bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Probe Stem Surface Suction on the Aerodynamic Performance of a Compressor
Authors: Zhong Yafei , Ma Hongwei , Yang Yi
Published: September 2021

Pneumatic probes can be used to obtain the flow field parameters such as pressure, temperature and air flow angle, and has been widely used to measure the flow field in compressors. When probes are inserted into the compressor to measure the flow field, the probe stems will cause blockage in the flow field and interfere with it, reducing the pressure ratio and efficiency of the compressor. This paper proposes a method to reduce the interference of the stems by their surface suction. Three-dimensional models of a compressor with different types of probe stems were established. Computational Fluid Dynamics (CFD) simulations of the flow within a low-speed compressor without/with the probe stems and the stems having surface suction holes were conducted. The involved numerical methods were validated by the experimental data. The effects of the surface suction holes on the performance of this compressor were compared and analyzed in terms of blockage coefficient in the passage by the vortex identification method. The results show that probe stem surface suction can reduce the blockage of the stems on the downstream flow field. Compared with the situation of no suction, there is an optimal suction mass flow rate that can minimize the adverse effect of probe stems on the compressor aerodynamic performance. For the same type of the probe stems, the compressor performances, i.e., pressure ratio, efficiency and stability margin, are recovered with the increase of the number of suction holes along the span-wise direction.
NOx Emission Modelling for Lean Premixed Industrial Combustors With a Diffusion Pilot Burner
Authors: Reumschüssel Johann Moritz , von Saldern Jakob G. R. , Kaiser Thomas Ludwig , Reichel Thoralf , Beuth Jan Paul , Ćosić Bernhard , Genin Franklin , Oberleithner Kilian , Paschereit Christian Oliver
Published: September 2021

In gas turbine combustion systems, the reduction of emissions of harmful combustion by-products is a main development goal. This study provides a methodology to model NOX emissions effectively for varying levels of pilot fuel flows at different operational points. It combines one-dimensional flame simulations using detailed chemistry with a stochastic approach for equivalence ratio fluctuations to account for the effect of fuel-air unmixedness. This split allows for computationally fast variations of the gas inlet condition and the consideration of different shares of pilot gas. The generation of emissions is split into a share of prompt formation at the flame front and a slower formation mechanism, occurring within the combustion products in the post flame region. The influence of unmixedness of the fuel-air mixture on both effects is taken into consideration by means of probability density functions (PDFs) of the equivalence ratio. These are modeled on the basis of sampled values from Large Eddy Simulations at the flame front and adapted for different shares of pilot gas. It is shown that with a superposition of Gaussian PDFs the equivalence ratio distribution at the flame front resulting from the main gas supply and the pilot share can be well approximated. Measurement data from experiments in atmospheric conditions as well as emission measurements from high pressure tests are used to evaluate the model. Good agreement is found for atmospheric data, allowing for explanations on the effect of pilot fuel ratio on emissions. For elevated pressure, only qualitative trends could be reproduced. Hypotheses to explain this deviation are made that motivate further research.
Detached Eddy Simulation: Recent Development and Application to Compressor Tip Leakage Flow
Authors: He Xiao , Zhao Fanzhou , Vahdati Mehdi
Published: September 2021

Detached Eddy Simulation (DES) and its variants are emerging tools for turbomachinery simulations. In this paper, the state-of-the-art upgrades of DES are reviewed, and their capabilities in predicting compressor tip leakage flow are discussed. The upgrade with the best potential is identified as the Delayed DES (DDES) method with the grid spacing FKHΔhyb, which unlocks the physics of the Kelvin-Helmholtz instability in compressor tip leakage flow. The upgraded grid spacing FKHΔhyb is compared against the widely used default one Δmax in a backward-facing step and a low-speed axial compressor rotor. Results show that the DDES method with FKHΔhyb predicts both the main flow field and the turbulence field with reasonably good accuracy. However, the original DDES method with Δmax predicts a delayed transition to turbulence, which leads to an inaccurate prediction of the main flow field when using a coarse mesh. The findings in this paper highlight the future opportunities for using the DDES-FKHΔhyb method to predict tip-driven compressor stall and generate a turbulence database for turbulence model development.
Optimal Design of Renewable Hydrogen Production for Gas Turbine Test Facilities
Authors: Ancona M. A. , Bianchi M. , Branchini L. , De Pascale A. , Ferrari F. , Melino F. , Peretto A.
Published: September 2021

The growing attention to environmental issues has led to an increase in renewable source exploitation. These resources, in addition to their characteristic of zero emissions, can be employed where there is no connection to the electricity grid or to produce synthetic fuels (e.g. hydrogen or synthetic natural gas) via power-to-gas technologies.

In the context of the ERA-Net Project ZEHTC (Zero Emission Hydrogen Turbine Center), the aim of this paper is the development of a design calculation model for the ZEHTC pilot plant, consisting in the first gas turbine test facility making use of the power produced during tests — along with renewables — for hydrogen production, integrated with batteries. The hydrogen is locally used — mixed with natural gas — to run the gas turbine, reducing its environmental impact.

The developed code aims at maximizing the conversion of the renewable source into hydrogen and guaranteeing its availability for the planned tests. It includes physical-mathematical models for each component and has been used to perform a parametric analysis varying the main components size, thus estimating the total produced hydrogen.

The main innovation of the ZEHTC micro-grid project consists in the use of a gas turbine — instead of a fuel cell — as system to reconvert the stored hydrogen.
Preliminarily Design of Supercritical CO2 Compression Test System
Authors: Teng Geng , Chen Laijie , Shen Xin , Ouyang Hua , Zhu Yubo , Fan Wei , Liu Zhigang
Published: September 2021

The centrifugal compressor is the core component of the supercritical carbon dioxide (SCO2) power cycle. It is essential to carry out component-level experimental research on it and test the working characteristics of the compressor and its auxiliary equipment. Building an accurate closed-loop simulation model of closed SCO2 compression loop is a necessary preparation for selecting loop key parameters and establishing system control strategy, which is also an important prerequisite for the stable operation of compressor under test parameters. In this paper, the thermodynamic model of compressor, pre-cooler, orifice plate and other components in supercritical CO2 compression test system is studied, and the simulation model of compression test system is established. Moreover, based on the system enthalpy equations and physical property model of real gas, the compressor, pre-cooler and other components in the test loop are preliminarily designed by using the thermodynamic model of components. Since the operating conditions are in the vicinity of the critical point, when the operating conditions change slightly, the physical properties of the working fluid will change significantly, which might have a greater impact on the operating performance of the system. So the operating performance and the parameter changes of key nodes in the test loop under different operating conditions are calculated, which will provide theoretical guidance for the construction of subsequent experimental loops.
Surge Prevention Techniques for a Turbocharged Solid Oxide Fuel Cell Hybrid System
Authors: Mantelli L. , Ferrari M. L. , Traverso A.
Published: September 2021

Pressurized solid oxide fuel cell (SOFC) systems are one of the most promising technologies to achieve high energy conversion efficiencies and reduce pollutant emissions. The most common solution for pressurization is the integration with a micro gas turbine, a device capable of exploiting the residual energy of the exhaust gas to compress the fuel cell air intake and, at the same time, generating additional electrical power. The focus of this study is on an alternative layout, based on an automotive turbocharger, which has been more recently considered by the research community to improve cost effectiveness at small size (< 100 kW), despite reducing slightly the top achievable performance.

Such turbocharged SOFC system poses two main challenges. On one side, the absence of an electrical generator does not allow the direct control of the rotational speed, which is determined by the power balance between turbine and compressor. On the other side, the presence of a large volume between compressor and turbine, due to the fuel cell stack, alters the dynamic behavior of the turbocharger during transients, increasing the risk of compressor surge. The pressure oscillations associated with such event are particularly detrimental for the system, because they could easily damage the materials of the fuel cells.

The aim of this paper is to investigate different techniques to drive the operative point of the compressor far from the surge condition when needed, reducing the risks related to transients and increasing its reliability. By means of a system dynamic model, developed using the TRANSEO simulation tool by TPG, the effect of different anti-surge solutions is simulated: (i) intake air conditioning, (ii) water spray at compressor inlet, (iii) air bleed and recirculation, and (iv) installation of an ejector at the compressor intake. The pressurized fuel cell system is simulated with two different control strategies, i.e. constant fuel mass flow and constant turbine inlet temperature. Different solutions are evaluated based on surge margin behavior, both in the short and long terms, but also monitoring other relevant physical quantities of the system, such as compressor pressure ratio and turbocharger rotational speed.
Thermoacoustic Stability Analysis of a Full-Annular Lean Combustor for Heavy-Duty Applications
Authors: Pampaloni Daniele , Andreini Antonio , Marini Alessandro , Riccio Giovanni , Ceccherini Gianni
Published: September 2021

Thermoacoustic characterization of gas turbine combustion systems is of primary importance for successful development of gas turbine technology, to meet the stringent targets on pollutant emissions. In this context, it becomes more and more necessary to develop reliable tools to be used in the industrial design process.

The dynamics of a lean-premixed full-annular combustor for heavy-duty applications has been numerically studied in this work. The well-established CFD-SI method has been used to investigate the flame response varying operational parameters such as the flame temperature (global equivalence ratio) and the fuel split between premixed and pilot fuel injections: such a wide range experimental characterization represents an opportunity to validate the employed numerical methods and to give a deeper insight into the flame dynamics. URANS simulations have been performed, due to their affordable computational costs from the industrial perspective, after validating their accuracy through the comparison against LES results. Furthermore, an approach where the pilot and the premixed flame responses are analyzed separately is proposed, exploiting the independence of their evolution.

The calculated FTFs have been implemented in a 3D FEM model of the chamber, in order to perform linear stability analysis and to validate the numerical approach. A boundary condition for rotational periodicity based on Bloch-Wave theory has been implemented into the Helmholtz solver and validated against full-annular chamber simulations, allowing a significant reduction in computational time. The reliability of the numerical procedure has been assessed through the comparison against full-annular experimental results.
A New Experimental Approach for Heat Transfer Coefficient and Adiabatic Wall Temperature Measurements on a Nozzle Guide Vane With Inlet Temperature Distortions
Authors: Bacci T. , Picchi A. , Facchini B. , Cubeda S.
Published: September 2021

Modern gas turbines lean combustors allow to limit NOx pollutant emissions by controlling the flame temperature, while maintaining high turbine inlet temperatures. On the other hand, their adoption presents other challenges, especially concerning the combustor-turbine interaction. Turbine inlet conditions are generally characterized by severe temperature distortions and swirl degree, which, in turn, is responsible for very high turbulence intensities. Several past studies have focused on the description of the effects of these phenomena on the behavior of the high pressure stages of the turbine, both considering them as separated aspects, and, in very recent years, accounting for their combined impact. Nevertheless, very limited experimental results are available when it comes to evaluate the heat transfer coefficient (HTC) on the nozzle guide vane external surface, since relevant temperature distortions present a severe challenge for the commonly adopted measurement techniques. The work presented in this paper was carried out on a non-reactive, annular, three-sector test rig, made by a combustor simulator and a NGV cascade. Making use of three real hardware burners of a Baker Hughes heavy-duty gas turbine, operated in similitude conditions, it can reproduce a representative swirling flow, with temperature distortions at the combustor-turbine interface plane. This test apparatus was exploited to develop an experimental approach to retrieve reliable heat transfer coefficient and adiabatic wall temperature distributions simultaneously, in order to overcome the known limitations imposed by temperature gradients on state-of-the-art methods for HTC calculation from transient tests. A non-cooled mockup of a NGV doublet, manufactured using low thermal diffusivity plastic material, was used for the tests, carried out using IR thermography with a transient approach. In the authors’ knowledge, this presents the first experimental attempt of measuring a nozzle guide vane heat transfer coefficient in the presence of relevant temperature distortions and swirl.
Effect of Pad Material, Copper vs. Steel, on the Performance of a Tilting Pad Journal Bearing: Measurements and Predictions
Authors: San Andrés Luis , Kaizar Hussain , Jani Hardik , Thorat Manish
Published: September 2021

High temperature operation limits the life of fluid film bearings; hence the need to quantify the effect of pad material on the performance of tilting pad journal bearings (TPJBs). The paper presents measurements of performance conducted on a copper-pads bearing (C-PB) and a steel-pads bearing (S-PB). Both bearings have the same geometry and differ on the pads’ backing material, copper vs. steel, and slightly in the assembled cold clearance. The journal diameter D = 102 mm, and a bearing has five pads with length L = 0.4D, nominal radial clearance 0.064 mm, and pad preload of 0.42. The pads are 12.3 mm in thickness and have a 50% offset pivot, ball-in-socket type. The bearings operate at four shaft speeds ranging from 6 krpm (32 m/s surface speed) to 14 krpm (74 m/s) and under multiple specific loads ranging from 0.17 MPa to 2.1 MPa. ISO VG 32 oil, at a supply temperature of 49 °C, lubricates a test bearing configured with end seals (flooded bearing). At the highest load (on pad) and low shaft speed, the S-PB static eccentricity is up to 37% higher than that for the C-PB. The oil exit temperature rise is similar for both bearings, the maximum difference reaches 6 °C. For all operating conditions, the pads’ peak temperature rise, having a maximum difference of 5 °C to 16 °C, is larger for the S-PB. The S-PB produces a ∼ 5% lower drag power loss than that in the C-PB. Drag power in both bearings increases with shaft speed and is largely independent of applied load. From dynamic load tests with multiple excitation frequencies to 250 Hz, the C-PB direct stiffness KYY (along the load direction) is up to 30% higher than the S-PB stiffness, while the difference in KXX between the C-PB and the S-PB ranges from 60% to 90%. Similar to the stiffness results, the C-PB produces larger direct damping coefficients; CYY and CXX are up to 25% and 40% larger than those for the S-PB. Both bearings, however, show symmetry in the damping coefficients, i.e., CXX ∼ CYY. Virtual mass coefficients (MXX, MYY) are significant in magnitude though having a large uncertainty. A computational physics model predicts the TPJB performance under identical conditions. The exhaustive comparison conducted with a sound dimensional characterization of parameters reveals that predictions agree well with measurements of journal eccentricity, oil exit temperature, pad surface temperatures, and stiffness and damping force coefficients. The differences amount to 20% or less. The model relies on specifying the material properties for pads and pivots and the operating (hot) clearance to produce accurate thermo-mechanically induced deformations that affect bearing performance at high loads and high surface speed operation.
Conjugate Heat Transfer Characteristics of Double Wall Cooling With Gradient Diameter of Film and Impingement Holes
Authors: He Juan , Deng Qinghua , Feng Zhenping
Published: September 2021

Double wall cooling, consisting of internal impingement cooling and external film cooling, is believed to be the most advanced technique in modern turbine blades cooling. In this paper, to improve the uniformity of temperature distribution, a flat plate double wall cooling model with gradient diameter of film and impingement holes was proposed, and the heat transfer and flow characteristics were investigated by solving steady three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with SST k-ω turbulence model. The influence of gradient diameter on overall cooling effectiveness and total pressure loss was studied by comparing with the uniform pattern at the blowing ratios ranging from 0.5 to 2. For gradient diameter of film hole patterns, results show that −10% film pattern always has the lowest film flow non-uniformity coefficient. The laterally averaged overall cooling effectiveness of uniform pattern lies between that of +10% and −10% film patterns, but the intersection of three patterns moves upstream from the middle of flow direction with the increase of blowing ratio. Therefore, the −10% film pattern exerts the highest area averaged cooling effectiveness, which is improved by up to 1.6% and 1% at BR = 0.5 and 1 respectively compared with a uniform pattern. However, at higher blowing ratios, the +10% film pattern maintains higher cooling effectiveness and lower total pressure loss. For gradient diameter of impingement hole patterns, the intersection of laterally averaged overall cooling effectiveness in three patterns is located near the middle of flow direction under all blowing ratios. The uniform pattern has the highest area averaged cooling effectiveness and the smallest non-uniform coefficient, but the −10% jet pattern has advantages of reducing pressure loss, especially in the laminated loss.
Estimation of Design Parameters and Performance for a State-of-the-Art Turbofan
Authors: Sjögren Oliver , Xisto Carlos , Grönstedt Tomas
Published: September 2021

The aim of this study is to explore the possibility of matching a cycle performance model to public data on a state-of-the-art commercial aircraft engine (GEnx-1B). The study is focused on obtaining valuable information on figure of merits for the technology level of the low-pressure system and associated uncertainties. It is therefore directed more specifically towards the fan and low-pressure turbine efficiencies, the Mach number at the fan-face, the distribution of power between the core and the bypass stream as well as the fan pressure ratio. Available cycle performance data have been extracted from the engine emission databank provided by the International Civil Aviation Organization (ICAO), type certificate datasheets from the European Union Aviation Safety Agency (EASA) and the Federal Aviation Administration (FAA), as well as publicly available data from engine manufacturer. Uncertainties in the available source data are estimated and randomly sampled to generate inputs for a model matching procedure. The results show that fuel performance can be estimated with some degree of confidence. However, the study also indicates that a high degree of uncertainty is expected in the prediction of key low-pressure system performance metrics, when relying solely on publicly available data. This outcome highlights the importance of statistic-based methods as a support tool for the inverse design procedures. It also provides a better understanding on the limitations of conventional thermodynamic matching procedures, and the need to complement with methods that take into account conceptual design, cost and fuel burn.
Incipient Surge Analysis in Time and Frequency Domain for Centrifugal Compressors
Authors: Silvestri Paolo , Marelli Silvia , Capobianco Massimo
Published: September 2021

The use of centrifugal compressors has been increasing tremendously in the last decade as they are a key component in the present energy scenario both in the modern internal combustion engine design and in advanced cycles and innovative plant layouts as fuel cell systems.

Instability phenomena limit the operating range of the whole compressor system, especially during fast transients. The target is therefore to extend the minimum flow limit in order to improve the operability of each unit, while avoiding compressor surge operation and guaranteeing safe operation. For this reason, it is necessary to develop a monitoring system capable of preventing surge and extending operating range of these machines, their performance, and reliability to allow the integration with the other plant components.

The experimental investigation, carried out at the University of Genoa turbocharger test facility and presented in this work, consists of steady state and transient measurements used to characterize and identify compressor behaviour in correspondence of surge inception conditions to determine different techniques which could represent surge precursors. The data analysis concentrates on pressure and vibro-acoustic signals by applying different signal processing techniques in time and frequency domain to classify compressor operation as stable or unstable. The cross correlation function and wavelet analysis have been identified as techniques to define a precursor able to detect incipient surge conditions. Through cross correlation function analysis, it has been possible to identify the presence of propagation phenomena in the system and to evaluate how these events become more significant near an unstable low-mass flow rate condition. At low mass flow rate condition, spikes of significant amplitude are well detectable in the cross correlation function indicating the rise of significant random content in the system responses associated to the rise of incipient surge condition.

Additionally, the continuous wavelet transform has been applied to operational signals to show how their time-dependent spectral structure responses can highlight the rise of unstable phenomena, not easily identifiable with traditional signal processing techniques. Exploiting its features in terms of good frequency and time resolution it allowed to identify different contents in system responses regarding phenomena which take place close to surge line and was able to detect their nature in conditions very close to deep surge ones (e.g. rotating stall with its intermitting characteristic nature).

Moreover, system response was studied in high frequency range and through a demodulation technique it was found how blade pass frequency energy content change interacting with rotating stall inception, moving close to surge line.

The obtained results provide an interesting diagnostic and predictive solution to detect compressor instabilities at low mass flow rate operating conditions and to prevent compressor fails.
Computational and Experimental Studies of Model Fans for Advanced Turbofan Engines
Authors: Pankov S. V. , Korzhnev V. N. , Mileshin V. I. , Fateev V. A.
Published: September 2021

The paper presents the results of aeromechanical design of a large-scale model stage for a high-efficient low-noise fan designed for an advanced civil geared turbofan engines with ultra-low rotational speeds of rotor blades (313.4 m/s), high flow specific capacity (up to 202 kg/m2/s) and high bypass ratio (13.5). Total pressure ratio in the bypass duct of the fan model stage is 1.38.

To ensure the experimental studies, characteristics are calculated from choking to a surge line within a wide range of rotational speeds.

For the studies of the experimental fan model (EFM), a design project is developed and used in manufacturing a fan stage with 0.7-m rotor diameter for tests at the C-3A acoustic test facility.

The manufacturing technology for blades made of polymer composite materials (PCM) is of particular importance. Rotor blades of the geared fan model are made of PCM.

The analysis of experimental data and their comparison with the computation results within the range of corrected rotational speeds from 0.325 to 1.0 are presented. At first, only gas-dynamic and strength characteristics of the stage are studied. The analysis shows a good agreement of calculated integral parameters with the experimental data. Acoustic performances of the EFM will be studied later on.
Fouling Effects on Wet Gas Compressor Performance: An Experimental Investigation
Authors: Mæland Dagfinn , Bakken Lars E.
Published: September 2021

Achieving profitability in mature areas such as the Norwegian continental shelf forces the oil and gas industry to apply innovative solutions to increase oil recovery and to reduce both operational and investment costs. Wet gas compressors are promising machines for increasing oil recovery from existing fields and to allow for production from small satellite fields in the proximity of existing infrastructure. A prerequisite for successful implementation of subsea wet gas compressors high reliability. Knowledge of possible failure modes is important.

The effect of performance degradation due to fouling has been observed during wet gas compressor testing at K-Lab and has initiated further work to better understand and quantify the effects of fouling in wet conditions compared to dry conditions. A test campaign was conducted at the Norwegian University of Science and Technology (NTNU) to investigate the effect of fouled centrifugal compressor performance in both wet and dry conditions. The results documenting these effects are presented together with a proposed model for correcting the effects of fouling between dry and wet conditions.
Design and Validation of a Novel Turbogenerator’s Robotized Inspection System
Authors: Pignone Enrico , Pistone Alessandro , Canali Carlo , D’Agostino Fabrizio , Martorana Gianfranco
Published: September 2021

The inspection of power generators is a critical activity that will grow in importance during the next decades as operators are seeking solutions to continuously reduce outage duration and improve availability and reliability of the equipment. Automatic and systematic data collection on the status of health of the generator enables the possibility to implement predictive diagnostic/maintenance strategies and reduce the downtime due to repair activities. In this context robotic inspections play a crucial role since they allow a quick and efficient method to acquire data on the status of the generator. This paper describes an innovative robotic system that, thanks to a novel multi-sensor analysis method, is able to inspect and evaluate the overall status of power generators. The detection system, which is located on board a crawler robot, consists of inspection cameras, a micro-hammering system that is able to detect the acoustic response of fixing components of the generator bars and an Electromagnetic Core Imperfection Detection (EL-CID) sensor, which aims to detect insulation failures. Additionally, there is a description of how the robot has been designed to be adaptable to a wide range of different generators, and how it was tested and validated in the field.
Reconstruction of Temperature Distribution for a Turbulent Free Jet Using Background Oriented Schlieren
Authors: Wahls Benjamin H. , Ramakrishnan Kishore Ranganath , Ekkad Srinath
Published: September 2021

Background Oriented Schlieren (BOS) has been shown to be an excellent tool for qualitative flow visualization, and more recently, literature has shown that the technique can be expanded to yield quantitative measurements as well. In this study, a BOS setup was built to construct the temperature distribution of a heated turbulent free 12mm diameter jet near the nozzle. A 1080p DSLR camera was used to view a black and white speckled background plane through the heated free jet in question. Comparing images of the background with and without flow present using a cross correlation algorithm gave the apparent displacement of all points on the background viewed through the flow. Once this displacement field was obtained, a ray-tracing algorithm was implemented to reconstruct the refractive index of the center plane of the jet. Then, the Gladstone-Dale and ideal gas relations were combined and used to calculate the temperature of the center plane. Reynolds number, based on the jet diameter, was held constant at 6,000 for all cases, and steady state nozzle temperature was varied from 57°C to 135°C. Reconstructed temperature distributions were validated using K-type thermocouple measurements by allowing the system to reach steady state before acquiring data. Average agreement of 4–6% was observed between thermocouple and BOS measurements for axial locations of at least 30 mm downstream. Due to experimental error, accuracy decreases as axial location moves towards the nozzle, and as nozzle temperature increases. Improvements to the setup are being considered to improve the agreement in low accuracy regions. Further, this technique has the potential to be used to determine the temperatures in open and optically accessible closed reactive flows. Having information about near wall temperature in closed reactive flows will give insight into wall convective heat transfer characterization and will also help benchmark combustion based numerical models in applications such as gas turbines.
The Effect of Inlet Conditions on Turbine Endwall Loss
Authors: Coull John D. , Clark Christopher J.
Published: September 2021

There can be significant variation and uncertainty in the flow conditions entering a blade row. This paper explores how this variability can affect endwall loss in axial turbines.

A computational study of three cascades with collinear inlet boundary layers is conducted. Endwall loss varies by more than a factor of 3 depending on the inlet conditions. This variation is caused by dissipation of Secondary Kinetic Energy (SKE).

The results can be understood by observing that the inlet conditions predominantly control how secondary vorticity is distributed within the blade passage. Modestly-thick inlet boundary layers with high shape factor tend to displace vorticity towards the center of the passage. This displacement reduces vorticity cancellation, increasing secondary velocities and SKE.

A general method is formulated to estimate SKE in preliminary design. Optimum aspect ratio is shown to depend on the inlet boundary condition. Strategies to reduce endwall loss and minimize sensitivity to inlet conditions are then highlighted.
Erosion Evaluation of Gas-Turbine Grade CMC’s at Room and Elevated Temperatures
Authors: Eftekharian Amirhossein , Panakarajupally Ragav P. , Morscher Gregory N. , Huang Dade , Abdi Frank , Choi Sung
Published: September 2021

The objective of this study is to predict ceramic matrix composites (CMCs) erosion behavior and Retained Strength (RS) under environmental conditions using an Integrated Computational Material Engineering (ICME) physics-based approach.

The state-of-the-art erosion analysis using phenomenological algorithms and Finite Element Models (FEM) models follows a test duplication methodology and is not able to capture the physics of erosion.

In this effort, two CMC systems are chosen for Erosion evaluation: (a) Oxide/Oxide N720/alumina; and (b) MI SiC/SiC. Experiments are conducted at room and elevated temperatures (RT/ ET). Erosion testing considers: (i) a high velocity oxygen fuel (HVOF) burner rig for ET, and (ii) a pressurized helium impact gun for RT. Erodent particles are chosen as alumina and garnet. Experimental observations show that the type of erodent materials affects CMC erosion degradation at ET. Alumina exhibits to be an effective erodent for maintaining a solid phase particle erosion, while Garnet, experiences some degree of melting. Erosion of the oxide/oxide composite is more severe for the same erodent, temperature, mass, and velocity conditions than the MI SiC/SiC composite for all conditions tested. In general, increasing erosion temperature results in increasing erosion rate for the same erodent mass/velocity condition.

In conjunction with experiments, a computational Multi-Scale Progressive Failure Analysis (MS-PFA) is also used to predict erosion of the above-mentioned material systems at RT/ET. The MS-PFA augments FEM by a de-homogenized material modeling that includes micro-crack density, fiber/matrix, interphase, and degrades both fiber and matrix simultaneously during the erosion process. Erodent particles are modeled by Smooth Particle Hydrodynamic (SPH) elements. Erosion evolution in CMCs considering strain rate effect predicts a) spallation, b) mass-loss, and c) damages in fiber, matrix, and their interphase. ICME modeling is capable of predicting the erosion process and reproducing the test observation for the MI SiC/SiC at RT, where: a) erodent particles break up the layer of matrix covering fiber due to interlaminar shear (delamination); b) fiber is fractured because of brittle behavior; c) the process (erosion tunneling) continues till it gets to the next thick matrix layer that slows down the tunneling; and d) Erosion tunnel widens as exposed fiber layers are removed (eroded). Simulations are also performed for erosion of the oxide/oxide due to glass beads at RT and ET. Predictions show that erosion rate is lower at ET because voids in the CMC vanish and the glass beads are less effective at ET. Finally, prediction of retained strength of eroded CMC test specimens is predicted by MS-PFA.
A Semi-Analytical Model for Prediction of Wall Quenching Distances of Premixed Flames
Authors: Xia Huang , Weijie Liu
Published: September 2021

In order to predict the variation of the wall quenching distance of a premixed flame under different equivalence ratios and incoming flow velocities, a semi-analytical model applied to both lean single-layer flame and rich double-layer flame has been derived based on the conservation of energy in the quenching zone. In this model the flame surface radiation plays an important role. Factors influencing the radiation have been analyzed, respectively. The model indicates that the factors affecting the quenching distance in premixed flame are more complicated than that in single-wall flames or flames in tube. To fit the empirical coefficient in this model, a methane-air premixed flame quenching distance experiment under both lean and rich conditions has been performed. The comparison between the theoretical prediction and the experiment result shows that this semi-analytical model gives a suitable description of the quenching distance. The relative error of the quenching distance under different equivalence ratios and incoming flow velocities is less than ±15%.
Analysis of the Loss Production Mechanism due to Cavity-Main Flow Interaction in a LPT Stage
Authors: Barsi D. , Lengani D. , Simoni D. , Venturino G. , Bertini F. , Giovannini M. , Rubechini F.
Published: September 2021

In the present work URANS simulations are presented to describe the unsteady interaction process between the flow ingested/ejected from a cavity system and the main flow evolving into a Low Pressure Turbine stage. Particular care is posed on the analysis of the loss generation mechanisms acting outside the stator row and in the rear part of the axial gap separating the cavity flow ejection section and the leading edge plane of the downstream rotor row. The simulated geometry reproduces a typical engine cavity configuration, with upstream and downstream rotor rows reproduced by means of moving bars. Experimental results have been used to validate the simulations. This experimental data cannot explain and quantify alone the overall interaction process between the cavity flows and the main flow. The results of a simulation made by removing the domain of the cavity have been employed in order to better highlight and quantify the effects due to main flow and cavity flows interaction on total pressure loss. A deep inspection of the loss amount along the axial direction makes evident that losses generated in the vane row are basically increased prior to enter into the downstream rotor bars, due to cavity main flow interaction.
Investigation of Adjacent Lifted Flames Interaction in an Inline and Inclined Multi-Burner Arrangement
Authors: Shamma Mohamed , Hoffmann Sven , Harth Stefan Raphael , Zarzalis Nikolaos , Trimis Dimosthenis , Koch Rainer , Bauer Hans-Jörg , Langone Leonardo , Galeotti Sofia , Andreini Antonio
Published: September 2021

The main objective of this research is to assess an innovative, low nitrogen oxides emission combustor concept, which has the potential to achieve the long term European emissions goals for aircraft engines. Lean lifted spray flames and their very low nitrogen oxides emissions are combined with an inclination of burners in annular combustor leading to a more compact combustor with superior stability range. The presented combustor concept was developed in the frame of the European research project CHAIRLIFT (Compact Helical Arranged combustoRs with lean LIFTed flames). CHAIRLIFT combustor concept is based on “low swirl” lean lifted spray flames, which features a high degree of premixing and consequently significantly reduced nitrogen oxides emissions and flashback risk compared to conventional swirl stabilized flames. In the CHAIRLIFT combustor concept, the lifted flames are combined with Short Helical Combustors arrangement to attain stable combustion by tilting the axis of the flames relative to the axis of the turbine to enhance the interaction of adjacent flames in a circumferential direction. A series of experimental tests were conducted at a multi-burner array test rig consisting of up to five modular burners at different burner inclination angles (0° and 45°), equivalence ratios, and relative air pressure drop at ambient conditions. For all investigated configurations, a remarkable high lean blow out for non-piloted burners (ϕLBO = 0.29–0.37), was measured. The multi-burner configurations were observed having a superior stability range in contrast to the typical decrease in stability from single to high swirl multi-burner. The unwanted flow deflection of highly swirled flames in Short Helical Combustors arrangement, could be avoided with the investigated low swirl lifted flames. Moreover, the flame chemiluminescence (OH*) measurements were used to provide a qualitative characterization of the flame topology. Complementary numerical investigations were carried out using different numbers of burners to evaluate the effect of boundary conditions.
Film Cooling and Aerodynamic Performance on Multi-Cavity Squealer Tip of a Turbine Blade
Authors: Li Feng , Liu Zhao , Feng Zhenping
Published: September 2021

The blade tip region of the shroud-less high-pressure gas turbine is exposed to an extremely operating condition with combined high temperature and high heat transfer coefficient. It is critical to design new tip structures and apply effective cooling method to protect the blade tip. Multi-cavity squealer tip has the potential to reduce the huge thermal loads and improve the aerodynamic performance of the blade tip region. In this paper, numerical simulations were performed to predict the aerothermal performance of the multi-cavity squealer tip in a heavy-duty gas turbine cascade. Different turbulence models were validated by comparing to the experimental data. It was found that results predicted by the shear-stress transport with the γ-Reθ transition model have the best precision. Then, the film cooling performance, the flow field in the tip gap and the leakage losses were presented with several different multi-cavity squealer tip structures, under various coolant to mainstream mass flow ratios (MFR) from 0.05% to 0.15%. The results show that the ribs in the multi-cavity squealer tip could change the flow structure in the tip gap for that they would block the coolant and the leakage flow. In this study, the case with one-cavity (1C) achieves the best film cooling performance under a lower MFR. However, the cases with multi-cavity (2C, 3C, 4C) show higher film cooling effectiveness under a higher MFR of 0.15%, which are 32.6%%, 34.2%% and 41.0% higher than that of the 1C case. For the aerodynamic performance, the case with single-cavity has the largest total pressure loss coefficient in all MFR studied, whereas the case with two-cavity obtains the smallest total pressure loss coefficient, which is 7.6% lower than that of the 1C case.
Novel End-End System for Combustor Design and Analysis
Authors: Kannan Ashwin , Thewlis Jonathan , Keskin Akin
Published: September 2021

High quality geometry creation is a key step in the design process for complex modern turbomachinery subsystems such as an annular combustor assembly. In particular, parametric generation of 3D CAD geometry is an enabler for design studies and multi-disciplinary analysis. In a traditional approach, 3D CAD models are either created in a bespoke manner with respect to the engine of interest or if a parametric approach is used, the geometry is for one particular combustor configuration, which typically leads to insufficient flexibility for topological variations. In either of these cases for every combustor design, substantial manual efforts are involved in geometry creation as well as in geometry manipulation towards creation of a truncated sector model suitable for meshing and analysis. A more flexible and fully parametric approach in highly integrated and automated design processes during all product design phases is therefore necessary.

The present paper focuses on the exploitation and integration of a novel geometry modelling approach into an existing and well-established combustor design and analysis system called Prometheus in order to achieve a massive step toward a fully End-to-End (E2E) system. The new system is enabling rapid combustor design and analysis by combining feature-based geometry modelling approach that enables automatic creation of an analysis compatible combustor assembly with a geometry-centric optimization system. The automated design system can manipulate 3D geometry, to create necessary script files for meshing, simulation and post-processing for a typical CFD analysis, and execute the process to analyze different designs with respect to defined design objectives and constraints. The improved system enables engineers to assess different design concepts quickly early in the design process by providing best trade-offs between design objectives but also allows the use of detailed simulation models and boundary conditions in later more mature designs stages.

The paper will discuss the robustness and flexibility of the underlying parametric CAD approach, how it augments the downstream processes, which is able to handle and translate significant topological changes throughout the E2E system. It will also clearly demonstrate the efficiency gain of the automated combustor design process, which enables design engineers to make better decision faster.
Experimental Investigation of the Effects of High Temperature Treatment on Quasi-Static Mechanical Characteristics of EMWM Materials
Authors: Ma Yanhong , Liang Tianyu , Hong Jie
Published: September 2021

This paper investigates the influence of high temperature treatment processes on the mechanical characteristics of entangled metallic wire materials (EMWM) via quasi-static compression tests. The treatment methods including high-temperature treatment and high-temperature with loading treatment were tested. The variation effects of size in molding direction, tangent modulus and loss factor were obtained by contrast results of EMWM specimens via the treatment processes with initial performance. The results indicate that the treatment processes proposed in this study can significantly improve the mechanical properties of EMWM materials and have a wide range of application for EMWM specimens with different structural parameters. After the treatment processes, the size of specimens in molding direction decreased slightly, the tangent modulus increased significantly, and the loss factor decreased slightly. With the increase of treatment temperature, the variation of mechanical parameters intensified. For EMWM specimens with different relative densities and heights, the treatment processes still have a significant improvement effect on quasi-static mechanical properties. Finally, the secondary molding theory is carried out to explain the influence of high temperature treatment process on EMWM’s dimensions and mechanical properties. The effects of treatment temperature and repetition times obtained in this study are relevant to the design of treatment processes for EMWM materials.
Experimental and Numerical Similitude Study Using a Novel Turbocompressor Test Facility Operating With Helium-Neon Gas Mixtures
Authors: Podeur Maxime , Vogt Damian M.
Published: September 2021

A novel turbocompressor test facility has been designed for helium-neon gas mixtures and its specific features are presented. To account for the heat transfer originating from the motor coolant, a surrogate model has been derived. By combining these results with additional numerical ones, a similitude study is conducted quantifying the individual effects and contributions on efficiency of the Reynolds number, tip Mach number and specific heat ratio. Decoupling the effect of the different parameters shows that their respective contribution on efficiency variation is highly correlated to the Reynolds number actual value. The negative contribution of the tip Mach number and the positive effect of Reynolds number can be used to explain the efficiency variation with increasing tip Mach number. Specific heat ratio variation leads to minor changes in polytropic efficiency except at low tip Mach numbers.