Bi-directional Turbine Research Articles

The Experiment Study on the Utilization of Standing Wave Thermoacoustic Engine to Drive Wells Bi-Directional Turbine

Standing wave thermoacoustic engine (SWTE) is a device for converting heat to propagate acoustic wave within straight and tubular of the resonator. The advantages of this engine include being able to use the waste heat as a source of heating, no moving parts and environmentally friendly. The utilization of this acoustic wave is to rotate air turbine because its movement that goes back and forth. The type of air turbine that appropriates to this character one of these is Wells bi-directional turbine, which is always rotated in the same direction regardless of the moving air direction. This study aims to investigate the performance of Wells turbine when paired with SWTE in the variation on geometry shape of blade and hub to tip ratio. The Wells turbine was embedded inside resonator of this engine has a diameter of 50 mm in the manner of the hub to tip ratio 0.6. The geometry shape of blade varied with airfoil type of NACA 0015, NACA 0018 and NACA 0024. SWTE was generating 4,67 kPa acoustic pressure and 138 Hz frequency within 52 mm inside diameter, 390 mm length of the resonator. The result was the Wells turbine NACA 0018 has rotational motion 2449 rpm, higher than the others types. Wells turbine NACA 0018 then tested with variations of the hub to tip ratio. Results showed that are generated rotational motion at 2614 rpm, 2449 rpm and 1555 rpm for 0.5, 0.6, 0.7 hub to tip ratio, respectively.. It can be concluded that the Well turbine NACA 0018 with hub to tip ratio 0,5 has best performance compare to the others.

A Traveling Wave Thermoacoustic Engine—Design and Test

Abstract The demand for clean, sustainable, and cost-effective energy continues to increase due to global population growth and the corresponding use of consumer products. The provision of heat to a thermoacoustic prime mover results in the generation of an acoustic wave that can be converted into electrical power. Thermoacoustic devices offer highly reliable and transportable power generation with low environmental impact using a variety of fuel sources. This paper focuses on the design and testing of a single-stage, traveling-wave, thermoacoustic engine. The system configuration, component design, and integration of sensors will be described. Performance testing and system analysis show that for a 300 W heat source, the thermoacoustic machine generates a 54 Hz acoustic wave with a thermal efficiency of 7.8%. The system’s acoustic power output may be increased by 84% through improved heat exchanger design. Tuning of the acoustic system and optimization of the bi-directional turbine merit attention to realize an applicable waste heat energy harvesting system.

Oscillating Water Column Wave Energy Converter for Low Wave Height Conditions

For continuous and uninterrupted extraction of energy from marine wave motion, majority of wave energy extraction systems employ bi-directional turbines. The aerodynamic loss due to symmetrical placement of guide vanes causes a major loss in power output of the system. To optimize this problem, researchers have developed and tested a variety of oscillating water column air turbines. Most commonly used are the axial turbines because of their simplicity and operational ease. The present work focuses upon design of an oscillating water column energy extraction system based on uni-directional axial impulse turbine with a novel rectifying system arrangement which primarily focuses to minimize the losses due to downstream guide vanes and in turn shoot up the power output for low wave height conditions. A numerical model was developed and investigated using RANS equations and k-omega SST turbulence model. The results obtained portrays that the proposed flap based bi-directional impulse system is operationally viable and produces substantially greater power output in comparison to conventional bi-directional and uni-directional turbine systems under low wave height conditions. A hybrid choking scheme was followed which resulted in additional power output. Results show that full choking of the idle turbine is ensured during the inhalation cycle, which was not possible in existing models. During the exhalation cycle, additional power output was also obtained from the secondary turbine i.e., front end turbine during exhalation cycle. The proposed system generates maximum total power output at around flow coefficient of 1.

Design of a new turbine for OWC wave energy converters: The DDT concept

Oscillating Water Column (OWC) has attracted significant research efforts in the field of wave energy technology in the last decades. Recently, the Twin Turbines Configuration (TTC) has received attention because it is based on the use of unidirectional turbines which are much more efficient. Nevertheless, its main disadvantage with respect to classic OWC systems equipped with bidirectional turbines is the duplicity of equipment. To overcome this limitation, the Double Decker Turbine (DDT) concept is presented here as a new turbine which combines the best of both solutions, the TTC and the bidirectional turbine, in which the geometrical design of the DDT has been carried out based on a well-tested geometry taken from the bibliography. In addition, CFD modelling has been used to obtain an optimized DDT by means of a comparison between two new geometries for the outer turbine; while the inner turbine geometry has been already taken from the literature. Outer turbine has been further validated through experimental measurements of a manufactured prototype. Finally, a non-steady analysis of the proposed double turbine is carried out assuming sinusoidal flow conditions. Results demonstrate that the DDT concept can compete with the other alternatives, even envisaging high-performance characteristics to be developed in future works.

Acoustic characteristics of bi-directional turbines for thermoacoustic generators

Bi-directional turbines combined with rotary motors may be a feasible option for developing high power thermoacoustic generators with low cost. A general expression for the acoustic characteristics of the bi-directional turbine was proposed based on theoretical derivation, which was validated by computational fluid dynamics modeling of an impulse turbine with fixed guide vanes. The structure of the turbine was optimized primarily using steady flow with an efficiency of near 70% (the shaft power divided by the total energy consumed by the turbine). The turbine in the oscillating flow was treated in a lumped-parameter model to extract the acoustic impedance characteristics from the simulation results. The key acoustic impedance characteristic of the turbine was the resistance and inertance due to complex flow condition in the turbine, whereas the capacitance was treated as an adiabatic case because of the large-scale flow channel relative to the heat penetration depth. Correlations for the impedance were obtained from both theoretical predictions and numerical fittings. The good fit of the correlations shows that these characteristics are valid for describing the bi-directional turbine, providing the basis for optimization of the coupling between the thermoacoustic engine and the turbine using quasi-one-dimensional theory in the frequency domain.

Experimental study of a small scale bi-directional axial impulse turbine for acoustic-to-mechanical power conversion

Abstract Axial impulse turbines have been utilized for oscillating water column wave-energy conversion because of their wide operating range without stalling point. Previous studies in the oscillating-flow environment gave no information on the performance of these turbines at high frequencies. This study extends the use of these turbines to conditions close to those encountered in thermoacoustic power generators, which require the turbine to operate at a large frequency in a closed duct. The use of bi-directional turbines as acoustic-to-mechanical power converters brings several advantages, such as their low acoustic impedance, in comparison with linear alternators, which facilitates integration with thermoacoustic engines. In the study, a variable-frequency test rig is set up using atmospheric air. Then, the performance of the bi-directional impulse turbine is studied at different rotor inlet/exit angle, rotor space-to-chord ratio, stator space-to-chord ratio, stator exit angle, and tip clearance. The dependence of the conversion efficiency on flow coefficient is reported over a set of constant input gas parcel velocities. The study also introduces an impedance segment to simulate the turbine on Delta-EC. The peak efficiency of the improved case is found to be 35.2% at a flow coefficient of 0.22, resulting an improvement of 38% over the reference case.

THE ANALYSIS OF FLUID DYNAMICS OF WAVE POWER STATION WITH WELLS TURBIN BY CFD

Natural energy such as wind, wave and other natural vibrations is one of the high potential renewable energy sources. The Wells turbine is based on the use of bidirectional turbines, which act as axial-flow self-rectifying turbines that employs a symmetrical blade profile and rotating unidirectionally in reciprocating airflows generated by the air chamber to extract energy from vibrations. These topics have been extensively studied both numerically and experimentally such as research on the parameters of the effects of structure, angle of attack, blade shape, etc. In this paper, numerical simulation is carried out using commercially available tool Fluent for fluid dynamics analysis and focus on oscillating predictions, with particular attention to the behavior of the flow. Based on the Numerical Wave Tank (NWT) model is simulated in a two dimensional used in this model, which is constructed mainly based on the spatially averaged Navier Stokes equation with the k-ε model for simulating the turbulence and modeled with Volume of Fluid (VOF). Axial-flow turbines system and future development as well as the proposed limitations will be discussed in detail.

THE ANALYSIS OF FLUID DYNAMICS OF WAVE POWER STATION WITH WELLS TURBIN BY CFD

Natural energy such as wind, wave and other natural vibrations is one of the high potential renewable energy sources. The Wells turbine is based on the use of bidirectional turbines, which act as axial-flow self-rectifying turbines that employs a symmetrical blade profile and rotating unidirectionally in reciprocating airflows generated by the air chamber to extract energy from vibrations. These topics have been extensively studied both numerically and experimentally such as research on the parameters of the effects of structure, angle of attack, blade shape, etc. In this paper, numerical simulation is carried out using commercially available tool Fluent for fluid dynamics analysis and focus on oscillating predictions, with particular attention to the behavior of the flow. Based on the Numerical Wave Tank (NWT) model is simulated in a two dimensional used in this model, which is constructed mainly based on the spatially averaged Navier Stokes equation with the k-ε model for simulating the turbulence and modeled with Volume of Fluid (VOF). Axial-flow turbines system and future development as well as the proposed limitations will be discussed in detail.

Effect of wall inclination on the dynamic behaviour of an oscillating water column system

The Oscillating Water Column device (OWC) is one of the most used Wave Energy Converters (WECs) for wave energy harvesting. It consists essentially of two parts: the pneumatic chamber made of concrete and the bidirectional turbine linked to a generator group for energy production. In this study we are interested in the water motion oscillation inside the chamber resulting from the water level perturbation. This process is characterized by its own natural frequency and global damping. The vertical OWC chamber model is limited by the number of parameters defining the natural frequency and the global damping. The objective of this paper is to improve the performances obtained for the vertical OWC by considering an OWC with inclined sidewalls. For maximum efficiency, the device must operate in the resonance domain where the damping is low and the frequency of incoming waves matches with the natural frequency of the OWC. This will theoretically amplify the pneumatic energy to be converted to a mechanical one in the turbine.

Performance Evaluation of a Tidal Current Turbine with Bidirectional Symmetrical Foils

As one might expect, tidal currents in terms of ebb and flood tides are approximately bidirectional. A Horizontal Axial Tidal Turbine (HATT) with unidirectional foils has to be able to face the current directions in order to maximize current energy harvesting. There are two regular solutions to keep a HATT always facing the direction of the flow, which are transferred from wind turbine applications. One is to yaw the turbine around the supporting structure with a yaw mechanism. The other is to reverse the blade pitch angle through 180° with a pitch-adjusting mechanism. The above solutions are not cost-effective in marine applications due to the harsh marine environment and high cost of installation and maintenance. In order to avoid the above disadvantages, a turbine with bidirectional foils is presented in this paper. A bare turbine with bidirectional foils is characterized in that it has nearly the same energy conversion capability in both tidal current directions without using the yaw or pitch mechanism. Considering the working conditions of the bidirectional turbine in which the turbine is installed on a mono-pile, the effect of the mono-pile on the turbine’s performance is evaluated in this paper, especially when the turbine is downstream of the mono-pile. The paper was focused on the evaluation of the hydrodynamic performance of the bidirectional turbine. The hydrodynamic performance of the bare bidirectional turbine without any supporting structure was evaluated based on a steady-state computational fluid dynamics (CFD) model and model tests. Performance comparison has been made between the turbine with bidirectional foils and the turbine with NACA foils. The effect of the mono-pile on the performance of the bidirectional turbine was studied by using the steady-state and the transient CFD model. The steady-state CFD model was used to evaluate the effect of the mono-pile clearance, which is the distance between the mono-pile and the turbine on the performance of the turbine. The transient CFD model was used to determine the time-dependent characteristics of the turbine, such as time-dependent power and drag coefficients. The results show that the bare bidirectional turbine has nearly the same energy conversion capability in both tidal current directions. The performance of the bidirectional turbine is inferior to the turbine with NACA foils. At the designed tip speed ratio, the power coefficient of the turbine with NACA foils is 0.4498, which increases by 1.6% compared to the 0.4338 of the bidirectional turbine. The turbine’s performance decreases due to the introduction of the mono-pile, and the closer the turbine is to the mono-pile, the greater effect on the turbine’s performance the mono-pile has. At the designed clearance of 1.5 DS, the presence of a mono-pile decreases the peak Cp value by 1.82% and 3.17% to a value of 0.4156 and 0.4004 for the turbine located in the mono-pile upstream and downstream, respectively. The mono-pile can result in the fluctuation of the turbine’s performance. This fluctuation will detrimentally harm the life of the turbine as it will lead to increased wear and fatigue issues.

Characterization of bidirectional impulse turbines for thermoacoustic engines.

A bidirectional impulse turbine to convert thermoacoustic power into electricity is investigated. Experimental measurements are done with a loudspeaker for varying acoustic conditions and turbine loads. The results are used to characterize the turbine performance and compare it to steady flow turbomachinery and turbines in oscillating water columns. A dimensional analysis is done to identify the variables that influence the turbine performance, after which a scaling is determined that uniquely determines the efficiency of the turbine. The work is finished by providing the impedance of the bidirectional turbine such that it can be implemented in a thermoacoustic engine.

A comparative study of bi-directional airflow turbines

A comparative study of bi-directional airflow turbines

Nature-inspired design of a turbine blade harnessing wave energy

A bidirectional turbine used in an oscillating water column device extracts wave energy from oscillating airflow. To improve its power output, a concept of static extended trailing edge found in the wings of owl and merganser was adopted. The static extended trailing edge with 0–10% of chord length ( C) was analyzed for different flow coefficients via Reynolds-averaged Navier–Stokes equation-based computational fluid dynamics (CFD) analysis. ANSYS-CFX 15.0 was used to simulate the flow. Grid convergence index was calculated to obtain optimum mesh, and numerical validation was done with experimental results. The static extended trailing edge with 5% C enhanced relative mean torque by 23.4% and, reduced relative mean efficiency by 5.4%, before stall condition. The modification increased pressure difference between the suction side and the pressure side and enhanced torque. The increased pressure drop reduced the efficiency. A further longer static extended trailing edge showed poorer stall characteristics.

ЕКСПЕРИМЕНТАЛЬНІ ДОСЛІДЖЕННЯ РОБОЧИХ ПРОЦЕСІВ В ТЕРМОАКУСТИЧНОМУ ТУРБОГЕНЕРАТОРІ

Thermoacoustic thermal machines (TATM) is a relatively new and non-common type of thermal machines that differs significantly from conventional mechanical systems due to the lack of moving elements, environmental safety, and the ability to operate from external sources of energy. Thermoacoustic engines (TAE) - direct-acting thermal machines that are capable of converting thermal energy into mechanical in the form of powerful acoustic waves. The growing interest to TATM is related to the possibility of using them in energy saving systems since the introduction of energy saving technologies is an effective method for increasing the efficiency of power plants and reducing their harmful effects on the environment. The wide introduction of TATM is hampered by their low specific power, the complexity of the transformation of acoustic oscillations into mechanical work and lack of experience.The article presents the results of experimental research on the operational characteristics of the thermoacoustic turbogenerator (TATG). The TATG consists of a thermoacoustic engine, which operates in the Brighton thermodynamic cycle and an electric generator. As an actuator of an electric generator, a pulsed bi-directional turbine was used. It is capable of converting the oscillatory motion of the working medium into mechanical energy. In the course of experiments, data were obtained on external characteristics of both TAE and TATG at different load conditions. The interaction of a pulsed bi-directional turbine with a pulsating working medium leads to the appearance of complex radial currents in the resonator that affects the efficiency of the energy conversion processes.In the work, using CFD simulation, the peculiarities of formation and development of radial currents were studied. Boundary and initial conditions were imposed based on experimental data. The results of CFD experiments allowed us to study the influence of various factors on the intensity of radial currents. It is shown that radial currents exist in the form of quasistationary pulsating structures whose length depends on the amplitude of the oscillatory motion of the pulsating medium and the frequency of acoustic oscillations. The presence of these currents leads to the "desired" flow of input into the rectifying apparatus of the impulse turbine. According to the results of the research, technical solutions are proposed that prevent the formation of such currents.

The Experimental Study of Bi-Directional Impulse Turbine on Standing Wave Thermoacoustic Engine

Bi-directional air turbine has one of the primary functions, namely changing the linear movement of air into a rotating motion. This rotating motion is always in the same direction regardless of the direction of air movement. This bi-directional turbine impulse type moves by using thermoacoustic waves which result from the conversion of heat energy into acoustic energy. T he turbine using in this research has a diameter of 48 mm and 50 mm. Besides, the turbine also has a variety of blade numbers and variations of distance from the sound source. The impulse turbine research with 50o inlet angle obtained results that the maximum rotational motion in the turbine with a diameter of 50 mm and the number of blades 28. The optimal results were purchased at a distance of 20 0 m m from the sound source which was 361 rpm.

High-performance ocean energy harvesting turbine design – Detailed flow analysis with blade leaning strategy

Oscillating water column wave energy converter is having low efficiency because of its principal component, a bidirectional turbine. An analysis of the internal flow of the turbine gives an idea of improving the performance through optimization of geometrical parameters. In this study, an impulse turbine of 0.3 m diameter with fixed guide vanes is numerically simulated by solving three-dimensional incompressible steady Reynolds averaged Navier-stokes equation with two-equation turbulence closure model. This study shows that the numerical results very well match with the experimental results. The detailed flow physics demonstrates that different types of losses occur in this type of turbine and shows that the downstream diverging path of the rotor and guide vane is responsible for low performance. In this study, the effect of guide vane lean, as well as the combined rotor and guide vane lean on the performance of the turbine, has been discussed in detail and found to increase the efficiency of the turbine.

Review on the conversion of thermoacoustic power into electricity.

Thermoacoustic engines convert heat energy into high amplitude acoustic waves and subsequently into electric power. This article provides a review of the four main methods to convert the (thermo)acoustic power into electricity. First, loudspeakers and linear alternators are discussed in a section on electromagnetic devices. This is followed by sections on piezoelectric transducers, magnetohydrodynamic generators, and bidirectional turbines. Each segment provides a literature review of the given technology for the field of thermoacoustics, focusing on possible configurations, operating characteristics, output performance, and analytical and numerical methods to study the devices. This information is used as an input to discuss the performance and feasibility of each method, and to identify challenges that should be overcome for a more successful implementation in thermoacoustic engines. The work is concluded by a comparison of the four technologies, concentrating on the possible areas of application, the conversion efficiency, maximum electrical power output and more generally the suggested focus for future work in the field.

Effect of Blade Profiles on the performance of Bidirectional Wave Energy Turbine

To fulfill the ever growing demands of world energy consumption, the wave energy should be extracted economically. The oscillating water column is most commonly used to xtract energy from waves. It consists of a chamber in which waves drives the entrapped air column to rotate the Wells turbine. The Wells turbine is a self-rectifying low-pressure axial reaction turbine with 90ο stagger angle. These turbines consist of symmetrical airfoil profile to achieve unidirectional rotation for the bi-directional airflow. The turbine performance predominantly depends on the aerodynamic characteristics of the airfoil profile used. In this study, the performance of Wells turbine with various symmetrical airfoil profiles was analysed using ANSYS CFX 14.5. The CFD analysis was performed by solving three dimensional steady Reynolds averaged Navier-Stokes equation with k-ω SST turbulence closure model. The reference geometry has NACA0015 as blade profile and the CFD results were compared with the experimental values. The performance characteristics of the new airfoil profiles were compared with the reference case to analyse the suitability of airfoils in wave energy extraction. The NACA0021 airfoil profile showed better performance in the post-stall regime compared to the NACA0015 and the S1046 airfoil profiles.

Output Power Improvement of Bi-directional Impulse Turbine with Flow Collector for Tidal Energy Conversion

Output Power Improvement of Bi-directional Impulse Turbine with Flow Collector for Tidal Energy Conversion

Measurement of conversion efficiency from acoustic power to axial output using bidirectional impulse turbine

Measurement of conversion efficiency from acoustic power to axial output using bidirectional impulse turbine