Investigation of the Solidity Ratio in a Horizontal Wind Turbine

A wind turbine-generator system; Parameters such as wind speed, turbine blade diameter, number of blades, turbine height, tip speed ratio and solidity ratio are affected. In this study, horizontal axis wind turbine with diameter of 130 cm and blade solidity ratio values of 7%, 8,6% and 9,8% were constructed and the tests were made according to different blade speed ratios. The required blades were obtained from PVC pipes of different diameters. The experimental study was actualized in Erciyes University Mechanical Engineering, Engines Laboratory. For each profile, blade rotational speeds and wind speeds at various distances have been studied. It has been determined that the wind speed is reduced by the distance difference and accordingly the number of blade speed is decreased visibly. In the wing profiles with different blade solidity ratios resulting from the work done, the wing structure with the solidity ratio of 8.6% gave the best performance. CL and CD coefficients of the profiled specimens were analyzed by FLUENTTM, a program of computational fluid dynamics. One of the factors that should be taken into consideration in the production of wind turbines is the blade solidity ratio.

Effects of the airfoil section, chord and twist angle distributions on the starting torque of small horizontal axis wind turbines

Small wind turbines usually suffer from poor efficincy, low power and lack of public incentives. This study is focused on investigating the effects of the geometry of the airfoil sections and blades on the starting torque and minimum wind speed for energy generation. The Blade Element Momentum Theory is used to develop a numerical code where the airfoil S832 is used as a reference for comparison and validation. The investigated parameters include three airfoil sections Joukowski J9.513, Gottingen GO447, and S832, linear and elliptic chord distributions, linear twist angle distribution and multiple airfoil sections along the blade. The results show that large local solidity ratio at the intermediate region of elliptic chord distribution produces significant reduction in the local generated torque of about 5-21% and that the linear chord distribution along the blade length increases the torque by about 27-77% and thus permits lower starting wind speeds. For rotors with high solidity ratio as in the case of elliptic chord distribution, the distribution of twist angle for constant angle of attack reduces the generated torque by about 13-19%. The J9.513 airfoil based rotor shows 20-35% more start torque than the S832 and GO447 airfoils based rotors. The linear chord distribution is shows better results for all the three airfoils based rotors. The linear twist angle distribution increases significantly the start torque of the rotors with the proposed airfoils sections. The three airfoils S832, GO447 and J9.513with linear twist angle distribution are viable options for small wind turbines. The J9.513 with linear chord and linear twist angle distribution shows the lowest wind speed for electricity generation. The use of multiple airfoils on the blade length shows marginal improvement of the starting torque.

Influence of the Solidity Ratio on the Small Wind Turbine Aerodynamics

Increasing popularity of individualised electricity generation from wind by prosumers creates a strong demand for profitable and highly efficient small wind turbines. This paper investigates the influence of rotor blade solidity parameter on device efficiency in hope of determining its optimal value as a part of the development process of the GUST small wind turbine. The study involved experimental analysis in the wind tunnel and numerical simulations performed in QBlade software. Different solidities of the rotor were achieved by alteration of (1) number of blades and (2) chord distribution along the blade span. The increase of rotor solidity resulted in augmentation of the aerodynamic efficiency in both approaches. The elongation of the chord by 33% in a 3-bladed rotor resulted in a bigger power coefficient increment than addition of a 4th blade with original chord distribution. Even though the solidity was the same, the 3-bladed rotor performed better, possibly due to lower form drag. The results emphasize the importance of the rotor solidity optimization during the small wind turbine rotor development and may significantly influence overall power output.

Turbulence anisotropy with higher-order moments in flow through passive grid under rigid boundary influence

The investigation presents the estimate of the degree of deviation from the isotropic turbulence in terms of Reynolds stress tensor for grid generated turbulence under the influence of bottom boundary. The turbulence triangle, Eigen values, and the invariant functions are presented at near and far field regions of the grids with different solidity ratio. In addition, the work also deals with the analysis based on third-order moments of the velocity fluctuations and the ratio of momentum flux to the turbulent kinetic energy in the frequency domain. The Reynolds stress anisotropy exposes that the anisotropic invariant maps possess a closed looping trend in the near field region and an open looping trend in the far-field region of the grid. Further, to describe the physical behaviour of the velocity time-series of random fluctuating components in the stream-wise directions, the probability distribution function are estimated and interpreted.

Numerical Analysis of a Floating Fish Cage With Feeding Systems

A modern marine-based fish farm normally consists of a feeding barge, several fish cages, and feeding tubes. Although many studies, both experimental and numerical, are available in the literature to investigate the global responses of the fish cages under wave and current conditions, research on the coupled system including both the fish cage and the feeding system is very limited. This paper presents a numerical study on the coupled system with a floating fish cage and the feeding system. The purpose is to study the dynamic responses of the coupled system under different environmental conditions and configurations of the fish farm. A numerical model is firstly established in the numerical program OrcaFlex, comprising of a feeding barge, a gravity-based floating fish cage with mooring systems, and a feeding tube between the barge and the cage. Time-domain simulations of this coupled system are then performed under environmental conditions corresponding to 1-year and 50-year return periods for a reference site. The deformation of the fish cage, the tensions in the anchor lines and in the feeding tube are compared under various conditions. Sensitivity studies on the solidity ratio of the fish net as well as the lengths of the feeding tube are addressed, and their influences on the responses of the coupled system are also discussed.

Experimental study on wind force coefficient of a truss arch tower with multiple skewbacks

A truss arch tower is a large-span arch structure with multiple skewbacks. This tower is made of a large number of members with unique form, and contains more than five kinds of geometric features. The wind forces and the corresponding wind effects on the truss arch tower are notably complicated. In this study, wind tunnel tests were conducted to evaluate the wind forces on the steel latticed structure mentioned above using the high-frequency base balance technique. Four segmental models, including one arch foot of main truss, two arch feet of sub-truss, and one arch crown of main truss were tested in nominally smooth flow. The drag forces were measured and compared with several existing codes, including the British, American, and Chinese codes. The incidence angle effects and the interference effects on the drag coefficient were analyzed. The testing results showed that the direction of the wind forces has a marked effect on the whole truss tower. The solidity ratio and layout of the segmental models, including the cross-section and the centerline of the members, have critical effects on the drag forces.

A Perforated Baffle Design to Improve Mixing in Contact Tanks

In this study, a perforated baffle design is proposed to improve mixing in contact tanks. Turbulent flow through the perforated baffle is studied at the perforation hole scale. The contribution of jets emerging from the perforations to the mixing process is evaluated in terms of standard mixing indexes for various perforation parameters, such as the solidity ratio and hole diameter. Based on numerical simulation results, the two sets of perforated baffles that yielded the highest performance were manufactured from polycarbonate and tracer studies were conducted on a laboratory model. Comparison of numerical and experimental results demonstrates that the numerical model developed is reliable in simulating the flow through the perforated baffles and the associated mixing level in the contact tank. Numerical simulations indicate that the jet flow structure through the perforated baffle penetrates to the recirculation zones in the neighboring chambers and turns the dead zones into active mixing zones. Furthermore, large scale turbulent eddies shed by the perforations contribute to the mixing process in the chambers of the tank. With the use of the perforated baffle design, it is shown that the hydraulic efficiency of the tank can be improved from average to superior according to the baffling factor, and the associated mixing in the proposed design can be improved by 31% according to the Morrill index.

Effects of Design Factors on Drag Forces and Deformations on Marine Aquaculture Cages: A Parametric Study Based on Numerical Simulations

In Japan, the marine aquaculture net cage has an important role in farming pacific bluefin tuna farming in oceans, and the design of the net cage needs to ensure robustness against hostile oceanic conditions. Accordingly, this study focuses on the drag forces and the cage volume of the net cage, and on their variations induced by different design parameters (netting solidity ratio, netting height, and bottom weight). A series of parametric studies on drag force and deformation of the net cage was conducted using a numerical simulation model. Accordingly, the contribution of each parameter to the drag and volume was analyzed using a generalized additive model. The results indicate that the bottom weight had the highest contribution to the holding ratio of the cage volume, whereas the netting height had the highest contribution to the drag coefficient of the net cage. Finally, a fast prediction model was created by a backpropagation (BP) neural network model and was examined for the accurate prediction of the objective variables.

Study on the Influence of Mesh Grouping on Numerical Simulation Results of Fish Cages

The Morison Model is widely applied in the numerical simulation for the hydrodynamics assessment of fish cage. In the Morison model, hydrodynamic forces are calculated based on twines. To reduce the computational time, mesh grouping methods (replacement of multiple meshes with less number of equivalent meshes) have been implemented widely in the calculation. However, as the hydrodynamic equation for a mesh is quite different under wave and current, it is not appropriate to use the classical mesh grouping. On the basis of basic hydrodynamic equations of the meshes with current and wave, this paper carried out the study about theoretical analysis of two methods (the equivalent area method and the equivalent volume method) of the mesh grouping, using main parameters of nets such as the diameter, solidity ratio and elastic modulus related to mesh grouping. A single-point mooring cage, of which tension and displacement could be calculated with finite element method, was selected as a case to carry out the verification of two mesh grouping methods. Flume model experiment was used to validate the accuracy of mesh grouping methods. The results indicated that, the equivalent area method has a higher accuracy in the pure current condition, while the equivalent volume method was more accurate in combined waves and current. The accuracy of results using mesh grouping to analyze hydrodynamics of nets within a certain range of grouping times could be insured with an improved calculation speed. This paper can provide practical advice on the mesh grouping process in the numerical simulation of fish cages and fishing gear.