Blade Surface Research Articles

Influence of freestream turbulence on boundary layer transition over a controlled-diffusion compressor blade

The influence of inlet freestream turbulence (FST) on the boundary layer transition over the suction surface of a controlled-diffusion compressor blade is demonstrated here by employing a well-resolved large-eddy simulation. Inherent to low Reynolds number conditions, a laminar separation bubble (LSB) forms on the suction surface, attributing to substantial flow diffusion. Inlet FST levels ranging from 1.5% to 7.6% are systematically varied, while maintaining a constant Reynolds number based on axial chord and inlet velocity at 2.1 × 105. Transition of the shear layer is initiated via Kelvin–Helmholtz instability with the amplification of selective frequencies until an inlet FST of 2.3%. Secondary instability emerges in the second half of the LSB, attributed to the amplification of perturbations in the braid region, ultimately leading to breakdown near the reattachment. At a moderate FST level of 4.2%, longitudinal streaks in the first half of the blade elongate downstream, causing the LSB to disappear, while the flow becomes inflectional at the mid-chord. Thus, the boundary layer transition in the second half of the blade is attributed to the high receptivity of the inflectional layer and breakdown of streaks, leading to an exponential growth of disturbances. Finally, at an inlet FST of 7.6%, the boundary layer appears pre-transitional in the first half of the blade, exhibiting significant turbulence levels. In the latter half, excitation occurs primarily through the breakdown of streaks, reflecting an algebraic growth of disturbances. Flow features and oscillations in the Nusselt number in this case suggest the outer mode of streak-induced instability.

Aerodynamic conditions measured at a rotor blade of large wind turbine prototype

In this paper we present high resolution pressure distributions measured on the surface of a rotor blade of an 8 MW offshore prototype. We investigate two time intervals of approximately 10 minute duration acquired in April 2022. During the first time interval the turbine is operated at rated power, during the second time interval the turbine is operated below rated power. We see a clear increase and decrease of pressure values on the pressure side and suction side of the rotor blade, respectively. Also, 1P frequency oscillations are found in all sensors except during idling state. We find a decreasing signal to noise ratio in these oscillations with increasing distance from leading edge towards trailing edge, indicating higher turbulence in the air flow. Additionally, pressure changes during pitching movements can be observed. These data present the first data set of pressure distribution measured over a longer time period on a state-of-the-art sized offshore wind turbine prototype and therefore, provide important input for model validation and further understanding of the aerodynamic conditions at a rotor blade.

Preventive maintenance of horizontal wind turbines via computational fluid dynamics-driven wall shear stress evaluation

Wind energy is a source of renewable energy that can be converted to electricity using a wind turbine. The typical lifespan of a wind turbine is at least 20–25 years. However, regular monitoring and preventive maintenance are required to ensure optimal performance and to extend the working life of wind turbines. Blade erosion and fatigue are the main structural issues which degrade wind turbine efficiency and lifespan. One method to identify the causes of these structural issues is computational fluid dynamics (CFD) that can be used to investigate relevant physical parameters affecting wind turbine performance. The current study investigated wall shear stress (WSS) or the force per area exerted by the wind close to the surfaces of the turbine blades and simulated the WSS at various points on the blade. The 3-parameter lognormal distribution that represented WSS probability density functions revealed that wind speed, rotational blade speed, and WSS were positively related, with the highest WSS levels occurring at the blade's leading edge, particularly in the region near the blade tip. Based on these findings, regular preventive maintenance plans should carefully monitor the blade leading edges, while protective coatings should be applied. These strategies would help to prevent blade erosion and fatigue, ultimately improving the efficiency and lifespan of the wind turbine. However, further research is needed to refine these CFD simulations and to validate the results based on additional experimental data.

Design and optimization of a modular Electro-Thermal Ice Protection System for a Horizontal Axis Wind Turbine

In this work, an Electro-Thermal Ice Protection System (IPS) design was refined and optimized on the NREL 5 MW reference wind turbine. These improvements involved optimization of the distribution of heat flux in both the stream-wise and span-wise directions to minimize power consumption and avoid run-back ice formation. The design conditions focus on a 3-hour rime ice accretion event. The chosen optimization algorithm is a derivative-free method called Mesh Adaptive Direct Search. his optimization effort results in a 55% reduction in power consumption necessary to maintain a completely clean blade surface. The power and energy losses associated with this new optimized design are compared with those from various ice shapes and with the clean blade conditions established in the initial design phase from previous work. The new optimized design allows to keep the blade clean from ice with much larger energy saving. Indeed, only initially, during the first two hours of ice accretion, the energy losses due to this IPS design are higher than without IPS. Beyond this short initial period, substantial energy savings are achieved, especially considering that after the accretion event, the blade remains ice-free, and there are no more power losses.

A method for cleaning the surface of gas turbine engine blades from chromium, nickel, molybdenum, cobalt and tungsten oxides using reducing properties of hydrogen

A method for cleaning the surface of gas turbine engine blades from chromium, nickel, molybdenum, cobalt and tungsten oxides using reducing properties of hydrogen

Eugenia (Myrtaceae) from Reserva Natural Vale, Espírito Santo, a center of plant endemism in the Brazilian Atlantic Rainforest

Eugenia includes ca. 1,100 species worldwide and is the richest angiosperm genus of Brazilian flora with a remarkable biodiversity in the Atlantic Rainforest. In Espírito Santo state, the central-north region conserves the biggest forest fragment and is composed by the lowland coastal forests known as Tabuleiro. Considering the scarcity of studies approaching this vegetation and the high diversity of Eugenia species, this work presents a taxonomic treatment of Eugenia species from Reserva Natural Vale. The study area is located at the municipalities of Linhares and Sooretama, in the northern part of the coastal mesoregion of the state. For the taxonomic treatment, fieldwork was carried out between August 2015 and March 2019 and herbarium collections of BHCB, CVRD, CEPEC, ESA, HRCB, HPL, HUFSJ, ICN, K, MBM, MBML, RB, RBR, SORO, SP, SPF, SPSF, UB, UEC, and VIES were consulted, as well as images of nomenclatural types available online. This work points out the occurrence of 48 species of Eugenia within Reserva Natural Vale, encompassing 48% of the Eugenia species recorded in the Espírito Santo state. Six of them are presented as new occurrences for the reserve (Eugenia arenaria, E. disperma, E. florida, E. handroi, E. pachnantha and E. schottiana); two (E. pachnantha and E. schottiana) are first recorded for the state; E. adenophylla and E. infuscata are described as new. Eugenia adenophylla, E. atlantica, Eugenia cataphyllea, E. flavicarpa, E. hispidiflora, E. ochracea, E. penduliflora, and E. soteriana are endemic to Tabuleiro coastal forest, and E. handroi is the only record for Espírito Santo state. The most useful characters to distinguish the species are hair colours, especially in the floral structures, midvein on the adaxial surface of leaf blades, inflorescence type, connation and persistence of bracteoles, and the presence or absence of indumentum on the flowers’ hypanthia. Furthermore, morphological descriptions, distribution and phenology data, taxonomic comments, species illustrations, and an identification key for the species in the reserve are presented.

Enhancing Savonius Rotor Performance With Zigzag Surface Investigated at Drag Force, Pressure, and Flow Visualization Analysis

Savonius, a type of vertical-axis wind turbine, is a small-scale energy conversion device suitable for low wind speeds, such as those characteristic of Indonesian wind speeds, yet has low efficiency. Savonius is a drag-type turbine. Drag force on the surface is affected by roughness or wavyness. The purpose of this study is to analyze the impact of applying wavy (zigzag) variations to the concave surface of Savonius blades on their performance. This was achieved by the use of 3D computational fluid dynamics simulation at TSR 0.6 with a velocity inlet of 5 m/s. The model was semicircular, zigzag on the concave surface on semicircular with t = 0.75, t = 0.25, and t = 1 mm. The result of this study's CD maximum is 1,817 at the zigzag model with t = 1 and CD avrg =1.24. The average drag coefficient increased by 14 percent compared to the conventional semicircular rotor. The maximum Cp value is also found at t = 1 mm, which is 0.315. The power coefficient increased by 29 percent compared to the conventional semicircular rotor. The total pressure on the blade shows the highest model with t = 1 mm at the same angle of attack (α = 30). Zigzag on the concave surface affects blade pressure, which improves the performance of the Savonius rotor.

Research on gas–liquid two-phase transient process of reactor coolant pump under stuck shaft accident

The stuck shaft accident (SSA) is a typical and severe accident of the reactor coolant pump (RCP). During this accident, significant friction and heat generation result in gas–liquid two-phase flow, which adversely affects the working performance and stability of the RCP. In order to explore the internal flow field and transient pressure fluctuation of the two-phase flow in the RCP under the SSA, this study adopts three methods of standard k-ε, Large Eddy Simulation (LES) and Lattice Boltzmann Method-Large Eddy Simulation (LBM-LES) for refined simulation and then are validated by experiments. It finds that the gas volume fraction (GVF) is relatively high in the inlet path of the guide vane during the initial stage, and then the gas disperses from the suction surface of the impeller blade to the pressure surface. When the GVF increases, the small gas masses accumulate into large masses and collapses in the RCP. At this time, the vorticity in the impeller path increases and then decreases at the outlet. The pressure fluctuation on the pressure surface at the impeller outlet increases with the increase of GVF. The impact of the GVF on the pressure surface is greater than that on the suction surface, particularly in the high-frequency band during the initial stages of the SSA. Among these three models, LBM-LES demonstrates the highest accuracy with a maximum deviation of only 8.84% when the inlet GVF is 10%. The research results improve the prevention and mitigation ability of related accidents, and provide theoretical basis and technical support for subsequent optimization and improvement.

Accumulation characteristics of precipitation static on rotating wind turbine blades and its influence on the lightning attachment characteristics

AbstractThe linear velocity at the tip of large wind turbine blades can reach 100 m/s, generating static electricity through friction with airborne particles. However, the accumulation characteristics of precipitation static on the blade surface and its impact on the lightning attachment characteristics are rarely reported. The authors constructed a platform for measuring charges on rotating wind turbine blades and employed the electrostatic probe method to obtain the accumulation characteristics of surface charges under different environmental conditions. The experimental results show that positive charges accumulate on the blade surfaces, peaking at 0.69 μC/m2 under experimental conditions. The charge density is positively correlated with airborne particle concentration and blade rotation speed, while it is negatively correlated with relative air humidity. Additionally, the authors developed a model of the electric field distribution on wind turbine blades considering the effects of precipitation static. Simulation results indicate that the electrostatic field induced by precipitation static weakens the field strength in the vicinity of receptors, reaching a minimum of only 38% of the original strength, thereby increasing the probability of lightning protection failure. The findings provide an effective supplement to the lightning attachment mechanism of rotating wind turbine blades.

Preparation of n-Tetradecane Phase Change Microencapsulated Polyurethane Coating and Experiment on Anti-Icing Performance for Wind Turbine Blades

Icing is a common physical phenomenon, and the icing of wind turbine blades can significantly affect the performance of wind turbines. Therefore, researching methods to prevent icing is of great significance, and the coating method of anti-icing is an effective way to delay icing, with advantages such as low energy consumption and easy implementation. In this study, using the coating method as the background, tetradecane phase change microcapsules were prepared, with a melting enthalpy of 90.8 J/g and a crystallization enthalpy of 96.3 J/g, exhibiting good coverage and energy storage efficiency. After mixing tetradecane phase change microcapsules (PCMS) with polyurethane coating (PUR) and coating them on wind turbine blades, after a 5 min icing wind tunnel test, the coating could significantly delay the icing on the blade surface, with the highest anti-icing rate reaching 60.41%. This indicates that the coating has a good anti-icing effect and provides basic research data for exploring new anti-icing methods.

Design and optimization of slot number in supercooled vapor suction in steam turbine blades for reducing the wetness

An enormous amount of the world's electricity is produced by steam power plants. The existence of a liquid phase in the steam turbine results in an efficiency drop and mechanical losses, which are very expensive due to its high price. Creating a suction slot in the stationary blade of the steam turbine for sucking the supercooled vapor and wetness fraction in the low-pressure stages of the turbine is one of the most effective methods of preserving the rotor blades against corrosion and erosion. The Eulerian-Eulerian method is employed for modeling the condensing flow. In the current research, the impact of the suction slot location and number on the surfaces of the turbine blades is investigated on condensation, total suction ratio, liquid suction ratio, average droplet radius, and condensation losses. Optimization is performed by the TOPSIS algorithm. Based on the results, the location and number of the suction slots affect the flow pattern in the turbine blade. Creating a suction slot in the optimal case has a total suction ratio of 4.1 %, which decreases the liquid suction ratio, condensation losses, and average droplet radius, respectively, by 5.28 %, 6 %, and 25 % compared to the original case.

An Experimental Study of Surface Icing Characteristics on Blade Airfoil for Offshore Wind Turbines: Effects of Chord Length and Angle of Attack

Offshore wind turbines operating in frigid and humid climates may encounter icing on the blade surface. This phenomenon adversely impacts the aerodynamic efficiency of the turbine, consequently diminishing power generation efficacy. Investigating the distribution characteristics of icing on the blade surface is imperative. Hence, this study undertook icing wind tunnel tests on segments of DU25 airfoil, a prevalent type for offshore wind turbines, to examine such characteristics as different chord lengths and angles of attack. The results show a simultaneous increase in the blade icing area and growth rate of the net icing area with augmenting the chord length and angles of attack. The total icing area rate decreases by a factor of two when the chord length is doubled. The relative positioning of icing and the average icing thickness remain consistent across the airfoil blades with varying chord lengths. Comparing the icing shapes on blades of varying scales shows a similarity ranging from 84.06% to 88.72%. The results of this study provide insight into the icing characteristics of offshore wind turbines.

Research on formation mechanism and output effect of wind turbine ice-covered blades

Considering the physical characteristics of wind turbine wing icing, icing synthesis rate, and icing type, we selected the icing type and surface roughness of ice-coated blades as sensitive parameters. The focus of our research was on the equivalent particle roughness height correction model, and we numerically analyzed the two icing processes (frost ice and clear ice) on wind turbine blade surfaces by combining FENSAP-ICE and FLUENT analysis tools. We predicted the ice type on blade surfaces using a multi-time step method and analyzed how variations in icing shape and ice surface roughness affect the aerodynamic performance of blades during frost ice formation or clear ice formation. Our results indicate that differences in blade surface roughness and heat flux lead to disparities in both ice formation rate and shape between frost ice and clear ice. Clear ice has a greater impact on aerodynamics compared to frost ice, while frost ice is significantly influenced by the roughness of its icy surface. These findings can serve as valuable references for wind power operators and manufacturers seeking solutions to issues related to blade surface icing under extremely cold conditions.

Dynamic stress prediction for a Pump-Turbine in Low-Load Conditions: Experimental validation and phenomenological analysis

To meet the increasing demand for higher flexibility in hydropower, an operating range extension in an existing hydroelectric powerplant is considered. To this end, the dynamic flow and structural behavior of the low-head pump-turbine is investigated in turbine mode in partial load and deep partial load conditions, to evaluate the feasibility of this flexibilization due to the increased high cycle fatigue damage. In a first step, different numerical simulation approaches that combine fluid dynamics and structural dynamics are applied and compared to in-situ dynamic strain and pressure measurements on the impeller. As a result, the modelling requirements for a numerical workflow that leads to unmatched accuracy in predicting the broad-band dynamic stresses of deep partial load are identified. In a second step, the operating-point-dependent fatigue crack initiation spots are identified based on dynamic stresses. Herein, the emergence of an additional dominant critical spot near the blade leading edge is observed, which is unexpected for low-head pump turbines. Thanks to the detailed numerical flow and structural analyses, the root cause for the dynamic stress concentration is studied and the emergence of the new critical spot is understood. It turns out in deep partial load, that the main source of pressure oscillations on the impeller blade surfaces is the vortex-dominated flow detachment zone around the blade leading edge, which, in combination with the geometry of the investigated impeller, translates into the main stress oscillations. The results of this work were later used to extend the operating range of the hydroelectric powerplant from initially 25% to 100% power output to now 0% to 100%.

Taxonomic studies in Wedelia (Asteraceae, Heliantheae) reveal a new species for the Brazilian Cerrado

Wedelia is the largest genus of Ecliptinae (Heliantheae, Asteraceae), comprising about 110 species. The Brazilian Cerrado is a highly threatened phytogeographic domain, which harbors the richest flora in the world among other savannas. A new subshrubby species of Wedelia was revealed occurring in the central part of Cerrado and is herein described as W. tenuinervia. This new species resembles W. foliacea in vegetative traits but differs mainly by having leaves with brochidodromous venation, pistillate ray flowers, glandular trichomes on the abaxial surface of the leaf blade, corolla lobes and apical anther appendages, phyllaries abaxial surface strigillose and disc cypselae 4–5-angled, keeled at the angles, without basal scars or elaiosomes, and carpopodium inconspicuous (vs. acrodromous venation, neuter ray flower, abaxial surface of the leaf blade, corolla lobes and apical anther appendage lacking glandular trichomes, phyllaries abaxial surface setose or glabrescent, and disc cypselae biconvex, not keeled, with basal scars or elaiosomes, and carpopodium in two plates or one shallowly lobed). Among the species with pistillate ray flowers, W. tenuinervia can be morphologically related to W. oligocephala, differing mainly by the membranaceous leaf blades with flat margins, brochidodromous venation, and solitary capitula (vs. subcoriaceous leaf blades with revolute margins, acrodromous venation and capitula in dichasia). Illustrations, comments, a preliminary conservation status, and the typification of W. foliacea’s synonyms are proposed.

Five-Axis Finish Milling Machining for an Inconel 718 Alloy Monolithic Blisk

Blisks subjected to rough machining for channel creation must undergo finishing processes, and such processes must achieve the required tolerance limits. A high-quality surface finish and predictable long tool life are critical for the finish milling of blisks. Accordingly, the aim of this study was to optimize parameters for the finish machining of an Inconel 718 alloy monolithic blisk. Ball-cone mills were used to machine the blade surface at a constant depth. A sensory tool holder was used to collect cutting force signals during machining, and a digital microscope was used to examine tool wear. The surface texture measuring instrument was used to measure blisk blade surface roughness to evaluate processing quality. This study manipulated two cutting parameters, namely cutting speed and feed per tooth, and investigated their effects. The relationship between cutting conditions and machining efficiency was analyzed. According to the experimental results, we identified a set of optimal parameters at effective cutting speeds of 46.53 m/min, feed per tooth of 0.1 mm/tooth, and depth of cut of 0.05 mm for marginal tool wear and fast cutting speeds. Then the corresponding tool life was estimated by using the derived parameters.

Cutinsomes of Malus Mill. (Rosaceae) leaf and pericarp: genesis, localization, and transport

New data were obtained on specific bionanostructures, cutinsomes, which are involved in the formation of cuticles on the surface of leaf blades and pericarp of Malus domestica Borkh (Malus Mill., Rosaceae)introduced to the mountains at the altitudes of 1200 and 1700 m above sea level. Cutinsomes, which are electron-dense structures of spherical shape, have been identified by transmission electron microscopy. It was demonstrated that plastids can be involved in the synthesis of their constituent nanocomponents. The greatest number of nanoparticles was observed in the granal thylakoid lumen of the chloroplasts in palisade mesophyll cells and pericarp hypodermal cells. The transmembrane transport of cutinsomes into the cell wall cuticle proper by exocytosis has been visualized for the first time. The plasma membrane is directly involved in the excretion of nanostructures from the cell. Nanoparticles of cutinsomes in the form of necklace-like formations line up in a chain near cell walls, merge into larger conglomerates and are loaded into plasmalemma invaginations, and then, in membrane packing, they move into the cuticle, which covers both outer and inner cell walls of external tissues. The original materials obtained by us supplement the ideas about the non-enzymatic synthesis of cuticle components available in the literature and expand the cell compartment geography involved in this process.

Effect of Tip Gap Size on the Tip Flow Structure and Turbulence Generation in a Low Reynolds Number Compressor Cascade

Abstract Efficient and compact axial compressors are currently undergoing rapid development for use in microcooling systems and small-scale vehicles. Limited experimental work concentrates on the inner flow field of the compressors working at such low Reynolds numbers (Re∼104). This study examines the vortical structures and the resulting turbulence production in the transitional flow over a C4 compressor blade at a Reynolds number Re of 24,000, with a specific focus on the impact of tip clearance. The particle image velocimetry measurements reveal the tip flow structures in detail, including the tip leakage vortex (TLV) and its induced complex vortical structures. The tip secondary flow at the low Reynolds number can be divided as the tip leakage flow (TLF)/vortex and transitional boundary layer both at the end walls and the blade surfaces. The TLV propagates at the highest spanwise positions and farthest pitchwise positions at the middle tip gap size (τ/C = 3%) for the three tip gap sizes investigated. The tip flow fluctuations decrease from τ/C = 5% to τ/C = 3% and then increase from τ/C = 3% to τ/C = 1%. The spatial distribution, streamwise evolution, and individual Reynolds normal stress components contributing to the turbulent kinetic energy (TKE) are discussed. The primary contributors to the turbulence generation are examined to elucidate the flow mechanism leading to the distinct anisotropic turbulence structure in the tip region with various tip gap sizes.

Numerical Analysis of a Novel Casing Treatment in an Axial Flow Fan

The present paper reports the use of a slotted casing treatment of trapezoidal shape to enhance the stall margin of an axial flow fan. The Taguchi method was used to optimize the rectangular slotted casing treatment based on that which the trapezoidal slots were designed. The unsteady numerical simulations were carried out using the shear-stress-transport turbulence model. The rotor with trapezoidal slots led to the stall margin improvement of 23.4% and mild pressure rise of 0.54%. Without the casing treatment, the tip leakage trajectory was directed from the suction surface of the blade toward the pressure surface of the adjacent blade. After incorporating the trapezoidal slots, the tip leakage trajectory was significantly shifted toward the suction surface of the same blade. This alteration in flow characteristics near the blade-tip region may be attributed to the exchange of momentum due to the simultaneous suction and blowing through the trapezoidal slots. It was also found that the trapezoidal slots improved the axial flow velocity and reduced the diffusion factor in the blade-tip region as compared to the baseline case.

Numerical Analysis of the Blade Coating Process Using Non‐Newtonian Nanofluid with Magnetohydrodynamic (MHD) and Slip Effects

AbstractThe coating process is widely used in various industries to enhance the production quality and efficiency. This study gives a comprehensive analysis of non‐isothermal blade coating of non‐Newtonian nanofluid incorporating magnetic, thermophoresis, and Brownian effects. The mathematical equations derived from mass, momentum, and energy conservation laws are initially streamlined by means of lubrication approximation theory (LAT). Subsequently, these dimensionless equations are solved in dimensionless form numerically using fourth order Runge–Kutta and Newton–Raphson methods. This study includes the effects of the slip parameter, magnetohydrodynamic (MHD) and other material parameters on the coating thickness (), blade load, velocity, temperature, concentration, and pressure profiles through graphs and tables. The velocity of molten polymer increases near the substrate while it decreases near the blade surface as the slip parameter increases. The temperature distribution increases as the Brinkman number rises, with the maximum temperature occurring in the nip region of the flow. The coating thickness and load‐carrying force for both plane and exponential coater increase with higher values of the magnetohydrodynamic (MHD) parameter.