bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvement of Steam Turbine Blade Foil With Biomimetic Design and its Influence on Aerodynamic Performance
Authors: Wu Fan , Xie Danmei , Zhang Jing , Zhang Hengliang , Wang Chun
Published: November 2019

To improve the steam turbines’ efficiency, researchers have put their efforts on blade foil design. Aiming at improve the aerodynamic performance of steam turbine at low load, this paper will study the effect of blade foil with bionics design on steam turbine aerodynamic performance, based on humpback whale’s fin. This paper mainly discusses a bionic foil design used on steam turbine. There are three main control parameters for each tubercle structure — amplitude, wavelength, and thickness. Taking the axial torque as the decisive consideration data and combining the vorticity diagram to analyze the flow, and on this basis, the influence of the vortex pair on the flow of the turbine blade is studied. The greater the torque, the stronger the function, so the steam turbines’ efficiency is higher.

The flow condition of the optimized blade shape is improved compared to the original blade shape because it fits the blade more closely and the separated flow vortex is suppressed.
Design and Test of a Novel Highly-Loaded Compressor
Authors: Yang Chengwu , Han Ge , Zhao Shengfeng , Lu Xingen , Zhang Yanfeng , Li Ziliang
Published: November 2019

The blades of rear stages in small size core compressors are reduced to shorter than 20 mm or even less due to overall high pressure ratio. The growing of tip clearance-to-blade height ratio of the rear stages enhance the leakage flow and increase the possibility of a strong clearance sensitivity, thus limiting the compressor efficiency and stability. A new concept of compressor, namely diffuser passage compressor (DP), for small size core compressors was introduced. The design aims at making the compressors robust to tip clearance leakage flow by reducing pressure difference between pressure and suction surfaces. To validate the concept, the second stage of a two-stage highly loaded axial compressor was designed with DP rotor according to a diffuser map. The diffuser passage stage has the same inlet condition and loading as the conventional compressor (CNV) stage, of which the work coefficient is around 0.37. The predicted performance and flow field of the DP were compared with the conventional axial compressor in detail. The rig testing was supplemented with the numerical predictions. Results reveal that the throttle characteristic of DP indicates higher pressure rise and the loss reduction in tip clearance is mainly responsible for the performance improvement. For the compressor with DP, the pressure and flow angle are more uniform on exit plane. What’s more, the rotor with diffused passage reveals more robust than the conventional rotor at double clearance gap. Furthermore, the experimental data indicate that DP presents higher pressure rise at design and part speeds. At design speed, the stall margin was extended by 7.25%. Moreover, peak adiabatic efficiency of DP is also higher than that of CNV by about 0.7%.
Analysis of Solid Particle Ingestion and Dynamics in a Turbomachine Using Large-Eddy Simulation
Authors: Martin Benjamin , Thomas Martin , Dombard Jérôme , Duchaine Florent , Gicquel Laurent
Published: November 2019

Erosion of compressor and turbine blades operating in extreme environment fouled with sand particles, ash or soot is a serious problem for gas turbine manufacturers and users. Indeed, operation of a gas turbine engine in such hostile conditions leads to drastic degradation of the aerodynamic performance of the components, mostly through surface roughness modification, tip clearance height increase or blunting of blade leading edges. To evaluate associated risks, the computation of particle trajectories and impacts through multiple turbomachinery stages by Computational Fluid Dynamics (CFD) seems a decent path but remains a challenge. The numerical prediction of complex turbulent flows in compressors and turbines is however necessary in such a context and validations are still required. Recently, Large-Eddy Simulation (LES) has shown promising results for compressor and turbine configurations for a wide range of operating conditions at an acceptable cost. With this in mind, this article presents the assessment of a LES solver able to treat turbomachine configurations to predict solid particle motion. To do so, the governing equations of particle dynamics are introduced using the Lagrangian formalism and are solved to compute locations and conditions of impact, namely particle velocity, angle and radius. The fully unsteady and coupled strategy is applied to blade geometries for studying the main areas and conditions of impacts obtained with LES. For comparison, a one-way coupling computation based on a mean steady flow field where only the Lagrangian particles are advanced in time is performed to evaluate the gain and drawbacks of both methods.
Deficiencies in Turbulence Modelling for the Prediction of the Stability Boundary in Highly Loaded Compressors
Authors: Moreno Jose , Dodds John , Vahdati Mehdi , Stapelfeldt Sina
Published: November 2019

Reynolds-averaged Navier-Stokes (RANS) equations are employed for aerodynamic and aeroelastic modelling in axial compressors. Their solutions are highly dependent on the turbulence models for closure. The main objective of this work is to assess the widely used Spalart-Allmaras model’s suitability for compressor flows. For this purpose, an extensive investigation of the sources of uncertainties in a high-speed multi-stage compressor rig was carried out. The grid resolution near the casing end wall, which affects the tip leakage flow and casing boundary layer, was found to have a major effect on the stability limit prediction. Refinements in this region led to a stall margin loss prediction. It was found that this loss was exclusively due to the destruction term in the SA model.
Validation of Fracture Prediction Model to Design CMC Turbine Vane
Authors: Sato Hayao , Ueda Yusuke , Andoh Masaharu , Honda Tatsuhito
Published: November 2019

Ceramics matrix composites (CMCs) have higher heat resistance and specific strength than conventional metal. These effects can contribute to not only reducing cooling air and parts weight, but also increasing turbine inlet temperature (TIT). As a result, CMCs have potential to improve aero-engine performance and reducing emission. CMCs also have complicated material characteristics to apply aero engine turbine parts. Stress-strain curve shows not only non-liner behavior in higher stress level but also anisotropy. The behavior and fracture toughness show the anisotropy because of material internal structure. Material strengths indicate anisotropy as well. Low cycle fatigue (LCF) strength indicates dependency of stress gradient. Thus, conventional design methods using linear elastic analysis model and peak stress assessment are too conservative to design CMC parts. IHI is developing SiC-SiC 3D woven fabric which is used for aero engine turbine vane and also building up a fracture prediction model to design the CMC turbine vane. Fracture prediction model is composed of structural analysis model to estimate deformation and fracture evaluation model to predict strength. The material model is assumed as a homogeneous substance and this material model constitutive equation is constructed from the theory of continuum damage mechanics (TCDM). In fracture model, that strength parameter is calculated with averaging stress fields. Multi-axial stress fields are evaluated by engineering equations referred to Hashin’s criteria. To validate our fracture prediction model, specific structural feature test were conducted. Sub-component tests were based on the building block approach that was general to validate structural reliability of composite material parts. Static tests and low cycle and high cycle fatigue tests were carried out at room temperature and high temperature. The validation test results showed good agreement with prediction. Finally we have made sure the validation of this fracture prediction model.
Surrogate Estimations of Complete Flow Fields of Fan Stage Designs via Deep Neural Networks
Authors: Aulich Marcel , Küppers Fabian , Schmitz Andreas , Voß Christian
Published: November 2019

This paper presents a first step to adapt deep neural networks (DNN) to turbomachinery designs. It is demonstrated that DNNs can predict complete flow solutions, using xyzcoordinates of the CFD mesh, rotational speed and boundary conditions as input to predict the velocities, pressure and density in the flow field.

The presented DNN is trained by only twenty random 3D fan stage designs (training members). These designs were part of the initialization process of a previous optimization. The approximation quality of the DNN is validated on a random and a Pareto optimal design. The random design is a statistical outlier with low efficiency while the Pareto optimal design dominates the training members in terms of efficiency. So both test members require some extrapolation quality of the DNN. The DNN reproduces characteristics of the flow of both designs, showing its capability of generalization and potential for future applications.

The paper begins with an explanation of the DNN concept, which is based on convolutional layers. Based on the working principal of these layers a conversion of a CFD mesh to a suitable DNN input is derived. This conversion ensures that the DNNs can work in a similar way as in image recognition, where DNNs show superior results in comparison to other models.
Numerical Investigation of a Turbine Guide Vane Exposed to Rotating Detonation Exhaust Flow
Authors: Asli Majid , Cuciumita Cleopatra , Stathopoulos Panagiotis , Paschereit Christian Oliver
Published: November 2019

Detonative Pressure Gain Combustion has the potential to increase the propulsion efficiency of aero-engines and the thermal efficiency of stationary gas turbines. Important advances were made in this field, especially in the case of Rotating Detonation Combustion (RDC). Although experimental and numerical studies reported in the literature have significantly increased in number, the major open problem is a lack of efficient turbomachinery to transform the fluctuating potential energy from an RDC into power output. For this problem to be properly addressed, time resolved data at the outlet of an RDC needs to be collected. As a first step, numerical data can be used to generate a geometry for the turbine, which must be validated experimentally. To determine the performance of a turbine vane row, total pressure losses need to be measured. There are several challenges in measuring the total pressure between the outlet of an RDC and the inlet of a turbine vane row. The high temperature values, the distance of the pressure transducer from the outlet of the combustor lead to a lower time resolution of the pressure signal. The confined space is also an issue, allowing for very few options in measuring the total pressure. Another major problem is the shock wave that may form as a detached shock wave with respect to the body of the pressure probe at certain moments in the flow cycle, which leads to measuring a different value rather than the actual value of the flow field. To address these issues, the current study presents a numerical investigation of a guide vane row that was experimentally tested at the outlet of an RDC working on hydrogen and air under stoichiometric conditions. One of the vane rows was 3D printed with a geometry allowing the measurement of total pressure. Static pressure at the outlet of the RDC was also measured. It was observed that the measured pressures are average values in time. Based on these averages, the total inlet pressure and velocity variations in time were reconstructed in an exponential trend, according to the ones reported in the literature and the aforementioned experiments. These variations were set as inlet conditions for transient numerical simulations. Results show that the total pressure amplitude decreases significantly when the flow passes the annulus and the vanes as well. By looking in to the flow field detail, the presence of shock wave in front of the blade is investigated. Additionally, it is calculated that the average total pressure decreases 7.9% by the vane row.
High Speed Single Cavity Rig With Axial Throughflow of Cooling Air: Rig Structure and Periphery
Authors: Diemel Eric , Odenbach Stefan , Uffrecht Wieland , Villazon Jose Rey , Valencia Antonio Guijarro , Reinecke Mike
Published: November 2019

Appropriate understanding of heat transfer and temperature distribution of gas-turbine compressor disks is very important for mechanical rotor design. Accurate prediction of disk metal temperatures is key to ensure safe operation and furthermore rotor tip clearances has a significant influence on the compressor efficiency. Despite great improvements in the prediction of fluid motion and heat transfer in complex systems, the increasingly demanding requirement for more efficient compressors demands more accurate understanding of the flow around those disks. Therefore, a research rig has been designed and built which has thermal and aerodynamic analogy to high pressure compressor rotor cavities in gas-turbine engines aiming at gathering data at engine representative conditions. The rig consists of two disks, a cylindrical shroud and a stationary inner shaft. To simulate those conditions a heating and chilling module has been designed to enable the emulation of disk thermal gradients. For changing the operating point a flow delivery system with ten valves and two air heaters will be used. By measuring the radial pressure distribution inside the cavity it is possible to calculate the tangential velocity of the fluid core. In addition to that the disc and fluid temperature inside the cavity will be measured by a telemetry system, as well as the inlet and outlet condition of the fluid entering and leaving the cavity.
Towards Scale Resolving Computations of Condensing Wet Steam Flows
Authors: Post Pascal , Sembritzky Marwick , di Mare Francesca
Published: November 2019

In this paper we present a turbomachinery density-based CFD solver optimized for CPUs as well as GPUs, which accounts for complex thermodynamics including non-equilibrium condensation and two-phase flow, making extensive use of tabulation techniques. The two-phase flow is treated by means of the mono-dispersed Source-Term Euler-Euler model. The non-equilibrium wet-steam model is validated in classical nozzle test cases and its application in turbomachinery configuration is demonstrated in a well-documented steam turbine cascade in the context of classic RANS modeling. Finally, the LES-solver performance and scalability, together with its accuracy, are assessed and discussed on the basis of the well-known and theoretically relevant experiment by Comte-Bellot and Corrsin. For both, standard RANS computations, where an upwind schemes has been adopted, as well as for the LES computations, where a central scheme in skew-symmetric form has been employed, the solver shows remarkable computational speed and accuracy for non-ideal gas applications, rendering it suitable for more complex LES computations in steam turbine flows.
Structural Analysis of an Auxetic Casing Structure Incorporating Tip Blowing Casing Treatment Modification
Authors: Schmidt Tobias , Lorenz Jan , Gümmer Volker , Hupfer Andreas
Published: November 2019

In axial compressor design for aero engines high system efficiency and operational stability are two main objectives. Both depend on clearance-induced losses. Previous investigations at the Institute have resulted in a passive clearance controlled compressor design using additively manufactured auxetic casing structures. The extension to an active clearance controlled device to keep an approximately constant tip gap ratio during the entire flight mission is currently investigated. Constructive on these deliverables, the implementation of tip blowing casing treatment modification in a double-walled compressor casing including an auxetic inner structure is covered in this work and studied for maximum load conditions by means of Finite Element Analysis. The idea to supplement the current auxetic casing construction with casing treatment modification emerges from the aspiration to generate further stability improvements in the high-pressure domain and the exploitation of the design freedom provided by additive manufacturing. Key issues addressed in this work by conducting parameter studies are casing treatment positioning and corresponding structural correlations depending on circumferential quantity. The evaluation section concentrates mainly on the calculated stress level associated with tip blowing casing treatments because this value is crucial for prospective fatigue predictions. In order to compare the results, the auxetic casing structure without casing treatment modification serves as reference. Promising solutions for local stress reductions are also proposed and discussed.

From a structural mechanics perspective, the casing treatment modification generates very high and comparable notch stress levels at each position. Placing the casing treatments at the framework of the auxetic cells and splitting the inner casing ring results in tolerable stress levels.
Reducing Secondary Flow Losses in Low-Pressure Turbines With Blade Fences: Part II — Experimental Validation on Linear Cascades
Authors: Giovannini Matteo , Rubechini Filippo , Amato Giorgio , Arnone Andrea , Simoni Daniele , Yepmo Vianney , Satta Francesca , Bertini Francesco
Published: November 2019

This paper deals with the design of passive control devices for reducing the impact of secondary flows on the aerodynamics of low-pressure turbine (LPT) stages. A novel kind of device is introduced which consists of shelf-like fences to be added to the blade surface. Such a device is intended to contrast the development of secondary flows, thus reducing losses and flow turning deviation with respect to the straight blade.

In this second part, an experimental campaign on a linear cascade is presented which is aimed at proving the beneficial impact of the blade fences. Experiments were carried out on a low-speed test-rig, equipped with a large scale blade representative of the stators of the engine-like environment considered in part I. Measurements are mainly focused on the stator losses and on the flow field at the stator exit. The performance of the blade fences was evaluated by comparing the straight cascade and the fenced ones. The measurements highlighted the impact of the blade fences on the development of the secondary flows, affecting both the stator losses and the non-uniformity of the flow field over the exit plane, which, in the actual stage environment, impacts the operation of the downstream blade row. Moreover, the comparison between CFD and experiments proved the accuracy of the CFD setup, thus suggesting its reliability in predicting the stage performance in the engine-like configuration.
Favre-Averaged Fourier-Based Methods for Gas Turbine Flows
Authors: Wang Feng , di Mare Luca , Adami Paolo
Published: November 2019

Steady Reynolds-Averaged Navier-Stokes (RANS) simulations are the workhorse of turbomachinery design. Recent trends in gas turbine design require full consideration of flow unsteadiness at the design stage to address issues of performance as well as integrity. Unsteady calculations using non-linear time marching methods are too computationally expensive to be used at the design stage. An alternative way is needed to reduce computational cost whilst retaining control on the accuracy of the simulations. To address this need, this paper presents a framework of Fourier-based methods for turbomachinery flows. The method is based on the non-linear harmonic (NLH) method. The method uses the favourable properties of Favre-averaging to obtain a simpler and more flexible formulation of the time-averaged system for NLH. This is ideal for implementing NLH in a CFD code where minimum modifications are desired. The approach allows the fidelity of the simulations to be tuned by switching on or off the coupling between the flow perturbations and the mean flow or the cross-coupling among the harmonics. This leads to a range of modelling fidelity for unsteady flows. For example, if the unsteady flow is linear, a linear harmonic method is sufficient for the design instead of using a harmonic balance simulation which has extra computational cost and slower convergence. The method has been tested on compressors and turbines which covers gas turbine flows in a range of flow regimes. Good agreement with data from non-linear time marching simulations are observed for all cases.
The Effect of Surface Tension on Bubble Generation in Gas-Sheared Liquid Films
Authors: Vasques João , Ibrahim Abubakr , Hann David , Simmons Kathy , Walsh Michael
Published: November 2019

In the bearings of an aero-engine, oil is supplied not only for lubrication, but mostly for cooling, where heat is removed from the hot walls of the chambers by the oil films that are formed there. Based on prior work, it is observed that air bubbles can become trapped within liquid films potentially affecting fluid behavior.

This paper reports on experiments conducted in a horizontal rectangular duct, where the liquid phase was sheared by a strong gas stream. In this configuration, air bubbles are seen to be entrapped in a similar manner to what was observed within prior bearing chamber visualization research. Of particular interest in this paper, is the effect of surface tension on air bubble generation in the liquid phase and its consequences for appropriate oil selection criteria. The surface tension was controlled by testing solutions with reduced surface tension by up to 47% of that of water, while maintaining the density and viscosity parameters constant. The results were obtained using a Brightness-Based Laser-Induced Fluorescence technique.

Results show that reducing surface tension leads to a higher number of bubbles being generated, thus increasing the level of aeration of the liquid phase. Additionally, the velocity of the bubbles was also measured and seen to be lower for the lower surface tension cases.
Accuracy Assessment of Steady and Unsteady Multistage High Pressure Compressor Simulations
Authors: Lück Sebastian , Kuntzagk Stefan , Doebbener Guido , Kellersmann Andreas , Bode Christoph , Friedrichs Jens
Published: November 2019

In this paper a comparison of the performance parameters and flow characteristics of a mature commercial high bypass engine’s 9-stages high pressure compressor (HPC) with steady-state mixing-plane (RANS) and unsteady RANS (URANS) CFD is carried out. The investigation is based on a numerical model of the CFM56-5C engine’s HPC which is installed on the Airbus A340-300 aircraft. The compressor under investigation features the so called 3D blading which is the first of two performance improvement packages available. An experimental engine of this type equipped with extensive additional instrumentation is in use by Lufthansa Technik to deliver detailed experimental data of the gas path. Experimental results have been discussed in previous works of the authors.

In order to provide long-term forecasts of an engine’s state the aforementioned CFD model has been included into a multilevel engine model.

To be able to evaluate the significance and applicability of the CFD results into such model, it is of great interest to which extent and level of detail it can deliver accurate performance predictions.

From the comparison of both steady-state and unsteady simulation results it is found that overall compressor performance only differs negligibly while stage performance can differ significantly. It is depicted that among the stator vanes of the front stages local supersonic flow and flow separation can occur. These are not captured by the steady-state simulation to the same degree a time resolved simulation does. In rear stages differences fade and unsteady methods tend to predict better stage performance which may be due to favourable effects of rotor-stator interaction.
Comparison of Machine Learning Algorithms in the Interpolation and Extrapolation of Flame Describing Functions
Authors: McCartney Michael , Haeringer Matthias , Polifke Wolfgang
Published: November 2019

This paper examines and compares commonly used Machine Learning algorithms in their performance in interpolation and extrapolation of FDFs, based on experimental and simulation data. Algorithm performance is evaluated by interpolating and extrapolating FDFs and then the impact of errors on the limit cycle amplitudes are evaluated using the xFDF framework. The best algorithms in interpolation and extrapolation were found to be the widely used cubic spline interpolation, as well as the Gaussian Processes regressor. The data itself was found to be an important factor in defining the predictive performance of a model, therefore a method of optimally selecting data points at test time using Gaussian Processes was demonstrated. The aim of this is to allow a minimal amount of data points to be collected while still providing enough information to model the FDF accurately. The extrapolation performance was shown to decay very quickly with distance from the domain and so emphasis should be put on selecting measurement points in order to expand the covered domain. Gaussian Processes also give an indication of confidence on its predictions and is used to carry out uncertainty quantification, in order to understand model sensitivities. This was demonstrated through application to the xFDF framework.
An Inverse Approach to Identify Tuned Aerodynamic Damping, System Frequencies and Mistuning: Part 3 — Application to Engine Data
Authors: Figaschewsky Felix , Kühhorn Arnold , Beirow Bernd , Giersch Thomas , Schrape Sven , Nipkau Jens
Published: November 2019

A novel approach for the identification of tuned aerodynamic damping, system frequencies, forcing and mistuning has been introduced in the first part of this paper. It is based on the forced response equations of motion for a blade dominated mode family. A least squares formulation allows to identify the system’s parameters directly from measured frequency response functions (FRFs) of all blades recorded during a sweep through a resonance. The second part has dealt with its modification and application to experimental modal analyses of blisks at rest.

This 3rd part aims at presenting the application of the approach to blade tip timing (BTT) data acquired in rig tests. Therefore, blisk rotors of two different engines are studied: a single stage fan rig and a 4.5 stage high pressure compressor (HPC) rig. The rig test campaign of the fan blisk included also an intentional mistuning experiment that allows to study the performance of the identification approach for a similar rotor with two different mistuning levels. It is demonstrated that the approach can identify aerodynamic damping curves, system frequencies, mistuning pattern and forced travelling wave modes (TWMs) from state of the art BTT data monitored during rig or engine tests. All derived mistuning patterns could be verified with reference measurements at standstill. The derived aerodynamic damping curves and system frequencies show a reasonable agreement with simulations. For the HPC case a multitude of excited TWMs could be identified which also lines up with previous simulations.
An Overview of Initial Operational Experience With the Closed-Loop sCO2 Test Facility at Cranfield University
Authors: Anselmi Eduardo , Bunce Ian , Pachidis Vassilios
Published: November 2019

An experimental facility is currently operating at Cranfield University in the UK and it is being used to explore supercritical carbon dioxide as a working fluid for future bottoming power cycle applications. The initial objective of this experimental programme is to de-risk and demonstrate the robustness of a closed-loop system, whilst proving the function and performance of individual components and various measurement and control modules. This paper describes the first operational experience gained whilst operating the test facility. More specifically, it summarizes the lessons learned from the commissioning phase and first test campaigns carried out in 2018.
Transient Thermodynamic Modeling of Air Cooler in Supercritical CO2 Brayton Cycle for Solar Molten Salt Application
Authors: Deshmukh Ankur , Kapat Jayanta , Khadse Akshay
Published: November 2019

Supercritical CO2 Brayton power cycle is getting commercially attractive for power generation due to its numerous advantages like zero water discharge, compactness, low environmental emission and potential to reach high thermal efficiency at lower costs. A typical recuperated sCO2 closed cycle consists of three heat exchangers (main heat exchanger, cooler and recuperator) and two turbomachinery (sCO2 turbine and sCO2 compressor). The cooler which can use air or water as heat sink is the focus of this study. The purpose of the paper is investigation of behavior of thermodynamic parameters of cooler during transient operations. In this study, dynamic simulation is performed to analyze the transient behavior of air cooler in sCO2 cycle using molten salt as heat source from solar energy. Transient study is critical to understand the thermodynamic behavior of each system with time. Rapid changes in ambient temperature, operating loads, start-ups and shutdowns affect the performance of the turbomachinery and heat exchangers. The change in the thermal performance of air cooler with the change in boundary conditions is demonstrated here. The simulation is setup by having a steady state design of 100MWe sCO2 cycle with operating temperature of 700°C and pressure of 250 barA. Dynamic calculations are done using LMS AMESim. Transients studied in this paper include (i) step variation (ii) standard variation (iii) linear variation of air temperature. This work thus serves as a framework to develop a design basis for sCO2 cycle components as a function of transient operating conditions.
Application Concepts and Experimental Validation of Constitutive Material Models for Creep-Fatigue Assessment of Components
Authors: Kontermann Christian , Linn Stefan , Oechsner Matthias
Published: November 2019

The possibility to use real operational data as an input for lifetime assessment methods is a key requirement in terms of both service applications as well as within the design of components by underlying specific service relevant scenarios. To address this, so called “Constitutive Viscoplastic Material Models” have been developed which represent a more generalized alternative for assessing turbo machinery components which undergo an irregular creep-fatigue loading.

Based on several experimental and theory related national research programs, performed within the German working group W10 in the last years, the current status of the model development and the performance potentials are summarized in this paper. Within the first part, the general and developed model structure of one candidate material model is introduced by discussing different aspects of the equation system together with the specific practical related aspects. Secondly, the validation of this constitutive material model is shown by comparing the model results with a set of conducted complex experiments, like ansiothermal service like experiments performed on smooth, notched and biaxially loaded cruciform test samples. As the third focus, the applicability and the potential of using such a model for assessing real components will be discussed e.g. by introducing extrapolation or cycle jump concepts which allows to majorly reduce the calculation time without decreasing the result accuracy significantly. Finally, future potentials will be introduced with the goal to use such sophisticated models to train meta-models and finally allow for a machine-learning based on-site and service related on-line component assessment.
Assessment of Thermo-Electric Power Plants for Rotorcraft Application
Authors: Roumeliotis Ioannis , Mourouzidis Christos , Zafferetti Mirko , Pachidis Vassilios , Broca Olivier , Unlu Deniz
Published: November 2019

This paper assesses a parallel electric hybrid propulsion system utilizing simple and recuperated cycle gas turbine configurations. An adapted engine model capable to reproduce a turboshaft engine steady state and transient operation is built in Simcenter Amesim and used as a baseline for a recuperated engine. The transient operation of the recuperated engine is assessed for different values of heat exchanger effectiveness, quantifying the engine lag and the surge margin reduction which are results of the heat exchanger addition.

An oil and gas mission of a twin engine medium helicopter has been used for assessing the parallel hybrid configuration. The thermo-electric system brings a certain level of flexibility allowing for better engine utilization, thus firstly a hybrid configuration based on simple cycle gas turbine scaled down from the baseline engine is assessed in terms of performance and weight. Following the recuperated engine thermo-electric power plant is assessed and the performance enhancement is compared against the simple cycle conventional and hybrid configurations.

The results indicate that a recuperated gas turbine based thermo–electric power plant may provide significant fuel economy despite the increased weight. At the same time the electric power train can be used to compensate for the reduced specific power and potentially for the throttle response change due to the heat exchanger addition.
Numerical Performance Assessment of a Turbine Blade Row Operating Under Pulsed Detonation Combustion Inlet Conditions
Authors: Cuciumita Cleopatra , Paschereit Christian Oliver
Published: November 2019

Pulsed detonation combustion is not a new research topic. However, since the detonation process was first observed in 1881, the interest in it grew substantially in the last decades. Because the gas turbines have reached their technological maturity, the scientific community has started looking into novel thermodynamic cycles, such as detonation-based cycles. Numerous studies have been recently published in the field of pulsed detonation combustion, both numerical and experimental and major breakthroughs have been achieved in understanding and controlling the phenomena. However, the topic remains of mostly academic interest, one of the reasons is that practical implementation of it is reliant turbomachinery that would efficiently convert the pulsed, high peak, pressure into useful work. The few studies conducted on classical, existing turbines, show an efficiency of around 50% when coupled with a PDC. The low efficiency has been directly connected with the shock wave losses. For this reason, the design of turbines with supersonic inlet, and associated performance assessments have been researched. This work, however, has supersonic steady inlet Mach number or sinusoidal pulsating conditions around an average subsonic value. No public literature exists on the performances of turbines operating at pulsating inlet conditions similar to the outlet of a PDC. The current paper tackles exactly this issue. The geometry for a turbine stator row was designed based on supersonic inlet design criteria. This geometry was then subjected to CFD numerical simulations. First, the pressure losses associated with a constant supersonic inlet were numerically determined to be a little over 26%. The next step was to assess the pressure losses of the same turbine row geometry in a transient approach. This time, the inlet conditions were set to be variable in time. The values were taken from a 1D in-house code computing the parameters at the outlet of a PDC working on hydrogen and air under stoichiometric conditions. This inlet conditions give a much better insight with respect to the flow within a turbine row when coupled with a PDC. It was observed that the pressure losses, computed as a time average for a period corresponding to the PDC functioning frequency were of 12%. This value is much less than that for a constant supersonic inlet, mostly due to the turbine being exposed to the shock waves for less time.
Selecting the Optimum Supercritical CO2 Cycle for Indirect-Fired Applications
Authors: Tom Brittany , Smith January , McClung Aaron M.
Published: November 2019

Existing research has demonstrated the viability of supercritical carbon dioxide as an efficient working fluid with numerous advantages over steam in power cycle applications. Selecting the appropriate power cycle configuration for a given application depends on expected operating conditions and performance goals. This paper presents a comparison for three indirect fired sCO2 cycles: recompression closed Brayton cycle, dual loop cascaded cycle, and partial condensation cycle. Each cycle was modeled in NPSS with an air side heater, given the same baseline assumptions and optimized over a range of conditions. Additionally, limitations on the heater system are discussed.
Acoustic and Convective Mechanisms Contributing to Non-Synchronous-Vibrations in a Multistage Compressor
Authors: Brandstetter Christoph , Paoletti Benoit , Ottavy Xavier
Published: November 2019

In the present paper we show an analysis of Non-Synchronous-Oscillations in the rear stage of an experimental high-speed 3.5 stage compressor. The machine CREATE is representative of the rear median-stages of a modern civil turbofan engine except for an increased tip clearance on middle and last stage. Using distributed unsteady pressure measurements a comprehensive dataset during transient throttling maneuvers is presented, including temporal and spatial mode decomposition and the derivation of wave propagation speeds. To support the aerodynamic characterization, the steady flow structure at near stall conditions has been investigated using Laser-Doppler-Anemometry and unsteady pressure probes. In repeated experiments the machine has encountered alternating circumferential modes, several hundred revolutions before rotating stall at design speed. It was found that acoustic resonance of an upstream cut-on mode between the compressor stages enforces the development of particular modes. These phenomena have not been observed on the same machine with regular tip clearance. In contrast to front-stage observations reported in literature, where leading edge separations cause strong excitations of the blade eigenmodes, initially weak modulations of the flow in the rotor tip region are observed to be amplified due to acoustic feedback. With rising amplitude lock-in to distinct circumferential mode orders develops. Apart from the final lock-in procedure, signatures of solely aerodynamic fluctuations, discussed in literature as ‘Rotating Instabilities’ or ‘Part Span Stall’, are observed intermittently at different speedlines.
Nonlinear Aerodynamic Damping in a Highly Loaded Vibrating Compressor Cascade
Authors: Schuff Matthias , Chenaux Virginie
Published: November 2019

A numerical aeroelastic study of a 2D linear compressor cascade based on the non-rotating annular compressor cascade with a NACA3506 profile was performed using a one-way coupled technique (prescribed-motion approach). Subsonic and transonic flow conditions with strong shocks in the blade passage were imposed. Using a nonlinear harmonic balance solver, unsteady simulations were performed by enforcing one blade oscillation motion. For each blade structural mode, the blade deflection amplitude was varied and its influence on the blade aerodynamic response was determined in terms of aerodynamic damping. The blade modes investigated consisted of one pitching and two heaving oscillation motion. In transonic flows and for the three structural modes investigated, the cascade shows nonlinear aerodynamic responses depending on the vibration amplitude. The results presented in this work show that nonlinear frequency domain methods are able to capture the blade nonlinear aeroelastic behavior coming from amplitude-dependent aerodynamic responses.
Comprehensive Smith Charts for Axial Compressor Design
Authors: Anderson Mark R.
Published: November 2019

The “Smith Chart” has been recognized as an indispensable technique when applied to the initial design of axial compressors and turbines. The Smith Chart offers a simple method to locate the region of optimum efficiency which is achievable as a function of flow and work coefficient. The result is a targeted flow state represented by the velocity triangles that result from these coefficients.

The process was originally developed, and is best documented, for axial turbines1. Over the years, several publications, of similar methods for axial compressors have been put forward. The author presented one such work2 which made significant use of optimization to develop an improved Smith chart for moderate Mach number compressor designs. In the current work, these results are expanded to both low Mach number (basically incompressible) to high-speed transonic cases as well. Similar to the previous work, the effort makes extensive use of optimization to systematically explore the optimum 2D profile shapes for a wide range of target flow and work coefficients. The method uses an FNS quasi-3D CFD solver, coupled to an efficiently parameterized geometry generator, combined with an automated optimization process. The process was applied independently to dozens of flow and work coefficient points to generate comprehensive maps of performance.

Results are shown for three different relative inflow Mach numbers: 0.2, 0.75, and 1.1. The maps are displayed in classic Smith chart format of islands of stage efficiency as a function of the flow and work coefficient. Specifically, the results are for axial compressor stages of 50% reaction, the theoretical ideal reaction for 2D flow. The results and the implications over varying Mach numbers are discussed. Also included is an expanded discussion of the range and accuracy of various meanline modeling methods, along with their ability to determine the optimum design condition.
Digital Solutions for Power Plant Operators in a Dynamic Market Place: An Advanced Automated Gas Turbine Combustion Tuning for Low Emissions and Operational Flexibility
Authors: Demougeot Nicolas , Steinbrenner Alexander , Wang Wenping , Yaquinto Matt
Published: November 2019

Since the advent of premix combustion technology in industrial gas turbines, regular manual combustion tuning and engine adjustments have been necessary to maintain engines within emission regulatory limits and to control combustion dynamics (pulsations) for hardware integrity. The emissions and pulsation signatures of premix combustors are strongly driven by ambient conditions, engine performance, degradation and fuel composition. As emissions limits became more stringent over the years, higher combustion dynamics were encountered and challenges to maintain acceptable settings after yearly combustion inspections were regularly encountered. This challenge was further increased as sites operating advanced Gas Turbines (GT) eliminated Combustion Inspections (CI) and required uninterrupted generation at optimum settings for up to three years. The case for automated tuning systems became evident for the Industrial Gas Turbine (IGT) market in the mid 2000’s and different IGT manufacturers and service providers began developing them. Power Systems Manufacturing (PSM) developed the AutoTune (AT) system in 2008 and has since installed it in over fifty units, accumulating close to a million hours of operation. The history of PSM’s AT system development as well as a description of its fundamental principles and capabilities are discussed.

The power generation market is changing rapidly with the injection of renewables, thus driving the demand for operational flexibility, the design of PSM’s multi-platform compatible, AutoTune system; allowing for increased peak power, extended turndown and transient tuning is discussed. The paper also describes, how, using the same tuning principles, the application for an AutoTune system can be extended to the Balance Of Plant (BOP) equipment.
A Numerical Thermohydrodynamic Study of Fixed Pad Oil Lubricated Thrust Bearings
Authors: Dousti Saeid , Allaire Paul , Cao Jianming , Nichols Bradley , Dimond Timothy
Published: November 2019

Hydrodynamic thrust bearings are vital components of rotating machinery and often undergo high axial loads and temperatures. High loads and the consequent shear heating result in high temperature development and viscosity drop of the lubricant. This phenomenon is captured in the solution of a three dimensional energy equation problem. The inlet flow temperature via a groove mixing model and its interaction with outflow from the previous pad is also included in the analysis. Traditionally, capturing the heat conduction at the lubricant solid interfaces in the energy solution for the fixed pad, lubricant, and rotating disk (runner) have faced significant convergence problems. In this study, an integrated method is proposed to remedy this issue. The effects of various model features on the computed results are investigated.
Numerical Simulation of Surge in a Centrifugal Compressor With Different Operating Condition Using the Plenum Model
Authors: Jia Cheng , Qin Guoliang , Chen Xuefei , Wang Yi
Published: November 2019

Surge happens when the mass flow rate reduces to a certain value in the centrifugal compressor and pipe network system. Surge will cause fatal damage to the centrifugal compressor. So researchers need to capture the surge fluctuation in the compressor and pipe system by methods. These works can research more details of surge. This study takes an attempt to use the CFD method with a plenum model to investigate the surge fluctuation in a centrifugal compressor and pipe system. Using the three dimensional transient numerical simulation, authors obtain the low frequency fluctuation of the mass flow rate and the total pressure at the diffuser outlet over simulation time. The flow field in the impeller and the diffuser passage are also obtained in the simulation. Authors take more detail researches on the surge fluctuation by the flow field result. By changing the plenum volume and the compressor operating point, authors compare and analyze the surge fluctuation under different operating conditions. The changing plenum volume has great influence on the mass flowrate fluctuation and the total pressure fluctuation. Only rotating stall will occur when connecting a smaller capacity pipe network. But the rotating stall will lead to the surge of the system when connecting a larger capacity pipe network. The decreasing mass flow rate has little influence on the fluctuation frequency but the fluctuation amplitude increases. It is verified that the surge in the compressor system is much more serious when connecting a larger capacity pipe system or decreasing the centrifugal compressor operating mass flowrate.