Rotor Performance Research Articles

Numerical Investigation on Improvement of Savonius Rotor Performance and Design Optimization

Numerical Investigation on Improvement of Savonius Rotor Performance and Design Optimization

Research of Unsteady Aerodynamic Characteristics of Electrically Controlled Rotor Airfoils with Trailing-Edge Flaps

An electrically controlled rotor (ECR), also known as a swashplateless rotor, eliminates the swashplate system to implement the primary control via the trailing-edge flaps (TEFs), which can result in enhancements in rotor performance, as well as substantial reductions in weight, drag, and cost. In this paper, the unsteady aerodynamic characteristics of the airfoil with TEF of a sample ECR under unsteady freestream condition are investigated. The CFD results are obtained with sliding and overset grid techniques that simulate the airfoil pitching and flap deflection. Comparative analysis of the aerodynamic characteristics under steady and unsteady freestream conditions at different advance ratios is conducted. At various advance ratios, the lift and drag coefficients are higher at a small angle of attack under unsteady freestream condition; however, it is the opposite at a large angle of attack. The peak values of the lift and drag coefficients show an increased trend with the increase in the advance ratio. On the contrary, the pitch moment and flap hinge moment coefficients demonstrate minor variation under unsteady freestream condition. Furthermore, the aerodynamic characteristics of airfoils become more unsteady with variation in the freestream. Therefore, the lift and drag coefficients of the ECR airfoil with TEF show significant differences between steady and unsteady freestream conditions; however, the pitch moment and the flap hinge moment coefficients show little difference.

Hydrodynamic performance enhancement of Savonius hydrokinetic turbine using wedge-shaped triangular deflector in conjunction with circular deflector

Savonius hydrokinetic turbine is a viable technology for producing small-scale hydropower. The present numerical study proposed a novel deflector system to guide the incoming water stream effectively and to improve the hydrodynamic performance of the conventional Savonius turbine rotor. The combined deflector system comprises two deflectors: a newly proposed wedge-shaped triangular deflector and a circular cylindrical deflector. The triangular deflector is placed upstream of the returning blade, and the circular deflector is positioned upstream of the advancing blade. Different configurations of the proposed deflector system are obtained by varying the dimensions and location of the triangular deflector (deflector 1), while the diameter and location of the circular deflector (deflector 2) are fixed in all configurations. Without a deflector system, the Savonius rotor yields a maximum power coefficient equal to 0.248 at a tip speed ratio (TSR) of 0.7. The best configuration of the combined deflector system yields a maximum power coefficient of around 0.432 at a (TSR) value of 1.0. The deflector-augmented Savonius hydrokinetic rotor records a 73.7% increase in the maximum power coefficient (CPmax) compared to the conventional Savonius rotor. Further, the flow contours verify improved flow interaction with turbine blades and enhanced hydrodynamic performance.

Numerical Investigation on Aerodynamic Performance of Helical Savonius Rotor Inspired by Natural Shapes

There have been extensive studies conducted on Horizontal Axis Wind Turbines (HAWT) at relatively moderate to high wind speed regions. However, such detailed investigations for Vertical Axis Wind Turbines (VAWT), specifically for low wind speed terrains are amply reported. This motivates us to conduct research to explore possibilities in improving performance of VAWT in low wind speed terrains, which is attempted in the present work. This is required due to the fact that most of regions do not have sufficient extractable wind energy due to low speeds. VAWTs can perform at such low wind speed, but are less efficient. Improving efficiency of VAWT will solve the purpose. Hence, the present study is aimed at finding the performance characteristics of VAWT for low Wind speed configurations. Various parameters affecting power generation are investigated. Numerical analyses on various configurations are conducted to study the effects of twist angle, free stream velocity, number of blades. Computational results obtained have been in good agreement with the established results for semi-circular Savonius rotor profile. The results suggest that for low wind speed terrains, there is a need to explore the combination of lift and drag type of profiles, which could be used for the utilization of available wind power. Hence, naturally inspired shapes (profiles) were investigated for the possible solution of combined lift and drag type wind turbines at low speeds. The blade shape for such combined lift and drag type wind turbine were deduced from the available literature. It is well established that the naturally inspired shapes as noted in sea conch follow golden ratio in its contours. The present study provides an insight on the characteristic curves of VAWT for low wind speed terrains, effects of various geometric and flow parameters suitable for low wind speed terrains.

Dynamic characteristics analysis of a rotor system with loose support considering internal friction in couplings

Along with the rotating machinery advances toward high speeds, the significance of the excitation force of the seal fluid in the rotor system is growing, which can cause serious accidents. Most of the previous research on rotors in rotating machinery has predominantly focused on the effects of misalignment in couplings. In this article, a novel model is proposed, introducing an analytical approach that combines both internal friction in couplings and loosening support faults. Additionally, an analysis and discussion of the vibration characteristics of the rotating system under the influence of internal friction are presented. This method allows for a more comprehensive assessment of the performance of rotors in engineering applications. Assuming that the left support of the rotor is loose, this model focused on how various factors such as rotor speeds, eccentricity, seal disc mass, and left-end support mass affect the labyrinth seal rotor system's dynamic characteristics. Based on the findings, The emergence of internal friction forces advances the chaos of the rotor. It seems that as the rotating speed increases, there will be a small frequency range, resulting in fluid oscillation, and the system stability will be reduced at this time. The improvement in the seal disc's quality has minimal impact on the stability of the left journal, but it will reduce the stability of the seal disc. The increase in the mass of the left end support will increase the stability of the movement at the left journal and reduce the stability of the movement at the seal disc.

Hydrokinetic hybrid vertical axis rotor performance at difference blade shape and angles of attack

We must invest in renewable energy research to combat pollution from fuel combustion and promote affordable energy. Hydrokinetic rotors produce mechanical torque using kinetic energy in rivers, canals, and ocean water. Hydrokinetic integrated Darrieus-Savonius rotors are a vertical axis type with good properties, but only a few researchers are interested in them. Only one Savonius rotor has the ability to self-prime, despite having poor performance but high torque. Darrieus rotors are effective but challenging to start. In order to find the best configuration, hydrokinetic integrated rotor performance is experimentally studied in this work. The study was conducted in a water flume at Egypt's National Water Research Centre, Hydraulics Research Institute (HRI). The number of Darrieus blades, Darrieus blade attack angles, and airfoil shape are studied and compared for four different NACA airfoils: NACA 012, 015, 018, and NACA 021. Semi-circular Savonius blades were employed in this work, the fact that the Savonios rotor in double-stage is always the best in terms of performance for an integrated rotor. The results showed that NACA 21 with a three-bladed Darrieus rotor and 15° angle of attack produced the highest power factor, as the maximum obtained value is 0.334 at a tip speed ratio of 1.8.

Numerical Investigations of Bump Effects on the Performance of Double-Ended Airfoils and ABC Rotors

Numerical Investigations of Bump Effects on the Performance of Double-Ended Airfoils and ABC Rotors

Effects of solidity on startup performance and flow characteristics of a vertical-axis hydrokinetic rotor with three helical blades

Effects of solidity on startup performance and flow characteristics of a vertical-axis hydrokinetic rotor with three helical blades

Design and performance test of series underwater Savonius rotors with horizontal axis

<span lang="EN-US">The energy of river water flow or irrigation canals can be utilized by using a horizontal axis Savonius turbine, which converts low-speed river flow into electrical power with good design. The design of this turbine needs to pay attention to several parameters, namely, the deflector angle, the number of blades, the diameter and thickness of the blades, and the diameter and thickness of the end plates. However, the problem usually encountered is imperfect turbine construction due to the large drag force that occurs so that the power generated is low. Based on this background, it is proposed to manufacture and test the performance of a series Savonius underwater rotors with a horizontal axis. The research results found that the generator voltage without load was 25.6 V when the turbine only rotated at 47.2 rpm, whereas when under load, the average power produced was 8.5 watts with an average turbine speed of 31 rpm. The highest efficiency value on the rotor is 86.73%, with a torque value of 3.36 at a turbine speed of 29.9 rpm. This indicates that the tool can generate large torque at low speeds.</span>

To What Extent Is Aeroelasticity Impacting Multi-Megawatt Wind Turbine Upscaling? A Critical Assessment

Aeroelasticity is recognized as the key enabler that allowed for the massive upscaling of wind turbines in the last decade, leading to long, slender, and flexible blades that equip rotors with lower specific power and unprecedented energy conversion capabilities. In this study, a selection of case studies with increasing size, specifically the NREL 5 MW, the DTU 10 MW, and the IEA 15 MW Reference Wind Turbines (RWTs) is considered to explore to what extent aeroelastic effects impact the functioning of these rotors. The rotors are not only different in size, with the 15 MW having blades nearly double the length of its 5 MW predecessor, but also in technological level as they belong to different phases of wind turbine development. To evaluate how these machines interact with complex inflow conditions, equivalent boundary conditions have been considered for all simulations, including a realistic atmospheric boundary layer, atmospheric turbulence, and wind shear. To carry out the comparative study, a new aero-servo-elastic module called CALMA is introduced herein, by coupling the engineering software OpenFAST with the CFD software CONVERGE, which solves the wind field and provides inflow conditions for the calculation of loads. Results show how not only aeroelasticity increasingly affects the power performance of the new-generation rotors, but is also a key driver of structural design, for example allowing for an alleviation of 1P load variations due to a sheared and turbulent inflow, thus proving that the inclusion of aeroelasticity in the design process is a key enabler to current and future upscaling trends.

Experimental investigation of unmanned air vehicle rotor aeroacoustics using benchmark geometries

A series of benchmark and off-the-shelf unmanned air vehicle rotors with diameters around 12 inches was tested in the newly-built anechoic chamber at the Łukasiewicz Research Network - Institute of Aviation, as well as in an open field. The aerodynamic performance of the rotors was assessed using thrust and torque meters embedded in a custom testing rig, and their acoustic characteristics, including directivity, were determined using a column of free-field microphones. The characteristics of the anechoic chamber, including the spatial distribution of background noise and the anechoic condition, were evaluated in detail, and the comparison with open-field measurements enabled confirmation of its suitability for testing of low Reynolds number rotors. The measurements of rotor performance were compared with published results, and the agreement between the data sets validated the methodologies employed in this study. Furthermore, a new benchmark is defined based on an 8-inch commercial rotor, for which broadband noise is more significant than for larger diameters. A full set of aeroacoustic characteristics is presented, broadening the range of available benchmark cases.

Optimization design and performance analysis of a bio-inspired fish-tail vertical axis wind rotor

To improve the wind power efficiency of the traditional Savonius rotor. Focusing on the influence of the blade characteristic parameters, a bio-inspired fish-tail wind rotor based on the two-bladed Savonius rotor is proposed. A series of transient simulations are performed to investigate the power coefficient of each rotor; The orthogonal experiments of four factors and three levels are carried out for the blade characteristic parameters, and a Box-Behnken Design (BBD) response surface model is constructed, which defines the relationship between the optimization objective power coefficient and the design parameters to explore the optimal results. The results show that the peak power coefficients for the response surface optimized rotor and the orthogonal experimental optimized rotor are 0.267 and 0.26, respectively. These values are improved by 9.4% and 6.6%when comparing the Savonius rotor. The performance analysis reveals that the blade number and minor arc have a more significant effect on the performance of the fish-tail wind rotor.

Dynamic Characteristic and Performance Analysis of Claw Vacuum Pumps with Multi-Claw Rotors

The number of lobes of multi-claw rotors determines the performance of claw vacuum pumps including the pumping speed, dynamic characteristics, and operating conditions. In order to reveal the effects of the number of lobes on rotor performance, in this study, a geometric model of multi-claw rotors was established. The structure and geometric performance of multi-claw rotors including suction port and discharge port, pumping speed, and volumetric utilization ratio were compared. Furthermore, a dynamic characteristic model of claw rotors was established, and, therefore, axial gas forces, radial gas forces, and gas resistance torques of multi-claw rotors were obtained. The results indicate that double-claw rotors increased 34.67 % and 4.59 % in terms of pumping speed and volumetric utilization ratio compared to single-claw rotors, and triple-claw rotors showed similar increases as double-claw rotors. The triple-claw rotors have a 49.39 % and 31.38 % reduction in compression duration compared to the double-claw rotors and single-claw rotors. The gas resistance torques of the multi-claw right rotors are consistently more than that of the left rotors, which demonstrates that the multi-claw right rotors are more suitable to serve as the driving rotors. The research contents of this paper are of great theoretical significance for the selection of rotor lobes and the design of claw vacuum pumps with prominent dynamic characteristics.

Study on a performance matching method of wind rotor and generator based on energy transfer.

Wind power systems are a promising form of energy supply. At present, most of the studies focuses on the performance of individual components such as wind rotors or generators, and the overall output effect of wind power system is determined by the characteristics of wind rotor and generator and their combined characteristics. However, the evaluation of the overall output characteristics of the system is rarely considered. In order to investigate the overall output of the system quickly, a performance matching method of wind rotor and generator based on energy transfer is proposed in this paper. Based on the series operating characteristics of the wind power system model, the energy transformation process of the wind rotor, generator and the whole system are unified described by energy transfer. On the premise that the performance of wind rotor and generator is known, the transfer function model of each component is established, and on this basis, the transfer function model of the overall system is obtained. Then, the overall output effect of the system is analyzed and evaluated by this system transfer function model. The performance of the model is analyzed and compared by using a vertical axis wind power system coupling test bench and MATLAB/Simulink software. The results show that the error between the system output based on the theoretical model and the wind tunnel test is less than 6.5%, and the trend of the simulation and the test curve of the system output is consistent. Therefore, this method can be used to quickly predict the overall output performance of the wind turbine and generator on the premise that the performance of each component is known, without the need to connect each component to a wind power system for testing.

Understanding the Effect of Three-Dimensional Design in Tandem Blade

Abstract In order to maximize the pressure ratio and efficiency, compressor designers have tried several unconventional design approaches. Tandem blading is one such unconventional design that promises a higher pressure ratio per stage through a higher diffusion factor. The nozzle shape created between the forward and aft blades of a tandem configuration acts as a passive boundary layer control mechanism. The boundary layer growth over the aft rotor is therefore effectively controlled with the help of this gap-nozzle flow. The flow complexity is likely to increase in the case of a tandem rotor due to the twin leakage vortices, twin wake regions, and their interaction with the hub and casing boundary layers. Modern compressor blades are often designed with three-dimensional blade techniques such as sweep, lean, dihedral, end bent, etc., to reduce the various losses and achieve optimum performance. However, to the best of the author’s knowledge, the effect of 3D blade designs on the performance of tandem rotors has not been fully explored so far. A comprehensive numerical investigation is undertaken to understand the effect of 3D designs on the performance of tandem blades. Axial sweep and dihedral failed to improve the performance of the tandem rotor. Significant improvement in the stall margin is observed for the forward chordwise-swept and negative lean tandem rotors and is largely attributed to lower tip incidence. The performance penalty of the forward-swept and negatively leaned cases can be reduced by integrating compound or variable lean and sweep into the design.

Airfoils optimization based on deep reinforcement learning to improve the aerodynamic performance of rotors

Airfoil optimization is the key to improving the aerodynamic performance of a rotor. However, conventional optimization approaches cannot modify the airfoil shape intelligently in the way that an aircraft designer would. Because the optimization process is largely uninterpretable and ungeneralizable, the optimization knowledge and experience cannot be extracted and applied to similar optimization tasks. To address these issues, we propose an optimization framework for rotor airfoils based on deep reinforcement learning (DRL). Our DRL-based framework is capable of learning an interpretable and generalizable optimization strategy for alleviating the dynamic stall of a rotor airfoil. First, to enhance the efficiency of airfoil dynamic stall optimization, a deep neural network is trained to predict the dynamic stall hysteresis loops of rotor airfoils as a surrogate model. The asynchronous advantage actor–critic reinforcement learning algorithm is employed to train and learn the optimization strategy for alleviating the dynamic stall of the rotor airfoil. Next, the OA212 rotor airfoil is optimized using the well-trained optimization strategy. The results show that the dynamic stall characteristics of the airfoil are improved after optimization. The lift coefficients of the optimized airfoil are significantly enhanced, and the drag and moment coefficients peaks are reduced by 46.3% and 73.8%, respectively, compared with the baseline airfoil. Then, 20 airfoils are optimized using the well-trained optimization strategy to evaluate the generalizability of the dynamic stall optimization strategy. The results demonstrate that the optimization strategy learned by DRL for the rotor airfoil optimization is generalizable. Finally, the numerical simulation results comparing a rotor with baseline airfoils to one with optimized airfoils demonstrate that the aerodynamic performance of the optimized rotor is superior to that of the baseline rotor.

Role of tip leakage flow in an ultra-highly loaded transonic rotor aerodynamics

Tip clearance size is a very critical design parameter for the modern transonic rotor. This investigation attempts to reveal the role of tip leakage flow in an ultra-highly loaded low reaction transonic rotor (loading coefficient equals to 0.782) aerodynamics. Flow fields in the rotor with varied tip clearance sizes, ranging from 0 to 3 times of the datum case, are discussed at length. Both performance variation and stall mechanisms involved are elaborated. As a result, the rotor performance presents a continuous decline with the increased tip clearance size as a result of the additional secondary flow loss induced by the tip leakage flow. While for stall margin, an optimal tip clearance size exists, and it happens to be the datum case. The tip leakage flow is found to have the ability to blow away the low-energy flow accumulated in the rotor tip suction side. Specially, the forward portion of tip leakage flow plays the dominate role in extending the rotor stall margin. However, as the tip clearance size exceeds the datum case, the shock-tip leakage vortex interaction causes the tip leakage vortex breakdown and the stall margin is hence narrowed.

Acoustic signature of sUAS rotors undergoing edgewise forward flight

This presentation shares preliminary experimental results from a new sUAS rotor test rig installed in UNSW’s Anechoic Wind Tunnel (UAT). This new test rig allows acoustic and aerodynamic performance testing of small drone-scale rotor blades under edgewise forward flight conditions at a range of shaft angles. The study of sUAS rotors under edgewise forward flight presents asymmetric inflow to the rotor and unsteady loading on the blades themselves, with different flow conditions experienced by the advancing and retreating rotor blades. This means the acoustic signature of a rotor undergoing edgewise flight is significantly changed compared to static thrust or axial flight conditions of drone rotors or propellers. This presentation aims to outline changes to the acoustic signature of a collection of conventional off the shelf (COTS) rotor and propeller designs between static, axial flight and edgewise flight conditions, coupling this with rotor performance metrics.

Numerical investigation of blade roughness impact on the aerodynamic performance and wake behavior of horizontal axis wind turbine

The prolonged operation of wind turbines in harsh offshore environments leads to deterioration and roughness accumulation on the blade surface. This roughness, particularly on the leading edge and other surfaces, can affect the laminar-to-turbulent transition, alter the flow characteristics in the turbine wake and turbulent boundary layer, and become critical for the accurate design and performance analysis of offshore horizontal axis wind turbines (HAWT). This study investigates the effects of blade surface roughness on the aerodynamic performance and wake evolution of the NREL Phase VI wind turbine rotor using the Reynolds-Averaged Navier-Stokes (RANS) technique. First, 2D simulations are validated against experimental data of the S809 airfoil. Then, full-scale 3D simulations of the complete turbine model are conducted with roughness effects to simulate natural conditions. The results show that surface roughness reduces the blade’s aerodynamic performance. The rough surface increases the boundary layer thickness, causing flow separation and turbulence, which decrease the lift generated by the blade and increase its drag, resulting in decreased overall blade performance. At higher wind speeds, surface roughness has a negligible effect on turbine performance due to flow separation at the leading edge. The analysis of surface roughness effects on the turbine wake flow indicates that blade roughness positively correlates with wake recovery, where the wake velocity recovers faster with an increase in roughness height.

Research on pumping laws of different-shaped Roots rotors for multi-stage vacuum pump design

Multi-stage Roots dry vacuum pumps are widely used in the semiconductor industry, metallurgy, pharmaceuticals, solar photovoltaic, thin film equipment, and other such fields. There are many combinations of rotors from the inlet to the exhaust of the multi-stage Roots vacuum pump. Depending on the application process of the multi-stage Roots vacuum pump, different rotation and self-combination designs are required. Currently, the pumping characteristics of different rotor types of the multi-stage Roots dry vacuum pump are not clear, and the combined design of the multi-stage pump rotor cannot be supported. In order to realize the applicability analysis of different rotors in different pressure ranges, a vacuum pump test platform and an adjustable rotor Roots experimental pump were designed. The pumping performance and power consumption of two-lobe Roots rotors, three-lobe Roots rotors and five-lobe Roots rotors in different pressure ranges were tested in experiments, and the internal flow conditions of multi-stage pump exhaust stages were numerically simulated. The results demonstrate that considering the ultimate performance and power consumption, the two-lobe Roots rotors and the three-lobe Roots rotors are more suitable for the exhaust pressure range of 1–10,000 Pa. With the increase of the exhaust pressure, the pumping performance of the three-lobe Roots rotors begins to gradually improve, and the pumping performance has obvious advantages. When the exhaust pressure exceeds 50,000 Pa, the advantages of the five-lobe Roots rotors gradually become obvious. The five-lobe Roots rotors can better handle the process of direct exhaust to atmosphere. The research methods and conclusions adopted in this paper can provide a reference for the design of the rotor combination scheme of the multi-stage Roots dry vacuum pump.