Leading Edge Research Articles

Numerical Analysis of Broadband Noise Generated by an Airfoil with Spanwise-Varying Leading Edges

Here, the single-target parameterization of alternatives to leading-edge noise is carried out using analytical models based on the Wiener–Hopf technique. Four leading-edge serration profiles with different frequencies, amplitudes, and phases are implemented to aid the understanding of sound suppression mechanisms. The effects of the serrated shape factor, wavelength, and amplitude are analyzed at tip-to-root ratios of 0.5, 1, and 2, respectively. An effective double-wavelength sinusoidal serration design can substantially reduce the noise emissions of 5.2 dB at h¯ = 2. Additionally, compared to single-wavelength serrations, an additional 1.47 dB noise reduction effect can be obtained by double-wavelength serrations under the appropriate design parameters. The surface pressure and phase distribution of different spanwise-varying leading edges indicate that the phase interference effect affected by source-radiated noise reduction is enhanced by this serration at the hills for serrations with a small curvature, and noise emission in the low-frequency band is more effectively suppressed. The sharper the serration is, the more conducive it is to a reduction in high-frequency noise. Nevertheless, the effectiveness of serrations is usually partially limited by the non-negligible trailing-edge self-noise. The sound source intensity of the root is decreased by the ogee-shaped serrations with a large curvature transition. A secondary noise reduction mechanism with a local source cut-off effect caused by nonlinearity is demonstrated.

Purge–Mainstream Interactions in a Turbine Stage With Rotor Endwall Contouring

Abstract Purge flows are prevalent in modern gas turbine design, allowing for increased turbine entry temperatures. The purge flow passes through a rim seal and interacts with the mainstream flow, modifying the blade secondary flow structures and reducing stage efficiency. These structures may be controlled using end wall contouring (EWC), though experimental demonstration of their benefit is seldom reported in the literature. The optically accessible turbine at the University of Bath was designed to directly measure and visualize the flow field within the blade passage for a rotor with EWC. The single-stage turbine enables phase-locked flow field measurements with volumetric particle image velocimetry (PIV). Purge flow was supplied to investigate a range of operating conditions in which the secondary flow structures were modified. The modular turbine rotor allowed for expedient change of a bladed ring, or bling, featuring non-axisymmetric EWC. The identified secondary flow structures were the pressure-side leg of the horse shoe vortex (PS-HSV) and an egress vortex (EV) of concurrent rotational direction. An increase in purge flowrate monotonically shifted the EV toward the suction-side (SS) of the adjacent blade. The migration of the PS-HSV toward the SS caused the two aforementioned vortices to merge. The EWC rotor design included a leading-edge (LE) feature to alter the PS-HSV and a trough to guide the EV low spanwise in the passage and maintain displacement from the adjacent suction-side. The EWC rotor was found to be effective at altering the formation and positioning of the secondary flow structures at a range of purge flow conditions.

The analog front end for FastRICH: an ASIC for the LHCb RICH detector upgrade

This work presents the analog circuitry of the FastRICH ASIC, a 16-channel ASIC, developed in a 65 nm CMOS technology specifically designed for the RICH detector at LHCb to readout detectors like Photomultiplier Tubes to be used at the LHC Run 4 and Silicon Photomultipliers candidates for Run 5. The front-end (FE) stage has an input impedance below 50 Ω and an input dynamic range from 5 μA to 5 mA with a power consumption of ∼5 mW/channel. The chip includes a Leading Edge Comparator (LED) and a Constant Fraction Discriminator (CFD) for time pick-off and a Time-to-Digital Converter (TDC) for digitization.

Comparative Assessment on Unsteady Aerodynamics of Thin and Thick Airfoils Subjected to Pitching Motion

This article presents the comparison between the unsteady flow characteristics of thick (t/c ≥ 6%) and thin (t/c ≤ 6%) airfoils performing pitching motion at Reynolds number Re = 3.6 × 10 5 . For the analysis, the considered airfoils are NACA 0012 as thick and symmetric airfoil and GOE 417A as thin and highly cambered airfoil. The analysis in this study is restricted to only two airfoils because from the preliminary investigations, similar aerodynamic characteristics with slight variation in their flow field development under same conditions were observed. The influence of reduced frequency, pitching amplitude and mean angle of attack on the airfoil’s aerodynamic performance in terms of instantaneous force coefficients is thoroughly investigated. Further, the flow surrounding the airfoils is also investigated. It is noticed that the aforementioned parameters substantially affect the instantaneous force coefficients (both qualitatively and quantitatively). Under certain conditions, the formation of reverse Karman vortex street was observed indicating airfoil’s thrust force generation. It must be noted that the conditions where the thrust force generation occurs for thick and symmetric airfoils like NACA 0012 are quite different from that of thin and cambered airfoils like GOE 417A. Additionally, a drastic change in the flow field around the airfoils is observed under similar conditions. For NACA 0012 airfoil, the formation and convection of the Leading Edge Vortex (LEV) under certain conditions has detrimental effects on its aerodynamic characteristics as it encourages early flow separation. However, the same cannot be true for thin and highly cambered airfoils like GOE 417A. Under the similar conditions with negligible variation, the LEV contributes toward providing extra suction over the GOE 417A airfoil’s suction side. This significantly improves airfoil’s aerodynamic characteristics.

Numerical Analysis of the Wing Leading Edge Electro-Impulse De-Icing Process Based on Cohesive Zone Model

Aircraft icing has historically been a critical cause of airplane crashes. The electro-impulse de-icing system has a wide range of applications in aircraft de-icing due to its lightweight design, low energy consumption, high efficiency, and other advantages. However, there has been little study into accurate wing electric-impulse de-icing simulation methods and the parameters impacting de-icing efficacy. Based on the damage mechanics principle and considering the influence mechanisms of interface debonding and ice fracture on ice shedding, this paper establishes a more accurate numerical model of wing electric-impulse de-icing using the Cohesive Zone Model (CZM). It simulates the process of electric-impulse de-icing at the leading edge of the NACA 0012 wing. The numerical results are compared to the experimental results, revealing that the constructed wing electro-impulse de-icing numerical model is superior. Lastly, the effects of varying ice–skin interface shear adhesion strengths, doubler loading positions, and impulse sequences on de-icing effectiveness were studied. The de-icing rate is a quantitative description of the electro-impulse’s de-icing action, defined in the numerical model as the ratio of cohesive element deletions to the total elements at the ice–skin interface. The findings reveal that varying shear adhesion strengths at the ice–skin interface significantly impact the de-icing effect. The de-icing rate steadily falls with increasing shear adhesion strength, from 66% to 56%. When two, four, and seven impulses were applied to doubler two, the de-icing rates were 59%, 71%, and 71%, respectively, significantly increasing the de-icing efficiency compared to when impulses were applied to doubler one. Doubler one and two impulse responses are overlaid differently depending on the impulse sequences, resulting in varying de-icing rates. When the impulse sequence is 20 ms, the superposition results are optimal, and the de-icing rate reaches 100%. These studies can guide the development and implementation of a wing electric-impulse de-icing system.

Heat Transfer and of Flow Structure of a Turbine Blade’s Air-cooled Leading Edge Considering Different Hole Shapes and Additional Flow Angles

Heat Transfer and of Flow Structure of a Turbine Blade’s Air-cooled Leading Edge Considering Different Hole Shapes and Additional Flow Angles

Rain erosion atlas for wind turbine blades based on ERA5 and NORA3 for Scandinavia

Leading edge erosion on wind turbine blades is a common issue, particularly for wind turbines placed in regions characterized by high wind speeds and precipitation. This study presents the development of a rain erosion atlas for Scandinavia and Finland, based on ERA5 reanalysis and NORA3 mesoscale model data on rainfall intensity and wind speed over five years. The IEA 15 MW reference wind turbine is used as an example to evaluate impingement water impact and erosion onset time for a commercial coating material. The damage progression is modeled by combining the wind speed and rainfall data with an empirical damage model that relates impinged water (H) as a function of impact velocity to the time of erosion onset. Comparative analyses at two weather station locations show that NORA3 data more accurately aligns with measurements in terms of power spectral density, mean wind speed, rainfall, and erosion prediction than ERA5. NORA3-based atlas layers offer finer spatial detail and predict shorter erosion onset times over land compared to ERA5, particularly in complex terrain. Conversely, the ERA5-based atlas suggests a shorter onset of erosion offshore. Based on NORA3 data, erosion onset time is estimated at 5 years on average for Baltic Sea wind farm sites and 3.2 years for sites in the North Sea.

Heat Transfer and Flow Characteristics of Channel Impingement Cooling Structure at Leading Edge Inside Turbine Blades Using Large Eddy Simulation

Abstract As a main part of multichannel wall jet cooling structure, channel impingement cooling is a cooling strategy of great concern at the leading edge inside of the turbine blade. In this paper, heat transfer and flow behavior in the channel impingement cooling structure are investigated by large eddy simulation (LES). The results imply that impingement created by curvature-induced centrifugal instabilities in the turning region of the cooling channel is dominated by a streamwise vortex system containing a counter-rotating Dean vortex, which presents high heat transfer streaks along the streamwise direction on the target wall. The intensely unsteady nature of the cooling jet induced by a lack of equilibrium between the pressure gradient and the centrifugal force is precisely captured herein by LES. An attaching-wall jet formed on the outer wall downstream of the cooling channel has highly three-dimensional characteristics not observed by Reynolds-averaged Navier–Stokes equations (RANS). Heat transfer augmentation on the target wall of the cooling channel is mainly due to the intensifying streamwise vortex system developing in the turning region as driven by the centrifugal force. This research work will provide a reference for the optimization and application of multichannel wall jet cooling for gas turbine blades.

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Aerodynamic Performance Enhancement of Low Aspect Ratio Military Drone Aircraft Wing through Employing Leading Edge Tubercles

Present study aim to improve the aerodynamic performance of low Aspect Ratio (AR) military drone aircraft wing, through employing leading edge tubercle. For that purpose two wing model were design one with smooth leading edge and second with tubercle leading edge. The wing models were developed by using NACA0012 airfoil profile, whereas tubercles of amplitude 5% of chord (c) and wavelength of 11% of c is employed. The numerical simulation as performed at chord based Reynolds number of 140000 in pre-stall and post stall regime. The computational fluid dynamic simulation is performed at different angle of attack ranging from 0 degree to 25 degree with the interval of 5 degree. Computational Fluid Dynamics (CFD) results reveal that tubercle at the leading edge of the low AR wing has favorable effect on the wing performance. Aerodynamic performance of both smooth leading edge and tubercle leading edge wing is similar up to 15o angle of attack, whereas at 20 degree and 25 degree significant improvement in Lift-to-Drag L/D ratio is observed. It is estimated that at maximum increment of 53% in lift coefficient ii achieved at 25 degree angle of attack for as compared to smooth LE wing model. Moreover, maximum 20.5% decrease in drag coefficient is estimated in case of tubercle leading edge as compared to baseline model at 20 degree angle of attack. The critical observation of field around the tubercle leading edge wing is found that tubercles restrict flow separation through generation of low strength vortices; these vortices enhance momentum exchange within the boundary layer.

Vortex dynamics and boundary layer transition in flow around a rectangular cylinder with different aspect ratios at medium Reynolds number

The numerical investigation focuses on the flow patterns around a rectangular cylinder with three aspect ratios ( $L/D=5$ , $10$ , $15$ ) at a Reynolds number of $1000$ . The study delves into the dynamics of vortices, their associated frequencies, the evolution of the boundary layer and the decay of the wake. Kelvin–Helmholtz (KH) vortices originate from the leading edge (LE) shear layer and transform into hairpin vortices. Specifically, at $L/D=5$ , three KH vortices merge into a single LE vortex. However, at $L/D=10$ and $15$ , two KH vortices combine to form a LE vortex, with the rapid formation of hairpin vortex packets. A fractional harmonic arises due to feedback from the split LE shear layer moving upstream, triggering interaction with the reverse flow. Trailing edge (TE) vortices shed, creating a Kármán-like street in the wake. The intensity of wake oscillation at $L/D=5$ surpasses that in the other two cases. Boundary layer transition occurs after the saturation of disturbance energy for $L/D=10$ and $15$ , but not for $L/D=5$ . The low-frequency disturbances are selected to generate streaks inside the boundary layer. The TE vortex shedding induces the formation of a favourable pressure gradient, accelerating the flow and fostering boundary layer relaminarization. The self-similarity of the velocity defect is observed in all three wakes, accompanied by the decay of disturbance energy. Importantly, the decrease in the shedding frequency of LE (TE) vortices significantly contributes to the overall decay of disturbance energy. This comprehensive exploration provides insights into complex flow phenomena and their underlying dynamics.

Design of Sinusoidal Leading Edge for Low-Speed Axial Fans Operating under Inflow Distortion

Axial fans may be equipped with passive flow control devices to enhance rotor efficiency or minimize noise emissions. In this regard, blade designs influenced by biomimicry, such as rotors with sinusoidal leading edges (LEs), have gained popularity in recent years. However, their design is predominantly driven by a trial-and-error approach, with limited systematic studies on the influence of rotor performance. Furthermore, their effectiveness is typically evaluated under controlled conditions that may significantly differ from operations in real installation layouts. In this work, a systematic review of the design process for sinusoidal LE axial fan rotors is provided, aiming to summarize previous design experiences. Then, a modified sinusoidal LE is designed and fitted to a 7.3 m low-speed axial fan for air-cooled condensers (ACCs). These fans operate at environmental conditions, providing a quasi-zero static pressure rise, often with inflow non-uniformities. A series of RANS computations were run to simulate the performance of the baseline fan and that of the sinusoidal leading edge, considering a real installation setup at Stellenbosh University, where the ACC is constrained between buildings and has a channel running on the ground below the fan inlet. The aim is to explore the nonbalanced inflow condition effects in both rotor geometries and to test the effect of the installation layout on fan performance. The results show that the modification to the rotor allows for a more even distribution of flow in the blade-to-blade passages with respect to the baseline geometry.

Dynamically Mapping the Topography and Stiffness of the Leading Edge of Migrating Cells Using AFM in Fast-QI Mode.

Cell migration profoundly influences cellular function, often resulting in adverse effects in various pathologies including cancer metastasis. Directly assessing and quantifying the nanoscale dynamics of living cell structure and mechanics has remained a challenge. At the forefront of cell movement, the flat actin modules─the lamellipodium and the lamellum─interact to propel cell migration. The lamellipodium extends from the lamellum and undergoes rapid changes within seconds, making measurement of its stiffness a persistent hurdle. In this study, we introduce the fast-quantitative imaging (fast-QI) mode, demonstrating its capability to simultaneously map both the lamellipodium and the lamellum with enhanced spatiotemporal resolution compared with the classic quantitative imaging (QI) mode. Specifically, our findings reveal nanoscale stiffness gradients in the lamellipodium at the leading edge, where it appears to be slightly thinner and significantly softer than the lamellum. Additionally, we illustrate the fast-QI mode's accuracy in generating maps of height and effective stiffness through a streamlined and efficient processing of force-distance curves. These results underscore the potential of the fast-QI mode for investigating the role of motile cell structures in mechanosensing.

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Investigation on Aerodynamic Robustness of Compressor Blade with Asymmetric Leading Edge

Investigation on Aerodynamic Robustness of Compressor Blade with Asymmetric Leading Edge

Numerical study of the evolution of unsteady cavitation flow around hydrofoils with leading-edge tubercles

Humpback leading-edge (LE) tubercles are applied to the cavitation control of hydrofoils, and the effect of LE tubercles on hydrofoil cavitation characteristics under different cavitation numbers (σ) is discussed. The results show that LE tubercles can promote hydrofoil initial cavitation, with cavitation appearing first in the groove. This is because the separation effect of LE tubercles induces flow from peak to trough, resulting in an accelerated flow rate and a local low-pressure area. The quasiperiodic properties of the cloud-cavitation stage are not improved, but LE tubercles considerably reduced hydrofoil cavitation, resulting in a cavitation volume reduction of roughly 16.5%–20.4% and maximum cavitation volume reduction of roughly 10.5%–21.8%. The flow field at the tubercle was analyzed, and it was found that vortex cavitation was induced by the spiral vortex. The pressure pulsation on the hydrofoil is highly related to the cavitating evolution. The dominant frequency of the pressure pulsation increases with the decrease of σ and is not affected by the LE tubercles. Finally, LE tubercles are observed to facilitate the transformation of laminar flow to turbulent flow, hence increasing wake disturbance and facilitating the disintegration of the wake vortex structure.

Reliability-based leading edge erosion maintenance strategy selection framework

Leading edge erosion has become one of the most prevailing failure modes of wind turbines. Its effects can evolve from an aerodynamic modification of the properties of the blade to a potential structural failure of the leading edge. The first produces a reduction of energy production and the second can produce a catastrophic failure of the blade. Considering the uncertainties and constraints involved in the design of optimal operation and maintenance (O&M) strategies for offshore assets and the influence of site-specific parameters on the dynamics of this particular failure mode, the task becomes complex. In this study, a framework to evaluate the influence of different maintenance strategies considering uncertainties in weather, material behaviour and repair success is presented. Monte Carlo Simulation (MCS) is used alongside a computational framework for Leading Edge Erosion (LEE) degradation to evaluate the lifetime cost distribution and probability of failure of the chosen maintenance strategies. The use of the framework is demonstrated in a case study considering a 5-MW offshore wind turbine located in the north of Germany. The influence of the modification of the maintenance interval or time between repairs and the comparison with maintenance activities executed only during months with milder weather is analysed in terms of cost and reliability. A Pareto front plot considering the probability of failure and the median of the cost is used to jointly compare strategies considering both aspects to provide a tool for risk-informed maintenance selection. Finally, the potential benefits of condition-based maintenance and autonomous decision-making systems are discussed. The case of study shows the benefits of repairs during summer months and the importance of the relation risk/O&M cost for different maintenance strategies.

Editorial Calendar

The Editorial Calendar details upcoming publication plans for The Leading Edge. This includes special sections, guest editors, and information about submitting articles to TLE.

Study and Validation of an Electrical Anti-Ice Integrated System for Carbon Fiber Leading Edge Airplane Wing Section

Study and Validation of an Electrical Anti-Ice Integrated System for Carbon Fiber Leading Edge Airplane Wing Section

Experimental investigations on the heat transfer characteristic of impingement/swirl cooling structures inside turbine blade leading edge

Experimental investigations were performed to study the heat transfer characteristics of impingement/swirl cooling structures inside a turbine leading edge (LE) as measured using the transient thermochromic liquid crystal (TLC) technique. The considered Reynolds numbers (Re) were 10,000, 20,000, and 30,000, and the effects of Re and the ratio of the impingement cooling hole offset distance to the impingement cooling hole diameter (e/d) on the heat transfer performance of the impingement/swirl cooling structures inside the blade LE were analyzed. The effects of the coolant outflow mode were also considered. The results show that the heat transfer intensity of the high heat transfer region of impingement/swirl cooling structures increases with Re. The e/d on the local Nusselt number (Nu) distributions for the two shooting areas are similar under different Re conditions. Changes in e/d significantly influence the heat transfer characteristics. As e/d increases from −1.5 to 1.5, the heat transfer effect and thermal uniformity of the LE inner wall chamber improved. Comparative analyses with the experimental results of the LE model without film cooling holes show that the thermal uniformity of the LE model significantly improves when including film cooling holes.