bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Jets in Crossflow in Deposition Mitigation on Full 3D NGV With Endwall Features
Authors: Oliani Stefano , Casari Nicola , Pinelli Michele , Suman Alessio , Carnevale Mauro
Published: January 2021

Particle ingestion is a major concern for the operation of gas turbines. In the case of an aircraft, particle dispersed in the air ingested by the engine can threaten flight safety. Swallowed particles can erode or stick to aerodynamic surfaces. Both the occurrences translate in a reduction of performance due to variation in shape and in roughness of the aerodynamic surfaces. This work is devoted to the analysis of fouling, i.e. the deposition of particles over time. By observing that the deposition pattern is strongly influenced by the flow field in the nearby of the walls, the central idea of this work is to employ Active Flow Control (AFC) to mitigate fouling when emergency conditions are met by the aircraft. The proposed system will inject air bled from compressor discharge in front of the critical locations where fouling is supposed to occur. The present work aspires to lay the foundations for the development of such an AFC device, by focusing on the modified aerodynamics consequent to the introduction of the transverse jet. The potential of this device is evaluated quantitatively using CFD simulations. An energy-based sticking model, coupled with a mesh-morphing solver, is used to track the airfoil deposition thickness evolution in time. The work is two-fold: first, the dynamics of the interaction between flow structures and particle transport is addressed. Second, the attention is posed on correlating fouling pattern variation to the modified aerodynamics of the vane consequent to the introduction of the device. Three design concepts are investigated on the 3D test case geometry of an HPT NGV cascade. The counter-rotating vortex pair (CVP) is detected as the main responsible for jet-particle interaction. Finally, the jet impact on aerodynamic performance is also assessed.
A Simplified Model for Predicting Natural Draft Wet Cooling Tower Performance of Large Steam Power Plants
Authors: aus der Wiesche Stefan
Published: January 2021

Flexible plant operation and rapid load changes become major issues for steam turbine operation. In thermal power plants, the steam turbine performance is closely related to the condenser, and an accurate prediction of coolant temperature as function of changing weather conditions is necessary in order to optimize power plant fleet operation. In this contribution, a one-dimensional model for simulating the performance of large natural draft wet cooling towers is presented. The evaporation zone model rests on the evaporative cooling theory developed by Merkel and Poppe. The off-design behavior of the cooling tower, that is relevant to part load performance, is modeled by an empirical power-law approach. A user-friendly method is presented in order to identify required model parameters by means of already available power plant data. The simulation tool can be employed easily for existing power plants for which the original cooling tower design and construction data lost their validity. The outcome of the present calculation method is successfully compared with field data from representative cooling towers at Middle-European sites.
Design Optimization of a Multi-kW Thermoacoustic Electric Generator Using DeltaEC Model
Authors: Somu Srinath , Lacoste Deanna , Saxena Saumitra , Roberts William L. , Keolian Robert M.
Published: January 2021

Waste heat recovery from power plants and industries requires a new type of electricity generators and related technological developments. The current research work is aimed at the design of a multi-kilowatt thermoacoustic electric generator, which can be employed as the bottoming cycle of a gas-turbine power plant or for industrial waste heat recovery. The proposed device converts thermal energy into acoustic power and subsequently uses a piezoelectric alternator to convert acoustic power into electricity. The challenge in designing such a device is that it has to be acoustically balanced and the performance of the device is greatly affected by numerous parameters such as frequency of the traveling acoustic wave, heat exchanger parameters, regenerator dimensions, acoustic feedback loop, etc. The proposed device is a lab-scale demonstration targeted to produce a few kilowatts of electric power from a 20 kWth heat source. To achieve the acoustically balanced configuration of the device, DeltaEC software is used. The DeltaEC model outcomes are used to arrive at the optimized design of the device and its components. The analytical method, the optimized geometrical dimensions of thermoacoustic components and the minimum required conditions of heat source input are presented in this paper.
Digital Hybrid Evaporative Cooler: An Adaptive, Modulated Evaporative Cooler for Combined Cycle Power Plants With Improved Heat Rate and Water Expense
Authors: Sammak Majed , Jupudi Maruthi , Kippel Brad , Zia Jalal
Published: January 2021

This paper introduces a novel evaporative cooling system. The digital hybrid evaporative cooler works under a wide range of evaporative cooling effectiveness from 0% to 100%. It consists of several evaporative cooling media installed in a row with a fixed space in between. By operating the evaporative cooling system with varied numbers of evaporative cooling media in service, the evaporative cooling percentage can be changed from 0% to 100%. This digital hybrid evaporative cooler can thus be used to achieve a desired combined cycle power and heat rate as well as reduced water consumption.

The study was performed on GE heavy duty gas turbine. The selected combined cycle was 1-on-1 (one gas turbine, one heat recovery steam generator and one steam turbine train). The heat recovery steam generator was a 3-pressure level with reheat.

The study showed the evaporative cooling effectiveness impact on gas turbine parameters. The studied parameters were firing temperature, gas turbine exhaust temperature, exhaust energy, gas turbine power and heat rate.

Furthermore, the combined cycle heat rate improvement at different combined cycle loads and cooling effectiveness was analysed. The analysis was performed on combined cycle loads from 100% to 80% load with 5% interval. The selected evaporative cooling effectiveness at these loads were 90, 70, 50 and 30 percent respectively.

The combined cycle heat rate at 80%-part load and 30% evaporative cooling effectiveness was calculated at two ambient conditions in a selected site in the Middle East. At the ambient conditions of 43°C/30%RH, the combined cycle heat rate improvement was 0.56%. At the ambient conditions of 35°C/40%RH, the combined cycle heat rate improvement was 0.38%.

The digital evaporative cooler is also a mean of achieving water expense target. Reducing the evaporative cooling effectiveness from 90% to 30% would allow for an approximate of 60% saving in water consumption.

This digital hybrid evaporative cooler is connected to a control system which collects data from the gas turbine key parameters and depending on the requirements the system determines the number of evaporative cooling media in service.
Experimental Investigation of Surge Phenomena in a Transonic Centrifugal Compressor With Inlet Distortion
Authors: Ito Sasuga , Furukawa Masato , Gunjishima Satoshi , Ota Takafumi , Konishi Kazuhito , Yamada Kazutoyo
Published: January 2021

Inlet distortion has influence on the aerodynamic performance of turbomachinery such as compressors, turbines and fans. On turbochargers, bent pipes are installed around the compressor due to the spatial limitations in the engine room of the vehicle. As the result, the compressor is operated with the distorted inflow. In the low flow rate operation, the distorted inflow also affects the flow instability like stall and surge. Especially, the operation range on the low flow rate side is defined based on the flow rate where surge occurs, so it is important to investigate the effect of the distorted inflow on surge. In this study, the effect of the inlet distortion to surge phenomena has been investigated by the experiments with a transonic centrifugal compressor. A bent pipe has been installed at the upstream of the compressor to generate a distorted flow. Experiments have been also conducted under the condition that a straight pipe was installed upstream of the compressor, and unsteady measurements with high response pressure sensors and an I-type hot wire probe have been carried out to each experiments. In addition, Fast Fourier transform (FFT) and Wavelet transform have been applied to the unsteady measurement results obtained from each experiment.
Part 2: Design Optimisation Strategies for a Fuel Spray Nozzle
Authors: Andreou Thomas , White Craig , Kontis Konstantinos , Shahpar Shahrokh , Brown Nicholas
Published: January 2021

Reducing emissions and improving fuel economy has become a key target for advanced aircraft engine platforms. The competitive aviation market requires a drastic reduction in current aircraft emission levels, which leads to the requirement of optimising the entire combustion process. Lean burn pre-mixed systems are an efficient way of reducing NOx emissions. Starting from a datum blade generated in a companion paper, shape optimisation strategies applied to a fuel spray nozzle have been explored. Making use of three different design space parametrisation methods and several optimisation algorithms, an optimised passage has been generated. The optimised design achieves a considerable pressure loss reduction in comparison to the baseline design.
Ignition Probability and Lean Ignition Behaviour of a Swirled Premixed Bluff Body Stabilised Annular Combustor
Authors: Ciardiello Roberto , Pathania Rohit S. , Allison Patton M. , de Oliveira Pedro M. , Mastorakos Epaminondas
Published: January 2021

An experimental investigation was performed in a premixed annular combustor equipped with multiple swirl, bluff body burners to assess the ignition probability and to provide insights into the mechanisms of failure and of successful propagation. The experiments are done at conditions that are close to the lean blow-off limit (LBO) and hence the ignition is difficult and close to the limiting condition when ignition is not possible. Two configurations were employed, with 12 and 18 burners, the mixture velocity was varied between 10 and 30 m/s, and the equivalence ratio (ϕ) between 0.58 and 0.68. Ignition was initiated by a sequence of sparks (2 mm gap, 10 sparks of 10 ms each) and “ignition” is defined as successful ignition of the whole annular combustor. The mechanism of success and failure of the ignition process and the flame propagation patterns were investigated via high-speed imaging (10 kHz) of OH* chemiluminescence. The lean ignition limits were evaluated and compared to the lean blow-off limits, finding the 12-burner configuration is more stable than the 18-burner. It was found that failure is linked to the trapping of the initial flame kernel inside the inner recirculation zone (IRZ) of a single burner adjacent to the spark, followed by localised quenching on the bluff body probably due to heat losses. In contrast, for a successful ignition, it was necessary for the flame kernel to propagate to the adjacent burner or for a flame pocket to be convected downstream in the chamber to grow and start propagating upwards. Finally, the ignition probability (Pign) was obtained for different spark locations. It was found that sparking inside the recirculation zone resulted in Pign ∼ 0 for most conditions, while Pign increased moving the spark away from the bluff-body or placing it between two burners and peaked to Pign ∼ 1 when the spark was located downstream in the combustion chamber, where the velocities are lower and the turbulence less intense. The results provide information on the most favourable conditions for achieving ignition in a complex multi-burner geometry and could help the design and optimisation of realistic gas turbine combustors.
Reconstructing Compressor Non-Uniform Circumferential Flow Field From Spatially Undersampled Data: Part 2 — Practical Application for Experiments
Authors: Lou Fangyuan , Matthews Douglas R. , Kormanik Nicholas J. , Key Nicole L.
Published: January 2021

In the previous part of the paper, a novel method to reconstruct the compressor non-uniform circumferential flow field using spatially under-sampled data points is developed. In this part of the paper, the method is applied to two compressor research articles to further demonstrate the potential of the novel method in resolving the important flow features associated with these circumferential non-uniformities. In the first experiment, the static pressure field at the leading edge of a vaned diffuser in a high-speed centrifugal compressor is reconstructed using pressure readings from nine static pressure taps placed on the hub of the diffuser. The magnitude and phase information for the first three dominant wavelets are characterized. Additionally, the method shows significant advantages over the traditional averaging methods for calculating repeatable mean values of the static pressure. While using the multi-wavelet approximation method, the errors in the mean static pressure with one dropout measurement are 70% less than the pitchwise-averaging method. In the second experiment, the full-annulus total pressure field downstream of Stator 2 in a three-stage axial compressor is reconstructed from a small segment of data representing 20% coverage of the annulus. Results show very good agreement between the reconstructed total pressure profile and the experiment at a variety of spanwise locations from near hub to near shroud. The features associated with blade-row interactions accounting for passage-to-passage variations are resolved in the reconstructed total pressure profile.
Optimization of Airfoil Blend Limits With As-Manufactured Geometry Finite Element Models
Authors: Brown Jeffrey M. , Kaszynski Alex A. , Gillaugh Daniel L. , Carper Emily B. , Beck Joeseph A.
Published: January 2021

Conventional airfoil blend repair limits are established using nominal, design intent geometry. This convention does not explicitly consider the inherent blade-to-blade structural response variation associated with geometric manufacturing deviations. In this work, we explore whether accounting for these variations leads to significant differences in blend depths and develop a novel approach to effectively predict blade-specific blend allowables. These blade-specific values maximize the part repairability according to their proximity to defined structural integrity constraints. The methodology is demonstrated on the as-manufactured geometry of an aerodynamic research rig compressor rotor. Geometric point cloud data of this rotor is used to construct as-built finite element models (FEMs) of each airfoil. The effect of two large blends on these airfoils demonstrates the opportunity of blade-specific blend limits. A new approach to determine each airfoil’s blend repair capacity is developed that uses sequential least squares quadratic programming and a parametric blended blade FEM that accounts for manufacturing geometry variations and variable blend geometry. A mesh morphing algorithm modifies a nominal geometry model to match the as-built airfoil surface and blend geometry. The numerical optimization maximizes blend depth values within frequency, mode shape, and high cycle fatigue (HCF) constraint boundaries. It is found that there are large variations in blend depth allowables between blades and competing structural integrity criteria are responsible for their limits. It is also found that, despite complex modal behavior caused by eigenvalue veering, the proposed optimization approach converges. The developed methodologies may be used in the future to extend blend limits, enable continued operations, and reduce sustainment costs.
Analysis of Measured and Predicted Turbine Maps From Start-Up to Design Point
Authors: Scotti del Greco Alberto , Biagiotti Sara , Michelassi Vittorio , Jurek Tomasz , Di Benedetto Daniele , Francini Stefano , Marconcini Michele
Published: January 2021

This paper describes a coupled experimental and CFD campaign conducted on a 1.5 intermediate turbine stage in the full range of operating conditions, from start-up to design point under variable expansion ratio and physical speed. The test maintains engine similitude conditions and allows direct comparison with CFD data to assess the predictions accuracy. The choice of variables to describe the speedlines is also addressed by using both measured and predicted data. A discussion on velocity ratio versus corrected speed illustrates the advantages of the former parameter the adoption of which produces constant shape curves in a very wide range of operating conditions. The comparison between measurements and predictions suggests that CFD, in conjunction with performance correlations, is a viable tool to predict speedlines in a fairly wide range of conditions, provided that geometrical and operational details are carefully matched.
Investigation of a Rotor Blade With Tip Cooling Subject to a Nonuniform Temperature Profile
Authors: Kahveci Harika S.
Published: January 2021

One of the challenges in the design of a high-pressure turbine blade is that a considerable amount of cooling is required so that the blade can survive high temperature levels during engine operation. Another challenge is that the addition of cooling should not adversely affect blade aerodynamic performance. Besides, the tip region of a blade is exposed to further complexities due to tip leakage flow that is known to affect flow features and to cause additional pressure losses. The typical flat tips used in designs have evolved into squealer form that implements rims on the tip, which has been reported in several studies to achieve better heat transfer characteristics as well as to decrease pressure losses at the tip. This paper demonstrates a numerical study focusing on a squealer turbine blade tip that is operating in a turbine environment matching the typical design ratios of pressure, temperature and coolant blowing. The blades rotate at a realistic rpm and are subjected to a turbine rotor inlet temperature profile that has a nonuniform shape. For comparison, a uniform profile is also considered as it is typically used in computational studies for simplicity. The model used in the simulations is the tip section of the GE-E3 first stage blade. Two different configurations with and without cooling are considered using the same tip geometry. The cooled blade tip has seven holes on the tip floor lined up near the blade pressure side. The paper demonstrates the impact of the temperature profile nonuniformity and the addition of cooling on the complex blade tip flow field and heat transfer. Results confirm that these boundary conditions are the drivers for loss generation, and they further increase losses when combined. Temperature profile migration is not pronounced with a uniform profile, but shows distinct features with a nonuniform profile for which hot gas migration toward the blade pressure side is clearly observed. The blade tip also receives higher coolant coverage when subject to the nonuniform profile.
CFD–Aided Design Methodology for PCHE-Type Recuperators in Supercritical CO2 Recompression Power Cycles
Authors: Stamatellos George , Stamatellou Antiopi-Malvina , Kalfas Anestis I.
Published: January 2021

The supercritical carbon dioxide (sCO2) cycle has emerged as a promising power cycle for various types of power conversion systems, based on its high thermal efficiency, (approaching 60%), small-size and compactness. The recompression Brayton cycle with sCO2 is based on high capacity regenerators processing a large amount of heat making their effectiveness critical for the overall cycle efficiency. Printed Circuit Heat Exchangers (PCHEs) are used in these cycles because of their high attainable effectiveness values. The design process for these regenerators is demanding, considering the peculiarities of variation of CO2 density and thermal properties near the critical temperature. On the other hand, a reduced computation time is necessary for the quick assessment of alternative design options.

A hybrid design methodology for the high-temperature and the low-temperature recuperator (HTR and LTR) is presented in this paper, which employs 3D CFD conjugate heat transfer computation of the performance of a small two-channel module of the PCHE type. The results of the module computation are deployed in a 1D segmental method for the performance computation of the full heat exchanger’s channel length. Thus, the thermal effectiveness and pressure drop characteristics for the full heat exchanger are computed fast and with high accuracy. Application of the proposed methodology is carried out for the HTR and LTR computation in a recompression sCO2 Brayton cycle of a 600 MWth size power plant.
Design and Optimization of a Boundary Layer Ingesting Propulsor
Authors: Mandal Pritesh , Holder Justin , Turner Mark G. , Celestina Mark L.
Published: January 2021

The boundary layer ingestion concept has the potential to improve propulsion efficiency that will lead to better fuel economy of commercial aircraft. This design concept has been explored by NASA as the Single-aisle Turboelectric Aircraft with Aft Boundary-Layer propulsor “STARC-ABL.” This paper discusses the 1D-3D aerodynamic design and optimization process as well as the structural analysis of the rotor of a propulsor with incoming distortion. The propulsor is at the tail of the fuselage, and consists of an Inlet Guide Vane (IGV), Rotor, and Outlet Guide Vane (OGV). The design process presented accounts for only the large radial distortion and not the circumferential distortion. The paper also describes a pragmatic way of choosing orthogonal design parameters to proceed with the optimization process using a genetic algorithm. The final optimized design is highly dependent on the objective function to be optimized. A Modified Adiabatic Efficiency (MAE) has been defined to account for the loss of kinetic energy downstream of the propulsor CFD exit plane. This lost kinetic energy is essentially an approximation of the mixing loss of the tangential, axial and radial components of velocity at the OGV exit. The three blade-row adiabatic efficiency and MAE for an intermediate design case was 88.91% and 86.10% respectively. Upon further optimization and a different incoming distortion, using MAE as the objective function improved the MAE by 2.14% and adiabatic efficiency by 0.25% for the final design case presented in this paper. The rotor-only adiabatic efficiency for this case is 94.49%, the IGV-Rotor two blade-row efficiency is 92.71% and the Rotor-OGV two blade-row efficiency is 90.94%. The IGV is necessary to support the nacelle in this configuration. It also allows for the rotor work distribution to be optimized. The resulting rotor blade satisfies the static structural limit of a 1.1 safety factor for titanium at 110% speed. It also includes the pressure loads from the design point. The process uses an open source parametric blade generator whose source and input files for this geometry are on GitHub.
Process Automation for Aero Engine Secondary Air System Seal Design
Authors: Nasti Adele
Published: January 2021

Secondary air system seals are crucial in aero engine design as they have a direct impact on specific fuel consumption. Their behavior is affected by several aspects of the physics of the system: the air system, the engine thermal physics, the effect of flight loads and several other effects. As a consequence, their design is a complex and iterative process, which is highly dependent on the location of the seal in the engine, on the system requirements and on the system behavior.

This paper describes a methodology for multi-disciplinary assessment of secondary air system seals within an engine environment and supports standard seal design, trade-off studies on novel concepts and system-level optimization.

Defining the seal design intent for a specific engine location in the form of objectives, it is possible to embed process automation into traditionally manual multi-disciplinary design processes. This allows transforming modelling and simulation tools, which typically provide predictions for a specific seal design over reference cycles, into design and optimization tools, which can provide the optimum seal design for a specific set of requirements.

This approach provides predictive models of both seal performance and performance degradation and is capable of taking into account all sources of variation, for instance manufacturing variations or engine operating conditions, delivering a robust design, specific to the engine location.

The methodology enables a holistic approach to system and sub-system design and provides a deeper understanding of the impact of the seal onto system and of the system onto the seal, allowing optimization of the overall solution and informing the business case for introduction of different sealing strategies. Examples of the application of this methodology are provided for both labyrinth seals and leaf seals.
Design of a Mixed-Flow Transonic Compressor for Active High-Lift System Using a 3D Inverse Design Methodology
Authors: Wang Peng , Vera-Morales Maria , La Patrick , Zangeneh Mehrdad , Maroldt Niklas , Willers Ole , Kauth Felix , Seume Jörg
Published: January 2021

This paper presents the redesign of an electrically driven mixed flow transonic compressor by using a 3D inverse design methodology. The compressor will be used for an active high-lift system application that aims to delay the onset of stall and thus contributing to the reduction of both the aircraft noise footprint and the impact of aviation emission on local air quality.

As part of a collaborative work between the Institute of Turbomachinery and Fluid Dynamics of the Leibniz University Hannover and Advanced Design Technology Ltd., an existing optimized compressor stage for this application is redesigned using a 3D inverse method. The new compressor design presents an increase in pressure ratio and total-to-total isentropic efficiency of more than 5.5% and 1% respectively at design point. The higher PR at design point allows the compressor to be run at lower rotational speeds, which decreases the load on the electric motor and the power electronic systems, and hence contributing further to the overall weight reduction of the entire system.

The advantage of using an inverse design methodology is shown in this paper as a method that allows a very simple parameterization, reducing significantly the design time and hence allowing the exploration of wider design spaces, with the potential of reaching more innovative and efficient designs. The fast and reliable design and analysis of components represents an important advantage for the enhancement of aircraft electrification, where long design times are often a barrier for the exploration of system configurations.
Cycle Considerations for the Conceptual Design of a Pumped Heat Energy Storage System
Authors: Tom Brittany , Smith Natalie , McClung Aaron
Published: January 2021

Grid-scale energy storage technologies that provide greater than ten hours of electricity at full power are a critical enabler for full penetration of renewables on electricity grids worldwide. These technologies minimize renewable curtailment, while maximizing grid security and reliability. Other energy storage solutions such as pumped hydro and compressed air energy have geological and geographical constraints that widespread adoption.

Pumped Heat Electricity Storage (PHES) systems can store energy thermally in any location at the low costs necessary for displacing fossil fuels, reducing foreign fuel imports, and reducing emissions to maintain the energy security of the world. PHES systems operate in two modes, a charge mode in which the system operates as a heat pump to convert electricity into a thermal potential which is stored in a suitable storage media, and a discharge mode which uses a heat engine to convert the stored thermal energy to electricity. These systems offer a potential Round-Trip Efficiency (RTE) greater than 60%. This is a key parameter of interest for energy storage application systems, defined as the ratio between energy into the system to the energy retrieved.

Efficient PHES system design represents a compromise between thermal storage temperatures, system configuration, machinery selection, and minimization of secondary losses. This paper examines design trades associated with turbomachinery, system pressure ratio, and storage temperatures and the impact on RTE for a recuperated full scale PHES system progressing through conceptual design, and wraps up with turbomachinery evaluation and selection and resulting cycle for a small-scale system demonstrator used for demonstrating PHES system startup and operational control.
Computational Investigation of a Multiphase Turbo Expander for Heat Pumps and Refrigeration Cycles
Authors: Giakoumis Zoitis , Engelbrecht E. Geoffrey , Chasoglou Alexandros , Chokani Ndaona
Published: January 2021

The design and development of an innovative Tesla style turbo expander for two-phase fluids is proposed, as a substitute for the lamination valve of a traditional Heat Pump cycle. Thereby enhancing the overall performance of the Heat Pump, by recovering mechanical work to offset the compressor requirements. The major challenge in such configurations is the reliable operation of the expander, when phase change occurs across it, from a purely liquid flow to a mainly vapour flow by volume with a dense cloud of liquid droplets.

To investigate the phase change, a modelling approach is adopted which is routinely applied to modelling fuel-flashing in direct injection diesel engines, where the phase change deviates strongly from equilibrium. The Homogeneous Relaxation Model (HRM) is employed, which utilizes an Eulerian approach.

The proposed computational model is firstly validated against experimental results available in the literature. A sensitivity analysis of the phase change model relaxation parameter is performed. It was found that a value 10 times lower than the published value gave closer agreement to the measured results. It is believed that this result is due to the roughened walls of the experiment, which would produce more nucleation sites for vapour bubble formation. This suggests that this model maybe is sensitive to the geometry of the turbine.

Following this validation, the detailed flow profile in the proposed Tesla turbo-expander is investigated. Two different expander designs are considered in this project, one working with water [4,20] and the other with butane (R600). This study focuses particularly on the butane expander design. The expander performance is evaluated for rotational speeds up to 32’000 RPM.

Results on the turbo-expander under investigation, showed that the presence of a dense cloud of liquid droplets produces a significant pressure drop across the turbine rotor, which increases with RPM, postponing the phase change. High volume-fraction of liquid was predicted to penetrate deeper inside the rotor above 16’000 RPM for the butane expander. The resulting lower liquid flow velocity relative to the rotor disk speed at the inlet of the rotor is predicted to significantly degrade the performance of the turbine at high rotational speeds. Decreasing the nozzle throat area improves the situation, by initiating the phase change further upstream and increasing the RPM operational range by 50%. Angling the nozzle radially inward by 10° was found to not have a great impact on the performance of the turbine. It was determined from this study that it is critical to predict correctly where the phase change starts, in order to accurately predict the performance of the turbine. Important is to remove as much liquid as possible from the flow, before it enters the rotor, to minimize the impact of the phase change on the turbine performance.
Atomization of High Viscosity Liquids Using a Two-Fluid Counterflow Nozzle: Experiments and Modeling
Authors: Rangarajan Roshan , Zhang Hongyuan , Strykowski Paul J. , Hoxie Alison , Yang Suo , Srinivasan Vinod
Published: January 2021

We study the enhanced atomization of viscous liquids by employing a novel two-fluid atomizer. The nozzle establishes a countercurrent flow configuration in which the gas and liquid are directed in opposite directions, establishing a two-phase mixing layer. Detailed measurements of droplet size distributions were carried out using laser shadowgraphy, along with high speed flow visualization. The measurements suggest that the liquid emerges as a spray with little further secondary atomization. The performance of this nozzle is compared to the ‘flow-blurring’ nozzle studied by other investigators for four test liquids of viscosity ranging from 1 to 133.5 mPa.s. The counterflow nozzle produces a spray whose characteristics are relatively insensitive to fluid viscosity over the range studied, for gas-liquid mass flow ratios between 0.25 and 1. To gain insight into the mixing process inside the nozzle, simulations are carried out using an Eulerian-Eulerian Volume of Fluid (VoF) approach for representative experimental conditions. The simulation reveals the detailed process of self-sustained flow oscillations and the physical mechanism that generate liquid filaments and final droplets.
Identification of the Essential Features of the Transient Amplification of Mistuned Systems
Authors: Carassale Luigi , Denoël Vincent , Martel Carlos , Panning-von Scheidt Lars
Published: January 2021

The dynamic behavior of bladed disks in resonance crossing has been intensively investigated in the community of turbomachinery, addressing the attention to (1) the transienttype response that appear when the resonance is crossed with a finite sweep rate and (2) the localization of the vibration in the disk due to the blade mistuning. In real conditions, the two mentioned effects coexist and can interact in a complex manner. This paper investigates the problem by means of analytic solutions obtained through asymptotic expansions, as well as numerical simulations. The mechanical system is assumed as simple as possible: a 2-dof linear system defined through the three parameters: damping ratio ξ, frequency mistuning Δ, rotor acceleration Ω˙. The analytic solutions are calculated through the multiple-scale method.
Analysis of Autoignition Chemistry in Aeroderivative Premixers at Engine Conditions
Authors: Jella Sandeep , Bourque Gilles , Gauthier Pierre , Versailles Philippe , Bergthorson Jeffrey , Park Ji-Woong , Lu Tianfeng , Panigrahy Snehashish , Curran Henry
Published: January 2021

The minimization of autoignition risk is critical to the design of premixers of high power aeroderivative gas turbines as an increased use of highly reactive future fuels (for example, hydrogen or higher hydrocarbons) is anticipated. Safety factors based on ignition delays of homogeneous mixtures, are generally used to guide the choice of a residence time for a given premixer. However, autoignition chemistry at aeroderivative conditions is fast (0.5–2 milliseconds) and can be initiated within typical premixer residence times. The analysis of what takes place in this short period necessarily involves the study of low-temperature autoignition precursor chemistry, but precursors can change with fuel and local reactivity.

Chemical Explosive Modes are a natural alternative to study this as they can provide a measure of autoignition risk by considering the whole thermochemical state in the framework of an eigenvalue problem. When transport effects are included by coupling the evolution of the Chemical Explosive Modes to turbulence, it is possible to obtain a measure of spatial autoignition risk where both chemical (e.g. ignition delay) and aerodynamic (e.g. local residence time) influences are unified.

In this article, we describe a method that couples Large Eddy Simulation to newly developed, reduced autoignition chemical kinetics to study autoignition precursors in an example pre-mixer representative of real life geometric complexity. A blend of pure methane and dimethyl ether (DME), a common fuel used for experimental autoignition studies, was transported using the reduced mechanism (38 species / 238 reactions) at engine conditions at increasing levels of DME concentration until exothermic autoignition kernels were formed. The resolution of species profiles was ensured by using a thickened flame model where dynamic thickening was carried out with a flame sensor modified to work with multi-stage heat release.

The paper is outlined as follows: First, a reduced mechanism is constructed and validated for modeling methane as well as di-methyl ether (DME) autoignition. Second, sensitivity analysis is used to show the need for Chemical Explosive Modes. Third, the thickened flame model modifications are described and then applied to an example premixer at 25 bar / 890K preheat. The Chemical Explosive Mode analysis closely follows the large thermochemical changes in the premixer as a function of DME concentration and identifies where the premixer is sensitive and flame anchoring is likely to occur.
Cyclostationary Approach for Instabilities Detection and Condition Monitoring of Centrifugal Compressor
Authors: Stajuda Mateusz , Garcia Cava David , Liśkiewicz Grzegorz
Published: January 2021

This study intends to explore the capabilities of the cyclostationary approach for instabilities detection and operating conditions monitoring of centrifugal compressors.

Cyclostationary approach offers powerful signal analysis methods, applicable to different processes. It was proven useful for analysis of vibration, acoustic and pressure data for systems exhibiting periodicity. Cyclostationarity has been used for extracting subtle changes between cycles of the periodic signal which could be used for condition monitoring. Recent research focuses on employing this method for fault indication. Cyclostationary approach has not been extensively used in the field of turbomachinery, except for a few cases when it was proven to give a better insight into flow structure than standard signal processing techniques and allow for the detection of instabilities in flow systems. Thus, the cyclostationary approach may be suitable for instabilities detection and condition monitoring in centrifugal compressors.

This paper exploits various techniques employing a cyclostationary framework for instabilities detection and operating conditions monitoring with the use of pressure signals from the low-speed centrifugal compressor. The most prospective cyclostationarity-based indicators are applied for the detection of instabilities. Due to a lack of second-order cyclostationarity, the study confines to the analysis of first-order cyclostationarity strongly exhibited in the compressor pressure signal. First-order cyclostationarity analysis provides an indication of instabilities and working conditions differentiation, but due to time-domain sampling, it is not fully robust and reliable. The highest potential is perceived in the cyclostationary approach use to extract changes between cycles. Different measures of change in variability could serve as a valuable indicator of instabilities.
Experimental Investigation of Innovative Cooling Schemes on an Additively Manufactured Engine Scale Turbine Nozzle Guide Vane
Authors: Hossain Mohammad A. , Ameri Ali , Gregory James W. , Bons Jeffrey P.
Published: January 2021

This study includes the design, validation, and fabrication via Direct Metal Laser Sintering (DMLS) of a gas turbine nozzle guide vanes (NGV) that incorporates three innovative cooling schemes specifically enabled by additive manufacturing. The novel NGV design is the culmination of an extensive research and development effort over a period of four years that included low and high speed cascade testing coupled with unsteady CFD for numerous candidate innovative cooling architectures. The final vane design (SJ-vane) consists of sweeping jet (SJ) film cooling holes on the suction surface, sweeping jet impingement holes at the leading edge and double-wall partial length triangular pin-fin with impinging jet at the trailing edge. For comparison purposes, a second DMLS enabled vane (777-vane) was designed and fabricated with prototypical cooling circuits to serve as a baseline. This vane consists of a shaped film cooling holes on the suction surface, circular impingement holes at the leading edge and full length cylindrical pin-fins at the trailing edge. Experiments with the two DMLS enabled vanes were performed at the Ohio State University Turbine Reacting Flow Rig (TuRFR) at engine relevant temperature (1375K) and Mach number conditions. Infrared (IR) thermography was utilized to measure the wall temperature of the pressure and suction surface at several coolant mass flow rates to estimate the overall cooling effectiveness (ϕ). Results showed improved cooling performance for the advanced cooling schemes (sweeping jet film cooling, impingement cooling and triangular pin-fin cooling) compared to the baseline cooling schemes.
An Integrated Principal Component Analysis, Artificial Neural Network and Gas Path Analysis Approach for Multi-Component Fault Diagnostics of Gas Turbine Engines
Authors: Alozie Ogechukwu , Li Yi-Guang , Pilidis Pericles , Liu Yang , Wu Xin , Shong Xingchao , Ren Wencheng , Korakianitis Theodosios
Published: January 2021

Gas path diagnostics is a key aspect of the engine health monitoring (EHM) process that aims to detect, identify and predict engine component faults, using information from installed sensors, in order to guide maintenance action, maintain engine efficiency and prevent catastrophic failures. To achieve high prediction accuracies, current data-derived diagnostic models tend to be engine specific while the model-based methods are known to be time-consuming, especially for complex engine configurations. This paper proposes an integrated approach for accurate and accelerated isolation and prediction of multiple-degraded gas turbine component faults that comprises 3 steps — feature extraction using the Principal Component Analysis (PCA), machine learning classification with a multi-layer perceptron, artificial neural network (MLP-ANN) and model-based fault prediction via the non-linear Gas Path Analysis (GPA) technique. In this hybrid approach, the PCA first transforms the measurement fault signature into a fault-feature domain, which becomes an input to the multi-label ANN classifier used to isolate the potential faulty components. The non-linear GPA finally quantifies the magnitude of degradation that produced the recorded fault signature. Once trained and validated, the PCA-ANN model is deployed as part of the data processing mechanism prior to the actual GPA calculation. This method was assessed and validated using the thermodynamic performance model of a 2-shaft, high-bypass ratio, turbofan engine. For training and testing the PCA-ANN classifier, a total of 28,000 final samples for 14 measurement parameters, each averaged from 10 data points with Gaussian noise of zero mean and unit standard deviation, and implanted with single-, double- and triple-component fault cases of various magnitude, were generated by steady-state performance simulation of the engine model at its reference operating condition. Correlation analysis of this data set revealed the optimum sensor subset to be used for multi-component diagnostics. A quantitative analysis of the PCA-ANN fault isolation on the test set produced a classification accuracy of 96.6% and performed better on all metrics, compared to other multi-label classification algorithms. Finally, the proposed integrated approach achieved an average of 94.35% reduction in processing time, when compared to the conventional non-linear GPA by component-fault-cases (CFCs), while predicting implanted faults to the same accuracy.
Impingement Heat Transfer From a Jet-Array With In-Between Return Holes for the Crossflow
Authors: Tang Chen , Acharya Sumanta
Published: January 2021

Jet-impingement heat transfer is commonly used for vane leading edges and end-walls of turbine components for cooling the surfaces. One of the factors that limit high heat transfer rates is the effect of the crossflow which builds up downstream and adversely impacts the jet penetration and the impingement heat transfer rates. The present paper investigates the concept of introducing return holes (RH) for the crossflow to prevent its build-up and therefore reduce its deleterious effects. In the present experimental study, a 3 by 9 jet-array impinging on a target surface is considered with and without return holes. The return holes are located in an in-line pattern between the impingement holes. Experiments are conducted in an impingement channel with closed side walls and for jet-to-target distances (H/D) of 1D to 9D and a jet-Reynolds number of 20,000. Two different crossflow schemes combined with three return hole (RH) configurations are studied. The two crossflow arrangements are: (1) one radial exit and RH’s open for the spent air to exit and (2) all radial exits blocked with the spent air exiting through the RH’s only. Three different area-openings for the RH’s are considered and correspond to 33.3%, 66.7%, and 100% of the total return hole area open. In addition, a baseline case with no RH’s and one radial exit is studied. A transient liquid-crystal based study is conducted using a thin sheet of narrowband Thermochromic Liquid Crystal glued on an acrylic plate serving as the target surface. Local heat transfer coefficients are obtained based on the measured surface temperature and the solution of 1D transient heat conduction in the target acrylic plate. Return holes have significant influence on the crossflow-induced degradation effects at small jet-to-target spacing. The all-blocked crossflow scheme demonstrates good uniformity and axisymmetric Nusselt number distributions.