Blade Technology Research Articles

CFD analysis of key factors impacting the aerodynamic performance of the S830 wind turbine airfoil

The Global Wind Energy Council (GWEC) reported that in 2021, global wind capacity increased by 93.6 GW (+12%), reaching a total of 837 GW, most of which was contributed by wind turbines. Improving wind turbine performance primarily hinges on advancements in blade technology and airfoil design. This study examines the effect of profile thickness on the aerodynamic performance of the S830 airfoil at a Reynolds number of 25,148, as part of the NREL airfoil's aerodynamic performance research. However, the impacts of additional variables—such as angle of attack, Reynolds number, speed range, and particularly ice accretion—have not been thoroughly investigated. This study utilized a 2D CFD model provided by the commercial software ANSYS Fluent and FENSAP-ICE. The lift-to-drag ratio of the S830 wind turbine airfoil was examined, considering the effects of angle of attack, wind speed, Reynolds number, airfoil thickness, and ice accretion. Additionally, design-related solutions will be suggested. The research indicates that the optimal angle of attack increases the lift-to-drag ratio by approximately 250% compared to a zero angle of attack. An increase in wind speed causes this coefficient to rise nonlinearly within the studied velocity range. The Reynolds number directly influences the optimal angle of attack. According to CFD results, the lift-to-drag ratio can be increased by 50% if the airfoil's thickness is reduced by 20% compared to the original profile. For the ice accretion simulation model, a case test of the NACA 0012 airfoil was conducted to verify the model's parameters. Subsequently, a survey of this phenomenon on the S830 airfoil revealed that the lift coefficient decreased by 5.25% after 90 minutes of ice accretion.

Macrolithic retouched blades from Kałdus and Stare Marzy: foreign technology and new ideology in the lithic traditions of the TRB communities in the Lower Vistula region

At the turn of the 20th and 21st century, over a dozen macrolithic retouched blades or their fragments were obtained from archaeological sites at Kałdus and Stare Marzy, located in the Lower Vistula region in northern Poland. The context of deposition links the blades to the settlements of the younger Funnel Beaker culture (3650/3500–3300/3100 BC). This article presents and discusses the results of morphological, technological, and raw material investigations of the macrolithic retouched blades or their fragments from Kałdus and Stare Marzy and relates them to the patterns of use and cultural significance of the macrolithic industry in the local TRB communities. The obtained results show that the retouched blades were made of high-quality flint materials sourced from the Polish and Ukrainian Uplands, namely Świeciechów, Volhynian and Jurassic flints. The results, furthermore, indicate that production technology of macrolithic retouched blades is very specific and, what is more important, it is not rooted in the lithic traditions of the region. Archaeological evidence from this study suggests exceptional patterns of use of macrolithic retouched blades in the Lower Vistula region and their perception by local TRB people, which can be traced to the Eneolithic milieu located southeast of the Polish Lowlands.

Small Blade and Bladelet Production in Central Asia at the Turn of MIS 7 and 6: Cores from Kulbulak Layer 23

We describe 27 parallel, narrow-faced, and burin-cores for small blades and bladelets from Kulbulak layer 23, Western Tien Shan, excavated in 2016 and 2017. In terms of typology, flat-faced (longitudinal and transverse), prismatic (carinated, subconical, and subcylindrical), and narrow-faced cores (including burin[1]cores) were identified. Scar pattern analysis suggests that regardless of the typological affiliation of cores, a uniform technological scheme was used—staggered sequence of blanks. This Middle Paleolithic non-prismatic pattern probably indicates the initial steps in the formation of a technology that would subsequently influence the Middle Paleolithic blade industries in western Central Asia and become one of the sources for the regional Upper Paleolithic in the second half of MIS 3. It is concluded that small blade technology emerged within Middle Paleolithic industries of western Central Asia at the turn of MIS 7 and 6. In the Obi-Rakhmat industry (MIS 5a), this technology is represented in its fully developed form.

Innovations in Wind Turbine Blade Engineering: Exploring Materials, Sustainability, and Market Dynamics

This manuscript delves into the transformative advancements in wind turbine blade technology, emphasizing the integration of innovative materials, dynamic aerodynamic designs, and sustainable manufacturing practices. Through an exploration of the evolution from traditional materials to cutting-edge composites, the paper highlights how these developments significantly enhance the efficiency, durability, and environmental compatibility of wind turbines. Detailed case studies of notable global projects, such as the Hornsea Project One, the Gansu Wind Farm, and the Block Island Wind Farm, illustrate the practical applications of these technologies and their impact on energy production and sustainability. Additionally, the manuscript examines the critical role of regulatory frameworks and industry standards in fostering these technological advancements, ensuring safety, and promoting global adoption. By analyzing the current trends and future directions, this study underscores the potential of modern turbine technologies to meet the increasing global demand for renewable energy and contribute to sustainable development goals. The findings advocate for continued innovation and policy alignment to fully harness the potential of wind energy in the renewable energy landscape.

Adhesive Snap-Fit Joints for Modular Wind Turbine Blades: A Numerical Feasibility Study

Larger rotor diameters are sought by wind turbine manufacturers as they favour cost-effective energy generation. However, manufacturing, transporting, and installing longer blades gets increasingly complicated, time-consuming, and costly. While a potential solution lies in spanwise segmentation, available modular blade technologies are still relatively immature, have drawbacks, and are yet to be used for blades exceeding 80 meters. A key challenge to blade segmentation is the addition of joints, which can result in both structural as well as aeroelastic penalties, when comparing segmented designs to their monolithic counterparts. To tackle these issues, in this study, we present the proof of concept and initial feasibility of an adhesively bonded snap-fit joint. The study assesses the joint’s load carrying capacity under quasi-static loading conditions at two levels: first, at the component level, focusing on the snap-fit elements, and second, at the system level, examining the integration of these components into the blade section. Under the specified assumptions, the results highlight the hybrid joint’s capability to withstand substantial loads of the order of magnitude required to meet operating requirements.

Investigation on the Aerodynamic Performance and Flow Mechanism of Transonic Ultra-Highly Loaded Tandem-Rotor Stage

The compressor serves as a crucial component that influences the performance of the gas turbine engine. Researchers have been endeavoring to explore compressor types that possess a high loading level and high-efficiency characteristics concurrently. In this study, tandem blade technology was applied to a transonic ultra-highly loaded axial compressor, and the Baseline single-blade rotor was replaced by a tandem rotor to take into account the loading level and compressor performance. Detailed investigations were carried out to identify the effects on the aerodynamic performance of the ultra-highly loaded stage and the fundamental flow mechanism within the tandem-rotor stage. This paper presents original design maps for the tandem-rotor stage, and the selection criteria for tandem parameters in tandem-rotor stage are refined. The results indicate that the peak efficiency improved by 0.83%, the stall margin increased by 2.16%, and the choke flow rate rose by 0.30% for the optimal tandem-rotor configuration. The meridional division position of the rotor primarily affects the ratio of loading of the front and rear blades, while the circumferential relative position of the tandem rotor mainly influences the channel types formed by the front and rear blades. Larger values for the meridional division position parameter and smaller values for circumferential relative position parameter should be selected for the tandem rotor design to optimize both the isentropic efficiency and total pressure ratio. This investigation offers the theoretical foundation for the design of a transonic ultra-highly loaded tandem-rotor compressor.

A Cold Habitat: Mapping Blade Assemblages Between the Siberian Altai and the Tibetan Plateau During MIS 3

How and why early hunter–gatherers expanded into the challenging environments of the Tibetan Plateau during the Pleistocene remain largely unexplained. The discovery of the archaeological site of Nwya Devu, characterized by lithic blade production, brings new evidence of human expansion to high elevations ca. 40–30 ka. The blade assemblage currently lacks technological antecedents in East Asia. During Marine Isotope Stage 3, the surrounding lowlands to the Plateau were dominated by a distinct type of industry broadly named “core and flake.” It is suggested that the Nwya Devu blade assemblage derives from traditions in the eastern Eurasian Steppe, a clustered hub for Upper Paleolithic blade technology. In contrast to the East Asian lowlands, the Tibetan Plateau shares a number of environmental similarities with North and Central Asia such as low temperature and humidity, long winters, strong seasonality, and grassland landscapes. Blade and core-and-flake technologies tend to be associated with different environments in eastern Asia. We hypothesize that this geographic distribution indicates different sets of behavioral adaptations that map onto distinct ecozones and are relevant to human expansion to the Tibetan Plateau during Marine Isotope Stage 3. To evaluate the working model, we characterized the environmental parameters for both blade and core-and-flake technologies in eastern Asia during the period. The results show that environmental conditions on the Plateau and at the Nwya Devu site align with those of blade assemblages documented in the Eurasian Steppe and contrast with those of core-and-flake assemblages. Blade technology is strongly associated with low-temperature environments. These findings suggest that hunter–gatherers from the steppe belt may have benefited from their behaviorally adaptive advantages when moving into the highland environments of the Tibetan Plateau, 40–30 ka.

Study on the Particle Deposition Characteristics of Transpiration Cooling Structures with Sintered Wire Mesh.

Transpiration cooling based on a porous structure has an ultra-high cooling efficiency, which is expected to be one solution to improve the cooling technology of aero-engine turbine blades. However, particulate impurities in the gas flow channel continue to deposit on the surface of turbine components, blocking cooling holes, which causes great harm to the cooling of turbine blades. In this study, a sintered metal mesh plate was selected as the transpiration cooling structure, and the evolution of particle deposition quality and deposition thickness on the transpiration cooling surface with time, as well as spatial distributions of particle deposition thickness at different times, were explored through experimental and simulation methods. The results showed that, with the increase in spray time, deposition quality and maximum deposition thickness of the transpiration cooling surface gradually increased. Along the main-stream direction, when spray time was short, deposition thickness was higher in a narrow range upstream of the experimental specimen. With the increase in spray time, deposition thickness gradually decreased along the direction of the transpiration cooling mainstream. In the spanwise direction, when spray time was very short, deposition thickness in the spanwise direction was more consistent and, after spray time increased further, the deposition thickness distribution began to tend to a "∩"-type distribution. It can be seen from the simulation results of the metal wire mesh particle deposition that particles were easily deposited on the windward side of the metal wire in the main-stream direction, which agreed with the experimental distribution characteristics of the metal wire mesh deposition. Moreover, the increase in blowing ratio reduced the deposition of particles on the wall of the metal wire mesh.

Obsidian-tipped Spears from the Admiralty Islands in the Oceania Collection of the Museum of Ethnography in Budapest

The authors studied 36 obsidian-tipped spears in the Oceania collection of the Museum of Ethnography in Budapest. In addition to describing the objects from the Admiralty Islands collected before 1897, the paper provides a summary of the related ethnographic information, including the technological and technical details of spear point making and the characterisation of the obsidian raw material used.The blades used for making the obsidian points presented in this study showed no sign of standardisation (an indicator of advanced blade technology) in the spear point-making process. According to 19th-century ethnographic sources, the functional part of the points was the most important, and much time and effort were invested in ensuring that the blades were effective weapons. Later, as a sign of decline, primary production of obsidian blades ceased, and manufacturers started scavenging old artefacts and utilising waste and by-products. As a result, the blades decreased in size and became more irregular, and an increasingly large number included parts of the cortex, the crust of obsidian. After 1911, the relative importance of decoration increased, and the type became more standardised.The irregular shape of the spear points presented in the study and the thin, weak shafts with an awkward curvature raise questions about whether the spears were actual weapons. At the same time, the artistic decoration of the mounting sockets and ethnographic parallels suggest that the pieces in the collection were likely status objects instead.

한성기 백제토기 생산시스템 발달과 사회 변화의 상관성

In ancient society, earthenware had a meaning beyond its original purpose of containing, storing, or cooking food, and can be seen to have been directly and indirectly influenced politically and socially. The influx of new material culture promoted the emergence of new cultures, divided classes, and gave rise to new food cultures. Additionally, those in demand developed earthenware production technology. In the Hanseong period, with the development of Baekje pottery production technology, the production time was shortened with the spread of blade technology, cutting face, and rotating table, which became the basis for mass production. As firing technology developed, kiln firing, overlap firing, and high-density firing became possible, and complex production methods were operated depending on the model. In addition, it became possible to produce a special type of black polished earthenware. Additionally, with the development of earthenware production technology, the diversity of tableware and eating patterns were established. Exclusive ceremonial earthenware used in ceremonial activities was produced. The production of ultra-large storage containers increased surplus production, and the emergence of ultra-large cooking utensils was used for banquets and ceremonial purposes. And the spread of steaming cooking methods using steaming pots, long-shaped earthenware, and stoves means that alcohol, rice cakes, etc. were manufactured. This technological development and use of earthenware is due to the increase in demand for Baekje earthenware during the Hanseong period, and it can be seen that these earthenware were very closely related to the process of social change. In ancient society, the production and consumption of earthenware triggered social changes, and as society became more complex and diverse, cooking methods and eating methods also became more complex. This is because earthenware and food are related to social stratification and overall culture. It should be seen that Baekje pottery during the Han Dynasty was changed and developed according to various political and social interactions at the time.

`Ainab 1 and the Eastward Expansion of Early PPNB Traditions: Unveiling Neolithic Connections between the Levant and Arabia through the Lenses of Chipped Stone Industry

Abstract. `Ainab 1, situated in southeastern Jordan near the Saudi Arabian border, represents a unique archaeological site discovered by H. G. K. Gebel. This small open-air hunting encampment encompasses 11 structures, with structure A selected for excavation during the 2014 season. The excavations yielded over 5,000 chipped industry specimens, complemented by fragments of animal bones and ground stones. The camp’s dating to the Early Pre-Pottery Neolithic B (EPPNB) era relies on the exclusive presence of diagnostic Helwan points, Hagdud truncation and bidirectional blade technology. As such, `Ainab 1 signifies the farthest known EPPNB outpost boasting structures in Transjordan and the Arabian Peninsula. This research paper presents the findings from spatial, technological, typological, and raw material analyses of all chipped stone artefacts procured from structure A’s surface and excavation. The comparative investigation of technical, typological, and spatial patterns has facilitated the reconstruction of the chipped industry’s chrono-spatial patterns. These results illuminate new perspectives on the dialogue between the Levantine core area of the Fertile Crescent and peripheral Jordanian regions and further provide fresh insights into the spread of Neolithic into the Arabian Peninsula.

Cultural Hybridity in Central and Southern Jordan at the End of the Pre-Pottery Neolithic A

Abstract. Our understanding of the transition from the PPNA to the PPNB in central and southern Jordan has undergone significant changes in recent decades. Initially, it appeared that the PPNB arrived in the region fully formed during the Middle PPNB, expressed at sites such as Beidha. Yet it retained features like circular architecture associated with the PPNA, and was thus presumed to indicate a time lag in its arrival from the north, where such structures had largely disappeared by the Middle PPNB. Fieldwork has uncovered a rich PPNA record in Jordan, but a marked cultural gulf between the PPNA and PPNB remains visible, for example visible in the contrast between pisé semi-subterranean PPNA architecture and the aboveground stone PPNB buildings, and in the appearance of naviform technology in PPNB chipped stone repertoires. Ongoing research has narrowed this gap, documenting a shift from semi-subterranean pisé constructions to circular free-standing stone structures during the Late PPNA, as well as the cessation of el-Khiam point manufacture and the emergence of an opposed platform blade technology that appears to echo parallel Early PPNB developments in chipped stone technology to the North. There is now no chronological gap between the Late PPNA and the Middle PPNB, and it appears that this central and southern Jordanian Late PPNA is an indigenous trajectory that developed into a local Middle PPNB while simultaneously adopting further external influences such as true naviform technology. However, recent work on the western edges of the Badia has identified a fully developed Early PPNB roughly contemporaneous with Late PPNA settlements in the adjacent wadi systems to the west. Out of sync with local developments, this Early PPNB presence suggests the arrival of a distinct group in the western Badia who maintained their identity, adding to the mix of local, already highly diverse, early Neolithic communities of central and southern Jordan. Interactions between these populations continued and through a process of cultural hybridisation formed the characteristic Middle and Late PPNB of the area.

State-of-the-art value chain roadmap for sustainable end-of-life wind turbine blades

Increasing volumes of wind turbine blades (WTBs) meeting their end-of-life are expected in the coming years, while establishing sustainable value chains for handling the blades is still at an early stage. Through a systematic literature identification and review process, current literature on sustainable end-of-life management and technologies for wind turbine blades is identified to map state-of-the-art. The review resulted in the identification of four overarching research themes with sixteen underlying research topics. The study findings highlight that research so far has mainly been focused on recycling technologies and material properties of recovered WTB material. Furthermore, none of the reviewed literature contained empirical data from end-of-life blade projects. Thus, there is a lack of data and knowledge on the complete value chain, including processes of logistics, sectioning, pre-processing, and refining recovered materials for secondary applications. Furthermore, the understanding of the environmental, social, and cost impacts of these processes are also found to be absent. Based on a consolidation of findings, a complete value chain roadmap of required processes and technologies for sustainable end-of-life routes of WTBs is presented. The roadmap and results illustrate a baseline for current practices but also calls for further research into optimization and impact assessment of value chains. Thus, the presented roadmap has implications for academia, wind turbine producers and owners to aid the assessment of which practices and technologies to utilize when decommissioning WTBs.

Jet engine blade: Design, material, and manufacturing

The engine is the most important part of an airplane. Since the blades of an engine are a major factor in jet engine performance, the research of engine blades has always been a hot topic in the field of aerospace. This paper summarizes the research status in the field of jet engine blades. As for the design of the jet engine blade, the design of aerofoil and the geometrical structure of the engine blade is introduced. In the material selection of engine blades, titanium alloy materials, and the application of composite materials are introduced. Electrochemical machining (ECM) and additive technology of engine blades are introduced. The differences between them and traditional casting techniques are compared. The comprehensive analysis shows that the research on engine blades is becoming more and more mature, but there are some challenges in further optimization of manufacturing technology and materials. This paper may offer a reference for the design of jet engine blade.

How to Repair the Next Generation of Wind Turbine Blades

Ensuring the sustainability of wind turbine blades will be an important requirement for new wind turbines to be installed in the coming years and decades. Several new wind turbines with blades from recyclable materials have already been installed, among which are blades based on recyclamine® and EzCiclo. The wind turbines of the new generation are subject to extreme mechanical and physical loading, can be damaged during service time, and will require maintenance and repair. In this paper, technologies for the repair and recycling of the new generation of materials for wind turbine blades are reviewed. Repair technologies for thermoplastic blades, recyclamine®- and vitrimer-based composites, and other new blade composites are discussed.

Ecological Constraints and Drivers for Human Dispersals and Adaptations in the Late Pleistocene and Early Holocene Environments of the East Siberian Arctic

Starting roughly 50,000 years ago, the Arctic region of East Siberia remained continuously populated by groups of anatomically modern humans including the most uncomfortable episodes in the development of the late Quaternary environment; for some of them, human presence in the area became ephemeral. At present, archaeological fossil records allow for distinguishing three main stages in human occupation of the area: Early (~50 to ~29 ka, MIS 3), middle (~29 to ~11.7 ka, MIS 2), and late (from 11.7 to ~8 ka). For most of the time, they the populated open landscapes of the Mammoth Steppe, which declined at the onset of the Holocene. Human settlement of the Arctic was driven by various abiotic and biotic factors and thus archaeologically visible cardinal cultural and technological changes correspond to the most important paleoclimatic and habitat changes in the late Pleistocene and early Holocene. Successful peopling of the Arctic was largely facilitated by the adoption of critically important innovations such as sewing technology based on the use of the eyed bone needle and the manufacture of long shafts and pointed implements made of mammoth tusks. Mammoth exploitation is seen in mass accumulations of mammoths formed by hunting. An obvious connection between archaeological materials and such accumulations is observed in the archaeological record. In the lithic technology, the early stage is presented by archaic-looking flake industries. Starting the LGM, the wedge-core based-microblade technology known as the Beringian microblade tradition spread widely following the shrinkage of the mammoth range. At the late stage, starting at the Holocene boundary, microprismatic blade technology occurs. In all stages, the complex social behavior of the ancient Arctic settlers is revealed. The long-distance transport of products, knowledge, and genes occurs due to the introduction of the land transportation system. Initial human settlement of this region is associated with carriers of the West Eurasian genome who became replaced by the population with East Asian ancestry constantly moving North under the pressure of climate change.

The Initial Upper Paleolithic of the Altai: New radiocarbon determinations for the Kara-Bom site

The Initial Upper Paleolithic (IUP) is one of the most important phases in the recent period of the evolution of humans. During a narrow period in the first half of Marine Isotope Stage 3 laminar industries, accompanied by developed symbolism and specific blade technology, emerged over a vast area, replacing different variants of the Middle Paleolithic. In western Eurasia, the earliest appearance of IUP technology is seen at the Boker Tachtit site, dated ca. 50 ka cal BP. The earliest evidence of IUP industries in the Balkans and Central Europe, linked to the spread of Homo sapiens, has been dated to around 48 ka cal BP. A key area of IUP dispersals are the mountains and piedmont of southern Siberia and eastern Central Asia. One of the reference assemblages here is Kara-Bom, an open-air site in the Siberian Altai. Three major settlement phases are distinguished in the sediment sequence. In this paper, we present the results of new radiocarbon determinations and Bayesian models. We find that the latest phase of the IUP, Upper Paleolithic 1 (‘UP1’) is bracketed between 43 and 35 ka cal BP (at 95.4% probability). The earliest IUP phase, ‘UP2’, begins to accumulate from ca. 49 ka cal BP and ends by ca. 45 ka cal BP. The Middle Paleolithic ‘MP2’ assemblages all fall prior to 50 ka cal BP. We can detect a spatial distribution of dates from the geographic core of the IUP beyond the Altai where it appears around 47–45 ka cal BP. The current distribution of dates suggests a west–east dispersal of the IUP technocomplex along the mountain belts of Central Asia and South Siberia.

Small tool production in the Howiesons Poort: a view from Montagu Cave, South Africa

ABSTRACT In southern Africa, the Howiesons Poort is one of the earliest technocomplexes in which small blades and bladelets were systematically produced and retouched into formal tools. While the presence of small lithic artefacts in an assemblage is well-documented, little is known about production pathways. This paper reports on the analysis of the lithic assemblage from Horizon 6/7 of Charles Keller’s excavations of Montagu Cave, South Africa, to evaluate how raw material and decision-making affects the size of stone tools in Howiesons Poort assemblages. It addresses the following questions: how were small blades produced? Was it a deliberate choice or a constraint imposed by raw material availability? Results show branching modes of production for large and small blanks beginning with raw material acquisition. The independent production of small blanks is reinforced by the presence of cores on flakes in the assemblage. However, a relatively standardised core reduction process was used consistently, regardless of core size. The main technological and typological features observed in Horizon 6/7 are in line with other known Howiesons Poort assemblages. Considered as a whole, these observations highlight the consistency of Howiesons Poort blade technology and the deliberate production of small blanks and tools.

Development of a passive blade-pitch mechanism to reduce the loads on a tidal turbine in high-flow conditions

Maintenance of tidal turbines is expensive, and relies upon suitable weather conditions and vessel availability, which can lead to costly delays. Turbine reliability can be improved by eliminating complexity in the design. The use of fixed-pitch blades, for example, can greatly reduce maintenance costs by avoiding complex active blade-pitch mechanisms which are the main source of failure in wind turbines.
 Pitching rotor blades to feather in high-flow conditions is, however, the most effective means of reducing loads on the rotor. Turbines with fixed-pitch blades therefore necessarily have smaller rotor diameters compared to those with active-pitch systems, in order to keep the thrust force, flap-wise bending moment, and power output within allowable limits. In low-flow conditions, power output is proportional to the square of the rotor diameter, so turbines with small diameter rotors capture less energy over their lifetime.
 This study seeks to develop a novel passive-pitch mechanism for tidal turbine blades. This mechanism must be reliable, and should act to reduce the loads on the rotor in high-flow conditions so that a larger diameter rotor can be installed, increasing power capture.
 An initial design for a passive-pitch mechanism, which is actuated by the hydrodynamic forces developed by the rotor such that the blades pitch-to-feather in high-flow conditions, has been developed. The design is compatible with proven passive reversible rotor blade technology, eliminating the requirement for a maintenance sensitive yaw mechanism.
 Since initial concept design, work has been undertaken to build a tool, based on NREL’s OpenFAST blade element momentum code, which models the forces acting on the rotor blades, coupled with the mechanical response of the passive blade-pitch mechanism. This tool has been used to predict the performance of the turbine for a range of operating conditions, allowing the influence of parameters such as blade geometry, rotor diameter and passive-pitch response to be analysed in terms of rotor loading and turbine performance.
 Initial analysis suggests that installing blades with a passive-pitch mechanism could reduce the loads on the rotor in high-flow conditions down to just 25% of the loads that would act on an equivalent rotor with fixed-pitch blades. This would allow larger diameter rotors to be installed which could improve annual energy yield by over 40% at a typical site.
 Despite these significant potential performance improvements, the challenges of developing a passive blade-pitch mechanism for tidal turbines are not well understood, as tidal developers have all so far implemented fixed or active pitch mechanisms. These challenges will be addressed throughout the remainder of this study, which will involve detailed design followed by physical tank testing.

Design and Demonstration of a Passive Pitch System for Tidal Turbines

Tidal currents are renewable and predictable energy sources that could prove fundamental to the transition to a sustainable use of renewable energy resources. Over a tidal period, changes in the flow speed in a tidal channel require that the blade pitch is adjusted to maximise power extraction. This is currently achieved with active pitch actuation, which however increases the capital and maintenance cost of the turbine. Furthermore, because of turbulence in the tidal stream, turbine yaw, wave-induced currents, etc., tidal turbine blades experience high-frequency velocity fluctuations that result in power and thrust unsteadiness, both of which are transmitted to the generator, the tower, and the active pitching mechanism, shortening the operating life due to fatigue loading.
 A passive morphing blade concept capable of reducing the load fluctuations without affecting the mean loads has recently been formulated and demonstrated with low-order simulations (https://doi.org/10.1016/j.renene.2021.10.085) and measurements (https://doi.org/10.1016/j.renene.2023.01.051). The system allows both passive pitch adjustment to changes in the mean flow speed over the tidal period, and the mitigation of high-frequency fluctuations.
 In this paper, we present the recent progress on the development of morphing blade technology, including with numerical simulations and experimental tests on a 1.2-m diameter turbine. Two different design concepts have been tested in the FloWave facility at the University of Edinburgh and in the recirculating channel at the Institute for Marine Engineering of the Italian National Research Council, respectively.
 Experimental results show that the amplitude of power variations over a wide range of flow speeds is substantially decreased, while thrust variations with changes in freestream speed are essentially suppressed. The detrimental effect of yawed inflow is, in addition, almost entirely cancelled. The fluctuations in the root-bending moment, thrust and torque are consistently reduced over a broad range of tip-speed ratios. We also show that such a system, if improperly designed, could result in a negative starting torque, and we show the steps necessary to avoid this issue.
 Furthermore, we present a theoretical and numerical framework that allows the design of passive pitch blades that can cancel either thrust or power fluctuations in specific flow conditions, as well as mitigating both types of fluctuations over a wide range of conditions. Specifically, we show that for any quasi-steady change in the relative flow speed and direction, there is a pitching axis that allows a chosen force component to be kept constant. High-frequency force fluctuations can also be substantially mitigated, and the extent of the mitigation depends on the inertia and friction in the system.
 Overall this paper demonstrates experimentally the effectiveness of morphing blades for tidal turbines and presents a theoretical and numerical framework for the future development of this technology.