Blade Chord Length Research Articles

Numerical simulation and optimization of aerodynamic noise for claw pole alternator

This study aims at minimizing the aerodynamic noise generated by claw pole alternator used in vehicles. In this paper, an effective and efficient hybrid test-analysis engineering approach has been proposed to predict and optimize acoustic performance of claw pole alternator. First, an experimental analysis was performed to predict the main components of the aerodynamic noise generated by the claw pole alternator. Then a hybrid approach was proposed to calculate the aerodynamic noise of the alternator. A computational fluid dynamics model of the claw pole alternator was developed for calculating the flow-field of the alternator. The pressure fluctuation in the flow field was analyzed to validate the computational fluid dynamics simulation. After the computational fluid dynamics simulation, the far-field aerodynamic noise generated by the flow field was calculated by adopting the acoustic finite element method. The accuracy and feasibility of the acoustic finite element model were validated with the experimental data. After the validation, the effects of the cooling fan parameters on the aerodynamic noise of the alternator were discussed and analyzed. According to the sound source information and the generation mechanism of the aerodynamic noise, the blade spacing angle of the cooling fan was optimized by establishing a theoretical model. The blade chord length of the cooling fan, the blade installation angle of the cooling fan and the tilt angle of the grille on end cap were optimized by structuring different surrogate models. After the optimizations, a significant reduction in the noise level of the claw pole alternator was found by the finite element method simulation. The overall sound power level has been decreased by about 6 dB (A).

Global Search of a Three-dimensional Low Solidity Circular Cascade Diffuser for Centrifugal Blowers by Meta-model Assisted Optimization

A three-dimensional blade of a low solidity circular cascade diffuser in centrifugal blowers is designed by means of a multi-point optimization technique. The optimization aims at improving static pressure coefficient at a design point and at a small flow rate condition. Moreover, a clear definition of secondary flow expressed by positive radial velocity at hub side is taken into consideration in constraints. The number of design parameters for three-dimensional blade reaches to 10 in this study, such as a radial gap, a radial chord length and mean camber angle distribution of the LSD blade with five control points, control point between hub and shroud with two design freedom. Optimization results show clear Pareto front and selected optimum design shows good improvement of pressure rise in diffuser at small flow rate conditions. It is found that three-dimensional blade has advantage to stabilize the secondary flow effect with improving pressure recovery of the low solidity circular cascade diffuser.

Review on Numerical and Experimental Research on Conventional and Unconventional Propeller Blade Design

This paper reviews the research conducted on propeller blades based on the performance evaluation method and available design. The review includes the propeller blades used for aircrafts, unmanned aerial vehicles, marine vehicles and wind turbines, as the working principle remain the same, differing only in operating conditions. Both experimental and numerical methods were discussed to provide a reliable procedure to investigate the performance of propeller blades. In addition, the propeller blades design was discussed, including conventional and unconventional blade designs. Blade shape, chord length and twist angle are the basic parameters for optimization method on conventional design. Optimization managed to improve propeller performance at an impressive rate. Many designs are currently being developed allowing more possibilities for blade design advancement.

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

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

Influence of Solidity and Wind Shear on the Performance of VAWT using a Free Vortex Model

Performance analysis of a VAWT and HAWT is highly complex due to fluid structure interactions and blade vortex interactions.However, there are simplified methods such as momentum theory to most expensive CFD modelsavailable forperformance prediction. CACTUS is neither as simple as the momentum theory nor as complex as the CFD models, it is an open source code that uses the free vortex method to predict the performance of a wind turbine.In this paper, the effect of solidity and wind shear on the performance of an H-type Darrius VAWT is studied using CACTUS. Variation of solidity was achieved by changing the chord length ( c/R 0.04-0.07) and number of blades ( N 2,3). It has been observed that at lower tip speed ratio (TSR 3) shorter c/R was more efficient due to relatively low wake blade interaction. Effect of wind shear due to the tower height from the ground using the power law equation with values of power law coefficient ranging from 0.1 to 0.3has also been studied.Itis observedthat the power coefficients of the VAWT under a turbulent boundary layer are in congruence with the experimental results.

Study on Performance Evaluation of Small Axial Fan

In order to establish the design methodology of a small axial fan, the axial fan with impeller diameter of 36 mm was designed, manufactured and tested. Especially, in order to investigate the influence of difference in blade cord length and blade thickness on performance characteristics, the performance characteristics obtained by the designed axial fans with difference blade shapes were examined. Also, by using CFD, the same flow field as the experiment was visualized. It was found that the lift of the blade was increased and the performance was improved in high flow rate region by thinning of the blade thickness and by extending the blade chord length.

The efficiency analysis of high-altitude propeller based on vortex lattice lifting line theory

ABSTRACTIn this paper, we proposed a simple approach to analyse the efficiency and propulsive characteristics of the high-altitude propeller in accordance to the Vortex Lattice Lifting line Method (VLM) theory, which is commonly used in preliminary design and parametric studies of propeller propulsion. The Computational Fluid Dynamics (CFD) method was used to obtain aerofoil aerodynamic data. The optimal pitch angle and propeller blade chord length (along the radial direction) can be calculated using the information from the database. The propeller wake model sees helical slipstreams applied to both lightly and moderately loaded propellers. The proposed method is capable of identifying the optimal efficiency through varying the number of propeller blades, radius and the rotational speed. The relationship between the optimal efficiency and design parameters is then established. This method was verified using CFD calculations.

CFD를 이용한 180,000 DWT Bulk Carrier용 Pre-Swirl Duct의 파라메트릭 설계

In this study, a pre-swirl duct for the 180,000 DWT bulk carrier has been designed from a propulsion standpoint using CFD. The stern duct - designed by NMRI - was selected as the initial duct. The objective function is to minimize the value of delivered power in model scale. Design variables of the duct include duct angle, diameter, chord length, and vertical and horizontal displacements from the center. Design variables of the stators are blade number, arrangement angle, chord length, and pitch angle. A parametric design was carried out with the objective function obtained using CFD. Reynolds averaged Navier-Stokes equations have been solved; and the Reynolds stress model applied for the turbulent closure. A double body model is used for the treatment of free-surface. MRF and sliding mesh models have been applied to simulate the actuating propeller. A self-propulsion point has been obtained from the results of towing and self-propelled computations, i.e., form factor obtained from towing computation and towing forces obtained from self-propelled computations of two propeller rotating speeds. The reduction rate of the delivered power of the improved stern duct is 2.9%, whereas that of the initial stern duct is 1.3%. The pre-swirl duct with one inner stator in upper starboard and three outer stators in portside has been designed. The delivered power due to the designed pre-swirl duct is reduced by 5.8%.

Performance and dynamic characteristics of a multi stages vertical axis wind turbine

Vertical axis wind turbines (VAWTs) are used to convert wind energy to mechanical output or electricity. Vertical axis wind turbines are favorable at buildings as it can receive wind from any direction, have a design that can be integrated simply with building architecture and they have better response in turbulent wind flow which is common in urban areas. Using a calculation code based on the Double Multiple Stream Tube theory, symmetrical straight-bladed NACA0012 wind turbine performance was evaluated. The induction factor for both upwind and downwind zone is determined with the aid of a root-finding algorithm. This numerical analysis highlighted how turbine performance is strongly influenced by the wind speed (Reynolds number) and rotor solidity (turbine radius and blade chord length). Also a dimensional analysis is introduced and is to be considered in such a way to generalize the design for different turbine specifications. One of the qualities provided by dimensional analysis is that geometrically similar turbines will produce the same non-dimensional results. This allows one to make comparison between different sizes wind turbines in terms of power output and other related variables. One of the main problems affecting the turbine performance and dynamics is the torque ripple phenomena. So in this paper a turbine design configuration is introduced in order to decrease the turbine torque fluctuation. This design is carried out by constructing more similar turbine units (stages) on the vertical axis on top of each other with different orientation phase angles. The results showed that using even number of turbine assembly is better than odd number to avoid torque fluctuation and mechanical vibrations acting on the turbine. Also it is preferred to use four turbine stages as the eight stages will have no sensible effect on decreasing the torque fluctuation.

Propeller Design and Loss Mechanisms in Low-Reynolds-Number Flows

To develop a highly efficient propeller for small-scale unmanned aerial vehicles, the influences of induced and profile losses determined by design parameters are investigated at . The propeller blade shapes, such as chord length and twist angle distributions in the spanwise direction, are determined using the Adkins–Liebeck method. For a fixed designated thrust value and a forward velocity, the influences of a propeller normalized radius, a blade number, and a tip speed ratio on the propeller performance are discussed. Results show that the profile loss can be larger than the induced loss. For such a case, it is beneficial to reduce the blade number and the propeller rotational speed to increase the blade chord length and the Reynolds number; consequently, the propeller efficiency increases even if the induced drag increases.

Flap-wise loads reduction of rotor blades by embedded flap-wise absorbers

ABSTRACTElastomeric and Fluidlastic®absorbers are proposed to be embedded in blade cavity to reduce troublesome second harmonic flap-wise blade loads of rigid rotors. A simple model of a blade with a flap-wise dynamic absorber is derived to investigate centrifugal force effects on the absorber's rotating frequency. The system's dynamic equations of motion indicate that centrifugal force has no effect on absorber's frequency under rotation. Aeroelastic simulation of the coupled rotor and absorber system based on an elastic beam model in generalised force formulation is used to explore load reduction extent and dynamic absorber behaviour. At a forward speed of 200 km/h, the elastomeric absorber reduces the second harmonic flap-wise root-bending moment by 88.8% for unacceptably large stroke; the Fluidlastic®absorber reduces the moment by 78.5% with a stroke 4.26% of blade chord length. Results indicate that placing an embedded Fluidlastic®absorber in the blade's flap-wise direction has potential for reducing load in different flight states with relatively small strokes. Increasing tuning port area ratio or Fluidlastic®absorber mass can distinctly decrease strokes without increasing loads. However, deviation from normal rotor speed significantly lowers Fluidlastic®absorber performance.

Influence analysis of blade chord length on the performance of a four-bladed Wollongong wind turbine

The Wollongong wind turbine is a new kind of vertical axis wind turbine (VAWT) with its blades rotated by only 180° for each full revolution of the main rotor. A computational study on the effect of blade chord length on the turbine output performance of a four-bladed Wollongong turbine has been conducted using the commercial computational fluid dynamics (CFD) code ANSYS 13.0. A validation study was performed using a Savonius turbine and good agreement was obtained with experimental data. Both rotating and steady CFD simulations were conducted to investigate the performance of the VAWT. Rotating two-dimensional CFD simulations demonstrated that a turbine with a blade length of 550 mm has the highest power curve with a maximum averaged power coefficient of 0.3639, which is almost twice as high as that of a non-modified Savonius turbine. Steady two-dimensional CFD simulations indicated that the Wollongong turbine has a good self-starting capability with an averaged static torque coefficient of 1.09, which is about six times as high as that of a Savonius turbine.

Effects of Reynolds Number on the Energy Conversion and Near-Wake Dynamics of a High Solidity Vertical-Axis Cross-Flow Turbine

Experiments were performed with a large laboratory-scale high solidity cross-flow turbine to investigate Reynolds number effects on performance and wake characteristics and to establish scale thresholds for physical and numerical modeling of individual devices and arrays. It was demonstrated that the performance of the cross-flow turbine becomes essentially R e -independent at a Reynolds number based on the rotor diameter R eD ≈ 106 or an approximate average Reynolds number based on the blade chord length R ec ≈ 2 × 105 . A simple model that calculates the peak torque coefficient from static foil data and cross-flow turbine kinematics was shown to be a reasonable predictor for Reynolds number dependence of an actual cross-flow turbine operating under dynamic conditions. Mean velocity and turbulence measurements in the near-wake showed subtle differences over the range of R e investigated. However, when transport terms for the streamwise momentum and mean kinetic energy were calculated, a similar R e threshold was revealed. These results imply that physical model studies of cross-flow turbines should achieve R eD ∼ 106 to properly approximate both the performance and wake dynamics of full-scale devices and arrays.

A Method for Propeller Blade Optimization and Cavitation Inception Mitigation

Propeller blade design for fast ships is often driven by cavitation constraints. A tradeoff exists, in which larger chord lengths and section thicknesses typically improve cavitation performance but result in lower efficiency. Typically, chord lengths are optimized for the design condition (ship endurance speed) with some specified margin to prevent cavitation off-design (at maximum ship speed). Cavitation performance at the maximum speed is considered postfacto, and blade shape often needs to be modified for cavitation considerations in high-speed operation. This article presents an improved method for blade shape optimization. The present method simultaneously considers the cavitation performance at the endurance speed design point and a maximum speed off-design point, and blade chord lengths and thicknesses are set to prevent cavitation at both operational conditions. During the present design optimization routine, the on-design load distribution is optimized, and the off design performance is determined such that the chord lengths can be set to a minimum that still prevents cavitation at both the on- and off-design conditions. A case study is presented, considering the notional design of a propeller for the U.S. Navy DDG51 destroyer-class ship. Propellers designed using standard chord/thickness optimization procedures are compared with those designed using the present procedures. Cavitation performance is compared for the two design methods.

A Method for Propeller Blade Optimization and Cavitation Inception Mitigation

Propeller blade design for fast ships is often driven by cavitation constraints. A tradeoff exists, in which larger chord lengths and section thicknesses typically improve cavitation performance but result in lower efficiency. Typically, chord lengths are optimized for the design condition (ship endurance speed) with some specified margin to prevent cavitation off-design (at maximum ship speed). Cavitation performance at the maximum speed is considered postfacto, and blade shape often needs to be modified for cavitation considerations in high-speed operation. This article presents an improved method for blade shape optimization. The present method simultaneously considers the cavitation performance at the endurance speed design point and a maximum speed off-design point, and blade chord lengths and thicknesses are set to prevent cavitation at both operational conditions. During the present design optimization routine, the on-design load distribution is optimized, and the off-design performance is determined such that the chord lengths can be set to a minimum that still prevents cavitation at both the on- and off-design conditions. A case study is presented, considering the notional design of a propeller for the U.S. Navy DDG51 destroyer-class ship. Propellers designed using standard chord/thickness optimization procedures are compared with those designed using the present procedures. Cavitation performance is compared for the two design methods.

Design & optimization of a small wind turbine blade for operation at low wind speed

A small wind turbine blade was designed and optimized in this research paper. The blade plays an important role, because it is the most important part of the energy absorption system. Consequently, the blade has to be designed carefully to enable to absorb energy with its greatest efficiency. The main objective of this paper is to optimized blade number and selection of tip speed ratio corresponding to the solidity. The power performance of small horizontal axis wind turbines was simulated in detail using blade element momentum methods (BEM). In this paper for wind blade design various factors such as tip loss, hub loss, drag coefficient, and wake were considered. The design process includes the selection of the wind turbine type and the determination of the blade airfoil, twist angle distribution along the radius, and chord length distribution along the radius. A parametric study that will determine if the optimized values of blade twist angle and chord length create the most efficient blade geometry. The 3-bladed, 5-bladed and 7-bladed rotor achieved maximum values of Cp 0.46, 0.5 and 0.48 at the tip speed ratio 7, 5 and 4 respectively. It was observed that using BEM theory, maximum Cp varied with strongly solidity and weakly with the blade number. The studies showed that the power coefficient increases upto blade number B = 5, while the blade number if increased above 5 then the power coefficient decreases at operating pitch angle equal to 3°. Highest Cp would have solidity between 4% to 6% for number of blade 3 and design point tip speed ratio of about "7". Highest Cp would have solidity ranging from 5% to 10% for number of blade 5 and 7 and design point tip speed ratio of about 5 and 4 respectively.

0504 直線翼垂直軸風車の特性に与える端板の効果に関する数値シミュレーション

Three-dimensional computational fluid dynamics (CFD) has been carried out in order to investigate the effects of endplates on the performance of straight-bladed vertical axis wind turbine. The computational wind turbine model has two blades; the rotor diameter is 0.75m; the blade span length is 0.5m; the blade chord length c is 0.08m. The endplate is assumed to be an airfoil-like shape, which outline is larger than the blade section by length of s. The results of the CFD showed that the endplates with s/c = 6.25% give almost no influence on the condition of tip vortex shedding. However, the power coefficient increases about 8.1 % due to the endplates.

Unsteady Flow Numerical Simulation of Vertical Axis Wind Turbine

This paper sets up model of the flow field for vertical axis wind turbine based on airfoil DU93-W–210. FLUENT is used to solve the two dimensional unsteady incompressible N-S equations with RNG κ-ɛ turbulence model. COUPLE algorithm and sliding mesh is used to simulate the 2-D unsteady flow field of the wind turbine. The rotor power coefficient of wind energy and the variation of the wind turbine's total torque are analyzed under the variation of varied blade installation angle and chord length. As the result shows, the power coefficient of wind energy at the best installation angle is increased by 2%, and the power coefficient of wind energy in the best solidity is increased by 15%.

Film cooling performance in a low speed 1.5-stage turbine: effects of mainstream Reynolds number and turbulence

The effects of mainstream Reynolds number and turbulence to film cooling performance were investigated experimentally and computationally under rotating conditions in a 1.5-stage turbine. The rotor of the turbine included 18 blades with chord of 124.3 mm and height of 99 mm. A film hole was set in the middle span of the rotor blade surface with injection angles of 28° on the pressure side and 36° on the suction side respectively. The Reynolds number based on the mainstream velocity of the turbine outlet and the chord length of the rotor blade varied from 1.9 × 105 to 2.1 × 105. Measurements were made at three different rotation speeds of 702, 737 and 800 rpm to keep the rotating number consistent at 0.0280 while the blowing ratio varied from 0.5 to 2.0. Air and CO2 worked as coolant to achieve the density ratio of 1.03 and 1.57, respectively. Computational investigation was performed using the hexahedral structured grids and k-e turbulence model. Results showed that the film coverage and cooling effectiveness are enlarged while the film deflection is weakened as the mainstream Reynolds number increases. Furthermore, the mainstream turbulence plays a negative role in the film coverage and cooling effectiveness at lower blowing ratio on both the pressure side and suction side while it promotes the film reattachment at higher blowing ratio on the suction side.

Predicting Double-Blade Vertical Axis Wind Turbine Performance by a Quadruple-Multiple Streamtube Model

Abstract Double-blade vertical axis wind turbines (DB-VAWTs) can improve the self-starting performance of lift-driven VAWTs. We here propose the quadruple-multiple streamtube model (QMS), based on the blade element momentum (BEM) theory, for simulating DB-VAWT performance. Model validity is investigated by comparison to computational fluid dynamics (CFD) prediction for two kinds of two-dimensional DB-VAWT rotors for two rotor scales with three inner-outer radius ratios: 0.25, 0.5, and 0.75. The BEM-QMS model does not consider the effects of an inner rotor on the flow speed in the upwind half of the rotor, so we introduce a correction factor for this flow speed. The maximum power coefficient predicted by the modified BEM-QMS model for a DB-VAWT is thus closer to the CFD prediction. Keywords : Wind turbine, Double-blade rotor, VAWT, BEM, CFD, QMS. 1. Introduction Vertical axis wind turbines (VAWTs) offer lower costs due to the simplified mechanics, because the wind direction is unimportant to performance. However, small-scale lift-driven VAWTs typically have poor self-starting performance [1]. Therefore, a variety of steps have been tried to improve self-starting performance: increasing blade chord length, adding more blades, using drag-driven wind turbines as a starter, and designing blade airfoils for high aerodynamic performance (for example, [2]). Double-blade vertical axis wind turbines (DB-VAWTs), such as the one shown in Fig. 1 (a), are an example for improving self-starting performance. DB-VAWTs can produce larger starting torque than conventional single-rotor VAWTs with the same blade chord length. Figure 1(b) shows a new type of VAWT with multiple looped blades forming a double-blade rotor structure, as in a DB-VAWT. This VAWT was named the butterfly wind turbine (BWT) [3] because as it rotates around the vertical axis it has the shape of a butterfly. The BWT may offer reduced costs, good self-starting performance, high energy efficiency, and good vibration handling because of the direct installation of the armless looped blades on the central axis. Although propeller-type horizontal axis wind turbines (HAWTs) are the primary turbines for large-scale wind power generation, large-scale VAWTs have been recently proposed and developed for offshore wind power because of their low operational and maintenance costs [4]–[10]. A large-scale VAWT requires struts or arms that connect the blades and central rotating axis, and the cross-section of the struts should also be airfoils to reduce drag. These airfoil struts produce lift force if they incline against the horizontal plane, and so the structure can be regarded as a partial double-blade rotor. Since the flow field of a double-blade rotor is very complex, it is difficult to predict performance by using conventional blade