Effect of shroud on the performance of horizontal axis hydrokinetic turbines

The idea of wind turbine power enhancement by means of a shroud has been investigated for decades with no commercial success. However, due to some beneficial aspects, shrouds are poised to serve the hydrokinetic turbine industry. We report on the experimental measurements performed in a water tunnel on a 19.8 cm diameter horizontal axis hydrokinetic model turbine utilizing two shrouds. Power and thrust coefficients of the model turbine with and without the shrouds investigated are obtained over the range of the power curve. A maximum power enhancement of 91% over the unshrouded turbine is obtained with one of the shrouds. Maximum power coefficients are recalculated based on the maximum area of shroud and are found to be comparable to that of the unshrouded turbine. At flow speed of 1 m/s, an extended blade that generates the same power as the shrouded turbine is found to have a diameter equal to the diameter of the shroud exit. This aspect is critical as the use of shrouds contrary to much of the literature is not to increase the hydrokinetic turbine efficiency, but to gain advantages in the powertrain design, and have the turbine power less impacted by changes in the flow direction.