Reaction Turbines Research Articles

Comparison of Organic Rankine Cycle Systems under Varying Conditions Using Turbine and Twin-Screw Expanders

A multi-variable optimization program has been developed to investigate the performance of Organic Rankine Cycles (ORCs) for low temperature heat recovery applications using both turbine and twin-screw expanders when account is taken of performance variation due to changes in ambient conditions. The cycle simulation contains thermodynamic models of both types of expander. In the case of the twin-screw machine, the methods used to match the operation of the expander to the requirements of the cycle are described. The performance of turbine expanders in a superheated ORC has been modelled using correlations derived from operational data for single stage reaction turbines to predict the turbine efficiency at “off-design” conditions. Several turbine configurations have been considered including variable nozzle area and variable speed. The capability of the cycle model has been demonstrated for the case of heat recovery from a steady source of pressurized hot water at 120 °C. The system parameters are optimised for a typical operating condition, which determines the required size of heat exchangers and the expander characteristics. Performance at off-design conditions can then be optimized within these constraints. This allows a rigorous investigation of the effect of air temperature variation on the system performance, and the seasonal variation in net power output for the turbine and twin-screw ORC systems. A case study is presented for a low temperature heat recovery application with system electrical power output of around 100 kWe at design conditions. The results indicate that similar overall performance can be achieved for ORC systems using either type of expander.

Studying Issues of Compressed Gas Energy Recovery

Background/Objectives: One of promising researches to increase efficiency of oil and gas production is connected with compressed gas energy recovery. Potential gas energy may be converted to thermal energy or electric power using special gas turbines. Methods: The known methods for converting compressed gas energy into thermal or electric energy involve the use of impulse and reaction turbines. But high price for turbines hinders works on the use of compressed gas energy. Development of technologies for compressed gas energy recovery should be aimed at creating simpler and cheaper equipment. When developing new turbines for thermal generator, options using looped blades have been analyzed. Findings: At this stage of research and development work we have developed a new thermal generator, equipped with a gas turbine and a heat transfer fluid circulation loop. Looped blades were used in the turbine creation. A distinctive feature of the created turbine is that the working gas flow is directed along a plane that is perpendicular to the turbine rotation axis. In the known turbines, equipped with looped blades, the working gas flow is directed along the turbine rotation axis. Application of these results brings about the opportunity for creating simpler and less expensive power plants operating by means of compressed gas energy for a wider power range - from a few kilowatts to several hundred kilowatts. Application/Improvements: The basic field of application for the created plant is associated with the production facilities of oil and gas industry. However, individual results can be used in other industries, for example, when creating machinery for sea and air transport, where weight reduction and improving the reliability of the equipment is particularly relevant.

Numerical Study of Cavitation in Francis Turbine of a Small Hydro Power Plant

Cavitation is undesirable phenomena and more prone in reaction turbines. It is one of the challenges in any hydro power plant which cause vibration, degradation of performance and the damage to the hydraulic turbine components. Under the present study, an attempt has been made to carry out a numerical analysis to investigate the cavitation effect in a Francis turbine. Three dimensional numerical study approach of unsteady and SST turbulence model are considered for the numerical analysis under multiphase flow such as cavitating flow. The performance parameters and cavitating flow under different operating conditions have been predicted using commercial CFX code. Three different operating conditions under cavitation and without cavitation with part load and overload conditions of the turbine for a plant sigma factor are investigated. The results are presented in the form of efficiency, pressure fluctuation, vortex rope and vapor volume fraction. It has been observed that variation in efficiency and vapor volume fraction is found to be nominal between cavitation and without cavitation conditionsat rated discharge and rated head. Turbine efficiency loss and vapor bubbles formation towards suction side of the runner blade are found to be maximum under overload condition. However, the pressure pulsation has been found maximum under part load condition in the draft tube. The simulation results are found to be in good agreement with model test results for efficiency. The locations of cavitating zone observed wellwith the result of previous studies.

Design and numerical study of turbines operating with MDM as working fluid

Abstract Design processes and numerical simulations have been presented for a few cases of turbines designated to work in ORC systems. The chosen working fluid isMDM. The considered design configurations include single stage centripetal reaction and centrifugal impulse turbines as well as multistage axial turbines. The power outputs vary from about 75 kW to 1 MW. The flow in single stage turbines is supersonic and requires special design of blades. The internal efficiencies of these configurations exceed 80% which is considered high for these type of machines. The efficiency of axial turbines exceed 90%. Possible turbine optimization directions have been also outlined in the work.

Tiny bubbles challenge giant turbines: Three Gorges puzzle.

Since the birth of the first prototype of the modern reaction turbine, cavitation as conjectured by Euler in 1754 always presents as a challenge. Following his theory, the evolution of modern reaction (Francis and Kaplan) turbines has been completed by adding the final piece of the element 'draft-tube' that enables turbines to explore water energy at efficiencies of almost 100%. However, during the last two and a half centuries, with increasing unit capacity and specific speed, the problem of cavitation has been manifested and complicated by the draft-tube surges rather than being solved. Particularly, during the last 20 years, the fierce competition in the international market for extremely large turbines with compact design has encouraged the development of giant Francis turbines of 700-1000 MW. The first group (24 units) of such giant turbines of 700 MW each was installed in the Three Gorges project. Immediately after commission, a strange erosion phenomenon appeared on the guide vane of the machines that has puzzled professionals. From a multi-disciplinary analysis, this Three Gorges puzzle could reflect an unknown type of cavitation inception presumably triggered by turbulence production from the boundary-layer streak transitional process. It thus presents a fresh challenge not only to this old turbine industry, but also to the fundamental sciences.

Numerical predictions and stability analysis of cavitating draft tube vortices at high head in a model Francis turbine

Draft tube vortex is one of the main causes of hydraulic instability in hydraulic reaction turbines, in particular Francis turbines. A method of cavitation calculations was proposed to predict the pressure fluctuations induced by draft tube vortices in a model Francis turbine, by solving RANS equations with RNG k-turbulence model and ZGB cavitation model, with modified turbulence viscosity. Three cases with different flow rates at high head were studied. In the study case of part load, two modes of revolutions with the same rotating direction, revolution around the axis of the draft tube cone, and revolution around the core of the vortex rope, can be recognized. The elliptical shaped vortex rope causes anisotropic characteristics of pressure fluctuations around the centerline of the draft tube cone. By analyzing the phase angles of the pressure fluctuations, the role of the vortex rope as an exciter in the oscillating case can be recognized. An analysis of Batchelor instability, i.e. instability in q-vortex like flow structure, has been carried out on the draft tube vortices in these three cases. It can be concluded that the trajectory for study case with part load lies in the region of absolute instability (AI), and it lies in the region of convective instability (CI) for study case with design flow rate. Trajectory for study case with over load lies in the AI region at the inlet of the draft tube, and enters CI region near the end of the elbow.

A dimensional analysis for determining optimal discharge and penstock diameter in impulse and reaction water turbines

This paper presents a dimensional analysis for determining optimal flow discharge and optimal penstock diameter when designing impulse and reaction turbines for hydropower systems. The aim of this analysis is to provide general insights for minimizing water consumption when producing hydropower. This analysis is based on the geometric and hydraulic characteristics of the penstock, the total hydraulic head and the desired power production. As part of this analysis, various dimensionless relationships between power production, flow discharge and head losses were derived. These relationships were used to withdraw general insights on determining optimal flow discharge and optimal penstock diameter. For instance, it was found that for minimizing water consumption, the ratio of head loss to gross head should not exceed about 15%. Two examples of application are presented to illustrate the procedure for determining optimal flow discharge and optimal penstock diameter for impulse and reaction turbines.

Hydro turbine prototype testing and generation of performance curves: Fully automated approach

This paper presents a technology that can accelerate the development of hydro turbines by fully automating the initial testing process of prototype turbine models and automatically converting the acquired data into efficiency hill charts that allow straight forward comparison of prototypes' performance. The testing procedure of both reaction and impulse turbines is illustrated using models of Francis and Pelton turbines respectively. For the development of an appropriate hill chart containing no less than 780 points the average duration of the fully automated test is 4 h while the acquired data files can be processed into descriptive standard efficiency hill charts within less than a minute. These hill charts can then be used in research and development to quickly evaluate and compare the performance of initial turbine prototype designs before proceeding to much lengthier and more expensive development stage of the chosen design.

Performance Evaluation of Pelton Turbine: A Review

Earlier only experimental techniques were used to predict the performance of turbines. With advanced numerical techniques and increase in processing power of computers, Computational Fluid Dynamics (CFD) has emerged as an effective tool for the performance prediction of Pelton hydraulic turbine involving multi-fluid flow. Extensive work has been done for design optimization of reaction turbines using CFD. Now it is being extended for impulse turbines. The flow in reaction turbines involves only water as working medium, but in case of impulse turbines, water and air are working medium. The water jet issued from nozzle is surrounded by air and pressure around the jet and turbine is atmospheric. The performance of Pelton turbine depends upon the shape, size and quality of jet as well as shape of the buckets. In the present paper, the literature review on applications of CFD for performance prediction, design optimization of Pelton turbine have been discussed.DOI: http://dx.doi.org/10.3126/hn.v13i0.10042HYDRO NEPAL Journal of Water, Energy and EnvironmentIssue No. 13, July 2013Page: 28-35Uploaded date: 3/13/2014

Numerical and experimental analysis of the hydraulic performance of a prototype Pelton turbine

Unlike the reaction turbines, the hydraulic performance of Pelton turbines varies due to the unsteady flow of the rotating buckets in time and space. This study experimentally and numerically investigates the dynamic performance of a Pelton turbine at five different operating conditions. The unsteady numerical simulations were performed with the SST turbulence model. The three-dimensional unsteady free surface sheet flow behavior in the rotating buckets was modeled by the two-phase homogeneous model. The model was used to analyze the dynamic flow patterns and the torque variations as the buckets rotated. The predicted hydraulic performance at different unit discharge rates are compared with the field test while the free surface flow patterns are compared with previous experimental and numerical results. The predicted relative efficiency agrees well with the field test results. The calculations were used to clarify the hydraulic mechanisms with unsteady free surface sheet flow in the rotating bucket.

The Effect of the Degree of Reaction on the Leakage Loss in Steam Turbines

The degree of reaction selected in designing steam turbines is of paramount importance. There has been competition between 50% reaction and impulse turbines over a century. It is, therefore, important to understand the effect of the degree of reaction on aerodynamic performance. In particular, a change in the degree of reaction affects the leakage flow substantially in both the stationary and rotating blades due to a change in the blade loading. The effect of the degree of reaction on the efficiency loss due to leakage flows is systematically investigated in this paper using analytical models. It is shown that the appropriate way to understand the efficiency loss due to leakage flows is to estimate the kinetic energy dissipation rather than the leakage mass flow rate, as demonstrated by Yoon et al. (Yoon, S., Curtis, E., Denton, J., and Longley, J., 2010, “The Effect of Clearance on Shrouded and Unshrouded Turbine at Two Different Levels of Reaction,” ASME Paper No. GT2010-22541). In order to estimate the efficiency loss due to leakage flows, the well-known Denton model (Denton, J. D., 1993, “Loss Mechanisms in Turbomachinery,” ASME J. Turbomach., 115, pp. 621–656) is extended by considering the velocity triangles in a repeating turbine stage. The extended model is compared with experimental data, at different degrees of reaction, and shows good agreement with measurements. It is shown that a reduction in the degree of reaction, at a fixed flow coefficient and a fixed work coefficient, results in an increase in the efficiency loss across the stationary blade but a decrease in that across the rotating blade. However, the efficiency loss across the stationary blade hub is estimated to be smaller than the efficiency loss across the rotating blade tip. A stationary blade can be better sealed than a rotating blade by applying multiple seals and using a leakage path with a low radius. The efficiency loss due to the tip leakage flow is substantially influenced by the choice of the tip configuration. Shrouded blades show several aerodynamic advantages over unshrouded blades in reducing the tip leakage efficiency loss. Employing multiple seals over the shroud decreases the tip leakage mass flow rate significantly. Moreover, as the degree of reaction approaches zero, the tip leakage mass flow rate over the shroud becomes small since the axial pressure drop across the rotating blade becomes small. In unshrouded blades, a reduction in the degree of reaction is shown to increase the leakage mass flow rate over the tip because the circumferential pressure difference between the blade pressure side and blade suction side generally increases when the pitch-to-chord ratio remains unchanged.

Numerical simulation of unsteady free surface flow and dynamic performance for a Pelton turbine

Different from the reaction turbines, the hydraulic performance of the Pelton turbine is dynamic due to the unsteady free surface flow in the rotating buckets in time and space. This paper aims to present the results of investigations conducted on the free surface flow in a Pelton turbine rotating buckets. The unsteady numerical simulations were performed with the CFX code by using the Realizable k-ε turbulence model coupling the two-phase flow volume of fluid method. The unsteady free surface flow patterns and torque varying with the bucket rotating were analysed. The predicted relative performance at five operating conditions was compared with the field test results. The study was also conducted the interactions between the bucket rear and the water jet.

Effect of Runner Solidity on Performance of Elbow Draft Tube

The significant amount of kinetic energy comes out of runner in reaction turbines and the draft tube is used to recover this kinetic energy into useful pressure energy. The energy recovery in draft tube depends on its design and magnitude of velocity components at runner exit. Further the amount of kinetic energy coming out of runner depends on the solidity of runner as well as its rotational speed. Hence draft tube is important component of turbine next to runner. In this paper, 3D viscous turbulent flow simulation has been done in the complete flow passage of Francis turbine using commercial Computational Fluid Dynamics (CFD) code for three runner solidities at different rotational speeds. The draft tube performance parameters in non-dimensional form are computed from simulation results and the effects of runner solidity and operating speed on draft tube performance are discussed. The simulation results are also compared with the experimental results for validation and are found to be within reasonable accuracy.

Observation and Analysis of Affinity Law Deviations through Tested Performance of Liquefied Gas Reaction Turbines

Liquefied gas reaction turbines are subject to the hydraulic affinity laws. Particularly for liquefied hydrocarbon gas‐driven turbines, deviations from the affinity laws are encountered. In the case of reaction turbines, where the geometry is fixed, the affinity law relationships between flow, head, and rotational speed are relevant. Field experience confirms that the affinity law relationships are adequate, but that the predictions made also tend to deviate from real turbine performance. Part of the deviations seen may be attributed to the nonideal fluid; however, further examination is warranted. This paper presents an investigation into the affinity law relationships between head, flow, and rotational speed in conjunction with actual turbine performance. The three basic affinity law relationships are combined to form the most general performance equation. This equation subsequently incorporates both the affinity law relationships and the conservation of energy principal. Application of real turbine test data shows that this general performance equation presents a more accurate representation of turbine performance than the affinity law relationships alone.

Numerical prediction of dynamic performance of Pelton turbine

Different from the reaction turbines, the hydraulic performance of Pelton turbine is dynamic due to the unsteady flow in the rotating buckets in time and space. The dynamic energy efficiency of bucket η EB and power efficiency of bucket η PB within a short period can be predicted from the dynamic flow pattern of the free-surface sheet flow in the rotating bucket, whereas the dynamic discharge efficiency of bucket is defined as the resident discharge in the bucket at the respective moment. η QB Under the operation of higher unit speed nDH than the optimum one, the power efficiency of bucket is deteriorated by the jet interference with the rear surface of bucket ΔP rear at the first stage of the dynamic performance, as well as the loss power due to the spilt flow from the cutout of bucket at the later stage of performance. Based on the dynamic performance prediction presented, the future possibility of the quantitative investigation for the negative scale effect of Pelton turbines was discussed.

Control of dynamic effects in small hydro with long hydraulic circuits

Lab tests in a long hydraulic circuit were developed to analyse hydrotransients induced by waterhammer effects under runaway conditions. The definition of suitable design criteria in hydraulic systems is of utmost importance and has become a priority for good design implementation. The dynamic behaviour of turbo-generators of small reaction turbines and the interaction with long hydraulic circuits are the major constraints for design criteria. In small reaction turbines, runaway conditions may cause significant discharge variations and consequently pressure fluctuations. A benchmark analysis based on the hydrodynamic behaviour of the system through computer simulations and experimental tests was developed. Specific unconventional protection devices were selected to control overpressures induced by runaway conditions in small hydropower systems with lesser environmental impacts. A spectral analysis was used in order to identify the influence of each type of disturbances in the system response.

Dynamic orifice model on waterhammer analysis of high or medium heads of small hydropower schemes

The most severe hydropower transients are induced in long hydraulic circuits due to extreme operating conditions. A computational model was developed in order to on one hand ensure waterhammer system control and, on the other hand, provide a more reliable and easier analysis for different specific speed turbines and alternative solutions of the system as a whole, through interaction between different hydraulic components. In reaction turbines, runaway conditions and guide vane closure cause significant discharge variations and pressure fluctuations that can affect the design of conveyance systems. A new approach for groups modelling as dynamic orifices concept was developed enabling the characterisation of the integrated system. The simulation results were compared with laboratory tests. This model can be used in the initial stages of civil works design as an efficient way to better characterise the hydrodynamic behaviour of the system when equipped with reaction turbines.

Turbofan engine with reduced noise

A noise reduction kit for modifying a two (2) spool axial flow turbofan engine with multi-stage compressors and fan driven by multi-stage reaction turbines, and a thrust of at least about 18,000 lbs. at sea level. There is a fan at the upstream end of the core engine for generating axial fan air flow through bypass ducts terminating at a common nozzle, the common nozzle having a mixing plane area for each of the fan air flow and for the exhaust gas in a range between 700 and 800 square inches. A target thrust reverser includes opposing doors rotatable into position to block and divert the flow of exhaust gas for generating reverse thrust. Mixing means for radially diverting fan air and permitting radially outward expansion of exhaust gas is provided coaxially downstream to the core engine. An acoustically dampened light bulb-shaped nose cone is provided for coaxial attachment to an upstream end of the core engine. The axial flow front fan is axially separated from the inlet guide vane is extended relatively forwardly. A bleed air valve, selectively operational to bleed air from the core engine when the valve is open, is ducted for directing bleed air to the vicinity of the common nozzle.

Computer-Aided Analysis of Hydraulic Reaction Turbines

A microcomputer-based educational software package designed to help mechanical engineering students to understand hydraulic reaction turbines is described. The software is interactive, menu-driven, and easy-to-use, is written in the Pascal computer language, and runs on IBM PC, or compatible, computers. The program can handle radial, mixed, or axial flow turbine problems by solving for unknown variables through a complete set of equations covering the turbine installation. Using similarity laws, model-prototype problems or operation under different conditions can also be tackled. Furthermore, the program is equipped with graphical utilities that include many diagrammatic sketches of reaction turbines, some recommended charts, and the possibility of drawing velocity triangles when corresponding variables are available. The most important feature of the package is an option that allows one to plot the variation of any parameter versus any other one. Through this option, the student can easily understand and discuss the effects of varying design parameters on the overall performance of the machine. Finally, some special features that are important in making the package user-friendly and encouraging-to-use are also available, and the comprehensive example problem provided demonstrates the capabilities of the package as an instructional tool.

Design of two-phase turbines and geothermal electric power-plants in Hungary

A description is given of a private project to produce electric energy from geothermal fluids in Hungary. Single-stage and multi-stage action and reaction turbines of the axial flow type are recommended for this purpose, together with the associated equipment and power plants.