Improved Blade Design Research Articles

Improving the performance of a sugarcane harvester extractor using design changes validated by computational fluid dynamic modelling and experiment

Sugarcane harvester extractors are used to separate impurities during mechanical harvesting and their performance directly determines the impurity content of sugarcane billets. In this study, computational fluid mechanics (CFD) was used to analyse the flow field near the impeller of original design of extractor. The SST k-ω model and realisable k-ε model were used to calculate the turbulence in 2D and 3D flow fields respectively. The simulation results of 2D models showed that sharply shape from the leading to trailing edges of the original blade design could cause more energy losses. An improved blade design with smoother leading edge and trailing edges had improved performance with a maximum lift coefficient increased by 28.7%. 3D simulation results showed that when the fan speed was 1050 rpm, 1350 rpm and 1650 rpm respectively, the total pressure efficiency of the improved extractor was 11.45%, 9.03% and 6.7% higher than the original extractor, respectively. Impurity content experiments showed that when the feed rate was 1 kg s−1, 2 kg s−1 and 3 kg s−1, compared with the original extractor, the impurity content of the improved extractor decreased by 0.46, 0.41 and 0.71 percentage points at most. The results showed that the impurity content and energy consumption of the improved extractor was less than that of the original design of extractor.

Experimental verification of improved performance of Savonius turbine with a combined lift and drag based blade profile for ultra-low head river application

Savonius turbine is a prominent drag based turbine used for harnessing wind or water power. It can be customized for run-off river stream locations having ultra-low head (<1 m) and low water velocities, for the turbine is self-starting and requires low starting torque. However, considering its low efficiency, an improved blade design of the turbine is needed to enhance its performance. If a Savonius turbine can generate power by utilizing lift force in addition to drag force then its performance can be improved; however any changes in its design need to be experimentally verified. In this paper, the performance of a combined lift and drag based modified Savonius water turbine is investigated in an open flow water channel at different water velocities between 0.3 m/s and 0.5 m/s, which are commonly found in a perennial river. The semi-circular blade design is modified by combining straight (drag profile) and airfoil (lift profile) blades. Detailed measurements show that maximum coefficient of power (0.268) is higher than some of the recently modified designs of Savonius water turbine. Further, correlation equations for power curves of the improved design for river stream application are also developed. The present work delineates the significance of modified Savonius turbine for efficient and cleaner production of water power.

Improved Blade Design for Tidal Current Turbines

The efficiency and reliability of blades are key indicators for a tidal current turbine (TCT). A traditional blade design is often an empirical design on hydrodynamics and structure, sequentially. A hydrofoil with a low lift–drag ratio is considered when the structural strength cannot satisfy requirements. However, efficiency is then sacrificed. A redundant design is generally adopted to protect from load uncertainty, but this increases blade weight and cost. In this paper, we present an improved blade design method to enhance the blade reliability of TCTs with relatively high efficiency for energy generation. An equivalent S–N curve model describing the relationship between axial load and cycle times and a simplified load spectrum including load caused by shear flow and turbulence are proposed for the first time for convenient lifetime estimation. A multi-objective genetic algorithm is used to optimize the chord length, twist angle, and thickness of the blade for the best match between lifetime and efficiency. This blade design method was conducted on a 4.4 m length blade of a 120 kW TCT. Comparisons between the original design and optimal designs indicate that the comprehensive performance in terms of the hydrodynamics, structure, and lifetime of the blade presented significant improvements with a small, acceptable efficiency loss. The results also provide more alternative blade solutions for developers as a reference.

Rotor blade optimization and flight testing of a small UAV rotorcraft

Rotor blade optimization with blade airfoil Reynolds numbers between 100 000 and 500 000 — characteristic of small single-rotor unmanned aerial vehicles (UAV) — was performed for hover using blade element momentum theory (BEMT) and demonstrated via flight tests. BEMT was used to test various airfoil profiles and rotor blade shapes using airfoil data from 2D computational fluid dynamics simulations with Reynolds numbers representative of the blade elements. Selected blade designs were manufactured and flight tested on a Blade 600X single main-rotor UAV (671 mm blade radius) to validate the theoretical results. The parameters considered during the optimization process were the rotor frequency, radius, taper ratio, twist, chord length, airfoil profile, and blade number. The best of the improved blade designs increased the figure of merit, a measure of rotor efficiency, from 0.31 to 0.68 and reduced power consumption by 54%. Reducing the rotational frequency accounted for 45% of the improvement in power consumption, while the taper ratio and blade number accounted for 25% and 17%, respectively. The blade twist and airfoil profile only had a minor effect on the power consumption, contributing 7% and 6% to the improvement. The rotor diameter and root chord were kept identical to the original rotor and hence had no contribution. The presented results could serve as useful guidelines to single-rotor UAV manufacturers and operators for increasing endurance and payload capabilities.

On the need for the development of low wind speed turbine generator system

The study focused on the need for the development of a low cut-in wind speed turbine system with a view to challenge for concerted efforts towards improvement in design in such a way that favours operation at wind speeds as low as 1.5 to 2.0 m/s. It reviewed some existing reports on rotor designs with major focus on improved blade design for enhanced turbine performance and structural integrity. It found that despite the advances in turbine blade designs, there is the need to further the design to include those that can drive generators not just for small wind turbine applications but also for operation under lower cut-in speeds (less than 2.0 m/s). It further demonstrated the need to have improvement in wind turbine generator design that eliminates/reduce lubrication parts and possibly employ electro-magneto-mechanical principles for operation.

Improved Blade Designs and Manufacturing Processes Reduce the Cost of Wind Energy

One way to reduce the cost of wind energy is to improve the design and manufacturing processes for wind turbine blades to increase their strength and reliability. Because the mechanical properties of the blades determine the loads transmitted to the other components in the turbine, improved blade designs can also increase overall turbine performance. New blade shape designs produced through the U.S. Department of Energy’s (DOE’s) Wind Program have increased wind turbine performance by as much as 30% over designs used just 10 years ago. As wind turbine blades increase in length, the blade weight increases faster than the energy it can produce. To produce blades for larger machines without increasing costs, industry researchers at the National Renewable Energy Laboratory (NREL) and Sandia National Laboratories are investigating new materials like carbon or glass-carbon hybrids, new manufacturing processes that improve fiber alignment and compaction, and new rotor designs. As part of the new design process, NREL researchers conduct tests such as the two-axis fatigue test being conducted on an Enron Wind EW-750 wind turbine blade at the laboratory’s Industrial User Facility. Fatigue tests simulate continuous operating loads to help designers understand blade materials and the structural details of the design. Structural details such as joints, ply drops, and geometric transitions are more difficult to model during early design work and are often the weak link in a blade’s structure.

Improved turbine-blade design techniques using 4th-order parametric-spline segments

The paper presents a method for generating blade shapes to be used as inputs to direct- or inverse-blade-design sequences. Isolated airfoils and gas-turbine-blade cascades are designed by a mixture of iterative and direct- and inverse-blade-design methods. In the direct-design method, the designer inputs the geometry of the airfoils, and flow solvers are used to study the resulting performance in terms of Mach numbers or pressure distributions along the airfoil surfaces. In the inverse-design method, the designer specifies as input the desirable performance along the airfoil surfaces, and flow solvers are used to compute the airfoil geometry that will provide the performance. The design iterations are enormously reduced if the initial blade shape has performance characteristics that are near the desirable ones. The method can be used to generate airfoils for compressors and turbines, or isolated airfoils, but the discussion in the paper is limited to subsonic-exit axial-turbine blade rows. The desirable performance characteristics are presented, and ways to specify the input aiming for such characteristics (minimizing design iterations) are discussed. It is shown that continuous curvature and continuous slope of curvature are necessary conditions for improved blade designs. A set of parametric curves that satisfy the above conditions is developed, and used to specify the geometry of turbine cascades. Thickness distributions satisfying the same conditions are used near the leading edge of the cascades. The performance characteristics of two turbine cascades generated by this method are included. The shape and distribution of curvature of the suction and pressure surfaces of the airfoil are particularly important for the aerodynamic and heat-trasfer performance. The 4th-order (continuous-slope-of-curvature) parametric splines should be used wherever separation in fluid streams at the walls would be detrimental to performance, and they have additional applications in smooth-surface-generation activities such as automobile-surface design.

Prescribed-Curvature-Distribution Airfoils for the Preliminary Geometric Design of Axial-Turbomachinery Cascades

Blade surfaces with continuous curvature and continuous slope of curvature minimize the possibility of flow separation, lead to improved blade designs, and reduce the direct and inverse blade-design iterations for the selection of isolated airfoils and gas-turbine-blade cascades. A method for generating two-dimensional blade shapes is presented. The geometry near the trailing edge is specified by an analytic polynomial, the main portion of the blade surface is mapped using as input a prescribed surface-curvature distribution, and the leading edge is specified as a thickness distribution added to a construction line. This procedure is similar for the suction and pressure surfaces, and by specification it constructs continuous slope-of-curvature surfaces that result in smooth surface-Mach-number and surface-pressure distributions. The method can be used to generate subsonic or supersonic airfoils for compressors and turbines, or isolated airfoils. The resulting geometric shapes can be used as inputs to various blade-design sequences. It is shown that, with other cascade-design parameters being equal, increasing the stagger angle of turbine blades results in more front-loaded and thinner blades, and that there is an optimum stagger angle resulting in minimum wake thickness. The subsonic axial-turbine blade rows included for discussion in this paper have been designed by iterative modifications of the blade geometry to obtain a desirable velocity distribution. The blade-design method can be used to improve the aerodynamic and heat transfer performance of turbine cascades, and it can result in high-performance airfoils, even if using the direct method exclusively, in very few iterations.

Hierarchical Development of Three Direct-Design Methods for Two-Dimensional Axial-Turbomachinery Cascades

The direct and inverse blade-design iterations for the selection of isolated airfoils and gas turbine blade cascades are enormously reduced if the initial blade shape has performance characteristics near the desirable ones. This paper presents the hierarchical development of three direct blade-design methods of increasing utility for generating two-dimensional blade shapes. The methods can be used to generate inputs to the direct- or inverse-blade-design sequences for subsonic or supersonic airfoils for compressors and turbines, or isolated airfoils. The examples included for illustration are typical modern turbine cascades, and they have been designed by the direct method exclusively. The first method specifies the airfoil shapes with analytical polynomials. It shows that continuous curvature and continuous slope of curvature are necessary conditions to minimize the possibility of flow separation, and to lead to improved blade designs. The second method specifies the airfoil shapes with parametric fourth-order polynomials, which result in continuous-slope-of-curvature airfoils, with smooth Mach number and pressure distributions. This method is time consuming. The third method specifies the airfoil shapes by using a mixture of analytical polynomials and mapping the airfoil surfaces from a desirable curvature distribution. The third method provides blade surfaces with desirable performance in very few direct-design iterations. In all methods the geometry near the leading edge is specified by a thickness distribution added to a construction line, which eliminates the leading edge overspeed and laminar-separation regions. The blade-design methods presented in this paper can be used to improve the aerodynamic and heat transfer performance of turbomachinery cascades, and they can result in high-performance airfoils in very few iterations.

Turbine-Blade Vibration and Strength

Abstract In the design of turbines, the strength of the blades is a matter of great importance since blading is the heart of the turbine. The authors discuss the factors which affect the strength of turbine blades and show what recent progress has been made and what studies are under way toward improved blade designs. The discussion is limited to the full-admission type of blade row which is subjected to steam flow through its full annulus, the most common type of blade row. A discussion of the problems of designing partial-admission rows was given by R. P. Kroon in a paper presented before the Society in 1939.