bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and Numerical Investigation of Low-Pressure Preswirl Stator-Rotor Cooling System
Authors: Kutlu B. F. , Ealy B. T. , Hossain J. , Wang W. , Kapat Jay , Lee C. P. , Marra J. , Um Jae , Prakash C.
Published: September 2016

Stator-rotor systems are commonly used in many different types of turbomachinery applications to supply an air for secondary air flows. Commercial CFD codes with variety of turbulence models are widely used in order to estimate the amount of flow supplied by the preswirl stator-rotor system. CFD investigations can provide detailed information about the local flow field which is extremely difficult to obtain from rotating rig due to the measurement limitations in rotating frame, however the accuracy of CFD needs to be investigated by conducting experiments. In this study the purpose is to evaluate how accurate CFD simulations with different turbulence models can predict the flow rate supplied by the system. An experimental rig composed of a stationary preswirler, a rotating disk with an internal flow path and a stator-rotor cavity with a rim seal was used in this study. Air is supplied to the stator from the ambient due to the suction provided by the rotor which can rotate at up to 3100 rpm. Incoming air first flows through annular preswirl guide vanes located inside the stator then discharges into the stator-rotor cavity located downstream of the preswirl guide vanes. Some fraction of the flow induced into the rotor by the help of inlet guides which are attached to the rotor face and angled to match the flow angle in rotating frame. Remaining part of the flow passes through rim seal and discharges out to the ambient. Two experimental cases, one with preswirl guide vanes without endwall contouring and the other with endwall contouring were been investigated at 3100 rpm. Mass flow rate at the inlet was 14.6% higher for the case with endwall contoured configuration compared to the case without endwall contouring. For both of the cases approximately 90% of the inlet flow was purged through rim seal while remaining 10% flows through the radial rotor disk passages. CFD analysis of the rotating rig were conducted using commercial code STAR CCM+. Turbulence models of k-ε, k-ω, Reynolds stress (RST) and Spalart-Allmaras were used and the mass flow rate drawn into the system was compared with experiments. The mass flow rate into the rig from experimental measurements was 7.4% higher compared to the best CFD prediction given by RST Linear. Among all turbulence models k-w was the worst performer by predicting mass flow 13% lower compared to the experimental value. Different sub-options of these turbulence models were also investigated. This study provided significant information for preswirl stator-rotor system designers in terms of the amount of flow rate that can be obtained and how well can it be predicted by CFD.
Numerical Investigation of Shock Effects on Performance and Flow Field in a Transonic Centrifugal Impeller
Authors: Zhao Huijing , Wang Zhiheng , Yu Hongshi , Jiang Chaoyang , Xi Guang
Published: September 2016

In transonic centrifugal compressors, the losses and blockage are increased dominantly by the shock, shock/tip leakage vortex (TLV) interaction and shock/boundary layers interaction on the blade suction side. Therefore, a detailed investigation of shock effects is seriously important to improve the aerodynamic performance and extend the stable operating range of a centrifugal compressor. This paper firstly analyzes the shock structures in the transonic impeller at the design and off-design conditions. It is found that the shock structure is three-dimensional and swept along the span, with the shock becoming normal to the shroud near the blade tip. As the mass flow rate decreases, the swept shock moves upstream, and the shock/TLV interaction becomes stronger, inducing the vortex breakdown at the near stall condition. Then a comparative study is conducted on the flow structures in the transonic centrifugal impeller without the tip clearance (OTC impeller). Compared with the impeller with a tip clearance (WTC impeller), the splitter shock strength in the passage between the main blade and splitter is enhanced and the separation caused by the splitter shock /boundary layers interaction is induced, due to the lack of the blockage in the inducer induced by the shock/TLV of main blade interaction in the WTC impeller. Thus, at a large mass flow rate, the efficiency of the OTC impeller is lower than that of the WTC impeller because the stronger splitter shock induces larger flow separation in the passages between the main blade and splitter. However, at a small mass flow rate, the WTC impeller has a lower efficiency because the losses in the inducer induced by the interaction between the shock and the TLV of main blade are dominant.
Wake and Loss Analysis for a Double Bladed Swept Propeller
Authors: Capitao Patrao Alexandre , Avellán Richard , Lundbladh Anders , Grönstedt Tomas
Published: September 2016

Inspired by Prandtl’s theory on aircraft wings with minimum induced drag, the authors introduced a double-bladed propeller, the Boxprop, intended for high-speed flight. The basic idea is to join the propeller blades pair-wise at the tip to improve aerodynamics and mechanical properties compared to the conventional propeller. The rather complex geometry of the double blades gives rise to new questions, particularly regarding the aerodynamics.

This paper presents a propeller wake energy analysis method which gives a better understanding of the potential performance benefits of the Boxprop and a means to improve its design.

CFD analysis of a five bladed Boxprop demonstrated its ability to generate typical levels of cruise thrust at a flight speed of Mach 0.75. The present work shows that the near tip velocity variations in the wake are weaker for this propeller than a conventional one, which is an indication that a counter rotating propeller designed with a Boxprop employed at the front may exhibit lower interaction noise.
Thermodynamic Analysis of Organic Rankine Cycle (ORC) Systems Based on Turbine Performance Prediction
Authors: Song Jian , Gu Chun-wei
Published: September 2016

Energy shortage and environmental deterioration are two crucial issues that the developing world must face. As a promising solution, the conversion of low grade energies is attracting more and more attention. Among all of the existing technologies, Organic Rankine Cycle (ORC) has been proven to be an effective method to utilize the low grade energies. Thermodynamic analysis is important for working fluid selection and system parameter determination in the ORC system. In conventional studies, the efficiency of the organic turbine is fixed at a constant value. However, the turbine efficiency is evidently related to the working fluid property and system operating condition. Thus, the constant turbine efficiency is unreasonable and may lead to sub-optimal thermal results. To enhance the reliability and accuracy of ORC system analysis, the one-dimensional analysis model is used to predict the turbine performance in this paper. The calculated one-dimensional turbine efficiency replaces the constant efficiency in the system analysis. The influence of the working fluid property and system operating condition on the turbine performance is evaluated. Thermal performances of the ORC systems with the one-dimensional turbine efficiency and the constant turbine efficiency are simulated and compared. The results reveal that the turbine efficiency plays a significant role in working fluid selection and system parameter determination for the ORC system.
Aerodynamic and Acoustic Performance of a Single Stage Axial Fan With Extensive Blade Sweep Designed to Limit Noise Emissions
Authors: Giesecke Daniel , Friedrichs Jens , Stark Udo , Dierks Maik
Published: September 2016

Not only the aerodynamic performance of axial flow fans is important but also the acoustic behaviour plays a vital role. It is to be expected that in the future noise limits will be more regulated by legislation. The aim of this project is to develop a very versatile tool for efficient and noise reduced axial flow fans in rotor / stator configuration.

This paper describes the design, numerical verification and tests of a highly loaded single stage axial flow fan making use of extensive blade sweep in rotor and stator for acoustic reasons. The tests include aerodynamic and acoustic investigations.

The stage is a conventional free vortex design with unconventional blades of a special planform. The blade sections of both rotor and stator are NACA 65-sections on circular arc mean lines. Sectional diffusion factors and de Haller numbers are close to their respective limits, especially for the sections next to the rotor and stator hubs.

The rotor is characterised by a forward-swept leading edge with increasing sweep angle towards hub and tip and an unswept trailing edge. The leading edge of the stator blades is forward-swept as before but this time at an almost constant sweep angle between the hub and the two-thirds position of the blade span. The trailing edge is straightened for reducing the previously mentioned aerodynamic loadings.

The study shows that the numerical results are consistent with the experimental outcome. It concludes that the advanced design features show potential aerodynamic and acoustic benefits by sweeping the blade in the described manner. This is particularly the case when comparing to single row designs.
Hybrid RANS-LES Modeling of the Aero-Thermal Field in an Annular Hot Streak Generator for the Study of Combustor-Turbine Interaction
Authors: Andreini A. , Bacci T. , Insinna M. , Mazzei L. , Salvadori S.
Published: September 2016

Turbine entry conditions are characterized by unsteady and strongly non-uniform velocity, temperature and pressure fields. The uncertainty and the lack of confidence associated with these conditions require the application of wide safety margins during the design of the turbine cooling systems, with a detrimental effect on engine efficiency. The adoption of lean-burn technology in modern aero-engines to reduce NOx emissions exacerbates the situation, as the absence of dilution holes keeps the strong swirl component generated by the burners up to the combustor outlet and prevents to control the pattern factor. Complexity and costs associated with the experimental investigation of combustor-turbine interaction, makes Computational Fluid Dynamics (CFD) paramount to understand the physical phenomena involved. Moreover, due to the well-known limitations of the Reynolds-Averaged Navier-Stokes (RANS) approach and the increase in computational resources, hybrid RANS-LES models, such as Scale Adaptive Simulation (SAS), are proving to be a viable approach to capture the main structures of the flow field. This paper reports the main findings of the numerical investigation on a test rig representative of a lean-burn, effusion cooled, annular combustor, developed in the context of the EU Project FACTOR (Full Aerothermal Combustor-Turbine interactiOns Research) with the aim of studying combustor-turbine interaction. Results obtained with RANS and unsteady SAS were critically compared to experimental data and analysed in order to better understand the flow physics within such a device, as well as to assess the improvements related to the use of hybrid models. The main discrepancies between RANS and SAS are highlighted in predicting the recirculating region, which has slight influence on the velocity field at the combustor outlet, but affects dramatically mixing and the resulting temperature distribution. Accuracy of the results achieved suggest a possible exploitation of SAS model with a view to the future inclusion of the nozzle guide vanes within the test rig.
Methods for the Extraction and Analysis of the Global Mode in Swirling Jets Undergoing Vortex Breakdown
Authors: Rukes Lothar , Sieber Moritz , Paschereit C. Oliver , Oberleithner Kilian
Published: September 2016

Swirling jets undergoing vortex breakdown are widely used in combustion applications, due to their ability to provide aerodynamic flame stabilization. It is well known that vortex breakdown is accompanied by a dominant coherent structure, the so called precessing vortex core (PVC). Reports on the impact of the PVC on the combustion process range from beneficial to detrimental. In any event, efficient methods for the analysis of the PVC help to increase the benefit or reduce the penalty resulting from it. This study uses Particle Image Velocimetry (PIV) measurements of a generic non-isothermal swirling jet to demonstrate the use of advanced data analysis techniques. In particular, the Finite Time Lyapunov Exponent (FTLE) and local linear stability analysis (LSA) are shown to reveal deep insight into the physical mechanisms that drive the PVC. Particularly, it is demonstrated that the PVC amplitude is strongly reduced, if heating is applied at the wavemaker of the flow. These techniques are complemented by the traditionally used Proper Orthogonal Decomposition (POD) and spatial correlation techniques. It is demonstrated how these methods complement each other and lead to a comprehensive understanding of the PVC that lays out the path to efficient control strategies.
The Optimization of a Centrifugal Impeller Based on a New Multi-Objective Evolutionary Strategy
Authors: Li Xiaojian , Zhao Yijia , Liu Zhengxian , Chen Hua
Published: September 2016

Centrifugal compressors with high aerodynamic performance are widely used in turbochargers, aero-engines and petrochemical engineering. The impeller is the core component and plays a key role in determining the compressor performance.

This paper reports the optimisation of the aerodynamic performance of an industrial centrifugal impeller by a multi-objective evolutionary strategy. Firstly the 3-D modeling method for parameterisation of impeller’s geometry was described. Secondly the traditional NSGA-II method was modified to improve its ability and efficiency. Employed CFD code was first validated using the experimental data of an existing impeller. The optimisation was applied to the industrial centrifugal impeller through a two-step optimization process to allow for significant variations of the impeller geometry and speedy finding of the optimum. The optimisation was completed within 53 hours on a workstation with two 24-core processors (Xeon(R) E5-2670 v3 2.3GHz). The results indicated that the isentropic efficiency of the impeller increased by 5.3 percents and the total pressure ratio by 20.5 percents at design condition.
Developing Additive Manufacturing Technology for Burner Repair
Authors: Andersson Olov , Graichen Andreas , Brodin Håkan , Navrotsky Vladimir
Published: September 2016

Low emission combustion is one of the most important requirements for Industrial gas turbines. Siemens Industrial gas turbines SGT-800 and SGT-700 use DLE (Dry Low Emission) technology and are equipped with 3rd generation of DLE burners. These burners demonstrate high performance and reliable operation for the duration of their design lifetime. The design and shape of the burner tip is of great importance in order to achieve a good fuel/ air mixture and at the same time a resistance to the fatigue created by heat radiation input. This gives a requirement for a tip structure with delicate internal channels combined with thicker structure for load carrying and production reasons. It was found that the extension of the burner lifetime beyond the original design life could be accomplished by means of repair of the burner tip.

Initially the tip repair has been done by conventional methods — i.e. cutting off the tip and replacing it with a premanufactured one. Due to the sophisticated internal structure of the burner the cuts have to be made fairly high upstream to avoid having the weld in the delicate channel area.

Through the use of AM (Additive Manufacturing) technology it has been possible to simplify the repair and only replace the damaged part of the tip.

Special processes have been developed for AM repair procedure, including:

a) machining off of the damaged and oxidized tip,

b) positioning the sintered model on the burner face,

c) sintering a new tip in place,

d) quality assurance and inspection methods,

e) powder handling,

f) material qualification including bonding zone,

g) development of methods for mechanical integrity calculation,

h) qualification of the whole repair process.

This paper describes how we have developed and qualified SGT-800 and SGT-700 DLE burners repair with the help of additive manufacturing technology and our research work performed. In addition, this paper highlights the challenges we faced during design, materials qualification and repair work shop set-up.
Assessment of RANS Against LES for the Aero-Thermal Behavior of High Pressure Turbine Stages Under Realistic Inlet Conditions
Authors: Vagnoli Stefano , Verstraete Tom , Koupper Charlie , Bonneau Guillaume
Published: September 2016

Modern Lean Burn combustors generate a complex field at the High Pressure turbine (HPT) inlet, characterized by non-uniform velocity and temperature distributions, together with very high turbulence levels (up to 25%). For these extreme conditions, classical numerical methods employed for the HPT design, such as Reynolds Averaged Navier Stokes (RANS) simulation, suffer from a lack of validation. This leads to a reduced confidence in predicting the combustor-turbine interactions, which requires to use extra safety margins, to the detriment of the overall engine performance.

Within the European FACTOR project, a 360° non reactive combustor simulator and a 1.5 HPT stage are designed to get more insight into the mutual interaction of these two components. A first experimental and numerical campaign has demonstrated the potential of Large Eddy Simulations (LES) to accurately reproduce the turbulent flow field development at the combustor outlet.

The aim of the present paper is to exploit the accuracy of LES to validate less time-consuming RANS models in predicting the hot streak migration in the turbine stage. In this sense, LES results are used as a reference to discriminate the different RANS simulations in terms of turbulence modeling and aerothermal predictions.

The current investigations clearly indicate that turbulence and hot streak diffusion within the HPT are strongly linked. In this sense, the choice of the RANS turbulence model and the inlet turbulent conditions plays a major role in modeling the thermal behavior for the stator and rotor blades.
Accounting for Uncontrolled Variations in Low-Speed Turbine Experiments
Authors: Evans K. R. , Longley J. P.
Published: September 2016

It is common to assume that the performance of low-speed turbines depend only on the flow coefficient and Reynolds number. As such the required operating point is achieved by controlling the values of these two non-dimensional quantities by, for example, appropriate choices for the mass flow rate and applied brake torque. However, when the turbine has an atmospheric inlet and uses unconditioned air, variations in ambient pressure, temperature and humidity are introduced. Whilst it is still possible to maintain the required values for the flow coefficient and Reynolds number, the ambient variations affect additional non-dimensional quantities which are related to the blade speed and gas properties. Generally, the values of these additional non-dimensional quantities cannot be controlled and, consequently, they affect the turbine performance. In addition, thermal effects, which are exacerbated by the use of plastic blades, can cause changes in the blade row seal clearance and these also affect the performance. Therefore to obtain measurements with greater accuracy and repeatability, the changes in the uncontrolled non-dimensional quantities must be accounted.

This paper contains four parts. Firstly, it is described how suitable data acquisition parameters can be determined to eliminate short time scale facility unsteadiness within the measurements. Secondly, by the analysis of models, the most appropriate forms for the additional non-dimensional quantities that influence turbine performance are obtained. Since the variations in the uncontrolled non-dimensional quantities affect repeatability the size of the effect on the turbine performance is quantified. Thirdly, a best-fit accounting methodology is described which reduces the effects of the uncontrolled non-dimensional quantities on turbine performance provided sufficient directly related measurements are available. Finally, the observations are generalised to high-speed turbomachines.
Unsteady Adjoint of Pressure Loss for a Fundamental Transonic Turbine Vane
Authors: Talnikar Chaitanya , Wang Qiqi , Laskowski Gregory M.
Published: September 2016

High fidelity simulations, e.g., large eddy simulation are often needed for accurately predicting pressure losses due to wake mixing and boundary layer development in turbomachinery applications. An unsteady adjoint of high fidelity simulations is useful for design optimization in such aerodynamic applications. In this paper we present unsteady adjoint solutions using a large eddy simulation model for a vane from VKI using aerothermal objectives. The unsteady adjoint method is effective in capturing the gradient for a short time interval aerothermal objective, whereas the method provides diverging gradients for long time-averaged thermal objectives. As the boundary layer on the suction side near the trailing edge of the vane is turbulent, it poses a challenge for the adjoint solver. The chaotic dynamics cause the adjoint solution to diverge exponentially from the trailing edge region when solved backwards in time. This results in the corruption of the sensitivities obtained from the adjoint solutions. An energy analysis of the unsteady compressible Navier-Stokes adjoint equations indicates that adding artificial viscosity to the adjoint equations can dissipate the adjoint energy while potentially maintain the accuracy of the adjoint sensitivities. Analyzing the growth term of the adjoint energy provides a metric for identifying the regions in the flow where the adjoint term is diverging. Results for the vane from simulations performed on the Titan supercomputer are demonstrated.
Numerical and Experimental Investigation of Aerodynamics on Flow Around a Highly Loaded Low-Pressure Turbine Blade With Flow Separation Under Steady and Periodic Unsteady Inlet Flow Condition
Authors: Nikparto Ali , Schobeiri Meinhard T.
Published: September 2016

Understanding the behavior of flow field around a turbine blade is of importance in gas turbine engineering and it can affect the design and performance of engine elements. An important phenomena that can affect the flow regime is the effect that impinging wakes, originating from stator blades, have on the flow around rotor blades. Reynolds Averaged Navier-Stokes (RANS) equation, in conjunction with turbulence models enables us to model flow fields. This study numerically and experimentally investigates the behavior of the boundary layer development along the suction and pressure surfaces of a highly loaded low-pressure turbine blade under steady and unsteady inlet flow condition. For unsteady case a range of reduced frequencies of the incoming wakes were modeled and studied. Also it includes a comprehensive assessment of predictive capability of RANS numerical tools. To evaluate the reliability of current RANS-based numerical method, a rigorous boundary layer and heat transfer measurement were done in unsteady boundary layer cascade facility of Turbomachinery Performance and Flow Research Lab (TPFL) of Texas A&M University. Aerodynamics experiments include measuring the onset of the boundary layer, its transition, separation and re-attachment using miniature hot wire probes. All measurements were performed for different wake frequencies and flow conditions and results were compared to the obtained simulation results. Comparisons of the experimental and numerical results detail the differences in predictive capabilities of the RANS methods in terms of the locating the onset and length of separation, velocity profile inside boundary layer, velocity fluctuations.
DNS of Low-Pressure Turbine Cascade Flows With Elevated Inflow Turbulence Using a Discontinuous-Galerkin Spectral-Element Method
Authors: Garai Anirban , Diosady Laslo T. , Murman Scott M. , Madavan Nateri K.
Published: September 2016

Recent progress towards developing a new computational capability for accurate and efficient high–fidelity direct numerical simulation (DNS) and large–eddy simulation (LES) of turbomachinery is described. This capability is based on an entropy– stable Discontinuous–Galerkin spectral–element approach that extends to arbitrarily high orders of spatial and temporal accuracy, and is implemented in a computationally efficient manner on a modern high performance computer architecture. An inflow turbulence generation procedure based on a linear forcing approach has been incorporated in this framework and DNS conducted to study the effect of inflow turbulence on the suction–side separation bubble in low–pressure turbine (LPT) cascades. The T106 series of airfoil cascades in both lightly (T106A) and highly loaded (T106C) configurations at exit isentropic Reynolds numbers of 60,000 and 80,000, respectively, are considered. The numerical simulations are performed using 8th–order accurate spatial and 4th–order accurate temporal discretizations. The changes in separation bubble topology due to elevated inflow turbulence are captured by the present method and the physical mechanisms leading to the changes are explained. The present results are in good agreement with prior numerical simulations but some expected discrepancies with the experimental data for the T106C case are noted and discussed.
Optimized NOX Control by Injection of Fine Water Spray Into Compressor Discharge
Authors: Ingistov Steve , Savic Sasa
Published: September 2016

The Watson Cogeneration Plant (WCP) is situated within Los Angeles Refinery Complex. A portion of generated power and steam is sent to Refinery. Major power producers are the combustion gas turbines, GE-made, Frame No 7, Model EA. These turbines are furnished with diffusion-type combustors which can burn mixture of treated refinery gas and natural gas from the pipe line. These combustors are capable of burning pure butane gas too, as required. The NOX control is achieved by injection of DE-NOX steam into the combustors. The Refinery change in processes was reflected in the refinery gas composition where the percentage of Hydrogen grew. Hydrogen combustion generates more NOX, at the same firing temperature and additional steam injection is necessary. During the years, since 1987, startup of WCP, steam demand from Refinery steadily grew. This Paper describes the efforts to curtail further DE-NOX demands and instead of additional DE-NOX steam, use water injection into gas turbine housing element called the “wrapper”.
Inverse Design of Axial-Flow Compressor Blades Using Elastic Surface Algorithm in Subsonic and Transonic Flow Regimes With Separation
Authors: Noorsalehi M. H. , Nili-Ahamadabadi M. , Shirani E. , Safari M.
Published: September 2016

In this study, a new inverse design method called Elastic Surface Algorithm (ESA) is developed and enhanced for axial-flow compressor blade design in subsonic and transonic flow regimes with separation. ESA is a physically based iterative inverse design method that uses a 2D flow analysis code to estimate the pressure distribution on the solid structure, i.e. airfoil, and a 2D solid beam finite element code to calculate the deflections due to the difference between the calculated and target pressure distributions. In order to enhance the ESA, the wall shear stress distribution, besides pressure distribution, is applied to deflect the shape of the airfoil. The enhanced method is validated through the inverse design of the rotor blade of the first stage of an axial-flow compressor in transonic viscous flow regime. In addition, some design examples are presented to prove the effectiveness and robustness of the method. The results of this study show that the enhanced Elastic Surface Algorithm is an effective inverse design method in flow regimes with separation and normal shock.
An Alignment Monitoring Device for the Output Shafting of Marine Gas Turbine
Authors: Xue-You Wen , Dong-ming Xiao , Bin Dong , Zi-gang Song , Dan Kou
Published: September 2016

When a marine gas turbine is installed on the ship, the alignment among the power turbine, the output shaft and the reduction gearbox needs to be examined and adjusted precisely. After a long period of gas turbine operation, the alignment of the shafting needs be reviewed and adjusted regularly according to relevant regulations as well.

The paper introduces an alignment monitoring device, by which the alignment of the shafting under static and dynamic conditions can be acquired at any time. The device has been verified by real shipboard tests and the on-condition maintenance can be realized. The device can reduce significantly the workload of scheduled maintenance and can be used as a recorder for the responds of gas turbine against various dynamic shocks.
Linear to Nonlinear Transition During the Spike Stall Process in a Low Speed Axial Flow Compressor Rotor
Authors: Qian Yuping , Jin Yuzhi , Zhuge Weilin , Zhang Yangjun , Lu Yajun
Published: September 2016

A linear to nonlinear transition during the spike stall process of an axial flow compressor rotor is presented. Recently, some researchers thought that spike stall inception is directly induced by the tip leakage flow. However, the authors utilized unsteady full annular simulations and found that a second-order disturbance appeared two revolutions before the breakdown of the tip leakage flow in an axial rotor, associate with spike stall inception while the tip leakage flow is still stable. This second-order disturbance grew rapidly in the next two revolutions and the process was unlike the low order disturbance development in modal stall inception. The response of the compression system was still linear in this process. The rapidly developing second-order disturbance made the tip leakage flow unstable, leading to the start of spike stall inception. The response of the compression system became nonlinear in this process.
Influence of Main Swirler Vane Angle on the Ignition Performance of TeLESS-II Combustor
Authors: Wang Bo , Zhang Chi , Lin Yuzhen , Hui Xin , Li Jibao
Published: September 2016

In order to balance the low emission and wide stabilization for lean premixed prevaporized combustion, the centrally staged layout is preferred in advanced aero-engine combustors. However, compared with the conventional combustor, it is more difficult for the centrally staged combustor to light up as the main stage air layer will prevent the pilot fuel droplets arriving at igniter tip. The goal of the present paper is to study the effect of the main stage air on the ignition of the centrally staged combustor. Two cases of the main swirler vane angle of the TeLESS-II combustor, 20° and 30° are researched. The ignition results at room inlet temperature and pressure show that the ignition performance of the 30° vane angle case is better than that of the 20° vane angle case. High speed camera, PLIF and CFD are used to better understand the ignition results. The high-speed camera has recorded the ignition process, indicated that an initial kernel forms just adjacent the liner wall after the igniter is turned on, the kernel propagates along the radial direction to the combustor center and begins to grow into a big flame, and then it spreads to the exit of the pilot stage, and eventually stabilizes the flame. CFD of the cold flow field coupled with spray field is conducted. A verification of the CFD method has been applied with PLIF measurement, and the simulation results can qualitatively represent the experimental data in terms of fuel distribution. The CFD results show that the radial dimensions of the primary recirculation zone of the two cases are very similar, and the dominant cause of the different ignition results is the vapor distribution of the fuel. The concentration of kerosene vapor of the 30° vane angle case is much larger than that of the 20° vane angle case close to the igniter tip and along the propagation route of the kernel, therefore, the 30° vane angle case has a better ignition performance. For the consideration of the ignition performance, a larger main swirler vane angle of 30° is suggested for the better fuel distribution when designing a centrally staged combustor.
Uncertainty Quantification in Turbomachinery Simulations
Authors: Emory Michael , Iaccarino Gianluca , Laskowski Gregory M.
Published: September 2016

Numerical simulations based on Reynolds averaged Navier-Stokes models are routinely used in the analysis and design of turbomachinery components. It is however known that RANS closures are fundamentally limited in their ability to represent turbulent processes — introducing epistemic model-form uncertainties in the predictions. These are compounded by variability (aleatory uncertainties) introduced by limited information regarding, for example, the operating upstream conditions of turbo machinery components. In this work we consider a polynomial chaos approach to characterize and rank the aleatory uncertainty sources and a novel, non-probabilistic strategy to characterize the model-form errors. The present analysis enables us to break down the relative importance of epistemic and aleatory uncertainty and to build confidence intervals on the predictions. We consider simulations of a turbine guide vane cascade and assess the effect of combined uncertainties on the prediction of the wall heat flux.
Creep/Fatigue Tests on Full Scale Hollow Turbine Blades Considering Temperature Gradient
Authors: Chen Cao , Yan Xiaojun
Published: September 2016

Working in a harsh environment with high temperature gas and high rotation speed, hollow turbine blades of gas turbine engine commonly endure both creep damage and low cycle fatigue damage at the same time. It is difficult to predict the life of hollow turbine blades accurately because of a strong coupling effect between creep and low cycle fatigue (creep/fatigue) damage. To address this difficulty, one effective way is to carry out creep/fatigue tests on full scale hollow turbine blades in a bench environment. The present creep/fatigue test methods on full scale hollow turbine blades usually do not consider the temperature gradient between the wall of cooling hole and blade surface. It does not matches the actual working circumstance of hollow turbine blades, under which the temperature gradient at the blade body can reached 150°C or even more higher. This investigation proposes a new experimental setup of creep/fatigue tests on full scale hollow turbine blades, in which real hollow turbine blades are heated by the eddy current induction heating furnace and cooled by cooling air which goes through the hollow blade’s cooling hole. During the tests, the temperature gradient between the wall of cooling holes and blade surfaces were controlled by adjusting the power of eddy current induction heating furnace and the flux of cool-air. Several thermocouples are employed to measure and validate the temperature gradient at the key/critical section, among them three are embed inside the wall of cooling hole by cutting the hollow turbine blade along cooling hole into three parts, and two are glued on the blade’s surface. Tests results show that, when the eddy current induction heating furnace is working stably with an output power of 6.4 Kw and meanwhile the flux of cooling air which goes through the hollow turbine blade’s cooling hole reaches 10 liter per minute, the temperature gradient of the hollow turbine blade at the key/critical section can be well simulated in a bench environment. Eight full scale hollow turbine blades have been tested at four different stress levels in this investigation. The test data are processed to obtain the field life based on equivalent damage principle. The field life data of the hollow turbine blades fits well with that of their flight experience.
A Damage Evaluation Model of Turbine Blade for Gas Turbine
Authors: Zhou Dengji , Chen Meishan , Zhang Huisheng , Weng Shilie
Published: September 2016

Current maintenance, having a great impact on the safety, reliability and economics of gas turbine, becomes the major obstacle of the application of gas turbine in energy field. An effective solution is to process Condition based Maintenance (CBM) thoroughly for gas turbine. Maintenance of high temperature blade, accounting for most of the maintenance cost and time, is the crucial section of gas turbine maintenance. The suggested life of high temperature blade by Original Equipment Manufacturer (OEM) is based on several certain operating conditions, which is used for Time based Maintenance (TBM). Thus, for the requirement of gas turbine CBM, a damage evaluation model is demanded to estimate the life consumption in real time. A physics-based model is built, consisting of thermodynamic performance simulation model, mechanical stress estimation model, thermal estimation model, creep damage analysis model and fatigue damage analysis model. Unmeasured parameters are simulated by the thermodynamic performance simulation model, as the input of the mechanical stress estimation model and the thermal estimation model. Then the stress and temperature distribution of blades will be got as the input of the creep damage analysis model and the fatigue damage analysis model. The real-time damage of blades will be evaluated based on the creep and fatigue analysis results. To validate this physics-based model, it is used to calculate the lifes of high temperature blade under several certain operating conditions. And the results are compared to the suggestion value of OEM. An application case is designed to evaluate the application effect of this model. The result shows that the relative error of this model is less than 10.4% in selected cases. And it can cut overhaul costs and increase the availability of gas turbine significantly. Therefore, the physical-based damage evaluation model proposed in this paper, is found to be a useful tool to tracing the real-time life consumption of high temperature blade, to support the implementation of CBM for gas turbine, and to guarantee the reliability of gas turbine with lowest maintenance costs.
Performance Optimization and Economic Analysis of Geothermal Power Generation by Subcritical and Supercritical Organic Rankine Cycles
Authors: Liu Changwei , Gao Tieyu , Zhu Jiangnan , Xu Jiamin
Published: September 2016

In a sustainability context, using renewable energy sources to hedge against increasing consumption of fossil fuels and reduce greenhouse gas emissions becomes increasingly important. The geothermal resource has a great application prospect due to its rich reserves and convenient utilization, and Organic Rankine Cycle (ORC) is a effective method to convert the low-grade geothermal to electricity. To improve the performance of geothermal ORC system, working fluid selection, system parameter optimization and the cycle design are the main approaches. Zeotropic mixtures may show superiority as ORC working fluids due to the temperature glides during the phase transitions, which leads to better temperature matches between the working fluid and the heat source/sink. Moreover, owing to the changing temperature during the transition from liquid to vapor in the vapor generator, supercritical ORC provides a great potential in geothermal utilization and irreversibility reduction.

This paper displays an investigation on the performance optimization and economic analysis of various working fluids under subcritical and supercritical conditions. To avoid the silica oversaturation, the geothermal water reinjection temperature should not be less than 70 °C. Turbine inlet temperature, condenser outlet temperature as well as turbine inlet pressure (for supercritical ORC) are optimized to maximize the net power output. Moreover, economic analysis is conducted by taking heat exchanger area per unit power output (APR) and the specific investment cost (SIC) as indicators under the optimal net power output condition. The results shows that working fluid with a medium critical temperature yields greater net power output in supercritical ORC and mixture produces larger net power output compared with its pure components in subcritical ORC. Compared with isobutane (R600a) under subcritical condition, isobutane/isopentane (R600a/R601a) and isobutane/pentane (R600a/R601) under subcritical condition, R134a and R1234ze(E) under supercritical condition yield 3.9%, 3.8%, 8.5% and 8.8% more net power outputs, respectively. In addition, R600a/R601a and R600a/R601 under subcritical condition own higher APR and SIC while R134a and R1234ze(E) under supercritical condition possess lower APR and SIC.
Emissions Characteristics of Combustion of Lean Secondary Premixed Gas Jets Injected Into Burned Gas From Primary Stage by Lean Premixed Combustion Supported by Reverse Jet Flame Holding
Authors: Saitoh Takumi , Nakasu Takafumi , Hiroi Takumi , Yamada Hideshi , Hayashi Shigeru
Published: September 2016

The emissions characteristics of a model gas turbine combustor characterized by the enhancement of the reactions of the secondary mixtures of lean to ultra-lean compositions by the burned gas from the primary stage were investigated at atmospheric pressure. A cylindrical quartz tube with the bottom end closed was used as the combustion chamber and the mixture injector was extending co-axially into the combustion chamber to the bottom wall. The stagnation point reverse flow combustion was used for the primary stage where the primary mixture was injected toward the end wall. The secondary mixture was injected radially from the multiple holes in the outer wall of the injector into the burned gas from the primary stage. The effects of the positions for injection of the primary and secondary mixtures as well as mixture temperatures on NOx, CO and HC emissions were investigated over a range of the primary and secondary mixture equivalence ratios at atmospheric pressure.
Endwall Secondary Flow Control in a High Speed Compressor Cascade With Vortex Generator Jets
Authors: Liu Huaping , Li Deying , Lu Bingxiao , Yu Menghan
Published: September 2016

This paper presents a numerical investigation of secondary flow control in a high speed compressor cascade for different incoming flow incidences by means of endwall vortex generator jets (VGJs). The inlet Reynolds number is 560,000 in corresponding to an inlet Mach number of 0.67. Based on the detail analysis of the flow field and cascade performance, two effect mechanisms of the vortex induced by the VGJ are proposed. The first is to enhance the mixing between the endwall boundary layer and the mainstream. The second is to block the cross flow as an air obstacle. Therefore, the low energy fluids accumulation in the corner region could be decreased significantly, weakening the separation on the suction side and reducing the losses effectively. This benefit becomes more obvious with the increase of the incidence from i = −2° to 4°. Additionally, a more uniform flow angle as well as static pressure profile along the blade height is obtained at the cascade outlet. The maximum loss reduction is up to 12.9% while i = 4° with a jet mass flow ratio of 0.2%. However, the unfavorable impact of the VGJs is also detected in the up-washed region, where the loss is increased by the mixing processes between the mainstream fluids and the low energy fluids. For the case i = −4°, a strengthened induced vortex is generated due to the increased angle between the jet and incoming flow, resulting in loss increase in the up-washed region. Besides, a more rapid corner boundary layer development appears in the rear part of the passage, contributing to severe separation and loss enhancement, which suggests that the VGJ should be switched off for this incidence. Therefore, the advice to the application of the VGJ according the incidence is further obtained.
Influence of Reynolds Number on the Performance of Process Centrifugal Compressors
Authors: Liu Yan , Tao Li-hua , Wang Jian , Wang Yang , Wang Xue-jun , Wang Wei
Published: September 2016

Over the past 60 years, effects of changes in Reynolds number on performance of centrifugal compressors have been widely investigated. However most of cases deal with those compressors with small or medium flow coefficients. Studies on the influence of Reynolds number on centrifugal compressors with large flow coefficients and high machine Mach number are rarely seen in the literature.

This paper deals with two types of centrifugal compressors. One type of compressor (Model 1) has a relatively large capacity with high machine Mach number. The flow coefficient and machine Mach number are 0.16 and 1.05 respectively at the design condition. Those design parameters for the other type of compressor (Model 2) are 0.11 and 0.7 respectively. Both experimental and numerical results show that with increase in Re, aerodynamic performance of centrifugal compressors is improved. However, to what extent that improvement is gained depends on properties of the baseline compressor. When Reynolds number of Model 1 becomes about 5 times large due to increase in the inlet pressure, its polytropic efficiency is only improved 0.7% at the design point in experiment. Flow field inside the impeller is similar to its prototype. For Model 2, when Reynolds number becomes 1.78 times large due to scaling up, the polytropic efficiency of the enlarged one is improved about 2% at the design point. These results demonstrate that for a compressor with large flow coefficient and high machine Mach number, i.e. originally high Reynolds number, the influence of Reynolds number on its performance is limited.

In addition to experiment and CFD, two empirical formulas are applied to work out performance correction due to a change in Reynolds number for Model 1 and Model 2. Although CFD results are more accurate than the empirical results, empirical formula is still useful to get relatively reliable performance correction.
Influence of Trailing Edge Coolant Ejection Rate and Cut-Back Length on Energy Loss and Shockwave Intensity of a Transonic Turbine Blade
Authors: Wang Yufeng , Zhou Xun , Liu Xun , Wang Songtao
Published: September 2016

As part of our efforts to understand better ways and means to further improve jet engine performance, the influence of trailing edge coolant ejection rate and cut-back length on energy loss and shockwave intensity of a transonic turbine blade is numerically investigated with an exit Mach number of 1.2 for different coolant/main stream mass-flux ratios and cut-back lengths. Test results indicate both coolant ejection rate and cutback length have their optimum values, and the best ejection rate and the best cut-back length correlate with each other. From the view of minimizing the energy loss coefficient, the best ejection rate decreases with the increasing cut-back length. And from the view of minimizing the trailing edge shockwave intensity, a higher trailing edge coolant ejection rate and a longer trailing edge cut-back can reduce the shockwave intensity. It is therefore believed that these findings can of course facilitate the design of a trailing edge cooling system for transonic turbine blade to further improve jet engine performance. Moreover, trailing edge coolant ejection can be considered as an active flow control method at the same time.