a propulsion system in multihull, high-performance racing vessels (for instance, the AC50 and AC72 America’s Cup yacht classes). This article documents 2D and 3D numerical analyses of wing sail systems imitating those of an AC72 racing yacht class. It depicts methods employed in two- and three-dimensional steady-state flow simulations, compares systems equipped with various geometries of mainsails, and details a comprehensive examination of the airflow around the vessel using spatial analyses. Numerical calculations were carried out using ANSYS CFX and ANSYS Fluent (with overset feature) for 2D and 3D models, respectively. All simulations were conducted under conditions similar to those acting on the real system, i.e., high Reynolds number (order of magnitude 10⁶ to 10⁷) and atmospheric boundary layer (in the 3D model). Full article

Ice accretion is inevitable on fix-wing UAVs (unmanned aerial vehicles) when they are applied to surveillance and mapping over colder climates and arctic regions. Subsequent aerodynamic profile changes have caused the current interest in the better prediction of the effect of icing shapes/sizes/distribution patterns on the aerodynamic performances of an aircraft. This study employs a numerical model which investigates the RG-15 aerofoil’s response to various icing scenarios at a Reynolds number of $Re=2\times {10}^5$. Under icing conditions, compared to a clean aerofoil, a reduction in the lift coefficient and an increase in the drag coefficient are observed. Lower temperatures and reduced liquid water content lead to a decrease in the maximum thickness of ice accretion on the RG-15 aerofoil. Particularly noteworthy is the 10.85% reduction in the lift coefficient at a 10° angle of attack, which is in the icing condition at −10 °C with a mean volume diameter of 15 μm. Power consumption increases in the range of 0.46% to 26.5% under various icing conditions, showing synchronization with the rise in drag coefficient. This study underscores the need for future research to investigate various cloud conditions comprehensively and deeply in the context of aerofoil icing. Full article

Drag-dominant tidal turbine energy holds tremendous clean energy potential but faces significant hurdles as unsuitability of the actuator disc model due to the varying swept blockage area, unaccounted bypass flow downstream interaction, and rotor parasitic drag, whereas blade element momentum theory is computably effective for majorly 3-blade lift-dominated aerofoil. This study validates a novel method to find the optimal TSR of any turbine with a cost-effective and user-friendly moment balancing algorithm to support robust tidal energy development. Performance analysis CFD study of Pinwheel and Savonius tidal turbines in a Biffis canal hydrodynamic system was carried out. Thrust and idle moment are analyzed as functions of only inlet fluid velocity and rotational speed, respectively. These relationships were verified through regression analysis, and the turbines’ net moment equations were established based on these parameters. In both simulation models, rotational speed and inlet velocity were proved excellent predictor variables (R² value ≈ 1) for idle and thrust moments, respectively. The optimal TSR values for Pinwheel and Savonius turbines were 2.537 and 0.671, respectively, within an acceptable error range for experimental validation. The optimal basin efficiency (η_opt, TSR) values for Pinwheel and Savonius in the 12% blockage channel were (29.09%, 4.0) and (25.67%, 2.87), respectively. The trade-off between TSR_opt and η_opt is the key instruction concerning electricity generation and environmental impact. Full article

Small-Scale Turbines (SSTs) are among the most important energy-extraction-enabling technologies in domestic power production systems. However, owing to centrifugal forces, the high rotating speed of SSTs causes excessive strains in the aerofoil portions of the turbine blades. In this paper, a structural performance analysis is provided by combining Finite Element Methods (FEM) with Computational Fluid Dynamics (CFD). The primary objective was to examine the mechanical stresses of a Small-Scale Radial Turbine (SSRT) constructed utilizing 3D printing technology and a novel plastic material, RGD 525, to construct a SSRT model experimentally. After introducing a suitable turbine aerodynamics model, the turbine assembly and related loads were translated to a structural model. Subsequently, a structural analysis was conducted under various loading situations to determine the influence of different rotational speed values and blade shapes on the stress distribution and displacement. Maximum von Mises and maximum main stresses are significantly affected by both the rotor rotational speed and the working fluid input temperature, according to the findings of this research. The maximum permitted deformation, on the other hand, was more influenced by rotational speed, while the maximum allowable fatigue life was more influenced by rotating speed and fluid intake temperature. Also, the region of the tip shroud in the rotor had greater deflection values of 21% of the blade tip width. Full article

Current performance analysis processes for drag-dominant tidal turbines are unsuitable as disk actuator theory lacks support for varying swept blockage area, bypass flow downstream interaction, and parasitic rotor drag, whereas blade element momentum theory is computably effective for three-blade lift-dominated aerofoil. This study proposes a novel technique to calculate the optimal turbine tip speed ratio (TSR) with a cost-effective and user-friendly moment balancing algorithm. A reliable dynamic TSR matrix was developed with varying rotational speeds and fluid velocities, unlike previous works simulated at a fixed fluid velocity. Thrust and idle moments are introduced as functions of inlet fluid velocity and rotational speed, respectively. The quadratic relationships are verified through regression analysis, and net moment equations are established. Rotational speed was a reliable predictor for Pinwheel’s idle moment, while inlet velocity was a reliable predictor for thrust moment for both models. The optimal (C_p, TSR) values for Pinwheel and Savonius turbines were (0.223, 2.37) and (0.63, 0.29), respectively, within an acceptable error range for experimental validation. This study aims to improve prevailing industry practices by enhancing an engineer’s understanding of optimal blade design by adjusting the rotor speed to suit the inlet flow case compared to ‘trial and error’ with cost-intensive simulations. Full article