Flat-plate Blades Research Articles

The design of a double-fold blade wind turbine with flat-plate blade sections

This study presents a double-fold blade wind turbine design with flat plate blade sections that enables the usage of sheet-like materials and a cheaper fabrication method. The purpose of the current study is to analyze the performance of the blades, which are mainly controlled by four factors, namely the root fold-axis, tip fold-axis, root fold, and tip fold angles. The computational fluid dynamics results show that double-fold design configurations outperform single-fold configurations. For example, the highest peak power coefficient for the single-fold case (root fold-axis, root fold, and tip fold angles of 30°, 15°, and 0° respectively) is 0.2018, while it is 0.2565 for the double-fold case (root fold-axis, tip fold-axis, root fold, and tip fold angles of 30°, 30°, 37.5° and 30° respectively). These findings gave new insights into the relationships between the fold axes and fold angles and the power coefficients of the proposed double-fold blade design.

A centimetre-scale bi-directional wind turbine for energy harvesting applications: design and experimental tests

In this work, new cm-scale wind turbines for powering sensor nodes devoted to monitoring/diagnostic of railway vehicles are designed, built and tested in a wind tunnel. Two rotors, having four airfoil blades with a diameter of 3 and 4 cm, are designed following the blade element momentum-based approach. The two rotors, tested in a wind tunnel, reach a power coefficient (without considering the losses in the conditioning circuit) ranging between 20% and 30%, in line with the maximum values of the Schmitz theory; the correspondence between the numerical estimates and the experimental data is discrete. The 4 cm diameter rotor, once connected to a conditioning circuit, reaches a maximum net efficiency of about 15%, equal to the maximum value found in the literature, but with a 13,5 cm diameter rotor. Considering the practical application on trains and the fact that the rotor has to work for two opposite velocity directions (it must be bi-directional), a 4 cm diameter symmetrical rotor with a constant blade pitch and flat plate blade section is also built. With the symmetric rotor, we can observe that the generated power is about 50% lower than that produced by the same rotor with airfoil blades. Finally, the turbine is set inside a duct to protect it and increase performance. The tests performed on this ducted turbine (4 cm diameter, symmetric) allow us to understand that the duct significantly increases the performance of the rotor in downwind conditions, from 1% to 6%, while it is almost irrelevant in upwind conditions. Moreover, the diffuser increases the efficiency by about 20%, while the contraction cone does not significantly modify the performance of the turbine.

Canonical sound fields in the frequency-domain theory of supersonic leading-edge noise

This paper determines the three-dimensional structure of certain single-frequency canonical sound fields occurring in the theory of blade–vortex interaction when the flow velocity relative to the blade is supersonic. A relative velocity of this magnitude occurs at the outer part of the fan blades in an aeroengine, at which the incoming vorticity has either been ingested from the atmosphere or created in the aeroengine itself. The sound fields analysed are those produced by the leading edge of a flat-plate blade at zero angle of attack on being struck by a gust which is either (i) localized along the span, or (ii) non-localized but discontinuous. The canonical gusts of type (i) have either a delta-function or Gaussian shape, and those of type (ii) are either anti-symmetric or described by a Heaviside function; these gusts give rise to the four basic canonical sound fields. The paper also analyses a fifth sound field, produced by a single-frequency top-hat gust. This sound field has a complex structure involving aspects of both (i) and (ii), but can nevertheless be analysed in terms of the canonical sound fields. The main results of the paper are exact and approximate analytical formulae giving the dependence of the acoustic field on gust-shape and flow parameters, and also a simple formula which is ideal for numerical work. The last of these is used to assess in detail the numerical accuracy of all the approximate formulae, which are of either Fresnel or Keller type. A key result is that Keller-type formulae, representing sound rays produced in accord with the geometrical theory of diffraction, have a very wide range of validity. A companion paper (Chapman & Powles 2019) determines the canonical sound fields in the corresponding time-domain theory.

部分構造合成法による低次元化モデルを用いたタービン翼のミスチューン応答解析

When calculating the resonant response of bladed turbine disks, it has been convenient to assume that all blades on a given disk are identical. This leads to the prediction that all blades experience the same amplitude of displacement and stress when excited by forces harmonically related to the rotor speed. However, it has been shown experimentally that significant variations in these amplitudes occur for different blades on the same disk. These variations arise due to the effects of mistuning, which refers to small differences in characteristics between blades. In this paper, a reduced-order model is created with modal data from eigenvalue analysis in Nastran (RESVEC method). After creating a whole-blade model by component mode synthesis, eigenvalue analysis is carried out again and the modal data is sorted to pick out modal family data. This frequency analysis is faster than FEM because the final degree of freedom is equal to the number of blades. This method is verified for the 1st and 2nd mode family of a simple bladed disk with flat plate blades, and a Monte Carlo simulation is carried out. Finally, this method is applied to an actual bladed disk used in steam turbine.

Experimental study of the effect of blade curvature and aspect ratio on the performance of a rotary-wing decelerator

The effects of different blade configurations on a vertically falling rotating blade decelerator (pararotor) are studied. A pararotor model equipped with cambered plate blades with different curvatures was tested in a wind tunnel. The parameters measured were flow velocity, rotation velocity, the drag generated by the model, and the blade pitch angle. The parameters selected for the analysis of the results were the drag coefficient of the model and the velocity ratio (ratio between the falling and rotation velocities). These parameters were determined and compared with those obtained for flat-plate blades. Flat-plate blades with different aspect ratios were also tested and analyzed. The results obtained show that the velocity ratio increases with camber, and the equivalent drag coefficient remains unaltered by camber and aspect ratio variations.

0502 せん断流中におけるオルソプタ風車の性能に関する研究

The performance of the orthopter-type wind turbine in a shear flow was investigated. The orthopter-type wind turbine is one of the vertical-axis wind turbines (VAWT) which each blade combines a rotating movement around its own axis and a rotating movement around turbine's axis. The diameter and height of wind turbine were 510mm and 400mm, respectively. The number of flat plate blade was three. The experiments were carried out in an open circuit wind tunnel. The effects of the location of wind turbine and the strength of shear flow on the performances of the orthopter-type wind turbine were found. The power of the wind turbine increased when porous plate installed the backward side.

Numerical and experimental studies of a small vertical-axis wind turbine with variable-pitch straight blades

This thesis presents numerical simulations and experiments on the effect of the variable pitch angle of blade rotor on the performance of small vertical-axis wind turbines (Darrieus and Orthopter wind turbine). The power, torque, and flow around blade rotor of VAWTS were analyzed by two-dimensional unsteady computational fluid dynamics simulations using ANSYS Fluent 13.0 program. The Darrieus rotor was composed using three NACA0018 airfoil straight blades. Three different rotor blade configurations were employed which i.e., a fixed-pitch blade with a pitch angle, variable blade pitch angle. The Orthopter rotor blades rotate movement around its own axis a half relative to the main rotor in one revolution. The configurations of different aspect ratio and number of blade (of the Orthopter rotor blade were employed. The effects of the variable-pitch angle, tip speed ratio, and three turbulent models, i.e., the RNG k-e, Realizable k-e, and SST k-ω turbulent models, on the performance of Darrieus wind turbine were investigated. The effect of number of blades, tip speed ratio, and aspect ratio of the Orthopter wind turbine with flat-plate blades rotor were also investigated by numerical simulation using RNG k-e turbulent model. The result predictions of numerical were validated by open circuit wind tunnel experimental data. The numerical simulations results of both a VAWT with variable pitch blade and the orthopter wind turbine had good qualitative agreement with the experiments results. The predictions of performance of using the RNG k-e turbulence model were very close with experimental data. The VAWT with variable-pitch blades has better performance than a VAWT with fixed-pitch blades and by RNG k-e and SST k-ω turbulent models, its can suppress the occurrence of a vortex on its blades at a low tip speed ratio. The performance of the Orthopter is influenced by aspect ratio, number of blade, and tip speed ratio. The highest performance of Orthopter wind turbine at AR=1. The high tip speed ratio lead to reducing torque generation especially at downstream area. The simulations show effects of number of blade on the performance. The high number of blade reduces torque generation of one blade. However, the overall of performance was increased.

Study on Vibration Characteristics of Mistuned Bladed Disk (Vibration Response Analysis by Reduced Model FMM)

It is well known that asymmetric vane spacing can result in decreased levels of the excitation at specific frequencies. In the previous paper, the resonant response reduction of mistuned bladed disks due to asymmetric vane spacing was studied by use of the equivalent spring-mass model. Although the mistuned bladed disk should be analyzed by FEA to accurately evaluate the resonant response reduction effect of asymmetric vane spacing, it is unrealistic due to enormous computational time. Therefore, in this study, the mistuned bladed disk is modeled by use of FMM (Fundamental Mistuning Model) to evaluate the resonant response reduction effect of asymmetric vane spacing accurately and practically. First, the frequency response analysis of a simple mistuned bladed disk consisting of flat plate blades is carried out for symmetric vane spacing, using both of FMM and the direct FE model, and the calculated results are compared to confirm the validity of FMM. Second, the frequency response analysis of a realistic bladed disk is carried out for asymmetric vane spacing, using FMM, to examine the effect of resonant response reduction effect.

Computational fluid dynamics simulation of sound propagation through a blade row

The propagation of sound waves through a blade row is investigated numerically. A wave splitting method in a two-dimensional duct with arbitrary mean flow is presented, based on which pressure amplitude of different wave mode can be extracted at an axial plane. The propagation of sound wave through a flat plate blade row has been simulated by solving the unsteady Reynolds average Navier-Stokes equations (URANS). The transmission and reflection coefficients obtained by Computational Fluid Dynamics (CFD) are compared with semi-analytical results. It indicates that the low order URANS scheme will cause large errors if the sound pressure level is lower than -100 dB (with as reference pressure the product of density, main flow velocity, and speed of sound). The CFD code has sufficient precision when solving the interaction of sound wave and blade row providing the boundary reflections have no substantial influence. Finally, the effects of flow Mach number, blade thickness, and blade turning angle on sound propagation are studied.

0403 可変ピッチ式平板翼を有する抗力型垂直軸風車の性能に関する研究(OS02-1 自然と生物の流れ現象とその有効利用,オーガナイズドセッション 2:「自然と生物の流れ現象とその有効利用」)

0403 可変ピッチ式平板翼を有する抗力型垂直軸風車の性能に関する研究(OS02-1 自然と生物の流れ現象とその有効利用,オーガナイズドセッション 2:「自然と生物の流れ現象とその有効利用」)

Numerical Analysis of the Performance of a Drag-type Vertical-Axis Wind Turbine with Variable Pitch Flat Plate Blades

Numerical Analysis of the Performance of a Drag-type Vertical-Axis Wind Turbine with Variable Pitch Flat Plate Blades

S051021 可変ピッチ式平板翼を有する抗力型垂直軸風車の性能 : 翼端板とリブの影響

S051021 可変ピッチ式平板翼を有する抗力型垂直軸風車の性能 : 翼端板とリブの影響

On a uniformly valid analytical rectilinear cascade response function

This paper extends an existing analytical model of the aeroacoustic response of a rectilinear cascade of flat-plate blades to three-dimensional incident vortical gusts, by providing closed-form expressions for the acoustic field inside the inter-blade channels, as well as for the pressure jump over the blades in subsonic flows. The extended formulation is dedicated to future implementation in a fan-broadband-noise-prediction tool. The intended applications include the modern turbofan engines, for which analytical modelling is believed to be a good alternative to more expensive numerical techniques. The initial model taken as a reference is based on the Wiener–Hopf technique. An analytical solution valid over the whole space is first derived by making an extensive use of the residue theorem. The accuracy of the model is shown by comparing with numerical predictions of benchmark configurations available in the literature. This full exact solution could be used as a reference for future assessment of numerical solvers, of linearized Euler equations for instance, in rectilinear or narrow-annulus configurations. In addition, the pressure jump is a key piece of information because it can be used as a source term in an acoustic analogy when the rectilinear-cascade model is applied to three-dimensional blade rows by resorting to a strip-theory approach. When used as such in a true rectilinear-cascade configuration, it reproduces the exact radiated field that can be derived directly. The solution is also compared to a classical single-airfoil formulation to highlight the cascade effect. This effect is found important when the blades of the cascade overlap significantly, but the cascade solution tends to the single-airfoil one as the overlap goes to zero. This suggests that both models can be used as the continuation of each other if needed.

On the use of a uniformly valid analytical cascade response function for fan broadband noise predictions

The present paper extends an existing analytical model of the aeroacoustic response of a rectilinear cascade of flat-plate blades to three-dimensional incident vortical gusts, to the prediction of the noise generated by a three-dimensional annular blade-row. The extended formulation is meant to be implemented in a fan broadband noise prediction tool. The intended applications include the modern turbofan engines, for which analytical modelling is believed to be a good alternative to more expensive numerical techniques. The prediction noise model resorts to a strip theory approach based on a three-dimensional rectilinear cascade model. The latter is based on the Wiener–Hopf technique, and yields the pressure field in the blade passage and the unsteady blade loading. The analytical pressure solution is derived by making an extensive use of the residue theorem. The obtained unsteady blade loading distribution over the blades is then used as a dipole source distribution in an acoustic analogy applied in the annular rigid duct with uniform mean flow. The new achievements are then tested on threedimensional annular-benchmark configurations and compared with three-dimensional lifting-surface models and three-dimensional Euler linearized codes available in the literature. The accuracy of the model is shown for high hub-to-tip ratio cases. When used as such in a true rectilinear-cascade configuration, it also reproduces the exact radiated field that can be derived directly. For low hub-to-tip ratio configurations, the model departs from three-dimensional computations, both regarding the blade loading and the acoustic radiation. A correction is proposed to account for the actual annular dispersion relation in the rectilinear-cascade response function. The results suggest that the proposed correction is necessary to get closer to the underlying physics of the annular-space wave equation, but that it is yet not sufficient to fully reproduce three-dimensional results.

NUMERICAL INVESTIGATION OF THE CAVITATION IN PUMP INDUCER

A numerical investigation of the non-cavitating and cavitating performance of a three-blade pump inducer under nominal and off-design operating conditions is presented. Three different simulated hydrofoils; a flat plate, “NACA0004", and "Clark-Y-6%" has been selected to represent the profile of the inducer blade. A 2D, steady, incompressible, turbulent, and isothermal flow field between the inducer blades is simulated using the FVM. The "Interface Tracking" model is selected to predict the cavity profile of the attached cavitation and the cavitating performance drop. For each blade profile, the influence of solidity in the range of (1.8 to 3.0) and blade angle in the range of (20° to 35°) on the inducer performance is studied. Comparing the present model with available experimental and numerical results, confirms that the developed model well predicts the general non-cavitating performance for an inducer having a flat plate blade profile. For "NACA0004", or "Clark-Y-6%" hydrofoil blade profiles, a reduction in the operating range of these inducers is produced. In addition, the developed model predicts the inception of cavitation earlier than the experimental results. The predicted cavitating head drop curve of an inducer having a flat plate blade profile is compared with available experimental results and a good agreement is obtained. The drop curve occurs suddenly and simultaneously with the experimental one. For "NACA0004“, or "Clark-Y-6%" hydrofoil blade profiles, a smooth curves with simultaneous or gradual head drop occurs with the experimental one, respectively. Generally, the agreement between the results is satisfactory

Instantaneous Pressure Measurement on a Rotating Blade of a Cross-Flow Impeller

For further improvement of indoor environments concerning air and noise pollutions, ventilation is one of the key factors. In this study, we develop the measuring technique of unsteady pressure on a rotating blade surface, to reveal the basic features of a cross-flow impeller. Specifically speaking, we consider the simplest model as the fundamental study, namely, the flow around the cross-flow impeller rotating with flat-plate blades in open space without any casings. On this impeller's blade, we measure the fluctuating pressures, which are discussed in comparison with flow visualizations with the particle-image velocimeter (PIV), velocity measurements by a hot-wire velocimeter (HW) and numerical simulations. As a result, by the compensation of the centrifugal-force effect, we get accurate pressures on the rotating blade, which are conditionally-averaged over a number of periods. The obtained experimental results can be also dedicated to CFD as standard benchmarks.

Instantaneous Pressure Measurement on a Rotating Blade of a Cross-Flow Impeller

For further improvement of indoor environments concerning air and noise pollutions, ventilation is one of the key factors. In this study, we develop the measuring technique of unsteady pressure on a rotating blade surface, to reveal the basic features of a cross-flow impeller. Specifically speaking, we consider the simplest model as the fundamental study, namely, the flow around the cross-flow impeller rotating with flat-plate blades in open space without any casings. On this impeller's blade, we measure the fluctuating pressures, which are discussed in comparison with flow visualizations with the particle-image velocimeter (PIV), velocity measurements by a hot-wire velocimeter (HW) and numerical simulations. As a result, by the compensation of the centrifugal-force effect, we get accurate pressures on the rotating blade, which are conditionally-averaged over a number of periods. The obtained experimental results can be also dedicated to CFD as standard benchmarks.

Aspect-Ratio and Reynolds-number Effect On Cross-Flow Impellers(Fluid Machinery)

The purpose of this experimental research is to investigate both the aspect-ratio effect and the Reynolds-number effect, especially for the flow of impellers with short axes. Particle-image-velocimetry (PIV) technique and a hot-wire anemometer are used for measurements of flow velocity. The impeller rotates in open space without any casings. The authors have studied two kinds of the impeller, that is with forward-curved blades and with flat-plate blades. As a result, the following were obtained. Observing eccentric vortex revolution using hot-wire measurements and flow visualization, we classified the flow into three modes. And according to this classification, we showed stability diagrams for both impellers. Using PIV results, we defined outflow rate Q from impeller. Outflow rate coefficient C_Q is independent of Re for both impellers. For a flat-blade-impeller, C_Q is not affected by aspect ratio L/D_2. But, for a forward-curved-impeller, C_Q increases with L/D_2.

Solidity and Blade Number Effects on a Fixed Pitch, 50 W Horizontal Axis Wind Turbine

Experimental studies were conducted on a modified Rutland 500 horizontal axis wind turbine to evaluate numerical implications of solidity and blade number on the aerodynamic performance. Wind tunnel data were acquired on the turbine with flat-plate, constant-chord blade sets and optimum-designed blade sets to compare with theoretical trends, which had indicated that increased solidity and blade number more than conventional 3-bladed designs, would yield larger power coefficients, CP. The data for the flat plate blades demonstrated power coefficient improvements as the range of solidities was increased from 7% to 27%, but did not indicate performance gains for increased blade numbers. It was also observed that larger pitch angles decreased the optimum tip speed ratio range significantly with a small (5% or less) change in maximum CP. The optimum-design 3-bladed rotors produced an increased experimental CP as solidity increased, with reduced tip speed ratio, at the optimum operating point. As blade number was increased at a constant solidity of 10% from 3 to 12 blades, aerodynamic efficiency and power sharply decreased, contrary to the numerical predictions and the flat plate experimental results. Low Reynolds numbers and wind tunnel blockage effects limit these conclusions and a full scale prototype rotor is being constructed to examine the results of the numerical and experimental studies using a side-by-side comparison with a commercially available wind turbine at the Clarkson University wind-turbine test site.

The Standing Wave Formed in the Wake of a Flat Plate Blade and the Coherent Structure

The Standing Wave Formed in the Wake of a Flat Plate Blade and the Coherent Structure