Blade Chord Length Research Articles

Analysis of Aerodynamic Characteristics of Vertical Axis Wind Turbine (VAWT) Based on Modified Double Multiple Stream Tube Model

To further improvement of the aerodynamic performance simulation model accuracy of Vertical Axis Wind Turbine (VAWT), based on the traditional double multi-flow tube theoretical model, the aerodynamic parameters of the airfoil before and after stall are modified by the Lanchester method. Prand model is used to modify the aspect ratio of the airfoil under the condition of the small angle of attack before stall. Viterna Corrigan model is used to modify the aspect ratio, lift and drag coefficients of the airfoil under the stall. And a relaxation factor is introduced to correct the induction factor, also to improve the iterative non-convergence of the simulation under the condition of large tip speed ratio. The simulation results match the experimental data very well. Based on this new aerodynamic performance analysis method, the influence of blade tip speed ratio, blade number, blade chord length, rotor radius, and incoming wind speed on power coefficient and tangential force coefficient is studied, which can provide a reference for the design of aerodynamic performance parameters of the wind turbine.

Blade planform design optimization to enhance turbine wake control

AbstractThis study considers optimizing the planform of wind turbine blades to ultimately enhance wind plant controls, namely, wake steering strategies. Adjoint‐enabled unsteady actuator line simulations are carried out to obtain gradients for optimization of several different performance objectives with respect to blade chord length at 10 locations along blade span. We demonstrate different blade design optimizations that can maximize time‐averaged lateral wake deflection, entrainment of kinetic energy, or total power of multiple turbines. Our optimized designs can produce a 4+% increase in wake deflection, a 4× increase in vertical kinetic energy entrainment, or a 3.6% increase in power when compared with the baseline case. While lateral wake deflection is only modestly sensitive to chord changes, we find that increasing the outboard chord length can dramatically increase kinetic energy entrainment, resulting in faster wake recovery and gains in net power. While this work develops only a few case studies emphasizing relative performance improvements and general trends, these results show the promise of a framework that combines mid‐fidelity computation with adjoint‐based optimization for control and design problems.

Study on Structural Performance of Horizontal Axis Wind Turbine with Air Duct for Coal Mine

Considering the characteristics of narrow underground space and energy distribution, based on blade element momentum theory, Wilson optimization model and MATLAB programming calculation results, the torsion angle and chord length of wind turbine blade under the optimized conditions were obtained. Through coordinate transformation, the data were transformed into three-dimensional form. The three-dimensional model of the blade was constructed, and the horizontal axis wind turbine blade under the underground low wind speed environment was designed. The static structural analysis and modal analysis were carried out. Structural design, optimization calculation and aerodynamic analysis were carried out for three kinds of air ducts: external convex, internal concave and linear. The results show that the velocity distribution in the throat of linear air duct is relatively uniform and the growth rate is large, so it should be preferred. When the tunnel wind speed is 4.3 m/s and the rated speed is 224 rad/s, the maximum displacement of the blade is in the blade tip area and the maximum stress is at the blade root, which is not easy to resonate. The change rate of displacement, stress and strain of blade is positively correlated with speed. The energy of blade vibration is mainly concentrated in the swing vibration of the first and second modes. With the increase in vibration mode order, the amplitude and shape of the blade gradually transition to the coupling vibration of swing, swing and torsion. The stress and strain of the blade are lower than the allowable stress and strain of glass fiber reinforced plastics (FRP), and resonance is not easy to occur in the first two steps. The blade is generally safe and meets the design requirements.

Influence of Various Stator Parameters on the Open-Water Performance of Pump-Jet Propulsion

In order to improve the hydrodynamic performance of pump-jet propulsion (PJP) when matching stator with the rotor, the RANS method with SST k-ω turbulence model is employed to study the influence of six kinds of stator parameters, which are classified into three groups, i.e., stator solidity, stator angles and rotor–stator spacing (S). Results show that the stator solidity involves the blade number (Ns) and chord length (L), has an obvious acceleration effect at and after stator, and produces a higher thrust and torque with a slight efficiency change. Further comparing Ns and L results, we find greater distinctions between the two cases when stator solidity is greatly adjusted. Three stator angles, i.e., stagger angle (α), lean angle (γ), and sweep angle (β), are studied. The α has the biggest effect on the thrust, torque, and efficiency; meanwhile, it shifts the advance number that corresponds to maximum efficiency. The effect of γ is similar to α, but its influence is far less than α. However, there is little difference between various β cases except for off-design conditions, where the efficiency drops dramatically as β increases. The S has a slight effect on PJP performance. Even though S decreases 34% relative to the original PJP, the rotor thrust and torque increase by less than 1%. In addition, we compare torque balance locations under various parameters, and each component force is analyzed in detail to explain the reason for performance variation. The present work is conducive to future optimization in PJP design.

Surrogate models for predicting noise emission and aerodynamic performance of propellers

This paper deals with the innovative development of surrogate models suitable for the simulation of aerodynamic performance and acoustic emission in terms of tonal components, of multi-propeller systems like those applicable in urban air-mobility vehicles. These can be of great help particularly when designing distributed-electric-propulsion configurations, as they provide an agile tool that avoids the need for computationally expensive CFD/CAA predictions. Without losing the generality of the conclusions that can be drawn about the capability of the proposed surrogate models to accurately describe multi-propeller aerodynamic and aeroacoustic responses, applications to a single propeller configuration are presented. Focusing on the simulation of the effects due to the spanwise distribution of blade twist and chord length, two surrogate modelling techniques are examined: one based on Artificial Neural Networks and one based on Genetic Programming. The numerical database for the identification of these models is determined by the combined application of a boundary integral formulation suitable for the potential aerodynamics solution around lifting/thrusting bodies, and the Farassat 1A formulation for the evaluation of the noise field. The numerical investigation demonstrates that both metamodelling techniques are able to reproduce propeller aerodynamic performance and radiated noise with a very good level of accuracy, certainly suitable for preliminary design applications.

Effect of impeller solidity on the generating performance for solar power generation

According to current solar power research, both the generating unit's minimum start-up speed and power generation system's minimum flow rate for operation decrease with the increase in the impeller solidity. Ideally, a high solidity should be achieved, as this translates more power for a solar power system in the start-up and shut-down cycles. However, increasing the number of blades does not increase the impeller solidity; therefore, there is an optimal number of blades needed to achieve the preferred solidity. This paper begins by selecting the blade airfoil and then performs a theoretical analysis based on the relationship between the blade number and chord length. Experiments are conducted to measure the starting and stopping wind speeds and power characteristics for different numbers of blades. The results show that a maximum impeller solidity of 0.2862 is achieved, as well as the minimum flow speed at the start-up, and the maintenance of the solar chimney power generation system is optimized when there are four blades.

Effects of wetness and humidity on transonic compressor of gas turbine

Moist air flows with and without consideration of inlet wetness and assuming fogging were numerically investigated in a transonic compressor of an industrial gas turbine, and the causal relationship between the wetness and the deposition of water droplets on the blade surface was clarified. First, we simulated three-dimensional moist-air flows through the 1.5-stage rotor and stator blade rows in the transonic compressor of an industrial gas turbine operating at a Tokyo Electrical power plant, considering variations in the inlet wetness and the number of aerosol particles. The results indicated that the shock generated in the first-stage rotor passage was the primary factor in the evaporation of the moist air, decreasing its temperature, whereas the wetness was highly dependant on the deposition of water droplets on the blade surface. We further simulated two-dimensional humid-air flows through a transonic compressor cascade channel under a number of conditions, varying the aerosol particle size, number of aerosol particles, humidity, blade chord length and pressure ratio. The results indicated that the condensation of humid air was captured locally in the supersonic region, while the deposition of the condensed water droplets was mainly influenced by the first three factors. Overall, this study indicates that wetness and deposition are in a trade-off relationship with regard to the performance of gas turbines.

Blade Structure Design Based on Multi-objective Optimization of Automotive Fan

In order to improve the fan noise, the multi-objective optimization algorithm was implemented to optimize the fan blade structure. Firstly, the theoretical model with the noise, flow rate and power of fan as the objectives was established and verified; then, the global sensitivity analysis method based on sobol’ method was used to obtain the contributions of each parameter to the performance objectives of the fan by taking the fan blade angle and chord length as the analysis parameters; finally, the sensitive parameters are selected to obtain the best noise-oriented comprehensive performance of the fan by the genetic algorithm. The result shows that the noise is reduced by 3.1dB, the flow rate is increased by 7.7% and the power is reduced by 7.9% after optimizing fan blade structure, and the overall performance of the fan is significantly improved.

Experimental Study on Film Cooling Effectiveness of Blade With Chevron-Shaped Holes Under Wake Influence

Abstract Gas turbines have been widely used. With the continuous improvement of the performance of gas turbines, the turbine inlet temperature has greatly exceeded the heat-resistance limit of the turbine blade material, so advanced cooling technology is required. The film cooling effectiveness distribution over the blade under the effect of wake was obtained by the pressure-sensitive paint (PSP) technique. The test blade has five rows of chevron film holes on the pressure side, three rows of cylindrical film holes on the leading edge, and three rows of chevron film holes on the suction side. The mainstream Reynolds number is 130,000 based on the blade chord length, and the mainstream turbulence intensity is 2.7%. The upstream wake was simulated by the spoken-wheel type wake generator. The film cooling effectiveness was measured at three wake Strouhal numbers (0, 0.12, and 0.36) and three mass flux ratios (MFR1, MFR2, and MFR3). The results show that the increase of mass flux ratio leads to a decrease of the film cooling effectiveness on the suction surface. In the wake condition, the effect of mass flux ratio is weakened. Wake leads to a marked decrease of the film cooling effectiveness over most blade surface except for the surface near leading edge on the pressure surface. In the high mass flux ratio condition, the effect of wake on the film cooling effectiveness is weakened on the suction surface and strengthened on the pressure surface.

Solidity Optimization for an H-Darrieus Wind Turbine

Solidity is one of the main factors that influence the performance of a wind turbine. The solidity of an H-Darrieus wind turbine is optimized in terms of blade number, chord length, and rotor radius to get the maximum power coefficient using Taguchi L16 (4^3) array. Power coefficient values are calculated by the Double Multiple Stream Tube model by in house built MATLAB code according to Taguchi orthogonal array. The maximum power coefficient is found as 0.4728 for the two-bladed rotor with a chord length of 0.2 m and a radius of 2 m. Relation of maximum power coefficient respect to blade number, chord length, and rotor radius is derived. Predicted mean values of the maximum power coefficient are in agreement with calculated values. Furthermore, an equation for the maximum power coefficient is obtained for rotor solidity. Derived equations can be useful to estimate the maximum power coefficient values of H-Darrieus wind turbines.

Flow separation control in an axial compressor cascade using various arrangement of plasma actuator

The present work is concerned with the control of separation which occurs on an axial compressor cascade by plasma actuator (PA). The results show that PA reduces energy losses. Also, a lift-to-drag ratio enhancement up to 18% can be obtained using PA at 15% of the blade chord length. The flow control obtained by PA at low Reynolds numbers and low angle of attack is more effective on the performance of the compressor. Also, two and three pairs of electrodes are applied and the results show using three pairs of electrodes can enhance the performance up to 40%.

A Study on Relationship among Blade Camber Direction and Pitch Angle and Performance of a Small Straight-Blade Darrieus Wind Turbine by Using Scale Test Model and Gurney Flap

Straight-blade Darrieus vertical axis wind turbines are used as medium and small size wind turbine because of higher power output in vertical axis wind turbine (VAWT). In our previous study, the relationship between the performance and Reynolds number based on airfoil chord length had been investigated by using small-scale test models of lift-type VAWT, and the results showed that the performance of tested wind turbine models with small diameter was clearly lower than that of the large-scale field test machine, and its performance also varies significantly with the blade pitch angle. In this study, we focused on the performance of a small-scale straight-blade Darrieus VAWT, the relationship among the blade airfoil camber direction and the pitch angle, and the performance of the small-scale VAWT was examined experimentally by using a small-scale VAWT test model with Gurney flap which was a small flat plate. Gurney flaps with its height h, as a ratio to the blade chord length c, h/c = 0.036 to 0.055, were attached to the blades of the VAWT test model, in addition, the attaching direction of the Gurney flap on the blade was examined for both inward and outward of the rotor, and the pitch angle was also examined for a range of −5 to 10 degrees. These results are discussed comparing with the result of the VAWT without Gurney flap and considering the numerical results for the single blade with/without the Gurney flap. The results showed that the performance of the tested VAWT was reversed between the inward and outward Gurney flaps around a pitch angle of 10 degrees. That is, the inward Gurney flap was superior at a pitch angle of less than 10 degrees, while the outward Gurney flap was effective at a pitch angle of more than 10 degrees. Furthermore, for the tested small-scale VAWT model, the optimum pitch angle was about 5 degrees, and the inward and shorter Gurney flap showed higher power performance of the VAWT under this pitch angle condition.

Experimental flow analysis of vertical axis turbine for power generation in open channel system

In this experimental study, flow structure over a three bladed vertical axis Darrieus turbine is investigated experimentally for Reynold Number, Re=9000 in an open channel. Rigidity ratio (σ), angle of attack, optimum values of blade chord length (CL), turbine radius (R) and height of turbine blades (H) are used as approximately 1.1 and α=-2°, CL=5 cm, R=13.75 cm and H=20 cm, respectively. According to the values, ¼ scale model of a vertical axis Darrieus turbine has been used in order to perform experimental flow analysis. In experimental flow analysis, two different azimuth angles, θ=270° and θ=240° are used to examine the flow characteristics in the Particle İmage Velocimetry (PIV) experiments. As a result of the experiments, time averaged velocity vectors , averaged streamlines , and averaged vortex fields , are obtained and interpreted time averaged velocity vectors , averaged streamlines , and averaged vortex fields , changes with the turbine blade positions. As a result, it is seen that turbine azimuthal angle affetcs the flow structure and streamline focal points, positive and negative vortex are formed in the flow region behind the turbine. Only one focal point at θ=240° is occurred while two focal points and one stagnation point are occurred at the angle of θ=270°.

Multidisciplinary Design Optimization for Performance Improvement of an Axial Flow Fan Using Free-Form Deformation

Abstract This paper describes a multidisciplinary design optimization for performance improvement of an electric-ducted fan rotor using free-form deformation (FFD) and data mining techniques. A practical partitioning approach for FFD parameterization was applied in combination with engineering design parameters to optimize the fan rotor. Regression analysis was used to initially determine an approximation function for the blade static stress and subsequently integrated into a fully coupled iterative loop to optimize the blade considering two operating points. Two optimization solutions for 10 and 12 blades were performed. Percentage improvements in the efficiency of 1.05% and 1.32% were realized for 10 and 12 blades, respectively, at near peak efficiency flowrate. Also, blade static stress was reduced by percentages of 5.49% and 12.37% for 10 and 12 blades compared with the baseline. Data mining results revealed key design variable sensitivities where blade twist, sweep, chord, and hub thickness distribution were found to be the most influential for 12 blades while for 10 blades, blade lean, sweep and chord at the midspan and tip. The optimized blades were found to have a significant increase in chord from midspan to tip mimicking a wide chord fan blade particularly for 10 blades. Analysis of the flow field revealed that the axial velocity from 0.4 to 0.8 spanwise length increased significantly for the optimum blades due to the increase in blade twist and chord length at all stable operating points. However, the leakage trajectory relative to the blade chord was observed to be larger and interacted with the trailing edge wake flow downstream for the optimum blades at near-stall conditions. Furthermore, the increase in chord length and the thinning of the blade close to the trailing edge from 0.4 to 0.8 span reduced the suction-side blade loading and static stress.

Effects of stator splitter blades on aerodynamic performance of a single-stage transonic axial compressor

Splitter blades located between stator blades in a single-stage axial compressor were proposed and investigated in this work to find their effects on aerodynamic performance and operating stability. Aerodynamic performance of the compressor was evaluated using three-dimensional Reynolds-averaged Navier-Stokes equations using the k-e turbulence model with a scalable wall function. The numerical results for the typical performance parameters without stator splitter blades were validated in comparison with experimental data. The numerical results of a parametric study using four geometric parameters (chord length, coverage angle, height and position) of the stator splitter blades showed that the operational stability of the single-stage axial compressor enhances remarkably using the stator splitter blades. The splitters were effective in suppressing flow separation in the stator domain of the compressor at near-stall condition which affects considerably the aerodynamic performance of the compressor.

‘Design of wind blades for the development of low-power wind turbines using Betz and Schmitz methods.’

ABSTRACT This paper deals with wind turbine design and production for low power generation, and is tailored for residential usage constraints. The design process involves choosing the type of material for wind turbine and deciding the distribution of the blade aerofoil, pitch angle, and chord length along the radius. The distributions of the pitch angle and chord length are calculated based on the conservation of angular momentum and the theory of aerodynamic forces on an aerofoil. Blade Element Momentum theory is first developed, and then used to perform a parametric analysis to decide if the optimised blade pitch and chord length values establish the most effective blade geometry. Finally, two separate approaches are evaluated to decide which one produces the most effective blade of wind turbines and also provides a discussion of the most critical parameters in the design of the blade of wind turbines to optimise effectiveness. The performance of wind turbine can be improved using this theory in designing of wind turbine blades.

Design and Performance Analysis of Mixed Flow Turbine Rotors With Extended Blade Chord

Abstract Mixed flow turbines offer additional design freedom compared with conventional radial turbines. This is useful in the automotive turbocharger application to reduce rotor inertia, which can be very beneficial for the transient response of a highly boosted downsized passenger car powertrain. A previously published study from the authors analyzed a series of nine mixed flow turbine rotors with varying blade cone angle and inlet blade angle. This paper reports an extension of that study with two further mixed flow turbine rotors where the chord length of the rotor blade was extended. The aim of this work was to understand both the aerodynamic and mechanical impacts of varying the chord length, particularly for the turbocharger application where off-design performance and transient response are very important. The baseline mixed flow rotor for this study had a blade cone angle of 30 deg and an inlet blade angle of 30 deg. Two further variations were produced; one with the trailing edge (TE) extended in the downstream direction across the entire blade span. In the second variation, the chord was extended at the hub corner only, while the shroud corner of the TE remained unchanged, with the aim of achieving some aerodynamic improvement while meeting mechanical requirements. When the blade was extended at both the hub and shroud, the inertia and stress levels increased significantly and the blade eigenfrequencies reduced. There was a significant improvement in peak efficiency, but the mechanical performance was unfavourable. The improvement in peak efficiency was mainly due to better exhaust diffuser performance and, therefore, would not be realized in most turbocharger installations. The blade that was extended at only the hub corner incurred very little additional inertia, and the centrifugal stresses and blade eigenfrequencies were improved. Consequently, it was possible to reduce the blade thickness at the TE in order to achieve a more aerodynamically optimized design. In this case, the mechanical performance was acceptable and there were efficiency improvements of up to 1.1% points at off-design conditions, with no reduction in peak efficiency or maximum mass flowrate. Therefore, the blade that was extended only at the hub produced some improvement within acceptable mechanical limits. The flow field features were considered for the three rotor geometries to explain the changes in loss and efficiency across the operating range.

Performance and Wake Characterization of a Model Hydrokinetic Turbine: The Reference Model 1 (RM1) Dual Rotor Tidal Energy Converter

The mechanical power and wake flow field of a 1:40 scale model of the US Department of Energy’s Reference Model 1 (RM1) dual rotor tidal energy converter are characterized in an open-channel flume to evaluate power performance and wake flow recovery. The NACA-63(4)-24 hydrofoil profile in the original RM1 design is replaced with a NACA-4415 profile to minimize the Reynolds dependency of lift and drag characteristics at the test chord Reynolds number. Precise blade angular position and torque measurements were synchronized with three acoustic Doppler velocimeters (ADV) aligned with each rotor centerline and the midpoint between the rotor axes. Flow conditions for each case were controlled to maintain a hub height velocity, uhub= 1.04 ms−1, a flow Reynolds number, ReD= 4.4 × 105, and a blade chord length Reynolds number, Rec= 3.1 × 105. Performance was measured for a range of tip-speed ratios by varying rotor angular velocity. Peak power coefficients, CP= 0.48 (right rotor) and CP= 0.43 (left rotor), were observed at a tip speed ratio, λ= 5.1. Vertical velocity profiles collected in the wake of each rotor between 1 and 10 rotor diameters are used to estimate the turbulent flow recovery in the wake, as well as the interaction of the counter-rotating rotor wakes. The observed performance characteristics of the dual rotor configuration in the present study are found to be similar to those for single rotor investigations in other studies. Similarities between dual and single rotor far-wake characteristics are also observed.

CFD Investigation of Separation Control on a Vertical Axis Wind Turbine: Steady and Unsteady Suction

High-fidelity two-dimensional unsteady Reynolds-averaged Navier-Stokes (URANS) simulations are employed to investigate the influence of boundary layer suction through a slot located near the leading edge of a vertical axis wind turbine operating in dynamic stall. The analysis includes both steady and unsteady suction with different frequencies. The results shows that: (i) when the suction slot is located within the chordwise extent of the laminar separation bubble, dynamic stall can be avoided with minimal suction amplitude; (ii) the most promising suction location is the most upstream suction location studied, at 8.5%c where c is the blade chord length; (iii) the suction only needs to be applied during the azimuthal angles when dynamic stall occurs; (iv) the oscillation frequency of the suction velocity has insignificant influence on the obtained turbine power gain; (v) applying unsteady suction is interesting as it reduces the energy consumption of the suction system, thus the net power gain.

Analysis of the effect of freestream turbulence on dynamic stall of wind turbine blades

The aerodynamics of a wind turbine blade at various fixed and dynamically changing angles of attack for laminar and turbulent freestream is investigated by large-eddy simulations. The effects of freestream turbulence on the aerodynamic coefficients are analyzed for dynamic stall conditions being generated by prescribing gusts, i.e., periodically changing incoming velocity fields, onto a ClarkY airfoil at a chord based Reynolds number of Re=150,000. A synthetic turbulence generation (STG) method is extended and applied to produce the turbulent gusts in a time varying mean flow with predefined turbulence statistics, such as mean velocity, Reynolds stress tensor components, and velocity spectra. The length scales in the turbulent freestream are smaller than the blade chord length. The reduced frequency of the incoming laminar and turbulent gusts is kred=0.2 based on the freestream velocity, chord length, and gust frequency. Dynamic stall is analyzed for an angle of attack ranging from 10° to 25°. It is shown how much the freestream turbulence level delays stall and increases lift at high angle of attack. The effect of the turbulence is most evident on the aerodynamic forces during the phase of decreasing angle of attack of the dynamic stall process, in which the reattachment of the boundary layer is enhanced by the freestream turbulence. The negative damping from the moment coefficient is also significantly reduced due to the incoming turbulence. The results show that the freestream turbulence in a turbulent flow at a turbulence level of 5% improves the aerodynamic performance of the wind turbine blade.