Bidirectional Impulse Turbine Research Articles

Transient aerodynamic performance of bidirectional impulse turbine in reciprocating airflows for hydrokinetic energy conversion systems

As a part of hydrokinetic energy conversion systems, bidirectional impulse turbines are used in oscillating water columns (OWCs) to extract wave energy. Transient numerical simulations were implemented to predict the unsteady behaviors of reciprocating airflow. Firstly, the effects of blade thickness, blade rotation angle, and blade incident angle on the aerodynamics performance were investigated, and results shows that blade thickness has a slightly influence on turbine efficiency under steady-state condition, however, both the decrease of the rotation angle and the incident angle significantly increased the turbine efficiency. An efficiency peak of 57% was achieved with α = -6° and a flow coefficient of 1.0. Secondly, and pressure fluctuations of an impulse turbine were analyzed under sinusoidal flow, which shows that the energy loss of the turbine is attributed to the vortex generated near the downstream guide vanes. It is also shown that the pressure fluctuation is mainly caused by the unsteady incident wave, moreover, the pressure fluctuation frequency of blade surface is near to the incident wave frequency or a multiple of the incident wave frequency.

Bidirectional Impulse Turbine With Spiral Flow Collector for Tidal Energy Conversion

Abstract In order to make use of ocean renewable energy, a combination system of a bidirectional impulse turbine and a bidirectional flow collector for tidal current energy conversion is investigated in this paper. It is the advantage that this turbine system does not need an operation of orientation change according to the reversal of regular tidal orientation when fixed on the seabed. The experimental investigations by using both a circulating water tank and a towing tank showed that the turbine power output could be increased by adopting the flow collector proposed in this study. Then the flow collector with a fixed spiral vane named spiral flow collector was investigated by both a circulating water tank test and computational fluid dynamics (CFD) analysis. The experimental result of the spiral flow collector showed that the performance improvement was found on the increase of axial velocity in the turbine which contributed to the increase of the turbine power output. The results of CFD analysis showed that 180 deg of the skew angle of the fixed spiral vane was suitable in view of the angular moment at the turbine inlet in this case.

Экспериментальное исследование двунаправленной импульсной турбины в постоянном потоке газа

Экспериментальное исследование двунаправленной импульсной турбины в постоянном потоке газа

Surrogate based optimization of a Bi-Directional impulse turbine for OWC-WEC: Effect of guide vane lean and stagger angle for pseudo-sinusoidal wave conditions

An oscillating water column (OWC) wave energy device can use a bidirectional flow impulse turbine for energy extraction. The airflow velocity profiles during inhalation and exhalation of the OWC are asymmetric, and the flowrate at exhalation is higher. Hence, this article presents an optimized turbine to work for asymmetrical airflow conditions. The rotor blade setting angle (γ) was made asymmetric with a non-zero setting angle, and the guide vane shape was optimized. The unsteady Reynolds-averaged Navier-Stokes equations (URANS) were solved to get the objective function values for the Latin hypercube sampling (LHS) generated design space. A pseudo-sinusoidal velocity profile replicating the flow inside the OWC device was used for the transient simulations. A weighted average surrogate model generated the initial population for a hybrid genetic algorithm to produce optimum designs. The effect of turbine induced damping and starting characteristics were analyzed under irregular flow conditions obtained from the Pierson–Moskowitz wave spectrum. The optimized turbine resulted in better starting and running characteristics. Also, the mean efficiency of the optimized turbine was increased relatively by 9.5%.

Implementing a bidirectional impulse turbine into a thermoacoustic refrigerator.

A thermoacoustic model is used to efficiently implement a bidirectional impulse turbine into a thermoacoustic refrigerator. Experiments are done for several gas types and mean pressures to identify its influence on the turbine efficiency. A scaling is investigated in an attempt to provide a unique function of the turbine efficiency for all operating conditions. Furthermore, the ratio of acoustic power absorbed by the turbine over to the total amount of available power is examined for varying conditions. Finally, the results are used to present a case study in which the turbine is used to drive the fluid pumps of the device. The remaining acoustic power is used for cooling, thus providing an off-grid thermoacoustic refrigerator that works purely with low-grade heat as an input.

Coupled CAD-CFD automated optimization for leading and trailing edge of an axial impulse turbine blade

A bidirectional impulse turbine with fixed guide vanes is used in an oscillating water column to extract wave energy. The turbine suffers from low aerodynamic efficiency, and it is required to improve performance. In the present study, coupled CAD-CFD automated optimization of the blade leading and trailing edge ratio was performed to maximize the efficiency. The design points were generated using a central composite design sampling technique and response surface optimization method estimated the optimum design. The optimization pipeline was automated using the Ansys Design Exploration module. Ansys Turbo Grid was used for generating structured hexahedral elements in the computational domain, and the problem was solved in Ansys CFX® v16.2. The results showed that the modified leading and trailing edge enhanced the performance compared to the reference blade by minimizing the pressure drop. The optimized design improved the relative peak efficiency and torque by 3.4% and 2% respectively. Additionally, a detailed flow analysis has been reported in this paper.

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.

Experimental Investigation of a Bidirectional Impulse Turbine for Oscillating Flows at Various Resistive Loads

A bidirectional impulse turbine is a self-rectifying air turbine used in an oscillating water column wave energy converters. Most of the study on bidirectional impulse turbines involves steady-state performance analysis; however, the performance under oscillating airflow conditions is necessary to understand its behavior. The objective of this study is to experimentally analyze an optimized and numerically investigated bidirectional impulse turbine with fixed guide vane subjected to oscillating airflow conditions. A bidirectional airflow test facility developed at Indian Institute of Technology Madras, Chennai, India is employed to determine the aerodynamic characterization of the turbine and the dynamics involved in each of the coupling stages. The test rig consists of a piston chamber assembly, which provides different airflow rates by varying the stroke length (SL) and cycle time. Emphasis is made on the pressure and flow rate coefficients of the turbine, turbine-generator coupling, and power developed for different input conditions. The operating range of the turbine is mapped for four different frequencies and three SLs. Different electrical loading and the power output were analyzed for accelerations and decelerations of inflow and outflow. The preliminary dynamic characterization of the turbine with respect to nondimentionalized pressure coefficient and flow coefficient was determined for inflow and outflow. The power output is found to be in strong correlation with the flow rate and angular rotation of the rotor. The turbine analyzed in the experimental test rig will be proceeded with real sea testing on the Indian coast by the National Institute of Ocean Technology, Chennai, India.

Optimizing bidirectional impulse turbines for thermoacoustic engines.

The design of a bidirectional impulse turbine to convert thermoacoustic power into electricity is experimentally optimized. The turbine efficiency is measured for rotors with and without a shroud ring and for a varying tip clearance. Furthermore, the axial spacing between the guide vanes and rotor is varied with respect to the displacement amplitude of the acoustic wave. All measurements are carried out for several turbine loads and acoustic frequencies. For a chosen implementation, a design study on the guide vane and rotor blade geometry is presented to further optimize the bidirectional impulse turbine for thermoacoustic engines.

Experimental Investigation on Bi-Directiona Impulse Turbine with Flow Collector for Tidal Energy Conversion

The bi-directional impulse turbine and the bi-directional flow collector for tidal energy conversion is investigated in this paper. The bi-directional impulse turbine with fixed guide vanes is adopted because the turbine has a high efficiency and an advantage of maintenance. The turbine characteristics of the combined system of impulse turbine and collector are investigated experimentally by using the water tunnel. This system is proved to produce the power by a tidal flow experimentally. Three types of flow collector A, B and C are investigated, where the maximum radius of collector A is smaller than the ones of collector B and C. The velocity ratio of collector A is much smaller than the one for the cases of collector B and collector C, and the output power of collector A is very small compared to the other collectors. Nevertheless, the effect of flow collector is large because velocity ratio of collector A is much larger than the one without collector. Among three cases of 0.5, 0.6 and 0.7 of hub-to-tip ratio, the difference of turbine performance is not so large, but it is observed that the case for 0.5 of hub-to-tip ratio has inferior performance and the case for 0.6 of hubto-tip ratio has the performance among them. Further, the comparison of circulating water tank test and towing tank test was done to show the effect of choking ratio of cross sectional area of channel.

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.

Performance enhancement of an impulse turbine for OWC using grouped grey wolf optimizer based controller

This work deals with unsteady analysis and control of a bi-directional impulse turbine equipped in oscillating water column (OWC) wave energy converter (WEC). The Unsteady Reynolds-averaged Navier-Stokes equations (URANS) were solved to get the turbine characteristics and the maximum efficiency tracking for different axial velocities. The grouped grey wolf optimization (GGWO) algorithm finds the optimal gains of proportional-integral-derivative (PID) controllers of a permanent magnet synchronous generator (PMSG), such that a maximum efficiency tracking can be achieved. The URANS analysis show that the best efficiency point (BEP) occurs at a flow coefficient of 1.25. The GGWO based controller increases efficiency by 61.5% and 4% compared to the uncontrolled and conventionally controlled case, respectively and limits the peak-to-average power ratio by 38.6% compared to the uncontrolled case.

Effect of hub-to-tip ratio on the performance of bi-directional impulse turbine with flow collector for tidal energy conversion

The bi-directional impulse turbine and the bi-directional flow collector for tidal energy conversion is investigated in this paper. The bi-directional impulse turbine with fixed guide vanes is adopted because the turbine has a high efficiency and an advantage of maintenance. The turbine characteristics of the combined system of impulse turbine and collector are investigated experimentally by using the water tunnel. This system is proved to produce the power by a tidal flow experimentally. Three types of collector A, B and C are investigated, where the maximum radius of collector A is smaller than the ones of collector B and C. The velocity ratio of collector A is much smaller than the one for the cases of collector B and collector C, and the output power of collector A is very small compared to the other collectors. Nevertheless, the effect of flow collector is large because velocity ratio of collector A is much larger than the one without collector. Among three cases of 0.5, 0.6 and 0.7 of hub-to-tip ratio, the difference of turbine performance is not so large, but it is observed that the case for 0.5 of hub-to-tip ratio has inferior performance and the case for 0.6 of hub-to-tip ratio has the performance among them.

Numerical Analysis of Bi-directional Impulse Turbine Performance for Thermoacoustic Power Generators

As a new type of acoustoelectric conversion method, bi-directional impulse turbine provides great potential for developing large scale and economic thermoacoustic power generators. In this paper, the performance of bi-directional impulse turbine with fixed guide vanes has been studied via 2D CFD modelling by commercial software Fluent. Firstly, the effects of blade structure and gas flow incident angles on the shaft power and efficiency have been investigated. Then the performance of the turbine has been studied under both steady and oscillating flow. Additionally, flow field features for the turbine in oscillating flow were presented for a better understanding. The results show that optimal flow incident angle for shaft power and efficiency are 20° and 70° respectively which indicates the difficulties in turbine design. The angles of the fluid including the gas flow incident angle and the blade angle are the most important parameter for turbine performance. The shaft power of rotor blades is more sensitive to the blade angle around the optimal incident angle region while the efficiency is not. The optimum flow coefficient is 2-3for maximum efficiency both in steady flow and oscillating flow. Increasing of the incoming flow oscillation frequency decrease the efficiency of the turbine. This loss mainly due to increased flow hysteresis effect which make the flow angle deviate from the design more.

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

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

Shape optimization of a bidirectional impulse turbine via surrogate models

ABSTRACTIn this work, a bidirectional impulse turbine used in a wave energy device is simulated using a CFD technique and a shape optimization performed with multiple surrogates-assisted multi-objective evolutionary algorithm. The surrogates have been generated using the validated CFD technique. The objectives for the optimization are to maximize the shaft power and to minimize the pressure drop across the turbine. The hub and the tip thickness of the rotor blade profiles are modified and considered as the design variables. The Latin hypercube sampling technique generated design points are evaluated in the CFD solver, the objective responses are used to construct multiple surrogates, and a Pareto optimal front is generated through a multi-objective optimization approach. The turbine efficiency, which is the function of pressure drop and shaft power, is relatively increased by 10.4%.Abbreviations: BPS: best PRESS; GV: Guide vane; KRG: kriging; LE: leading edge; MOO: multi-objective optimization; OWC: oscillating water column; PRESS: predicted error sum of squares; PS: pressure side or pressure surface; RB: rotor blade; RBNN: radial basis neural network; Ref: reference; RMS: root mean square; RSA: response surface approximation; SS: suction side or suction surface; TE: trailing edge; WAS: weighted average surrogates

Study on Bi-Directional Impulse Turbine with Flow Collector for Tidal Energy Conversion

Study on Bi-Directional Impulse Turbine with Flow Collector for Tidal Energy Conversion

Possibility of using a bi-directional impulse turbine in a thermo-acoustic engine

The paper is devoted to one of engine types with external heating a thermoacoustic engine. Ways of transforming the energy of a shock wave of oscillating gas flow into electric energy are discussed. The authors suggest using a bidirectional impulse turbine as an energy converter. The distinctive feature of this kind of turbine is that the shock wave of oscillating gas flow passing through the turbine is reflected and passes through the turbine again in the opposite direction. The direction of turbine rotation does not change in the process. Different types of bidirectional impulse turbines for thermoacoustic engines are analyzed. The Wells turbine is the simplest and least efficient of them. A radial impulse turbine has more complicated design and is more efficient than the Wells turbine. The most appropriate type of impulse turbine was chosen. This type is an axial impulse turbine which has a simpler design than that of a radial turbine and similar efficiency. The peculiarities of the method of calculating an impulse turbine are discussed. They include changes in gas pressure and velocity as functions of time during the generation of gas oscillating flow shock waves in a thermoacoustic system.

Multi-objective optimization of a bidirectional impulse turbine

Real-life engineering problems have multiple objectives, which mostly are conflicting in nature, and these problems can be solved through multi-objective optimization (MOO) procedure. In the present problem, a high-fidelity computational fluid dynamics model coupled with multiple-surrogate assisted genetic algorithm based MOO has been solved for performance enhancement of a wave energy extracting axial impulse turbine. Response surface approximation, Kriging, neural network and a weighted-average surrogate (WAS) were used to generate population for the MOO procedure and Pareto optimal fronts (PoF) of the objectives were produced. The design variables were number of rotor blade and guide vanes and the objectives were minimization of pressure drop and maximization of shaft power of the turbine. It was found that a cross-validation error analysis is inevitable to find the degree of fitness of a surrogate. The WAS-produced PoF shows better performance as compared to that of the other surrogates. The surrogates based on minimum cross-validation errors produce slightly lesser performance than the WAS. The efficiency, which is a function of both the objectives, was relatively increased by ∼11% through the current investigation.