bluuebunny/crossref_metadata_2025 huggingface dataset:
An Ensemble of Recurrent Neural Networks for Real Time Performance Modelling of Three-Spool Aero-Derivative Gas Turbine Engine
Authors: Ibrahem Ibrahem M. A. , Akhrif Ouassima , Moustapha Hany , Staniszewski Martin
Published: January 2021

Gas turbine is a complex system operating in non-stationary operation conditions for which traditional model-based modelling approaches have poor generalization capabilities. To address this, an investigation of a novel data driven neural networks based model approach for a three-spool aero-derivative gas turbine engine (ADGTE) for power generation during its loading and unloading conditions is reported in this paper. For this purpose, a non-linear autoregressive network with exogenous inputs (NARX) is used to develop this model in MATLAB environment using operational closed-loop data collected from Siemens (SGT-A65) ADGTE. Inspired by the way biological neural networks process information and by their structure which changes depending on their function, multiple-input single-output (MISO) NARX models with different configurations were used to represent each of the ADGTE output parameters with the same input parameters. First, data preprocessing and estimation of the order of these MISO models were performed. Next, a computer program code was developed to perform a comparative study and to select the best NARX model configuration, which can represent the system dynamics. Usage of a single neural network to represent each of the system output parameters may not be able to provide an accurate prediction for unseen data and as a consequence, provides poor generalization. To overcome this problem, an ensemble of MISO NARX models is used to represent each output parameter. The major challenge of the ensemble generation is to decide how to combine results produced by the ensemble’s components. In this paper, a novel hybrid dynamic weighting method (HDWM) is proposed. The verification of this method was performed by comparing its performance with three of the most popular basic methods for ensemble integration: basic ensemble method (BEM), median rule and dynamic weighting method (DWM). Finally, the generated ensembles of MISO NARX models for each output parameter were evaluated using unseen data (testing data). The simulation results based on datasets consisting for experimental data as well as data provided by Siemens high fidelity thermodynamic transient simulation program show improvement in accuracy and robustness by using the proposed modelling approach.
Fluctuation of Inducer Recirculation Stemming From Diffuser Stall in Centrifugal Turbomachinery Near Surge Condition
Authors: Tsukamoto Kazuhiro , Kato Chisachi
Published: January 2021

This work investigates the unsteady fluctuation of inducer recirculation stemming from the diffuser stall that occurs near the surge condition. Experiments and unsteady numerical simulation were utilized for the investigation.

Inducer recirculation is known to occur near the surge occurrence flow rate, where the flow rate has a positive slope of the performance curve and the recirculation extends to the upstream of the impeller inlet when decreasing the flow rate more. However, few papers have investigated the unsteady phenomenon of the recirculation, even though the surge is what causes it. Clarifying the recirculation phenomenon is essential in terms of expanding the operation range to the lower flow rate for centrifugal turbomachinery. This was our motivation for investigating the unsteady oscillation phenomenon of the inducer recirculation.

We investigated a single-stage centrifugal blower with the maximum pressure rise ratio of 1.2 and focused on the flow rates near surge occurrence. The blower was equipped with an open type centrifugal impeller, a vane-less diffuser, and a scroll casing. The blower performance and pressure time-history data were obtained by experiments. Unsteady simulations using large eddy simulation (LES) were conducted to investigate the flow field in the blower for each flow rate.

The obtained performance curve showed that the positive slope of the pressure rise at the lower flow rate was due to the impeller stall and that the inducer recirculation extending upstream of the suction pipe near the slope of the curve was flat. LES analysis revealed that this inducer recirculation had two typical fluctuation peaks, one at 20% of the rotation frequency and the other at 95%. We also found that the stall cell at the impeller inlet propagated in the circumferential direction and swirled at almost the same frequency as the impeller rotation. In addition, the fluctuation at the diffuser derived from the diffuser rotating stall propagated to the suction pipe.
Theoretical and Experimental Investigation of a 34 Watt Radial-Inflow Steam Turbine With Partial-Admission
Authors: Wagner Patrick H. , Van herle Jan , Schiffmann Jürg
Published: January 2021

A micro steam turbine with a tip diameter of 15 mm was designed and experimentally characterized. At the nominal mass flow rate and total-to-total pressure ratio of 2.3 kg h−1 and 2, respectively, the turbine yields a power of 34 W and a total-to-static isentropic efficiency of 37%. The steam turbine is conceived as a radial-inflow, low-reaction (15%), and partial admission (21%) machine. Since the steam mass flow rate is limited by the heat provided of the system (solid oxide fuel cell), a low-reaction and high-power-density design is preferred. The partial-admission design allows for reduced losses: The turbine rotor and stator blades are prismatic, have a radial chord length of 1 mm and a height of 0.59 mm. Since the relative rotor blade tip clearance (0.24) is high, the blade tip leakage losses are significant. Considering a fixed steam supply, this design allows to increase the blade height, and thus reducing the losses. The steam turbine drives a fan, which operates at low Mach numbers. The rotor is supported on dynamic steam-lubricated bearings; the nominal rotational speed is 175 krpm. A numerical simulation of the steam turbine is in good agreement with the experimental results. Furthermore, a novel test rig setup, featuring extremely-thin thermocouples (ϕ0.15 mm) is investigated for an operation with ambient and hot air at 220 °C. Conventional zero and one-dimensional pre-design models correlate well to the experimental results, despite the small size of the turbine blades.
Influence of Shunt Injection on Predicted Rotordynamic Coefficients of a Labyrinth Seal Using Transient CFD
Authors: Thorat Manish R. , Jin Hanxiang , Pettinato Brian
Published: January 2021

Shunt injection is one of the methods used to improve rotordynamic stability of centrifugal compressors. It involves eliminating swirl by injecting fluid in an intermediate cavity of a seal. The fluid injection is usually directed from the discharge volute or diffuser section of the compressor. In this paper, shunt injection is modeled for a center seal in a back-to-back compressor arrangement. The test case is from an actual machine which was shown to be unstable during a factory loaded mechanical test (as per API standard 617) without shunt injection and stable with shunt injection. The center seal is a tooth-on-rotor type of labyrinth seal. Impeller back-face cavity passages at the entrance and exit of the seal are also modeled. To investigate the influence on shunt injection, models with and without shunt injection geometry are considered.

Steady state Computational Fluid Dynamics (CFD) is used to study the influence on steady state characteristics such as leakage rate and swirl ratio. The CFD analysis shows a significant swirl reduction with shunt injection at the injection location. The estimated swirl ratio is 0.55 at the injection location without shunt injection and approximately 0 with shunt injection. Frequency dependent seal rotordynamic coefficients are evaluated using transient CFD. Both translational and moment coefficients are evaluated for the seal and impeller passages. For the case without shunt injection, CFD results show negative (destabilizing) effective damping from the seal at the rotor first damped natural frequency. Shunt injection case shows a positive (stabilizing) estimated effective damping at the frequency of interest. The CFD results are shown to be consistent with the factory test case observations.
Investigation of Recirculating Casing Treatment for Low-Pressure Ratio Mixed-Flow Micro-Compressor
Authors: Xu Kewei , Zha Gecheng
Published: January 2021

This paper investigates the recirculating casing treatment (RCT) of a low total pressure ratio micro-compressor to achieve stall margin enhancement while minimizing the design point efficiency penalty. Three RCT injection and extraction configurations are studied, including combined slot-duct, ducts only, and slot only. The numerical approach is validated with a tested micro-compressor using RCT. A very good agreement is achieved between the predicted speedlines and the measured results. To minimize the design point efficiency loss, it is observed that the optimal location of extraction and injection is where the recirculated flow rate can be minimized at the design point. To maximize stall margin, extraction location should favor minimizing the tip blockage such as at the location where the tip flow separation of the baseline blade is fully developed. In addition, the slot configuration that generates pre-swirl to the upstream flow is beneficial to improve stall margin due to reduced incidence. The highest stall margin enhancement achieved is 9.49% with the slot geometry that has the extraction at the 62%C chordwise location, but has a design point efficiency loss of 1.9%. Overall, a small efficiency penalty of 0.6% at the design point is achieved for the final design with the stall margin increased by 6.2%.
Ignition Studies of C1–C7 Natural Gas Blends at Gas-Turbine Relevant Conditions
Authors: Sahu Amrit Bikram , Mohamed A. Abd El-Sabor , Panigrahy Snehasish , Bourque Gilles , Curran Henry
Published: January 2021

New ignition delay time measurements of natural gas mixtures enriched with small amounts of n-hexane and n-heptane were performed in a rapid compression machine to interpret the sensitization effect of heavier hydrocarbons on auto-ignition at gas-turbine relevant conditions. The experimental data of natural gas mixtures containing alkanes from methane to n-heptane were carried out over a wide range of temperatures (840–1050 K), pressures (20–30 bar), and equivalence ratios (φ = 0.5 and 1.5). The experiments were complimented with numerical simulations using a detailed kinetic model developed to investigate the effect of n-hexane and n-heptane additions. Model predictions show that the addition of even small amounts (1–2%) of n-hexane and n-heptane can lead to increase in reactivity by ∼40–60 ms at compressed temperature (TC) = 700 K. The ignition delay time (IDT) of these mixtures decrease rapidly with an increase in concentration of up to 7.5% but becomes almost independent of the C6/C7 concentration beyond 10%. This sensitization effect of C6 and C7 is also found to be more pronounced in the temperature range 700–900 K compared to that at higher temperatures (> 900 K). The reason is attributed to the dependence of IDT primarily on H2O2(+M) ↔ 2ȮH(+M) at higher temperatures while the fuel dependent reactions such as H-atom abstraction, RȮ2 dissociation or Q.OOH + O2 reactions are less important compared to 700–900 K, where they are very important.
Large Eddy Simulations on Fan Shaped Film Cooling Hole With Various Inlet Turbulence Generation Methods
Authors: Kang Young Seok , Jun Sangook , Rhee Dong-Ho
Published: January 2021

Large eddy simulations on well-known 7-7-7 fan shaped cooling hole have been carried out. Film cooling methods are generally applied to high pressure turbine, of which flow condition is extremely turbulent because high pressure turbines are generally located downstream combustor in gas turbines. However, different to RANS simulations, implementing turbulence at the main flow inlet is not simple in LES. For this reason, several numerical techniques have been devised to give turbulence information at the inlet boundary condition in LES. In this study, rectangular turbulator was located in front of the cooling hole to generate turbulent boundary flow in the main flow. Another method used in this study is transient table method to simulate turbulent flow at the main flow inlet. Without turbulent velocity components in approaching flow, laterally discharged cooling flow touches wall while it forms a vortex structure. Then high film cooling effectiveness region around the cooling hole appears. In the meanwhile, when approaching flow is turbulent, the laterally discharged cooling flow no more forms vortex structure and dissipated to the main flow and resultant high effectiveness region disappears. Both turbulence generation methods showed that turbulent intensity of the main flow affects effective range of the cooling flow and resultant film cooling effectiveness distributions. Also high turbulence intensity of the main flow stimulates early break down of the vortex structure coming out of the cooling hole and its dissipation to the main flow. It means high turbulent intensity restricts film cooling flow coverage. Another lesson from the study is that vortex generated from the cooling hole, its development and dissipation to the main flow, have an important role to understand film cooling effectiveness distributions around the cooling hole.
Dynamics of Effusion Cooling Fluid in a Pressurized Swirl Combustor Flow
Authors: Chandh Aravind , Kazbekov Askar , Zhang Angie , Adhikari Subodh , Wu David , Emerson Ben , Rezvani Reza , Proscia William , Lieuwen Tim , Steinberg Adam
Published: January 2021

This paper presents measurements of 10 kHz acetone planar laser induced fluorescence (PLIF) to study the behavior of effusion cooling fluid injected into a non-reacting gas turbine combustor flow at elevated pressure. This study was performed as part of a larger effort to understand potential interactions of the swirling flame with the cooling air. The combustor — which was representative of a rich-burn/quick-quench/lean-burn (RQL) configuration — consisted of a swirl nozzle, quench jets, and a modular liner that could be fitted with various effusion cooling panels and optical access windows. Primary air was seeded with acetone, and passed through the swirl nozzle. Unseeded secondary air was passed on the outside of the liner, entering the combustion chamber through the quench jets and effusion panels. The PLIF laser sheet was arranged parallel to the effusion panel at various offset distances to visualize the mixing between the core flow and effusion jets. The PLIF images were analyzed with a POD-based methodology to de-noise the images and identify patterns in the effusion jet characteristics. The results show that high blowing ratios produce individual effusion jets rather than a single, coalesced film. The effusion jets are highly unsteady, interacting strongly with the turbulent flow from the swirl nozzle and dilution jets. Furthermore, the average trajectories of effusion jets are non-uniform across the panel and are shaped by upstream features in the combustor, namely swirl and dilution jets.
Integration of an Open Source Blade Geometry Generator Using a Physics Based Parameterization With the Engineering Sketch Pad
Authors: Sharma Mayank , Dannenhoffer John F. , Holder Justin , Turner Mark G.
Published: January 2021

This paper reviews an in-house turbomachinery blade generation system which integrates easily in an MDAO driven design process while providing the designer with a flexible and parsimonious parameterization scheme along with insights gained from interaction with 3D geometry. T-Blade3 is an open source 3D parametric blade geometry generator which uses a novel parameterization scheme based on the specification of the second derivative of the mean-line and a continuous modified NACA four digit thickness distribution as B-spline control points. The second derivative parameterization ensures curvature and slope of curvature continuity on the airfoil surface which leads to a smooth surface pressure distribution. Use of spanwise B-spline control points ensures the creation of smooth 3D geometries and keeps the overall parameterization space small. The Engineering Sketch Pad (ESP) is an open-source interactive web-enabled solid modeling system based on WebViewer and OpenCSM. The open-source nature of OpenCSM allows the use of user-defined primitives to create solid blade models using T-Blade3 geometries. OpenCSM also allows the computation of the sensitivity of surface points to design parameters using a combination of analytical derivatives and finite differences. Thus, the T-Blade3/ESP combinations allows a designer to interact with parametrically generated geometries and make improvements to the design using sensitivity information and a gradient based optimization loop. Furthermore, ESP enables the addition of flends (similar to fillets) to solid blade models. The resulting blades with applied centrifugal and pressure loads are then analyzed with a commercial FEM structural solver to get factor of safety relative to yield strength, natural frequencies and mode shapes.
Numerical Investigation of Dump Diffuser Combustor Performance at Uniform and Non-Uniform Inlet Conditions
Authors: Wang Heyu , Luo Kai Hong
Published: January 2021

A numerical investigation has been conducted for an axisymmetric dump diffuser combustor, which is a simplified geometry of a typical lean-burn combustor in a modern civil aero-engine gas turbine. The aerodynamic performance of the combustor is analyzed with an emphasis on two common performance parameters: static pressure recovery and total pressure loss. The former is essential in maintaining high-pressure air flow across the liner, whereas the latter involves the specific fuel consumption of the aero-engine. At first, the effects of geometrical parameters of the dump diffuser combustor are investigated. A high diffuser angle seems to be detrimental to both static pressure recovery and total pressure loss. On the other hand, a high dump gap ratio is beneficial from the aerodynamic performance point of view. However, all these desired characteristics are subject to mechanical constraints and their implications for specific consumption. Optimum values of those parameters should exist for a given desired aerodynamics performance. The majority of previous researches, including the first part of this study, have been carried out with uniform inlet conditions due to a typical independent design cycle of each component. The effects of compressor exit conditions are usually not considered in the early stage design process. In the second part of this study, various inlet conditions representing a more realistic compressor exit condition such as inlet symmetrical and asymmetrical boundary layer thickness are investigated. The performance of an asymmetrical configuration with a thin boundary layer thickness near the outer annulus is almost comparable to that of its uniform counterpart. Findings of this study provide useful input for combustor designers to improve the combustor’s performance based on the compressor exit conditions.
Development of an Integrated Procedure for Combustor Aero-Thermal Preliminary Design
Authors: Elmi Carlo Alberto , Agnolio Fabio , Ferraro Roberto , Menard Anne , Reese Hauke , Andreini Antonio
Published: January 2021

In the development of an aero-engine combustor, the definition of a preliminary design is a practice in which know-how, product experience and design rules are focal in deriving a configuration able to meet the functional requirements. Several configurations, and hence multiple geometries resulting in different behaviours, are iteratively analysed in this phase to extensively explore the design space. In this context, an automated procedure ranging from preliminary design to life estimation is necessary and crucial. A framework in which the tools employed in the design workflow are integrated and the low-added-value tasks are automated can allow the reduction of time per analysis within the loop and the enhancement of the procedure’s robustness.

In this paper will be presented the Combustor Design System Integration (DSI), a methodology aimed at easing and streamlining the design process of aero-engine combustors. To do this, digitization has been taken as the common thread for developing a data-centric approach. The logic behind the procedure will be reported, to focus then on the aero-thermal preliminary design. The procedure, for this phase, is composed of three main integrated components: a CAD generation system, which collects all the geometries for creating an exportable 3D model, a 1D thermal solver for the positioning and sizing of the aero feature on liners (i.e. cooling, dilution...) and a CFD environment with automated pre/post processing operations for reacting-flow analysis.

The aim of this work is to contextualize the DSI approach in the combustor design process and to provide a first description of the methodology designed and developed in GE Avio. For that purpose, a straight-through configuration — the lean combustor NEWAC developed in the homonymous EU project — will be exploited as a test case. The development of the procedure is still in progress, so a validation through test cell data comparison, as well as highly-resolved CFD results, will be the subject for future papers.
Progress on Forcing Pulsations for Acoustic, Thermoacoustic or Flow Control Purpose in a Pressurised Vessel by Means of a Siren
Authors: Giuliani Fabrice , Stütz Markus , Paulitsch Nina , Andracher Lukas
Published: January 2021

A siren is a robust fast-valve that generates effective flow pulsations and powerful noise levels under combustor field conditions. Its principle relies on a sonic jet sheared periodically by a cogged wheel rotating at a given speed. Developed for experiments in combustion stability, it offers an alternative to loudspeakers when the use of these is made difficult because of aggressive flow conditions (e.g. elevated conditions of pressure and temperature, presence of impurities in the gas). While the siren was designed for laboratory applications, its technology is a promising candidate for effective flow control on gas turbine fleets. By scanning through a given frequency range, one detects the acoustic resonance of specific parts of the combustor assembly and identifies a zone of combustion instability during a sensitivity analysis where the flame is exposed to calibrated perturbations. Regarding control applications, it can act out of phase for damping purposes in the low-frequency domain (phase control), or transfer the acoustic energy to a higher and less harmful sub-harmonic (modal control). Since a chocked nozzle is involved, the siren’s actuation is decoupled from the flow condition downstream, which is convenient for control. Following-up to previous works where a siren model was introduced with the capacity to vary the amplitude of pulsation independently from the frequency [GT2011-45071], this paper describes into details new features as follows. First, the performance of the apparatus was improved to visit frequencies in the 0–6 kHz range so that the operation is extended to frequencies met by precessing vortex cores in a burner or tangential instabilities in an annular combustor. Next, the discharge configuration is tested and validated as an alternative to the conventional blow-down operation with the siren placed upstream of the pressurised test cell. There, the siren is placed downstream of the test cell, deriving a small part of the pressurised air in the plenum. Finally, a new calibration procedure for fast pressure probes and accelerometers is presented and tested. A multi-modal excitation is introduced where more than one frequency peak is being produced and where the excited frequencies create a kind of a chord. In conclusion the siren is recommended as an effective flow controller, and as a broadband and powerful calibrator.
Design and Optimization of Non-Supercritical CO2 Thermal Power Cycle for “P2H2P” Energy Storage System
Authors: Burian Ondrej , Skoda Radek
Published: January 2021

Most of the current research and development of CO2 cycles for power to heat - heat to power (P2H2P) energy storage systems are focused on applications of supercritical CO2 cycles. However, this work is focused on alternative application of CO2 power cycle with standard (i.e., non-supercritical) cycle and modified industrial turboexpanders as main working machines. Thermal Cycle for power storage system with thermal energy accumulator for energy storage and non-supercritical CO2 power cycle for backward production of electricity is described in this paper. The CO2 cycle is compared with Nitrogen cycle with same parameters as well. Initially, the thermal accumulator design, option of accumulation media (molten salts or liquid metals), and its parameters are described. The main part of the paper is focused on non-supercritical CO2 power cycles. Possible configurations of cycle, design aspects of main parts of cycle, possibilities of efficiency improvement are discussed; such as regeneration or intercooling. Finally, advantages and disadvantages of this CO2 and N2 cycle are discussed and compared. The concluding result of this paper is a very similar efficiency of the two working fluids at the selected parameters.
Adjoint-Based Optimization of a Modern Jet-Engine Fan Blade
Authors: Giugno Andrea , Shahpar Shahrokh , Traverso Alberto
Published: January 2021

A Multi-point Approximation Method (MAM) coupled with adjoint is presented to increase the efficiency of a modern jet-engine fan blade. The study performed makes use of Rolls-Royce in-house suite of codes and its discrete adjoint capability. The adjoint gradient is used along with MAM to create a Design Of Experiment to enhance the optimization process. A generalized Free-Form Deformation (FFD) technique is used to parametrize the geometry, creating a design space of 180 parameters. The resulting optimum blade at design conditions is then evaluated at off-design conditions to produce the characteristic curve, which is compared with real test data. Finally, a preliminary Active Design Subspace (ADS) representing the fan efficiency is created to evaluate the robustness of the objective function in respect to the most significant design parameters. The ADS allows to collapse a large design space of the order of hundreds parameters to the few most important variables, measuring their contribution. This map is valuable in many respects to the fan designers and manufacture engineers to identify any ridges where the performance may deteriorate rapidly, hence a more robust part of the design space can easily be visualized and identified.
Experiments With a Rotor-Hybrid Gas Bearing System Undergoing Maneuver Loads From its Base Support
Authors: San Andrés Luis , Rodríguez Bryan
Published: January 2021

Gas bearings enable microturbomachinery (MTM) with a large power to weight ratio, low part count and nearly frictionless motion, thus resulting in systems operating over extended maintenance intervals and with improved fuel efficiency. Envisioned oil-free vehicle transportation systems implementing gas bearings range from small size gas turbines, to unmanned aerial vehicles, to turbochargers (TC), and more to come. In these vehicles, base or support transient displacements transmit forces exciting the rotor-bearing system; hence, the need to characterize system integrity under stringent operating conditions. This paper reports experiments demonstrating the ability of a hybrid gas bearing-rotor system to withstand maneuver actions that suddenly remove the ground support. The test rig consists of a rigid motor-rotor, supported on tilting pad hybrid gas bearings supplied with pressurized air. The rotor is housed in a thick steel casing that is attached to a rigid base plate. The whole test rig, hangs from a crane; two steel cables connect to one side of the base and a nylon webbing attaches to the other side of the base. The other end of the webbing ties to a release mechanism, which when released, frees one side of the rig base. Suddenly, the whole test rig rotates and displaces downwards while the tensions in the taut cables rapidly increase and pull the test rig as it swings back and forth. The crane support enables two release maneuvers; one turns the rig ∼90°, and the other flips it 180°, both events occurring while the rotor spins at 70 krpm (surface speed 105 m/s). The measured rotor displacements relative to the casing demonstrate a momentary increase in motion amplitude, up to ∼1.15 mm since the bearings also displace, along with a maximum casing deceleration of ∼7 g when the cables stop the rig fall. The measurements show the rotor response is free of sub synchronous whirl frequencies that could evidence a rotor dynamic instability. Very low frequency motions denote the swing frequency of the hanging rig and jerk motions from the crane lifting and bouncing when the rig is at its lowest vertical position. In one instance, power to the motor unexpectedly interrupted and the rotor underwent an unplanned shaft speed coastdown. In spite of the large displacements recorded, the rotor survived both events. It continues to operate to this day. The experiments demonstrate that the hybrid gas bearing system could withstand large amplitude rotor excursions. The measurements provide a novel method for testing gas bearings, as the induced excitations are multidirectional, while the test rig encounters a short period of free falling, followed by a quick deceleration with large forces. A simple kinetics model of the test rig drop produces peak decelerations similar in magnitude to those measured.
Analysis of the Design Bounds in Performance Limits for Industrial Axial Flow Fans
Authors: Cravero Carlo , Milanese Gabriele
Published: January 2021

The design of an industrial axial flow fan can take great advantage from the knowledge of performance limits and favourable design choices determined from its specific fluid-dynamic characteristics. As for other turbomachinery types, this fact is generally experienced through the entire design flow-path, from the preliminary design phase to the final optimization. Correlations, data and charts available from literature as well as proprietary database, exploited with many techniques (including machine learning) are resources in widespread use for this purpose. Despite the fluid dynamics of axial flow fans can be considered a well-known topic, nevertheless some specific points (e.g. the maximum achievable total-to-static efficiency) can be the subject of discussions, misunderstanding or bad design choices. The present work addresses this problem in two parts. In the first part a simple 1D model is built, for fans with and without stator, from classical theory of axial fans for pressure rise coefficient, head coefficient, flow angles and diffusion efficiency. The most relevant quantities (e.g. total-to-total efficiency, total-to-static efficiency), obtained with the 1D model, are plotted on hill charts as a function of the non-dimensional pressure rise and flow coefficient. This tool provides information that can be used for preliminary design evaluations, to understand and exploit the impact of the main design choices on the basic flow characteristics and the related performance. In the second part of the work a numerical investigation is presented on the main 3D flow characteristics that are observed to limit, both in CFD simulations and experimental tests, the performance of industrial axial fans at high-pressure rise and low-to-medium flow coefficients. Simulations results highlighted that local critical swirl ratios exist for the hub and the tip regions which, when exceeded, lead with different flow topology changes to a strong performance degradation.
Thermal Profiling of Automotive Turbochargers in Durability Tests
Authors: Pilgrim Christopher C. , Ehrhard Jan , Schinnerl Mario , Araguás-Rodríguez Silvia , Peral David , Straka Marc-Sebastian , Genschmar Mike , Karagiannopoulos Solon , Pacheco-Gutierrez Salvador , Feist Jörg P.
Published: January 2021

A major portion of the development of an automotive powertrain system is devoted to robustness and durability testing to ascertain the viability of the design. For turbochargers, thermo-mechanical fatigue is often considered as life limiting failure mechanism for the turbine section, therefore, these tests involve repeated and continuous cycling of the turbocharger for hundreds of hours. Thermocouples are used to monitor the temperature during the test, however, they only provide information at the location to which they are attached, are practically challenging to apply to all areas of interest and are prone to fail due to the thermal cycling throughout the test. As a result, there may be very limited temperature data at the end of the test. If a failure occurred in the system during the testing, the lack of temperature data can inhibit the understanding of the cause. Further testing may be required and delay product release, which add significant expense to the product development.

The Thermal History Coatings (THC) developed by Sensor Coating Systems can offer a new and unique solution to provide complimentary temperature information for this purpose. THCs are applied to the surface of a component and, when heated, the coating permanently changes according to the maximum temperature of exposure. A laser-based instrumentation system is then used to measure the coating or paint, and through calibration, the maximum temperature profile of the surface can be recorded. Although this technique is relatively new, it has been used in several turbomachinery, and other applications to capture the spatial temperature distribution of critical components. However, the turbocharger durability test presents new challenges for the technique. It has not been tested in this type of application and the extended and repeated cycling operation can test the durability of the coating and will influence the response of the coating, hence, the temperature measurements. The internal surfaces of the turbocharger will also be exposed to the exhaust gases of the combustion process.

In this paper, the capability of the THC for this application was investigated. For the first time, the effect of cyclic operation on the THC is reported. The measurement capability was demonstrated on two turbine housings tested on a gas stand, one for a single cycle, another for 10 cycles. The results show that the surface temperature profile of the two turbine housings can be accurately recorded and the results are validated against the installed thermocouples. The demonstration indicates that the THC can be used to acquire accurate and detailed spatial temperature distributions, which significantly enhance the information from thermocouples alone. This information can be used to improve the interpretation of the durability test and hence accelerate new product release.
Axial Compressor Fouling and its Effect on Gas Turbine Fuel Consumption and Emissions
Authors: Allen Cody W. , Balaji Purushotham , de Oliveira Maurício
Published: January 2021

The literature contains many studies relating gas turbine axial compressor degradation with impurities entering the inlet flow path. The collision and adhering of these impurities onto compressor blades can produce both recoverable and non-recoverable degradation in the compressor, leading to lost overall efficiency. More recently, the topic of how to optimally schedule when compressor washes should occur has been investigated. In many of the scheduling optimization studies, the cost associated with the change in fuel flow for a given fouled state is characterized indirectly as part of an overall fuel calculation for a given fouled state.

In this paper, we aim to quantitatively answer the question of what this small quantity of fuel due to compressor fouling actually is. Additionally, we show how this can be included in solving for optimal schedules of compressor washes and estimate the CO2 emissions attributable to compressor fouling. We begin with a look at the literature on compressor fouling to identify common methods and assumptions of how fouling can manifest or be imposed. We then derive a first principles, steady state equation to relate compressor performance parameters with fuel flow. We validate this equation at nominal conditions with data obtained from Solar Turbine’s test cells. Additionally, we develop a generic industrial gas turbine model using the Numerical Propulsion System Simulation software and apply the fouling constraints found from the literature review to run a fouling simulation. The results further validate our equation and provide insight into the quantity of fuel resulting from compressor fouling. We end the paper with a look at how the derived model can be used in the problem of optimizing compressor wash schedules as well as give an estimate on increases in CO2 emissions due to compressor fouling.
Numerical Analysis of Flutter in Variable Geometry Compressors
Authors: Suzuki Kentaro , Zhao Fanzhou , Vahdati Mehdi
Published: January 2021

Aeroelastic behaviour of a transonic rotor in a newly designed 1.5 stage compressor with variable geometry is studied numerically in this paper. The stage is intended to be the front part of a one-shafted large frame industrial gas turbine (IGT) compressor. The compressor was designed using open-source software MULTALL and numerical computations were performed using the three-dimensional aeroelasticity code AU3d, which has been tested and validated for many aeroelastic test cases over the past 25 years. Flutter analysis for the 1F mode was performed at various design and off-design operating conditions which are typically experienced in IGT (varied inlet temperature and inlet guide vane angle). Although in all the cases the rotor remained stable, clear trends in aerodynamic damping were observed, which can be explained by shock position. In the last phase, the effects of increased tip gap size on the flutter stability were studied. The increase in tip clearance did not result in flutter; unsteady computations without blade motion showed a tip rotating instability with 11 cells travelling at 84% of the shaft speed in the stationary frame. Due to the frequency proximity between the rotating instability and blade natural vibration mode, large amplitude displacement driven by lock-in was observed in the fluid-structure coupled simulation. It was concluded that this type of aeroelastic instability which can be mistaken for flutter is the main threat for this IGT compressor.
Physical Quantity Synergy in the Internal Flow Field and Application in Radial-Inflow Turbines
Authors: Shao Ziyi , Zhang Xuehui , Wang Xing , Zhu Yangli , Li Wen , Chen Haisheng
Published: January 2021

The internal flow field and loss distributions are quite complicated in the radial-inflow turbine. It is necessary to reinforce physical understandings of the relationship between the flow and loss. Inspired by the synergy principle in the convective heat transfer, the synergy applicable for the radial turbine is innovatively derived from the Navier-Stokes equations. According to the mathematical expression, the smaller the synergy angle is, the higher flow resistance and loss should be. The paper attempts to assess the validation of the synergy principle in the radial turbine based on numerical simulations firstly, then the relationship between the synergy angle and loss is analyzed in detail. It is found that the regions where high total pressure loss coefficient and high dimensionless entropy generation locate correspond to the relatively small synergy angle, which agrees well with the mathematical analysis. The relatively low streamwise synergy angle corresponds to the high-loss regions near the suction side and wake on the blade-to-blade stream surface. The relatively low spanwise and circumferential synergy angle correspond to the high-loss regions near the tip clearance and wake on the span-theta stream surface. Under off-designed conditions, the synergy principle also shows great performance as an apparent negative correlation of total pressure loss coefficient versus circumferential synergy angle could be perceived.
Multi-Variable Adaptive Control Method for Turbofan Engine With Dynamic and Input Uncertainties
Authors: Liu Jiashuai , Wang Xi , Zhu Meiyin , Miao Keqiang
Published: January 2021

The dynamic characteristics of the turbofan engine vary greatly in the full flight envelope, which makes the problem of dynamic uncertainty and input uncertainty very prominent. This brings different degrees of performance impact to the engine control system and even makes it lose stability. This paper proposes an adaptive variable parameter control method for dealing with multivariable dynamic uncertainty and input uncertainty. In this paper, the dynamic uncertainty and input uncertainty are mathematically converted into standard matched uncertainty, which can be handled more conveniently. Firstly, in the state space model, for the case where the number of state variables is less than or equal to the number of input variables and the input matrix satisfies the full-rank condition of the row, the existence of the right pseudo-inverse matrix of the input matrix can be guaranteed. So the dynamic uncertainty can be separated from the system matrix, and the input uncertainty can be separated from the input matrix. Thus these uncertainties are equivalently transformed into parametric matched uncertainty. Then the matched uncertainty model with two vectors of bounded basis functions is established. Secondly, the Lyapunov quadratic function is constructed by the closed-loop tracking error vector and the adaptively adjustable control parameter estimation errors, and the Lyapunov stability constraint is considered. Then, under the premise of considering the dynamic characteristics of the actuator, an adaptive control algorithm for multivariable matched uncertainty model of turbofan engine is derived. Finally, ground and high altitude simulations are carried out on the dual-loop control system based on the nonlinear dynamic model of the turbofan engine. The results show that the control system has robust stability and anti-interference performance for dynamic uncertainty and input uncertainty of turbofan engine in the full flight envelope. The fan speed control loop basically achieves no static error tracking. The dynamic error of the core speed control loop is less than 0.6% and the steady state error is less than 0.05%. By introducing stronger parameter change rate information to the controller, its performance can be further improved, and the transient state control is more stable.
Effects of Film Hole Shape and Turbulence Intensity on the Thermal Field Downstream of Single Row Film Holes
Authors: Zhang Zheng , Zhu Hui-ren , Xu Wei-jiang , Liu Cun-liang , Wu Zhuang
Published: January 2021

A nylon mesh coated with broadband thermochromic liquid crystal was set in different planes perpendicular to the mainstream direction at various locations downstream of the film hole. By the temperature visualization technique, the colorful non-dimensional temperature images on the nylon mesh of cylindrical hole, water-drop hole and dustpan shaped hole at different blowing ratios and turbulence at angle of 30° and 60° were visualized. The visualization experiment visually studied the effects of hole shape, hole inclination angle, blowing ratio and mainstream turbulence on the distribution of the film. The results show that stream-wise diffusion of water-drop hole reduces kidney vortex intensity, making higher attachment of the film of water-drop than that of cylindrical hole, consequently the lateral coverage range of water-drop hole film is wider than that of cylindrical hole film. The lateral diffusion of dustpan shaped hole further reduces the kidney vortex intensity. This obviously increases the film coverage and strengthens the adhesion of film of dustpan shaped hole. Increasing the inclination angle of the hole and the blowing ratio will increase the normal velocity of the jet and increase the thickness of the film. however, increasing inclination angle and blowing ratio will enhance kidney vortex intensity and decrease the film cooling effectiveness. The high turbulent intensity of mainstream will enhance the lateral diffusion of the film and enhance the mixing of the secondary flow and mainstream, so the continuity and uniformity of film are better. However, the intense mix of secondary flow and mainstream results in the non-dimensional temperature of the film drops sharply and the film coverage reduced accordingly.
Wetness Measurement and Droplet Transport Analysis in Actual Steam Test on a Scaled Low Pressure Turbine
Authors: Sasao Yasuhiro , Segawa Kiyoshi , Kudo Takeshi , Takata Ryo , Osako Masaki , Yamamoto Satoru
Published: January 2021

Understanding the phenomenon and quantitative prediction of wet loss, quantitative prediction of erosion are still challenges in ST development. The aim of the actual steam test reported in this paper was to verify the performance of a newly developed ST. Still a comprehensive understanding of the wetness phenomenon is also a significant issue. Therefore, in connection with the actual steam test, efforts were made to develop a method for analyzing the three-dimensional causes of wetness loss and erosion. As the first report on the wet phenomenon analysis performed in this actual steam test, this paper reports wet measurement results and analysis results. In the actual steam testing of a 0.33 scaled steam turbine, wetness measurements were carried out at the third stage (L-1) and the final stage (L-0), and its characteristic wetness distribution was analyzed using our original CFD-code MHPS-NT.

This 0.33 scaled steam turbine consists of the final three stages (LP-end) and the inlet steam conditioning stage (total of four stages), and wetness distributions in the blade height-wise were measured using two different wetness probes under several operating conditions. Wetness distribution did not change linearly with changes in ST inlet temperature, but dynamic changes in peak position and shape were observed. From the ST inlet to the exhaust chamber, the generation of fine droplets, the capturing of droplets by the wall surfaces, and the behavior of water films and coarse droplets were comprehensively analyzed using a three-dimensional (3-D) unsteady Eulerian-Lagrangian coupling solver that takes into account non-equilibrium condensation. This CFD code (MHPS-NT) is an improved version of Original-NT developed by Tohoku University. By considering the relative position and structure of the wet probe and blade cascade in CFD, it was found that the wetness is formed remarkable circumferential distribution by the moisture separation of the upstream blade rows and end-walls. The circumferential distribution of wetness can be a factor that makes it difficult to grasp the liquid phase distribution inside the steam turbine as an error factor independent of the accuracy of the optical measurement device. Due to the effects of water droplet capturing, the LP-end outlet wetness at the design point may be underestimated by 21% relative. It is also reported that because the wetness has a distribution in the meridian direction, wetness measurements by the wet probe may contain measurement errors independent of the measurement accuracy.