Abdus Samad

A Gurney flap (GF) placed at pressure side of the trailing edge of an airfoil and perpendicular to the chord line enhances lift in aircraft wings, helicopter rotors, and wind turbines, etc. In this article, the GF concept was introduced for Wells turbine blade used to harvest wave energy with special consideration as the blades are having symmetric airfoil and faces bidirectional flow. Hence, the flap was extended to both pressure and suction sides of the trailing edge (TE) to maintain blade symmetry, and the turbine performance was evaluated using opensource computational fluid dynamics code OpenFOAM 4.0. Different GF-lengths (0.5–3% chord length) were considered, and the performance parameters such as non-dimensional torque, pressure drop and efficiency were evaluated. The GF blades produced a counter-rotating vortex pair behind the TE which modified the TE Kutta condition and increased the circulation and lift. In addition, the GF blades increased the blade loading and enhanced the torque generated. However, the increased pressure drop lead to decrement in efficiency.

The present paper investigates the leading edge (LE) undulations of a Wells turbine blade through numerical analysis. The aspiration for this modification came from humpback whales, which have uneven protrusions at the LE of their pectoral flippers. The flippers help whales to maneuver during swimming. The work is performed by using three-dimensional steady, incompressible Reynolds Averaged Navier-Stokes (RANS) equations with turbulent closer model. The LE of the turbine blades is modified with undulations of three different amplitudes: 1mm, 2.5mm, and 4mm. The results show that the undulation changes the turbine performance. The amplitude 2.5mm gives the peak performance. The comparison between blades with different amplitudes and the reference blade has been discussed throughout this study.

The present study attempts to enhance a Wells turbine performance by adopting a leading-edge microcylinder (LEM) as a passive flow control device. The microcylinder is placed near the blade leading edge so that its axis lies on the chord line of the rotor blade. The influence of turbine performance, due to parameters such as microcylinder diameter and the distance between the cylinder and the blade leading edge, is evaluated by solving the steady Reynolds-averaged Navier–Stoke (RANS) equations with the k-ω SST turbulence model. The performance parameters of the microcylinder rotor were compared with the reference rotor. It was found that the pair of counter-rotating and co-rotating vortices shed from the microcylinder feed kinetic energy to the separated flow and re-energize the boundary layer. This phenomenon delays the flow separation and enhances the operating range. Moreover, a parametric investigation of the microcylinder rotor reveals that the diameter and space between the microcylinder and the rotor blade are instrumental in delaying flow separation. It was found that a cylinder diameter equal to 0.02C (C is blade chord) and a distance between the leading edge and the micro cylinder equal to 0.035C resulted in increases in the working range and in the average torque equal to about 22% and 49%, respectively.

In this article, a Wells turbine geometry is created with the modification of multiple geometric parameters, i.e., blade sweep/skew, endplate, casing groove, and guide vane. The experiment of a bidirectional turbine is conducted at the wave and fluid engineering laboratory, IIT Madras. The preliminary objective of the study is to measure the starting characteristics and corresponding flow velocity, revolution per minute (rpm), differential pressure of higher and lower pressure sides of the turbine. The output parameters are measured at different cycle times and the stroke length of a piston-cylinder combination, which simulates different wave conditions. After starting the Wells turbine, rotational and axial speeds increase for some time. After that, it will fluctuate between a specific range, and pressure is prepositional to the airflow rate. The wave energy can be converted into pneumatic energy with the help of wave energy converting(WEC) devices, i.e., oscillating water column(OWC) that can be further converted into mechanical energy and then into electrical energy with some appropriate devices. In this article, an experimental analysis of the turbine geometry is reported.

Guide vanes (GVs) improve the performance of a turbine in terms of efficiency, torque, or operating range. In this work, a concept of different orientations of GVs in between a two-row biplane wells turbine (BWT) was introduced and analyzed for the performance improvement. The fluid flow was simulated numerically with a commercial software ANSYS CFX 16.1. The Reynolds-averaged Navier-Stokes equations with the k-Ï ‰ turbulence closure model were solved for different designs and flow conditions. For the base model, the results from simulation and experiments are in close agreement. Among the designs considered, the configuration, where the blades are in one line (zero circumferential angle between blades of two plane) and the midplane guide vane has concave side to the leading edge of the blade, performed relatively better. However, the performance was still less compared to the base model. The reason behind the reduction in performance from the base model is attributed to the blockage of flow and the change of flow path occurring due to the presence of the midplane GVs. The flow analysis of different cases and the comparison with the base model are presented in the current study.

Wells turbine is one type of axial turbine exclusively used for wave energy conversion in Oscillating Water Column type wave energy conversion device. It is a bi-directional turbine which can rotate in one direction irrespective of the direction of airflow. One of the main disadvantages of this turbine is the stall phenomenon, where the torque, as well as efficiency, drops drastically at a particular angle of attack. The postponement of stall can be achieved by installing fences along the chord of the blade at a distance from the hub. In the present work, a numerical analysis of Wells turbine with the stall fence is carried out using commercial CFD tool ANSYS. The performance characteristics of the turbine are investigated for different number of stall fences at different distances along the span of the blade. A detail flow analysis is presented to explain the effect of the stall fence on this particular turbine.

The Wells turbine is a self-rectifying air turbine, used in oscillating water column (OWC) to harvest wave energy. It produces unidirectional torque as the flow oscillates inside the OWC chamber. It has inherent disadvantage of narrow operating range due to stall at high airflow rate. Whereas, a wider operating range is essential to improve the turbine power output. A casing groove modifies the tip leakage flow pattern and improves the operating range. In addition, a radiused tip can alter the tip leakage flow and delay the stall. To enhance the performance further, this paper investigates the combined effect of tip groove and radiused tip (CG&RT) design modification. The flow was simulated by solving steady, incompressible Reynolds averaged Navier–Stokes equations in Ansys CFX 15.0. As expected, the CG&RT blade enhanced the relative operating range and the turbine power output by 44.4% and 23.8%, respectively.

A fluidic diode (FD) cascading concept was proposed and analyzed to determine the effect on the oscillating water column (OWC) wave energy converter performance. The FD, coupled with a twin-turbine, can improve energy conversion. The performance of the FD is given by the diodicity, which is the ratio of pressure drops. In this paper, the concept of cascading of FD is numerically investigated by solving the three-dimensional Reynolds Averaged Navier Stokes (RANS) equations. The commercial computational fluid dynamics (CFD) tool ANSYS FLUENT 16.1 is used for the present investigation. The present study showed that the cascading increased pressure drops in both directions, which reduces the diodicity compared to the base model. The performance of the twin turbine with cascade FD underperformed than the twin-turbine without FD model.

The oscillating water column type wave energy converters equipped with Wells turbine are one of the popular wave energy conversion devices. In most of the numerical and experimental studies, the Wells turbine characteristics are examined in no-load condition or with a fixed loading to achieve a fixed rotational speed. In the present work, a biplane Wells turbine is designed and tested in an experimental test facility. The test facility consists of a piston-chamber assembly that can generate sinusoidal airflow inside a duct. The turbine is placed inside the duct and tested for different stroke lengths and time periods of the piston, which produces a sinusoidal inlet airflow of different amplitude and time period. The turbine characteristics are studied at the no-load condition and for different values of resistive loading connected with the generator. The hysteresis behavior of the turbine is studied for two different flow coefficients based on experimentally observed and numerically calculated volume flow rates. Based on the experimental results, a detailed analysis of the turbine performance is presented for different operating conditions.

The Wells turbine is one of the candidates for use in Oscillating Water Column (OWC) type wave energy conversion devices. The narrow operating range of a Wells turbine limits its application to a small range of ocean environments. At a high angle of attack, the turbine performance drops suddenly due to a phenomenon known as stall. The present study introduces stall fences in the Wells turbine blade to postpone stall and widen the operating range. The stall fences are defined by the length, height, and thickness in percentage of blade chord length. For the present study, dimensions of the stall fences are determined by using a surrogate-based optimization technique. The modified and reference turbine are numerically studied by solving the Reynolds-Averaged-Navier-Stokes equations in the commercial CFD software ANSYS CFX 16.1. The comparison of fenced turbine with reference turbine shows 16.6% improvement in operating range at the cost of peak torque developed by the turbine. The peak-to-average power ratio in the stall-free range is reduced by 16.7% when stall fences are used. The change in internal flow due to the presence of stall fences is analyzed in detail in the present work.