Solidity Ratio Research Articles

Drag force and filtration performance of square-frame ichthyoplankton sampling net

A constant-depth ichthyoplankton sampler (CDIS) is widely employed for quantitative sampling surveys, yet challenges related to sampling distortion due to unstable tows of the CDIS persist. The drag force of the square-frame sampling net is pivotal in maintaining the dynamic stability of the CDIS during horizontal towing. This study delves into the hydrodynamics and filtration performance of square-frame sampling nets through flume-tank experiments and numerical simulations. The results show that the drag coefficient for the square-frame ichthyoplankton sampling net initially decreases and then increases as the solidity ratio rises from 0.3 to 0.7. It becomes greater as the net length becomes shorter and the net mouth area becomes larger. A response model for the drag force for the square-frame sampling net is proposed that is capable of accurate predictions. The results also reveal that the flow decelerates at the net mouth and gradually accelerates in the posterior section of the net, and the filtration efficiency increases as the net length and mouth area increase but decreases slightly as the solidity ratio increases. Our study provides vital scientific data for reference and methodologies for designing or modifying a square-frame CDIS, fostering enhanced stability and accuracy in ichthyoplankton surveys.

Hydrodynamics of focused waves acting on netting that extends above the mean sea level

Extreme ocean waves are typically strongly nonlinear, with extreme wave energy concentrated above the static water surface, which has a complex impact on the hydrodynamics of structures extending above the mean sea level. In this study, we designed netting with three different heights above the water surface and two different solidities, and tested the hydrodynamics of these netting under a series of focused waves through physical model tests. The three heights (h) were designed to account for possible nearshore tidal and wave variations. The results indicate that the wave forces of the netting having sharper and steeper crest than those of the wave surface in the time domain, while it is opposite in frequency domain. Moreover, the wave forces changed significantly with increasing height of the netting above the water surface. Wave forces on netting above water were up to 0.8 and 2.0 times greater than those below water for h = 7.25 cm and h = 14.5 cm, respectively. Regardless of solidity, the rate of increase in netting wave forces gradually decreased with growing wave amplitude when h = 0 cm or h = 7.25 cm, but gradually increased when h = 14.5 cm. The force ratios of the two netting solidities were relatively stable and did not change with wave amplitude. The force ratios were always greater than the solidity ratio, mainly because of the drag coefficient in Morison's equation. Furthermore, steep waves acting on netting wound cause obvious vibration of the wave force because of water jet phenomenon, while the jet have little effect on wave surface elevation in 0.5 m behind the netting. Therefore, for aquaculture facilities such as fixed marine aquaculture cages, the netting design is not only limited by the solidity, but should also consider the hydrodynamic influence of the height that the netting extends above the water.

Trade-off between drag and catch performance when designing zooplankton trawls

The aquaculture sector is in pursuit of sustainable and cost-effective raw materials for feed, and the copepod Calanus finmarchicus is a marine zooplankton species of commercial interest because of its high abundance in northern areas. These copepods have the potential to meet the demand for vast quantities of marine raw materials. However, the lack of an energy- and catch-efficient trawl technology has limited the development of this fishery. Therefore, this study investigated the effect of two central trawl net design parameters mesh size and taper angle to identify which values that provide optimal trade-off balance between gear drag and catch efficiency. We conducted flume tank experiments using a series of plankton nets varying in mesh size (250–1000 μm), solidity ratio (0.54–0.76), and taper angle (5°– 30°) to acquire data on gear drag. The same nets were then used in fishing trials to obtain data on their catch performance. This study shows that zooplankton nets with a mesh size of approximately 500 μm and a low taper angle of about 5° provided the best trade-off between drag and catch performance.

CFD and Taguchi based optimization of air driven single stage partial admission axial turbine blade profiles

Single-stage axial flow turbines are typically used in underground mining machines and underwater vehicles due to their safety and small size. However, the high-pressure ratio and small mass flow rates force the flow inside the turbine to be supersonic. The blade design of such turbines with high-flow velocity leads to high losses and low turbine efficiencies at conventional design values. In this paper, the 1D design of the turbine is carried out using the meanline design method. The results of the design algorithm are compared with both experimental, CFD (Computational Fluid Dynamics), and a well-known commercial software AxSTREAM. After validating the design, Taguchi method is used to analyze 6 different parameters (Blade Shape, Nozzle Shape, Cord Length, Solidity Ratio, Nozzle Angle and Blade Thickness) affecting the turbine performance and the optimum blade profile is compared with the conventional blade design. The optimum design isentropic efficiency (68.267%) outperformed the conventional design turbine isentropic efficiency (61.759%) by about 11%. This paper provides a different insight into the conventional turbine design method.

Hydrophobic phytic acid conversion layers for corrosion protection of steel surfaces

AbstractThe possibility for a good conversion protection based on phytic acid (PA) solutions is described many times in the literature.1,2 The latest results show that PA cannot improve the corrosion protective properties with an organic coating,2 although PA conversion layers without organic coatings have already successfully been applied on different surfaces and the development of layers with enhanced corrosion protective behavior was possible.3,4 The reason why PA does not work together with an organic coating is based on the hydrophilic surface and therefore the low contact angle of the PA conversion layer.2 One solution is to modify PA directly and/or change the solution properties to increase the hydrophobic properties. In this work, a new and innovative way to synthesize a new type of sustainable organic PA-based conversion layers on steel, which works completely without titanium or zirconium and is a new approach for hydrophobic conversion layers, is presented.5 The results prove the formation of a pure PA-based conversion layer on the surface. The infrared (IR), Raman, and nuclear magnetic resonance (NMR) spectroscopy verified the new synthesis products and by means of the vibration spectroscopy, the resulting conversion layers. To analyze the new physical properties, the contact angle of the conversion layers was detected. By means of the electrochemical impedance spectroscopy (EIS), the electrochemical stability of the conversion was studied and with cyclic voltammetry (CV), the solidity ratio was investigated. At last, the corrosion protective performance of the layers in combination with an E-coat in the salt spray test (SST) was examined. All modified PA-based conversion layers in combination with E-coats increased the corrosion protective properties in relation to industrial used phosphate conversion layers of steel surfaces. The overall result is a new kind of hydrophobic phytic acid-based conversion layer which shows advanced anticorrosion and coatability properties compared to other layers based on PA. The results if the EIS measurements show that the resistance of the coating significantly increased, and diffusion could be suppressed by coating the metal surface with PA conversion layers. The comparison of the SST results for the reference and the modified PA underline these observations. The overall SST rating increased by 2 and the delamination went down to 1.9 mm while the corrosion was 0.1, comparable to phosphated steel.

Impact of solidity and speed ratio on the performance of a contra-rotating fan

In this study, the effects of solidity and rotor speed ratio on the performance of a contra-rotating fan are investigated numerically. Simulation results have been validated by experimental tests. The test stand construction and the measurements have been performed according to ISO-5801 standard. In order to investigate the effect of blade solidity, simulations have been conducted with constant blade count of the front rotor and four configurations of the rear rotor (having 6, 8, 12 and 16 blades), and also constant blade count of the rear rotor and three configurations of the front rotor (having 8, 12, and 16 blades). Results suggest that there is an optimum solidity for the rear rotor, which gives maximum pressure rise and efficiency. Furthermore, the effects of the rotor speed ratios have been investigated in this study. It is shown that the speed of the front rotor is more effective on the fan performance, as compared to the rear rotor. Results reveal that the performance drop caused by a 25% reduction in the rear rotor blade count, can be compensated by 5% increase of the front rotor rotational speed. Therefore, a suitable choice of the speed ratio can result in light-weight and high-performance contra-rotating stages.

Optic Canal Size is an Indicator for the Accessory Optic Canal: Applications for Anterior Clinoidectomy

BackgroundThe ophthalmic artery normally travels with the optic nerve through the optic canal. However, sometimes, the ophthalmic artery travels through a foramen within the optic strut named an accessory optic canal, double optic canal, or ophthalmic canal. This variant puts individuals at an increased risk for blindness or death during anterior clinoidectomy due to unforeseen hemorrhage of the ophthalmic artery or internal carotid artery when the optic strut is separated from the body of the sphenoid bone. Several features make the accessory optic canal difficult to recognize on imaging: its variant nature, small size, and ability to masquerade as a caroticoclinoid foramen or a pneumatized sphenoidal structure. Hence, improved methods of presurgical identification are warranted. The aim of this study was to assess the size and shape of the optic canal, with and without a concomitant accessory optic canal, to determine whether measurement of the optic canal may provide useful information regarding the presence of an accessory optic canal. MethodsIn 191 dry crania, optic canals with and without concomitant accessory optic canals were assessed for the following parameters: canal area, canal perimeter, circularity, solidity, the axes and aspect ratio of a best fit ellipse, and roundness. ResultsNormal optic canals were found to have a larger area (p=0.036), perimeter (p=0.043), and minor axis of a best fit ellipse (p=0.031) than the optic canals that occurred alongside accessory optic canals. ConclusionsAsymmetry in optic canal size can help indicate the presence of a unilateral accessory optic canal prior to surgery.

Sinking Behavior of Netting Panels Made with Various Twine Materials, Solidity Ratios, Knot Types, and Leadline Weights in Flume Tank

Netting is an important component of fishing gear design, and its ability to sink determines the effectiveness of fishing gears such as purse seines, falling nets, and stick-held nets. Therefore, it is crucial to thoroughly investigate the sinking parameters (sinking depth and sinking speed) of the netting panel as a function of the leadline weights using various twine materials, knot types, and solidity ratios. In this study, a generalized additive model (GAM) was utilized to analyze the impact of each factor on the sinking performances of the netting. The results revealed that the sinking depth of the netting was positively correlated with sinking time and leadline weight. However, the netting featured a maximum sinking depth limit, indicating that the sinking depth would not increase beyond a leadline weight of 69.5 g. During the initial phase of the sinking process, the sinking velocity of each netting panel initially increased but gradually decreased over time. The incorporation of a leadline weight reduced sinking time. Thereby, polyester netting exhibited the shortest average sinking time. A comparison of netting types with similar solidity ratios showed that the maximum sinking depth of the nylon netting was 13.20% and 10.11% greater than that of polyethylene and polyester nettings, respectively. In addition, nylon nets’ time average sinking speed was 64.58% and 4.62% greater than that of polyethylene and polyester nettings, respectively. The analysis of the GAM model clearly showed that the leadline weight has a significant effect on the netting sinking speed and depth. To ensure that the netting can reach its maximum sinking speed, it is strongly recommended to use nylon and polyester nettings with a low solidity ratio, i.e., a lower twine diameter and greater mesh size with a higher leadline weight, when constructing fishing gear such as purse seines with higher net leadline weights.

A Numerical study on the effect of solidity on the performance of Transverse Axis Crossflow Tidal Turbines

This paper presents a three-dimensional numerical study employing an actuator line model to investigate the effect of turbine solidity on the performance of a Transverse Axis Crossflow Turbine (TACTs). Transverse Axis Crossflow Turbines have a low rectangular form and are ideally suited to relatively shallow tidal and riverine sites due to their ability to handle bi-directional flow intake. Lift based TACTs are not well understood due to their complex hydrodynamics when the downstream sweep passes through the wake produced by the turbine shaft and the upstream sweep. The blade loading, hydrodynamics and ultimately power produced during the downstream sweep depends on the number of blades and turbine solidity. This numerical study is carried out using OpenFOAM and replicates planned fieldwork where the power and in-service blade loading will be monitored as a function of turbine solidity. Turbine solidity is a dimensionless parameter that measures the proportion of blade area to the projected turbine frontal area. Turbines achieve peak performance at an optimum solidity and tip speed ratio. Solidity can be varied by changing the number of blades or changing the turbine radius. An increase in solidity causes the peak performance to reduce and shift to a lower tip speed ratio albeit with a greater torque.
 This paper also explores the effect that maintaining turbine solidity has on turbine performance over a range of typical inflow velocities. Turbine solidity is held constant by varying both the number of blades and turbine diameter. Iso-solidity has been investigated for horizontal axis wind turbines but little is known about the effect of maintaining turbine solidity on TACT performance.

Hydrodynamic characteristics of fine-mesh minnow netting for sampling nets

Fine-mesh minnow nettings with a high solidity ratio (defined as the ratio of the projected area to the total area enclosed by the outline area) of 0.44–0.72 were used to investigate the hydrodynamic characteristics for various angles of attack (0°–90°). A brief summary of knotless plane netting in an expanded solidity ratio range of 0.075–0.75 is given. Experimental results show that the drag coefficient of minnow netting in a solidity ratio range of 0.44–0.72 is 0.13 to 0.035 in the parallel case and 1.60 to 1.86 in the normal case. The dual effect of the solidity ratio on the drag coefficient of knotless plane netting is confirmed in a wider solidity-ratio range. The maximum lift coefficient of minnow netting increases from 0.55 to 1.02 for an angle of attack of 40° as the solidity ratio increases from 0.44 to 0.72. The proposed empirical formulas of the hydrodynamic model in terms of drag and lift coefficient for knotless plane netting varying a wider solidity ratio and angle of attack are more accurate than those of previous models. Therefore, the present formulas allow precise numerical calculation for the optimal design of sampling nets and fishing gear.

Effect of Solidity and Aspect Ratio on the Aerodynamic Performance of Axial-Flow Fans With 0.2 Hub-to-Tip Ratio

AbstractAspect ratio and solidity play complementary roles in the aerodynamic design of axial fan rotor blades. Few studies have experimented the effect of the aspect ratio of rotor blades on the performance of low-speed axial fans or its interaction with blade solidity in terms of fan aerodynamic performance. This study examined the selection of the solidity and blade aspect ratio in the preliminary design of low-pressure industrial fans with minimized hub-to-tip ratios. The aim of this study was to make available to the fan community experimental data that allow the determination of the optimal aspect ratio for practical applications as a function of the blade solidity. Various aspects of the performance of 16 prototypes of a 315-mm-diameter propeller fan were compared. The industrial fan prototypes all had a hub-to-tip ratio of 0.2 and were derived from four baseline designs conceived to ideally achieve the same best efficiency operation with different values of the aspect ratio. In addition, the prototypes’ assemblies were conceived to allow operation with different blade counts, i.e., with different rotor solidities at a fixed blade aspect ratio. The aerodynamic performance of the fans, measured in accordance with the ISO-5801 standard, was evaluated to assess the sensitivity and trends of the fan pressure and efficiency with respect to the blade aspect ratio and solidity at fixed tip clearance. The measured effects of the aspect ratio and solidity are discussed on the basis of data available in the literature. The results of the experimental analysis were used to formulate general guidelines for the preliminary design of propeller fans with minimized hub-to-tip ratios.

Effects of Reynolds number and solidity ratio on advection dominated mixing in a high-altitude instrument

Due to the role of ClO and BrO in the rate-limiting step of the catalytic cycles enabling ozone loss, measurement of concentrations of these halogen molecules is of critical importance to understanding the loss rate of ozone in the stratosphere. A key advantage of in situ measurements is that these rate-limiting molecules can be observed simultaneously with ozone in the same volume element of the stratosphere, with high spatial and temporal resolution. Historically, these in situ measurements were made using instruments on the NASA ER-2 flight platform for a few hours at a time. However, the development and advancement of a high-altitude long-endurance (HALE) solar aircraft has made it possible to monitor these radicals continuously in the stratosphere. The slower flight speeds of the HALE aircraft will greatly improve molecule detection sensitivity and spatial resolution. To ensure proper mixing and accurate measurements, a quantitative dissection of the flow dynamics within the instrument architecture is required. Of particular importance are the turbulent behavior and the boundary layer growth, both of which affect measurement quality. The geometry of the NO injector used for titration is studied as a function of its solidity and the flight airspeed, to understand its effect on turbulence and boundary layer growth. A 3D Computational Fluid Dynamics simulation of an Eulerian mixture model is used to analyze the advection-dominated mixing inside the instrument. The injector inside the instrument is found to act as a flow-conditioning device, with a lower solidity causing the downstream flow to be increasingly turbulent. Additionally, a quantitative relationship between the Reynolds number of the inlet air and the volume fraction of the flow is demonstrated. Analysis of the boundary layer dependencies demonstrates that the boundary layer does not encroach on the optical sensing area in any of the cases.

Experimental Study of Wind Loads on Tubular Crossarms of Transmission Towers

The actions exerted by yawed wind on the crossarm substantially differ from those on the tower body due to the presence of the angle between the crossarm’s cross-section and the incoming flow, and this phenomenon deserves a better understanding. Focusing on the tubular crossarms with round-section members, this paper aims to determine insights into wind actions, as affected by various factors, such as the tower type, the mean width to mean height ratio, the solidity ratio, and the wind incidence angle, and thereby derive the wind loads for design. Accordingly, a succession of wind tunnel tests was conducted by using quadrilateral and triangular crossarm models with various solidity ratios and mean width to mean height ratios. The method of direct force measurement (DFM) is employed for the high frequency force balance (HFFB) test to attain the transverse and longitudinal forces on the crossarm simultaneously. It was found that the wind load coefficients increase with increases of the mean width to mean height ratio and decreases of the solidity ratio. Moreover, in the case of the incoming flow perpendicular to the crossarm face, it is concluded that compared to the quadrilateral crossarm, the triangular crossarm possesses a relatively smaller drag coefficient, provided a moderate mean width to mean height ratio of 1.19. Furthermore, an analysis of the experimental results shows that the skewed wind load factor specified in the relevant codes would overestimate the effects of the wind incidence angle and the variations in mean width to mean height ratio, which is evident in the tests but not considered in the codes. It is worth noting that the experimental results show that the crosswind force is pronounced, which is usually ignored in the skewed wind load factor-based approach. Comparatively, using wind load distribution factors seems to be more rational. Thus, the corresponding estimating equations are proposed for the wind load-distribution factors of the crossarms, which agree well with the experimental results. The developed equations would greatly facilitate the determination of wind loads on tubular crossarms.

Numerical and experimental analysis of the influence of solidity on rotor aeroacoustics at low Reynolds numbers

We compare medium and high fidelity numerical simulations to experiments conducted on low Reynolds number rotors typical of small scale Unmanned Aircraft Systems (UAS). We first show that these numerical approaches provide reasonable estimates of the aerodynamic performance and farfield tonal noise and hence apply them for the investigation of the influence of solidity ratio on the aerodynamics and acoustics of small scale rotors operating under hovering, iso-thrust conditions. We show that while solidity ratio has a weak impact on aerodynamic performance, it may help drastically reduce farfield tonal noise. This reduction is however found to depend on the interplay between thickness and loading noise such that increasing the solidity by increasing the number of blades at constant blades’ aspect ratio or by decreasing the blades’ aspect ratio keeping the number of blades constant may yield very different, sometimes opposite, trends.

Optimization Design of Aspect Ratio and Solidity of a Heavy-Duty Gas Turbine Transonic Compressor Rotor

To investigate the influence of blade aspect ratio and solidity on the performance of heavy-duty gas turbine transonic compressors, a multi-objective optimization design platform was built by adopting the blade parameterization method based on the superposition of thickness distribution on the suction surface, the Kriging surrogate model, and the NSGA-II optimization method. The spanwise distribution of solidity and number of blades were the optimization variables. The multi-objective optimization was carried out with isentropic efficiency and stall margin as the objective parameters for the inlet stage transonic rotor of an F-class heavy-duty gas turbine compressor. The results show that the isentropic efficiency and stall margin at design condition with a constant mass flow rate can be improved by 0.96% and 18.7%, respectively, and the total pressure ratio can also increase. The analysis shows that, for regions where the shock wave–boundary layer interaction is obvious, increasing the solidity can reduce the shock wave loss, the shock wave–boundary layer interaction loss, and the end wall loss, and reducing the aspect ratio can reduce the blade boundary layer loss. The spanwise distributions of solidity and aspect ratio determine the stall margin by affecting the radial matching of the load of each blade section. Tip solidity near the tip region needs to be determined according to the pressure field established by the bulk of the flow.

Experimental investigations on hydrodynamic interactions between the cylinder and nets of a typical offshore aquacultural structure in steady current

A series of physical experiments were performed in steady current to investigate the hydrodynamic interactions between the cylinder and nets which constitute a main part of offshore aquacultural platforms. The hydrodynamic characteristics of only the cylinder, only nets and combined cylinder-net structures are measured and analyzed systematically under different current velocities, inflow angles and solidity ratios of nets. Based on experimental data, fitted formulas for hydrodynamic coefficients of a single resin net are proposed and compared to previously published empirical formulas. It is observed that the existence of the cylinder brings an increment up to 9.2% to drag coefficient of net panels whose solidity ratios are higher than 0.347, whereas this effect is negligible for nets with lower solidity ratios and perpendicular to the inflow. For nets inclined with 45°, the increment of the drag coefficient of net panels due to the existence of the cylinder is more significant (up to 22.9%) than that for perpendicularly placed nets. Furthermore, the existence of nets also leads to a noticeable increase in the drag coefficient of the cylinder, up to 40.18% for a relatively large net solidity ratio of 0.458, representative of biofouling condition. The increment increases with the rise of the solidity ratio of nets and it is larger for nets placed perpendicularly to the inflow than inclined. Effects of the cylinder and nets on lift coefficients of each other are a bit complicated, leading to an increase or reduction of lift coefficients depending on the inflow velocity, inflow angle and net solidity ratios. Finally, it is worth noting that the hydrodynamic interaction between the cylinder and nets deserves to be considered in current practice of hybrid methods by combining potential flow theory, Morison and screen models for aquacultural structures, especially for biofouling conditions.

Revisit of underestimated wind drag coefficients and gust response factors of lattice transmission towers based on aeroelastic wind tunnel testing and multi-sensor data fusion

Accurate estimation of extreme wind-induced loads is key to the cost-effective and reliable performance-based design of overhead lattice transmission towers. Particularly, drag coefficient and gust response factors are among the main aerodynamic properties of these structures for the estimation of equivalent static wind loads. Wind design standards recommend values for these key properties for generic lattice frames based on the solidity ratio and height of the frames. However, the geometric properties of lattice transmission towers often vary along the height of the structure. Therefore, local drag coefficients and gust response factors of transmission towers must be assessed to reliably analyze the extreme wind performance of towers. This study estimates the drag coefficients and gust response factors of a double-circuit lattice transmission tower using an approach based on Kalman filtering. Multiple along-wind and crosswind responses of the tower were obtained from a series of aeroelastic wind tunnel tests that were conducted at the National Science Foundation (NSF) Natural Hazard Engineering Research Infrastructure (NHERI) Wall of Wind Experimental Facility (WOW EF) at Florida International University (FIU). The developed Kalman filtering model facilitates the fusion of noisy measurements from multiple sensors of the same and different types that were implemented in the wind tunnel experiments. This approach is integrated with an optimization technique to provide estimates of wind load parameters of interest with high spatial resolution and accuracy from measured responses. The derived drag coefficients and gust response factors are treated as new evidence along with the ASCE manual recommendations for these properties as priors in a Bayesian regression model to provide new recommendations. The findings of this study indicate larger drag coefficients and gust response factors than those suggested by ASCE No. 7 and No. 74 by up to 12% and 13%, respectively.

HFFB Test and Wind-Induced Vibration Analysis on 1 000 kV Transformer Frame

In order to propose a complete, wind-resistant design method for ultra-high voltage (UHV) transformer frames, the wind-induced vibration characteristics of a 1 000 kV transformer frame (TF1000) were studied using a high-frequency force balance (HFFB) test. Five section models and one whole model of the TF1000 were designed and constructed using 3D printing, and these were evaluated in a wind tunnel by means of HFFB tests for multiple loading scenarios. The finite element method (FEM) was used on the test data to analyze the wind-induced vibration on the TF1000. The results demonstrate that the shape factor of the TF1000 is significantly affected by the flow field type and solidity ratio; the minimum value occurs when the wind direction is between 30 and 45°. Moreover, all the shape factor values obtained by the test are larger than those established by the Chinese code. The wind-induced vibration analysis indicates that the most unfavorable wind direction for the TF1000 is approximately 60°, with a wind-induced vibration coefficient between 1,7 and 3,9.

Hydrodynamic analysis of a bottom-placed fine-mesh cage and its effects on the transport of particulate organic waste

The awareness of ocean sustainability has promoted the development of integrated multi-trophic aquaculture (IMTA) systems for seafood production. Bottom-placed fine-mesh cages could be a part of this system for the cultivation of benthos that feeds on sedimented particulates. However, the flow field around such cages is insufficiently researched. In this study, the flow field around two bottom-placed fine-mesh cages with a solidity ratio of 0.12 and 0.28 was examined experimentally and numerically, followed by a numerical evaluation of their performances for particulate waste collection. The velocity reduction factor along the centreline of the two cages was 12% (low-solidity cage) and 7% (high-solidity cage) lower than estimated using empirical equations by Løland (1993). The cages had little impact on the direction of the velocity field, and had no effect 0.8 times the cage length parallel. The two cages exhibited insignificant differences in the particulate collection efficiency. The high sedimentation ratio, due to the velocity reduction inside the cage, compensated for the particulate dispersion around the cage. This finding eliminates doubts about the blockage effects of mesh cages on particulate transport, stimulating further IMTA development.

Experimental investigation of the effect of blade solidity on micro-scale and low tip-speed ratio wind turbines

It is well-established that micro-scale wind turbines require high blade solidity in order to overtake friction torque of all mechanical parts and starts operating. Therefore, multi-bladed micro-scale rotors with a low design tip-speed ratio λ are advocated. However, no consensual blade solidity is admitted by the scientific community at low Reynolds number and low tip-speed ratio because the reliability of the airfoil data, used in the blade element momentum theory, is questionable. The vast majority of the open literature has focused on the number of blades rather than varying blade chord length to increase the solidity. This experimental study carried out in a wind tunnel serves two purposes: to examine blade solidity effect on the power Cp and torque coefficients Cτ vs. tip-speed ratio curves at a fixed number of blades and to investigate its effects on the velocity distributions using stereoscopic particle image velocimetry (SPIV) for three tip-speed ratio λ=0.5, λ=1 and λ=1.4. Six 200mm diameter runners with 8 blades and various blade solidity from σ=1.5 to σ=0.5 were designed at λ=1 without using airfoil data. The results emphasise that the maximum power coefficient increases with blade solidity up to a maximum value Cp,max=0.29 reached for σ=1.25. High-solidity rotors have a very low cut-in wind speed V0=3.8 m s−1 and their torque coefficient Cτ decreases drastically and linearly while increasing the tip-speed ratio λ. These specificities could be of particular interest for energy harvesting of low speed air flow in order to power low-energy appliances. However, for low-solidity rotors, the Cτ vs. λ curves present a similar trend than the lift coefficient vs. angle of attack polar plots of isolated airfoil which is characterised by a significant drop in Cτ illustrating stall effect. An increase in blade solidity postpones and attenuates the stall effects due to greater mutual blade interactions. The SPIV recordings reveal that for high-solidity rotors the magnitude and radial profiles of axial and tangential induction factors and the flow deflection were close to the design settings. Moreover, the analysis exhibits that an increase in the blade solidity and tip-speed ratio leads to higher axial and tangential induction factors. The investigation of the wake highlights that the aerodynamic torque generated by a wind turbine is not produced in a same way as changing the blade solidity or the tip-speed ratio. To conclude, the best compromise between the maximum power coefficient, the cut-in wind speed, the mass of filament and the stability of the wake is achieved for the rotor with a blade solidity of σ=1.25.