The primary objective of this investigation was to explore the aerodynamic impact of adding trailing edge serrations to a Wells turbine. The baseline turbine consists of eight NACA 0015 blades. The blade chord length was 0.125 m and the span was 0.100 m. Two modified serrated blade configurations were studied: (1) full-span, and (2) partial-span covering 0.288c of the trailing edge. The numerical simulations were carried out by solving the three-dimensional, incompressible steady-state Reynolds Averaged Navier-Stokes (RANS) equations using the k-ω SST turbulence model in ANSYS™ (CFX). The aerodynamic performance of the modified Wells turbine was compared to the baseline by calculating non-dimensional parameters (i.e., torque coefficient, pressure drop coefficient, and turbine efficiency). A comparison of the streamlines was performed to analyze the flow topology around the turbine blades for a flow coefficient range of 0.075 ≤ ϕ ≤ 0.275, representing an angle of attack range of 4.29° ≤ α ≤ 15.3°. The trailing edge serrations generated a substantial change in surface pressure and effectively reduced the separated flow region, thus improving efficiency in most cases. As a result, there was a modest peak efficiency increase of 1.51% and 1.22%, for the partial- and full-span trailing edge serrations, respectively.

Wave energy conversion devices incorporating the Oscillating Water Column (OWC) principle are the most extensively used wave energy converting technologies to date. In this paper, we explore the effect of a fixed blade Denniss-Auld turbine that is representative of the maximum pivot points which occur during OWC inhalation and exhalation. Whereas conventional Denniss-Auld turbines are mounted on an intricate hub system that allows for controlled blade rotation to optimize performance, we investigate the possibility of removing the mechanical complexity while maintaining good aerodynamic performance. The assessment of turbine performance is carried out using non-dimensional coefficients, i.e., torque, pressure drop, and efficiency. The simulations are completed by solving the incompressible, steady-state Reynolds Averaged Navier-Stokes (RANS) equations with the k-ω SST turbulence model using ANSYS™ CFX. Validation of our numerical approach was completed by comparing existing experimental and numerical data of a Wells turbine. Furthermore, a grid independence study was conducted to achieve accurate numerical results. Overall, the modified Denniss-Auld turbine does not stall at high flow coefficients and has an extended operating range similar to an impulse turbine; however, with a much lower maximum efficiency of 12%. Future work should explore a larger design space with blade optimization using parametric studies to improve device efficiency.

In the past decade, there has been renewed interest in wave energy harvesting utilizing oscillating water columns (OWC), one of the most well-studied wave energy harnessing technologies. In the OWC, pneumatic power from ocean waves is converted to mechanical energy by Wells turbines. It should be noted, however, that such turbines tend to perform poorly, have a limited operating range, and have low efficiency. In the present study, we incorporate a rectangular Gurney flap (GF) at the trailing edge (TE) of a Wells turbine consisting of hybrid airfoil (NACA 0015 and NACA 0025) blades with variable chord distribution along the span. This passive flow control mechanism was adopted to achieve increased power production by the Wells turbine. This study aimed to determine the aerodynamic performance of the variable chord turbine with GF compared to a turbine with a constant chord. By using ANSYS™ CFX, the three-dimensional, steady-state, incompressible Reynolds averaged Navier–Stokes (RANS) equations coupled with the k-ω SST turbulence model are solved. The performance was evaluated through the use of non-dimensional coefficients of torque, pressure drop, and efficiency. In addition, the numerical accuracy was achieved through a grid independence study. There was a good agreement between the computed results and the available experimental and numerical data. The GF increased the torque coefficient by 18.6% and 47.3% but with the expense of peak efficiency of 8.5% and 7.4% for the baseline and the hybrid turbine, respectively. Additionally, the hybrid turbine with GF delayed the onset of the stall by ~3° angle of attack (AOA).

Waste cooking oil can be a potential source of biodiesel that has least effect on the edible oil consumption. Increasing number of hotel-restaurants and more active monitoring by health authorities have increased the generation of waste cooking oil significantly in densely populated cities like Dhaka. If not used or disposed properly, waste cooking oil itself may generate lot of environmental issues. In this work, waste cooking oils from different restaurants within Dhaka City were collected and some relevant properties of these waste oils were measured. Based on the samples studied one with the highest potential as biodiesel feed was identified and processed for engine performance. Standard trans-esterification process was used to produce biodiesel from the selected waste cooking oil. Biodiesel blends of B20 and B40 category were made and tested on a single cylinder direct injection diesel engine. Engine performance parameters included - bhp, bsfc and exhaust emission for rated and part load conditions. Results give a quantitative assessment of the potential of using biodiesel from waste cooking oil as fuel for diesel engines in Bangladesh.

View Video Presentation: https://doi.org/10.2514/6.2022-3676.vid This study presents a three-dimensional steady-state Reynolds Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) investigation of a modified Denniss-Auld turbine. The k-ω SST turbulence model RANS equations are solved using ANSYS CFX. A comparison of the performance with a Wells turbine is presented using torque, operating range, and efficiency values. The peak efficiency of the Wells turbine (59.5%) is found superior to the modified Denniss-Auld turbine (41.1%). However, the Wells turbine stalls at a high flow coefficient (between 0.274 and 0.41) and fails to produce useful power, but the modified Denniss-Auld turbine performs better. Thus, the modified Denniss-Auld turbine is best suited for high angle-of-attack flow (i.e., high flow coefficient). Moreover, an investigation of the flow field around the turbine blades was performed and analyzed.