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a b s t r a c tDrag type wind turbines have strong potential in small and medium power applications due to their simple design. However, a major disadvantage of this design is the noticeable low conversion efficiency. Therefore, more research is required to improve the efficiency of this design. The present work introduces a novel design of a three-rotor Savonius turbine with rotors arranged in a triangular pattern. The performance of the new design is assessed by computational modeling of the flow around the three rotors. The 2D computational model is firstly applied to investigate the performance of a single rotor design to validate the model by comparison with experimental measurements. The model introduced an acceptable accuracy compared to the experimental measurements. The performance of the new design is then investigated using the same model. The results indicated that the new design performance has higher power coefficient compared with single rotor design. The peak power coefficient of the three rotor turbine is 44% higher than that of the single rotor design (relative increase). The improved performance is attributed to the favorable interaction between the rotors which accelerates the flow approaching the downstream rotors and generates higher turning moment in the direction of rotation of each rotor.

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This research aims to study the characteristics of the wake generated by twin cylinders. The cylinders are arranged in parallel side-by-side and staggered arrangements. The mainstream velocity is varied between 18 m/s and 20 m/s, which are equivalent to cylinder Reynolds numbers between 4750 and 5300. The cross-stream spacing ratios are 2, 3, 4, and 6 times the cylinder's diameter for the side-by-side arrangements. For the staggered arrangement, the cross-stream and streamwise spacing were varied between 2 and 4 times the cylinder diameter. The results show that the spacing ratio s/d has a significant effect on the wake development and interactions. The wakes of the side-by-side cylinders tend to merge into a single wake for cross-stream spacing of 2d and 3d at early stations, equivalent to 15 and 30 times the cylinder diameter, respectively, and merge completely at 50 and 100 times the cylinder diameter for 4d and 6d, respectively. Velocity measurements are used to develop a correlation that relates the wake merging distance to the cylinder spacing. Turbulence measurements are used to develop a correlation between the turbulence intensity and the streamwise distance. The comprehensive survey of the results and the correlations developed are provided in order to facilitate numerical model development and evaluation.

A model of Formula One racing car rotating dry wheel in contact with the ground is studied using a computational approach as a validation case. This validation case focuses on the computed surface pressure around the wheel's center line. This computed result is compared to an experimental one obtained from the available literature work and it showed good agreement. Another case study is considered with replacing the dry wheel model with another wetcondition wheel model. The wet-condition wheel's work is mainly concentrated on the developed aerodynamic forces especially the wheel moment values. This moment is translated to an expression of resistive torque developed by the air stream on the wheel and computed in each case study. In addition, general schematic pictures of the flow behavior around the wet wheel are presented.

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The wake effect is the biggest challenge when locating downwind turbines in wind farms which imposes large separation distances between turbines. In the present work, CFD simulations are presented to study possible configurations of wind farms of Savonius wind turbines. The farm is composed by in steps, starting from two-turbine configuration, adding one turbine until reaching a cluster of closely set ten rotors with an average power coefficient of 0.225. This value is very close to the single rotor’s power coefficient. The power density of the cluster is 7.55 W/m2 which is much higher than similar ten turbines located far apart to avoid wake effect. The maximum Cp of a downstream rotor in the cluster reached 0.323 which is about 40% higher than the single rotor. The adopted philosophy for placing downstream rotors is locating the rotor’s returning bucket in the low velocity region of the wake of the upstream rotor to get the least negative torque while the advancing bucket is located at the high velocity region getting higher positive torque which increases the performance. After that, two crosswind clusters are added to increase the power generated. The predicted average power coefficient for the 30 rotors farm is 0.246 which is higher than a similar isolated turbine. The increase of the Cp occurs due to the positive interactions between the clusters. The highest Cp in the farm rotors is found to be 0.411 which is higher than the single rotor’s Cp by 78%. The farm also provides a high power-density of 4.65 W/m2 which is 5 times higher than a farm with the same number of turbines located far apart.

The combustion performance of a cylindrical burner accommodating up to six multiple pairs of opposing methane-air mixtures with a cross-flow of hydrogen was addressed. The cross-flow initially duplicated the stagnation impact and enriched the vortical structures. Aided by the resulting flow strain, the transport of heat and active species from the hydrogen oxidation zone to the methane reaction zones accelerated the combustion across the opposing premixed flames and reduced the peak temperature across the outer diffusion flame. Increasing the cross-flow/opposing jets' velocity ratio to 0.89 merged the two stagnation centers and maximized the shearing stress. By the slight increase in the velocity ratio to 1.07, the H and OH pools provided for methane combustion became closer to the ports such that a hydrogen/methane mass percent of 10.3% extended the stoichiometric blowout velocity from 28.3 to 35.7 m/s. Since the turbulent kinetic energy thus increased to 8.4 m 2 /s 2 , the firing intensity reached values as high as 48.2 MW/m 3. Not only was there a reduction in the residence time for NOx formation, but also the blowout velocity relative gain overrode the relative increase in the NOx formation rates such that the NOx emission index decreased to 17 g/MWhr. By the excessive increase in velocity ratio, the vortical structures shrank such that the NOx exponential increase became dominant above 21 ppm. With fuel-lean mixtures, the hydrogen was partially combusted by the excess air from the opposing flames but the blowout velocity decreased to 13.1 m/s at È ¼ 0.50. The hydrogen flame NOx emissions decreased by providing the excess air at larger jets' diameter/separation ratios, thus reducing the residence times for thermal NOx formation and simultaneously interrupting the prompt NOx formation. At the lean operational limit, tripling the number of opposing jets decreased the hydrogen flame length by 54% such that the NOx emissions decreased by 38.4%.