bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Analysis of Blade-Casing Contacts in a Centrifugal Compressor: Vibration and Thermal Aspects
Authors: Guérin Nicolas , Gibert Claude , Thouverez Fabrice , Almeida Patricio
Published: January 2021

Due to an increasing need for efficiency of turboengines, rotor–stator clearances are being lowered. Therefore, new designs show higher probability for contacts between rotors and casings. When contacts occur, high dynamic excitation levels as well as high temperatures due to dissipative mechanical phenomena may be expected. While numerical investigations have been proposed in the past, experiments are of high interest to fully understand the underlying phenomena behind rotor-stator contact interactions. In order to assess this situation, and based on former work performed by part of the authors, a rotor–stator contact rig has been used to investigate the mechanical and thermal behavior of a centrifugal low-pressure helicopter engine compressor. This rig operates under vacuum conditions to significantly reduce influence of the air surrounding the studied components. A near-zero gap condition is set at rest, then a rotational speed sweep allows to target the specific operating range of interest. Both structures are fitted with strain gauges, and a torquemeter is installed on the shaft to measure resistive phenomena on the bladed disk. A scanning laser Doppler vibrometer is aimed at the casing through a window to provide additional displacement measurements. Temperatures are measured by an array of thermocouples equally spaced around the casing, close to the expected contact area. Also, using temperature-sensitive markings, overall temperature mappings on the impeller are performed. During the tests, multiple contact phases have been identified through increased vibration and temperature levels, as well as torque and rotational speed variations. A comprehensive analysis of the dynamic and thermal phenomena occurring during these experimental tests is proposed in this paper. Dynamic measurements are analyzed in the time and frequency domains, and nodal diameter contents are evaluated as well through full spectrum analyses. As a result, major influences from synchronous excitations in the frequency range of interest but also of higher modal families are highlighted. Post-trial observations indicate severe contact conditions leading to very high temperatures, abradable coating removal and material transfer between blade and casing.
Experimental and Numerical Assessment of Mistuning Effects on Vibratory Response of a Bladed Disk With Underplatform Dampers
Authors: Pourkiaee S. Mehrdad , Berruti Teresa , Zucca Stefano , Neuville Geoffrey
Published: January 2021

This paper presents experimental and numerical investigation of mistuned forced responses of an integrally bladed disk with full set of underplatform dampers (UPDs). This research aims at providing:

1. An experimental benchmark for nonlinear dynamics of a mistuned bladed disks with UPDs.

2. A numerical model that can account for features of a mistuned forced response level.

Accordingly, a detailed experimental campaign is conducted on a static test rig called Octopus. This rig is specifically designed to investigate the dynamics of a full-scale integrally bladed disk (blisk) with UPDs in a noncontact manner so that the dynamic response of the system is not modified.

The effect of mistuning on experimental forced response levels is assessed and a linearized model is proposed to predict the modulation of frequency response functions (FRFs) due to the frequency splitting.

In the development of the model, the mistuning pattern identified from the linear blisk without UPDs is used and it is assumed that adding the dampers does not change the structural mistuning of the blisk. In this study, the fundamental mistuning model identification (FMM ID) was employed to identify the mistuning pattern of the blisk.

It is shown that the proposed model successfully predicts the modulation of linear mistuned FRFs. The linearized model is also able to predict the modulation of nonlinear mistuned FRFs in stick condition (when nonlinear friction damping is negligible) with a good accuracy validating this assumption that adding the dampers does not change the mistuning pattern.
Laminar Flame Speed Measurements of Kerosene-Based Fuels Accounting for Uncertainties in Mixture Average Molecular Weight
Authors: Keesee Charles L. , Guo Bing , Petersen Eric L.
Published: January 2021

New laminar flame speed experiments have been collected for some kerosene-based liquid fuels: Jet-A, RP-1, and Diesel Fuel #2. Accurately understanding the combustion characteristics of these, and all kerosene-based fuels in general, is an important step in developing new chemical kinetics mechanisms that can be applied to these fuels. It is well known that the precise composition of these fuels changes from one production batch to the next, leading to significant uncertainty in the mixture average properties. For example, uncertainty in a fuel blend’s molecular weight can have a noticeable effect on defining an equivalence ratio for a typical fuel-air mixture, on the order of 15%. Because of these uncertainties, fuel mole fraction, Xfuel, is shown to be a more appropriate parameter for comparison between different batches of fuel. Additionally, a strong linear correlation was detected between the burned-gas Markstein length and the equivalence ratio. This correlation is shown to be useful in determining the acceptability and accuracy of individual data points. Spherically expanding flames were measured over a range of fuel mole fractions corresponding to equivalence ratios of φ = 0.7 to φ = 1.5, at initial conditions of 1 atm and 403 K in the high-temperature, high-pressure constant volume vessel at Texas A&M University. These new results are compared with the limited set of laminar flame speed data currently available in the literature for this fuel.
Hidden Advantages and Strategic Leaps for CODAG, CODELAG, CODELOG and Hybrid Propulsion Systems
Authors: Hendry Morgan L. , Bellamy Nicholas
Published: January 2021

Navies worldwide are increasingly considering and adopting propulsion plants with electric propulsion for cruise and ship silent operation, and gas turbines for boost propulsion for high speed. These propulsion plants, often referred to as hybrid propulsion, utilize water jets, controllable pitch propellers, or fixed pitch propellers, and have design and overall configuration to fit into naval ships with various size hulls such as would be the case with corvettes, frigates, destroyers, cruisers, etc. Therefore, size, weight, and space of the propulsion plant is important, but equally important is limiting associated machinery which must be used with a particular hybrid propulsion plant design selected.

In addition, propulsion design engineers, in conjunction with naval architects, shipyards and navies, must consider fuel efficiencies, machinery efficiencies, weight of all the associated machinery, placement in the hull, first time cost, and life cycle maintenance with associated cost when selecting the configuration of the propulsion system’s associated machinery. Manning levels are dictated by these parameters and in the end, it must be realized that the purpose of the ship mission can be compromised if reliability is not high and premature failures occur.

This paper is a more in depth analysis of hybrid propulsion systems for naval ships of various sizes, and analysis of the associate machinery emphasizing ship weight and space savings, fuel savings, cost savings, mean time between failures and mean time to repair which results in lower manning requirements and increased mission readiness.

By the time this paper is published, more than 250 SSS Clutches will be installed in US Navy Arleigh Burke Destroyers, 32 are operating in low speed propeller shafts of British Navy Type 23 ships, 2 in the Japanese Navy’s Asuka Class and 16 in low speed propeller shafts of Royal Korean Navy FFX Batch II frigates. At the time of abstract submission, all three programs referenced above have cumulatively had zero defects attributable to SSS Clutch material, function, design, or quality. While the US Navy are given occasional reminders of why alternative clutch designs remain ineffective, unreliable and remarkedly inefficient, other nations’ vertically tiered supply chains and inexperienced engineers are shielded from similar issues.
Aeroelastic Modelling of Three-Dimensional Lifting Bodies With an Accelerated Boundary Element Method
Authors: Könnecke Ludwig , Saverin Joseph
Published: January 2021

Investigated was the aeroelastic treatment of a three-dimensional NACA0006 wing by coupling the boundary element method (panel method) for the aerodynamic solution with a beam model (Chrono) for the structural-elastic solution to obtain an aeroelastic solution. Aerodynamic information is interpolated to the structural model by using radial basis functions. As a validation case an analytical model was set up by calculating the lift force from the lifting-line theory and the resulting deflection and torsion predicted with a linear beam theory. This analytical model considers a purely torsional aeroelastic case which is comparable with the simulation results. The distribution of the lift force over the span position of the simulation and the analytical model agrees well, particularly in comparison to the purely torsional case.
CO and OH Imaging in Flames Using a Single Broadband Femtosecond Laser Pulse
Authors: Parajuli Pradeep , Jain Ayush , Kulatilaka Waruna D.
Published: January 2021

Carbon monoxide (CO) and hydroxyl (OH) are the two key intermediate species formed during chemical reactions inside gas turbine combustors. Spatiotemporal information and a detailed understanding of CO formation in the reaction zone are important during the combustion processes as a major part of the heat release is obtained from the oxidation of CO to CO2. Turbulent flame structures and reaction zone in different flame conditions can also be visualized through the spatial distribution profiles of OH. In the current study, both these species are excited simultaneously using a single ultrashort, broad spectral bandwidth of approximately 100-femtosecond (fs) duration laser pulse at λ = 283.8 nm. Subsequent fluorescence signals are separated through spectral filters of appropriate bandwidth and imaged using two cameras. This present study was performed in a McKenna flat-flame burner with ethylene/air as a pilot flame and non-premixed turbulent ethylene jet at the center. The partial spectral overlap of CO–X (4,0) and OH A–X (1,0) transitions are utilized for simultaneous excitation, thereby characterize the overall flame structure (via OH) and regions of oxidation reactions (via CO) in a range of flame conditions. Besides, CO and OH profiles follow the trends obtained from model predictions for a range of equivalence ratios in ethylene/air flames stabilized over the Hencken calibration burner. These results are used for obtaining quantitative calibrations of CO and OH signals. Overall, the present study extends the applicability of a single, broadband fs laser pulse for simultaneous imaging of multiple chemical species in flame.
Effects of Inlet Distortion Patterns on Induced Swirl in a Highly Loaded Fan Stage
Authors: Orme Andrew D. , Gorrell Steven E. , Pulsipher Addison C.
Published: January 2021

Characterization of distortion transfer and generation through fans with distorted inlet conditions enables progress towards designs with improved distortion tolerance. The abruptness of transition from undistorted to distorted total pressure regions at the inlet impacts the induced swirl profile and therefore the distortion transfer and generation. These impacts are characterized using URANS simulations of PBS Rotor 4 geometry under a variety of inlet distortion profiles. A 90° and a 135° sector, both of 15% total pressure distortion, are considered. Variants of each sector size, with decreasing levels of distortion transition abruptness, are each applied to the fan. Fourier-based distortion descriptors are used to quantify levels of distortion transfer and generation at axial locations through the fan, principally at the stator inlet. It is shown that a gradual transition in distortion at the inlet results in decreased levels of distortion transfer and generation. The flow physics resulting in this reduction are explored.
Effects of Shock Wave Development on Secondary Flow Behavior in Linear Turbine Cascade at Transonic Condition
Authors: Tsujita Hoshio , Kaneko Masanao
Published: January 2021

Gas turbines widely applied to power generation and aerospace propulsion systems are continuously enhanced in efficiency for the reduction of environmental load. The energy recovery efficiency from working fluid in a turbine component constituting gas turbines can be enhanced by the increase of turbine blade loading. However, the increase of turbine blade loading inevitably intensifies the secondary flows, and consequently increases the associated loss generation. The development of the passage vortex is strongly influenced by the pitchwise pressure gradient on the endwall in the cascade passage. In addition, a practical high pressure turbine stage is generally driven under transonic flow conditions where the shock wave strongly influences the pressure distribution on the endwall. Therefore, it becomes very important to clarify the effects of the shock wave formation on the secondary flow behavior in order to increase the turbine blade loading without the deterioration of efficiency.

In this study, the two-dimensional and the three-dimensional transonic flows in the HS1A linear turbine cascade at the design incidence angle were analyzed numerically by using the commercial CFD code with the assumption of steady compressible flow. The isentropic exit Mach number was varied from the subsonic to the supersonic conditions in order to examine the effects of development of shock wave caused by the increase of exit Mach number on the secondary flow behavior. The increase of exit Mach number induced the shock across the passage and increased its obliqueness. The increase of obliqueness reduced the cross flow on the endwall by moving the local minimum point of static pressure along the suction surface toward the trailing edge. As a consequence, the increase of exit Mach number attenuated the passage vortex.
Combustion Tuning for a Gas Turbine Power Plant Using Data-Driven and Machine Learning Approach
Authors: Li Suhui , Zhu Huaxin , Zhu Min , Zhao Gang , Wei Xiaofeng
Published: January 2021

In this paper, we present a cross-disciplinary study on the combustion tuning of an F-class gas turbine that combines machine learning with physics understanding. An artificial-neural-network-based (ANN) model is developed to predict the combustion performance (outputs), including NOx emissions, combustion dynamics, combustor acceleration, and turbine exhaust temperature. The inputs of the ANN model are identified by analyzing the key operating variables that impact the combustion performance, such as the pilot and the premixed fuel flow, and the inlet guide vane angle. The ANN model is trained by field data from an F-class gas turbine power plant. The trained model is able to describe the combustion performance at an acceptable accuracy in a wide range of operating conditions. In combination with the genetic algorithm, the model is applied to optimize the combustion performance of the gas turbine. Results demonstrate that the data-driven method offers a promising alternative for combustion tuning at a low cost and fast turn-around.
Recirculation Zones During the Centrifugal Compressor Surge Cycle: CFD Simulation
Authors: Kulak Michał , Grapow Filip , Liśkiewicz Grzegorz
Published: January 2021

In this paper the flow recirculation regions during the full surge cycle were described. It is a known fact that the surge cycle consists of two periods: backflow and recovery. The aim of this paper is to add spatial dimension to this analysis. Therefore, the main target is to identify the regions of backflow and recirculation throughout the surge cycle. The full surge cycle modelled with an application of unsteady RANS methods is demonstrated — the significant push was put to realistic boundary conditions definition, narrowed to establishing pressure setting at both inlet and outlet positions located far from the impeller. The results show that all the backflow appears in the recirculation zones that grow and diminish throughout the surge cycle. The regions of inflow and backflow can concurrently exist at different stages of the surge. The analysis includes areas occupied by both structures and mass flowrates associated with them. Presented research is a part of a project aiming at design and construction of more efficient anti-surge systems. Its overall target is to eventually introduce the anti-surge systems that are made to fit the particular machine. Therefore, the understanding of local flows during and prior to surge are one of the key issues that need to be interpreted.
Phantom Cooling Effects on Rotor Blade Surface Heat Flux in a Transonic Full Scale 1+1/2 Stage Rotating Turbine
Authors: Anthony Richard J. , Finnegan John , Clark John P.
Published: January 2021

An experimental and numerical investigation of phantom cooling effects on cooled and uncooled rotating high pressure turbine blades in a full scale 1+1/2 stage turbine test is carried out. Objectives set to capture, separate, and quantify the effects of upstream vane film-cooling and leakage flows on the downstream rotor blade surface heat flux. Multiple series of 1+1/2 stage rotating high pressure turbine tests were carried out in the Air Force Research Laboratory, Turbine Research Facility, at Wright-Patterson Air Force Base, Ohio. A non-proprietary research turbine test article is uniquely instrumented with high frequency double-sided thin film heat flux gauges custom made at AFRL. High bandwidth, time resolved surface heat flux is measured on multiple film-cooled and non-film-cooled HPT rotor blades downstream of both film-cooled and non-film-cooled vane sectors. Upstream wake passing and heat flux is characterized on both rotor pressure and suction side surfaces, along with quantifying rotor phantom cooling effects from nonuniform 1st stage vane film cooling and leakage flows.

Fast response heat flux measurements quantify how rotor phantom cooling impacts the blade pressure side greatest; increasing along the pressure side towards the trailing edge. It is discovered upstream vane film-cooling alone can account for 50% of the rotor blade cooling effect, and even outweigh the rotor blade film cooling effect far from the blade showerhead holes. Added unsteady aero numerical simulation demonstrate how variations in inlet total temperature and incidence angle can also contribute to circumferentially non-uniform rotor heat flux.

Better understanding from this investigation aids modelling and design efforts in optimizing film cooling performance in real high pressure turbine flow fields. Understanding the behavior of such non-uniform circumferential rotor phantom cooling effects can be critical to optimize the efficiency, fuel consumption, range, and durability of advanced turbomachines.
Multidisciplinary Design of a Low-Noise Propeller: Part II — Efficient Aero-Acoustic-Mechanical Design Methodology Exploiting Surrogate Models in an Adaptive Design Space
Authors: Baert Lieven , Dumont Chloé , Beauthier Charlotte , Sainvitu Caroline , Lepot Ingrid , Blanchard Julien
Published: January 2021

The regional aircraft segment plays a crucial role in achieving the EU Flightpath 2050 objectives (increase connectivity through Europe, enforce Europe’s industrial leadership, and significantly reduce the environmental impact of aviation). Despite an outdated perception by the general public, turboprop aircraft are typically less expensive to operate than regional jets. The impact of new technologies is therefore even more evident. Achieving a significant reduction in perceived noise levels remains however a challenge for the success of further turboprop deployment.

This twofold paper discusses the design of an innovative low-noise propeller in the framework of the Clean Sky 2 Regional Aircraft IADP, with a focus on the design methodology itself in this second part. The design is inherently multidisciplinary — aerodynamic, acoustic, mechanical — with multiple flight conditions and a wind tunnel condition to be considered. In order to limit the number of expensive high-fidelity computations, an online surrogate-based optimisation (SBO) approach has been deployed. A high-dimensional design space has been considered to enable to identify disruptive low-noise concepts. By exploiting the results of low-fidelity tools (see the first part of the paper), combined with efficient machine learning techniques and data mining capabilities, a gradual increment of the design space from 57 to 111 design parameters has been considered. A significant noise reduction of about 6.5 dB has been achieved without major degradation of the aerodynamic efficiency — fully aligned with the objectives for the Regional Aircraft IADP.
Preliminary Study of a Centrifugal Compressor With Counter-Rotating Impellers: Design and Performances Study
Authors: Cheikh Brahim Abed , Sofiane Khelladi , Michael Deligant , Abdel El Marjani , Bakir Farid
Published: January 2021

Turbomachinery with double counter-rotating impellers offer more degrees of freedom in the choice of design and control parameters compared to conventional machines. For these innovative machines, the literature review shows that more published works are available concerning axial type turbomachines than centrifugal ones. This work deals with a preliminary design and performance analysis applied to two counter-rotating impellers of a centrifugal compressor. We present here the design practice developed based on 0D/1D models, also coupled with optimization and stream-curvature through-flow methods to satisfy the selected design-criteria. An analyze of aerodynamic performances results are made and compared to those available experimental and numerical data of a baseline configuration, composed of one centrifugal-impeller and a volute. The compressor studied here includes a first conventional impeller with an axial inlet and a mixed or centrifugal outlet. The second impeller is designed parametrically and can be considered as a rotating-diffuser with a radial or mixed inlet and outlet. Ultimately, the numerical simulation results of a selection of candidate solutions are discussed.
A Novel Sensor for Improving Flame Stability of Gas Fired Gas Turbine by Continuously Monitoring Fuel Gas Quality
Authors: Flot Patrice , Duval Alexis , Digneton Mathias
Published: January 2021

Gas networks are interconnected and strategically linked to multiple sources. Because of this, the quality of gas can change rapidly at a given location when switching from one source to another. When this occurs, these rapid changes can result in flashback or flame extinction.

To overcome combustion issues and instabilities of gas fired gas turbines due to the variability of gas incoming gas quality, a new sensor called NIRIS NG has been designed which analyzes the natural gas composition at the inlet of the turbine burners. The design of the NIRIS NG sensor boasts a short response time (less than one second), easy installation, simple maintenance, and low cost. This is primarily because unlike other gas quality sensors, the NIRIS NG sensor is based on spectrometry technology and the sensor has been specifically engineered for installation on turbine applications. By employing spectrometry, the NIRIS NG sensor is performing a technological breakthrough by using low cost optical components and proprietary signal treatment software within robust packaging that can sustain the vibration and heat over extended periods. The gas-pipe-plugged sensor provides fast response times and transmits the data to the turbine controller using CAN protocol. This paper will describe in detail the sensor hardware and software technologies, validation testing that has been completed to date, and the expected advantages on industrial gas fired gas turbines.
Numerical Investigations on the Effect of Pivot Shapes in Part Clearance Flow Field of Variable Area LP Turbine Nozzle Vane
Authors: Bhavsar Hardikkumar , Mistry Chetan S.
Published: January 2021

The performance of the gas turbine engines deteriorates under off-design conditions with the change of required power demand. The performance of the engine can be improved by actively controlling the mass flow rate through the engine turbine section using the variable area nozzle turbine (VANT). However, to implement VANT, vanes of the turbine nozzle need to be rotated, which demands part clearance to be provided near both the hub and tip region. In order to keep constant part clearance during vane turning, endwalls are modified to spherical shapes in such a way that distance between vane and upstream as well downstream rotor remains unaffected. Also, vanes are rotated about its pivot, which creates a blockage to the leakage flow in the part clearance. As pivot creates a blockage to the leakage flow, the shape of the pivot need to be selected in such a way that leakage losses can be reduced effectively. Hence, to analyze the effect of different pivot shapes on leakage losses, two different shapes of the pivot i.e., circular and elliptic, are explored in the present study. Also, three vane turning angles are analyzed to observe the effectiveness of these pivot shapes. The effect of the pivot is analyzed by entropy contours and total pressure loss coefficient in the exit plane, and it is found that the elliptic pivot performs better than a circular pivot as an elliptic pivot provides more blockage to the leakage flow and hence minimizing the overall losses.
The Limit Inlet Temperature of Refrigeration Centrifugal Compressor to Avoid Phase Change
Authors: YaFei Duan , YongHong Tang , ZhiHong Jin , HanSen Zou , Guang Xi
Published: January 2021

From the polytropic compression work formula, we can find that the consumed polytropic work will reduce with the decrease of inlet temperature while compressing the refrigerant to the same compression ratio. However, the refrigerant may condense if the inlet temperature is low enough. Though the principle that the acceleration of fluid may result in condensation has been proved by numerical simulations and experiments, and the liquid formation inside the supercritical carbon dioxide (SCO2) centrifugal compressor has been widely studied, there is still not a user-friendly method to predict whether the inlet condition may cause liquid formation inside the compressor.

The fluid flow in the space near the blade suction face of the leading edge (SNSL) is assumed to the similar flow in a converging nozzle when the mass flow is larger enough; the fluid impinges on the suction surface of blades, and the absolute velocity of fluid will not be greater than sound velocity. The fluid turns to impinge on the pressure surface with the decrease of mass flow rate, which is similar to the flow in a converging-diverging nozzle, and the maximum absolute velocity in the SNSL may be greater than the sound speed.

A method is proposed to predict the lowest inlet temperature of refrigeration centrifugal compressor to avoid phase change, which is called the limit temperature. The predicted lowest temperature shares the same trend with the numerical results. The condensation will occur inside the compressor when the inlet temperature is lower than the limit inlet temperature. The lowest temperature will first increase and then decrease as the mass flow increases, which should be taken into account while designing a refrigeration centrifugal compressor or adjusting the operating condition.
Influence of Blade Tip Fillet Structure on Aerodynamic Performance of a Compressor Rotor
Authors: Wang Haohao , Zhao Lei , Gao Limin , Li Yongzeng , Ma Chi
Published: January 2021

This paper deals with the numerical simulation of a passive control technology to increase the performance of the first rotor in a counter-rotating axial compressor. The objective is to extend the stable operating range of an axial compressor rotor using blade tip fillet structure that located on the blade tip pressure side. Firstly, the behavior of the tip leakage flow is investigated for the compressor rotor without passive treatment. The simulations show the loading of blade tip increases as the mass flow rate decreases, which pushed the location of tip leakage vortex and tip separation vortex forward to leading edge. A blockage in the rotor blade passage is also observed at near stall conditions. Then, a rotor blade tip fillet structure (TFS) is tested in order to control leakage flow in the tip region. Steady calculations were conducted to investigate the impact of TFS on the performance of the compressor rotor. The results show that TFS could extend the operating range with no penalty for efficiency when the fillet structure located on the blade tip pressure side. The flow control mechanisms of tip leakage flow are that TFS has a good ability to weaken the tip separation vortex and make the tip leakage vortex closer to the blade suction surface compared to origin rotor blade. It is founded that TFS may lead to a increase of leakage flow mass rate near tip clearance region that resulted in the addition of mixing loss. It is significant to obtain a balance between the benefits of weakening the tip separation vortex and the damage of mixing loss.
Development and Validation of a Model for Centrifugal Compressors in Reversed Flow Regimes
Authors: Powers Katherine H. , Kennedy Ian J. , Brace Chris J. , Milewski Paul A. , Copeland Colin D.
Published: January 2021

Turbochargers are widely used to help reduce the environmental impact of automotive engines. However, a limiting factor for turbochargers is compressor surge. Surge is an instability that induces pressure and flow oscillations that often damages the turbocharger and its installation.

Most predictions of the surge limit are based on low-order models, such as the Moore-Greitzer model. These models tend to rely on a characteristic curve for the compressor created by extrapolating the constant speed lines of a steady-state compressor map into the negative mass flow region. However, there is little validation of these assumptions in the public literature.

In this paper, we develop further the first-principles model for a compressor characteristic presented in Powers et al. [1], with a particular emphasis on reverse flow. We then perform experiments using a 58mm diameter centrifugal compressor provided by Cummins Turbo Technologies, where we feed air in the reverse direction though the compressor while the impeller is spinning in the forwards direction in order to obtain data in the negative mass flow region of the compressor map.

This demonstrated experimentally that there is a stable operating region in the reverse flow regime. The recorded data showed a good match with the theoretical model developed in this paper We also identified a change in characteristic behaviour as the impeller speed is increased which, to the authors knowledge, has not been observed in any previously published experimental work.
High Firing Temperature GT36 H-Class Low NOx Combustor Engine Validation and Performance
Authors: Granet V. , Sierra Sanchez P. , Cuquel A. , Günster P. , Wickström A. , Pennell D. , Singla G. , Früchtel G.
Published: January 2021

In order to minimize the footprint of human activities on the environment, technologies to reduce greenhouse gases while meeting constantly growing electricity demands are critical. Amongst the various sources of energy production, Gas Turbines (GT) are an efficient way to stabilize the grid with regards to renewable sources like wind and solar energies. The demand for higher efficiency, higher power output while reducing emission levels (especially NO and NO2) at high loads, and for higher flexibility within the H-class Gas Turbine market is thereby a natural consequence. The development and validation of a two-stage sequential combustor, so-called Constant Pressure Sequential Combustion (CPSC) system, to achieve these goals has been accomplished by Ansaldo Energia. The CPSC consists of a premix burner system (First Stage) and of a sequential burner (SB) in series within a can combustor. At the 2017 and 2019 ASME conferences, high pressure test rig validation results of the CPSC were introduced. The advantages with regards to fuel flexibility, hydrogen combustion and low emissions at high firing temperature were presented [1,2,3,4,5]. This article focuses on the validation of the combustor performance in Ansaldo Energia’s Validation Power Plant located in Birr, Switzerland, which includes detailed validation from ignition to full speed no load, part load operation and full load over various ambient and engine thermal state conditions. To allow for detailed validation, dedicated fully instrumented combustor cans were installed in the GT. Detailed validated air distribution and emission models support the results obtained on the engine. Ignition and ramps up to full speed no load have been validated with large variations of the first combustor stage firing temperature to minimize power consumption and start-up time. The potential of the CPSC with regards to turndown capability, with minimum environmental load (MEL) below 25% GT load while keeping CO levels low has been confirmed. The MEL can be kept low over a wide range of ambient temperature and fuel compositions by adjusting the inlet temperature of the sequential burner. Low NOx values were achieved at baseload and peak firing temperature. The operational flexibility and stability of the premixed first stage combustor over the load range and over a large variation of combustor inlet plenum pressures was as well validated along with the operation concept of the gas turbine.
Numerical Modeling of Centrifugal Compressors With Heterogeneous Incoming Flow due to Low Pressure Exhaust Gas Recirculation
Authors: Galindo José , Serrano José Ramón , Navarro Roberto , García-Olivas Guillermo
Published: January 2021

Low pressure EGR (LP-EGR) has become recently one of the most investigated technique in the field of internal combustion engines. When LP-EGR is active, two streams with different psychrometric conditions are mixed at the compressor inlet, i.e. fresh air (considered as cold and dry) and EGR (humid and warm). The main objective of the present work is to assess the impact of the inlet flow heterogeneity, associated with LP-EGR systems, in the performance of centrifugal compressor using 3D CFD simulations. Two intake configurations will be studied, namely a standard straight duct providing the compressor with a homogeneous flow and T junction with a mixing of air and EGR streams. 9 operating points using an EGR rate of 15% (or equivalent inlet conditions for the single duct) are explored. The temporal treatment is firstly assessed, comparing steady RANS simulations against unsteady ones for both intakes, discussing their behavior in terms of global variables and in mean flow field too. These studies show how the steady approach is not enough accurate for predicting the heterogeneity of the flow field in LP-EGR applications. After that, the comparison in global variables between the T-junction inlet and the standard inlet shows slightly differences in terms of compression ratio (around 0.5%) and isentropic efficiency (around 1%). However, in terms of local differences, the case with the standard inlet is clearly not able to predict the temperature heterogeneity of the case with a T-joint. Despite these issues, for an EGR rate of 15%, the global parameters of the compressor are not affected by the T-junction when equivalent operating points are considered in a single duct intake, so this approach can be employed to still use the standard compressor map for LP-EGR applications.
Design Space Exploration of Turbine Blade Shroud Interlock for Flutter Stability
Authors: Larrieta Olatz , Alonso Roberto , Escobar Óscar Pérez , Eryilmaz Ibrahim , Pachidis Vassilios
Published: January 2021

The geared turbofan engines bring the potential to rotate the fan at lower speed and allow an increase in diameter, which in turn leads to an increase in propulsive efficiency through high by-pass ratio. The low-pressure turbine stages driving the fan can also rotate at high speed resulting in fewer stages when compared to traditional turbofans. However, when operating at high speed, pressure fluctuations due to self-excited vibrations increase and may provoke flutter instabilities.

In a geared architecture, to deliver the high power required by the fan and the intermediate-pressure compressor, the low-pressure turbine system operates at higher temperatures compared to its predecessors. This phenomenon requires structural materials with higher heat resistance, which carries the inconvenience of poor welding suitability. That is the reason why alternative non-welded blade shroud joint techniques are so important, techniques as the blade interlock mechanism studied in this work.

This manuscript examines the effects of different design parameters of a low-pressure turbine blade shroud interlock on flutter stability, to make future recommendations for geared engines. The shrouded turbine rotor blades feature blade interlocks, which enhances the dynamic stability by providing stiffness to the rotor blade row. To assess the stability of the system, a parametric design of a turbine blade-disk assembly was prepared. In the parametric model the design variables that define the blade interlock are the interlock angle, interlock axial position, interlock contact length and height, knife seal position and pre-twist angle.

After parametrization, a finite element model of the turbine blade and disk assembly was prepared with cyclic symmetry boundary condition. The stresses caused by rotation were calculated in a static structural analysis and these were used as pre-stress boundary conditions in modal analysis. The modal results were afterwards exchanged with an aerodynamic model to obtain the aerodynamic damping for different blade interlock design configurations.

In the present work, the dynamic response of the first three excitation modes was analyzed. It was found that the third mode was stable for all the design points, whereas first and second modes were unstable at least for the reference design point. Among the considered six different parameters that define the blade interlock geometry, the interlock contact position turned to be the most influential parameter for modal response and for flutter stability. Moving the interlock contact position towards the trailing edge gave the most beneficial results. On the other hand, the interlock angle showed the least influence on both, the modal analysis and flutter behavior. The accomplished Design of Experiments and subsequent optimization process also conclude that there exists an interdependency between the studied parameters.
Quantification of Variation in Combustion Instability Amplitude in a Multi-Nozzle Can Combustor
Authors: Westfall Seth , Sekulich Olivia , Culler Wyatt , Peluso Stephen , O’Connor Jacqueline
Published: January 2021

In this work, we quantify the level of variation in unstable combustion oscillation amplitudes and identify the source of this variation in a multi-nozzle can combustor. At conditions where pollutant emissions are reduced, lean-premixed combustors can undergo thermoacoustic instability when pressure and heat release rate oscillations couple. A commonly used method for suppressing instability is fuel staging, which is a method where fuel is unevenly distributed between nozzles in a multi-nozzle combustor. Our work follows others who have characterized the effect of fuel staging on combustion instability and the mechanisms by which it works during both steady-state and transient operation. One of the outcomes from our previous work was that certain instability operating points display a high level of pressure oscillation amplitude variation. Instead of oscillating at a constant limit-cycle amplitude, the pressure oscillation amplitude varies significantly in time. In this work, we use the concept of permutation entropy to quantify the level of variation in the pressure fluctuation amplitude. We correlate the level of variation with a number of state variables over a range of operating conditions, 291 test cases in all. These state variables include mixture equivalence ratio; transient timescale, amplitude, and direction; hardware temperatures; gas temperatures; and thermoacoustic damping and growth rates. Significant pressure oscillation amplitude variation occurs when the thermoacoustic damping rate is low. The damping and growth rates can be low for a number of reasons, but they are highly correlated with the metal temperature of the centerbody, where the flames are anchored; lower temperatures result in lower damping rates during stable operation and lower growth rates during unstable operation. These results show the importance of the thermal boundary condition on the time-dependent behavior of the thermoacoustic instability.
Simulation of Premixed and Partially Premixed Jet-in-Crossflow Flames at High-Pressure
Authors: Stiehl Bernhard , Otero Michelle , Genova Tommy , Worbington Tyler , Reyes Jonathan , Ahmed Kareem , Martin Scott , Velez Carlos
Published: January 2021

In this paper we explore the operational map of a lean axial-staged combustor of premixed and partially premixed reacting jet-in-crossflow flames at high-pressure (5 atm). This study attempts to expand the data to relatively high pressure and could significantly aid scaling to real gas turbine engine conditions at 20–30 atm. High speed camera, PIV, CH* chemiluminescence, temperature and pressure measurements were taken and processed to allow accurate reconstruction of six operating points relative to CFD simulations under minimal adjustments. Variation of lean main stage (φ = 0.575 and 0.73) and rich jet (φ = 1.1, 4 and 8) equivalence ratio has been investigated for a four mm axial jet. The fully premixed flames were found to be controlled by the crossflow temperature before ignition and the crossflow oxygen content during combustion. Analysis of flame shape and position for the partially premixed operating points describes a lee stabilized as well as a more unsteady windward flame branch. Adjustment of added jet fuel and crossflow temperature along with its corresponding oxygen level is required to attain a compact flame body. The risk of delaying combustion progress is significantly increased at a richer jet φ = 8 and an overshooting, spatially divided flame was attained with a main stage φ = 0.73. Control towards a compact flame body is critical to allow combustion at reasonable reaction rate.
Smart Passive Control of Thermoacoustic Instability in a Bluff-Body Stabilized Combustor: A Lagrangian Analysis of Critical Structures
Authors: Premchand C. P. , Raghunathan Manikandan , Raghunath Midhun , Reeja K. V. , Sujith R. I. , Nair Vineeth
Published: January 2021

The tonal sound production during thermoacoustic instability is detrimental to the components of gas turbine and rocket engines. Identifying the root cause and controlling this oscillatory instability would enable manufacturers to save in costs of power outages and maintenance. An optimal method is to identify the structures in the flow-field that are critical to tonal sound production and perform control measures to disrupt those “critical structures”. Passive control experiments were performed by injecting a secondary micro-jet of air onto the identified regions with critical structures in the flow-field of a bluff-body stabilized, dump, turbulent combustor. Simultaneous measurements such as unsteady pressure, velocity, local and global heat release rate fluctuations are acquired in the regime of thermoacoustic instability before and after control action. The tonal sound production in this combustor is accompanied by a periodic flapping of the shear layer present in the region between the dump plane (backward-facing step) and the leading edge of the bluff-body. We obtain the trajectory of Lagrangian saddle points that dictate the flow and flame dynamics in the shear layer during thermoacoustic instability accurately by computing Lagrangian Coherent Structures. Upon injecting a secondary micro-jet with a mass flow rate of only 4% of the primary flow, nearly 90% suppression in the amplitude of pressure fluctuations are observed. The suppression thus results in sound pressure levels comparable to those obtained during stable operation of the combustor. Using Morlet wavelet transform, we see that the coherence in the dominant frequency of pressure and heat release rate oscillations during thermoacoustic instability is affected by secondary injection. The disruption of saddle point trajectories breaks the positive feedback loop between pressure and heat release rate fluctuations resulting in the observed break of coherence. Wavelet transform of global heat release rate shows a redistribution of energy content from the dominant instability frequency (acoustic time scale) to other time scales.
Numerical Studies of Novel Aero Engine Secondary Combustors for Low-NOx Emissions
Authors: Rolt Andrew , Martínez Bueno Victor , Romanelli Mirko , Sun Xiaoxiao , Gauthier Pierre , Sethi Vishal , Celis Cesar
Published: January 2021

Gas turbine thermal efficiency and fuel burn are very dependent on turbine entry temperature and overall pressure ratio (OPR). Unfortunately, increases in these two parameters compromise other key aspects of engine operation and tend to increase emissions of nitrogen oxides (NOx). The European Horizon 2020 ULTIMATE project researched advanced-cycle aero engines with synergistic combinations of novel technologies to increase thermal efficiency without increasing emissions. One candidate technology was the addition of secondary combustion to increase the mean temperature of heat addition to improve thermal efficiency while limiting the primary combustor flame temperatures and NOx formation. However, an overall reduction in NOx also requires the secondary combustor to be a low-NOx design. This paper describes numerical studies carried out on novel aero engine secondary combustor concepts developed in two MSc-thesis research projects. The studies have explored the potential of oxy-poor-flame combustion concepts. These annular combustor designs featured two distinct regions: (i) the vortex zone, which promotes recirculation of combustion products, a prerequisite for low-oxygen combustion, and (ii) a through-flow region where part of the incoming flow bypasses the vortex before the flows mix again. These studies have demonstrated the advantages and some limitations of the proposed designs and emissions assessments in comparison with previous secondary combustor studies. They suggest very low NOx is achievable with oxy-poor combustion, but will be more difficult if the incoming oxygen levels are above 10%. More-accurate assessments will require LES modelling and inclusion of the primary combustor in the simulations. However, if the low overall NOx emissions would include relatively higher levels of nitrous oxide (N2O) then this might raise concerns with respect to global warming.