Hydrokinetic Turbine Blades Research Articles

Surrogate modelling for high-lift multi-element hydrofoil shape optimization of a hydrokinetic turbine blade

The hydrodynamic shapeof a blade is one of the most important factorsin the design process of a horizontal axis hydrokinetic turbinethat influencesits performance. The present work is focused on thedesign and hydrodynamic analysis of a high-lift system using the optimization methodof surrogate models and computational fluid dynamics(CFD)analysis.The parameters that affectthe amount of the lift and the drag force thata hydrofoil cangenerate are the gap, the overlap, the flap deflection angle(δ), the flap chord length(C2) andthe angle of attackof the hydrofoil(α). These factors were varied to examine theturbine performancein terms ofthe ratio between the lift (CL) and the dragcoefficient(CD), and the minimum negative pressure coefficient (min Cpre) in order toavoid the cavitation inception. For this propose, surrogatemodels were implemented to analyse the CFDresultsand find the optimal combination of the design parameters of the high-lift hydrofoil.ThetraditionalEppler 420 hydrofoil was utilized for the design of the multi-element profile, which wascomposed of a main element and a flap. The multi-element design selected as optimal had a gap of 2.825 %C1, an overlap of 8.52 %C1, a δ of 19.765 ̊, a C2of 42.471 %C1and a αof -4 ̊, where C1refers to the chord length of the main element.In comparison with the traditionalEppler 420hydrofoil,CL/CDratio increasesfrom 39.050 to 42.517.

Design, Manufacture and Testing of an Open-Source Benchmark Composite Hydrokinetic Turbine Blade

In a trend towards clean energy alternatives, recent years have seen great strides in the marine energy space. This has resulted in a pressing need for the design, development, and validation of novel energy harvesting technologies such as hydrokinetic devices, which capture kinetic energy from waves, tides, and currents. However, these devices span numerous concepts and designs that often lack solid benchmark research that can be freely referenced. This work focuses on the design process of an open-source composite hydrokinetic turbine blade for a three-bladed marine turbine rotor assembly with a diameter of 2.5 m. The proposed blade consists of two structural composite skins that are bonded with an adhesive and filled with a foam core. This study will explore and contrast the efficiency and resolution of low-fidelity rapid design methodologies and comprehensive high-fidelity approaches for the blade design, modeling, and analysis efforts, a key objective in this research. Blade hydrodynamic loads were modeled and applied to finite-element blade models to study deformations and potential failure. Ongoing efforts will result in blade manufacture and structural testing at the National Renewable Energy Laboratory. In future work, multiple blades will be deployed at the Living Bridge site at the University of New Hampshire and will be compared to rigid aluminum blades of the same geometry, developed by Sandia National Laboratories. Ultimately, this research will lay foundational groundwork for researchers and manufacturers, establishing a baseline composite blade design that will serve as a benchmark in the development of future hydrokinetic turbine blades.

A novel method of optimizing the Savonius hydrokinetic turbine blades using Bezier curve

Renewable electricity is increasingly gaining importance due to the quest for energy security and the harmful effects of fuel-based energy sources. Savonius hydrokinetic turbine (SHKT) can be a suitable means to provide electricity using rivers, canals, etc. Optimization of blade shape can play a vital role in enhancing the efficiency of SHKTs. A novel method to generate blade shapes has been proposed in this work using a Bezier curve with six control points. The method involves splitting a blade into two halves and optimizing those separately to simultaneously increase the pressure difference and the normal incoming velocity. The generated blade shapes were studied using a 3D transient computational model, which was validated with the obtained experimental results. Results showed that the blades generated using the proposed model show superior performance compared to conventional semicircular blades as well as the blades generated using four points Taguchi method. The most optimum blade profile achieved a maximum power coefficient of 0.21 at a tip speed ratio of 0.8. The efficiency of this new blade profile was found to be 16.7% higher compared to the semicircular blade, while the best blade using four points method was merely 2.1% more efficient than the semicircular blade.

Determinations and performance investigations of hybrid composite properties for hydrokinetic turbine blades

In this experimental study, hybrid composite properties for hydrokinetic turbine blades were determined, and its performance was examined. The reinforcements included glass fiber, treated and untreated highland bamboo fiber, reinforced polyester-based composites and their hybrid composites, as well as row bamboo (bamboo culm). The row bamboo was prepared on the bamboo culm’s outer surface to get rid of any leftovers, before cutting in accordance with the specimen test standards. In order to make hybrid composite materials, polyester resin was mixed with fibers in the proportions of bamboo fiber/glass fiber (50%/50%), and fiber/matrix (30%/70%). The composite containing glass fiber has a flexural strength that is 12% and 21% higher than materials reinforced with alkali-treated and untreated highland bamboo fiber reinforced composites respectively. The alkali treatment of highland bamboo fiber improved its physical-mechanical properties, making it suitable for use different application. Alkaline treatment boosts the composite’s tensile and compressive strength by 37% and 3.4% for composite reinforced with untreated bamboo fiber, and 10.2% and 23.8% for composite reinforced with glass fiber, respectively. The fiber density of highland bamboo was increased by removing less dense non-cellulosic components (hemicellulose and lignin). However, the fiber’s moisture absorption is the main issue in using it in a composite that works submerged in water. This study investigated whether incorporating glass fiber in highland bamboo-glass fiber polyester hybrid composite reduces the composite material’s water uptake. A reduction was found, however, the density was increased. It is challenging to employ row bamboo for the construction of hydrokinetic turbine blades as water ingress of the composite must be avoided even in the presence of erosion caused by cavitation and impact with foreign bodies in the water.

Prediction of Unstable Hydrodynamic Forces on Submerged Structures under the Water Surface Using a Data-Driven Modeling Approach

Catastrophic failures of partially or fully submerged structures, e.g., offshore platforms, hydrokinetic turbine blades, bridge decks, etc., due to the dynamic impact of free surface flows such as waves or floods have revealed the need to evaluate their reliability. In this respect, an accurate estimation of hydrodynamic forces and their relationship to instability in structures is required. The computational fluid dynamics (CFD) solver is known as a powerful tool to identify dynamic characteristics of flow; however, it commonly consumes a huge computational cost, especially in cases of re-simulations needed. In this paper, an efficient surrogate model based on the Gaussian process is developed to rapidly predict the nonlinear hydrodynamic pressure coefficients on submerged bodies near the water surface. For this purpose, a CFD model is first developed, which is based on a two-dimensional incompressible Navier–Stokes solver incorporating free surface treatment and turbulent flow models. Then, an experimental design is adopted to generate initial training samples considering the effect of the submerged body shape ratio and flow Re number. Surrogate models of hydrodynamic pressure coefficients and their instability based on Gaussian process modeling are established using the outcome from the CFD simulations, where optimal trend and correlation functions are also investigated. Once surrogate models are obtained, the mean and oscillation amplitudes of hydrodynamic pressure coefficients on a submerged rectangular body, which represents the shape of most civil structures, can be rapidly predicted without the attempt at re-simulation. The findings can be practically applied in rapidly assessing hydrodynamic forces and their instability of existing submerged civil structures or in designing new structures, where a suitable shape ratio should be adopted to avoid flow-induced instability of hydrodynamic forces.

Cavitation Inception on Hydrokinetic Turbine Blades Shrouded by Diffuser

Diffuser technology placed around hydrokinetic rotors may improve the conversion of the fluid’s kinetic energy into shaft power. However, rotor blades are susceptible to the phenomenon of cavitation, which can impact the overall power efficiency. This paper presents the development of a new optimization model applied to hydrokinetic blades shrouded by a diffuser. The proposed geometry optimization takes into account the effect of cavitation inception. The main contribution of this work to the state of the art is the development of an optimization procedure that takes into account the effects of diffuser efficiency, ηd, and thrust, CTd. The authors are unaware of any other work available in the literature considering the effect of ηd and CTd on the cavitation of shrouded hydrokinetic blades. The model uses the Blade Element Momentum Theory to seek optimized blade geometry in order to minimize or even avoid the occurrence of cavitation. The minimum pressure coefficient is used as a criterion to avoid cavitation inception. Additionally, a Computational Fluid Dynamics investigation was carried out to validate the model based on the Reynolds-Averaged Navier–Stokes formulation, using the κ−ω Shear-Stress Transport turbulence and Rayleigh–Plesset models, to estimate cavitation by means of water vapor production. The methodology was applied to the design of a 10 m diameter hydrokinetic rotor, rated at 250 kW of output power at a flow velocity of 2.5 m/s. An analysis of the proposed model with and without a diffuser was carried out to evaluate the changes in the optimized geometry in terms of chord and twist angle distribution. It was found that the flow around a diffuser-augmented hydrokinetic blade doubles the cavitation inception relative to the unshrouded case. Additionally, the proposed optimization model can completely remove the cavitation occurrence, making it a good alternative for the design of diffuser-augmented hydrokinetic blades free of cavitation.

Calculation of the induced velocities in lifting line analyses of propellers and turbines

Lifting line analyses of propellers and horizontal-axis turbines require the axial and circumferential velocities induced by the helicoidal vorticity shed from the blades. These velocities can be found from the analytic solution for a helical vortex of constant radius and pitch due to Kawada and Hardin. This solution, however, involves infinite series of products of Bessel functions and their derivatives, whose evaluation is computationally intensive partly because the number of terms required for a specified accuracy increases without bound as the vortex is approached. We compare three closed-form approximations to the Kawada–Hardin equations. The first, due to Kawada and rediscovered by Lerbs, involves asymptotic expansions for large pitch whereas the second is a more general approximation derived by Wrench and subsequently by Okulov. The last uses additional terms found by Okulov. The three have comparable evaluation times but the third is more accurate. The accuracy of the approximations is assessed for N equispaced and identical helical vortices where N is the number of blades. We provide, for the first time, approximate “remainders” for the Kawada–Hardin equations which allow an assessment of the number of terms in the series required to achieve a specified accuracy. As a test case for assessing the calculations of induced velocity, we consider the design of a hydrokinetic turbine blade to avoid cavitation at two different operating conditions with different vortex pitch. The use of the approximated induced velocities is compared to Prandtl’s well-known tip loss factor. Near the hub and tip the blade shape is altered considerably by the induced velocities and the method used to calculate them.

Performance analysis of a modified Savonius hydrokinetic turbine blade for rural application

For rural areas situated in the deep topography of Sarawak, the distance from energy grids and plants are situated too far from the power appliances. Hence, sustainable alternative method of generating energy for the people should be put into consideration. For rural areas rich with riverine streams, the employment of hydrokinetic turbines (HKT) would be a good alternative to meet their daily requirements. The HKTs are fundamentally understood as a turbine that harnesses the kinetic motion of freestreams without the need of head. In the preceding years, the development of HKT turbines has undergone several breakthroughs in terms of efficiency and design. However, at low water depths cluttered with debris, it makes the implementation of certain HKT orientations limited. In such cases, the Savonius style SKTs would be one of the promising deployments in riverine systems. In this paper, a newly developed Savonius blade profile by Roy & Saha was simulated in a fluid medium of water through the CFD software StarCCM+. The two-dimensional unsteady Reynolds Averaged Navier Stokes equations was solved using the shear stress transport k-co turbulence model at a Reynolds number of 0.71-1.88×105 and water speed ranging from 0.3-0.8 m/s. The maximum power coefficient generated by the modified blade was 0.43 at TSR=1.0 and Re=1.88×105.

Optimization Technique for Hydrokinetic Turbine Blades: Pressure Minimization Approach

Everyday rise in world population push for more energy demand. The dependence and usage of fossil fuel in an uncontrolled manner has triggered environmental imbalance. A need to discourage the use of fossil fuel birth renewable energy is a form of energy which is not just environmentally friend but relatively cheap. Hydrokinetic turbine is a device which extracts kinetic energy from moving water to generate power. Hydrokinetic blade is an integral part of hydrokinetic turbine which is one of the components that determines the output power. There is power loss during the operation of the turbine and there is need to reduce this loss. This gives rise to a need to develop an optimization technique that can optimize turbine blade in addition to the existing models. Parameters concentrated on include pressure coefficient, axial induction factor, tangential induction factor, local tip speed ratio and angle of flow

Fatigue life estimation of hydrokinetic turbine blades

Fatigue analysis of hydrokinetic blades is essential as they are subjected to dynamic loads during their operation. This makes fatigue life estimation very important during turbine design. Therefore, this work investigates fatigue life of hydrokinetic turbine blades placed downstream of a hydroelectric power plant. The adopted methodology requires that variations in velocity, load, and stress need to be well established. Historical data of the river at the site are used as reference for variation in flow velocity. The blade element theory is implemented to calculate loads, while stresses are estimated from a finite element model. The S-N method, the rainflow count, and the Palmgren–Miner rule are used to calculate fatigue. This whole process is facilitated by the creation of computational tools to automate different steps. As a result, a life of approximately 20 years is predicted for the blade, neglecting the turbulence that occurs in the speed of the river. When considering a turbulence of 5%, the estimation is reduced to 17 years, indicating a reduction of 15% in life. The complete codes can be downloaded from https://github.com/engsergiocustodio/fatigueblades.

Multivariate sensitivity analysis for dynamic models with both random and random process inputs

Dynamic models with both random and random process inputs are frequently used in engineering. However, sensitivity analysis (SA) for such models is still a challenging problem. This paper, therefore, proposes a new multivariate SA technique to aid the safety design of these models. The new method can decompose the SA of dynamic models into a series of SA of their principle components based on singular value decomposition, which will make the SA of dynamic models much more efficient. It is shown that the effect of both random and random process inputs on the uncertainty of dynamic output can be measured from their effects on both the distributions and directions of the principle components, based on which the individual sensitivities are defined. The generalized sensitivities are then proposed to synthesize the information that is spread between the principal components to assess the influence of each input on the entire uncertainty of dynamic output. The properties of the new sensitivities are derived and an efficient estimation algorithm is proposed based on unscented transformation. Numerical results are discussed with application to a hydrokinetic turbine blade model, where the new method is compared with the existing variance-based method.

Real-time estimation error-guided active learning Kriging method for time-dependent reliability analysis

• A novel active learning and modeling method is proposed for time-dependent reliability analysis. • The real-time estimation error is quantified to measure the prediction accuracy. • A maximum error-guided adaptive refinement strategy is developed to reduce the estimation error. • The propose method is applied to the hydrokinetic turbine blade and self-balancing vehicle. Time-dependent reliability analysis using surrogate model has drawn much attention for avoiding the high computational burden. But the surrogate training strategies of existing methods do not directly consider the estimation error of failure probability, leading to the limitations that some computationally expensive samples are wasted or some algorithms tend to terminate prematurely. To address the challenges, this work proposes a real-time estimation error-guided sampling method. As the classification of random points may be not completely accurate, the wrong-classification probability is calculated by using the mean and variance of Kriging prediction. With this probability, the total numbers of wrongly classified points are obtained. Furthermore, the confidence intervals of the numbers are computed based on the probability theory, and the estimation error of failure probability is calculated through the confidence intervals. Subsequently, the point maximizing the probability is identified as the new sample for decreasing the estimation error, and the maximum error is used to guide when to stop the refinement of Kriging model. Results of three cases demonstrate the performance of the proposed method.

Time-Dependent System Reliability Analysis for Bivariate Responses

Time-dependent system reliability is computed as the probability that the responses of a system do not exceed prescribed failure thresholds over a time duration of interest. In this work, an efficient time-dependent reliability analysis method is proposed for systems with bivariate responses which are general functions of random variables and stochastic processes. Analytical expressions are derived first for the single and joint upcrossing rates based on the first-order reliability method (FORM). Time-dependent system failure probability is then estimated with the computed single and joint upcrossing rates. The method can efficiently and accurately estimate different types of upcrossing rates for the systems with bivariate responses when FORM is applicable. In addition, the developed method is applicable to general problems with random variables, stationary, and nonstationary stochastic processes. As the general system reliability can be approximated with the results from reliability analyses for individual responses and bivariate responses, the proposed method can be extended to reliability analysis of general systems with more than two responses. Three examples, including a parallel system, a series system, and a hydrokinetic turbine blade application, are used to demonstrate the effectiveness of the proposed method.

Flume-scale testing of an adaptive pitch marine hydrokinetic turbine

Modern marine hydrokinetic turbine blades are typically constructed from fiber reinforced polymer (FRP) composites, which provide superior strength- and stiffness-to-weight ratios and improved fatigue and corrosion resistance compared to traditional metallic alloys. Furthermore, numerical studies have demonstrated the possibility of tailoring the anisotropic properties of FRP composites to create an adaptive pitch mechanism that can improve system performance, especially in off-design or varying flow conditions. Potential benefits of an adaptive pitch system include increased lifetime energy capture, reduced hydro-elastic instabilities, reduced risk of mechanical failure, and improved efficiency, load shedding, fatigue life, and structural integrity. In this work, static and dynamic testing results for a flume-scale marine hydrokinetic turbine system are presented. Two sets of adaptive composite blades are compared to neutral pitch composite and rigid aluminum designs. Static testing was used to quantify the mechanical load-deformation response of each blade type. Additionally, instantaneous blade and full system loading was measured during dynamic flume testing, allowing a multilevel analysis of adaptive blade performance. Experimental results show notable shifts in the power and thrust coefficients and significant load adjustments induced through passive pitch adaptation, suggesting that adaptive pitch composite blades could be a valuable addition to marine hydrokinetic turbine technology.

Design and Pitch Angle Optimisation of Horizontal Axis Hydrokinetic Turbine with Constant Tip Speed Ratio

Booming population and associated energy demands, looming threat of exhaustion of conventional sources of energy and the severe environmental repercussions of the same call for alternate sources of clean energy. Hydrokinetic turbine is one such developing technology which harnesses zero-head free flow of water and affects hydrological ecology minimally. This paper discusses the optimisation of Horizontal Axis Hydrokinetic Turbine (HAHkT) blade chord length and twist angle using blade element momentum (BEM) theory to achieve a constant optimal angle of attack (AoA), thus maximising the power output. To achieve this while maintaining robustness at the hub end and eliminate cavitation, two different hydrofoils (S832 and E817) are selected. S832 is simulated using ANSYS 14.0 at low (0 0 ) and high (15 0 ) angles of attack and compared against more widely used NACA 4412 to study flow separation characteristics. This is followed by calculating angles of relative flow, ratios of chord length and subsequently twist angles for each blade element using MATLAB simulations. A blade model is thus developed for visualisation using computer aided designing after obtaining optimal chord lengths and pitch angles.

Time-Dependent Reliability Analysis Using a Vine-ARMA Load Model

A common strategy for the modeling of stochastic loads in time-dependent reliability analysis is to describe the loads as independent Gaussian stochastic processes. This assumption does not hold for many engineering applications. This paper proposes a Vine-autoregressive-moving average (Vine-ARMA) load model for time-dependent reliability analysis, in problems with a vector of correlated non-Gaussian stochastic loads. The marginal stochastic processes are modeled as univariate ARMA models. The correlations among different univariate ARMA models are captured using the Vine copula. The ARMA model maintains the correlation over time. The Vine copula represents not only the correlation among different ARMA models but also the tail dependence of different ARMA models. Therefore, the developed Vine-ARMA model can flexibly model a vector of high-dimensional correlated non-Gaussian stochastic processes with the consideration of tail dependence. Due to the complicated structure of the Vine-ARMA model, new challenges are introduced in time-dependent reliability analysis. In order to overcome these challenges, the Vine-ARMA model is integrated with a single-loop Kriging (SILK) surrogate modeling method. A hydrokinetic turbine blade subjected to a vector of correlated river flow loads is used to demonstrate the effectiveness of the proposed method.

Cavitating response of passively controlled tidal turbines

The use of passive pitch control in marine hydrokinetic turbine (MHK) blades has been shown to provide structural and performance improvements over similar systems with non-adaptive blades. Recent work has demonstrated such advantages as increased lifetime energy capture, reduced hydrodynamic instabilities, and improved efficiency, load shedding, fatigue behavior, and structural integrity. Additionally, passively adaptive blades have been shown to delay cavitation and decrease cavitation volume for marine propellers. For MHK turbines, a reduction in cavitation susceptibility could increase effectiveness of the turbine and reduce the rate of fatigue on the system. In this work, a previously validated, coupled 3-D boundary element method-finite element method solver is used to model two adaptive blades and a non-adaptive reference blade under both uniform and non-uniform inflow conditions. A numerical investigation of the onset of sheet cavitation on an MHK turbine blade and the structural response of a blade under cavitating conditions is presented. Results show that passive control can be used to delay cavitation and decrease cavitation volume under normal operating conditions. Cavitation is shown to increase the rate of fatigue on the system and has the potential to lead to unanticipated failures if proper cavitation analysis is not integral to the MHK turbine design process.

AN APPROACH FOR THE OPTIMUM HYDRODYNAMIC DESIGN OF HYDROKINETIC TURBINE BLADES

This work aims to develop a simple and efficient mathematical model applied to optimization of horizontal-axis hydrokinetic turbine blades considering the cavitation effect. The approach uses the pressure minimum coefficient as a criterion for the cavitation limit on the flow around the hydrokinetic blades. The methodology corrects the chord and twist angle at each blade section by a modification on the local thrust coefficient in order to takes into account the cavitation on the rotor shape. The optimization is based on the Blade Element Theory (BET), which is a well known method applied to design and performance analysis of wind and hydrokinetic turbines, which usually present good agreement with experimental data. The results are compared with data obtained from hydrokinetic turbines designed by the classical Glauert's optimization. The present method yields good behavior, and can be used as an alternative tool in efficient hydrokinetic turbine designs.

Design of Hydrokinetic Turbine Blades Considering Cavitation

Abstract The cavitation is a phenomenon that must be considered into a hydrokinetic turbines design. This assumption has been explored in the last years, principally for the turbine with large diameter, once the relative velocity near the hydrokinetic blade tip is increased, resulting in large angle of attack. Therefore, a mathematical approach for design of hydrokinetic blades is presented. In which a methodology for cavitation prevention is employed. The approach uses the minimum pressure coefficient criterion as a cavitation limit for the flow on the blades. The proposed methodology modifies the local relative velocity in order to prevent the cavitation occurrence on each blade section. The results are compared with data from hydrokinetic turbines designed using the classical Glauert's optimization, on which the proposed approach provides good performance, where the chord distribution along the blade is corrected, and can be used for efficient hydrokinetic turbines design.

Usability of the Selig S1223 Profile Airfoil as a High Lift Hydrofoil for Hydrokinetic Application

This work presents a numerical analysis of the ability of the high lift airfoil profile Selig S1223 for working as hydrofoil under water conditions. The geometry of the hydrofoil blade is designed through a suitable airfoil profile and then studied carefully by means of Computational Fluid Dynamics (CFD) in order to check its hydrodynamic behavior, i.e., including lift and drag analysis, and determinations of streamlines velocities and pressures fields. Finally conclusions on the use of this profile in a possible application for hydrokinetic turbine blades are detailed.