A small horizontal axis wind turbine has been tested experimentally to show the influence of shroud components on the turbine's overall performance. The reference case was the bare wind turbine. The different parts of the shroud are connecting ring, inducer, diffuser, and lens. The maximum power coefficient (Cp) of the used bare HAWT is 0.1969 (1st case). When the connecting ring was attached to the reference case (2nd case), the maximum Cp decreased to 0.1695. In the (3rd case) an inducer is attached to the connecting ring, maximum Cp increased to 0.2213, about 11% higher than the bare wind turbine. When adding a diffuser part to the inducer and the connecting ring (4th case), the performance increased to 0.347, which is improved by 36.2% compared to the third case and 43.26% to a bare wind turbine. In the (5th case) a lens was added to the diffuser outlet to construct a full shroud. For this construction, the best performance is obtained at Cp of 0.35. This case improved the performance by 43.74%, more than the bare turbine. To reduce the construction cost, in the (6th case), the inlet inducer is removed and the connecting ring with flanged diffuser assembly is examined, under the same working condition, the performance is reduced to 0.308. Although the performance, in this case, was lower than the case of a full shroud, it improved the performance over the bare turbine and the case of inducer-connecting ring assembly by 36.07% and 44.97% respectively.

The present study computationally investigates the steady incompressible flow behavior through Langston turbine cascade. A three dimensional numerical model was developed by ANSYS-Fluent software. The model solves the RANS governing equations along with the transition-SST (4eq.) model. The results of the model have been validated using experimental data obtained by Langston. A proposed configuration to improve the turbine performance is adopted using fence mounted close to the leading edge. The function of the fence is to reduce the pressure losses and accordingly improve the turbine performance. The results showed that the total pressure loss coefficient decreased by 5.244 % according to fence addition. The fence effectively disrupted the horseshoe vortex and modified the pressure flow field, leading to a weakened passage vortex and suppressed secondary flow. Adding a fence resulted in an enhancement of the flow uniformity and reduction of the vortex strength with improvements in the aerodynamic efficiency of the turbine cascade.

A three-dimensional computational fluid dynamics simulation for a micro-scale pump has been performed to investigate the sensitivity of the flow rate to fre-quency change during pump and supply phases. Applying dynamic mesh under different diaphragm actuation frequencies (8, 50, 100, 200, and 500 Hz) and si-nusoidal oscillation amplitude of 6.0 µm the results showed that at frequency f ≥ 100 Hz the flow separation has been formed in the diffuser direction for both supply and pump phases. At low frequency f ≤ 50 Hz there is no flow separation in the diffuser or the nozzle direction. The large recirculation zone is created at the diffuser bottom wall side. The flow separation was found to be frequency and direction dependent for the micro-diffuser half angle of 5o. The net flow rate increased linearly with the frequency while the net flow per cycle was less sen-sitive to the change of the frequency.