Search

The Oscillating Water Column (OWC) is the most promising self-rectifying device for power generation from ocean waves; over the past decade, its importance has been rekindled. The bidirectional airflow inside the OWC drives the Wells turbine connected to a generator to harness energy. This study evaluated the aerodynamic performance of two hybrid airfoil (NACA0015 and NACA0025) blade designs with variable chord distribution along the span of a Wells turbine. The present work examines the aerodynamic impact of the variable chord turbine and compares it with one with a constant chord. Ideally, Wells rotor blades with variable chords perform better since they have an even axial velocity distribution on their leading edge. The variable chord rotor blade configurations differ from hub to tip with taper ratios (Chord at Tip/Chord at Hub) of 1.58 and 0.63. The computation is performed in ANSYS™ CFX 2023 R2 by solving three-dimensional, steady-state, incompressible Reynolds Averaged Navier–Stokes (RANS) equations coupled with a k-ω Shear Stress Transport (SST) turbulence model in a non-inertial reference frame rotating with the turbine. The accuracy of the numerical results was achieved by performing a grid independence study. A refined mesh showed good agreement with the available experimental and numerical data in terms of efficiency, torque, and pressure drop at different flow coefficients. A variable chord Wells turbine with a taper ratio of 1.58 had a peak efficiency of 59.6%, as opposed to the one with a taper ratio of 0.63, which had a peak efficiency of 58.2%; the constant chord Wells turbine only had a peak efficiency of 58.5%. Furthermore, the variable chord rotor with the higher taper ratio had a larger operating range than others. There are significant improvements in the aerodynamic performance of the modified Wells turbine, compared to the conventional Wells turbine, which makes it suitable for wave energy harvesting. The flow field investigation around the turbine blades was conducted and analyzed.

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).

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.

A numerical investigation was carried out to explore the effects of a dielectric barrier discharge (DBD) plasma actuator on a three-dimensional incompressible, separated flow. The test article selected for the simulations was the National Aeronautical and Space Administration (NASA) wall-mounted hump model. The simulations were run at a Reynolds number of 936,000, based on hump chord length, and a freestream Mach number of 0.1. Hybrid partially averaged Navier−Stokes/large-eddy simulations (PANS/LES) were completed using CALC-LES, a well-validated computational fluid dynamics (CFD) code, developed by Chalmers University of Technology. The baseline code was modified to simulate the effects of the actuator, which were modeled as source terms in the momentum equation and were assumed to be steady and constant in the span-wise direction. The numerical simulations were carried out for a baseline (no control) case and five plasma control cases. To optimize the performance of the actuator, the variation of actuator location and voltage frequency was investigated. For the baseline case, a comparison of time-averaged skin friction, the coefficient of pressure, and velocity profiles was made of the available experimental results. The results of the baseline case showed good agreement for a hybrid turbulence model, thus strengthening the solver’s ability to predict a three-dimensional separated flow with reasonable accuracy. The results with the plasma actuator turned on showed improved flow characteristics compared to the baseline simulations by reducing the region of separated flow. The actuator placed just downstream of the separation point at an operational frequency of 5kHz completely eliminated the separated flow for our test conditions.