Inflow Turbine Research Articles

Comparison of inflow and outflow radial air turbines in vented and bidirectional OWC wave energy converters

This study analyses the aerodynamic performance of two unidirectional-radial-air-turbine configurations; inflow and outflow. These turbines were studied as the Power-Take-Off unit for application on a vented-OWC and a conventional-bidirectional-OWC with a twin-turbine topology, forming four different turbine-OWC configurations. These configurations were evaluated in terms of full-scale power extraction using extrapolated hydrodynamic experimental data of irregular waves for a King Island test site. The power extraction capacity was evaluated by defining a lower and upper bound of power generation under fixed and controlled-RPM schemes and the energy produced in each configuration was then compared against a state-of-the-art twin-rotor turbine. It was found that the difference between these power extraction bounds was lower in case of the outflow turbine, which shows this turbine is less sensitive to RPM variations than the inflow turbine. In addition, due to its lower resistance to the flow in direct mode, the outflow turbine has a smaller full-scale size than the inflow turbine. It was concluded that the outflow turbine provides better efficiency in a twin-turbine-OWC system, while the inflow turbine yields higher conversion efficiency in a vented-OWC system. The vented OWC equipped with a radial inflow turbine can obtain comparable power to the bidirectional OWC system.

Tip Clearance Effect on the Flow Pattern of a Radial Impulse Turbine for Wave Energy Conversion

Turbines for wave energy conversion have a special feature to be taken into account in the study of the tip leakage flow: These turbines are self-rectifying, which work inside a cyclically bidirectional flow alternatively as an inflow/outflow turbine. The phenomena at the blade tip will be different in these two situations. Moreover, it is necessary to take into account the tip clearance of the guide vanes because it has a significant influence on the rotor performance. A previously developed numerical model has been used for this study. The geometry proposed by Setoguchi et al. (2002, “A Performance Study of a Radial Impulse Turbine for Wave Energy Conversion,” Journal of Power and Energy, 216, pp. 15–22) is used in the model. Three different tip clearance sizes have been simulated to compare the influence of the tip clearance size on the performance. Results show that changing the size of the tip clearance from 0% to 4% of the blade span reduces the turbine maximum efficiency by up to 8%. However, the efficiency reduction is more pronounced when the turbine works as an inflow turbine because the tip clearance effect is more important in the inner part of the rotor, since flow velocities are higher and the relative casing motion is lower. This study achieves its main aim, which is to improve knowledge about the phenomena related to the tip clearance and its influence on the performance of radial impulse turbines.

Effect of mixing and mass transfer conditions on gellan production by Auromonas elodea

The effect of fermentor hydrodynamics on gellan fermentation kinetics and rheological properties of the culture broth were studied using various mixing and mass transfer conditions. Different impeller systems, such as a helical ribbon (HR250), Rushton turbines (RT600) and a pitched-blade turbine combined with an in-flow turbine (CT600) were tested along with extra oxygen supply (HR250Ox) or reduced nitrogen amount in the culture medium (HR250N). The highest gellan productions (around 13 g/ l of native gellan) were observed when oxygen transfer capacity was good ( i.e. HR250Ox, HR250N, CT800 and RT600). The volumetric power input was found to be a good tool to evaluate the gellan synthesis progress especially with the helical ribbon impeller where no stagnant zone formation occurred. Macromixing conditions affected the rheological properties of the final broth. For instance, the highly heterogeneous conditions (with RT600) led to a more shear-thinning broth with a lower yield stress value than the most homogeneous conditions (with HR250Ox). Good correlations between yield stress value and gellan concentration were established with respect to the fermentation pattern.