Rotor Diameter Research Articles

Experimental research on global active rotor noise control using near-field acoustic holography and sound field reproduction

This study employs a 1.6 m diameter rotor to validate the global active noise control method, developed from our previously work, which is based on near-field acoustic holography and sound field reproduction. The validation is conducted through experiments in an anechoic chamber. Additionally, we achieved control over nearly all acoustic modal components of multiple blade passing frequency (BPF) noises of the rotor by extending the time-domain least mean square (LMS) to the acoustic modal domain. The experimental results from near-field acoustic holography revealed that each BPF noise contained 3–4 main acoustic modal components, accounting for almost 90 % of the sound power. The global active noise control experiments demonstrated that the adaptive algorithm in the acoustic modal domain effectively mitigates the influence of rotation speed fluctuations, resulting in steady-state global noise reduction through sound field reproduction. Furthermore, for the first 3 BPF noise, our method achieved noise reduction of 9, 11, and 6 dB by controlling the first 3–4 main acoustic modal components, respectively. The concurrent reduction of various harmonic noises at all observation points validates the method's capability to globally control multiple harmonic noises.

Performance analysis of aluminium wound double fed induction generator for cost-efficient wind energy conversion systems

Abstract Currently, both limited fossil fuel resources and environmental factors have increased the use of renewable energy sources. Renewable energy resources, such as wind energy systems, are gaining popularity, resulting in increased competition among manufacturers. This study aims to achieve a cost-efficient wind energy conversion system by designing and analysing the performance of a 250 kVA aluminium wound double-fed induction generator (DFIG). The advantages and disadvantages of aluminium windings are compared with those of copper windings, and three DFIG models are created: Model-1 with a copper winding set, Model-2 with the same geometry as Model-1 but designed with an aluminium winding set, and Model-3 with an aluminium winding set and slightly different stator and rotor diameters. The three DFIG models were analysed using finite element analysis (FEA) in ANSYS Maxwell, and the simulation results were obtained. According to the FEA results, Model-1 with copper windings had a higher efficiency than Model-2 with aluminium windings, but Model-2 had better cost and weight performance than Model-1. Model-3 and Model-1 had similar efficiencies, but Model-3 had a slightly greater torque ripple compared to Model-1 because of a slightly different stator and rotor diameter. Although the total machine weight of the aluminium-wound DFIGs was slightly increased, the total manufacturing costs were less than those of the copper-wound DFIGs at the same efficiency levels.

Reliability analysis of 15MW horizontal axis wind turbine rotor blades using fluid-structure interaction simulation and adaptive kriging model

Over the course of the last four decades, the rotor diameter of Horizontal Axis Wind Turbines (HAWTs) has undergone a substantial increase, expanding from 15 m (30 kW) to an impressive 240 m (15MW), primarily aimed at enhancing their power generation capacity. This growth in blade swept area, however, gives rise to heightened loads, stresses and deflections, imposing more rigorous demands on the structural robustness of these components. To prevent sudden failure and to plan effective inspection, maintenance, and repair activities, it is vital to estimate the reliability of the rotor blades by considering all the forces (aerodynamic and structural dynamics) acting on them over the turbine's lifespan. This research proposes a comprehensive methodology that seamlessly combines fluid-structure interaction (FSI) simulation, Kriging model/algorithm and Adaptive Kriging Monte Carlo Simulation (AKMCS) to assess the reliability of the HAWT rotor blades. Firstly, high-fidelity FSI simulations are performed to investigate the dynamic response of the rotor blade under varying wind conditions. Recognizing the computationally intensive nature and time-consuming aspects of FSI simulations, a judicious approach involves harnessing an economical Kriging model as a surrogate. This surrogate model adeptly predicts blade deflection along its length, utilizing training and testing data derived from FSI simulations. Impressively, the Kriging model predicts blade deflection 400 times faster than the FSI simulations, showcasing its enhanced efficiency. The optimized surrogate model is then used to estimate the flap wise blade tip deflection for one million wind speed samples generated using Weibull distribution. Thereafter, to evaluate the reliability of the blades, statistical modeling using methods such as Monte Carlo Simulation (MCS), AKMCS is performed. The results demonstrate the faster convergence of AKMCS requiring only 21 samples, as opposed to 1 million samples for MCS with minimal reduction in the precision of the estimated probability of failure (Pf) and reliability index (β). Demonstrated on the backdrop of an IEA-15MW offshore reference WT rotor blade, the proposed methodology underscores its potential to be seamlessly incorporated into the creation of WT digital twins, due to its near real-time predictive capabilities for Pf and β assessments.

Control co-design of power take-off and bypass valve for OWC-based wave energy conversion systems

Wave energy is a significant source of renewable energy harnessed by wave energy converters (WECs). However, due to the relatively high levelised cost of energy (LCoE), wave energy has not attained a commercial stage yet. To minimise the LCoE, since the optimum (uncontrolled) WEC design typically differs from the optimum controlled WEC design, control co-design (CCD) techniques are essential. With CCD, the WEC control-related aspects are taken into account from the start of the WEC design phase and, ideally, the best control-informed WEC design is then achieved. This paper specifically focuses on CCD for an oscillating-water-column (OWC) WEC, equipped with a Wells turbine and a bypass valve. In essence, a parametric CCD approach is devised to find the optimum (control-informed) turbine rotor diameter, and bypass valve diameter, for the considered OWC WEC. In particular, the optimum design parameters minimise a ‘simplified’ LCoE, which is chosen as a suitable performance function. Despite the LCoE is primarily sensitive to the power take-off size, rather than to the bypass valve size, peak-shaving control with a bypass valve potentially increases the capacity factor and, consequently, can minimise the LCoE for small-to-medium sized turbines.

Profiling wind LiDAR measurements to quantify blockage for onshore wind turbines

AbstractFlow modifications induced by wind turbine rotors on the incoming atmospheric boundary layer (ABL), such as blockage and speedups, can be important factors affecting the power performance and annual energy production (AEP) of a wind farm. Further, these rotor‐induced effects on the incoming ABL can vary significantly with the characteristics of the incoming wind, such as wind shear, veer, and turbulence intensity, and turbine operative conditions. To better characterize the complex flow physics underpinning the interaction between turbine rotors and the ABL, a field campaign was performed by deploying profiling wind LiDARs both before and after the construction of an onshore wind turbine array. Considering that the magnitude of these rotor‐induced flow modifications represents a small percentage of the incoming wind speed ( ), high accuracy needs to be achieved for the analysis of the experimental data and generation of flow predictions. Further, flow distortions induced by the site topography and effects of the local climatology need to be quantified and differentiated from those induced by wind turbine rotors. To this aim, a suite of statistical and machine learning models, such as k‐means cluster analysis coupled with random forest predictions, are used to quantify and predict flow modifications for different wind and atmospheric conditions. The experimental results show that wind velocity reductions of up to 3% can be observed at an upstream distance of 1.5 rotor diameter from the leading wind turbine rotor, with more significant effects occurring for larger positive wind shear. For more complex wind conditions, such as negative shear and low‐level jet, the rotor induction becomes highly complex entailing either velocity reductions (down to 9%) below hub height and velocity increases (up to 3%) above hub height. The effects of the rotor induction on the incoming wind velocity field seem to be already roughly negligible at an upstream distance of three rotor diameters. The results from this field experiment will inform models to simulate wind‐turbine and wind‐farm operations with improved accuracy for flow predictions in the proximity of the rotor area, which will be instrumental for more accurate quantification of wind farm blockage and relative effects on AEP.

Wind tunnel experimental study on static aerodynamic performance of SB-VAWT without intermediate support axes

Wind power generation is considered an effective way for ships to harness wind energy, and the aerodynamic characteristics of wind turbines determine wind energy utilization and efficiency. However, traditional vertical axis wind turbines have intermediate shafts and support rods, which result in large negative effects in the research of the wind turbine aerodynamic characteristics. To address this issue, a Straight-Bladed Vertical Axis Wind Turbine (SB-VAWT) without intermediate support axes is proposed. The turbine can flexibly change the number of blades, rotor diameter, and installation position of blades. The static aerodynamic performance of the wind turbine with different combinations was tested in a wind tunnel laboratory at 10 m/s. The results show that the radius of the wind turbine has a greater effect on the drag coefficient for the same number of blades, with an inverse relationship between the drag coefficient and radius, and a positive association between lift coefficient, static torque coefficient, and radius. The drag coefficient is proportional to the number of blades at the same radius, while the static torque coefficient is inversely proportional to the number of blades. According to the results, placing the initial location in the azimuth range between 30° and 50° can obtain the maximum initial starting torque. Moreover, a wind turbine with a radius of 16 cm can achieve a higher average torque. Changes in the number of blades can significantly impact turbine properties, resulting in wind turbines with distinct features.

A techno‐economic assessment and optimization of Dumat Al‐Jandal wind farm in Kingdom of Saudi Arabia

AbstractOne major criterion in the selection of wind farm location is the cost of energy (COE). COE is the cost of producing 1 kWh electric energy on an annual basis. Mathematical model of COE includes site‐specific constants (such as reference height, mean wind speed, shape factors, wind shear coefficient, average temperature, and turbine altitude) and wind turbine parameters (such as maximum power coefficient, total loss of energy, cut‐in/cut‐off wind speed, rated wind speed, rated power, and the fix charge rate). In this work, we evaluate the COE of an onshore wind farm located at Dumat Al‐Jandal (Saudi Arabia) according to the hub height and rotor size. The 99 Vestas turbines can be mounted at a hub height ranging from 105 to 166 m with available rotor diameters of 105, 112, 117, 126, 136, 150, 155, or 163 m. Particle swarm optimization with a normal distribution is used to optimize the COE. Results show that COE is varying around the average value of $0.029335/kWh by ±$0.00021/kWh. The minimum COE was achieved with a rotor diameter of 150 m at hub height of 105 m. COE increases with the increase of hub height. At 105 m‐hub height, COE is almost the same, with a variation of 0.03% (It ranges between $0.029125/kWh and $0.029133/kWh). COE is more sensitive to rotor size than hub height. This investigation revealed that the COE estimation is in a range of 39%–48% greater than that announced COE by the developing project consortium.

Pseudo-optimum geometries for 1-100 ton spool compressors with low-GWP refrigerants

Simulation models are often employed for guiding compressor prototype development, particularly for novel devices like the spool compressor. The spool compressor is a novel compressor technology that can provide competitive performance for low-pressure refrigerants (like R1234ze(E)) with a compact design. A parametric study is presented to find the optimum geometric aspect ratio for five refrigerants (CO2, R134a, R454B, R468B and R1234ze(E)) and a range of cooling capacities between 1-100 RT. A pseudo-optimum geometry is explored by varying the aspect ratio, defined by the eccentricity ratio (rotor diameter to bore diameter), and the compressor L/D ratio (axial length to bore diameter), varying from 0.75-0.8 and 0.4-3, respectively. A scaling model is developed to vary the compressor geometry and ports. A spool compressor model, developed by Bradshaw and Groll (2013), is extended and by validating the model using data from 30 RT and 40 RT prototype compressors using R134a and R1234ze(E). The model is then used to predict the performance of a spool compressor with the various geometric inputs and refrigerants. The results suggest that the volumetric and isentropic efficiencies can be maximized by using an eccentricity ratio of 0.75 and L/D ratios from 1-1.5 for various displacement volumes. The results showed that the optimum isentropic efficiency increases asymtoptically from 1 to 100 RT for most working fluids and it increases linearly for CO2. Additionally, the compressor performance becomes insensitive to the aspect ratio for large compressor sizes.

Methods of improving the parameters of rotary-plate machines

The paper presents the results of theoretical analysis and experimental studies of power loads acting on the plates of a rotary-plate machine in order to significantly reduce power loads and drive power. Experimental studies of prototypes of RPMs with magnetic pressing of plates, performed according to the method of G. N. Trunov, have shown significant possibilities for reducing the friction of plates on the cylinder, as well as the possibility of using machines with significantly reduced drive power values. A series of micromachines for different rotor diameters are being created using magnetic squeezing devices, which makes it possible to significantly improve the dynamic characteristics of these micromachines, increase their efficiency and outline prospects for further research on improving the designs of RPMs.

Effect of the vertical wake deflection on the response of a 12MW semisubmersible FWT

The need to understand the interaction of floating wind turbines operating in the marine boundary layer with other surrounding turbines is of increasing importance as wind farms and rotor sizes get larger. For low wind speed conditions, the wake deflects upwards due to the floating wind turbine built-in rotor tilt and the platform pitch angle. Furthermore, based on field data from the North Sea, a convective atmosphere is likely to occur, especially for lower wind speeds. It is therefore key to understand the combined effect of meandering, wake deflection and atmospheric stability for low wind speed conditions on the floating wind turbines in a wind farm.In this work, to account for atmospheric stability, data from large-eddy simulation (LES) for a 7.5m/s wind speed scenario and three atmospheric stability conditions, are used as input to FAST. Farm to study the effect of the wake deflection upwards on a 12 MW semisubmersible placed 8 rotor diameters (D) downwind of a stationary wind turbine. Three built-in shaft tilt angles cases are considered for the fixed upwind turbine: 12°, 6° and no tilt angle. The main effects of the wake deflection are on the power output of the floating wind turbine in the wake, and on the tower top yaw moment. For stable conditions, the mean tower top yaw moment increases by more than three times. The findings of this work contribute to the investigation of the wake deflection as a control strategy to minimize wake losses in floating wind farms.

Experimental study on the evolution of wind turbine wake under streamwise pressure gradients

Wind tunnel experiments were conducted to explore how streamwise pressure gradients, commonly encountered in complex terrains, influence the wake behavior of a small-scale horizontal-axis wind turbine. The study involved measuring the wake characteristics up to 8 rotor diameters downstream in three pressure gradient scenarios: adverse (APG), favourable (FPG), and zero (ZPG) pressure gradients, assessed using the pressure coefficient (Cp) and its spatial gradient (ΔCp/Δx). These experiments were conducted at a rotor diameter Reynolds number of 96,000 with an inflow velocity of 10 m/s. The results indicate that while the pressure gradients have a more substantial impact on the wake’s velocity deficit, they have a minor effect on its velocity distribution. Nevertheless, non-zero pressure gradients cause significant deformations in the wake’s shape and vertical displacement of its center. Specifically, the FPG case demonstrates enhanced wake velocity recovery, whereas the APG case exhibits slower recovery than the ZPG case. Turbulent kinetic energy decreases as the wake progresses downstream in all cases, with the APG case consistently showing higher values at all measurement locations. Moreover, a consistent pattern of axial vorticity is observed close to the rotor across different pressure gradient cases, with the FPG case displaying notable organisation and amplification of axial vorticity.

Development of "Aria," a Compact, Quiet Personal Electric Helicopter

This paper describes the development and flight testing of a personal air vehicle by team Harmony for the GoFly Prize competition. The competition emphasized an open-air ight experience, and the nal aircraft was scored by size (≤ 8.5 ft), noise (<87 dBA), and speed (>30 kt). The highest scoring team would win a $1 million grand prize. Team Harmony endeavored to develop an aircraft which would maximize the competition score. A counterrotating coaxial electric helicopter con guration was chosen to maximize rotor area and reduce disk loading for efficiency and acoustic benefits. The rotors were designed through a parametric study using an in-house aerodynamics code, an in-house acoustics code, and CREATE TM -AV Helios CFD. A quiet electric power train and custom 11 kWh battery were developed. Flight control was implemented with dual, independent, electronically coupled swashplates. A one-third-scale prototype aircraft was first developed and flighttested. Then a full-scale, 520 lb (235.4 kg) prototype with an 8.45 ft(2.58 m) rotor diameter was developed and flight-tested. During hovering, the measured sound pressure levels at 50 ft(15.24 m) were 73 dBA. The full-scale vehicle crashed before its speed capabilities could be tested, but the aircraft would have likely scored well, achieving the goal of the project. This work encompassed several design trade-offs, especially between aerodynamic and acoustic performance in the rotor and blade design, and between acoustics and endurance in the power source selection, and in availability and flight-worthiness of off-the-shelf hardware for personal flight.

Wake interaction of aligned wind turbines over two-dimensional hills

An experimental investigation was carried out to explore the interaction and wake statistics of model wind turbines operating individually and in pairs over two-dimensional hills with varying heights. The hills shared a sinusoidal shape and extended L/D=20 in the streamwise direction, where D represents the diameter of the turbine rotor. The peak heights of the hills were H/D=0, 0.5, 1, and 1.5. The first turbine was located at the beginning of the hill development, and the second turbine was positioned halfway between the first and the hill's peak, downwind. The flow in the intermediate wake regions was characterized using particle image velocimetry, focusing on the recovery mechanisms of streamwise momentum on the windward side of the hills, ranging from gentle to steep-up slopes. The results indicate that the advection terms play a more significant role than turbulence in the wake recovery mechanism with steeper hill slopes. Associated reduced turbulence levels are attributed to flow acceleration, which led to a higher power availability at the top of the hills.

Difference in load predictions obtained with effective turbulence vs. a dynamic wake meandering modeling approach

Abstract. According to the international standard for wind turbine design, the effects of wind turbine wakes on structural loads can be considered in two ways: (1) by augmenting the ambient turbulence levels with the effective turbulence model (EFF) and then calculating the resulting loads and (2) by performing dynamic wake meandering (DWM) simulations, which compute wake effects and loads for all turbines on a farm at once. There is no definitive answer in scientific literature as to the consequences of choosing one model over the other, but the two approaches are unarguably very different. The work presented here expounds on these differences and investigates to what extent they affect the simulated structural loads. We consider an idealized 4×4 rectangular array of National Renewable Energy Laboratory 5 MW wind turbines with a spacing of 5 by 8 rotor diameters and three wind speed scenarios at high ambient turbulence. Load simulations are performed in OpenFAST with EFF and in FAST.Farm with the DWM implementation. We compare ambient turbulence, wind farm turbulence, and loads between both approaches. When omnidirectional results are compared, EFF wind farm turbulence intensity is consistently higher by 0.2 % (above-rated wind speed) to 2.7 % (below-rated wind speed). However, for certain wind directions, the EFF turbulence can be lower than FAST.Farm by almost 9 %. Wind speeds within the farm were found to differ by up to 3 m s−1 due to the lack of wake deficits in the EFF approach, leading to longer tails toward low values in the FAST.Farm mean load distributions. Consistent with the turbulence results, the median EFF load standard deviations are also consistently higher, by a maximum of 20 % and 17 % for blade-root out-of-plane and tower-base fore-aft moments, respectively.

Disentangling mechanisms responsible for wind energy effects on European bats

Mitigating anthropogenic climate change involves deployments of renewable energy worldwide, including wind energy, which can cause significant impacts on flying animals. Bats have highly contrasted responses to wind turbines (WT), either through attraction increasing collision risks, or avoidance leading to habitat losses. However, the underlying mechanisms remain largely unknown despite the expected rapid evolution of WT size and densities. Here, using an extensive acoustic sampling (i.e. 361 sites-nights) up to 1483 m from WT at regional scale, we disentangle the effects of WT size (ground clearance and rotor diameter), configuration (density and distance), and operation (blade rotation speed and wake effect) on hedgerow use by 8 bat species/groups and one vertical community distribution index. Our results reveal that all WT parameters affected bat activity and their vertical distribution. Especially, we show that the relative activity of high-flying species in the community was lower for higher WT density and lower ground clearance. Medium-flying species were sensitive to wind turbine distance, with either attraction or avoidance depending on proximity to the wake area and wind conditions. Specifically, wind turbine distance, wake effect and their interaction each affected the activity of one, three, and three species out of eight, respectively. Blade rotation and rotor diameter affected the activity of four and three species/groups, respectively, and ground clearance affected the activity of five ones. Taken together, WT configuration, operation, and size parameters affected the activity of three, five, and seven out of eight species/groups, respectively. These results call for the consideration of all these factors when assessing the ecological sustainability of future wind farms. The study especially advocates to avoid high WT densities, large rotors, and to site WT as far as possible from optimal habitats such as woody edges and not between them and the source of prevailing winds, in order to limit bats-WT interactions.

Effects of blade tip flow on aerodynamic characteristics of straight-bladed vertical axis wind turbines

Straight-bladed vertical axis wind turbines (SB-VAWTs) are increasingly recognized as a favorable choice for wind energy systems in both urban and offshore environments. This study examines the effects of the blade tip flow on the aerodynamic characteristics of SB-VAWTs by numerical simulation. The analysis employs a comprehensive set of 84 models, varying in parameters such as rotor diameters, blade chord lengths, tip speed ratios, blade aspect ratios (ARs), and airfoil types. Initially, the blade is modeled using the finite division method, followed by a comprehensive three-dimensional URANS numerical simulation. A comprehensive analysis of the aerodynamic performance across the blade span is conducted to quantify the effects of the blade tip flow. The findings indicate that, in addition to causing losses, the tip flow also encourages reattachment of the separated flow onto the blade surface, especially under conditions of stronger flow separation. The influence of the tip flow reduces with a higher AR for AR less than 8. However, when AR surpasses 8, the effect of tip flow stabilizes. This study will serve as a valuable reference for the design of SB-VAWTs and lay the groundwork for future research on blade tip optimization.

Effect of atmospheric stability on the dynamic wake meandering model applied to two 12 MW floating wind turbines

AbstractCurrent global analysis tools for floating wind turbines (FWTs) do not account for the combined effects of atmospheric stability and wakes from neighboring turbines. This work uses the mid‐fidelity dynamic wake meandering model, together with turbulent wind fields generated based on stable, neutral, and unstable atmospheric conditions, to study the low‐frequency content of the global responses of two semisubmersible FWTs separated by eight rotor diameters. Incoming wind fields based on the Kaimal spectrum and exponential coherence model, the Mann spectral tensor model, and a time‐series input‐based turbulence model are used. The respective input parameters for these models are fitted to high‐fidelity large eddy simulation data.In unstable, below‐rated conditions, meandering leads to an increase in the yaw standard deviation of the downwind turbine of almost three times larger than the upwind turbine. Deficit and the upwards wake deflection affect the mean pitch and yaw, especially for the below‐rated wind speed scenario. The mean pitch of the downwind turbine is reduced up to half the mean pitch value of the upwind turbine, whereas the mean yaw changes direction due to the enhanced effect of shear. The effect of meandering on the structural loading is highest on the standard deviation of the tower‐top yaw moment of the downstream turbine, which increases more than 2.2 times compared to the upwind turbine value. Based on these findings, atmospheric stability affects wake deficit and meandering which in turn have a profound effect on the low‐frequency global motions and structural response of floating wind turbines.

ПОИСК НОВЫХ ВАРИАНТОВ КОНСТРУКЦИИ ТЯГОВОГО ПРИВОДА НИЗКОПОЛЬНЫХ ЭКИПАЖЕЙ

The possibility of increasing locomotive traction properties without using drives with asynchronous traction electric motors (TED) and pulse width modulation is considered. It is proved that collector TED allows realizing the traction force in a continuous mode of 63.75 kN per axle with a wheel diameter of 1250 mm, while it is advisable to use a drive with a support frame suspension of TED and an axial gearbox. Due to the significant mass of collector TED, it is proposed to make a promising diesel locomotive in the form of two sections on three two-axle bogies and a booster on two two-axle bogies. Taking into account that electric arc asynchronous motors (EAAM) simplify the converter part of the drive by eliminating pulse width modulation, a design of a traction drive for EAAM with a hollow shaft in the recess formed by arc-shaped inductors is proposed, which makes it possible to realize EAAM torque and locomotive traction force by increasing the diameter of EAAM rotor.

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.

Performance Assessment of a Multi-Rotor Floating Tidal Energy System

Performance assessments of full-scale tidal turbines have been carried out for multiple machines deployed globally and reported in literature. The rotor number and diameter of the demonstrated tidal energy converters differs from single rotor devices in the MW class to scalable arrays of comparably small turbines. For multi-rotor systems (MRS), potential interaction, positive or negative, remains a key research question. Previous studies at Sustainable Marine prototype system (PLAT-I 4.63) have implied that variations in the incoming flow field are highly likely to cause deviations in rotor performance.
 Sustainable Marine has developed and built the pre-commercial PLAT-I 6.40 platform. PLAT-I 6.40 has been connected to the Canadian grid in May 2022. Between May and end of September 2022 the system has been undergone comprehensive commissioning and performance trials. PLAT-I 6.40, carries six 4m diameter SCHOTTEL Instream Turbines (SIT), each rated at 70 kW. This work presents the results of full-scale field tests that focussed on the assessment of differences in the performance between the individual turbines during summer 2022.
 To evaluate the variances in the flow field across all rotors, a specific test campaign has been conducted, where a flow speed sensor was sequentially positioned upstream of each turbine while a second flow measurement device was stationary as reference. For all test configurations the power curves have been determined following the guidance of the IEC TS 62600-200 based on the flow speeds measured with both devices.
 This paper presents the experimentally obtained power curves for each test configuration and compares it against the reference values. The results show that there are steady differences in the flow field resulting in varying power outputs across the different rotors (Figure 1). However, a comparison of the individual rotor power curves with the design predictions shows good agreement.