Variable Area Nozzle Research Articles

Improving part-load performance of combined-cycle gas turbines by optimizing variable geometry control strategy for compressor and power turbine combined adjustment

The variable geometry methods currently used in combined-cycle gas turbines are compressor variable inlet guide vanes (VIGV) or power turbine variable area nozzles (VAN). On this basis, this study presents the optimal variable geometry control strategy for compressor and power turbine combined adjustment ([Formula: see text]) using the Differential Evolutionary Algorithm with the LM2500+ gas turbine. The aim is to further improve the part-load performance of the combined-cycle gas turbine. Firstly, a part-load performance prediction model for variable geometry gas turbines is established based on the component method. Subsequently, a variable geometry gas turbine part-load performance optimization model is developed by combining the Differential Evolution Algorithm. Finally, the optimum combination of stagger angles for the compressor inlet vane and power turbine nozzle is calculated at each part-load condition. Compared to the VIGV and VAN control strategies, the [Formula: see text] control strategy proposed in this paper shows a higher stability margin and better economy. The [Formula: see text] control strategy maintains a constant exhaust temperature within a part load range from 20% to 100% with the stability margin exceeding 14%. In comparison with the VAN control strategy, the fuel flow rate decreases by 1.152% at 45% relative load power and by 3.435% at 20.0% relative load power with the [Formula: see text] control strategy.

Acoustic preliminary design of a low-noise fan stage considering a variable-area nozzle and variable-pitch rotor blades

A low-noise low-pressure ultra-high-bypass-ratio fan stage to be implemented in the next generation of aircraft engines is described and evaluated acoustically with semi-empirical and analytical methods suited for preliminary design. As expected, good reduction potentials are observed for the jet noise and fan tonal noise components when the UHBR design is compared to current fans in service. However, concerns are identified for fan broadband noise, which are attributed to the off-design operation of the UHBR fan too close from its stability limit. By unloading the fan and thus reducing the size of the rotor wakes, the variable-area nozzle provides a substantial fan broadband noise reduction with a nozzle opened by around 15% from its design value. Alternatively, with the variable-pitch fan, closing the rotor blades by roughly 5° turns out to be an even more effective method to reduce fan noise, as the unloading mechanism is combined with a stronger tilting of the rotor wakes and a lower intra-stage flow Mach number. Opening the nozzle or closing the blades beyond the setting that provides the best fan efficiency is not recommended as the acoustic benefit progressively vanishes, whereas technical feasibility becomes more challenging. Finally, the presence of one of these systems may allow for the design of a low-solidity rotor, with a smaller contribution from the rotor wakes and thus a weaker fan noise emission.

Diagnostics using a physics-based engine model in aero gas turbine engine verification tests

In the present study, the application of a diagnostic method using a physics-based model is proposed during engine verification testing. A physics-based engine model is constructed, based on a 0-dimensional system analysis method, and then revised through performance adaptation with a basic engine model. Adaptation factors are used for the compressor, secondary air system, nozzle, exhaust gas temperature, and engine thrust. Gas path analysis is conducted using the physics-based engine model and the performance test data in real time. A health parameter that can quantitatively evaluate the performance difference of components was defined. Health parameters for the compressor capacity and efficiency, secondary air system, and nozzle are calculated from the gas path analysis. The multi-variable Newton–Raphson method is employed for the performance adaptation and gas path analysis in real time. A single-shaft gas turbine engine, which is constructed based on the core part of a turbofan engine currently under development, is utilized to test and evaluate the effectiveness of the proposed method. Three tests are performed for engine verification. The proposed diagnostic method is applied to the aero gas turbine engine verification test. In 33 test cases, the fault detection rates for the compressor's variable guide vane, secondary air system, and variable area nozzle are 100%, 91%, and 79%, respectively. As a result, it is confirmed that the proposed method can simultaneously detect abnormalities in the compressor's variable guide vane, secondary air system, and variable area nozzle. In addition, this study indicates that applying the physics-based engine model to the diagnostics logic can effectively detect failures with a small amount of data.

Numerical assessment on constant rate of kinetic energy change (CKREC) based variable area supersonic nozzle

A supersonic nozzle converts pressure energy into kinetic energy of the fluid. It is vital to develop a nozzle based on kinetic energy change. In this study, the constant rate of kinetic energy change (CRKEC) approach has been developed for real fluid and utilized to compute nozzle profile and flow parameters. A MATLAB program was developed to compute the geometrical coordinates, fluid flow properties, and the nozzle at small steps (say 0.5 mm). The computational fluid dynamics (CFD) simulation used ANSYS-Fluent 14.0 on computed geometry. The variable area nozzle simulated results have been validated with 1D computed results. It has been found that the flow parameters such as Mach number, pressure, and temperature are in good agreement with each other with slight deviations. This approach is expected to help reduce loss due to shock compared to the conventional nozzle.

Design Optimization and Variable Geometries Implementation of a High Bypass Three-Shaft Turbofan Engine for EIS2050

Abstract This paper aims to develop an advanced three-shaft turbofan engine with ultrahigh bypass ratio (BPR) for entry-into-service (EIS)2050. The boundary approaching method is utilized to obtain the optimal engine for a series of engines with different fan diameters. Furthermore, the flight mission analysis was carried out to fully consider the engine performance and weight penalty. The optimum engine employs a 3.26 m fan diameter with ultrahigh BPR reaching 21.39. The corresponding specific fuel consumption (SFC) is 11.42 (g/s)/kN, which is 3.88% lower than the 2.95 m fan diameter engine. However, the weight penalty has offset part of the benefits, and the block fuel reduction is 2.5%. Sensitivity analysis results reveal that the low-pressure turbine (LPT) efficiency plays a dominant role in engine performance. Afterwards, the effects of variable geometry are investigated including the blow-off valve (BOV), variable inlet guide vane (VIGV), and bypass variable area nozzle (VAN). Results show that combining the three measures would boost engine performance and save fuel. The designed schedule for the combination of VIGV, BOV, and VAN has generated a reduction in block fuel, NOx, CO2, and H2O reaching 3.36%, 5.55%, 2.47%, and 2.53%, respectively.

Part-load efficiency boost in offshore organic Rankine cycles with a cooling water flow rate control strategy

Global concerns regarding greenhouse gas emissions and global warming have necessitated the speed up in using renewable energies and more efficient use of fossil fuels in the oil and gas industry. Harvesting gas turbine heat by organic Rankine bottoming cycles has raised as a potential solution to cut carbon dioxide emissions in offshore oil and gas installations. Offshore power cycles are expected to operate most of their operational life at part-loads where they suffer from poor efficiency. The purpose of this article is to boost the part-load efficiency of offshore organic Rankine cycles and keep it as close as possible to the design value. Here an operational strategy based on cooling water flow control is developed and added to a sliding pressure control logic and a variable area nozzle turbine control strategy. An in-house tool is developed for the design of organic Rankine cycles and the simulation of off-design control strategies. A design methodology is presented to optimize the cycle power output while minimizing the cycle footprint offshore. The proposed control strategy was successful in keeping the part-load efficiency close to design value and achieving a 5% reduction of annual carbon dioxide emissions.

Design and Geometrical Optimization of Nozzle to Reduce Noise for Jet Engine

A scientific payload is used for deep space observations. It consists of several components, which are used to observe and detect the objects and its details. Such payloads are used to collect data for tin-filer research and understanding about the universe and to know its hidden mysteries. This research is conducted using several observatory instruments like, X-ray spectroscope, hyper spectral image camera, laser ranging instruments, etc. In this project. a mechanical configuration of X-ray spectroscope is designed considering all the design parameters and constraints. Boeing recently tested a scaled variable area jet nozzle capable of a 20% area change Shape Memory Alloy actuators were used to position 12 interlocking panels at the nozzle exit. A closed loop control system was used to maintain a range of constant diameters with varying flow conditions and to vary the diameter under constant flow conditions. Acoustic data by sideline microphones and flow field measurements at several cross-sections using PIV was collected at each condition. In this paper the variable area nozzle's design is described. The effect of the nozzle's diameter on acoustic performance is presented flow field data is shown including the effects of the joints between the interlocking panels.

Assessment of Organic Rankine Cycle Part-Load Performance as Gas Turbine Bottoming Cycle with Variable Area Nozzle Turbine Technology

Power cycles on offshore oil and gas installations are expected to operate more at varied load conditions, especially when rapid growth in renewable energies puts them in a load-following operation. Part-load efficiency enhancement is advantageous since heat to power cycles suffer poor efficiency at part loads. The overall purpose of this article is to improve part-load efficiency in offshore combined cycles. Here, the organic Rankine bottoming cycle with a control strategy based on variable geometry turbine technology is studied to boost part-load efficiency. The Variable Area Nozzle turbine is selected to control cycle mass flow rate and pressure ratio independently. The design and performance of the proposed working strategy are assessed by an in-house developed tool. With the suggested solution, the part-load organic Rankine cycle efficiency is kept close to design value outperforming the other control strategies with sliding pressure, partial admission turbine, and throttling valve control operation. The combined cycle efficiency showed a clear improvement compared to the other strategies, resulting in 2.5 kilotons of annual carbon dioxide emission reduction per gas turbine unit. Compactness, autonomous operation, and acceptable technology readiness level for variable area nozzle turbines facilitate their application in offshore oil and gas installations.

Characterisation of Microstructure and Mechanical Properties of Linear Friction Welded α+β Titanium Alloy to Nitinol

A variable area nozzle integrated into the design of a high-bypass-ratio turbofan engine effectively saves up to 10% in aircraft fuel consumption. Additionally, noise emissions can be lowered at airports during take-off and landing by having better control of the nozzle diameter. Shape memory capabilities of Nitinol alloys could be availed in the form of actuators in the construction of such a nozzle. However, these Nitinol actuators must be joined to Ti-6Al-4V, a prominent alloy making up most of the rest of the nozzle. Because of the huge differences in the physical and metallurgical properties of these alloys, fusion welding is not as effective as solid-state welding. In the current study, a linear friction welding process was adopted to join Ti-6Al-4V to Nitinol successfully. The effect of friction welding on the evolution of weld macro and microstructures; hardness and tensile properties were studied and discussed. The macrostructure of Ti-6Al-4V and Nitinol’s dissimilar joint revealed flash formation mainly on the Ti-6Al-4V side due to its reduced flow strength at high temperatures. Optical microstructures revealed fine grains in Ti-6Al-4V immediately adjacent to the interface due to dynamic recrystallisation and strain hardening effects. In contrast, Nitinol remained mostly unaffected. An intermetallic compound (Ti2Ni) was seen to have formed at the interface due to the extreme rubbing action, and these adversely influenced the tensile strength and elongation values of the joints.

SHAPE MEMORY ALLOY ACTUATORS ARE USED TO CREATE A VARIABLE AREA JET NOZZLE FOR NOISE REDUCTION: A REVIEW

The real study details the design and implementation of Shape memory alloy actuators to produce a noise-reducing variable area jet nozzle. A subscale design specification of a changeable area jet nozzle was created using SMA actuators in an asymmetrical design. Commercial transportation planes must be quieter, cleaner, and more efficient, according to the international community. The aviation industry is reacting by developing new technology in order to achieve those objectives. Changing the area of a commercial jet engine's fan nozzle can result in substantial noise reduction and reduced fuel economy. At takeoff and approach, a bigger diameter reduces jet velocity, which reduces noise. In cruise, adjusting the diameter to account for variable Mach numbers, altitude, and other factors helps optimise fan loading and minimise fuel consumption and emissions. Boeing has tested a 20 percent area change scaled variable area jet nozzle. At the nozzle exit, Shape Memory Alloy actuators were utilised to place 12 interlocking panels. To maintain a range of consistent diameters with variable flow circumstances and to alter the diameter under constant flow conditions, a closed loop control system was utilised. At each condition, acoustic data was gathered using side line microphones, and flow field measurements were taken using PIV at various crosssections. The design of a variable area nozzle is explained in this work. The diameter of the nozzle and its influence on acoustic performance are discussed. The effects of the joints between the interlocking panels are seen in the flow field data.

Diagnostics Using First-Principles Based Digital Twin and Application for Gas Turbine Verification Test

In the present study, a diagnostic method using a first-principles based digital twin is proposed for application during engine verification test. The first-principles model is applied to generate the digital twin model using a small number of measurement data. A method is developed to identify abnormalities of components in a short time and to classify faults through detailed inspection. The digital twin model is generated through performance adaptation with a basic first-principles model. Performance adaptation factors are used for compressor, secondary air system, nozzle, exhaust gas temperature, and engine thrust. Gas path analysis is conducted using the digital twin and the performance test data in real time. Health parameters for compressor capacity and efficiency, secondary air system, and nozzle are calculated from the gas path analysis. Multi-variable Newton-Raphson method is employed for the performance adaptation and the gas path analysis in real time. A single-shaft gas turbine engine is utilized to test and evaluate the effectiveness of the proposed method. Three tests are performed for engine verification. The diagnostic method is applied to the engine test. As a result, it is confirmed that the proposed method can simultaneously detect abnormalities in HPC VGV, secondary air system, and variable area nozzle.

Variable Geometry in Miniature Gas Turbine for Improved Performance and Reduced Environmental Impact

A miniature gas turbine (MGT) is proposed as a promising future energy source. Increasingly stringent requirements related to harmful combustible gas emissions and a trend towards improved energy generation efficiency drive the quest for new MGT technologies. Variable geometry systems are promising due to enhanced heat management and flow control. Variable combustor cooling and dilution holes together with the variable area nozzle (VAN) system allow for the improvement of gas turbine performance and reduction in pollutant emissions. The proposed systems are based on hot-section geometry changes, in which the size of the combustion chamber holes and turbine nozzle angle can be adjusted. Component and module experimental research were performed at the Warsaw University of Technology, on an MGT test stand. A significant decrease in fuel consumption (up to 47% reduction) and harmful nitrogen oxide emission reduction (NO–by 78% and NO2–by 82%) were achieved. These results are related to combustor turbine inlet temperature (TIT) increase up to 1230 K. The tests of the variable geometry systems have also shown an impact on gas turbine power and specific fuel consumption.

Development of the constant rate of momentum change (CRMC) variable area nozzle

An advance propelling nozzle is designed in a different field of applications to accelerate the fluid from subsonic to supersonic/hypersonic. It regulates the flow properties of the liquid and provides the required thrust at a given design and operating conditions. The present study describes and evaluates geometry and its flow properties locally, along with the length of the nozzle. The developed 1-D gas dynamic equations with the real gas equation for the computation of geometry and flow properties assume that the momentum rate is constant. The constant rate of momentum change theory (CRMC) with frictional effect helps in the computation of nozzle coordinates with similar flow properties at any distance (say 0.5 mm in the present case). The results obtained have been validated by computational fluid dynamic (CFD) using ANSYS 14.0. The numerical results are in good agreement in comparison with modern CRMC theory at design conditions.

Performance analysis and optimized control strategy for a three-shaft, recuperated gas turbine with power turbine variable area nozzle

Performance analysis and optimization for a three-shaft, recuperated gas turbine with power turbine variable area nozzle (VAN) is conducted in this paper. A modified recuperator simulation model is obtained from recuperator experiment. A gas turbine performance simulation program is established. The influence of power turbine shaft speed on engine performance is studied and optimized control of power turbine shaft speed is proposed. Comparative performance analysis proves VAN angle control improves engine performance, but leads to less compressor surge margin and increased risk of over temperature. The optimized control of VAN angle under different safety operation temperature limits and ambient temperature is investigated. Power turbine shaft speed barely influences the optimized control of VAN angle, but temperature limits and ambient temperature greatly do. By decoupling power turbine shaft speed and VAN angle, an optimized control strategy for power turbine shaft speed and VAN angle is proposed, which brings 6.37%, 15.88%, 47.80% increases in output power, and 10.84%, 25.59%, 64.97% increase in thermal efficiency when relative high-pressure shaft speed is 0.95, 0.90 and 0.85, respectively. Maximum thermal efficiency could be achieved at part-load conditions rather than design-point if temperature limit is relaxed.

Experimental research of the small gas turbine with variable area nozzle

The main aim of this article is to present the experimental data of the operating parameters and emissions obtained in a small gas turbine equipped with a variable area nozzle system. The variable area nozzle is proposed as a means of improving turbine efficiency, which has been a popular trend in recent development of gas turbine engines. Based on turbine vane twisting, the proposed variable area nozzle system was developed and implemented in GTM-120 small gas turbine. The concept was experimentally investigated on the engine test bench and engine working parameters were accurately measured. Experimental research shows that significant improvement of engine specific fuel consumption (up to 4%) and specific thrust (up to 5%) has been achieved. Additionally, reduction in CO emissions (up to 64%), NO emissions (up to 7%) and NO2 emissions (up to 53%) has been noted. Experimental research results were compared with analytical engine model showing moderate, qualitative agreement between the experimental data and model outputs. Main advantages of variable area nozzle system and design challenges of the proposed concept are discussed in the article summary.

Evaluating performances of 1-D models to predict variable area supersonic gas ejector performances

The application of supersonic gas ejector with variable area nozzle can be found in different industries. However, due to different types of variable area nozzle, performance prediction is mainly focused on costly numerical simulations. In this paper, one-dimensional models for performance prediction of variable area gas ejector with specially designed nozzle, were compared. Additionally, operational lines and corresponding modes were analyzed. Two different variable area ejectors were experimentally tested. The first ejector used natural gas as motive fluid, whereas in the second one motive gas was the composition of alkane. Six distinct correlations of ejector component efficiencies were evaluated. Sum of absolute relative errors and coefficient of determination were used as goodness of fit criteria. The results showed that best model has coefficient of determination 0.76 and 0.63 in the case of natural and R2 gas as motive fluids, respectively. In order to improve prediction performances of entrainment ratio, the mixture of experts machine learning technique was used. Moreover, the results of obtained conditional probabilities of models are visualized in space spanned by area and pressure ratios. The presented analysis showed that one model is not generally better than others and can be improved by using an ensemble of models.

Global bounded variation solutions describing Fanno–Rayleigh fluid flows in nozzles

In this paper, we investigate the initial-boundary value problem of compressible Euler equations including friction and heating that model the transonic Fanno–Rayleigh flows through symmetric variable area nozzles. In particular, the case of contracting nozzles is considered. A new version of a generalized Glimm scheme (GGS) is presented for establishing the global existence of entropy solutions with bounded variation. Modified Riemann and boundary Riemann solutions are applied to design this GGS, which is constructed using the contraction matrices acting on the homogeneous Riemann (or boundary-Riemann) solutions. The extended Glimm–Goodman’s type of wave interaction estimates are investigated to determine the stability of the scheme and the positivity of gas velocity that results in the existence of the weak solution. The limit of approximation solutions serves as an entropy solution. Moreover, a quantitative relation between the shape of the nozzle, friction, and heat is proposed for the global existence result in the contracting nozzle. Numerical simulations of the contraction-expansion and expansion-contraction nozzles are presented to validate the scheme.

Comparison of novel variable area convergent-divergent nozzle performances obtained by analytic, computational and experimental methods

• A novel model of variable area convergent-divergent nozzle is presented. • Experimental and numerical studies of the supersonic ejector have been conducted. • The flow is visualized for different values of spindle positions and outlet pressures. • The velocity of the primary fluid at the nozzle exit is in accordance with the one dimesional analysis. • The performances are presented through relations between entrainment ratio, outlet pressure and spindle position. Different applications of a variable area convergent-divergent nozzle are found in various parts of the industry. This paper presents the development of a new design methodology for a variable area convergent-divergent nozzle, to maintain constant nozzle area ratio for different values of mass flow rates. The validation of the presented model was carried out on an example supersonic ejector using experimental, numerical and analytical data. Analytical (one dimensional) and computational fluid dynamics models showed satisfactory prediction performance in comparison with the experiment. The average entrainment ratio error was between 10% and 7%, respectively. Results confirmed that the velocity of the primary fluid at the nozzle outlet is in accordance with the one dimensional analysis. Although disturbances (strong and weak shock waves) are visible, their effects are negligible. Also, supersonic ejector performances are presented through relations between entrainment ratio, outlet pressure and spindle position. Disadvantages of variable area nozzle utilization in ejector applications are emphasized.

Особенности проектирования ступени силовой турбины транспортного ГТД с регулируемым сопловым аппаратом

Особенности проектирования ступени силовой турбины транспортного ГТД с регулируемым сопловым аппаратом

Characteristics of flow and thrust variations in a jet engine with a variable area nozzle

A numerical analysis of the internal flow field in an exhaust converging-diverging nozzle of a jet engine has been carried out. Variable area nozzle is required in a jet engine for optimal expansion and adjusting back pressure in the engine when the afterburner is operated. Steady-state and transient analyses are carried out for each condition with and without afterburner operation and as a function of the location of the nozzle flap. For a baseline power condition, mixture composition of combustion products is calculated by the chemical equilibrium analysis and the cold flow analysis is carried out based on the mixture composition. For the afterburner operating condition, additional fuel is injected from the inlet boundary and numerical analyses of reactive flow fields are carried out. With variable area nozzle adopted, combustion fields are variable in time, leading to periodically variable thrust. When nozzle flap is in a closed state, nozzle internal pressure and temperature are increased upon the afterburner operation and moment of a force at the pivot point is increased as well. These undesirable phenomena can be solved by control of a variable area nozzle. And, thrust level is also maximized by nozzle variation. During nozzle variation, unsteadiness effect is observed because of response lag of internal flow to nozzle variation. Both the design pressure and the optimum expansion of the nozzle can be attained by adopting the independent operation of a variable area nozzle.