Turbine Flow Path Research Articles

Design Calculation and Shaping of the Hydro-Steam Turbine Flow Path with Helical Nozzles

Design Calculation and Shaping of the Hydro-Steam Turbine Flow Path with Helical Nozzles

Simulation of Stack-Integrated Autothermal Reformer and Solid Oxide Fuel Cells for Operation in Aircraft Engines

Renewable liquified natural gas provides a potential sustainable aviation fuel, but with a volumetric energy density around 70% of conventional jet fuel. As such, alternative aircraft power plants such as hybrid gas turbine (GT) / solid oxide fuel cells (SOFCs) have been proposed to increase fuel conversion efficiency and support hybrid electric propulsion concepts. To enable reliable SOFC operation within aircraft gas turbine flow paths, stack architectures must be identified that sustain very high-power densities with direct inline air feeds from the gas turbine compressor outlet. Typical aircraft compressor outlet temperatures are below SOFC operating temperatures but high enough to light-off a catalytic autothermal reformer (ATR). The ATR combined with an air heat exchanger (HX) can preheat anode and cathode streams to desirable inlet temperatures above 500 °C for intermediate-temperature SOFCs that utilize gadolinia-doped ceria (GDC) electrolytes or thin-film, yttria-stabilized zirconia (YSZ) electrolytes. By packaging the inline ATR/HX within the SOFC stack and mixing partial anode exhaust recycle and bleed air with the ATR fuel stream, a volumetrically efficient inline stack architecture is being designed for demonstration at conditions simulating an aircraft gas-turbine compressor outlet. The combination of the ATR/HX and the high-power-density SOFC imposes significant temperature gradients within the stack that can impact performance. To assess suitable operating conditions and preferred designs for the ATR/HX/SOFC operating on renewable natural gas, a 3-D multi-physics CFD model has been developed. Simulation results for SOFCs with thin-film YSZ or GDC electrolytes show the challenge maintaining high-power densities while maintaining the full stack within expected temperature limits for expected cell materials.The ATR/HX/SOFC stack design includes the upstream ATR/HX, 3.6 cm in length. The ATR flow path is filled by a porous mesh with a washcoat-supported Pt catalyst for light off of CH4/bleed air/H2O inlet mixtures. The air-side flow paths in the ATR/HX are etched parallel channels that extract heat from the exothermic ATR reactions. The ATR/HX outlets feed the SOFC anode and cathode flow paths respectively. For this study, the SOFC membrane electrode assembly (MEA) 10 cm in length, consists of a porous Ni-YSZ anode-support (400 mm thick), dense YSZ or GDC electrolytes (≤ 20 mm thick), and a perovskite-YSZ composite cathode (35 mm thick). The anode flow passages over the support involve a high-porosity mesh that enables current collection. The cathode flow channels are etched ribs that enable high air flow rates to support high power density with adequate SOFC stack cooling. The ATR/HX/SOFC design has been incorporated into an ANSYS Fluent model to explore how integration of the ATR/HX in the stack can enable high-power performance of the SOFC while supporting light-off of the ATR fuel stream at aircraft compressor outlet conditions. The ANSYS Fluent model uses customized user-defined functions to handle the heterogeneous catalytic CH4oxidation surface chemistry for the ATR (supported Pt catalyst [1]) and for internal CH4 reforming in the Ni/cermet anode support in the SOFC [2]. The model simulates non-isothermal operation of a single ATR/HX/SOFC cell, representative of a full stack, at various inlet flow temperatures, pressures, flow rates, and fuel stream compositions, which are set by anode exhaust recycle fraction.CFD model results for thin-film YSZ-electrolyte MEAs illustrate a strong dependence of SOFC power density on the anode recycle fraction and cathode bleed air splits into the ATR fuel stream. For a 400 °C air inlet, the short ATR/HX is capable of achieving near-equilibrium CH4 conversion to an H2-rich reformate while preheating the cathode inlet up to 500 °C. Simulations over a range of anode recycle fractions show that lower recycle fractions increase ATR outlet temperatures and H2 mole fractions with SOFC power densities reaching 2.0 W cm-2, but at the risk of excessive anode temperatures and large temperature gradients across the length of the MEA. Increased cathode excess air ratios can lower the temperatures at the expense of stack power density. Higher anode recycle fractions decrease the temperature rise across the length of the MEA, but also at the expense power density. Further studies with GDC electrolytes based on recent GDC SOFC model developments [3] will explore how high-power densities of GDC can be supported within its operating temperature constraints.

Electricity Generation at Gas Distribution Stations from Gas Surplus Pressure Energy

At gas distribution stations (GDSs), the process of throttling (pressure reduction) of natural gas occurs on gas pressure regulators without generating useful energy. If the gas expansion process is created in a turbine, to the shaft where an electric generator is connected, then electricity can be obtained. At the same time, the recycling of secondary energy resources is provided, which is an important component in the efficient use of natural resources. The obtained electric power can be supplied to the external power grid and/or used for the GDS’s own needs. The process of generating electricity at the GDS from gas overpressure energy is an environmentally friendly, energy-saving technology that ensures an uninterrupted, autonomous operation of the GDS in the absence of an external energy supply. The power needs of a GDS with regard to electricity are relatively small (5 ÷ 20 kW). Expansion in throttling devices or turbine flow paths leads to gas cooling with a possible hydrate formation. It is prevented via gas preheating or vortex expansion equipment that keeps the further gas temperature at a necessary level. Turbogenerators can be created on the basis of vortex expansion turbomachines, which have many advantages compared to turbomachines of other types. This article studies how gas pressure (outlet: gas distribution station) and gas preheating (inlet: vortex expansion machine) influence turbogenerator parameters. Nine turbogenerator variants for the power needs of gas distribution stations have been assessed.

Comprehensive analysis of carbon emission reduction technologies (CRTs) in China's coal-fired power sector: A bottom-up approach

Carbon dioxide (CO2) reduction technologies (CRTs) in the coal-fired power sector play an imperative role in the mitigation of environmental challenges and reducing CO2 emissions to help achieve the 2 °C target. However, a compelling necessity persists for a unified framework that can effectively and accurately estimate the costs and potentials associated with CRTs, arising from the diversity of technologies and unit types. Therefore, this study employs a bottom-up approach to analyze the costs and potential of 25 advanced CRTs in the coal-fired power sector, excluding CO2 capture, utilization and storage (CCUS), across 19 types of coal-fired power units. This analysis amalgamates the CO2 reduction supply curve (CRSC) approach with levelized cost of CO2 reduction (LCOC) and a broken-even analysis which could reflect the sector's average carbon reduction cost. The outcomes reveal the following key insights: (1) These technologies collectively harbor a substantial CO2 conservation potential amounting to 925.61 Mt CO2, with a broken-even price of CNY 410.1/tCO2. This reduction could potentially lower 20%–25 % of CO2 emissions in China's power system in 2022, highlighting the crucial role of CRTs in achieving a low-carbon transition and national climate targets; (2)Steam turbine flow path retrofit (T8) not only offers a relatively high CO2 reduction potential (>60 Mt CO2), but also features a low cost (<CNY 150/tCO2) and high profit (>CNY 0.85/MWh). Prioritizing the development of this technology can significantly accelerate the low-carbon transition of coal power; (3) Carbon price have a paramount influence on the cost-effectiveness of CRTs and driving their adoption.

Design of the gas turbine flow path of a gas-cooled fast reactor secondary circuit

Design of the gas turbine flow path of a gas-cooled fast reactor secondary circuit

Axial turbine flow path design for concentrated solar power plants operating with CO2 blends

The utilisation of certain blends based on supercritical CO2 (sCO2), namely CO2/TiCl4, CO2/C6F6 and CO2/SO2, have been found to be promising for enhancing the performance of power cycles for Concentrated Solar Power (CSP) applications; allowing for up to a 6% enhancement in cycle efficiency with respect to a simple recuperated CO2 cycle, depending upon the nature of the used blend and the cycle configuration of choice. This paper presents an investigation of the impact of adopting these sCO2-based blends on the flow path design for a multi-stage axial turbine whilst accounting for aerodynamic, mechanical and rotordynamic considerations. This includes assessing the sensitivity of the turbine design to selected working fluid and imposed optimal cycle conditions. Ultimately, this study aims to provide the first indication that a high-efficiency turbine can be achieved for a large-scale axial turbine operating with these non-conventional working fluids and producing power in excess of 120 MW. To achieve this aim, mean-line aerodynamic design is integrated with mechanical and rotordynamic constraints, specified based on industrial experience, to ensure technically feasible solutions with maximum aerodynamic efficiency. Different turbine flow path designs have been produced for three sCO2 blends under different cycle boundary conditions. Specifically, flow paths have been obtained for optimal cycle configurations at five different molar fractions and two different turbine inlet pressure and temperature levels of 250 & 350 bar and 550 & 700 °C respectively. A total-to-total turbine efficiency in excess of 92% was achieved, which is considered promising for the future of CO2 plants. The highest efficiencies are achieved for designs with a large number of stages, corresponding to reduced hub diameters due to the need for a fixed synchronous rotational speed. The large number of stages is contrary to existing sCO2 turbine designs, but it is found that an increase from 4 to 14 stages can increase the efficiency by around 5%. Ultimately, based on the preliminary cost analysis results, the designs with a large number of stages were found to be financially feasible compared to the designs with a small number of stages.

Influence of geometrical design on the cooling process of double annular turbine section

The article describes the issue of gas turbine cooling after operation. Due to natural convection, an asymmetric temperature distribution occurs in the double annulus, which has a significant effect on the thermal bow of the rotor. At the same time, the desire to minimize radial clearances as this brings the advantage of higher engine efficiency is nowadays essential. On the other hand, it also requires the ability to understand and predict the cooling transient to avoid critical failures during engine restart. Based on a real engine, an experimental facility was designed to represent a simplified double annulus flow path in a section of the turbine flow path. Experimental measurements were performed and a computational model of natural convective flow during gas turbine cooling was developed. The time dependence of the temperature fields was observed and compared with computational model. Furthermore, the dependence of the temperature differences between the upper and lower double annulus was presented. The computational study is carried out with different geometrical setups, which were also validated by experimental measurements. It is shown that the thermal gradient of the rotor due to natural convection can be significantly affected by the choice of geometry and other constraints in this region. The results of the study showed several options to mitigate the rotor bow of a gas turbine. The applicability of the results may have a significant influence on the design and development of gas turbines nowadays.

Influence of Kinematic Parameters of Carbon Dioxide Turbine on Its Coefficient of Efficiency and Dimensions

To reduce carbon dioxide emissions into the environment, the energy sector develops oxygen-fuel energy cycles. One of the most promising cycles is the Allam cycle that features the highest efficiency of electricity generation among all others. One of the main elements of an oxy-fuel energy cycle is a high-temperature carbon dioxide turbine. The turbine’s working fluid and coolant consist predominantly of carbon dioxide at a supercritical pressure. Currently, there are no recommendations in the literature for the design of carbon dioxide turbines for an oxy-fuel energy system (OFES) operating according to the Allam cycle; therefore, there is a need to study the influence of parameters of the flow path of carbon dioxide turbines on its efficiency and overall performance. In this paper, we have presented the results of one-dimensional calculations of a flow path of the carbon dioxide turbine for the Allam cycle with a capacity of 300 MW, with an initial temperature and pressure of 1100 °C and 30 MPa, and an outlet pressure of 3 MPa. The study was carried out by varying the rotor speed, the reactivity level and the average diameter. Based on the results of one-dimensional calculations, we have found that the highest efficiency of the turbine flow path is achieved at a speed of 471 rad/s, a reactivity of 0.5, and an average diameter of 1.1 m for the first stage.

Development of Geothermal Equipment for and Construction of the Verkhne-Mutnovsk and Mutnovsk Geothermal Power Plants

Modern geothermal power generation systems have reached considerable commercial maturity and are successfully competing with other energy generation methods. Geothermal energy has a number of advantages: low cost of electricity, independence from climatic conditions, and high environmental friendliness. The geothermal power plant (GeoPP) capacity factor is well above the levels of this indicator for energy technologies that use other renewable energy sources. In Russia, there are prerequisites for effective use of geothermal energy for supplying power to remote and isolated regions that have huge reserves of geothermal resources. The article summarizes and analyzes the experience gained from development of domestic geothermal equipment and construction of modern geothermal power plants: the Verkhne-Mutnovsk GeoPP and Mutnovsk GeoPP. The geothermal fluid features influencing the design and process solutions applied in developing a GeoPP are considered. The principles of designing the block-modular Verkhne-Mutnovsk GeoPP are described, and the advantages and high efficiency of the steam treatment plant for ensuring reliable operation of the Verkhne-Mutnovsk GeoPP and Mutnovsk GeoPP turbine units are noted. The design features of the turbine flow paths at the Mutnovsk GeoPP with a capacity of 25 MW and Verkhne-Mutnovsk GeoPP with a capacity of 4 MW are given. The characteristics of unique air-cooled condensers for the Verkhne-Mutnovsk GeoPP and direct-contact condensers for the Mutnovsk GeoPP are presented. The further development lines of the Verkhne-Mutnovsk and Mutnovsk GeoPPs have been determined.

Steam turbine flow path drainage system under different operating conditions

One of the important elements of anti-erosion protection of the steam turbine last blades is the use of hollow stator blades. There are grooves on the blade surface that lead the steam mixture inside the blades. This mixture is blown to the diffuser area. However, the drain principle fails for low outputs of the turbine, during the so-called ventilation regimes. In the part of blade section the steam flow is reversed and the flow part drain stops working. It was confirmed using experiments of steam turbine carried out in a wide range of power outputs.

Identification of a mathematical model for a single-shaft power-generating GTE

The design and development processes of gas turbine engines rely on the usage of mathematical models representing the physics of engine functioning processes. One way of increasing the validity of a mathematical model is its identification based on engine test results. The identification of mathematical models of modern power-generating gas turbine engines (GTEs) presents a demanding and time-consuming task due to the necessity to identify the main controlled engine parameters determined in the course of experimental studies depending on a large number of the parameters that are not controlled during the experiment. In this regard the actual direction of reducing the labour intensity of the process of mathematical model identification is using identification program complexes. The object of the study was to solve the problem of structural-parametrical identification of the power-generating GTE functioning model detailing the turbine flow path calculations to the level of blade rows in order to obtain the GTE mathematical model that describes the characteristics of a real engine with given accuracy. To achieve the objective, the following problems were solved: variable parameters, controlled parameters and characteristics, ranges of their variations were selected from the total number of the mathematical model input data, the objective functions were defined; the task of the parametric identification according to the results of bench tests through GTE operating modes was performed; analytical approximating dependences for correcting coefficients (variable parameters) were obtained; structural-parametric identification of the mathematical model was performed. The novelty of the obtained results is the identification of the mathematical model of the nonlinear component GTE of the second level performed without model linearization (without its level lowering) by using the Optimum software packages. The methodological approach for the parametric identification of the mathematical model is proposed. This approach allows reducing the number of variable parameters under the modes lower that the maximum. It shows that the identified model allows obtaining the prediction results of the GTE parameters and characteristics through operating modes with a deviation of no more than 1.4% from the experimental data and, therefore, it will allow reduction of terms and an increase in the quality of power unit development.

Advanced Materials and Manufacturing Technology Developments for Extreme Environment Gas Turbine Applications

Abstract Electrical power generation is becoming increasingly reliant on gas turbines with multiple fuel capability, with research advances focusing on increased efficiency/power output and reduced emissions. Increasing gas turbine efficiency primarily requires higher operating temperatures and reduced coolant flow in the turbine flow path, which makes it challenging to increase component performance, as these will encounter high stresses and large temperature gradients. Current nickel-based alloys, which operate at operate at extreme environments, are exposed to stress caused by temperature or static/dynamic loading like creep and fatigue, oxidation and corrosion, wear, and damage due to vibrations. Higher turbine inlet temperatures are currently managed with internal/film cooling and thermal/environmental barrier coatings for hot section parts. Comprehensive solutions are needed to translate to achieve ultrahigh efficiencies, lower parts cost, reduced scrape rate, and life cycle savings. The paper discusses material developments coupled with innovative manufacturing approaches to be married with advanced design strategies to realize the needed improvements for hot gas path components. The case studies for combustion and turbine components will be presented to demonstrate the structure property relationships and improved component performance at lower cost.

Investigation of translation scheme turbine-based combined-cycle inlet mode transition

Smooth inlet mode transition is critical to turbine-based combined-cycle (TBCC) propulsion system. In this paper, we put forward a translation scheme TBCC inlet mode transition, that is the closing of turbine flowpath and opening of ramjet flowpath was conducted through the translation of mode transition device. The steady and unsteady flow characteristics of inlet mode transition were studied through wind tunnel tests and numerical simulations. The flow pattern and static pressure distribution from three-dimensional numerical simulations agreed well with wind tunnel tests results. According to wind tunnel tests and steady numerical simulations, smooth inlet mode transition can be achieved during translation scheme inlet mode transition. Based on the unsteady numerical simulation of inlet mode transition, as flight Mach number increased from 2.2 to 2.5, throat Mach number varied slightly from 1.35 to 1.36, which indicated that throat Mach number is not sensitive to freestream Mach number. The terminal shock wave generated from turbine flowpath oscillated around the leading edge of mode transition device until 2/4 mode and then moved downstream to turbine flowpath. In the meantime, ramjet engine took over and terminal shock wave moved from downstream ramjet flowpath to leading edge of mode transition device.

Calculation of Pressure Pulsations in the Flow Part of the First Stage of an Axial Turbine in the Rotor-Stator Interaction Zone

A serious problem in the development of reusable liquid-propellant rocket engines (LRE) is the provision of a high resource and reliability of gas turbines of turbopump, which supply fuel to the combustion chamber. This problem can be solved by reducing the level of pressure pulsations in the interaction zone of the turbine rotor-stator and dynamic loads acting on the working and stator blades. In this regard, a useful tool is the method of numerical simulation of the unsteady turbulent flow of a compressible gas in the turbine flow path with the determination of the amplitude of pressure pulsations in the axial clearance between the stator and rotor blade cascades. The calculation model includes the Navier-Stokes equations and equation of energy. Density, thermal conductivity and diffusion coefficient are linearly dependent on temperature and concentration. Calculations were performed on different meshes, proving the mesh convergence of the method upon reaching the quasi-stationary regime. The calculation results show that the pressure pulsations vary greatly with the axial clearance, and the main frequency of the pressure pulsations in the spectrum is the blade passing frequency. The frequency of dynamic moment acting on the blade also coincides with the indicated frequency.

Application of numerical modelling for determining the optimal position of the suction slot in the steam turbine vane cascade

The numerical investigations of liquid film development in the last stages of steam turbines were performed. This data was used to suggest the position of the suction slot used to evacuate the liquid phase from the turbine flow path. The object of study is a periphery 2D section of vanes cascade. The movement of coarse droplets in the blade passage was simulated. Their collision with the blade surfaces results in the appearance of additional sources of mass and momentum for liquid film. The influence of theoretical Mach number on the features of liquid film formation was studied. The distributions of main characteristics, reflecting the formation of the film, have been obtained. They were used to analyse the liquid phase flow along the surfaces and to point out base recommendations about the location of the suction slot.

Influence of Jet Position on Local Heat Transfer Distribution under an Array of Impinging Nozzles with Non-Planar Contour of the Cooled Surface

Many experimental and numerical investigations of arrays of impingement cooling jets have been performed. A lot of them have addressed the problem of cooling with jets directed perpendicularly or inclined to the planar plate. However, in many technical applications contour of the cooled surface is more complex. One of the examples is a casing of the low-pressure turbine of the jet engine. It’s shape is determined by the turbine flow path and position of the blades and vanes located circumferentially inside the casing. Position of the cooling jets is limited by surrounding components, thermal expansion, and vibrations occurring during the engine operation. The investigation focused on the area at which the air has to be blown to achieve most effective cooling system for the complex geometry of the cooled surface is still open. The main goal of the numerical investigation performed in this study was to examine various axial positions of the jets directed perpendicularly to the non-planar shape of the surface to achieve the most effective Nusselt number distribution. Twenty-one analyses with different locations of array of cooling nozzles and various temperature ratios were taken into consideration. The numerical calculations of the thermal and flow parameters were performed using computational fluid dynamics code Ansys CFX.

The operation of the last stage of steam turbine at low-flow rate modes

At the present time, thermal power plants and combined heat and power plants operate in highly manoeuvrable modes with almost daily deep unloading, shutdowns on weekends and holidays followed by launches from various thermal conditions. During start-ups, the operation at partial modes and shutdowns, the turbine flow path operates at low-flow rate modes and, as a result, varying tear-off phenomena appear — depending on a relative volumetric flow rate of steam Gv2 in the low-pressure cylinder starting from the last stage. This is especially true for the operation of the low-pressure path for cogeneration turbines. Under low-flow rate modes a change in the flow structure occurs accompanied by the appearance of the bushing tear-off, the rotating vortex in the gap between stator blades and rotor blades, and an increase in pressure in the main flow when switching to the operation at the compressor mode. The formation of the tear-off area is accompanied by a significant increase in the temperature of steam during its overheating due to ventilation losses created by vortex structures in the areas of tear-off. The temperature change along the working blade length is considered, the characteristic points of this change depending on the relative volumetric flow rate of steam are highlighted. The boundaries of transition from the wet steam to the su— perheated steam with decreasing Gv2 are determined. The power consumption for the operation of the stage with a decrease in the flow rate of steam and a change in the flow structure is considered.

Application of the Parametric Method for Profiling the Interblade Channels in the Nozzle Cascades of Axial-Flow Turbine Machines

Examples of successful application of the technique for parametrically profiling the blades of axial-flow turbine machines are given. The interconnection between the cascade parameters and the profile parameters that are used for representing the blade profile’s shape is described. The influence of each of the considered parameters on the flow characteristics downstream of the cascade, in particular, on the kinetic energy losses and working fluid outlet angle, is analyzed. The initial cascade is optimized for enhancing its aerodynamic efficiency by improving the streamlining of the blade suction side and trailing edge. The optimization results were confirmed by calculation and experimental investigations. By using the developed method, the problem of designing the turbine nozzle cascade for its operation under wet steam conditions with high-efficient removal of moisture from the steam turbine flow path has been solved. Based on the elaborated recommendations for controlling droplet flows through modifying the blade profile’s shape, the profile and cascade have been designed that make it possible to obtain highly intensive growth of liquid film thickness and flowrate on the interblade channel surfaces in the places from which it can be removed through the interchannel separation slots. The accomplished set of calculation and experimental investigations has confirmed the effectiveness of the selected approach.

Optimization of an axial turbine for a small scale ORC waste heat recovery system

Low power Organic Rankine Cycle (ORC) turbines are typically characterised by flow efficiencies much smaller than those of large power steam or gas turbines. The paper concentrates on a possibility of improving the flow efficiency of an ORC axial turbine working on toluene using several optimization algorithms such as a simplex method of Nelder-Mead, a hybrid of genetic algorithm with the Nelder-Mead method, as well as implicit filtering. Values of the maximized objective function, which is the isentropic efficiency of the turbine stage, are found from 3D RANS computation of the flowpath geometry changing during the optimization process. Among the optimized geometric parameters are stator and rotor profile parametrization variables, rotor blade twist angle, circumferential lean and axial sweep angles, as well as parameters characterising the shape of endwall contours within the stator and rotor domain. The process of optimization leads to new 3D designs featuring increased efficiency compared to the original design, mainly due to a reduction in secondary and tip leakage flow losses as well as boundary layer, separation and leaving energy losses. The results especially highlight a large potential of the method of implicit filtering in optimizing multi-parameter objective functions. • A 45 kW turbine prepared for a small ORC CHP is shown. • Deterministic and hybrid methods of optimization are applied. • A wide range of variation of ORC turbine flowpath are investigated. • Performance maps for the best results are shown. • Turbine mechanical qualification is performed.

Selection of optimum degree of partial admission in a laboratory organic vapour microturbine

Partial admission is often used in small ORC turbines due to a relatively low value of specific speed parameter. The paper aims at elaboration of new modeling and design approach for low power ORC turbines with partial admission. The approach is tested on a 3 kW turbine for a small ORC CHP system built at the laboratory of the Institute of Fluid-Flow Machinery. The obtained new turbine is a modernized version of the machine that has been extensively tested before in the laboratory. First, a 0D correlation-based turbine design is presented and the results are discussed. The obtained turbine flowpath geometry is shown and described. Subsequently, a series of RANS simulations is performed in order to investigate the performance of the new design and to create a set of CFD-based flow loss correlations, depending on the blade height, tip clearance size and degree of partial admission. The obtained correlations are used to create a final and more accurate turbine design with the optimum degree of partial admission.