Rotor Blade Profile Research Articles

Experimental investigation of solidity and blade profile effects on H-Darrieus wind rotor: Performance and self-starting analysis

The present study investigates the impact of rotor solidity and blade profile on the self-starting characteristics and performance of H-Darrieus wind rotors (H-rotors) through subsonic wind tunnel experiments. Three symmetrical (NACA 0018) and three unsymmetrical (NREL S823) H-rotors were analyzed to determine the coefficient of static torque (Cts) and coefficient of power (Cp) across three solidities (σ = 0.25, 0.3, and 0.35) and two free stream wind speeds (Uf = 6 and 8 m/s). The findings revealed that the NREL S823-bladed H-rotor outperformed the NACA 0018-bladed H-rotor, displaying 13% and 11% higher Cts values at σ = 0.25 (Uf = 6 and 8 m/s), 9% and 9% at σ = 0.3 (Uf = 6 and 8 m/s), and 13% and 11% at σ = 0.35 (Uf = 6 and 8 m/s). The NREL S823-bladed H-rotor achieved a maximum Cp of 0.197 at σ = 0.3 and Uf = 8 m/s, which is 6% higher than the maximum Cp obtained by the NACA 0018-bladed H-rotor. Furthermore, the trend of maximum Cp values for both H-rotors followed the order of Cp, max σ = 0.25 < Cp, max σ = 0.3 > Cp, max σ = 0.35. Based on the experimental findings, it is inferred that the NREL S823-bladed H-rotor with a solidity of 0.3 is suitable for small-scale wind turbines.

Совершенствование геометрических характеристик водометного движителя насосного типа для судов и кораблей

Object and purpose of research. This paper discusses pump jet propulsor. The purpose of the study was to improve its elements through experimental and theoretical investigation of its hydrodynamics and cavitation properties. This work is a part of the project intended to develop an application for a useful model. Subject matter and methods. To achieve its purposes, the work follows both theoretical and experimental research methods of ship theory. Numerical simulation of pump jet operation was performed in Siemens StarCCM+ commercial software package, and also as per in-house Krylov State Research Centre calculation methods for unviscous and viscous flows. Main results. The study suggests rotor and stator blade profiles that improve hydrodynamic and cavitation performance of basic pump jet versions. It also suggests updated shapes for pump jet stator and aft fairing. The study has shown that these improvements will increase the efficiency of pump jets by 3–5% as compared to the basic version, and will also eliminate several types of cavitation. Conclusion. The study was meant to improve pump jet elements so as to eliminate the flaws of the basic pump jet version. The results will be helpful in further pump jet design and development of the application for useful model.

Evolving a Bio-Inspired Blade Shape of the Drag-based Vertical-axis Wind Rotor Derived from Orange Sea-pen (Ptilosarcus Gurneyi)

Abstract Inspired by the polyp leaf of the Orange sea-pen (Ptilosarcus gurneyi), a novel blade shape of the Savonius vertical-axis wind rotor is developed. The similarities between the aerodynamic and the hydrodynamic aspects of the Savonius rotor blade profile and the sea-pen leaf are reviewed, and an appropriate analogy is thereby established. The shape of the sea-pen leaf is then extracted to fabricate the rotor blades. The performance of this sea-pen bladed rotor is evaluated in a low-speed subsonic wind tunnel at different wind velocities. The two-dimensional (2D) numerical analysis is also performed to support the experimental findings and to study the influence of blade shape on the pressure and the torque distributions of the rotor. The novel sea-pen bladed rotor, having lesser material requirements, is seen to demonstrate higher performance than that of the conventional semicircular bladed rotor in the tested range of low tip-speed ratio.

Performance analysis of novel V-shaped turbine blade profile by three-dimensional numerical investigations with varying overlap ratios for hydropower application

In the present paper, three-dimensional numerical simulations were carried out to examine the influence of the overlap ratio between the two straight edges on the advancing and returning blades of the novel V-shaped rotor blade profiles using the sliding mesh technique. The performance parameters were computed with respect to the tip speed ratio. The findings show that the coefficient of torque and power for the novel V-shaped turbine blade is maximum for the zero-overlap ratio compared to the turbine blade, with an overlap ratio ranging from 0.05 to 0.3. The blade profiles' flow field was visualized at different angular positions, and various significant zones developed during the turbine blade rotation were captured and analyzed. The new overlapping jet developed between the two straight edges of the advancing and returning blade profiles as the overlap ratio varies from 0.05 to 0.3. Therefore, the turbine's performance is reduced due to the development of an overlap jet as it travels parallel to the straight edges of the blade profile and does not impact the rear side of the returning blade profile.

Comparative Analysis of the Vibrational Response of a Homemade Helicopter Main Rotor Blade Profiles

This paper investigates the dynamics of homemade helicopter wooden and aluminum sheet rotor blades. The rotors are articulated and their blades are rigid. The main rotor implementation takes into account flap, lag, and feather degrees of freedom for each of the equispaced blades as well as their dynamic couplings. Transmitted vibrations due to the rotating rotor blades on the body structure (fuselage) are studied. This work presents an aerodynamic model of main rotor blades that allows us to analyse vibrational transmissions on the fuselage (body) of the craft. Vibrations in helicopters is a common problem which involves complex interactions between the inertial, structural and aerodynamic loads, especially in homemade helicopters. The major source of vibrations in helicopters is the main rotor. The efficiency and stability of the main rotor blades is determined by the magnitudes of the predominant frequencies they produce. These vibrations affect the functionality, durability of the engine component parts, increase maintenance frequency (cost), and cause structural failures. The aerodynamic model has been built up using blade element theory. The aerodynamic load creates vibrations on the homemade helicopter and these are analyzed on the fuselage by using a short time Fourier transform that brings out the vibrational spectrum. The results of the analysis serve as a reference to characterize the stability and efficiency of homemade main rotor blade profiles.

Performance prediction and design optimization of turbine blade profile with deep learning method

Aerodynamic design optimization of the blade profile is a critical approach to improve performance of turbomachinery. This paper aims to achieve the performance prediction with deep learning method and realize fast design optimization of a turbine blade. Two parameterization methods based on geometric relationships (PGR) and neural network (PNN) are proposed, which can generate smooth and complete blade profiles. A dual convolutional neural network (DCNN) is constructed to predict the physical fields and aerodynamic performance. The implementations of DCNN are accomplished based on the datasets generated by the two parameterization methods respectively, which are called PGR-DCNN and PNN-DCNN model. Results show that the prediction accuracy increases and then keeps stable as train size increases. The two models can offer the detailed physical field distribution within 3 ms and accurately predict the aerodynamic performance. The prediction errors of performance parameters for 99% samples in validation set are less than 0.5% with PGR-DCNN model, which are significantly better than conventional machine learning methods. Finally, based on the accurate predictive models, the gradient-based design optimization for rotor blade profile is completed in 38 s. The efficiency of the two optimal blades reaches 89.29% and 88.92% respectively, which verifies the feasibility of our method.

Thermographic Stall Detection by Model-Inspired Evaluation of the Dynamic Temperature Behaviour

Model-inspired signal processing approaches with an enhanced detectability of flow separation on thermographic images are presented. Flow separation causes performance loss, structural loads and increasing acoustic emissions on wind turbine rotor blades. However, due to the low thermal contrast between turbulent and separated flow regions, the non-invasive thermographic visualisation of flow separation is currently only possible for wind tunnel measurements, which are characterised by a high thermal contrast and a small measuring distance. The state-of-the-art signal processing approaches evaluate the surface temperature fluctuation of thermographic image series. However, understanding of the signal measurement chain with a distinct consideration of the influences on the dynamic surface temperature is incomplete. Therefore, designing model-inspired signal processing approaches which provide a high interpretability and a maximum contrast is an open task. The proposed signal processing approaches evaluate the surface response selectively, by using the amplitude information of the surface temperature response to an oscillating input signal or gradient-based for a transient input signal. The approaches are applied to wind tunnel measurements on a rotor blade profile at a near thermodynamic steady state and a transient thermodynamic behaviour at Reynolds numbers that are representative for operational wind turbines. The gradient-based evaluation shows an improved contrast for the detection of flow separation, but is only applicable to profiles with transient thermodynamic behaviour. The amplitude evaluation provides a high degree of interpretability of the processed images based on flow-dependent features and enables for an unambiguous identification of flow separation by a global amplitude minimum close to the separation point. Additionally, an increased spatial resolution for surface modifications is shown, while the contrast between flow regions is significantly decreased. Hence, the proposed approaches allow for an improved identifiability of flow separation with regard to future applications on wind turbines in operation.

Field reconstruction and off-design performance prediction of turbomachinery in energy systems based on deep learning techniques

Obtaining the off-design characteristics of core components such as turbines and compressors is the basis of off-design analysis for energy systems. However, the characteristics are difficult to accurately acquire in the initial design stage of turbomachinery. Based on deep learning techniques, an accurate and rapid field reconstruction and off-design aerodynamic performance prediction method is proposed. First, a Generative Adversarial Network with the added Bezier layer is employed to establish a database of turbine blade profiles. Then, a Dual Convolutional Neural Network (Dual-CNN) is established to reconstruct the pressure and temperature fields as well as predict the off-design performances of different profiles and working conditions. Based on the above two kinds of neural networks, a turbine in a solar-based supercritical carbon dioxide Brayton cycle is taken as an example. The field reconstruction and off-design performance prediction are conducted on the basis of the established rotor blade profile database. The accuracy of field reconstruction is guaranteed. The off-design performance prediction of the established Dual-CNN indicates that the example blade profile is suitable for operation with larger mass flow rate. Compared with the traditional method, Dual-CNN can reduce the off-design analysis time of one blade geometry from 38.4 h to 7.68s.

Formulation, Validation, and Application of a Novel 3D BEM Tool for Vertical Axis Wind Turbines of General Shape and Size

Low order models based on the Blade Element Momentum (BEM) theory exhibit modeling issues in the performance prediction of Vertical Axis Wind Turbines (VAWT) compared to Computational Fluid Dynamics, despite the widespread engineering practice of such methods. The present study shows that the capability of BEM codes applied to VAWTs can be greatly improved by implementing a novel three-dimensional set of high-order corrections and demonstrates this by comparing the BEM predictions against wind-tunnel experiments conducted on three small-scale VAWT models featuring different rotor design (H-shaped and Troposkein), blade profile (NACA0021 and DU-06-W200), and Reynolds number (from 0.8×105 to 2.5×105). Though based on the conventional Double Multiple Stream Tube (DMST) model, the here-presented in-house BEM code incorporates several two-dimensional and three-dimensional corrections including: accurate extended polar data, flow curvature, dynamic stall, a spanwise-distributed formulation of the tip losses, a fully 3D approach in the modeling of rotors featuring general shape (such as but not only, the Troposkein one), and accounting for the passive effects of supporting struts and pole. The detailed comparison with experimental data of the same models, tested in the large-scale wind tunnel of the Politecnico di Milano, suggests the very good predictive capability of the code in terms of power exchange, torque coefficient, and loads, on both time-mean and time-resolved basis. The peculiar formulation of the code allows including in a straightforward way the usual spanwise non-uniformity of the incoming wind and the effects of skew, thus allowing predicting the turbine operation in a realistic open-field in presence of the environmental boundary layer. A systematic study on the operation of VAWTs in multiple environments, such as in coastal regions or off-shore, and highlighting the sensitivity of VAWT performance to blade profile selection, rotor shape and size, wind shear, and rotor tilt concludes the paper.

Numerical and experimental investigation of modified V-shaped turbine blades for hydrokinetic energy generation

The Savonius rotor is one of the simple and cost-effective vertical axis drag type devices for hydropower generation. The main drawback of the Savonius hydrokinetic turbine is its low performance due to negative torque developed by returning blade profile. In this paper, the performance of modified V-shaped rotor blades with different V-angles ranging from 90° to 40°, by maintaining fixed edge length, arc radius and aspect ratio of 0.7 is investigated. The numerical analysis is carried out to estimate the optimum V-angle by maintaining 70 mm depth of water with an inlet velocity of 0.3090 m/s. The numerical study revealed that, for 80° V-angle rotor blade profile, the maximum coefficient of power was found to be 0.2279 at a tip speed ratio of 0.9. This optimum V-angle model was used for experimental analysis to study the effect of aspect ratio ranging from 0.7 to 1.75 using top, middle and bottom plates by maintaining 140 mm depth of water and inlet velocity of 0.513 m/s. The rotor blade with two endplates and one middle plate with an aspect ratio of 1.75 has shown a significant increase of performance by 86.13% at a tip speed ratio of 0.86 as compared to turbine blade with two endplates.

Experimental and numerical investigation of novel V-shaped rotor for hydropower utilization

Hydrokinetic technologies harvest renewable power by harnessing the kinetic energy of water from free-flowing rivers, streams, dam head/tailrace and irrigation channels. Savonius rotor is one of the simple and low-cost vertical axis drag type devices used for the extraction of hydrokinetic power. The main limitation of Savonius hydrokinetic turbine is its low efficiency due to negative torque developed by the returning blade without augmentation techniques. In this paper, an experimental investigation is carried out in a multipurpose tilting water flume using V-shaped rotor blade profiles by maintaining a fixed V-angle of 90°, varying length of V-edges, arc radius and with a constant aspect ratio of 0.7. The simulations were carried out using commercial software, ANSYS Fluent. From the experimental and numerical results, it was found that, the optimum blade profile (V4) has developed a maximum coefficient of power 0.22 and 0.21 respectively, at a tip speed ratio 0.87. It was found that, the maximum coefficient of power of optimal V-shaped blade profile (V4) is 19.3% higher than the semi-circular blade profile.

New Rotor Blade Profiles Performance Decay in Horizontal Axis Wind Turbines Operating in Aggressive Environment

At the present time many wind power plants have been developed in mountainous areas, in off-shore sites also at high latitudes and however operating in harsch climate or aggressive environment conditions. In these conditions HAWT’s rotor blades may experiment erosion, corrosion, exfoliation and icing and these operative conditions may cause a remarkable aerodynamical performance decay resulting in a reduction in energy production due to a lower machines availability too. Traditional aerodynamic profiles, as NACA ones, can show high sensitivity to the surface damage or augmented roughness, while new airfoils as FFA-W1 series may be very useful in maintaining higher aerodynamical performance. In the present paper the aerodynamic performances of new and old airfoils have been analysed and compared on a water table test bench and wind tunnel one, at “La Sapienza” University of Rome in DIMA’s laboratory, in several operative conditions, and, particularly, effects due to icing, erosion and other ones as corrosion and fouling. The results have been compared with literature data to obtain useful indications in design of new rotor blades.

CFD investigation of unsteady aerodynamics in gas turbine engine blade surface

Abstract The problem of unsteady excitations is quite common in turbomachinery as they're subject to dynamic conditions. These unsteady excitations induced in turbomachinery result in forced dynamic response and leading the fatigue failure of aircraft engine components. In this paper unsteady aerodynamic mechanism that governs, the forced response in the stator - rotor interaction of turbine stages is investigated. Two-dimensional numerical investigations to calculate the pressure distribution along with the rotor blade profile. The surface mid-span coordinates of the first stage stator-rotor are molded according to the open-source NACA geometry Coordinates. To predict the excitation forces acting on the rotating rotor blades function of time-resolved computation is carried. The pulsating pressure distribution along the stator-rotor interaction and excitation forces along the intra-blade-row is computed using the Fluent.

Design of Composite Gyrocopter Main Rotor Blade Involving Rib and Spar Elements

Abstract Gyrocopter or gyroplane is a type of rotorcraft that uses an unpowered main rotor in free autorotation to develop lift. Gyrocopter rotor blades have smaller cord length and longer span compared to helicopters blades. National Advisory Committee for Aeronautics (NACA) 8-H-12 gyrocopter rotor blade profile, unsymmetrical airfoil sections were used for this research. An attempt has been made in this work to investigate the effect of ribs and spar elements in response to applied load. Three possible modeling alternatives were studied to predict the actual induced stress and deformation of the blade: Model I is by considering the blade shell part only, Model II is blade shell with 25 numbers of ribs and without the spar element and Model III is blade shell with 25 numbers of ribs and with spar element. The rotor blade was sized based on single seat open frame and high-wind-start gyrocopter. Structural static analysis has been carried out to evaluate the strength of composite rotor blade using ANSYS Workbench 15. The results show that among these three proposed models; Model III had registered minimum Von Mises stress and deformation. Also the result reveals that by considering ribs and spar element during analysis of gyrocopter blade is crucial because, it will help to know the actual induced stress and deformation. The predicted value of induced stress and deformation is closer to the actual values will help the designer not to overdesign the parts. Consequently, the main drawbacks related to overdesign increase in weight and cost will be minimized; thereby the product operational efficiency will be improved.

Numerical modeling of aeroacoustic characteristics of different savonius blade profiles

Purpose This study aims to carry out numerical modeling to predict aerodynamic noise radiation from four different Savonius rotor blade profile. Design/methodology/approach Incompressible unsteady reynolds-averaged navier-stokes (URANS) approach using gamma–theta turbulence model is conducted to obtain the time accurate turbulent flow field. The Ffowcs Williams and Hawkings (FW-H) acoustic analogy formulation is used for noise predictions at optimal tip speed ratio (TSR). Findings The mean torque and power coefficients are compared with the experimental data and acceptable agreement is observed. The total and Mono+Dipole noise graphs are presented. A discrete tonal component at low frequencies in all graphs is attributed to the blade passing frequency at the given TSR. According to the noise prediction results, Bach type rotor has the lowest level of noise emission. The effect of TSR on the noise level from the Bach rotor is investigated. A direct relation between angular velocity and the noise emission is found. Practical implications The savonius rotor is a type of vertical axis wind turbines suited for mounting in the vicinity of residential areas. Also, wind turbines wherein operation are efficient sources of tonal and broadband noises and affect the inhabitable environment adversely. Therefore, the acoustic pollution assessment is essential for the installation of wind turbines in residential areas. Originality/value This study aims to investigate the radiated noise level of four common Savonius rotor blade profiles, namely, Bach type, Benesh type, semi-elliptic and conventional. As stated above, numbers of studies exploit the URANS method coupled with the FW-H analogy to predict the aeroacoustics behavior of wind turbines. Therefore, this approach is chosen in this research to deal with the aeroacoustics and aerodynamic calculation of the flow field around the aforementioned Savonius blade profiles. The effect of optimal TSR on the emitted noise and the contribution of thickness, loading and quadrupole sources are of interest in this study.

Evolution and Progress in the Development of Savonius Wind Turbine Rotor Blade Profiles and Shapes

The blade profiles and blade shapes of vertical-axis Savonius wind turbine rotors have undergone a series of changes over the past three decades. Wind turbine aerodynamicists have carried out numerous computational and experimental research to arrive at a suitable rotor blade design configuration so as to harvest maximum energy from the available wind. In most of the studies, the geometric and aerodynamic aspects of the rotor blade design have been reported. Interestingly enough, a couple of review papers got published in the area of Savonius rotors during the last one decade. However, there is not a single piece of literature that gives a comprehensive and a systematic review of Savonius rotor blade profiles and shapes. This paper aims to collate all the research findings related to these blade profiles/shapes and makes an attempt to highlight their features together with future recommendations.

Quadratic birational transformations in computer simulation of building structures

Quadratic transformations are a perspective way of form-making in architectural and engineering-construction design. A quadratic (nonlinear) transformation is based on the establishment of one-to-one correspondence between the algebraic n- and 2nd-order curves. In particular, lines correspond to the second-order curves, which are widely used in the design of gridwork building structures and utility lines. Quadratic transformations are used to model the profile of rotor blades of environmentally friendly wind farms. We developed algorithms for building corresponding points for the practical application of nonlinear transformations in the computer simulation of building structures. We have shown that the inversion relative to the circle is a central quadratic transformation with imaginary fundamental point, coinciding with the cyclic points of the plane. We considered an example of using the inversion for building the rotor blade profile of a wind power installation and a cam profile. Quadratic transformation algorithms are practically realized using computer graphics and specialized software tools.

Investigation of Energy Loss on Fractional Deposition in Last Stages of Condensing Steam Turbine Due to Blade Shape and Moisture Droplet Size

The steam consumption in a turbine within an operating pressure range determines the effectiveness of thermal energy conversion to electric power generation in a turbo-alternator. The low pressure (LP) stage of the steam turbine produces largest amount of steam to shaft-power in comparison to other stages of turbine although susceptible to various additional losses due to condensation of wet steam near penultimate and ultimate stages. The surface deposition in blade is caused by inertial impaction and turbulent-diffusion. With increasing blade stagger angle along the larger diameter of blading, the fractional deposition of wet steam is largely influenced by blade shape. From this background, the aim of this work is to predict the effect of mathematical models through computational fluid dynamics analysis on the characterization of thermodynamic and mechanical loss components based on unsaturated vapor water droplet size and pressure zones in LP stages of steam turbine and to investigate the influence of droplet size and rotor blade profile on cumulative energy losses due to condensation and provide an indication about the possible conceptual optimization of blade profile design to minimize moisture-induced energy losses.

Review of the Savonius rotor's blade profile and its performance

The utilization of urban wind energy through small wind turbines has become an arising technology to ease the conflicts between rising energy demands in buildings and depletion of traditional energy resources. Many studies have reported that drag type vertical axis wind turbines have superior performance in the unsteady wind because of their attractive features. Several review studies have been conducted on these turbines. They mainly focused on the geometrical design parameters, the flow patterns, the research methodology, and the wind tunnel blockage correction. However, less research has been conducted to classify the Savonius rotor based on the classification criterion of the blade profile and has made a comprehensive performance comparison between different types of Savonius rotors. The blade profile is the essential design issue for a Savonius rotor; therefore, the variation of the blade profile will change the design parameters and affect the rotor's performance significantly. So, the classification based on the blade profile can not only present the effect of key design parameters on rotor's performance for each blade profile easily but also obtain the functional features of different profiles and the comparison among different profiles. Hence, in this article, we aim to summarize the classification of Savonius wind turbines according to the blade profile and present the development of this promising low speed generator.

A Counter-Rotating Impulse Turbine for Wave Energy Conversion

Wave energy can be converted to the electrical energy by using a wave energy converter. The wave energy converter with oscillating water column (OWC) is one of the most promising devices because of its simple structure and easy maintenance. In this device, an oscillating water column due to the wave motion is used to drive an air column. An air turbine is used to convert the pneumatic energy of this bi-directional airflow into the mechanical energy. The counter-rotating impulse turbine for wave energy conversion has been proposed and tested so far, and the average efficiency has been shown to about 0.3. On the contrary, in another offshore experiment, it has been reported that the power generation efficiency of this turbine is larger than Wells turbine in case of small waves. However, there is a scarcity of the detailed characteristics data of counter-rotating impulse turbine. In a previous study, the authors investigated the effect of rotor blade solidity and setting angle of guide vane on the performance of this turbine, and they clarified that the efficiency of this turbine is higher than impulse turbine with single rotor in the range of high flow coefficients. The present study aimed to investigate the effect of rotor blade profile on the turbine performance by using the computation fluid dynamic (CFD) analysis. The inner and outer angles of turbine rotor blade are changed in the range of 50° to 70°. The commercial CFD software of SCRYU/Tetra of Cradle Co. Ltd. was used in the present work. The Reynolds averaged Navier-Stokes (RANS) equations were used as the governing equations and the low Reynold’s number SST k-ω model was used to predict the turbulent stresses. As a result, it was found that the inner angle of γ = 70° and the outer angle of γ = 60° of the turbine rotor blades can give the best turbine efficiency and it shows the efficiency close to the impulse turbine with single rotor, even in the range of low flow coefficients.