bluuebunny/crossref_metadata_2025 huggingface dataset:
An Integral Type µ Synthesis Method for Temperature and Pressure Control of Flight Environment Simulation Volume
Authors: Zhu Meiyin , Wang Xi
Published: August 2017

Flight Environment Simulation Volume (FESV) is the most important part of Altitude Ground Test Facilities (AGTF). It’s temperature and pressure control precision determines the level of test ability of AGTF. Therefore, in order to study the temperature and pressure control problem of FESV and improve the modeling precision of FESV, the energy equation and gas state equation are used to deduce the temperature and pressure differential equations of FESV. Meanwhile, the heat transfer influence of FESV has been taken into account in this paper and the transient heat conduction of FESV is established by using a discretizing method. The temperature and pressure differential equations of FESV are linearized around a balance point and the uncertainty of actuators has been considered in multiplicative uncertainty. The augmented system of linear model of FESV and the actuators are obtained. For the sake of making the controller design and weighting function choice more easily, a normalization method is used to normalize the augmented system. For the purpose of achieving the temperature and pressure synchronic control of FESV, a two-degree-of-freedom integral type μ synthesis control design method is proposed. What’s more, for guaranteeing the designed μ synthesis controller has servo tracking and disturbance attenuation performance, the performance weighting functions are designed according to the frequency division weighting principle and the control weighting functions are designed by using the principle of low frequency free limit, medium frequency gradually increase the limit, and high frequency maximum limit. The MATLAB Robust Control Toolbox function dksyn is used to design the μ controller.

In order to verify the effectiveness of designed μ controller, we assume two types of engine test conditions. The simulation results show, for the engine test condition one, the biggest relative tracking error of temperature is less than 0.5% and the relative steady state error of pressure is less than 0.1% and the relative tracking error of pressure slope signal is less than 3%. For the engine test condition two, the relative steady state error of temperature is less than 0.1% and the relative tracking error of temperature slope signal is less than 1%. To verify the advantage of designed μ controller, we designed a PID controller and compared the simulation results with μ controller. The comparison results showed that the designed μ controller provided better performance than the PID controller.
Characterization of Different Actuator Designs for the Control of the Precessing Vortex Core in a Swirl-Stabilized Combustor
Authors: Lückoff Finn , Sieber Moritz , Paschereit Christian Oliver , Oberleithner Kilian
Published: August 2017

The precessing vortex core (PVC) represents a helical-shaped coherent flow structure typically occurring in both reacting and non-reacting swirling flows. Until now the fundamental impact of the PVC on flame dynamics, thermoacoustic instabilities and pollutant emissions is still unclear. In order to identify and investigate these mechanisms, the PVC needs to be controlled effectively with a feedback control system. A previous study successfully applied feedback control in a generic swirling jet setup. The next step is to transfer this approach into a swirl-stabilized combustor, which poses big challenges on the actuator and sensor design and placement. In this paper, different actuator designs are investigated with the goal of controlling the PVC dynamics. The actuation strategy aims to force the flow near the origin of the instability — the so-called wavemaker. To monitor the PVC dynamics, arrays of pressure sensors are flush-mounted at the combustor inlet and the combustion chamber walls. The best sensor placement is evaluated with respect to the prediction of the PVC dynamics. Particle image velocimetry is used to evaluate the passive impact of the actuator shape on the mean flow field. The performance of each actautor design is evaluated from lock-in experiments showing excellent control authority for two out of seven actuators. All measurements are conducted at isothermal conditions in a prototype of a swirl-stabilized combustor.
A Physics-Based Dynamic Model for Boilers: Part 2 — Model Reduction in a Cogeneration Application
Authors: Blom Matthew J. , Brear Michael J. , Manzie Chris G. , Wiese Ashley P.
Published: August 2017

This paper is the second part of a two part study that develops, validates and integrates a one-dimensional, physics-based, dynamic boiler model. Part 1 of this study [1] extended and validated a particular modelling framework to boilers. This paper uses this framework to first present a higher order model of a gas turbine based cogeneration plant. The significant dynamics of the cogeneration system are then identified, corresponding to states in the gas path, the steam path, the gas turbine shaft, gas turbine wall temperatures and boiler wall temperatures. A model reduction process based on time scale separation and singular perturbation theory is then demonstrated.

Three candidate reduced order models are identified using this model reduction process, and the simplest, acceptable dynamic model of this integrated plant is found to require retention of both the gas turbine and boiler wall temperature dynamics. Subsequent analysis of computation times for the original physics-based one-dimensional model and the candidate, reduced order models demonstrates that significantly faster than real time simulation is possible in all cases. Furthermore, with systematic replacement of the algebraic states with feedforward maps in the reduced order models, further computational savings of up to one order of magnitude can be achieved. This combination of model fidelity and computational tractability suggest suggests that the resulting reduced order models may be suitable for use in model based control of cogeneration plants.
Quantitative CFD Analyses of Particle Deposition in a Heavy-Duty Subsonic Axial Compressor
Authors: Aldi Nicola , Casari Nicola , Dainese Devid , Morini Mirko , Pinelli Michele , Spina Pier Ruggero , Suman Alessio
Published: August 2017

Solid particle ingestion is one of the principal degradation mechanisms in the compressor and turbine sections of gas turbines. In particular, in industrial applications, the micro-particles not captured by the air filtration system can cause deposits on blading and, consequently, result in a decrease in compressor performance.

In literature there are some studies related to the fouling phenomena in transonic compressors, but in industrial applications (heavy-duty compressors, pump stations, etc.) the subsonic compressors are widespread. It is highly important for the manufacturer to gather information about the fouling phenomenon related to this type of compressor.

This paper presents three-dimensional numerical simulations of the micro-particle ingestion (0.15 μm – 1.50 μm) in a multistage (i.e. eight stage) subsonic axial compressor, carried out by means of a commercial computational fluid dynamic code. Particles of this size can follow the main air flow with relatively little slip, while being impacted by flow turbulence. It is of great interest to the industry to determine which zones of the compressor blades are impacted by these small particles. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separately from the continuous phase.

The adopted computational strategy allows the evaluation of particle deposition in a multistage axial compressor thanks to the use of a mixing plane approach to model the rotor/stator interaction. The compressor numerical model and the discrete phase model are set up and validated against the experimental and numerical data available in literature.

The number of particles and sizes are specified in order to perform a quantitative analysis of the particle impacts on the blade surface. The blade zones affected by particle impacts and the kinematic characteristics (velocity and angle) of the impact of micrometric and sub-micrometric particles with the blade surface are shown. Both blade zones affected by particle impact and deposition are analyzed.

The particle deposition is established by using the quantity called sticking probability, adopted from literature. The sticking probability links the kinematic characteristics of particle impact on the blade with the fouling phenomenon.

The results show that micro-particles tend to follow the flow by impacting on the compressor blades at full span. The suction side of the blade is only affected by the impacts of the smallest particles. Particular fluid dynamic phenomena, such as corner separations and clearance vortices, strongly influence the impact location of the particles.

The impact and deposition trends decrease according to the stages. The front stages appear more affected by particle impact and deposition than the rear ones.
Dry Gas Face Seal Design With Arbitrary Gap Shape
Authors: Vinogradov Aleksandr S. , Falaleev Sergey V. , Badykov Renat B.
Published: August 2017

Active use of dry gas seals for gas turbine engines is constrained by several important factors. One of them is a significant deformation of the sealing rings. This paper is dedicated to the creation of a technique of designing of a dry gas seal with spiral grooves with a consideration of arbitrary gap shape. A large number of studies for this type of seal have been conducted. But the technique of the seal designing which combines sealing leakage calculation with the calculation of the actual rings deformation has not been implemented. This article proposes a solution for this significant problem. Indeed, the increase in temperature and pressure drop results in a deformation of the rings surfaces. For the small gap, the impact of force and thermal deformation is critical. The seal designing without consideration of the surfaces deformation can lead to significant errors, but also to the failure of the seal in operation in the worst case. An improved mathematical model for calculating the leakage is proposed. On its basis, the designing technique has been developed. This technique combines the analytical calculation and calculation of deformation by finite element method. Implementation of this technique has a good practical result. The seal was created for a gas pumping unit. Experimental results have confirmed the computational results.
Small Radial Swirler Low NOx Combustors for Micro Gas Turbine Applications
Authors: Andrews Gordon E. , Kim Myeong
Published: August 2017

There is a growing interest in micro-gas turbines for distributed electric power production. This work examines the scale down of a successful low NOx radial swirler from a combustor of 140mm diameter to one of 76mm diameter, suitable for micro-gas turbines in the 30–100kW electric size range. A 40mm outlet eight bladed radial swirler was investigated for four radial swirler vane depths from 30.5mm to 12.2mm and a constant pressure loss of 2.7% at different reference Mach numbers or residence times. For a 740K inlet temperature and 0.6 equivalence ratio, Ø, these gave combustor thermal loadings at atmospheric pressure from 33 to 62 kW and heat release of 7–14 MW/m2bar. The small radial swirlers had lean stable flames with near lean flammability weak extinction. The vane passage single hole fuel injection achieved NOx emissions of 1–5ppm at 15% oxygen, 740K air inlet temperature and 1700K primary zone temperature, with <10ppm CO. The 1ppm NOx was for the smallest vane depth and lowest thermal power. The higher NOx for the larger heat release swirler designs were due to the longer flame development and a greater formation of prompt NOx, due to the high UHC for most of the flame development.
Prediction of Stress Relaxation in Power Plant Components Based on a Constitutive Model
Authors: Kostenko Y. , Naumenko K.
Published: August 2017

Many power plant components and joint connections are subjected to complex thermo-mechanical loading paths under severe temperature environments over a long period. An important part in the lifetime assessment is the reliable prediction of stress relaxation using improved creep modeling to avoid possible integrity or functionality issues and malfunction in such components.

The aim of this work is to analyze the proposed constitutive model for advanced high chromium steels with the goal of predicting stress relaxation over the long term. The evolution equations of the constitutive model for inelastic material behavior are introduced to account for hardening and softening phenomena. The material properties were identified for 9–12%CrMoV steels in the creep range.

The model is applied to the stress relaxation analysis of power plant components. The results for long-term assessment, which are encouragingly close to reality, will be presented and discussed. An outlook on further developments of the model and assessment procedure is also provided.
A Detailed Study of the Interaction Between Two Rows of Cooling Holes
Authors: Jiang Y. , Capone L. , Ireland P. , Romero E.
Published: August 2017

An optimal design of film cooling is a key factor in the effort of producing high efficiency gas turbine. Understanding of the fluid dynamics interaction between cooling holes can help engineers to improve overall thermal effectiveness. Modelling and correct prediction is a very complex problem, since the multiple phenomena involved, such as: mixing, turbulence and heat transfer. The present work performs an investigation of different cooling configurations ranging from single hole up to two rows. The main objective is to evaluate the double-rows interaction and the effect on film cooling. Strong nonlinear effects are underlined by different simulations, while varying blowing ratio and geometrical configuration of cooling holes. Meanwhile an initial analysis is performed using flat plate geometry, verification and validation is then extended to realistic stage of high pressure turbine. Multiple cooling holes configurations are embedded on the pressure and suction sides of the single stage. The main outcome is the verification of the thermal effectiveness improvement obtained by cooling jets interaction of multiple rows design. The effects of curvature surface and frame of reference rotation are also evaluated, underlying the differences with standard flat plate test cases.
Exhaust Volume Dependency of Turbocharger Turbine Design for a Heavy Duty Otto Cycle Engine
Authors: Anton Nicholas , Genrup Magnus , Fredriksson Carl , Larsson Per-Inge , Erlandsson-Christiansen Anders
Published: August 2017

This study is considering turbocharger turbine performance at “on-engine” conditions with respect to turbine design variables and exhaust manifold volume. The highly unsteady nature of the internal combustion engine will result in a very wide range of turbine operation, far from steady flow conditions. As most turbomachinery design work is conducted at steady state, the influence of the chosen turbine design variables on the crank-angle-resolved turbine performance will be of prime interest. In order to achieve high turbocharger efficiency with the greatest benefits for the engine, the turbine will need high efficiency at the energetic exhaust pressure pulse peak.

The starting point for this paper is a target full load power curve for a heavy duty Otto-cycle engine, which will dictate an initial compressor and turbine match. Three radial turbine designs are investigated, differing with respect to efficiency characteristics, using a common compressor stage. The influence of the chosen turbine design variables considering a main contributor to unsteadiness, exhaust manifold volume, is evaluated using 1D engine simulation software. A discussion is held in conjunction with this regarding the efficiency potential of each turbine design and limitations of turbine types.
Experimental Analysis of a NACA 0021 Airfoil Section Through 180-Degree Angle of Attack at Low Reynolds Numbers for Use in Wind Turbine Analysis
Authors: Holst D. , Church B. , Pechlivanoglou G. , Tüzüner E. , Saverin J. , Nayeri C. N. , Paschereit C. O.
Published: August 2017

Wind turbine industry has a special need for accurate post stall airfoil data. While literature often covers incidence ranges [−10deg,+25deg] smaller machines experience a range of up to 90 deg for horizontal axis and up to 360 deg for vertical axis wind turbines (VAWTs). The post stall data of airfoils is crucial to improve the prediction of the start-up behavior as well as the performance at low tip speed ratios. The present paper analyzes and discusses the performance of the symmetrical NACA 0021 airfoil at three Reynolds numbers (Re = 100k, 140k, and 180k) through 180 deg incidence. The typical problem of blockage within a wind tunnel was avoided using an open test section. The experiments were conducted in terms of surface pressure distribution over the airfoil for a tripped and a baseline configuration. The pressure was used to gain lift, pressure drag, moment data. Further investigations with positive and negative pitching revealed a second hysteresis loop in the deep post stall region resulting in a difference of 0.2 in moment coefficient and 0.5 in lift.
Optimized Gas Turbine Control System for Improved US Navy Landing Craft Air Cushion (LCAC) Operation
Authors: Oliver Sunit , Hampshire James , Engber Martin , Louie Alan
Published: August 2017

The United States Navy has successfully operated their Landing Craft Air Cushion (LCAC) with Vericor’s ETF40B engines since 2001. The engines interface with the craft drivetrain through sprag clutches, which engage when the engine output is greater than the drive shaft speed. Historically, sprag clutch failures have been observed on multiple LCACs, resulting in craft downtime and associated repair & replacement costs. Subsequently, a US Navy investigation revealed the presence of high frequency, low level fluctuations in the shaft rotational speed when operated at steady state conditions. The study also suggested that the speed governor fuel control could excite these fluctuations and induce sprag clutch failure. The original speed governor gains were tuned for maximum transient performance, but not necessarily steady state stability. The aggressive gain selection resulted in a governor response that could be characterized as “hyper-reactive” where the system was willing to respond to even the slightest disturbance, including common drivetrain noise. The US Navy requested that Vericor modify the Full Authority Digital Engine Controller (FADEC) speed governor logic to improve steady state stability while maintaining an acceptable transient response. This paper summarizes the basics of ETF40B operation on the LCAC and describes the effort that improved the governor response. As of the writing of this paper, two (2) years have passed in which no sprag clutch failures have been observed on US Navy LCACs operating with the optimized speed governor.
Influence of Rotor Tip Blockage on Near Stall Blade Vibrations in an Axial Compressor Rig
Authors: Möller Daniel , Jüngst Maximilian , Schiffer Heinz-Peter , Giersch Thomas , Heinichen Frank
Published: August 2017

Rotor blade vibrations observed in the Darmstadt transonic compressor rig are investigated in this paper. The vibrations are non-synchronous and occur in the near stall operating region. Rotor tip flow fluctuations traveling near the leading edge against the direction of rotation (in the rotor relative frame of reference) with about 50% blade tip speed are found to be the reason for the occurrence of the vibrations. The investigations show, that the blockage at the rotor tip is an important factor for the aeroelastic stability of the compressor in the near stall region. It is found, that by application of a recirculating tip injection casing treatment, the aeroelastic stability increases as a result of reduced blockage in the rotor tip region.
Managing Compressor Rotor Rim Fatigue Damage
Authors: Scheibel John R. , Dewey Robert P. , Richardson Jay , Shi Huawei , Swaminathan Swami
Published: August 2017

Described within this paper are the results derived from an investigation into the root cause of cracks which are prematurely forming within the aft end rotor rim attachments of large combustion turbine compressors. The overall objective for this program was to use these results to develop a means for projecting the remaining service life of similarly affected rotors based on non-destructive measurements which identified the degree of fatigue damage sustained in the critical disc rim fillets. Projected rotor retirement was identified by systematically calculating the change in stress intensity for a crack as it propagated from a corner of the attachment fillet through the disc rim. Risk of catastrophic failure was identified when the stress intensity along the front of a given crack size and depth exceeded the fracture toughness of the rotor material, risking failure. Estimates of both crack initiation and propagation relied on properties derived from fatigue tests of specimens obtained from a retired rotor and stress results from a transient thermal analysis of the stages. When compared, projections of crack growth correlated well against field measurements of damaged rims.
The Fabrication, High Heat Flux Testing, and Failure Analysis of Thermal Barrier Coatings for Power Generation Gas Turbines
Authors: McCay Mary Helen , Hsu Pei-feng , Croy D. Edward , Moreno David , Zhang Mengqi
Published: August 2017

Thermal barrier coatings (TBC) are used to protect the hot components of gas turbines engines to enhance thermal efficiency and component service life. The coating, based on yttria stabilized zirconia, is used in this study. In this paper high heat flux testing with a temperature gradient across the coating thickness of TBC coated coupons is presented. These buttons are subject to precisely-controlled laser heating on the top side and compressed air cooling on the bottom side. Analysis of the thermal conductivity change with respect to heating time and peak temperature, failure assessment, and metallurgical examination are also presented. Some important results of using this method of testing are: definition of the service time vs temperature relationship for TBC lifetime; improved durability of TBCs under severe environmental conditions; determination of effective steady-state sintering conductivity; identification of onset of coating cracking and delamination; adjustable peak temperature, automated and accelerated thermal cycling, etc. This leads to faster testing turn-around for TBC development.

Two different types of heating modes can be employed: soak test and cycle test. In soak tests, coated coupons are subjected to steady laser heat flux for up to 12 hr. In cycle tests, the laser heat flux is on for one hour and then off to cool the coated coupons for three minutes. Coupon top surface temperatures from 1200 to 1528°C are maintained in various test cases. At the highest temperature test cases, delamination of TBC (cycle test) and surface crack (soak test) are observed. All key measurements (temperatures, laser power to coupon, compressed air flow rate, etc.) are recorded per second. The normalized thermal conductivity can be computed in real time or processed after the test. It is found that the normalized thermal conductivity increases in the first few hours or cycles of heating and it either reaches a near steady state value or decreases due to surface cracking or delamination in the later state of testing.
Dynamic Properties of Multi-Lobe Water Lubricated Bearings With Temporal and Convective Inertia Considerations
Authors: Dousti Saeid , Allaire Paul , Nichols Bradley , Cao Jianming , Dimond Timothy
Published: August 2017

In this paper, the extended Reynolds equation proposed by Dousti et al. [1] is applied to predict the dynamic behavior of different fixed geometry bearings used in vertical water pumps. The influence of convective and temporal inertia effects is studied in regular and preloaded multi-lobe bearings. It is shown that the convective inertia is more influential at the presence of preload and higher rotational speeds and alters the stiffness and damping properties of the bearing. The temporal inertia leads to the prediction of considerable lubricant added mass coefficients in the order of journal mass. The stability analysis shows depending upon the geometry of the bearing, the new extended Reynolds equation may predict higher or lower logarithmic decrement.
Identification of Vibrational Resonances of Centrifugal Compressor and Radial Turbine Impellers Interacting With General Pressure Pulsations
Authors: Luo Zhusan , Stanko Mike , Schwarz Carl , Wang Zhihong Annie
Published: August 2017

Vibrational resonances of centrifugal compressor and radial inflow turbine impellers are usually identified using either Kushner’s or Singh’s parametric equations in product design and failure analysis. These equations were developed based on positive work accumulated within a certain time period. However, some resonances observed in simulation and testing cannot be understood with those resonance equations.

This paper presents an alternative method to derive vibrational resonance conditions. A new model of general pressure pulsations is developed by taking into account the disturbances resulting from stationary obstacles and rotating blades. Analytical solutions of the forced vibration responses of a rotating disk subjected to different pressure pulsations are then formulated. From the forced responses, both Kushner’s and Singh’s equations can be derived. They can further prove to be equivalent though they focus on different physics.

A general resonance condition is derived from the analytical solutions. This condition is a necessary condition, i.e. all resonances must meet this condition while a system following the condition may or may not be in resonance, depending upon excitation sources. It is noticed that the excitation sources could be related to harmonics due to stationary obstacles, harmonics with combined harmonic orders, or even harmonics to be understood. This general resonance condition can hence provide more “possible resonance points” and assist identifying resonances from more representative modes and more excitation sources. It has been validated by predicting vibrational resonances observed in three centrifugal compressors. This condition has also been successfully employed in the failure analysis and design modification of a radial inflow turbine impeller.
Fits and Starts: A Current Look at Marine and Industrial Gas Turbine Electric Start Systems
Authors: McAndrews Glenn
Published: August 2017

Electric starter development programs have been the subject of ASME technical papers for over two decades. Offering significant advantages over hydraulic or pneumatic starters, electric starters are now poised to be the preferred choice amongst gas turbine customers. That they are not now the dominant starter in the field after decades of investment and experimentation is attributable to many factors. As with any new technology, progress is often unsteady, depending on budgets, market conditions, customer buy-in, etc. Additionally, technological advances in the parent technologies, in this case electric motors, can abruptly and rapidly change, further disturbing the best laid introduction plans. It is therefore not too surprising that only recently, is the industry beginning to see the deployment of electric starters on production gas turbines. The earliest adoption occurred on smaller gas turbine units, generally less than 10 MW in power. More recently, gas turbines greater than 10 MWs are being sold with electric starters. The authors expect that regardless of their size or fuel supply, most all future gas turbine users will opt for electric starters. This may even include the “larger” frame machines with power greater than 100 MW. Starting with some past history, this paper will not only summarize past development efforts, it will attempt to examine the current deployment of electric starters throughout the marine and industrial gas turbine landscapes. The large-scale acceptance of electric start systems for both new production and retrofit will depend on the favorable cost/benefit assessment when weighing both first cost and life cycle cost. The current and intense activity in electric vehicle applications is giving rise to even more power dense motors. The paper will look at some of these exciting applications, the installed products, and the technologies behind the products. To what extent these new products may serve the needs of the gas turbine community will be the central question this paper attempts to answer.
Formation of Deposits From Heavy Fuel Oil Ash in an Accelerated Deposition Facility at Temperatures Up to 1206°C
Authors: Laycock Robert G. , Fletcher Thomas H.
Published: August 2017

Some industrial gas turbines are currently being fired directly using heavy fuel oil, which contains a small percentage of inorganic material that can lead to fouling and corrosion of turbine components. Deposits of heavy fuel oil ash were created in the Turbine Accelerated Deposition Facility (TADF) at Brigham Young University under gas turbine-related conditions. Ash was produced by burning heavy fuel oil in a downward-fired combustor and collecting the ash from the exhaust stream. The mass mean ash particle diameter from these tests was 33 microns. This ash was then introduced into the TADF and entrained in a hot gas flow that varied from 1088 to 1206°C. The gas and particle velocity was accelerated to over 200 m/s in these tests. This particle-laden hot gas stream then impinged on a nickel base superalloy metal coupon approximately 3 cm in diameter, and an ash deposit formed on the coupon. Sulfur dioxide was introduced to the system to achieve 1.1 mol% SO2 in the exhaust stream in order to simulate SO2 levels in turbines currently burning heavy fuel oil. The ash deposits were collected, and the capture efficiency, surface roughness, and deposit composition were measured. The deposits were then washed with deionized water, dried, and underwent the same analysis. It was found that, as the gas temperature increased, there was no effect on capture efficiency and the post-wash roughness of the samples decreased. Washing aided in the removal of sulfur, magnesium, potassium, and calcium.
Experimental and Analytical Assessment of Cavity Modes in a Gas Turbine Wheelspace
Authors: Berg Rachel A. , Tan C. S. , Ding Zhongman , Laskowski Gregory , Palafox Pepe , Miorini Rinaldo
Published: August 2017

Fast response pressure data acquired in a high-speed 1.5-stage turbine Hot Gas Ingestion Rig shows the existence of pressure oscillation modes in the rim-seal-wheelspace cavity of a high pressure gas turbine stage with purge flow. The experimental results and observations are complemented by computational assessments of pressure oscillation modes associated with the flow in canonical cavity configurations. The cavity modes identified include shallow cavity modes and Helmholtz resonance. The response of the cavity modes to variation in design and operating parameters are assessed. These parameters include cavity aspect ratio, purge flow ratio, and flow direction defined by the ratio of primary tangential to axial velocity. Scaling the cavity modal response based on computational results and available experimental data in terms of the appropriate reduced frequencies appears to indicate the potential presence of a deep cavity mode as well. While the role of cavity modes on hot gas ingestion cannot be clarified based on the current set of data, the unsteady pressure field associated with turbine rim cavity modal response can be expected to drive ingress/egress.
Erosion Properties of Ceramic Composite Material Based on Nano-Mullite Whisker and Zirconia-Toughened Alumina
Authors: Erazo Fabian , Robertson Taylor , Huang Xiao , Kearsey Rick , Yang Qi
Published: August 2017

The improvement of bulk ceramic properties through the addition of a secondary or even tertiary phase is a field of research that has been actively pursued since the mid twentieth century. This pursuit has become more relavent with the adoption of ceramic phases to protect structural components within the hotpath of gas turbines. Improving the properties of these ceramic coatings and tiles has the potential of reducing catastrophic damage events leading to an overall reduction in unplanned maintence and downtime.

To date, Several approaches have been undertaken to improve the physical properties of these ceramics including preferential microstructural grain growth and doping to develop metastable crystal phases. This paper examines the effect of whisker additions to a mechanical mixture of oxide ceramics on the erosion properties. The baseline structure is a mechanical mixture of zirconia and alumina particles in the ratio of 89.8vol% alumina to 10.2vol% partially stabalized zirconia. A ratio of 20.0vol% mullite whiskers is incorporated into the structure as a toughening agent. The mullite whiskers are grown using a molten salt method. The overall structural composition is 20.0vol% mullite whiskers, 8.2vol% partially stabilized zirconia, and 71.8vol% alumina. This whisker toughened material is compared to a baseline 89.8vol% alumina 10.2vol% zirconia ceramic.

Erosion tests were conducted using a 50 μm diameter alumina erodant with a velocity of 104 m/s. Impingement angles of 30°, 60° and 90° were examined to determine the effect of whisker additions at steeper attack angles. Despite the increased hardness, tensile strength and fracture toughness, whisker-enhanced zirconia-toughened alumina has shown similar erosion rate as non-reinforced ZTA at 30° ad 90° and much higher erostion at 60°. It can be surmised that whisker-enhanced toughening of ceramics has little positive effect on the erosion resistance of ceramics at room temperature and is potentially harmful. Microstructure analysis results are also presented within to illustrate the erosion material removal mode under different conditions.
Design Optimization of a 3D Parameterized Vane Cascade With Non-Axisymmetric Endwall Based on a Modified EGO Algorithm and Data Mining Techniques
Authors: Li Chenxi , Guo Zhendong , Song Liming , Li Jun , Feng Zhenping
Published: August 2017

The design of turbomachinery cascades is a typical high dimensional and computationally expensive problem, a metamodel-based global optimization and data mining method is proposed to solve it. A modified Efficient Global Optimization (EGO) algorithm named Multi-Point Search based Efficient Global Optimization (MSEGO) is proposed, which is characterized by adding multiple samples at per iteration. By testing on typical mathematical functions, MSEGO outperforms EGO in accuracy and convergence rate. MSEGO is used for the optimization of a turbine vane with non-axisymmetric endwall contouring (NEC), the total pressure coefficient of the optimal vane is increased by 0.499%. Under the same settings, another two optimization processes are conducted by using the EGO and an Adaptive Range Differential Evolution algorithm (ARDE), respectively. The optimal solution of MSEGO is far better than EGO. While achieving similar optimal solutions, the cost of MSEGO is only 3% of ARDE. Further, data mining techniques are used to extract information of design space and analyze the influence of variables on design performance. Through the analysis of variance (ANOVA), the variables of section profile are found to have most significant effects on cascade loss performance. However, the NEC seems not so important through the ANOVA analysis. This is due to the fact the performance difference between different NEC designs is very small in our prescribed space. However, the designs with NEC are always much better than the reference design as shown by parallel axis, i.e., the NEC would significantly influence the cascade performance. Further, it indicates that the ensemble learning by combing results of ANOVA and parallel axis is very useful to gain full knowledge from the design space.
Unsteady Flow in a Centrifugal Compressor Stage Equipped With a Vaned Diffuser and Cavities
Authors: Younsi Mohand , Corneloup Christophe , Moyroud François , Baldacci Antoine
Published: August 2017

The purpose of this work is to present the Computational Fluid Dynamics (CFD) transient flow simulations of a centrifugal compressor stage with cavities. The cavities are included in the CFD model for several reasons. First the leakage flows and the windage effects are important to predict the absolute level performance of the stage (efficiency). Secondly the cavities also play an important role in the generation of the aerodynamic forcing on the impeller as well as in the prediction of the aerodynamic damping. As the compressor stage contains unequal numbers of blades and vanes, the Time Transformation method, an extension of the time inclining method is used in this work. This method which requires only a few passages per row is employed to reduce computational load and accurately model the full wheel. The numerical procedure is applied at design point firstly and then extended to the off-design operating conditions, permitting to compare and understand the transient flow behavior. The ability of the method to predict the impeller/diffuser interactions and cavity unsteady pressure response is discussed. The respective contributions of the diffuser, impeller blade passages and side cavities in terms of impeller forcing amplitude and frequency content are studied. In addition to this, comparisons between the experiment, the reduced model and the equivalent part wheel periodic solution are made to demonstrate the accuracy and computational efficiency of the considered transformation method.
Nonlinear Vibration of a Saturated Water Journal Bearing and Bifurcation Analysis
Authors: Shoyama Tadayoshi
Published: August 2017

We developed a turbo compressor that has water-lubricated bearings driven at 30,000 rpm in a saturation condition, where the ambient pressure is at the saturation point of the discharged lubricant water. Such a saturated water journal bearing is located at both end of the rotor, each of which has a conical part to produce thrust force without another thrust bearing or a thrust collar. The bearings are supported with nonlinear elastomeric O-rings. At rotational speed over 15,000 rpm, the rotor showed many sub-harmonic vibrations that are nonlinear phenomena unpredictable from a linear equation of motion. Instead, a stability analysis with a bifurcation diagram is an effective method to tackle these problems. In this paper, we investigated these rotor vibrations by bifurcation diagrams of the vibrations measured in experiments of saturated water journal bearings. The angular velocity was used as a bifurcation parameter. The bifurcations among synchronous, sub-harmonic, and chaotic vibrations were shown. Next, the nonlinear dynamics of the rotating rigid shaft were analyzed numerically with the nonlinear stiffness obtained by a commercial code that utilizes the two-dimensional Reynolds equation. The dynamic properties of the supporting structure were modeled with a complex stiffness coefficient. The equation of motion of the rotating shaft was solved numerically in a time domain with these dynamic properties. MATLAB Simulink code was built to integrate the equations. As a result, a Hopf bifurcation was found and a sub-harmonic limit cycle appeared spontaneously. The rotational speed and such other properties as the unbalanced force and the damping of the supporting structures were parameterized to investigate the onset and the amplitude of these vibrations. These numerical results agreed well with the experimental results.
Secondary Flow in Variable Stator Vanes With Penny-Cavities
Authors: Stummann Simon , Pohl Daniel , Jeschke Peter , Wolf Hannes , Halcoussis Alexander , Franke Matthias
Published: August 2017

This paper presents a description of Detached Eddy Simulations being carried out on a variable stator vane with a penny-cavity in order to determine the secondary flow phenomena in the main flowpath. Variable stator vanes are common in multi-stage compressors to prevent flow separations on rotor and stator blades at off-design operation points. The bearing of the stators at hub and tip generate unavoidable circular-shaped ring gaps, which are called penny-cavities. The aim of this paper is to determine secondary flow phenomena in variable stator vanes on an annular cascade testbed resulting from the throughflow of the penny-cavities. Reynolds-Averaged-Navier-Stokes simulations and scale resolving Detached-Eddy-Simulations of a variable stator vane with hub penny-cavity were therefore performed using Ansys CFX. The results of these simulations will be compared to corresponding simulations without penny-cavity. The study shows secondary flow phenomena, which are comparable to the interaction of a transverse jet in a free stream. Due to the low momentum ratio of R = 0.5, the jet immediately veers in the direction of the main flow. The typical vortices which develop from a transverse jet in a free stream are identified. The steady RANS simulation shows an asymmetrical counter-rotating vortex pair. A lack of unsteady secondary flow interaction can be seen in the RANS simulations in contrast to the Detached-Eddy-Simulations, which resolve large turbulent scales. Hence an interaction between the counter-rotating vortex pair and the unsteady shear layer vortices in the stator is visible. In the Detached Eddy Simulations the counter-rotating vortex pair is superimposed by the unsteady shear-layer vortices. The vortices produce significant additional mixing losses, which will be shown in detail. By comparing simulations with and without penny-cavity, the penny-cavity losses are quantified. In conclusion, this paper will help design engineers become more aware of the significance of the penny-cavity with variable stator vanes.
Modeling of Minimum NOx in Staged-Combustion Architectures at Elevated Temperatures
Authors: Goh Edwin , Sirignano Matthew , Nair Vedanth , Emerson Benjamin , Lieuwen Tim , Seitzman Jerry
Published: August 2017

Current combined cycle plants can achieve cycle efficiencies of up to 62%. Further increases in cycle efficiency are achievable through higher turbine inlet temperatures. Such high temperatures pose a NOx-abatement limitation with current combustor architectures due to increased thermal NO formation. Staged combustion shows the potential for not only NOx-abatement at high firing temperatures, but also for enhanced turn-down performance. Staged combustion devices have been explored in the literature previously, as well as implemented commercially. The objective of this work is to identify the theoretical minimum NOx levels attainable with fuel-staging for a given firing temperature and combustor residence time, at the same time identifying the corresponding optimum staged combustor configurations. In other words, its objective is to understand, for an idealized case, the fundamental physical limits of this approach. A reactor model of an axially-staged combustor is incorporated in ANSYS Chemkin. The main burner is modeled as a conventional lean-premixed DLN-type combustor using a laminar flame calculation, while the axial fuel staging calculation for the minimum NOx is modeled as a perfect mixer followed by a constant-pressure batch reactor of fixed residence time. Optimum NOx levels are found by constraining CO emissions to a fixed percentage above equilibrium levels. Parametric studies are performed for a range of firing temperatures to find the optimum main combustor equivalence ratio (or fuel staging ratio) and secondary stage residence time, while fuel and air preheat temperatures and combustor pressure remain fixed. With the assumption of instantaneous mixing of secondary fuel and main combustor products, staging provides drastically reduced minimum NOx levels (∼ 1 ppm corrected to 15% excess air at 1975 K firing temperature) compared to conventional premixed architectures while providing significantly enhanced part-load CO performance. Moreover, the minimum theoretical NOx is relatively insensitive to firing temperature and overall combustor residence time over a practical range of values.
Computational and Experimental Study of a Platinum Thin-Film Based Oil Condition and Contamination Sensor
Authors: Sridhar V. , Chana K. S. , Singh D.
Published: August 2017

Lubrication systems form an integral part of aircraft and automobiles. Failure of lubrication systems can occur due to contamination or degradation of oil which can lead to excessive wear and failure of rotating components. This leads to unnecessary downtime and increase in maintenance costs. Oil contamination occurs when metallic or non-metallic particles are produced due to wear of the machine components such as bearings, gears etc. and these particles may not be always captured by the filtering system that are already in the lubrication system. Hence, the particles can clog oil paths and accelerate the wear of moving parts. In addition to this, variations in thermal stresses causes oxidation and thereby degradation of the oil. Contamination can also be in the form of liquids such as water droplets or fuel from heat exchangers. Currently, on-line oil condition monitoring systems use sensors that are based on eddy current, optical, capacitive to detect contamination in oil for preventive maintenance especially for aircraft engine bearings, aviation gearboxes etc. These sensors have some major drawbacks: prone to surface contamination, non-linearity, insensitive to detect extremely small particulates or false detection such as trapped bubbles.

A new sensor based on platinum thin film heat transfer gauges has been developed at the University of Oxford that works on the principle of measuring the change in thermal product of the material that is in contact. The sensor is able to detect any form of contamination in oil and can be used for both off-line and on-line condition monitoring. The sensor is found to be quite sensitive and can detect extremely small concentrations of contaminants of the order 0.01 % by volume. This paper presents a detailed computational and experimental study carried out to test contamination in oil at room temperatures. The three-dimensional, time-dependent, implicit numerical simulations were carried out using the commercial computational fluid dynamics package FLUENT®. The simulation incorporates conjugate heat transfer to obtain the heating curves of the sensor with and without contamination. This was necessary to understand the range of the sensor and also to study the variations in heat transfer from the sensor to the material that is in contact with the sensor, which otherwise would not have been possible through experiments. The numerical heating curves are then compared with experimentally obtained heating curves. The comparison showed that the numerical and experimental data to agree well and are within 1 %.