Axial Turbine Research Articles

Numerical Investigations on Effect of Inflow Parameters on Development of Secondary Flow Field for Linear Low-Pressure Turbine Cascade

Abstract Endwall flows contribute the most crucial role in loss generation for axial flow turbine and compressor blades. These losses lead to modifying the blade loading and overall performance in terms of stable operating range. The present study aimed to determine the endwall flow streams in a low-speed low-pressure linear turbine cascade vane using a numerical approach. The study includes two sections. The first section includes an attempt to understand different secondary flow streams available at the endwall. The location of the horseshoe vortex and subsequent vortex patterns are identified in the section. The selection of a suitable turbulence model among shear stress transport (SST) k–ω and SST γ–θ to identify endwall flow streams is studied prior to the section. The steady-state numerical study is performed using Reynolds Averaged Navier–Stokes equations closed by the SST γ–θ turbulence model. The computational results are validated with experimental results available in the literature and are found to be in good agreement. The study is extended for different inflow conditions in a later section. The second section includes the effect of flow incidence and turbulence intensity on the endwall secondary flow field. Four different inflow incidences are considered for the study. The inlet turbulence intensities are varied by 1% and 10% for each case. The results revealed different secondary flow patterns at an endwall and found the change in behavior with inflow conditions. SST γ–θ turbulence model with lower turbulence intensity is more suitable to identify such flow behavior.

Multi-objective optimization of the ORC axial turbine for a waste heat recovery system working in two modes: cogeneration and condensation

Due to the demand of the district heating network and electric power grid ORC turbines can operate in the condensation and cogeneration modes. This approach requires the design of an expander which is characterized by high efficiency in each mode of operation. The paper is devoted to a multi-objective efficiency optimization of a one stage axial ORC turbine working on MM (Hexamethyldisiloxane). An Implicit Filtering algorithm (IF) is used to find a flowpath with maximum efficiency. During the optimization the rotor profiles (at the hub and shroud) and the shape of endwall contours of the rotor domain are changed. Five optimization tasks are carried out with different weights of the efficiency of both modes of operation. Pareto fronts are obtained and a decision-making method is used to select an optimum solution. The optimization of the rotor row allows for significant efficiency improvements in two regimes of operation, with respect to a baseline geometric configuration designed with the help of classical methods.

Axial sCO[formula omitted] high-performance turbines parametric design

Supercritical CO2 thermal cycles provide low complexity and small size of equipment compared to the Rankine cycle. However, higher power units of hundreds of megawatts have not yet been implemented. This study focuses on sCO2turbines for high power cycles and presents an estimation of their dimensions, efficiency, and other parameters. For this purpose, a specialized calculation code named TACOS was built. The turbines are designed for inlet pressures of 25MPa and 30MPa and inlet temperatures from 300°C to 600°C. In total, more than 460 high-performance axial turbines were designed in this study. The turbines have been optimized with shaft power from 10MW to 2,000MW (one-flow configuration) for revolutions from 3,000rpm to 12,000rpm. The results show that supercritical CO2 turbines are about one-fifth the size of their steam alternatives with comparable efficiencies. Turbines with synchronous revolutions (50Hz) achieve the highest efficiency for shaft power in one-flow configuration up to 500MW and this correspond to an efficiency close to 90%. High-speed turbines are suitable for power levels up to 50MW with efficiencies of around 87%. The vast majority of turbines come out as three-stage or four-stage.

Experimental investigations on an inline low head axial flow turbine with hydrofoil shaped vanes

ABSTRACT Low-head propeller turbines are becoming more popular due to their ease of installation and low cost. The turbines are appropriate for some urban areas where a limited amount of power is required and renewable sources are readily available. The current study’s objective is to study such a turbine and alter its geometry to boost production. To improve the efficiency of the four-bladed turbine, the NACA 0012-shaped hydrofoil is used in place of conventional blades. The rotors were designed with different chord angles of attack in relation to flow direction. The experiments were carried out at the 95°, 100°, 105°, 110°, 115°, and 120° angles for the various corresponding head conditions. The redesigned rotors were all tested for different loads, Reynolds numbers, and flow discharge. The experimental results show that an angle of attack of 110° has an optimum performance of 86.70% for a head of 0.012 m. The maximum power produced by 110° is 0.204 W. The 95° angle for the same head had the lowest efficiency, which was 20.63%.

BINARY ELECTRICAL GENERATING INSTALLATION FOR UTILIZATION HEAT OF BOILER FLUE GASES

The work is devoted to the development of modern thermal schemes for the production of electrical energy while utilizing the heat of flue gases from boilers of power units. On the example of a typical district boiler house, the parameters and potential of heat discharged into the atmosphere with the flue gases of boilers are investigated, and it is determined that they are sufficient to generate electrical energy by implementing the so-called organic Rankine cycles. To utilize the heat of exhaust gases with a temperature of 280 °С at a flow rate of 10 kg/s, a three-loop power generating plant similar to those used in geothermal energy was studied. In the process of conducting research related to solving the problem, the thermal scheme was improved. A number of turbine working bodies that meet the necessary requirements are analyzed and the most suitable ones are recommended. Taking into account the characteristics of the heat source, in order to determine the rational configuration of the circuit, 50 calculations of thermal circuits of power plants on different working fluids were performed. The research results showed that the efficiency (electrical efficiency) and power of the turbine cycle are determined by the waste heat potential, the thermodynamic properties of the working fluid, the structural and parametric characteristics of the circuit. Among the studied indicators, the best indicators are: electrical efficiency of 20,6 %, a "useful" electrical power of 357 kW at a flue gas temperature of 131 °C was a three-circuit utilization plant with working bodies Water / R-245fa / R-245fa. The variant of the circuit with working fluids Water / R-600a / R-600a lost ~ 8 kW of electric power to the best variant, but was recognized as more promising, since R-600a (isopropane) Freon has consumer advantages over R-245fa. Computational studies of the binary thermal scheme of the power plant were also carried out, which showed that it is rational to use Water for the 1st circuit, R-600a for the 2nd circuit. This solution made it possible to obtain the calculated "useful" electric power of the energy complex ~ 290,8 kW (1st circuit ~ 129 kW, 2nd circuit ~ 161,8 kW). The loss of the binary scheme in terms of "useful" electric power to the promising version of the three-loop scheme is compensated by a significant simplification of the thermal scheme and, as a result, significantly lower capital costs. The specific mass of the proposed heat exchange equipment of the installation with a binary thermal scheme is ~ 150 kg/kW. Taking into account the properties of the working fluids, a preliminary study of the structures of the turbines of the 1st (Water) and 2nd (R-600a) circuits was carried out. For the 1st circuit, it is proposed to use a 6-stage axial turbine, for the 2nd – a single-stage radial. The geometric characteristics of the flow parts of turbines are determined by calculation. A preliminary simplified assessment of a simple payback period indicates good prospects for the implementation of the proposed energy-saving installation.

Global linear stability analysis of flow inside an axial swirl generator with a rotating vortex rope

In hydraulic turbines, either Francis or axial turbines, a high swirling flow is generated at PL conditions at the inlet of the draft tube resulting in the formation of a rotating vortex rope (RVR). This leads to pressure fluctuations which limit the operating range of single regulated turbines. In the present study, an axial hydraulic turbine has been numerically simulated by the k−ϵ and SST-based Scale-Adaptive Simulation model (SST SAS) turbulent models to capture helical RVR. Considering the formation of the RVR as the result of a global instability, linear global stability analysis of the time-averaged turbulent flow field has been conducted. For the first time in axial hydraulic turbines, how boundary conditions affect the unstable mode and which frequency, plunging or rotating, is related to the vortex rope instability have been studied. It is found that the flow inside the draft tube is sensitive to the asymmetrical disturbances with a frequency close to the rotational component.

On Dynamics of Flow past a Stage Axial Air Turbine

The air flow inside a single-stage test turbine is studied experimentally using the Particle Image Velocimetry technique. The measurements were performed at the axial-tangential plane just behind the rotor at the middle blade radius. The large vortical structures are identified in the shear layers between the blade wakes and channel jet. The phase-locked structures topology of random dynamical structures in the flow behind the stage are to be analysed using the Proper Orthogonal Decomposition method.

Experimental investigation on the effect of axial gap on performance and unsteady pressure pulsations of low head axial flow hydraulic turbine

The stable operation of axial flow turbines (AFTs) in the energy conversion process directly affects their safety and performance. Because of its unstable pressure features, a dynamic analysis of its internal flow characteristics is required. To analyze, evaluate, and compare the pressure variation within the turbine under the base gap (Ƣ = 0.05D) and different axial gaps (Ƣ) of 0.09D, 0.14D, and 0.18D, a reliable measurement approach is required. Pressure sensors were installed on the flow domain of the AFT to measure dynamic pressure pulsation under various Ƣ and running flow conditions. Based on the experimental result, a 28% and 2.8% increase in turbine efficiency was recorded when the Ƣ was increased from 0.05D to 0.09D at 0.8Qd (design flow rate) and 1.0Qd, respectively.Further analysis of the frequency spectra reveals different unsteadiness in the flow structures due to changes in Ƣ which resulted in various excitation signals. A decrease in the Ƣ leads to an increase in pressure pulsation intensity. Consequently, AFT with Ƣ of 0.09D was recommended since it provides maximum efficiency with fewer pulses compared with Ƣ = 0.05D, where the vibrations are at peak value. The findings above will aid in the optimum use of energy resources since energy generated from AFT is clean and free of pollution and can lead to a sustainable energy generation process.

A Recent Advance on Partial Evaporating Organic Rankine Cycle: Experimental Results on an Axial Turbine

The organic Rankine cycle (ORC) technology is an efficient way to convert low-grade heat from renewable sources or waste heat for power generation. The partial evaporating organic Rankine cycle (PEORC) can be considered as a promising alternative as it can offer a higher utilization of the heat source. An experimental investigation of a small ORC system used in full or partial evaporation mode is performed. First characterized in superheated mode, which corresponds to standard ORC behavior, a semi-empirical correlative approach involving traditional non-dimensional turbomachinery parameters (specific speed, pressure ratio) can accurately describe one-phase turbine performance. In a second step, two-phase behavior is experimentally investigated. The efficiency loss caused by the two-phase inlet condition is quantified and considered acceptable. The turbine two-phase operation allows for an increase in the amount of recovered heat source. The ability to operate in two phases provides a new degree of flexibility when designing a PEORC. The semi-empirical correlative approach is then completed to take into account the partially evaporated turbine inlet condition. The qualitative description and the quantitative correlations in the one-phase and two-phase modes were applied to different pure working fluids (Novec649TM, HFE7000 and HFE7100) as well as to a zeotropic mixture (Novec649TM/HFE7000).

An Advanced Multifidelity Multidisciplinary Design Analysis Optimization Toolkit for General Turbomachinery

The MDAO framework has become an essential part of almost all fields, apart from mechanical, transportation, and aerospace industries, for efficient energy conversion or otherwise. It enables rapid iterative interaction among several engineering disciplines at various fidelities using automation tools for design improvement. An advanced framework from low to high fidelity is developed for ducted and unducted turbomachinery blade designs. The parametric blade geometry tool is a key feature which converts low-fidelity results into 3D blade shapes and can readily be used in high-fidelity multidisciplinary simulations as part of an optimization cycle. The geometry generator and physics solvers are connected to DAKOTA, an open-source optimizer with parallel computation capability. The entire cycle is automated and new design iterations are generated with input parameter variations controlled by DAKOTA. Single- and multi-objective genetic algorithm and gradient method-based optimization cases are demonstrated for various applications. B-splines are used to define smooth perturbation of parametric variables chordwise and spanwise of the blade. The ability to create parametric 3D blade shapes quickly from low-fidelity analyses with advanced control is demonstrated to be unique and enables a rapid 3D design cycle. Non-intuitive designs are feasible in this framework and designers can really benefit from parametric geometry manipulation. Optimization at each fidelity is realized through automation. As part of the multidisciplinary analysis, 3D structural analysis is also performed using the unidirectional fluid–structure interaction for a few cases with imported pressure loads from the 3D RANS solution. Examples of axial turbofans, compressor rotors, turbines, radial compressors, propellers, wind and hydrokinetic turbines are demonstrated to prove generality.

Flow characteristics of last‐segment axial turbine adopted in compressed air energy storage system under low load and windage conditions

<scp>Flow</scp> characteristics of last‐segment axial turbine adopted in compressed air energy storage system under low load and windage conditions

Integrated Aerodynamic and Structural Blade Shape Optimization of Axial Turbines Operating With Supercritical Carbon Dioxide Blended With Dopants

Abstract Within this study, the blade shape of a large-scale axial turbine operating with sCO2 blended with dopants is optimized using an integrated aerodynamic-structural three-dimensional (3D) numerical model, whereby the optimization aims at maximizing the aerodynamic efficiency whilst meeting a set of stress constraints to ensure safe operation. Specifically, three candidate mixtures are considered, namely, CO2 blended with titanium tetrachloride (TiCl4), hexafluorobenzene (C6F6), or sulfur dioxide (SO2), where the selected blends and boundary conditions are defined by the EU project, SCARABEUS. A single passage axial turbine numerical model is setup and applied to the first stage of a large-scale multistage axial turbine design. The aerodynamic performance is simulated using a 3D steady-state viscous computational fluid dynamic (CFD) model while the blade stress distribution is obtained from a static structural finite element analysis simulation (FEA). A genetic algorithm is used to optimize parameters defining the blade angle and thickness distributions along the chord line while a surrogate model is used to provide fast and reliable model predictions during optimization using a genetic aggregation response surface. The uncertainty of the surrogate model, represented by the difference between the surrogate model results and the CFD/FEA model results, is evaluated using a set of verification points and is found to be less than 0.3% for aerodynamic efficiency and 1% for both the mass-flow rate and the maximum equivalent stresses. The comparison between the final optimized blade cross section has shown some common trends in optimizing the blade design by decreasing the stator and rotor trailing edge thickness, increasing the stator thickness near the trailing edge, and decreasing the rotor thickness near the trailing edge and decreasing the rotor outlet angle. Further investigations of the loss breakdown of the optimized and reference blade designs are presented to highlight the role of the optimization process in reducing aerodynamic losses. It has been noted that the performance improvement achieved through shape optimization is mainly due to decreasing the endwall losses with both the stator and rotor passages.

Estimation of the Induced Incidence of a High Reaction Axial Turbine Bucket

This paper describes the effect of the incidence angle of the bucket on the performance of the axial turbine stage. The off-design operating conditions of the turbine stage result in a change in the velocity diagrams. This results in a positive or negative incidence. One of the basic objectives in turbine stage design is to estimate the flow behaviour of the turbine stage during off-design operation as accurately as possible and to quantify the corresponding decrease in efficiency. The available loss prediction models allow the estimation of the loss distribution when the incidence angle changes in the preliminary design phase. However, the incidence angle is actually affected by the velocity of circulation, which changes the input velocity vector (induced incidence). Thus, the blade row angle of attack is different from the angle based on the velocity diagram calculations. The result of our paper is a relation for estimating the angular difference of the input flow angle to the bucket defined as a function of the turbine operation mode.

An Optimization Methodology for Turbines Driven by Pulsed Detonation Combustors

Abstract A step-change in efficiency of gas turbine technology and, subsequently, an emissions reduction from this technology requires conceptual changes. Substituting conventional combustion chambers with pressure gain combustion in the form of pulsed detonation combustion (PDC) is one of the promising methods that can reduce gas turbine emissions significantly. Nevertheless, the component matching for the respective systems and specifically that of turbine expanders working with the exhaust flow of PDC tubes is still not solved. The unsteady nature of PDC exhaust flow makes 3D-CFD simulations too expensive to be applied in optimization loops in early design stages. To address this question, the present paper introduces a new cost-effective but reliable methodology for turbine analysis and optimization, based on the unsteady exhaust flow of pulsed detonation combustors. The methodology unitizes a robust unsteady one-dimensional solver, a meanline performance analysis, and an adaptive surrogate optimization algorithm. A two-stage axial turbine is optimized considering all unsteady flow features of a hydrogen-air PDC configuration with five PDC tubes. A three-dimensional URANS simulation is performed for the optimized geometry and the baseline to evaluate the methodology. The results showed that the optimized turbine produces 16% lower entropy than the original one. Additionally, the turbine output power is increased by 14% by the optimized design. Based on the results, it is concluded that the approach is fast and reliable enough to be applied in optimizing any turbine working with unsteady flows, more specifically in PDC applications.

Experimental investigation of small axial hydro-kinetic turbines

In the present paper the prototypes of small axial hydro-kinetic turbines are designed, built and tested in laboratory conditions in order to demonstrate their operability. The hydrokinetic turbine prototypes have a 0.2 m tip diameter, three blades and are meant to be used in a free water stream flowing with 1 m/s velocity. Two geometries of the turbine runner are studied in order to determine the best correlation between the water flow velocity and the cross-sectional area of the turbine. The 3D designs of the turbine are used for the prototype printing in order to obtain a lightweight compact assembly of reduced dimensions. The experimental measurements are conducted in a closed-loop laboratory setup, specially designed for hydro-kinetic turbines prototypes testing. The flow velocity, runner speed and shaft torque are measured. The aim of the experimental testing is to determine the characteristic parameters for the tested turbines as power coefficient and mechanical power output.

Vortex rope interaction with radially protruded solid bodies in an axial turbine: a numerical study

Radially protruded solid rods and their interaction with the rotating vortex rope at part load condition are investigated numerically on an axial model turbine.The commercially available software ANSYS CFX was used to perform the simulation, and the test case was the Porjus U9 Kaplan turbine model operating at a fixed runner blade angle at part load condition. Four rods, with a rod diameter equal to 15% of the runner diameter were evenly distributed in a horizontal plane in the draft tube cone and protruded to a length set to intercept the RVR in its unperturbed trajectory. It is shown that the RVR plunging (synchronous) mode is completely mitigated upstream and downstream of the protruded rods. The RVR rotating (asynchronous) mode is reduced by 47% and 63% at the two monitor positions located upstream of the protruding rods, while only a minor reduction occurs to the first RVR harmonic at the monitor positions located downstream of the protruded rods. The perturbed RVR experiences an increased angular velocity due to the flow area decrease caused by the protruding rods, thus increasing the RVR frequency by approximately 53% compared to the unperturbed value. Investigation of the swirling flow indicates a locally increased swirl in the center of the draft tube downstream of the protruded rods which could explain the reduction of the RVR pressure amplitude. The overall turbine efficiency with solid rods protruded causes a marginally efficiency reduction of 0.85%. However, as the RVR pressure pulsations are reduced significantly, a more comprehensive investigation of the rods impact on the turbine performance and life time should be performed to elucidate the suitability of using solid rod protrusion for RVR mitigation.

Comparative Analysis of the Operating Modes of Axial and Orthogonal Hydraulic Turbines of Tidal Power Stations

Comparative Analysis of the Operating Modes of Axial and Orthogonal Hydraulic Turbines of Tidal Power Stations

Верификация и валидация компьютерных моделей

The paper considers the steps involved in building modern digital simulations, from a conceptual mathematical model to specific simulation settings, for example, meshing parameters. The paper presents a generalised approach to verification and validation of computer simulations and describes its main stages. The approach proposed is based on the assumption that the complex physical phenomena and objects to be simulated have a hierarchical structure that allows them to be split into constituent components (according to their design purpose, such as assemblies or parts, or according to the field of study, such as gas dynamics, combustion, heat transfer, etc.). Each element uses its own mathematical (or digital) model that will have undergone verification and validation. A complex computer simulation is verified and validated from the bottom up, that is, in the following order: individual parts, then assemblies, and finally the physical phenomenon or object under consideration. We consider a case study of verification and validation as pertaining to a comprehensive calculation of axial turbine parameters for a gas turbine engine. We also address issues concerning verification and certification of software used to develop digital simulations, as well as issues concerning verification and validation of digital product twins.

Intermittent cavitating flow field in tandem cascades of Kaplan turbines

Within the framework of the classical turbine design setup, we present a numerical investigation of unsteady cavitating flow in tandem cascades of guide vanes and rotor blades. The practical relevance of the present investigation is ensured by choosing real blade profiles and domain geometry for the large Kaplan turbines (9.5 m rotor diameter) from the Iron Gates I hydropower plant on the Danube River. The 2D tandem cascade setup is obtained with a conformal mapping of the circular guide vane cascade into a straight cascade, while the rotor blade cascade is by default a straight one for axial turbines. Both single-phase and two-phase cavitating flows results are presented and analysed. The single-phase liquid flow displays rather modest pressure and tangential force fluctuations, with the characteristic blade passing frequency, due to the interaction of the rotor blades with the wakes of guide vanes. The two-phase cavitating flow displays a completely different dynamics in comparison to the liquid flow, with periodic cavitation growth and collapse at a specific frequency lower than the blade-passing one. Moreover, the tangential force on the rotor blade displays severe intermittency and the force fluctuations are almost one order of magnitude larger than in the single-phase flow.

Rapid performance prediction model of axial turbine with coupling one-dimensional inverse design and direct analysis

The reasonable and rapid prediction of turbine performance based on design targets such as mass flow rate and pressure ratio is indispensable in the preliminary and conceptual design stage for gas turbine engines in the aviation and power generation industry. However, the lack of detailed geometrical and aerodynamic parameters in this stage significantly challenges the reasonable evaluation of turbine characteristics. The present work proposes a rapid prediction method of axial turbine performance by coupling the inverse design and direct analysis. Firstly, according to the one-dimensional mean line design theory with empirical loss and deviation correlation models, the basic aerodynamic and geometrical parameters are quickly obtained by solving the inverse problem to fulfill the design targets such as mass flow rate and pressure ratio with optimized efficiency. Then, by adopting the loss and deviation correlation models in the off-design conditions, the turbine characteristics in a wide range of operating conditions are obtained by solving the direct analysis problem. Thus, the reasonable and rapid prediction of the turbine characteristics can be realized by coupling the inverse design with direct analysis. Based on the built prediction model, the effect of various deviation models on the predicted turbine characteristics, which was not systematically investigated in previous studies, is clarified by comparing the predicted performance with published test results. Finally, an optimization method of the empirical coefficients in turbine loss and deviation models based on the Genetic Algorithm (GA) is introduced. This method employs optimization theory and existing experimental data to improve the prediction accuracy. The results show that the averaged prediction discrepancies of output powers and mass flow rates in a wide range of operating conditions are no more than 2% and 2.5% for test cases after the optimization of model coefficients. Therefore, this optimization method is expected to be used for updating the empirical coefficients to improve the model prediction accuracy, accompanying the evolution of turbine design strategy at present or in the future.