Maximum Cp Research Articles

Experimental evaluation of a shrouded horizontal axis hydrokinetic turbine with pre-swirl stators

Improving the efficiency and power output of hydrokinetic turbines is critical to making them a viable and cost-effective renewable energy solution. Diffusing shrouds have already been shown to improve the performance of horizontal axis, axial-flow turbines. It has been suggested that adding pre-swirl stators to the shroud could alter the inlet flow so as to maximize net tangential force on the turbine blades, thus increasing power output. There is a scarcity of published physical model test data from pre-swirl stator turbines. The present study explores this concept. Four different pre-swirl stator configurations were designed and tested on a shrouded 3-bladed turbine (26.54 cm diameter) in the 36.5 m towing tank at the United States Naval Academy. Three Reynolds numbers (6.07×104, 8.10×104, and 1.01×105 based on stator chord length), corresponding to flow speeds 0.91 m/s, 1.22 m/s, and 1.52 m/s respectively, were tested. At the lowest Reynolds number, all 4 stator configurations improved the maximum Cp by 5–23% compared to the turbine with shroud only. At the middle and highest Reynolds numbers, the stator effect was mostly neutral, with one configuration showing a negative effect at the highest Reynolds number (i.e., lowered the maximum Cp). These results indicate that pre-swirl stators have the potential to improve turbine performance, particularly at lower Reynolds numbers, where the flow is more laminar and the absolute velocities are lower (for a given blade dimension). Pre-swirl stators also appear to reduce the dependence of performance on Reynolds number, flattening the curve and allowing optimal performance over a wider range of operating conditions. Further analytical and computational studies are recommended to explore these findings further, and to develop broader guidance on when pre-swirl stators are advantageous.

Numerical modelling of a dual-rotor marine current turbine in a rectilinear tidal flow

In this study, numerical simulation is used to investigate a counter-rotating dual-rotor marine current turbine (MCT) that is aligned for a rectilinear tidal current. Results of power and thrust coefficients and the mean axial velocity in the wake are compared with that of the blade element momentum (BEM) method coupled with the Park wake model. For a single-rotor MCT, small discrepancies are observed for front rotor, and larger discrepancies for rear rotor when comparing the CFD and BEM results. The mean axial velocity in the wake agrees better with the higher turbulence intensity (TI). CFD results shows that the power coefficient (CP) of rear rotor depends on the ambient turbulence intensity. The maximum CP of dual-rotor turbine is 5% higher than that of just the front rotor. Streamlines show that a large vortex is formed behind the rear rotor. The numerical simulations give more credibility to the BEM Park model, but also points to its sensitivity to the incoming turbulence intensity.

The hydrodynamic performance of a tidal-stream turbine in shear flow

Tidal-stream turbines spend most of time in a shear flow environment, which leads to non-uniformity effect in stream vertical profile. To better understanding of such effect on tidal-stream turbine performance, the hydrodynamic performance and comparison between a bare turbine and a diffuser-augmented turbine under shear flow condition were numerically investigated. To closer to the real working environment of tidal-stream turbine, three major factors influence on hydrodynamic performance including flow shear rates, yaw angle and arrangement rule in array were discussed in detail. It is found that the different shear rate of flow will result in power and axis thrust slightly amplitude comparing with the uniform flow, and a diffuser turbine will further amplify this effect comparing with a bare turbine. The greater the yaw angle is, the more power and axis thrust is reduced. Additionally, there are “Advantageous Interaction” and “Disadvantage Interaction” in the wake effect on the energy extraction performance in the turbine array. The output power for each case is relatively concentrated at lower tip speed ratio (TSR) and divergent at higher TSR. Furthermore, each turbine in array operating at near 2D flow distance and relative deviation angle of 45° reaches its maximum CP.

Development of a semi-analytical model to select a suitable airfoil section for blades of horizontal axis hydrokinetic turbine

All modern hydro-kinetic turbines are being designed based on a lift, using airfoils, which should have a significant lift to drag ratio to achieve maximum efficiency.SG604X family airfoil has significant lift-to-drag ratio under an operating range of Re from 105–106, which also come under our working conditions. Blade Element Momentum (BEM) theory was used to obtain optimum blade shape. The iterative numerical approach was used in MATLAB to calculate optimized blade profile and coefficient of performance (Cp). After grid independency test, finally k-ω shear stress transport (SST) and the k-є model with enhanced wall treatment were used for calculation of the lift coefficient and the drag coefficient of airfoil SG6043. The performance of the rotor overall expected tip speed ratio (T.S.R (λ)) was calculated and found that maximum Cp,max is 0.51 at optimum λopt of 5. The suitability of SG6043 airfoil over NACA0012 airfoil in our case has been shown.

Optimal relationship between power and design-driving loads for wind turbine rotors using 1-D models

Abstract. We investigate the optimal relationship between the aerodynamic power, thrust loading and size of a wind turbine rotor when its design is constrained by a static aerodynamic load. Based on 1-D axial momentum theory, the captured power P̃ for a uniformly loaded rotor can be expressed in terms of the rotor radius R and the rotor thrust coefficient CT. Common types of static design-driving load constraints (DDLCs), e.g., limits on the permissible root-bending moment or tip deflection, may be generalized into a form that also depends on CT and R. The developed model is based on simple relations and makes explorations of overall parameters possible in the early stage of the rotor design process. Using these relationships to maximize P̃ subject to a DDLC shows that operating the rotor at the Betz limit (maximum CP) does not lead to the highest power capture. Rather, it is possible to improve performance with a larger rotor radius and lower CT without violating the DDLC. As an example, a rotor design driven by a tip-deflection constraint may achieve 1.9 % extra power capture P̃ compared to the baseline (Betz limit) rotor. This method is extended to the optimization of rotors with respect to annual energy production (AEP), in which the thrust characteristics CT(V) need to be determined together with R. This results in a much higher relative potential for improvement since the constraint limit can be met over a larger range of wind speeds. For example, a relative gain in AEP of +5.7 % is possible for a rotor design constrained by tip deflections, compared to a rotor designed for optimal CP. The optimal solution for AEP leads to a thrust curve with three distinct operational regimes and so-called thrust clipping.

Analysis of cross axis wind turbine blades designed and manufactured by FDM based additive manufacturing

Additive manufacturing is emerging as a preferred approach to manufacture complex three dimensional components easily within a short span of time. In this study, cross axis wind turbine blades and its components are produced using fusion deposition modeling using Acrylonitrile Butadiene Styrene (ABS) material. The 3D CAD models are converted into .STL file which are processed further in “Slicer” freeware software. This convert the model into series of thin layers and creates G-code file which acts as an input to automated 3D printing machine to lay layers of loaded thermoplastic material successively to build the model from series of cross sections. The components produced by additive manufacturing is assembled and the obtained cross axis wind turbine (CAWT) is investigated using an open jet wind tunnel for wind velocities varying from 4 m/s to 10 m/s. The dimensionless performance parameters i.e., coefficient of power (Cp) and tip speed ratio (λ) are plotted. In general, the Cp value of CAWT increases gradually and reaches the maximum value around λ = 1.20. A maximum Cp value of 0.02385 is observed for wind velocity Vα = 10 m/s. Thus, the 3D printed components by additive manufacturing can be used to produce small wind turbines.

Design and numerical analysis of an efficient H-Darrieus vertical-axis hydrokinetic turbine

Hydrokinetic turbines are one of the technological alternatives to generate and supply electricity for rural communities isolated from the national electrical grid with almost zero emission. The Darrieus turbine is one of the options that can be used as a hydrokinetic turbine due to its high power coefficient (Cp) and easy manufacture. In the present work, the design and hydrodynamic analysis of a Darrieus vertical-axis hydrokinetic turbine of 500 W was carried out. A free stream velocity of 1.5 m/s was used for the design of the blades. The diameter (D) and blade length (H) of the turbine were 1.5 m and 1.13 m, respectively. The blade profile used was NACA0025 with a chord length of 0.33 m and solidity () of 0.66. Two (2D) and three dimensional (3D) numerical analyses of the unsteady flow through the blades of the turbine were performed using ANSYS Fluent version 18.0, which is based on a Reynolds-Averaged Navier-Stokes (RANS) model. A transient 2D simulation was conducted for several tip speed ratios (TSR) using a k-ω Shear Stress Transport turbulence (SST) scheme. The optimal TSR was found to be around 1.75. Main hydrodynamic parameters, such as torque (T) and CP, were investigated. Additionally, 3 geometrical configurations of the turbine rotor were studied using a 3D numerical model in order to identify the best configuration with less Cp and T fluctuation. The maximum Cp average was 0.24 and the amplitude of Cp variation, near 0.24 for the turbine model with 3 blades of H equal to 1.13 m. On the other hand, for the turbine models with 6 and 9 blades of H equal to 0.565 m and 0.377 m, respectively, the maximum Cp averages were 0.51 and 0.55, respectively, and the amplitude of Cp variation, near 0.07 for the model with 6 blades and 0.17 for the model with 9 blades. This revealed that the hydrokinetic turbine with a geometrical configuration of 6 blades greatly improves the performance of the turbine due to this model has advantages compared to models with 3 and 9 blades, in terms of the reduction of their T curve fluctuation.

Simulation of turbulent wakes in model wind farm with arbitrary location for wind turbines

Wind energy is an important part of renewable energy sources in the Russian Federation. A new modern wind farm with 28 wind turbines was built on the territory of the Russian Federation, in the Ulyanovsk region in 2017-2018. When designing and operating a wind farm, it is necessary to assess correctly the power of each individual wind turbine. In this paper we used the open SOWFA library based on OpenFOAM 2.4.0 and URANS approach with k-e model of turbulence. The Actuator Line Model for the calculation of the forces from the wind turbines was used in pisoFoamTurbine.ALM solver. To set the boundary conditions at the input, the Precursor method was used. The unstructured grids with different number of cells were built. As a result of the calculation for 14 simulators of wind turbines, the values of the power coefficients Cp and thrust coefficients Ct were also determined. The maximum Cp value was in agreement with the Bets-Zhukovsky law for an ideal wind turbine. The new numerical case with 28 wind turbines was prepared for future simulations. The calculations were performed on a cluster of the UNICFD web-laboratory of ISP RAS. Each calculation was performed on 48-72 cpu cores.

Design and Fabrication of Small Horizontal axis wind Turbine Rotors at Low Reynolds Number

This research paper presents a design and fabrication of 100 Watt small horizontal axis wind turbine with 0.24 m and 0.35 m rotor radius and tip speed ratio varies from 2 to 10 was designed and development for operated at low wind speed with Low Reynolds number. In this paper, a new airfoil profile was designed and developed, it’s denoted by MK115. The numerical and experimental analysis for 6 airfoils using Xfoil software was conducted with a view to evaluating the lift-to-drag ratio and angle of attack by means of the SD7024, SG6043, NACA2412, S1210, E213, and New Airfoil (MK115) tested. In simulation, new MK115 airfoil was the most convenient airfoil to start high energy production for low-wind applications, on the Reynolds number 25000, 50000, 75000, and 100000 in improved airfoil (MK115) tests an Open type wind tunnel. An Xfoil analysis to obtain further data on the flow characteristics was also conducted. (MK115) airfoil have CLmax of 0.92, 1.25, 1.69, 1.67 at Re=25k, 50k, 75k and 100k for an angle of attack is equal to 100 .A maximum lift to drag ratio (Cl/Cd) of 7,16,50,63 at Re=25k, 50k, 75k and 100k for New airfoil (MK115) at angle of attack (α) =40, 40, 80, 80. SG6043, NACA2412, E214, SD7034, S1210 and MK115 (New airfoil) have the Maximum Cp=0.37, 0.36, 0.4, 0.39, 0.44, and 0.44 at tip speed ratio (λ) =6 for Reynolds number is equal to 100000. MK115, Maximum Torque obtained 0.9744 Nm, 1.389 Nm and 2.4866 Nm at blade angle =0, 15 and 30 degrees respectively. Power coefficient (Cp) =0.51, 0.5, 0.46, and 0.4 at Rotor shaft angle=00, 50, 100, and 150 respectively for the new airfoil results.

The effect of inner blade position on the performance of the Savonius rotor

In this study, the effect of the inner blade position on the performance of the Savonius rotor has been investigated numerically to determine the best position of the inner blade. Five values of inner blade angles are adopted (180°, 160°, 140°, 120°, and 100°). Two-dimensional simulation is performed for the conventional rotor, rotor with the inner blade tip parallel with rotor tip, and rotor with the inner blade parallel with rotor root keeping the main rotor diameter constant in each case. The simulation has been achieved using the k-ε/realizable turbulence model with the assist of the ANSYS-Fluent solver. The torque coefficient (Ct) and power coefficient (Cp) are estimated as a function of tip speed ratio (TSR) for each case. Finally, the total pressure, velocity, and streamlines are obtained and analyzed. The numerical results demonstrated the maximum Cp to be 0.1885 at TSR equal to 0.5 when the inner blade is placed parallel with rotor tip with inner blade angle of 120°. Moreover, results found that the maximum Ct is 0.407 at TSR = 0.4 for the rotor with 180° inner blade. Furthermore, the peak value of the torque found to be generated at the azimuth position of (θ = 105°).

Comparative chloroplast genomic analyses revealed extensive genomic arrangement in some core and non-core caryophyllales

The order Caryophyllales exhibit diverse diversity in morphology to molecules, which leads to taxonomic complexities in circumscribing especially to its families. The comparative analysis of the available chloroplast genome to detect pattern of genomic arrangement and variation is lacking; hence, the alignment pattern and genomic rearrangement across the Caryophyllales were detected, and the phylogenetic relationship among the families of the Caryophyllales based on maximum cp genes were inferred. The comparison of the Caryophyllales cp genomes based on representatives of 10 families with Taxillus chinensis as reference genome revealed that coding region were more conserved than the non-coding region; however, clpP, rpl16 and ycf15 were the most divergent coding region among all taxa. Further, the genomic rearrangement occurred in gene organization of the taxa among different families of Caryophyllales, the extensive rearrangement were observed in Amaranthaceae, Caryophyllaceae, Chenopodiaceae,Droseraceae and Cactaceae.

Design and CFD study of a hybrid vertical-axis wind turbine by employing a combined Bach-type and H-Darrieus rotor systems

Abstract The objective of this work was to design, simulate and evaluate the performance of an innovative hybrid vertical-axis wind turbine (VAWT) for obtaining an extended operational range and enhancing self-starting capabilities. An extensive research was conducted to explore the design parameters for obtaining an optimum novel hybrid VAWT configuration. The hybrid VAWT consisting of a 2-bladed modified Savonius Bach-type rotor and a 3-bladed Darrieus turbine was modeled and analyzed in computational fluid dynamics (CFD) to calculate the characteristic parameters of the rotor system. The geometry was then used to generate the grid in ANSYS Meshing for computational fluid dynamics (CFD) analyses to evaluate the performance of the designed hybrid VAWT. Results indicated that while the Darrieus turbine had the highest coefficient of power (Cp) of 48.4% at a TSR of 2.50, it suffered from high start-up torque requirements. The hybrid turbine demonstrated self-starting capabilities while reaching a maximum Cp of 41.4% at a TSR of 2.5 and operation up to a TSR value of 4.5. When compared to previous hybrid VAWT designs, the proposed configuration demonstrated improvements to the efficiency and operational range which support the energy sustainability prospects.

Influence of blade profiles on Savonius rotor performance: Numerical simulation and experimental validation

In this work, some notable blade profiles of drag-based vertical axis Savonius wind turbine rotor have been investigated both numerically and experimentally to judge their performances on a common platform. At the outset, 2D unsteady simulation is performed for semicircular, Benesh, modified Bach and elliptical profiles keeping the overall rotor diameter in each case to be constant. The simulation has been carried out using the Shear Stress Transport k-ω turbulence model with the help of the finite volume solver ANSYS Fluent. The torque and power coefficients, in each case, are estimated as a function of tip speed ratio. The total pressure, velocity magnitude, and turbulence intensity contours are obtained and analyzed. Finally, wind tunnel tests are conducted to validate the numerical results. From the numerical simulation, the maximum power coefficients for the semicircular, Benesh, modified Bach and elliptical profiles are found to be 0.272, 0.294, 0.304 and 0.34, respectively. However, the wind tunnel tests with the semicircular, Benesh, modified Bach and elliptical-bladed rotors demonstrated the maximum CP to be 0.158, 0.159, 0.162, and 0.19, respectively.

Study of influence of shading louvers on wind characteristics around buildings under different wind directions

In this paper, the wind characteristics on building with single-sided louvers under different wind directions were studied by using computational fluid dynamics (CFD) method. The RNG k-ε model was employed to establish the different outdoor airflow fields under different rotation angles θ of louvers. To investigate the wind pressure on facades, wind pressure coefficient CP was introduced and average surface difference ΔCP was applied to evaluate wind-induced cross ventilation between the shaded and the opposite building surfaces. Results show that airflow pattern around the studied building is highly dependent on the building envelope under shading conditions due to obstruction and diversion of louvers. In general, the larger rotation angle of louvers contributed to more differences in average surface CP under both normal and parallel wind directions. Shading louvers lead to an increase in ΔCP for parallel approach flow and a decrease in ΔCP for perpendicular approach flow. In simulations of this study, it could be seen that ΔCP decreases 0.01 (1.6%) for θ = 0° and 0.15 (18.0%) for θ = 60° under normal wind direction, while ΔCP increases 0.05 (436.1%) for θ = 0° and 0.15 (1393.5%) for θ = 60° under parallel wind direction. The results elucidates that a larger rotation angle can affect wind-induced cross ventilation more strongly. What’s more, the locations of minimum and maximum CP on some facades moved obviously after shading and turning up rotation angle. This study indicates that the influence of complex building envelopes like shading louvers, should be considered in ventilation design.

Improving VAWT performance through parametric studies of rotor design configurations using computational fluid dynamics

Vertical axis wind turbines present several advantages over the horizontal axis machines that make them suitable to a variety of wind conditions. However, due to the complexity of vertical axis wind turbine (VAWT) aerodynamics, available literature on VAWT performance in steady and turbulent wind conditions is limited. This paper aims to numerically predict the performance of a 5 kW VAWT under steady wind conditions through computational fluid dynamics modeling by varying turbine configuration parameters. Two-dimensional VAWT models using a cambered blade (1.5%) were created with open field boundary extents. Turbine configuration parameters studied include blade mounting position, blade fixing angle, and rotor solidity. Baseline case with peak Cp of 0.31 at tip-speed ratio of 4 has the following parameters: mounting position at 0.5c, zero fixing angle, and three blades (solidity = 0.3). Independent parametric studies were carried out and results show that a blade mounting position of 0.7c from the leading edge produces the best performance with maximum Cp = 0.315 while the worst case is a mounting position of 0.15c with peak Cp = 0.273. Fixing angle study reveals a toe-out setting of −1° producing the best performance with peak Cp of 0.315 and the worst setting at toe-in of 1.5° with peak Cp of 0.287. The solidity study resulted in the best case of four blades (solidity = 0.4) with peak Cp = 0.316 and the worst case of two blades (solidity = 0.2) with peak Cp = 0.283.

Effects of Solidity on Aerodynamic Performance of H-Type Vertical Axis Wind Turbine

In order to study the effects of solidity on aerodynamic performance of H-type vertical axis wind turbine(H-VAWT), the mechanical model of H-VAWT was established, numerical investigations were implemented for the different solidity by changing the radius, chord length and blade number. As the result shows, the H-VAWT with a lower solidity will obtain the maximum Cp at a high tip speed ratio and the maximum value will be larger, while the H-VAWT with a higher solidity has better starting performance but the value of Cp is smaller. For small H-VAWT, the suitable solidity range is 0.2∼1.28; for large H-VAWT, the suitable solidity range is 0.2∼0.6. The effects of changing the radius and blade number on aerodynamic performance are almost the same, the effect of changing the chord length on aerodynamic performance is different from the above two methods and the value of Cp increases with the increase of the solidity. Changing the chord length can increase the peak value of wind energy utilization rate, while the increase of the blade number will reduce the peak value of wind energy utilization rate.

Wind turbine Cp,max and drivetrain-losses estimation using Gaussian process machine learning

In this paper it is shown that measured data in a wind turbine, available to the controller, can be formulated into a polynomial regression problem in order to estimate the turbine’s maximum efficiency power coefficient, Cp,max, and drivetrain losses, assuming the latter can be well approximated as being linear. Gaussian process (GP) machine learning is used for the regression problem. These formulations are tested on data generated using the Supergen Exemplar 5 MW wind turbine model, with results indicating that this is a potential low cost method for detecting changes in aerodynamic efficiency and drivetrain losses. The GP approach is benchmarked against standard least-squares (LS) regression, with the GP shown to be the superior method in this case.

Effect analysis on power coefficient enhancement of a convective wind energy collecting device in the expressway

The purpose of this paper is to study the equipment parameters of expressway convective wind energy collection devices and determine the optimal structural parameters by numerical methods. Firstly, the characteristics of convection wind energy and flow field on the expressway are analyzed and the principle of wind energy utilization is determined. Based on traditional resistance wind turbines, two different blades of the device are designed and developed. Some structural parameters (such as blade height and the number of blades) of the device are discussed based on the flow field characteristics. Secondly, the device is numerically simulated using Star CCM+ software, and the optimal structural parameters are determined based on the power coefficient. Thirdly, the proposed numerical analysis method is verified and indirect verification is used to determine the most suitable turbulence model and grid independence based on the similarity principle. Based on the above research results, the experimental verification is used to determine the high reliability of the simulation model. Finally, the simulation results between the Rectangular turbine and the Savonius turbine are compared and obtained. The results show that the device is useful for the wind energy usage, wind energy conversion and the wind resistance reduction of the opposite vehicle. At the same time, when the inlet wind speed is 15 m/s, the tip speed ratio (TSR) is 1.4, the device is rectangular turbine (RT), the height of blade is 1.55 m, the number of blades is 4, and the maximum power coefficient Cp is 0.363.

Derating a single wind farm turbine for reducing its wake and fatigue

Derating of individual turbines is one of the options to implement wind farm performance optimization, although there are different ways to proceed with such derating at the turbine control level. The present paper develops an option based on the minimal thrust coefficient in accordance with the Cp and Ct contour levels. This strategy is compared for the region below rated wind speed with two other strategies where either the pitch or the tip speed ratio are maintained at their maximum Cp values from normal operation. The study concludes that maintaining the pitch at the optimal value from normal operation produces poorer performance from the thrust and the loads perspective. Practical implementation issues have also been detected.

Innovation in Vertical Axis Hydrokinetic Turbine – Straight Blade Cascaded (VAHT-SBC) design and testing for low current speed power generation

This study examines an innovative turbine with the addition of the number and arrangement of straight blade cascaded (SBC). SBC is a combination of passive variable-pitch and fixed pitch of each turbine arm. This study was conducted in an open channel flow that has a current velocity (V-m/s) of 1.1, 1.2, and 1.3. RPM and torque ware measured for coefficient of performance (Cp) and tip speed ratio (TSR) calculation. Without changing the turbine dimension, the employment of cascaded blade (three blades in each arm) contributes to improve energy extraction significantly. A significant increase in Cp value is seen when 9 blades (3 cascaded blades per arm) are used with a Cp 0.42 value at TSR 2.19. This value has reached 93% of the maximum theoritical Cp value.