Showing papers in "Journal of Engineering for Gas Turbines and Power-transactions of The Asme in 2022"

Machine-Learning Clustering Methods Applied to Detection of Noise Sources in Low-Speed Axial Fan

Abstract: The integration of rotating machineries in human-populated environments requires to limit noise emissions, with multiple aspects impacting on control of amplitude and frequency of the acoustic signature. This is a key issue to address and when combined with compliance of minimum efficiency grades, further complicates the design of axial fans. The aim of this research is to assess the capability of unsupervised learning techniques in unveiling the mechanisms that concur to the sound generation process in axial fans starting from high-fidelity simulations. To this aim, a numerical dataset was generated by means of LES simulation of a low-speed axial fan. The data set is enriched with sound source computed solving a-posteriori the perturbed convective wave equation (PCWE). First, the instantaneous flow features are associated to the sound sources through correlation matrices and then projected on latent basis to highlight the features with the highest importance. This analysis in also carried out on a reduced dataset, derived by considering two surfaces at 50% and 95% of the blade span. The sampled features on the surfaces are then exploited to train three cluster algorithms based on partitional, density and Gaussian criteria. The cluster algorithms are optimized and their results are compared, with the Gaussian Mixture one demonstrating the highest similarity (>80%). The derived clusters are analyzed, and the role of statistical distribution of velocity and pressure gradients is underlined. This suggests that design choices that affect these aspects may be beneficial to control the generation of noise sources.

Investigation of the Effect of Simulated Atmospheric Conditions At Different Altitudes On the Combustion Process in a Heavy-Duty Diesel Engine Based On Zero-Dimensional Modeling

Abstract: Plateau diesel engines suffer from increased fuel consumption and deteriorating emissions. These problems were mainly caused by the combustion worsening inside the chamber. However, limited research has been done specifically on the altitude effects on the combustion process of diesel engine cycles, which would obviate the feasibility of optimizing high altitude engines. Hence, the goal of this study was to apply the zero-dimensional modeling approach to deeply analyze the influence of altitude on diesel engine combustion. A triple Wiebe function model was calibrated based on the experimental results of a direct injection compression ignition engine operating from sea level to 5000 meters altitude. The analyses indicated that the increase in altitude lengthened the ignition delay, resulting in more fuel fraction being burned in the premixed combustion stage and therefore extending the duration of this phase. As for the main mixing-controlled combustion phase, operation at high altitude retarded the combustion initiation angle, shortened the burning duration, and reduced the diesel mass burned in this stage. Moreover, the higher altitude operation increased the energy release and prolonged the duration of the late combustion period, which was detrimental to clean emissions. All these impacts contributed to the reduced thermal and combustion efficiency of the highland engines. However, the engine phasing did not change with increasing altitude, suggesting that it was mainly the combustion degradation that caused the reduction in power output. Consequently, finding solutions to improve the spray formation quality is the key to compensate for the altitude negative effects.

Shapley Additive Explanations of Multigeometrical Variable Coupling Effect in Transonic Compressor

Abstract: Abstract Optimization algorithms in the compressor detailed design stage generate big data of geometries and corresponding performances, but these data are often not exploited efficiently to unveil hidden compressor design guidance. In this work, the Shapley additive explanations (SHAP) method from game theory is proposed as an efficient methodology to extract design guidelines from databases. A database was generated when optimizing the blade features (sweep, lean, and end-bend) of Rotor 37. Based on this, a neural network is trained to predict compressor efficiency. The SHAP method is then applied to explain the neural network behavior, which provides information on the sensitivity of single geometrical variables and the coupling effect between multiple geometrical variables. Results show that the near-tip sweep and midspan lean angles are most influential on efficiency. Within the same group of variables, the adjacent variables tend to present strong positive coupling effects on efficiency. Among different groups, evident coupling effects are observed between sweep and lean and between lean and end-bend, but the coupling effect between sweep and end-bend is negligible. Flow mechanisms behind the coupling effects are discussed. For near-tip lean angles L3 and L4, the positive coupling effect is due to the change of the passage shock. For near-tip lean angle L4 and sweep angle S4, the change of detached shock leads to a negative coupling effect. The proposed data mining method based on the neural network and SHAP is promising and transferable to other turbomachinery optimization databases in the future.

3D CFD Simulation and Mesh Size Effect of the Conversion of a Heavy-Duty Diesel Engine to Spark-Ignition Natural Gas Engine

Abstract: With developing in computer technology, 3D CFD IC engine simulations, which generally use reduced chemical kinetic mechanisms and simplified combustion models, can provide more accurate results along with less initial investment and calculation costs compared to experimental setup. In this study, a heavy-duty diesel engine effects on performance, combustion and emission characteristics by spraying natural gas from the intake port and transforming it into a spark-ignition engine were investigated through 3D ANSYS Forte CFD program. The spark time was accepted as 0.5 °CA bTDC, which was the start of injection time for the diesel injector. Analyzes were carried out at 2300 rpm, full load, 17.5: 1 of high compression ratio, constant air/fuel ratio. Six different global mesh sizes were used in the converted engine model. Performance, in-cylinder combustion, and emission values were examined for these six different global mesh sizes and the most suitable one was tried to be found. As a result of the global mesh size study, it was concluded that the most suitable size was 2.25 mm. In terms of performance, when the data obtained with usage of natural gas were compared to that of diesel fuel, the GIP, IMEP and ITE values were increased by 12.02%, 8.93%, and 8.7%, respectively, while the GISFC value was decreased by 9.78%. When the emission values were examined, it was seen that the engine met the Stage IIIB norms without usage of SCR, DPF and DOC under the conditions.

Dynamic Strain Reconstruction of Rotating Blades Based On Tip Timing and Response Transmissibility

Abstract: Dynamic strain of rotating blades is critical in turbomachinery health monitoring and residual life evaluation. Though blade tip time (BTT) is a promising technique to replace traditional strain gages, the lack of effective strain transformation through BTT hinders the implementation. In this paper, a non-intrusive dynamic strain reconstruction method of rotating blade is proposed based on the BTT technique and response transmissibility. Firstly, the displacement-to-strain transmissibility (DST) considering rotational speed is derived from the frequency response functions based on blade mode shapes. A quadratic polynomial function of DST with respect to rotational speed is provided to calibrate DST in blade rotational state. Secondly, the blade-tip displacement in resonance is obtained by BTT measurement and Circumferential Fourier Fit processing method. Thirdly, the dynamic strains of critical points on blades are calculated using the DST in conjunction with the tip displacement amplitude. In this paper, to validate the proposed method, acceleration and deceleration experiments, including both BTT and strain gages, are conducted on a spinning rotor rig. Experimental results demonstrate that the reconstructed dynamic strains of different positions on the rotating blades correspond well to the strain gage results. The mean relative error between the reconstructed and measured results is generally less than 9%.

Prediction of Pressure Rise in a Gas Turbine Exhaust Duct Under Flameout Scenarios While Operating on Hydrogen and Natural Gas Blends

Abstract: Abstract In recent years, there is a growing interest in blending hydrogen with natural gas fuels to produce low-carbon electricity. It is important to evaluate the safety of gas turbine packages under these conditions, such as late-light off and flameout scenarios. However, the assessment of the safety risks by performing experiments in full-scale exhaust ducts is a very expensive and, potentially, risky endeavor. Computational simulations using a high fidelity CFD model provide a cost-effective way of assessing the safety risk. In this study, a computational model is implemented to perform three-dimensional, compressible, and unsteady simulations of reacting flows in a gas turbine exhaust duct. Computational results were validated against data obtained at the simulated conditions in a representative geometry. Due to the enormous size of the geometry, special attention was given to the discretization of the computational domain and the combustion model. Results show that CFD model predicts the main features of the pressure rise driven by the combustion process. The peak pressures obtained computationally and experimentally differed by 20%. This difference increased up to 45% by reducing the preheated inflow conditions. The effects of rig geometry and flow conditions on the accuracy of the CFD model are discussed.

Making Better Swirl Brakes Using Computational Fluid Dynamics: Performance Enhancement From Geometry Variation

Abstract: Abstract A fluid with a large swirl (circumferential) velocity entering an annular pressure seal influences the seal cross-coupled dynamic stiffness coefficients, and hence it affects system stability. Typically comprising a large number of angled vanes around the seal circumference, a swirl brake (SB) is a mechanical element installed to reduce (even reverse) the swirl velocity entering an annular seal. SB design guidelines are not readily available, and existing configurations appear to reproduce a single source. By using a computational fluid dynamics (CFD) model, the paper details a process to engineer a SB upstream of a 16-tooth labyrinth seal (LS) with tip clearance Cr = 0.203 mm. The process begins with a known nominal SB* geometry and considers variations in vane length (LV* = 3.25 mm) and width (WV* = 1.02 mm), and stagger angle (θ* = 0 deg). The vane number NV* = 72 and vane height HV* = 2.01 mm remain unchanged. The SB–LS operates with air supplied at pressure PS = 70 bar, a pressure ratio PR = exit pressure Pa/PS = 0.5, and rotor speed Ω = 10.2 krpm (surface speed ΩR = 61 m/s). Just before the SB, the preswirl velocity ratio = average circumferential velocity U/shaft surface speed (ΩR) equals α = 0.5. For the given conditions, an increase in LV allows more space for the development of vortexes between two adjacent vanes. These are significant to the dissipation of fluid kinetic energy and thus control the reduction of α. A 42% increase in vane length (LV = 4.6 mm) produces a ∼43% drop in swirl ratio at the entrance of the LS (exit of the SB), from αE = 0.23 to 0.13. Based on the SB with LV = 4.6 mm, the stagger angle θ varies from 0 deg to 50 deg. The growth in angle amplifies a vortex at ∼70% of the vane height, while it weakens a vortex at 30% of HV. For θ = 40 deg, the influence of the two vortexes on the flow produces the smallest swirl ratio at the LS entrance, αE = −0.03. For a SB with LV = 4.6 mm and θ = 40 deg, the vane width WV varies from 0.51 mm to 1.52 mm (±50% of WV*). A reduction in WV provides more space for the strengthening of the vortex between adjacent vanes. Therefore, a SB with greater spacing of vanes also reduces the inlet circumferential velocity. For WV = 0.51 mm, αE further decreases to −0.07. Besides the design condition (α = 0.5), the engineered SB having LV = 4.6 mm, θ = 40 deg, and WV = 0.51 mm effectively reduces the circumferential velocity at the LS entrance for other inlet preswirl ratios equaling α = 0 and 1.3. Rather than relying on extensive experiments, the CFD analysis proves effective to quickly engineer a best SB configuration from the quantification of performance while varying the SB geometry and inlet swirl condition.

Influence of Lubricant Film Cavitation on the Vibration Behavior of a Semifloating Ring Supported Turbocharger Rotor With Thrust Bearing

Abstract: Abstract This contribution investigates the influence of outgassing processes on the vibration behavior of a hydrodynamic bearing supported turbocharger rotor. The examined rotor is supported radially by floating rings with outer squeeze-film damping and axially by thrust bearings. Due to the highly nonlinear bearing properties, the rotor can be excited via the lubricating film, which results in subsynchronous vibrations known as oil-whirl and oil-whip phenomena. A significant influence on the occurrence of oil-whip phenomena is attributed to the bearing stiffness and damping, which depend on the kinematic state of the supporting elements, the thermal condition, and the occurrence of outgassing processes. For modeling the bearing behavior, the Reynolds equation with mass-conserving cavitation regarding the two-phase model and the three-dimensional (3D) energy as well as heat conduction equation is solved. To evaluate the impact of cavitation, run-up simulations are carried out assuming a fully (half-Sommerfeld) or partially filled lubrication gap. The resulting rotor responses are compared with the shaft motion measurement. Also, the normalized eccentricity, the minimum lubricant fraction, and the thermal bearing condition are discussed.

Novel UAS Propeller Design Part 1: Using an Unloaded Tip to Reduce Power Requirements and Lower Generated Sound Levels for Propellers Designed for Minimum Induced Drag

Abstract: Today, over 500 eVTOL vehicles are being developed for everything from Urban Air Mobility to package delivery. In addition, Unmanned Aircraft Systems (UASs) are used in a variety of applications to include intelligence, surveillance, and reconnaissance (ISR) as well as resupply for the military. Most of these vehicles utilize electric propulsion systems with propellers. Efficient propellers with reduced noise generation are necessary for these vehicles to coexist in urban environments or be used for ISR missions. Traditional propeller design uses Blade Element Momentum Theory (BEMT) to minimize induced losses. The current investigation describes a novel propeller design approach that minimizes induced drag by reducing the thrust loading near tip. This reduces the tip vortex strength lowering the Sound Pressure Level (SPL) and power required. A parametric study of 18 propellers examined performance using traditional BEMT design near the hub and progressing to zero thrust loading at the tip. A microphone on a traverse mounted behind the propeller was used to measure the peak SPL and its location in a wind tunnel. The best performing unloaded tip propeller showed 5.2% reduction in power required and 12 dB SPL reduction compared to a commercial propeller at the same test conditions. Keywords: UAS propeller, propeller design, airfoil

Experimental Study of a Novel Centrifugal Compressor With Two Successive and Independent Rotors

Abstract: This study deals with a low pressure-ratio centrifugal compressor consisting of two counter-rotating rotors called a counter-rotating centrifugal compressor (CRCC). The design method based on the loss model was presented to determine the geometric parameters of the two counter-rotating rotors. According to this method, the rotor of a selected single rotor centrifugal compressor (SRCC) has been redesigned into two counter-rotating rotors (upstream and downstream rotors) by choosing the value of meridional length ratio (LR). The meridional view, the volute shape, and the operating parameters of SRCC are preserved during the design process. In a first step, the counter-rotating mode at a constant rotor speed of 11k rpm has been carried out. The overall characteristics of CRCC are compared to those of SRCC. In a second step, the map characteristic of CRCC is established for seven speed ratios. The results show that CRCC increases up to 4.6% for the pressure ratio and 3.5% for the efficiency compared to SRCC at the same tip-speed. In addition, CRCC can operate at a lower tip-speed by about 2k rpm to produce the same characteristics as SRCC, with better efficiency over a wide range of flow rates. However, the surge margin of the CRCC is shifted to higher flow rates. This disadvantage of the CRCC was solved by choosing the adequate pair of the rotational speeds of the two rotors that will be presented in other publication.

Synthesis of Methanol From a Chemical Looping Syngas for the Decarbonization of the Power Sector

Abstract: One promising pathway for carbon capture and utilization is represented by the coupling of chemical looping cycles with liquid fuel synthesis processes. Methanol is an interesting fuel for gas turbines, due to its potential reduction of NOX and particulate emissions along with the absence of SO2 emissions. In this work, methanol production from the syngas generated by a three-reactors chemical looping process is investigated by mass and energy balances. The cycle is composed by a reducer reactor, where Fe2O3 is reduced to FeO by a reducing agent; an oxidizer reactor, where FeO reacts with CO2 and H2O to produce a syngas; an air reactor, where Fe3O4 is regenerated to Fe2O3 by air. The produced syngas is then sent to a methanol synthesis plant. Several syngas compositions from different CO2/H2O molar fractions (1-3) at the oxidizer inlet are taken into account. The resulting methanol flow rates are almost equal in all investigated configurations (about 0.35 t/h). From an energy standpoint, the required electric power is greater for higher hydrogen mole fractions in the syngas. However, the case with 75% H2 content is characterized by the greatest methanol yield (12.6%), carbon efficiency (23%) and the lowest feed/recirculation ratio, thus representing the most indicated configuration among the investigated ones. Finally, by burning methanol in a gas turbine, the total CO2 emissions are halved with respect to the case without the system (if the CO2 associated with biogenic carbon in the reducer is considered as net-zero).

Experimental Study of Various Low-Friction Coatings for High-Temperature Gas Foil Bearings Under Cold-Start Conditions

Abstract: Abstract This article presents the experimental research carried out on five different materials with which the top foils have been coated. A foil bearing with these foils was tested under different load conditions. The key operating parameters were determined, such as the moment of friction during the run-up and run-down tests as well as the temperature of the top foil. The AS20 coating, like the TiAlN coating, was intact (with the exception of several places where it was worn and where the Inconel sheet was visible) and was suitable for further use. The WC/C coating was damaged in many places, which shows that this type of coating cannot be used in combination with a journal coated with chromium oxide. The foil coated with MoS2/C had many areas where the coating was worn and also many areas where it was erased completely, so this type of coating was not durable. The use of a combination of TiAlN and MoS2/C coatings resulted in minor wear of the outer coating (made of MoS2/C) and the appearance of the inner coating, which is more resistant to abrasion. The tested materials will be used in the future to build a foil bearing resistant to operation at elevated temperatures in a gas microturbine.

Hydrogen Thermal-Powered Aircraft Combustion and Propulsion System

Abstract: This article presents an assessment study of the propulsion system, the fuel distribution system, and the injector/combustor technologies enabling to eliminate CO2 emissions in aviation. In addition, the discussion is on NOx reduction methods and mitigation technologies, and a concept to fully eliminate NOx is proposed. To design and deploy an advanced thermal-powered aircraft based on liquid hydrogen fuel in future, it is important to provide key estimates that support feasibility of the methods and technologies developed and explored in this paper. This is conducted here for a typical narrow-body aircraft that will be retrofitted and considered. Once the design space and performance requirements are introduced, a compact low emission combustor including all components is discussed to operate with hydrogen swirled combustion to equip the turbofan engines of this conceptualized aircraft. The fuel tank is not only discussed with respect to the difference in power per unit volume and per unit mass between Sustainable Aviation Fuel (SAF) and H2 but also taking into account the Breguet range. This demonstrates that the volume of the tanks does not need to be four times more voluminous between H2 and SAF. The paper also presents a thermodynamics performance analysis for SAF fuel that is used to retrofit the engine with hydrogen fuel keeping inlet and outlet combustor stagnation temperatures equivalent. A method to derive the required flow split for future premixed combustor is described and conserve identical thermal power between SAF and H2 fuels. Flame stabilization challenges are also introduced.

Micro-Mixing Combustion for Highly Recuperated Gas Turbines: Effects of Inlet Temperature and Fuel Composition On Combustion Stability and Nox Emissions

Abstract: The micromix combustion concept offers an elegant compromise between premixed and non-premixed combustion. By mixing the fuel and air at the smallest scale possible, one can achieve NOx emissions comparable to premixed combustion while removing the risks of autoignition and flashback. Current literature reports multiple micromix designs that achieve low NOx emissions (<10 ppm) with hydrogen or hydrogen-rich fuels at combustor inlet temperatures representative of low to medium pressure ratio gas turbines (<650 K). This paper seeks to bridge the gap between current literature and the design requirements of highly recuperated ceramic gas turbines, which should allow low NOx operation with various fuels at combustor inlet temperatures upwards of 900 K. To this end, micromix injection nozzles were designed and tested at small-scale to investigate the effects of fuel composition and inlet temperature on combustion stability and NOx emissions. The nozzles were additively manufactured in Inconel 625 having hundreds of holes as small as 0.25 mm. An axial swirler is used to induce recirculation of the products behind the nozzle, which helps stabilize combustion with hydrocarbon fuels due to their longer reaction times and slower flame speeds. Experimental results show that NOx emissions can be decreased down to premixed levels if the jet Damköhler number is kept under a critical value, which requires increasingly smaller holes or higher jet velocities as the inlet temperature increases. Combustion instabilities are observed at low inlet temperatures with hydrocarbons, which are also correlated to the jet Damköhler number.

Sound Generation in Multicomponent Nozzle Flows with Dissipation

Abstract: Low emission aircraft engines burn in a lean regime, which makes the combustor susceptible to unsteady combustion. Along with improper mixing and air cooling, the unsteady combustion process gives rise to flow inhomogeneities. The acceleration of these inhomogeneities in the nozzle downstream of the combustor generates indirect combustion noise. If the acoustic waves that are reflected off the nozzle are sufficiently in phase with the heat released by the flame, thermoacoustic instabilities can occur. The generation and transmission of sound through the nozzle guide vane are typically modelled with a compact and isentropic nozzle model. Because the flow is non-isentropic due to losses from wall friction and recirculation zones, in the literature, a mismatch is observed between experimental and theoretical predictions in subsonic-choked regimes. In this work, we propose a low-order physical model to predict indirect noise in a multi-component nozzle flow with dissipation using conservation laws whilst modelling non-isentropicity using a friction factor. The model is generalized for finite-length (non-compact) arbitrary geometry nozzles. We show that the friction factor can account for wall friction and two (or three) dimensional effects, such as flow recirculation in a cross-averaged sense. We analyse the model numerically for both subsonic and supersonic nozzles, emphasizing the importance of non-isentropic and non-compact assumptions with compositional inhomogeneities. Further, we show the effect of the nozzle geometry. The results are validated with existing experimental data from the literature.

Experimental Characterization of Losses in Bladeless Turbine Prototype

Abstract: Abstract Multidisk bladeless turbines, also known as Tesla turbines, are promising in the field of small-scale power generation and energy harvesting due to their low sensitivity to down-scaling effects, retaining high rotor efficiency. However, low (less than 40%) overall isentropic efficiency has been recorded in the experimental literature. This article aims for the first time to a systematic experimental characterization of loss mechanisms in a 3 kW Tesla expander using compressed air as working fluid and producing electrical power through a high-speed generator (40 krpm). The sources of losses discussed are stator losses, stator–rotor peripheral viscous losses, end-wall ventilation losses, and leakage losses. After description of experimental prototype, methodology, and assessment of measurement accuracy, the article discusses such losses aiming at separating the effects that each loss has on the overall performance. Once effects are separated, their individual impact on the overall efficiency curves is presented. This experimental investigation, for the first time, gives the insight into the actual reasons of low performance of Tesla turbines, highlighting critical areas of improvement, and paving the way to next-generation Tesla turbines, competitive with state-of-the-art bladed expanders.

Data-Driven Approach for Identifying Mistuning in As-Manufactured Blisks

Abstract: Abstract Sector-to-sector geometry or material property variations in as-manufactured bladed disks, or blisks, can result in significantly greater vibration responses during operation compared to nominally cyclic symmetric designs. The dynamics of blisks are sensitive to these unavoidable deviations, known as mistuning, making the identification of mistuning in as-manufactured blisks necessary for accurately predicting their vibration. As in previous mistuning modeling and identification approaches, the mistuning of interest is small and is parameterized by using deviations in cantilever blade-alone frequencies. Such mistuning parameterization is popular because it can be applied through blade-to-blade stiffness deviations in computational reduced-order models used to predict blisk dynamics. Previous approaches to identify such mistuning parameters often require the identification of modal information or blade-isolation techniques such as blade detuning using masses or adding damping pads. However, modal information can be difficult to obtain accurately even in optimal bench conditions. In addition, in practice it can be difficult to isolate individual blades by restricting blade motion around the blisk or detuning individual blades through added masses due to geometric constraints. In this article, we present a method for mistuning identification using a data-driven approach based on a neural network. The network is first trained using surrogate computational data. Thus, the data-driven portion of the approach is executed using surrogate computational methods. With the trained network, mistuning in all sectors of blisks with the same nominal geometry can be identified by using a small number of forced responses and the forcing phase information from traveling-wave excitation. In this approach, no system or sector-level modal response information, restrictive blade isolation, or mass detuning are required. We additionally present a method for forcing frequency selection and response conditioning to improve identification accuracy. Validation of this approach is presented using a finite element blisk model containing stiffness mistuning within the blades to create computationally generated surrogate data. It is shown that mistuning can be predicted accurately using forced responses containing a significant amount of absolute and relative measurement noise, mimicking responses collected from experimental measurements. In addition, it is shown that mistuning can be predicted independently and accurately using different engine orders of excitation in regions of high modal density.

The Potential of a Separated Electric Compound Spark Ignition Engine for Hybrid Vehicle Application

Abstract: In-cylinder expansion of internal combustion engines based on Diesel or Otto cycles cannot be completely brought down to ambient pressure, causing a 20% theoretical energy loss. Several systems have been implemented to recover and use this energy such as turbocharging, turbo-mechanical and turbo-electrical compounding, or the implementation of Miller Cycles. In all these cases however, the amount of energy recovered is limited allowing the engine to reach an overall efficiency incremental improvement between 4% and 9%. Implementing an adequately designed expander-generator unit could efficiently recover the unexpanded exhaust gas energy and improve efficiency. In this work, the application of the expander-generator unit to a hybrid propulsion vehicle is considered, where the onboard energy storage receives power produced by an expander-generator, which could hence be employed for vehicle propulsion through an electric drivetrain. Starting from these considerations, a simple but effective modelling approach is used to evaluate the energetic potential of a spark-ignition engine electrically supercharged and equipped with an exhaust gas expander connected to an electric generator. The overall efficiency was compared to a reference turbocharged engine within a hybrid vehicle architecture. It was found that, if adequately recovered, the unexpanded gas energy could reduce engine fuel consumption and related pollutant emissions by 4% to 12%, depending on overall power output.

Experimental Investigation of Friction Damping in Blade Root Joints

Abstract: The design of disk assemblies requires the capability to predict their dynamic behavior. To achieve this objective, knowledge of friction damping on the contact between blade and disk is of paramount importance. This paper proposes an experimental technique to measure the loss factor and the dynamics, in terms of natural frequencies, of blade-disk attachment. The free decay is used to infer the dynamic parameters from dummy blades. The identification method is based on the Hilbert transform that al-lows extracting the dynamic parameters from non-linear system. This paper shows the test rig utilized in the experimental analysis and details the excitation system used to displace the dummy blade. This system must be a real or a "virtual" non-contact system to avoid injecting external damping into the blade under test. Tests were performed on both a dovetail and a fir-tree type attachments. On the dovetail, tests were performed both with dry contact surfaces and with contact surfaces covered by a film of lubricant to achieve a low coefficient of friction. This low coefficient of friction better simulates dry surfaces at high temperatures, as friction coefficients decrease with temperatures. This paper presents the results obtained on the first and second bending mode. The experimental results show the loss factor and the natural frequency for different axial loads. The measured loss factor depends on the amplitude of vibrations. The loss factor shows a maximum then approaching zero for large amplitude of vibrations and it decreases with increasing centrifugal loads.

Bayesian Calibration of Performance Degradation in a Gas Turbine-Driven Compressor Unit for Prognosis Health Management

Abstract: Prognosis health management is an effective way to improve the operational safety and economy of industrial equipment. The development of an accurate and quick response model to monitor equipment health status, predict performance, and diagnose faults is key to its implementation. However, the inevitable performance degradation of industrial equipment over time poses a significant challenge to such a model. In this work, we adopt a Bayesian approach to calibrate thermodynamic simulations with time-dependent parameters that account for performance degradation. The relationship between degradation and time is modeled through an assumed functional form, referred to as a health indicator. The proposed health indicator calibration method gives a rapid assessment of degraded equipment performance and elucidates how degradation relates to time. The novelty of this paper is that it regards performance degradation as an uncertainty quantification problem rather than a deterministic problem. The health indicator calibration method is validated on a natural gas compressor and a gas turbine. The results show that when severe degradation occurs, functional calibration improves predictive performance over non-functional calibration (i.e., independent of time). The introduced method provides valuable decision support to extend the service life and reduce maintenance costs for industrial equipment. Its feedback in operation can also perfect the service assessment criteria and inform the design of subsequent generations of industrial equipment.

Experimental Investigation On Spray Evaporation and Dispersion Characteristics of Impinged Biodiesel-butanol Blends

Abstract: The objective of the investigation is to explore the spray evaporation and dispersion characteristics of impinged biodiesel-butanol blends at various n-butanol ratios (0, 10%, 30%, 50%) and ambient conditions. A total of 180 experimental cases were performed in a constant-volume combustion chamber. The liquid- and vapor-phase sprays were captured by backlight imaging technique and schlieren imaging technique, respectively. Several macroscopic parameters were set and discussed, including impinged spray structure, width, height and area. Some novel parameters are derived to analyze spray evaporation and dispersion. Results show that biodiesel blended with 30% n-butanol transits better from liquid-phase to vapor-phase compared with other blends, displaying rapid liquid-phase evaporation, steady vapor-phase dispersion and the largest pure vapor-phase area percentage. After wall impingement, an increase in the ambient pressure or temperature hinders the liquid-phase dispersion in the vertical direction significantly, leading to a rapid decrease in the height of the impinged spray. The vapor-phase diffusion rate in the horizontal direction is about four times the rate in the vertical direction, and the rate ratio is slightly affected by ambient conditions and injection pressure. Compared with the free jet, the impinged spray is not beneficial for liquid-phase evaporation and vapor-phase dispersion, presenting larger liquid-phase area and smaller vapor-phase area. However, impinged biodiesel blended with 30% n-butanol displays better spray evaporation and dispersion.

Accelerated Creep Test Qualification of Creep-Resistance Using the Wilshire–Cano–Stewart Constitutive Model and Stepped Isostress Method

Abstract: In this study, a qualification of accelerated creep-resistance of Inconel 718 is assessed using the novel Wilshire-Cano-Stewart (WCS) model and the stepped isostress method (SSM) and predictions are made to conventional creep data. Conventional creep testing (CCT) is a long-term continuous process, in fact, the ASME B&PV III requires that 10,000+ hours of experiments must be conducted to each heat for materials employed in boilers and/or pressure vessel components. This process is costly and not feasible for rapid development of new materials. As an alternative, accelerated creep testing techniques have been developed to reduce the time needed to characterize the creep resistance of materials. Most techniques are based upon the time-temperature-stress superposition principle (TTSSP) that predicts minimum-creep-strain-rate (MCSR) and stress-rupture behaviors but lack the ability to predict creep deformation and consider deformation mechanisms that occur for experiments of longer duration. The stepped isostress method (SSM) has been developed which enables the prediction of creep deformation response as well as reduce the time needed for qualification of materials. The SSM approach has been successful for polymer, polymeric composites, and recently has been introduced for metals. In this study, the WCS constitutive model, calibrated to SSM test data, qualifies the creep resistance of Inconel 718 at 750°C and predictions are compared to CCT data. The WCS model has proven to make long-term predictions for stress-rupture, minimum-creep-strain-rate (MCSR), creep deformation, and damage in metallic materials. The SSM varies stress levels after time interval adding damage to the material, which can be tracked by the WCS model. The SSM data is calibrated into the model and the WCS model generates realistic predictions of stress-rupture, MSCR, damage, and creep deformation. The calibrated material constants are used to generate predictions of stress-rupture and are post-audit validated using the National Institute of Material Science (NIMS) database. Similarly, the MCSR predictions are compared from previous studies. Finally the creep deformation predictions are compared with real data and is determined that the results are well in between the expected boundaries. Material characterization and mechanical properties can be determined at a faster rate and with a more cost-effective method. This is beneficial for multiple applications such as in additive manufacturing, composites, spacecraft, and Industrial Gas Turbines (IGT).

Nonlinear Dynamics of Turbine Generator Shaft Trains: Evaluation of Bifurcation Sets Applying Numerical Continuation

Abstract: The nonlinear dynamics of turbine generator shaft trains for power generation are investigated in this paper. Realistic models of rotors, pedestals, and nonlinear bearings of partial arc and lemon bore configuration are implemented to compose a nonlinear set of differential equations for autonomous (balanced) and non-autonomous (unbalanced - per ISO) cases. The solution branches of the dynamic system are evaluated with the pseudo arc length continuation programmed by the authors, and the respective limit cycles are evaluated by an orthogonal collocation method, and investigated on their stability properties and quality of motion for the respective key design parameters for the rotor dynamic design of such systems, namely: bearing profile and respective pad length, preload and offset, pedestal stiffness and elevation (misalignment), and rotor slenderness. Model order reduction is applied to the finite element rotor model and the reduced system is validated in terms of unbalance response and stability characteristics. The main conclusion of the current investigation is that the system has the potential to develop instabilities in rotating speeds lower than the threshold speed of instability (evaluated by the linear approach) for specific unbalance magnitude and design properties. Unbalance response (with stable and unstable branches) is evaluated in severely reduced time compared to this applying time integration methods, enabling nonlinear rotor dynamic design of such systems as a standard procedure, and revealing the complete potential of motions (not only local).

Knowledge-Based Process Design Optimisation in Blisk Manufacturing

Abstract: The manufacturing process of blade-integrated disks (blisks) represents one of the most challenging tasks in turbomachinery manufacturing. The requirement is to machine complex, thin-walled blade geometries with high aspect ratios made of difficult-to-cut materials. In addition, extremely tight tolerances are required, since the smallest deviations can lead to a reduction in efficiency of the blisk in the later use. Nowadays, the ramp-up phase for the manufacturing of a new blisk is time and cost intensive. To find a suitable manufacturing process that meets the required tolerances of the blisk, many experimental tests with different process parameters and strategies are necessary. The used approach is often trial and error which offers limited testing opportunities, is time consuming and wastes resources. Therefore, the objective of this paper is to develop a knowledge-based process design optimization in blisk manufacturing. For this purpose, this paper picks up the results from our previous work. Based on these results, an experimental validation of the two process design tasks "number of blocks" and "block transition" is conducted. As part of the validation, the results of machining tests on a demonstrator blisk made of Inconel 718 are presented and discussed.

Assessment of Performance Boundaries and Operability of Low Specific Thrust GUHBPR Engines for EIS2025

Abstract: This paper aims to develop a robust design process by approaching the performance boundaries and evaluating the operability of the pursued geared turbofan engine with low specific thrust for EIS 2025. A two-spool direct-drive turbofan (DDTF) engine of EIS 2000 was improved according to aircraft specifications and technology boundaries in 2025. A series of optimized engines with consecutive fan diameters were established to seek the ideal engine by balancing SFC, weight and mission fuel burn. The fan diameter was proved to be a decisive factor for lowering SFC and energy usage. The cycle design optimization process achieved a thermal efficiency of approximately 52%, and a propulsive efficiency of 79.5%, which is 8.19% increase in propulsive efficiency by enlarging fan diameter from 1.6m to 1.9m. Meanwhile, the 1.9m-fan diameter engine achieved a reduction in SFC and fuel burn of 7.47% and 6.58% respectively which offers an overall reduction of 30.82% in block fuel burnt and CO2 emission compared to the DDTF engine. A feasibility check verified the viability of the designed optimum engine in terms of fan tip speed, stage loading and AN2. Dynamic simulation offered a deep understanding of transient behaviour and fundamental mechanism of the geared turbofan engine. An important aspect of this paper is the use of advanced CMC materials, which led to an improvement of 4.92% in block fuel burn and 2.93% in engine weight.

Power Flow Optimization for a Hybrid-Electric Propulsion System

Abstract: The present study deals with the optimization of performance for a hybrid-electric propulsion system. It focuses on the modeling and power management frameworks, while evaluation is done on a single flight basis. The main objective is to extract the maximum out of the novel powertrain archetype. Two hybridization factors are considered. The pair helps to describe the degree of hybridization at the power supply and power consumption levels. Their revised mathematical definition facilitates a unique method of hybrid-electric propulsion system modeling, that maximizes the conveyed amount of information. An in-house computational tool is developed. It employs a genetic algorithm optimizer in the interest of managing power usage during flight. Energy consumption is set as the objective function. The operation of a 19-seater, commuter aircraft is investigated. Turbo-electric, series-hybrid, parallel-hybrid and series-parallel variants are derived from a generic composition. An analysis on their optimized performance, with different technological readiness levels for 2020 and 2035, is aimed at identifying where each system performs best. Considering 2020 technology, it does not yield a viable hybrid-electric configuration, without suffering significant payload penalties. Architectures relying on mechanical propulsors show promise of 15% reduction to energy consumption, accounting for 2035 readiness levels. The concepts of Boundary Layer Ingestion and Distributed Propulsion display the potential to boost electrified propulsion. The series-hybrid and series-parallel configurations are the primary beneficiaries of these concepts, displaying up to 30% reduction in fuel and 20% reduction in energy consumption.

Unsteady Analysis of Aeroengine Intake Distortion Mechanisms: Vortex Dynamics in Crosswind Conditions

Abstract: The formation of a ground vortex and its ingestion into an aero-engine intake under crosswind conditions play a significant role in the aerodynamic excitation of the fan. Using steady and unsteady numerical simulations, an analysis of the dynamics of several distortion features is presented. For a simplified intake at high crosswind velocities, there is a substantial movement of the ingested ground vortex at the aerodynamic interface plane (AIP). The ingested ground vortex follows a specific trajectory while varying both in size and strength. The transition from a periodic to an aperiodic regime of the intake distortion at the AIP occurs as the crosswind velocity is increased. Circumferential mode decomposition shows that the largest amplitude of the distortion occurs at the first circumferential mode, and the amplitudes of the higher modes decrease monotonically. Furthermore, the amplitude of the spatial harmonics is time-dependent, which may be an influential feature at the time of assessing fan forced response.

Experimental Probe Into a Biogas Run Dual Fuel Diesel Engine Using Oxygenated Ternary Blends at Optimum Equivalence Ratio and Under the Effect of Intake Charge Preheating

Abstract: The key challenge of dual fuel mode (DFM) of a compression ignition (CI) diesel engine is to improve the engine overall performance, and to reduce the carbon monoxide (CO) and unburnt hydrocarbon (HC) emissions. The gaining popularity of DFM lies with its inherent ability to curb harmful pollutants nitrogen oxides (NOx) and smoke, besides offering operational flexibility to use gaseous and liquids fuels simultaneously. In addition, the use of renewable fuels in DFM is found to be the highly suitable to achieve the optimum engine overall performance. In this DFM study, biogas as the primary gaseous fuel is used in a diesel engine in conjunction with ternary blends of diesel-biodiesel-ethanol (TB-E), diesel-biodiesel-butanol (TB-BT) and diesel-biodiesel-diethyl ether (TB-DEE) as the renewable pilot fuels. For each combination, the experiments are conducted at the optimum global fuel-air equivalence ratio (?global) and with intake charge preheating to analyze the performance, combustion and emission characteristics of the engine. The important parameters such as brake thermal efficiency, actual diesel replacement, coefficient of variation of indicated mean effective pressure, relative cycle efficiency, cylinder mean gas temperature, ignition delay, combustion duration are investigated. The study demonstrates the optimum performance of the DFM engine with TB-DEE.