bluuebunny/crossref_metadata_2025 huggingface dataset:
Two Degree-of-Freedom µ Synthesis Control With Kalman Filter for Flight Environment Simulation Volume With Sensors Uncertainty
Authors: Zhu Meiyin , Wang Xi , Yang Shubo , Chen Huairong , Miao Keqiang , Gu Nannan
Published: November 2019

Flight Environment Simulation Volume (FESV) is the most important subsystem of Altitude Ground Test Facilities (AGTF). Its control precision of temperature and pressure determines the level of test ability of AGTF. However, in practice, the sensor hysteresis and noise may greatly affect the control precision of FESV. To improve the control performance of FESV in practice, a new control structure of two degree-of-freedom (DOF) μ synthesis control with the extended Kalman filter (EKF) considering actuators and sensors uncertainty is proposed, which constitutes a core support part of the paper. For the problem of sensors de-noising, an EKF is devised to provide a credible feedback signal to the two DOF μ controller. Aiming at the problem of reference command’s rapid change, one freedom feed forward is adopted, while another freedom output feedback is used to ensure good servo tracking as well as disturbance and noise rejection; furthermore to overcome the overshoot problem and acquire dynamic tuning, an integral is introduced in inner loop; additionally, two performance weighting functions are designed to achieve robustness and control energy limit considering the uncertainties in system.

In order to verify the effectiveness of the designed two DOF μ synthesis controller with EKF, we suppose a typical engine test condition with Zoom-Climb and Mach Dash and consider time delay and Gaussian noise in the sensors. The simulation results show that the designed two DOF μ synthesis controller with EKF has good servo tracking and noise rejection performance and the relative steady-state and transient errors of temperature and pressure are both less than 0.1% and 0.2% respectively. Additionally, we validate the robust performance of the designed two DOF μ controller with EKF by using the upper bound value of the uncertainty parameters. Furthermore, to verify the advantage of the designed two DOF μ controller with EKF, we compare its control results with those of without EKF and μ controller without considering sensor time delay. The comparison results show that the designed two DOF μ controller with EKF provides better performance. Finally, to verify the advantage of μ synthesis controller, we designed a PID controller and compare the simulation result with μ controller, the comparison result show that the designed μ controller is better than PID controller.
The Effect of Inlet Swirl on Brush Seal Bristle Deflections and Stability
Authors: Liu Yuxin , Chew John W. , Pekris Michael J. , Kong Xiaozhi
Published: November 2019

This paper considers 3D CFD and structural modelling of brush seals, and investigates the effects of inlet swirl on the bristle pack. The model couples aerodynamic forces generated by CFD to a structural model that includes interaction between bristles. At a critical value of inlet swirl, aerodynamic forces cause circumferential slip of the upstream bristle row. In practice this may lead to instability of the bristle pack and is consistent with anecdotal reports of seal behavior. The critical swirl velocity was reduced when the downstream pressure level was raised, keeping the same upstream total to downstream static pressure difference. This is caused by the increased dynamic head associated with the inlet swirl. Inclusion of a front plate in the seal design does not offer the intended protection to the bristle pack in highly swirling environments. This is associated with highly swirling flow impinging on the bristle tips. Fitting of roughness elements on the upstream face of the front plate could improve stability by reducing swirl of the flow impacting on the bristles. Increasing the bristle diameter and bristle stiffness does not necessarily prevent slip at higher inlet swirl velocities, but reduces the magnitude of slip of the upstream bristles.
Impact of Engine Degradation on Optimum Aircraft Trajectories: Short Range
Authors: Navaratne R. , Sethi V. , Lawson C.
Published: November 2019

This work aims to provide a methodology to enhance the conventional approach of the aircraft trajectory optimisation problem by including engine degradation and real aircraft flight paths within the optimisation framework; thereby the impact of engine degradation on optimum aircraft trajectories were assessed by quantifying the difference in fuel burn and emissions, when flying a trajectory which has been specifically optimised for an aircraft with degraded engines and flying a trajectory which has been optimised for clean engines. For the purpose of this study models of a clean and two degraded engines have been developed based on Exhaust Gas Temperature (EGT) margin deterioration. Aircraft performance model have been developed for short range aircraft with the capability of simulating vertical and horizontal flight profiles provides by the airlines. An emission prediction model was developed to assess NOx emissions of the mission. In addition, a multidisciplinary aircraft trajectory optimisation framework was developed to analyse short range flight trajectories under three cases. Case_1: Aircraft with clean engines, Case_2 and Case_3 were Aircraft with two levels of degraded engines. Two different multi objective optimisation studies were performed; (1) Fuel burn vs Flight time, and (2) Fuel burn vs NOx emission, Finally optimised trajectories generated with degraded engines were compared with the optimised trajectories generated with clean engines. The results have shown impact of engine degradation on optimum aircraft trajectories are significant and in order to reduce fuel burn and emissions aircraft need to fly on an optimised trajectory customised for the degraded engine performance.
Thermal End-Wall Contouring
Authors: Mimic Dajan , Oettinger Marcel , Jätz Christoph , Herbst Florian , Seume Joerg R.
Published: November 2019

In this paper, we propose the concept of thermal end-wall contouring (TEWC) as a novel approach to reducing secondary-flow and boundary-layer losses in turbomachines and ducts by means of thermally manipulating the boundary layer. We introduce, for the first time, the general concept of TEWC and provide a proof of concept using the example of a bent duct. The results demonstrate that a considerable impact on the flow field is achieved not only by mean heat flux across the end-wall of the duct, but also by the spatial distribution of the heat fluxes.
Influence of Fuel Injection Location in a Small Radial Swirler Low NOx Combustor for Micro Gas Turbine Applications
Authors: Andrews Gordon E. , Kim Su
Published: November 2019

The influence of fuel injection location in a low NOx (1) micro-gas turbine [MGT] in the ∼50kWe (kW electric) size range was investigated, for NG and propane, to extend the power turn down using a pilot fuel injector. The low NOx main combustor (1) was a radial swirler with vane passage fuel injection and had ultra-low NOx emissions of 3ppm at 15% O2 at 1800K with natural gas, NG at a combustion intensity of 11.2 MW/m2bara (MW thermal). This was a 40mm diameter outlet eight bladed radial swirler in a 76mm diameter combustor, investigated at 740K air temperature at atmospheric pressure. However, power turn down was poor and the present work was undertaken to determine the optimum position of pilot fuel injection that would enable leaner mixtures to be burned at low powers. Central injection of pilot fuel was investigated using 8 radial outward holes. This was compared with pilot fuel injected at the 76mm wall just downstream of the 40mm swirler outlet. It was show that the central injection pilot was poor with a worse weak extinction than for radial passage fuel injection. The 76mm outlet wall injection was much more successful as a pilot fuel location and had a weak extinction of 0.18Ø compared with 0.34Ø for vane passage fuel injection. NOx emissions were higher for wall fuel injection, but were still relatively low at 16ppm at 15% oxygen for natural gas. This indicates that wall fuel injection could be combined with vane passage fuel injection to improve the micro-gas turbine low NOx performance across the power range.
Validation of Chemistry Acceleration Techniques With an Industrial Gas Turbine
Authors: Mallouppas George , Goldin Graham , Zhang Yongzhe , Thakre Piyush , Rogerson Jim
Published: November 2019

Two different numerical techniques for chemistry acceleration are examined with Large Eddy Simulation of a commercial swirl industrial gas turbine combustor operating at 3 bar. This work presents the results for SGT-100 Dry Low Emission (DLE) gas turbine provided by Siemens Industrial Turbomachinery Ltd. The related experimental study was performed at the German Aerospace Centre, DLR, Stuttgart, Germany.

LES with detailed chemistry calculations is an attractive tool to study turbulent premixed flames in industrial gas turbine combustors, because it can help understand turbulence-chemistry interactions, detailed flame characteristics and pollutant formation. Detailed chemistry can capture kinetically dominated processes such as ignition, extinction and pollutant formation. However, computational resources required for such calculations are often prohibitive due to the computational costs of transporting and integration of a large number of species with a wide range of chemical time-scales. Chemistry acceleration techniques can substantially reduce run-time with ideally a small loss in accuracy. Therefore, the purpose of this work is to quantify the relative increase in performance and potential loss in accuracy with two chemistry acceleration techniques namely Clustering, Dynamic Mechanism Reduction (DMR) and their combination.

The results show that the different chemistry acceleration techniques do not compromise the time averaged flow statistics. However, there are some differences in NO and CO emissions. Chemistry acceleration techniques yield up to ∼3 times speed-up of the simulation.
Methane-Hydrogen Blends in Micro Gas Turbines: Comparison of Different Combustor Concepts
Authors: Tuccillo Raffaele , Cameretti Maria Cristina , De Robbio Roberta , Reale Fabrizio , Chiariello Fabio
Published: November 2019

The paper deals with the analysis of the response of two different types of combustors equipping micro gas turbines, when supplied with methane–hydrogen mixtures. Besides the expected reduction in carbon dioxide production, several problems have to be considered concerning the possible increase in nitric oxide formation and flashback phenomena as well.

The two combustors approach the lean-premixed or RQL concept and the study is carried out with a number of CFD simulations based on detailed kinetic schemes and accurate turbulence models. Some preliminary experimental validations support the numerical modelling of the lean-premixed combustor, so encouraging the authors to proceed with the analysis of increasing hydrogen / methane ratios. The RQL type combustor offers, in addition, the possibility of an effective split of the injection into two different streams, with evident benefits in terms of nitric oxides reduction.
A Novel Stall Warning Indicator: Part I — Applications and Limitations
Authors: Rückert Roland , Eck Mario , Peitsch Dieter , Lehmann Marc
Published: November 2019

The present work is the first of two papers investigating the operation principle of stall warning quantities. It discusses the use and implementation of novel stall warning techniques based on experimental tests. Each of the addressed techniques is based upon integral statistical analysis of time-resolved wall pressures in close proximity to the leading edge of a compressor rotor. The experiments were conducted on a low speed axial compressor test rig at the Chair of Aeroengines at the Technische Universität Berlin. The compressor suffers from a specific type of pre-stall instability. The signature within the frequency spectrum of this semi-stable operating point is in itself unique and was observed by many within the scientific community on numerous occasions and various axial compressor types, both low and high speed. Strong evidence has been elaborated which indicate that each of those so called stall warning indicator’s functionality is based upon the existence of this prestall phenomena. The first of two indicators is time-dependent as it evaluates the as-is state against surrounding operating points during transient manoeuvres. Furthermore, the impact of varying geometrical boundary conditions, which are known to regularly arise in flight operations, were taken into account. The functionality of the indicator is assured if the instrumentation is adjusted accordingly. The second indicator is mainly a location-dependent quantity as it evaluates the pressure signature along the axial direction within the rotor passage at various aerodynamic loadings. The latter also gave rise to some fundamental and preliminary understanding of the physics behind so called prestall disturbances.
Multi-Wave Vibration Caused by Flutter Instability and Nonlinear Tip Shroud Friction
Authors: Gross Johann , Krack Malte
Published: November 2019

Measurements revealed the contribution of multiple traveling waves to the flutter vibrations of bladed disks. Saturated flutter vibration, whether in this multi-wave or in its better-understood single-wave form, is a nonlinear phenomenon. However, it is still not understood of what physical origin the relevant nonlinearities are, and under what conditions single-wave or multi-wave flutter vibration occurs. Recent theoretical work suggests that multi-wave flutter vibration can be explained by strongly nonlinear frictional inter-blade coupling. The verity of this hypothesis is strictly limited by the simplicity of the considered model, namely a cyclic chain of seven oscillators with frictional coupling and rather unrealistic aeroelastic behavior.

In the present work, it is demonstrated that nonlinear dynamical contact interactions at tip shrouds are a likely cause for the observed multi-wave flutter vibration. To this end, a more realistic structural turbine blade row model with a more realistic aeroelastic behavior is considered. Some insight into its intriguing dynamics, dependence of limit states on initial conditions and eigenvalue placement is provided. For instance, it is shown that there is an intimate relation between internal combination resonance conditions of certain traveling wave modes and the spectral content of single- and multi-wave flutter oscillations.
Dynamic Analysis and Optimization on Assembly Parameters of Rod Fastening Rotor System With Manufacturing Tolerances
Authors: Zhao Bingxi , Yuan Qi , Li Pu
Published: November 2019

Rod fastening rotor (RFR), as a typical rotor structure of gas turbine which is different from the integral rotor, is comprised of a set of discs clamped together by a central tie rod or several tie rods on the pitch circle diameters. In process of machining, tolerances of the disc are inevitable, of which the parallelism error and mass imbalance are focused on in this paper. Firstly, the complex bending of RFR by accumulation of parallelism errors of discs is derived through the coordinate transmission. Then the static analysis of RFR is performed to obtain the additional pressure by the effect of unbalanced forces, which is related to the assembly angles and rotating speed, on contact surfaces using a linear hypothesis, based on which the distribution of contact pressure considering the original pre-tightening force is obtained. Then the Bifractal-Regular theory is adopted to acquire the micro-topography of the contact interface and derive the contact stiffness related to normal contact pressure, fractal upper length limit and regular shape of the contact interfaces. After that, the zero thickness element is introduced to obtain the equivalent stiffness matrices of the contact surface. In addition, the circumferential uniformly distributed rods are modeled as a spring element which provides additional bending stiffness for the RFR. Based on the analysis above, the dynamic model of the RFR-bearing system containing 10 discs is established using the Timoshenko beam element where the continuous part of the shaft is modeled by Timoshenko beam element considering shear effect. Finally, the multi-optimization is carried out on the vibration response by the coupled effects of both initial bending and mass imbalance of the RFR-bearing system through which the optimal assembly angles are obtained. The results show a good performance in decreasing vibration as well as bending of the RFR system.
Computational Fluid Dynamics Simulation of Syngas Nozzle of Gas Turbine for Syngas
Authors: Zhang Bo , Qin Ye , Shi Shaoping , Yan Shu , Mu Yanfei , Liu Xin , Chen Xinming , Guo Yutong , Zeng Chongji
Published: November 2019

Integrated Gasification Combined Cycle (IGCC) is a technology that integrates the coal gasification and combined cycle to produce electricity efficiently. Due to the fact that the heating value of syngas from coal gasification process is typically lower than that of the natural gas, the conventional gas turbine will have to be adapted for syngas. The nozzle adjustment is the key to the successful transformation since the ignition properties are different between syngas and natural gas which have totally different compositions. The nozzles suitable for natural gas have been prone to partially melting around the flame stabilization holes on sidewalls of the nozzle in real operation. Thus a computational fluid dynamics (CFD) model was constructed for the syngas nozzles as well as combustion chamber of the gas turbine for low heating value syngas to study the thermostability of the nozzle. The detailed structure of the syngas nozzle, the combustion characteristics of syngas, as well as the actual operation condition of the gas turbine were all employed in the CFD model to improve the simulation accuracy. The reason of partially melting of the nozzles suitable for natural gas can be attributed to that the syngas leaked from the flame stabilization holes into the mainstream air can quickly mix with air, adhere to the sidewalls of the nozzles and then ignite around the holes which result in temperatures high enough to melt the material of the nozzle around the holes through CFD simulation. Finally, a new structure of the syngas nozzle was proposed and validated by CFD simulations. The simulation result shows that the flames caused by the syngas leaked from the flame stabilization holes are no longer adhering to the nozzle sidewalls and local high temperature can be lowered by about 30% which will not be able to melt the nozzle material.
A Method to Evaluate the Sensitivity of Aerodynamic Damping to Mode Shape Perturbations
Authors: Li Jing , Chakrabarti Suryarghya , Ren Wei-Min
Published: November 2019

Turbomachinery blade mode shapes are routinely predicted by finite element method (FEM) programs and are then used in unsteady computational fluid dynamic (CFD) analyses to predict the aerodynamic damping. This flutter stability assessment process is critical for the last-stage blades (LSBs) of modern heavy-duty gas turbines (HDGTs) which can be particularly susceptible to flutter. Evidences suggest that actual mode shapes may deviate from the FEM predictions due to changes in the FEM boundary or loading conditions, effects of the nonlinear friction contacts, and blade-to-blade variations (mistuning), among others. This uncertainty in the mode shape is accompanied by a general lack of knowledge on the sensitivity of the aerodynamic damping to a small change in mode shape. This paper presents a method to perturb a mode shape and estimate the corresponding change in aerodynamic damping in a framework enabled by linear theories and a rigid-body, quasi-3D treatment of mode shapes. This method is of low computational cost and is suitable for use in the preliminary design cycle. The numerical validation and applications of the method are demonstrated on two LSB blades. Results suggest that the mode shape sensitivity can be substantial and may even exceed the change in aerodynamic damping of a frictionally damped system when subjected to various levels of excitation.
Validation of a New Turbulent Flame Speed Facility for the Study of Gas Turbine Fuel Blends at Elevated Pressure
Authors: Morones Anibal , Turner Mattias A. , León Victor , Ruehle Kyle , Petersen Eric L.
Published: November 2019

Turbulent combustion is a very active and challenging research topic of direct interest to the design and operation of gas turbine engines. A spherically expanding flame immersed in a turbulent field is one way to gain fundamental insight on the effect of turbulence on combustion. This kind of experiment is often conducted inside a fan-stirred flame bomb, preferably at conditions of high pressure, high temperature, and intense turbulence. A new fan-stirred flame bomb was designed and built to provide a device for conducting fundamental turbulent flame measurements at conditions of interest to gas turbine engines. A literature review on existing systems was used as guidance in the design of the turbulence-generation elements in the present rig. A few options of impellers were explored. The flow field produced by the chosen impeller was measured with Laser Doppler Velocimetry (LDV). A detailed exposition of the vessel engineering and construction are presented, including current activities that will extend the use of the facility for heated experiments up to at least 400 K. Before turbulent experiments were attempted, a validation of the rig accuracy and pressure worthiness was made. Finally, a demonstration of the new apparatus was made by testing a lean mixture of syngas. The experiment matrix using hydrogen and H2/CO mixtures included three levels of pressure (1, 5, and, 10 bar) and three levels of turbulence fluctuation rms (1.4, 2.8, and 5.5 m/s). Data based on the high-speed schlieren diagnostic are presented.
Probabilistic Fracture Mechanics Framework Including Crack Nucleation of Rotor Forging Flaws
Authors: Radaelli Francesco , Kadau Kai , Amann Christian , Gumbsch Peter
Published: November 2019

We present a probabilistic rotor life prediction framework that combines the forging flaw crack nucleation process and the subsequent crack growth to failure. Experimental fatigue tests of specimens including forging flaws show that the life cycle of a forging flaw can be described by a nucleation phase followed by a fatigue crack growth phase. These results demonstrate that the nucleation phase is a significant fraction of the whole life cycle to failure. However, as there is no engineering method available that describes reliably the nucleation phase, this portion is oftentimes neglected in engineering life prediction frameworks, therefore resulting in a conservative life quantification. In order to improve probabilistic life quantification methods, we introduce a rigorous scheme that convolutes the local crack nucleation probabilities and the local crack growth failure probabilities in order to provide a local failure probability. Integration over the whole component then yields the total probability of failure for the engineering part under a specific load spectrum. A specific direct simulation Monte Carlo numerical implementation is demonstrated. It is applied to fatigue crack nucleation from large gas turbine rotor disk forging flaws followed by crack growth to component failure. For different regions of the analyzed rotor components, the results show the probabilistic interplay of the different temperature and stress dependences of the applied empirical nucleation models and the fatigue crack growth models.

The presented probabilistic approach is generic and not restricted to the discussed fatigue nucleation and subsequent crack growth process in large rotor forgings. The framework can be applied to a variety of sequential failure processes including static and fatigue loading phenomena, as well as a multiplicity of failure modes and sequences relevant for engineering components.
Heat Transfer Prediction From Large Eddy Simulation of a Rotating Cavity With Radial Inflow
Authors: Onori Michel , Amirante Dario , Hills Nicholas J. , Chew John W.
Published: November 2019

The paper describes a Large Eddy Simulation (LES) conducted for a non adiabatic rotating cavity with a radial inflow introduced from the shroud. The dimensionless mass flow rate of the radial inflow is Cw = 3500 and the rotational Reynolds number, based on the cavity outer radius, is equal to Reθ = 1.2 × 106. The time averaged local Nusselt number on the heated wall is compared with the experimental data available from the literature, and with those derived from the solution of two Unsteady Reynolds Averaged Navier-Stokes (URANS) eddy viscosity models, namely the Spalart-Allmaras and the k-ω SST model. It is shown that the Nusselt number is under-predicted in the lower part of the disc and over-predicted in the outer region by both URANS models, whereas the LES provides a much better agreement with the measurements. The behaviour results primarily from a different flow structure in the source region, which, in the LES, is found to be considerably more extended and show localized buoyancy phenomena that the URANS models investigated do not capture.
Design and Testing of a Miniaturized Five-Hole Fast Response Pressure Probe With Large Frequency Bandwidth and High Angular Sensitivity
Authors: Boufidi Elissavet , Alati Marco , Fontaneto Fabrizio , Lavagnoli Sergio
Published: November 2019

A miniaturized five-hole fast response pressure probe is presented and the methods for the aerodynamic design and characterization performance are explained in detail. The probe design is aimed for three-dimensional time-resolved measurements in turbomachinery flows, therefore requiring high frequency response and directional sensitivity. It features five encapsulated piezoresistive pressure transducers, recessed inside the probe hemispherical head. Theoretical and numerical analyses are carried out to estimate the dynamic response of the pressure tap line-cavity systems and to investigate unsteady effects that can influence the pressure readings. A prototype is manufactured and submitted to experimental tests that demonstrate performance in line with the theoretical and numerical predictions of the dynamic response: the natural frequency of the central and lateral taps extend to 25 kHz and 200 kHz respectively. An aerodynamic calibration is also performed at different Reynolds and Mach numbers. The probe geometry offers a good angular sensitivity in a ±30° incidence range, while a frequency analysis reveals the presence of pressure oscillations related to vortex shedding at large angles of attack.
Quantifying the Effect of Kinetic Uncertainties on NO Predictions at Engine-Relevant Pressures in Premixed Methane-Air Flames
Authors: Durocher Antoine , Bourque Gilles , Bergthorson Jeffrey M.
Published: November 2019

Accurate and robust thermochemical models are required to identify future low-NOx technologies that can meet the increasingly stringent emissions regulations in the gas turbine industry. These mechanisms are generally optimized and validated for specific ranges of operating conditions, which result in an abundance of models offering accurate nominal solutions over different parameter ranges. At atmospheric conditions, and for methane combustion, a relatively good agreement between models and experiments is currently observed. At engine-relevant pressures, however, a large variability in predictions is obtained as the models are often used outside their validation region. The high levels of uncertainty found in chemical kinetic rates enable such discrepancies between models, even as the reactions are within recommended rate values. The current work investigates the effect of such kinetic uncertainties in NO predictions by propagating the uncertainties of 30 reactions, that are both uncertain and important to NO formation, through the combustion model at engine-relevant pressures. Understanding the uncertainty sources in model predictions and their effect on emissions at these pressures is key in developing accurate thermochemical models to design future combustion chambers with any confidence. Lean adiabatic, freely-propagating, laminar flames are therefore chosen to study the effect of parametric kinetic uncertainties. A non-intrusive, level 2, nested sparse-grid approach is used to obtain accurate surrogate models to quantify NO prediction intervals at various pressures. The forward analysis is carried up to 32 atm to quantify the uncertainty in emissions predictions to pressures relevant to the gas turbine community, which reveals that the NO prediction uncertainty decreases with pressure. After performing a Reaction Pathway Analysis, this reduction is attributed to the decreasing contribution of the prompt-NO pathway to total emissions, as the peak CH concentration and the CH layer thickness decrease with pressure. In the studied lean condition, the contribution of the pressure-dependent N2O production route increases rapidly up to 10 atm before stabilizing towards engine-relevant pressures. The uncertain prediction ranges provide insight into the accuracy and precision of simulations at high pressures and warrant further research to constrain the uncertainty limits of kinetic rates to capture NO concentrations with confidence in early design phases.
Effect of Steam Dilution on Laminar Flame Speeds of Syngas Fuel Blends at Elevated Pressures and Temperatures
Authors: Krejci Michael C. , Keesee Charles L. , Vissotski Andrew J. , Ravi Sankaranarayanan , Petersen Eric L.
Published: November 2019

Synthetic gas, syngas, is a popular alternative fuel for the gas turbine industry. However, the composition of syngas can contain different types and amounts of contaminates, such as carbon dioxide, moisture, and nitrogen, depending on the industrial process involved in its manufacturing. The presence of steam in syngas blends is of particular interest from a thermo-chemical perspective as there is limited information available in the literature. This study investigated the effect of moisture content (0–15% by volume), temperature (323–423 K), and pressure (1–10 atm) on syngas mixtures by measuring the laminar flame speed in a constant-volume, heated experimental facility. A design-of-experiments methodology was applied to these variables to efficiently cover the widest range of conditions that are relevant to the gas turbine industry. The experimental flame speed data were compared to a recent chemical kinetics model showing good agreement. Also, the measured Markstein lengths of atmospheric mixtures were compared and demonstrate that temperature and steam dilution have weak impacts on the sensitivity to stretch in comparison with an increase of carbon monoxide concentration. Mixtures with high levels of CO stabilize the flame structure of thermal-diffusive instability. The increase of steam dilution has only a small effect on the laminar flame speed of high-CO mixtures, while more hydrogen-dominated mixtures demonstrate a much larger and negative effect of increasing water content on the laminar flame speed.
Incipient Fault Diagnosis of the Planetary Gearbox Based on Improved Variational Mode Decomposition and Frequency-Weighted Energy Operator
Authors: Li Hongkun , Wang Chaoge , Ou Jiayu
Published: November 2019

Planetary gearbox is widely used in large and complex mechanical equipment such as wind power generation, helicopters and petrochemical industry. Gear failures occur frequently in working conditions at low speeds, high service load and harsh operating environments. Incipient fault diagnosis can avoid the occurrence of major accidents and loss of personnel property. Aiming at the problems that the incipient fault of planetary gearbox is difficult to recognize and the number of intrinsic mode functions (IMFs) decomposed by variational mode decomposition (VMD) must be set in advance and can not be adaptively selected, a improved VMD algorithm based on energy difference as an evaluation parameter to automatically determine the decomposition level k is proposed. On this basis, a new method for early fault feature extraction of planetary gearbox based on the improved VMD and frequency-weighted energy operator is proposed. Firstly, the vibration signal is pre-decomposed by VMD, and the energy difference between the component signal and the original signal under different K-values is calculated respectively. The optimal decomposition level k is determined according to the energy difference curve. Then, according to kurtosis criterion, sensitive components are selected from the k modal components obtained by the decomposition to reconstruct. Finally, a new frequency-weighted energy operator is used to demodulate the reconstructed signal. The fault characteristic frequency information of the planetary gearbox can be accurately extracted from the energy spectrum. The method is applied to the simulation fault data and actual data of planetary gearbox, and the weak fault characteristics of planetary gearbox are extracted effectively, and the early fault characteristics are distinguished. The results show that the new method has certain application value and practical significance.
Improvement and Analysis for a Gaseous Cavitation Model Applied in a Tilting-Pad Journal Bearing
Authors: Ding Aoshuang , Li Xuesong , Li Yuhong
Published: November 2019

Considering the gaseous cavitation rate is influenced by local pressure, a transient gaseous cavitation model is developed from an equilibrium gaseous cavitation model in consideration of transient gaseous cavitation theories and the Bunsen solubility. With the shear stress transport (SST) model with low-Re correction and air backflow from the bearing outlets, the transient gaseous cavitation model is applied to the three-dimensional simulations of an entire tilting-pad journal bearing at 3000 rpm speed and under 180 kN load. The simulated bearing pressure and load are in good agreement with the experimental data, indicating that the transient gaseous cavitation model performs well in the bearing simulations. Based on the comparisons of the simulated air and dissolved air distributions between the transient and equilibrium gaseous cavitation models, the simulated cavitation process of the transient gaseous cavitation is proved to be not in equilibrium and mass transfer occur between the backflow air and oil. The purpose of building the transient gaseous cavitation model is thus met. Analyses of the air distributions indicate that high cavitation rates and low dissolution rates makes air volume a major part of the total air volume and close to the physical gaseous cavitation process.
Experimental and Numerical Investigations of Steam Turbine Exhaust Hood Flow Field With Two Types of Diffusers
Authors: Tabata Soichiro , Fukushima Hisataka , Segawa Kiyoshi , Ishibashi Koji , Kuwamura Yoshihiro , Sugishita Hideaki
Published: November 2019

The exhaust hood performance of LP turbine plays an important role in the efficiency of steam turbine. By improving the exhaust performance, the kinetic energy of the last stage rotating blades can be converted to the potential energy and it becomes possible to improve the turbine efficiency. However, the flow field in the diffuser is closely related to the flow pattern of the last stage rotating blade, and the flow field inside the exhaust chamber afterward has a complicated three dimensional flow field. Therefore, in this study, it conducted a scaled model steam turbine test using two types of diffusers and CFD, and evaluated exhaust performance and flow pattern.

The verification test was carried out using a test turbine (4 stages) of × 0.33 scale, the velocity field and the pressure field were evaluated by traverse and the wall pressure measurements.

The corresponding CFD was calculated by ANSYS CFX. All four stages of blades and seals, exhaust chambers were accurately modeled. Due to the detailed CFD, the internal flow of the exhaust chamber exhibiting complicated three-dimensionality was visualized and the flow pattern was evaluated.

The verification test results and the corresponding CFD results were compared and evaluated, and it has been found that the overall performance predicted by CFD is well showing the verification test result. Therefore, it has been found that CFD can help to understand the internal flow of the exhaust chamber exhibiting complex three-dimensional characteristics.
Spray Flame Characteristics of Bio-Derived Fuels in a Simulated Gas Turbine Burner
Authors: Panchasara Heena , Kolhe Pankaj S. , Agrawal Ajay K.
Published: November 2019

Fuel injection plays an important role in liquid fueled gas turbine combustion. The strong interdependence of liquid breakup and atomization, turbulent dispersion of these droplets, droplet evaporation, and fuel-air mixing make the spray modeling an extremely challenging task. The physical processes are even more difficult to predict for alternative fuels with different thermophysical properties. In this study, spray flames of unheated and preheated vegetable oil (VO) produced by an air-blast atomizer in a swirl stabilized combustor are investigated experimentally. Phase Doppler particle analyzer (PDPA) is used to measure the instantaneous diameter and axial velocity of droplets at different axial and radial locations in both flames. Experiments are conducted at an equivalence ratio of 0.79 and atomizing air to liquid ratio (ALR) by mass of 2.5 to obtain stable VO flames. Radial profiles of mean axial velocity and Sauter mean diameter are presented to show the effect of fuel preheating. Joint Probability Density Functions (joint PDF) are presented to show the correlation between droplet diameter and axial velocity. Results are analyzed to show that both sprays exhibit self-similar droplet diameter distributions at different axial and radial locations when normalized properly. Thus, the vast amount of PDPA data in the spray can be reduced to simple distribution functions. A method to reconstruct the joint PDF from experimentally determined distribution functions is presented. We envision that the joint PDF approach outlined in this study could be implemented in high-fidelity computational fluid dynamic models to improve spray predictions in future studies.
Experimental Investigation on the Flat-Plate Film Cooling Enhancement Using the Vortex Generator Downstream for the Cylindrical Hole and Fan-Shaped Hole Configurations
Authors: Zhang Chao , Wang Jie , Luo Xin , Song Liming , Li Jun , Feng Zhenping
Published: November 2019

In our experiments, the film cooling performance of the configurations combined the different hole with the vortex generator was investigated experimentally, measured by the infrared camera. Four different configurations were studied at the blowing ratio varying at M = 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0. In all cases, the Reynold number of the mainstream based on the hole diameter remained at Re = 8000, and the density ratio kept at DR = 1.7. Experimental results show that for the two models combining the cylindrical hole and fan-shaped hole with the vortex generator respectively, the film cooling performance becomes better when the blowing ratio increases from M = 0.5 to M = 2.0, and then decreases when the blowing ratio increases from M = 2.0 to M = 3.0. The model combining the fan-shaped hole with the vortex generator performs the best among the four models at each blowing ratio. Its film attachment holds the most extensive lateral distribution and its overall film cooling effectiveness could keep at a high level at a wide range of blowing ratios from M = 1.0 to M = 3.0. The combined model of the fan-shaped hole could improve the area-averaged film effectiveness at most 25.5% than that of the single hole model at M = 2.0. Moreover, the combined model of the cylindrical hole could improve the area-averaged film cooling effectiveness at most 431% than that of the single cylindrical hole model at M = 3.0.
Influence of Excitation Frequency, Phase-Shift and Duty Cycle on Cooling Ratio in a Dynamically Forced Impingement Jet Array
Authors: Berthold Arne , Haucke Frank
Published: November 2019

The cooling ratio on a dynamically forced 7×7 impingement jet array is studied experimentally. The current study is focused on determining the influence of a phase-shift between every row of nozzles as well as the impact of a duty cycle variation on the cooling ratio. Both parameters are studied in dependency of the impingement distance (H/D = 2, 3, 5), the (nozzle-)Reynolds-number (ReD = 3200, 5200, 7200) and the excitation frequency (f = 0 Hz – 1000 Hz). For every set of parameters, the phase-shift between every row of nozzles is varied between Φ = 0% – 90% while the variation of the duty-cycle is performed between DC = 35% – 65%. During all investigations, the dimensionless distance between adjacent nozzles is fixed at x/D = y/D = 5 and liquid crystal thermography is used to acquire the wall temperatures, which are further processed to calculate the local Nusselt numbers. Generally, the implementation of an excitation frequency allows a case depending increase in cooling ratio of up to 52%. Further implementation of a phase-shift yields an additional frequency-depending improvement of the cooling ratio. In case of duty cycle variation, the best case revealed an additional 19% improvement in cooling ratio.
Detailed Experimental Investigation of the Operational Parameters of a 30 kW Micro Gas Turbine
Authors: Kislat Oliver , Zanger Jan , Krummrein Thomas , Kutne Peter , Aigner Manfred
Published: November 2019

Numerical studies discussing micro gas turbines (MGTs) as a basis for automotive range extenders can be found in literature. A comprehensive set of experimental measurement data for an MGT of adequate size, however, is currently not available. In this work, a test rig and demonstrator based on a 30 kWel liquid fueled MGT is built up. Its major components’ performance is characterized by measuring temperature and pressure at inlet and outlet, as well as corresponding fuel and air flows and the exhaust gas composition. A compressor bleed air tapping is installed to characterize the turbo components’ off-design behavior. Stationary load points and transient maneuvers are investigated. The presented data provide coherent information on the operational behavior and cycle parameters. This can be used to validate existing numerical investigations. It further provides a foundation to identify the optimization potential of MGT components and will serve as design baseline for subsequent optimization measures to meet the requirements of mobile applications.
Experimental Study on Centrifugal Compressor Performance at Pulsating Backpressure Conditions
Authors: Shu Mengying , Yang Mingyang , Zhang Kaiyue , Martinez-Botas Ricardo F. , Deng Kangyao
Published: November 2019

The flow in the intake manifold of a downsized internal combustion engine has become more unsteady due to the reduction of cylinder number and increasing boosting level. The turbocharger compressor is thus imposed by an unsteady backpressure when matched with an engine. It has been experimentally confirmed that the compressor performance is affected when exposed to pulsating backpressure. In order to enhance compressor stability and achieve better turbo-engine matching, it is necessary to understand behaviors of compressor at pulsating backpressure conditions. In this study, the performance of compressor exposed to pulsating backpressure is experimentally studied on the compressor test rig located in Shanghai Jiao Tong University. The results show that compressor performance with pulsating backpressure is notably different from the one with constant backpressure. Hysteresis loops which encapsulate the steady performance are generated at pulsating backpressure conditions due to filling-emptying effect. The mass flow rate, pulse frequency and compressor rotational speed all have evident influence on dynamic behaviors of the compressor. As the mass flow rate and rotational speed increase, hysteresis loops are enlarged and the unsteady behaviors are enhanced. The influence of pulsating backpressure on the compressor surge margin is analyzed in detail. Results demonstrate that the stable operation range is evidently influenced by the pulsating backpressure. Particularly, the mass flow rate of surge is postponed by 15.1% compared with the corresponding constant backpressure condition. Fast Fourier Transform method (FFT) is applied to identify the initiation of surge. The frequency domain analysis proves that the pulsating backpressure has little influence on the frequency of surge, but the strength of surge is alleviated indicated by the magnitude of fluctuations. The study provides an insight on the influence of pulsating backpressure on the centrifugal compressor, which can benefit the design methodology of compressor as well as turbo-engine matching.
Numerical Comparison of Static and Rotordynamic Characteristics for a Grooved-Stator/Smooth-Rotor and a Smooth-Stator/Grooved-Rotor Liquid Annular Seals
Authors: Li Zhigang , Fang Zhi , Li Jun , Feng Zhenping
Published: November 2019

Liquid annular seals with parallelly-grooved stator or rotor are used as replacements for smooth plain seals in centrifugal pumps to reduce leakage and break up contaminants within the working fluid. Parallelly-grooved liquid annular seals have advantages of less leakage and smaller possibility of abrasion when the seal rotor-stator rubs in comparison to smooth plain seals. This paper deals with the static and rotordynamic characteristics of parallelly-grooved liquid annular seals, which are limited in the literature.

Numerical results of leakage flow rates, drag powers and rotordynamic force coefficients were presented and compared for a grooved-stator/smooth-rotor (GS-SR) liquid annular seal and a smooth-stator/grooved-rotor (SS-GR) liquid annular seal, utilizing a modified transient CFD-based perturbation approach based on the multiple-frequency elliptical-orbit rotor whirling model. Both liquid annular seals have identical seal axial length, rotor diameter, sealing clearance, groove number and geometry. The present transient CFD-based perturbation method was adequately validated based on the published experiment data of leakage flow rates and frequency-independent rotordynamic force coefficients for the GS-SR and SS-GR liquid annular seals at various pressure drops with differential inlet preswirl ratios. Simulations were performed at three pressure drops (4.14 bar, 6.21 bar, 8.27 bar), three rotational speeds (2 krpm, 4 krpm, 6 krpm) and three inlet preswirl ratios (0, 0.5, 1.0), applying a wide rotor whirling frequency range up to 200 Hz, to analyze and compare the influences of operation conditions on the static and rotordynamic characteristics for both the GS-SR and SS-GR liquid annular seals. Results show that the present two liquid annular seals possess similar sealing capability, and the SS-GR seal produces a slightly larger (∼ 2–10%) drag power loss than the GS-SR seal. For small rotor whirling motion around a centered position, both seals have the identical direct force coefficients and the equal-magnitude opposite-sign cross-coupling force coefficients in the orthogonal directions x and y.

For all operation conditions, both the GS-SR and SS-GR liquid annular seals possess negative direct stiffness K and positive direct damping C. The GS-SR seal produces purely positive Ceff throughout the whirling frequency range for all operation conditions, while Ceff for the SS-GR seal shows a significant decrease and transitions to negative value at the crossover frequency fco with increasing rotational speed and inlet preswirl. From a rotordynamic viewpoint, the GS-SR liquid annular seal is a better seal concept for pumps.