bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Modeling of Static and Rotordynamic Characteristics for Three Types of Helically-Grooved Liquid Annular Seals
Authors: Li Zhigang , Fang Zhi , Li Jun , Feng Zhenping
Published: November 2019

This paper deals with numerical predictions of the leakage flow rates, drag power and rotordynamic force coefficients for three types of helically-grooved liquid annular seals, which include a liquid annular seal with helically-grooved stator (GS/SR seal), one with helically-grooved rotor (SS/GR seal), and one with helical grooves on stator and rotor (GS/GR seal). These seals are frequently used for multiple-stage centrifugal pumps as they have the advantage of low leakage (even to zero) due to the “pumping effect” of the helical grooves. However, the static and rotordynamic characteristics of helically-grooved liquid annular seals still are not fully understood, and even more pronounced is the lack of effective numerical models in the literature.

A novel transient CFD-based perturbation method was proposed for the predictions of the leakage flow rates, drag power and rotordynamic force coefficients of helically-grooved liquid annular seals. This method is based on the unsteady Reynolds-Averaged Navier–Stokes (RANS) solution with the mesh deformation technique and the multiple reference frame theory. The time-varying fluid-induced forces acting on the rotor/stator surface were obtained as a response to the time-dependent perturbation of the seal stator surface with the periodic motion, based on the multiple-frequency elliptical-orbit stator whirling model. The frequency-independent rotordynamic force coefficients were determined using curve fit and Fast Fourier Transform (FFT) in the frequency domain. The CFD-based method was adequately validated by comparisons to the published experiment data of leakage flow rates and fluid response forces for three types of helically-grooved liquid annular seals. Based on the transient CFD-based perturbation method, numerical results of the leakage flow rates, drag powers and rotordynamic force coefficients were presented and compared for three types of helically-grooved liquid annular seals at five rotational speeds (n = 0.5 krpm, 1.0 krpm, 2.0 krpm, 3.0 krpm and 4.0 krpm), paying special attention to the effective stiffness coefficient and effective damping coefficient. Results show that the GS/GR seal has the best sealing capability, followed by the GS/SR seal and then the SS/GR seal. The leakage flow rate of all three helically-grooved seals monotonically decreases with the increasing rotational speed. The GS/SR seal possesses the best stiffness and damping capability, followed by the SS/GR seal and then the GS/GR seal. Rotordynamic instability problems are more likely caused by the GS/GR seal in multi-stage centrifugal pumps. From a rotordynamic viewpoint, the GS/SR helically-grooved liquid annular seal is a better seal concept for multi-stage centrifugal pumps.
Sound Power Measurements at Radial Compressors Using Compressed Sensing Based Signal Processing Methods
Authors: Hurst Jakob , Behn Maximilian , Tapken Ulf , Enghardt Lars
Published: November 2019

Two sound power measurement approaches were developped that are easy to install and have the ability to detect the dominant modal content by applying the modern signal processing method, Compressed Sensing. In general Compressed Sensing requires only few measurement positions for an exact reconstruction of sparse acoustic mode fields. For a current study we have chosen two Compressed Sensing algorithms. Each require separate sensor array arrangements and deliver different modal contents, from which the sound power can be derived. Firstly, an Azimuthal Mode Analysis is conducted by applying the Enhanced Orthogonal Matching Pursuit (EOMP) algorithm to a sound pressure measurement vector. The measurements are obtained by using a sensor ring array with optimized positions. In a subsequent step, the sound power is calculated by referring the detected azimuthal mode spectrum to a model describing the energy distribution over the radial mode content. Secondly, using the Block Orthogonal Matching Pursuit (BOMP) algorithm, the radial mode amplitudes are determined directly. This algorithm requires the sensors to be placed at optimized azimuthal and axial positions and reconstructs a set of dominant radial modes that occur in groups. With the objective to verify both methods, the newly designed and optimized arrays in combination with the aforementioned mode reconstruction algorithms are applied to a numerical data set. This data was provided by URANS simulations of a radial compressor set-up, which is an exact replication of an actual test rig located at the RWTH Aachen University. The introduced estimation methods perform well as shown by comparison with an exact and high resolution Radial Mode Analysis Method. In the near future, the presented measurement approaches will be applied in an experimental study performed at the radial compressor test rig.
The Research on Compressor Performance Degradation Caused by Surface Roughness Enlargement due to Corrosion in Marine Environments
Authors: Sun Haiou , Ma Jingyuan , Wang Zhongyi , Cao Lei
Published: November 2019

In the marine environment, the corrosion on a compressor blade caused by salt spray severely affects the compressor performance and poses a threat to its operation reliability. This study simulated the corrosion on the blade made of X20Cr13 martensitic stainless steel caused by salt spray by using the static acceleration test. Average depth and density of surface corrosion pit were calculated by the actual corrosion with peak valley and different shapes and sizes. The value of average deviation Ra was calculated by average depth and density of corrosion pit. According to the empirical formula proposed by Koch and Smith (ks = 6.2 Ra), setting the equivalent sand grain roughness ks in CFX. NASA Stage67 as calculation model. Then analyzed the effects of various surface roughness on compressor performance and internal flow field through the numerical simulation method. The results revealed that with the increase in corrosion time, the flow rate, pressure ratio, torque, and power of the compressor decreased. The internal flow indicated the increasing internal loss and decreasing efficiency. On the basis of loss analysis, the binomial relationships between the service time and relative values of total pressure loss and efficiency loss, respectively, were established.
Impact of Varying High- and Low-Pressure Turbine Purge Flows on a Turbine Center Frame and Low-Pressure Turbine System
Authors: Sterzinger P. Z. , Zerobin S. , Merli F. , Wiesinger L. , Peters A. , Maini G. , Dellacasagrande M. , Heitmeir F. , Göttlich E.
Published: November 2019

This paper presents the experimental and numerical evaluation and comparison of the different flow fields downstream of a turbine center frame duct and a low-pressure turbine stage, generated by varying the inlet flow conditions to the turbine center frame duct. The measurements were carried out in an engine-representative two-stage two-spool test turbine facility at the Institute for Thermal Turbomachinery and Machine Dynamics at Graz University of Technology. The rig consists of a high-pressure (HPT) and a low-pressure (LPT) turbine stage, connected via a turbine center frame (TCF) with non-turning struts. Four individual high-pressure turbine purge flow rates and two low-pressure turbine purge flow rates were varied to achieve different engine-relevant TCF and LPT inlet flow conditions. The experimental data was acquired by means of five-hole-probe area traverses upstream and downstream of the TCF, and downstream of the LPT. A steady RANS simulation taking all purge flows in account was used for comparison and additional insight are gained from a numerical variation of the HPT and LPT purge flow rates.

The focus of this study is on the impact of the variations in TCF inlet conditions on the secondary flow generation through the TCF duct and the carry-over effects on the exit flow field and performance of the LPT stage. Existing work is limited by either investigating multi-stage LPT configurations with generally very few measurements behind the first stage or by not including relevant HPT secondary flow structures in setting up the LPT inflow conditions. This work addresses both of these shortcomings and presents new insight into the TCF and LPT aerodynamic behavior at varying the HPT and LPT purge flows. The results demonstrate the importance of the HPT flow structures and their evolution through the TCF duct for setting up the LPT inflow conditions, and ultimately for assessing the performance of the first LPT stage.
Prediction of Flow Properties on Turbine Vane Airfoil Surface From 3D Geometry With Convolutional Neural Network
Authors: Jin Yuan , Li Shan , Jung Olivier
Published: November 2019

Nowadays, Computational Fluid Dynamics (CFD) simulations play an increasingly important role for turbine airfoil design. This high-fidelity approach is capable to provide accurate information of flow fields. Meanwhile, the calculation accuracy is always gained at the expense of numerical cost. This gap limits opportunities for design space exploration. To address this problem, surrogate models (also known as metamodels) are introduced to approximate high-fidelity CFD models. However, traditional surrogate models, such as Kriging or Radial Basis Function, construct response surface on a design space with limited dimensions. This prevents users from predicting the flow fields directly from the geometry and performing interactive design of airfoil. In the present work, we propose a Convolutional Neural Network (CNN) based surrogate model to predict flow properties on turbine vane airfoil surface from 3D airfoil profile defined by point cloud. The proposed CNN architecture adopts a symmetric expanding path that is similar to the so-called U-Net. The geometries in the training and testing dataset are generated via varying the parameters defined by the Free-Form Deformation approach. The corresponding flow fields are obtained through high-fidelity CFD simulations performed in a finite volume context. Furthermore, a gaussian process based Bayesian optimization technique is utilized to tune automatically the hyperparameters of the network. In this work, we trained the CNN based surrogate model with static pressure and temperature on the mean section of turbine vane airfoil surface. The trained model is able to predict in a reliable and efficient way the corresponding property directly from the 3D geometry, which allows engineers to agilely adjust their airfoil design.
Experimental and Numerical Study on the Effect of Fan-Shaped Hole Configuration on Film Cooling Effectiveness
Authors: Seo Hyun Jae , Park Sang Hyeon , Kwak Jae Su , Kang Young Seok
Published: November 2019

Film cooling technique has been widely applied to protect gas turbine blades from high temperature combustion gases. In this study, to improve the cooling effectiveness of fan-shaped film cooling holes, the effect of the main shape parameters on the film cooling effectiveness was investigated through numerical and experimental studies. Commercial software based on Reynolds Averaged Navier-Stokes (RANS) analysis was used in the numerical study, and the PSP (Pressure Sensitive Paint) technique was used to experimentally measure the film cooling effectiveness. The design points for the optimization were derived by the Box-Behnken method, which is one of the design of experiments (DOE). Three shape parameters of a fan-shaped hole were selected as design variables: the forward expansion angle, the lateral expansion angle, and the length of cylindrical part of the hole. The area-averaged film cooling effectiveness was selected as an objective function and the optimal hole shape of each analysis was obtained using the response surface methodology (RSM). It was confirmed that the film cooling effectiveness was affected by all three variables in both numerical and experimental results. Both analyses showed similar trends of each variable on film cooling effectiveness, but the optimal hole shape obtained by each method was different. The difference is attributed to flow separation not captured by RANS based analysis and surface roughness caused by the manufacturing process and the PSP coating in experimental analysis. Notably, the experimentally optimized hole showed better film cooling effectiveness than that of the numerically optimized hole in the comparison experiments.
Effect of Additive Manufacturing Process Parameters on Turbine Cooling
Authors: Snyder Jacob C. , Thole Karen A.
Published: November 2019

Turbine cooling is a prime application for additive manufacturing because it enables quick development and implementation of innovative designs optimized for efficient heat removal, especially at the micro-scale. At the micro-scale, however, the surface finish plays a significant role in the heat transfer and pressure loss of any cooling design. Previous research on additively manufactured cooling channels has shown the surface roughness increases both heat transfer and pressure loss to similar levels as highly-engineered turbine cooling schemes. What has not been shown, however, is whether opportunities exist to tailor additively manufactured surfaces through control of the process parameters to further enhance the desired heat transfer and pressure loss characteristics.

The results presented in this paper uniquely show the potential of manipulating the parameters within the additive manufacturing process to control the surface morphology, directly influencing turbine cooling. To determine the effect of parameters on cooling performance, coupons were additively manufactured for common internal and external cooling methods using different laser powers, scan speeds, and scanning strategies. Internal and external cooling tests were performed at engine relevant conditions to measure appropriate metrics of performance. Results showed the process parameters have a significant impact on the surface morphology leading to differences in cooling performance. Specifically, internal and external cooling geometries react differently to changes in parameters, highlighting the opportunity to consider process parameters when implementing additive manufacturing for turbine cooling applications.
Physics-Based Simulation in Support of a Through-Life Gas Turbine Service Business Model
Authors: Dawes Bill , Hunt Matt , Meah Nabil , Kudryavtsev Andrey , Evans Rich
Published: November 2019

The overall aim of the work reported in this paper is to explore whether a physics-based simulation approach has the potential to reduce the uncertainty & variability associated with both predicting & managing maintenance costs and improving engine design to optimise through-life economic performance. The main novelty in the paper is to demonstrate how an innovative Digital Geometry model can represent typical in-service component degradation and then support appropriate simulation meshes to permit degraded performance to be predicted. Two examples are given: blade erosion from particulates; and a simulated cooled blade burn-through event.
Numerical Simulation of Combustor Effusion Cooling Flow Based on Source Term Method
Authors: Wang Jing , Mao Ronghai , Tao Wenjie , Wang Zhichao , Zhang Chi , Lin Yuzhen
Published: November 2019

A numerical method based on single-sided source term has been developed to investigate the effects of the effusion cooling air on the temperature distribution in a combustor. The principle of this method is to replace the cooling holes with uniform mass, momentum, energy and turbulence sources on the hot side of the combustor liner. A resolved model that comprises cooling holes and a simplified model based on single-sided source term method have been both numerically computed. The flow and temperature fields attained from the simplified model have been found to be in good agreement with those from the resolved model. Experimental tests of a tri-sector model combustor have been conducted, mainly focusing on its outlet temperature distribution profile. Comparison results showed that the numerical results about the trend of temperature distribution fit well with the experimental data.

Furthermore, the single-sided source term method has been employed onto a simplified model combustor to investigate the design variables of the cooling hole on the temperature distribution. It has been found that as the blowing ratio increases, the wall adiabatic film cooling effectiveness would increase. But the higher blowing ratio affects the formation of corner vortex zone and primary recirculation zone, which results in a higher exit core temperature. The inclination angle of injection flow has little effect on the temperature distribution. The simulation of effusion cooling flow based on the single-sided source term method significantly reduces computational costs without compromising the accuracy. It is expected to be applied in the multi-parameter optimization of the cooling structure in a combustor liner.
Experimental Investigation for Enhanced Control of Rotating Unsteady Flow Instabilities in an Unshrouded Centrifugal Compressor Impeller
Authors: Mischo B. , Jenny P. , Bidaut Y. , Fonzi N. , Hermann D. , Wirsum M. C.
Published: November 2019

Unshrouded industrial centrifugal compressor impellers operate at high rotational speeds and volume flow rates. Under such conditions impeller blade excitation is dominated by high frequency interaction with stationary parts, i.e. vaned diffusers or inlet guide vanes. In a previous study conducted on two full compression units of the original equipment manufacturer (OEM), the authors also identified, characterized and quantified resonant blade vibration caused by the interaction of the impeller blades with sub-synchronous rotating stall cells during severe off-design conditions. The resonant impeller excitation lead to significant dynamic stress in the blades. In a follow-up study the authors have reproduced this phenomenon under representative off-design conditions in a downscaled test rig and successfully reproduced the phenomenon with unsteady Computational Fluid Dynamics (CFD) and structural mechanical Finite Element Method (FEM) analysis. The gained knowledge of these studies was translated into a new diffuser design philosophy, based on a sectorwise circumferential variation of the leading edge angle. In this paper, the patented philosophy by the OEM is presented and verified experimentally on the same test rig configuration in terms of flow path geometry and measurement equipment that was used in the mentioned prior study to assess resonant blade interaction. The results confirm the design aims: rotating stall onset was delayed without affecting the aerodynamic performance of the stage. Resonant blade interaction with rotating stall observed in the baseline diffuser could not be avoided with the two new diffuser designs. However, with the two new diffusers, the induced mechanical stresses in the impeller and the excitability were reduced by up to 12%.
Effects of Axial Velocity of Main Stage on the Performances of a Centrally Staged LPP Combustor
Authors: Wang Zhichao , Hui Xin , Wang Jianchen , Lin Yuzhen , Zhang Chi
Published: November 2019

Characteristics of the main stage exert important effects on the performances in a centrally staged LPP combustor. The experiments on flow fields, spray, and combustion were carried out on the combustors with different axial velocity at the main stage exit (Vm). The NOx emissions, combustion efficiency and lean blowout are all tested in a rectangular model combustor under elevated temperature and pressure conditions, while flow field and spray characteristics are measured in an optical combustor by Kerosene-PLIF and PIV under non-reacting elevated temperature and pressure conditions.

The results show that with the Vm of the main stage changing from 61 m/s to 80 m/s, the NOx emission and combustion efficiency decreases. Meanwhile, lean-blow out (LBO) performance becomes worse. CFD simulation is conducted to investigate the flow fields, spray, emissions and LBO performance of the combustor. The simulation results show the turbulent intensity between the pilot and main stage flows is stronger for the combustor with higher Vm. Besides, the recirculating flow in the recirculation zone also has an increasing trend. The two reasons cause the temperature in the combustion zone decrease, which is beneficial to the NOx reduction. In addition, the stronger turbulence intensity between the main and pilot stage make the quenching of pilot flame more severe, causing the combustion efficiency lower. Moreover, the increase of the inverse flow also worsens the LBO performance.
Nonlinear Vibration Prediction of a Highly Flexible Rotor Supported by an Axial Groove Journal Bearing Considering Journal Angular Whirling Motion
Authors: Koondilogpiboon Nuntaphong , Inoue Tsuyoshi
Published: November 2019

In this study, the difference in dynamic behavior of the rotor-bearing system supported by the bearing model that considers both lateral and angular whirling motions of the journal (model A), and the model that considers only lateral whirling motion (model B) is investigated. The rotor model consists of a slender shaft, a large disk and two small disks supported by a self-aligning ball bearing and an axial groove journal bearing of L/D = 0.6. Three positions of the large disk: 410, 560, and 650 mm measured from the ball bearing, are investigated. Numerical integration of the rotor-bearing system which is modally reduced to the 1st forward mode is performed at above the onset speed of instability until either a steady state journal orbit or contact between the journal and the bearing occurs to identify the bifurcation type. Numerical results using model A indicate subcritical bifurcation with the contact between the journal and the inboard side of the bearing in all three large disk positions, whereas those of model B indicate subcritical bifurcation when the large disk position is at 410 mm, and supercritical bifurcation is observed in the other two cases. Lastly, the experiments at the same three large disk positions are performed. Subcritical bifurcation with the contact between the journal and the inboard side of the bearing is observed in all large disk positions, which conforms with the calculation result of model A. As a result, model A is essential in nonlinear vibration analysis of a highly flexible rotor system.
Re-Oriented POD for Feature Extraction From Time Resolved Reacting Flow Datasets
Authors: Ek H. , Proscia W. , Lieuwen T. , Emerson B.
Published: November 2019

Recent improvements in computational and experimental combustion have led to an increased availability of high-fidelity data sets. With the surge of high-quality data, the reduction and analysis of this information become a key aspect in improving our understanding of highly dynamic, reacting flow fields. This work utilizes simultaneous high-speed stereoscopic particle image velocimetry (sPIV), OH-planar laser induced fluorescence (PLIF) and fuel-PLIF measurements in a high pressure, liquid fueled swirl combustor. This work extends one of the most commonly used modal analysis techniques, proper orthogonal decomposition (POD). Instead of decomposing the data as a series of time coefficients and spatial modes, which is the result of snap-shot POD, the data is re-oriented such that the coefficients are a function of the transverse distance and the modes are a function of axial distance and time. This reoriented POD method, referred to as spatio-temporal POD, allows us to directly target convective flow structures while still extracting the same types of information as from snap-shot POD. Additionally, since the modes contain temporal information, phase speeds associated with the convective structures can easily be calculated from the phase portraits. This paper presents results of this analysis, allowing us to track the growth of coherent structures, their phase speeds, and their subsequent decay.
Effect of Blade Row Interaction on Rotor Film Cooling
Authors: Brind James , Pullan Graham
Published: November 2019

The mechanisms of blade row interaction affecting rotor film cooling are identified in order to make recommendations for the design of film cooling in the real, unsteady turbine environment. Present design practice makes the simplifying assumption of steady boundary conditions, despite intrinsic unsteadiness due to blade row interaction; we argue that if film cooling responds non-linearly to unsteadiness, the time-averaged performance will then be in error. Non-linear behaviour is confirmed using experimental measurements of flat-plate cylindrical film cooling holes, main-stream unsteadiness causing a reduction in film effectiveness of up to 31% at constant time-averaged boundary condition. Unsteady computations are used to identify the blade row interaction mechanisms in a high-pressure turbine rotor: a ‘negative jet’ associated with the upstream vane wake, and frozen and propagating vane potential field interactions. A quasi-steady model is used to predict unsteady excursions in momentum flux ratio of rotor cooling holes, with fluctuations of at least ±30% observed for all hole locations. Computations with modified upstream vanes are used to vary the relative strength of wake and potential field interactions. In general, both mechanisms contribute to rotor film cooling unsteadiness. It is recommended that the designer should choose a cooling configuration which behaves linearly over the expected unsteady excursions in momentum flux ratio as predicted by a quasi-steady hole model.
Multidisciplinary Design Optimization of a Bladed Disc for Small-Size Gas-Turbine Engines
Authors: Salnikov Anton , Danilov Maxim
Published: November 2019

One of the most important units of small-size gas-turbine engines (GTE) is a turbine bladed disk, since it determines the total engine efficiency. Designing a turbine disks is a complex challenge due to the high loads and a large number of structural and technological constraints, as well as a variety of requirements to the bladed disks for small-size GTEs (higher efficiency, lower mass and adequate strength characteristics, etc.).

Diverse requirements to the turbine bladed disks mean that modifying the structure in order to improve some characteristics will degrade other characteristics. A standard solution to this problem is to use the iterative approach, which reduces the design process to a consecutive iteration of setting and solving design problems concerning the bladed disk elements (blade and disk) separately for different aspects. The main drawback of this approach is its tremendous labor intensity and inferior quality of design, as this procedure does not consider the design object as a single entity.

This paper proposes an approach to the turbine bladed disks design based on the use of a single multidisciplinary parametrized 3D model that contains several specialized submodels. These submodels define the essential computational regions, as well as the characteristics of the physical processes and phenomena in the object under study. The model also enables integration and interaction of the submodels in a single computational region.

The single multidisciplinary model is modified and analyzed automatically, so the design problem is transformed into a multi-criteria optimization problem where the weight, gas dynamic and strength characteristics are used as criteria or constraints, and they are improved by varying the geometric parameters of the blade and disk.

Each submodel simulates and analyzes the essential characteristics at the level comparable to the standard engineering calculations. Therefore, the designs obtained as a result of optimization do not need significant improvements, which facilitates and enhances the design process.

The development of an integrated model is time consuming, but since the design and operation of bladed disks are similar, the created parametrized multidisciplinary 3D model can be used in the design of other similar disks after minor alternations taking into account the specifics of the new task.
Scaling Flat Plate, Low Temperature Adiabatic Effectiveness Results Using the Advective Capacity Ratio
Authors: Fischer Jacob P. , Rutledge James L. , McNamara Luke J. , Polanka Marc D.
Published: November 2019

Effective design of film cooled engine components requires the ability to predict behavior at engine conditions. This is commonly accomplished through low temperature testing on scaled up geometries. The adiabatic effectiveness, η, is one indicator of the performance of a film cooling scheme. Performing an experiment to measure η in a low temperature wind tunnel requires appropriate selection of the coolant flow rate. Perhaps the most common flow rate parameter that is used to characterize the coolant flow relative to the freestream is the mass flux ratio, or blowing ratio, M. This is usually used in lieu of the velocity ratio to account for the fact that the density of the coolant is typically much larger than that of the hot freestream gas. Numerous studies have taken place evaluating the ability of M to properly scale the effects of density ratio and its performance has produced mixed results. The momentum flux ratio, I, is an alternative that is also found to have mixed success, leading some to recommend matching the density ratio to allow simultaneous matching of M and I. Nevertheless, widely varying results in the literature regarding the efficacy of these coolant flow rate parameters to scale the density ratio suggests there may be other largely ignored effects playing a role in the thermal physics.

In the present work, thermal experiments were performed to measure adiabatic effectiveness on a flat plate with a single 7-7-7 shaped hole. Various coolant gases were used to give a large range of thermodynamic property variations. It is shown that a relatively new coolant flow rate parameter that accounts for not only density variations but also specific heat variations, the advective capacity ratio (ACR), far exceeds the ability of either M or I to provide matched adiabatic effectiveness between the various coolant gases that exhibit extreme property differences. Particularly considering that the specific heat of the coolant in an engine is significantly lower than the specific heat of the freestream gas, ACR is shown to be appropriate for characterizing non-separating coolant flow situations.
Modelling the Transient Behaviour of Gas Turbines
Authors: Petkovic Djordje , Banjac Milan , Milic Srdjan , Petrovic Milan V. , Wiedermann Alexander
Published: November 2019

As a consequence of the increasing share of renewable energy sources in present-day electrical grid systems, time variations of the power demand for fossil fuel plants can become more sudden. Therefore, an ability to respond to sudden load changes becomes an important issue for power generation gas turbines. This paper describes a real-time model for predicting the transient performance of gas turbines. The method includes basic transient phenomena, such as volume packing and the heat transfer between the working fluid and the structural elements. The dynamics of components are quantified by solving ordinary differential equations with appropriate initial and boundary conditions. Compressor and turbine operating points are determined from corresponding performance maps previously calculated using sophisticated aerodynamic, through-flow codes. This includes a sufficient number of such characteristics to account for the variations in speed and machine geometry. The developed dynamic model was verified by comparison of simulation results with experimentally recorded operating parameters for a real engine. This includes the start-up sequence and the change of load. Additional simulation covers the system response to a step increase in fuel flow. The simulation is carried out faster than the real process.
Synchrotron XRD Measurements of Thermal Barrier Coating Configurations With Rare Earth Elements for Phosphor Thermometry
Authors: Haldar Sandip , Warren Peter , Fouliard Quentin , Moreno David , McCay Mary , Park Jun Sang , Kenesei Peter , Almer Jonathan , Ghosh Ranajay , Raghavan Seetha
Published: November 2019

The development of temperature sensing Thermal Barrier Coating (TBC) systems by phosphor thermometry has significant potential to achieve accurate non-destructive temperature measurement in the coating. The doping of coatings using rare earth elements is a viable option to enable the temperature measurement by the virtue of their luminescence. While facilitating the temperature sensing, however, the thermo-mechanical and thermo-chemical stability of the coating must be maintained under extreme operating conditions. In this work, TBC configurations including a doped layer placed at the top or the bottom of the top coat have been fabricated via Air Plasma Spray (APS) using Yttria-Stabilized Zirconia (YSZ) that contains Europium (Eu) dopant. The TBC configurations have been characterized using high energy synchrotron X-ray diffraction (XRD) at both room temperature and high temperature. The TBC samples have been subjected to a single cycle thermal load during XRD data collection. The residual strain in the top coats of the TBCs have been quantified using XRD data. Residual strain in the top coat of the regular TBC configuration has been measured to be in the range of −0.8 × 10−4 to −1.0 × 10−4 for out-of-plane strain (e11) and 0.5 × 10−4 to 2.0 × 10−4 for in-plane strain (e22). The doped layer above the top coat was found to most significantly affect the spatial strain distribution across depth in the YSZ layer by increasing the strain magnitudes closer to the bond coat. However, the difference in strain distribution due to doped layers was found to be less than 1.0 × 10−4, which is close to the experimental limit. Thus, the doped layer did not significantly alter the overall residual strain states of the coating.
Power-Density vs Efficiency Trade-Off for a Recuperated Inside-Out Ceramic Turbine (ICT)
Authors: Picard B. , L.-Blais A. , Picard M. , Rancourt D.
Published: November 2019

Recuperated cycles can significantly increase the efficiency of small gas turbines that are today operating with low pressure ratios and uncooled or lightly cooled turbine blades. However, for mass-driven applications such as aeroengines, the efficiency benefit is typically outweighed by the increased weight associated with the heat exchanger (HX). Increase in specific power could overcome this penalty by reducing the mass flow through the system and therefore its weight and size. To do so, the Turbine Inlet Temperature (TIT) must be increased by ∼250 K over state-of-the-art small gas turbines. The Inside-out Ceramic Turbine (ICT) propose a new path to increase TIT of small turbines, where blade cooling schemes are impractical and costly. This new architecture increases the achievable TIT by using ceramic blades loaded in compression under centrifugal loads supported by an air-cooled rotating composite rim. This paper provides a system-level evaluation of the power-density to efficiency trade-off for the sub-megawatt class turbines using the ICT configuration. The numerical simulation includes 3 submodels to provide cycle efficiency and mass estimates for various cycle and HX design: (1) a station-based thermodynamic model; (2) a 1D-FEM HX model for a straight counterflow recuperator; and (3) a system-level mass model of the recuperated engine configured for a turboprop or turboshaft. At a TIT of 1550 K, the optimal ICT configuration provides a power density of 3 kW/kg and 40% thermal efficiency, which is 4 times lighter than recuperated turbines at 1300 K for the same efficiency level. Further increase in TIT to 1800 K would reach current state-of-the-art turboprop power densities (up to 5 kW/kg) while still achieving over 40% thermal efficiency or — for applications where power density can be traded for efficiency — up to 50% thermal efficiency while maintaining low pressure ratios and associated simplicity.
Surge and Stall Detection Using Acoustic Analysis for Gas Turbine Hybrid Cycles
Authors: Cabrera Cruz Keishaly , Pezzini Paolo , Shadle Lawrence , Bryden Kenneth M.
Published: November 2019

Compressor dynamics were studied in a gas turbine – fuel cell hybrid power system having a larger compressor volume than traditionally found in gas turbine systems. This larger compressor volume adversely affects the surge margin of the gas turbine. Industrial acoustic sensors were placed near the compressor to identify when the equipment was getting close to the surge line. Fast Fourier transform (FFT) mathematical analysis was used to obtain spectra representing the probability density across the frequency range (0–5000 Hz). Comparison between FFT spectra for nominal and transient operations revealed that higher amplitude spikes were observed during incipient stall at three different frequencies, 900, 1020, and 1800 Hz. These frequencies were compared to the natural frequencies of the equipment and the frequency for the rotating turbomachinery to identify more general nature of the acoustic signal typical of the onset of compressor surge. The primary goal of this acoustic analysis was to establish an online methodology to monitor compressor stability that can be anticipated and avoided.
A Statistical Imputation Method for Handling Missing Values in Generalized Polynomial Chaos Expansions
Authors: Andrews Mark , Jones Gavin , Leyde Brian , Xiong Lie , Xu Max , Chien Peter
Published: November 2019

Generalized Polynomial Chaos Expansion (gPCE) is widely used in uncertainty quantification and sensitivity analysis for applications in the aerospace industry. gPCE uses the spectrum projection to fit a polynomial model, the gPCE model, to a sparse grid Design of Experiments (DOEs). The gPCE model can be used to make predictions, analytically determine uncertainties, and calculate sensitivity indices. However, the model’s accuracy is very dependent on having complete DOEs. When a sampling point is missing from the sparse grid DOE, this severely impacts the accuracy of the gPCE analysis and often necessitates running a new DOE. Missing data points are a common occurrence in engineering testing and simulation. This problem complicates the use of the gPCE analysis.

In this paper, we present a statistical imputation method for addressing this missing data problem. This methodology allows gPCE modeling to handle missing values in the sparse grid DOE. Using a series of numerical results, the study demonstrates the convergence characteristics of the methodology with respect to reaching steady state values for the missing points. The article concludes with a discussion of the convergence rate, advantages, and feasibility of using the proposed methodology.
Fan Flow Field in an Installed Variable Pitch Fan Operating in Reverse Thrust for a Range of Aircraft Landing Speeds
Authors: Rajendran David John , Pachidis Vassilios
Published: November 2019

The installed flow field for a Variable Pitch Fan (VPF) operating in reverse thrust for the complete aircraft landing run is described in this paper. To do this, a VPF design to generate reverse thrust by reversing airflow direction is developed for a representative 40000 lbf modern high bypass ratio engine. Thereafter, to represent the actual flow conditions that the VPF would face, an engine model that includes the nacelle, core inlet splitter, outlet guide vanes, bypass nozzle, core exhaust duct, aft-body plug and core nozzle is designed. The engine model with the VPF is attached to a representative airframe in landing configuration to include the effects of installation. A rolling ground plane that mimics the runway during the landing run is also included to complete the model definition. 3D RANS solutions are carried out for two different VPF stagger angle settings and rotational speeds to obtain the fan flow field.

The dynamic installed VPF flow field is characterized by the interaction of the free stream and the reverse stream flows. The two streams meet in a shear layer in the fan passages and get deflected radially outwards before turning back onto themselves. The flow field changes with stagger setting, fan rotational speed and the aircraft landing speed because of the consequent changes in the momentum of the two streams. The description of the installed VPF flow field as generated in this study is necessary to: a) qualify VPF designs that are typically designed by considering only the uninstalled static flow field b) choose the VPF operating setting for different stages of the aircraft landing run.
Modeling the Torsional Cyclic Response of Direct Metal Laser Sintered Inconel 718
Authors: Siddiqui Sanna F. , Irmak Firat , O’Nora Nathan , Gordon Ali P.
Published: November 2019

The aerospace propulsion industry has seen strides in the use of the additive manufacturing (AM) technology in the rapid prototyping and geometric design flexibility of aerospace parts, with concurrent efforts on 3D printing turbine engine blades of Inconel 718 material [1] for use in aircraft engines. The tensile, compressive and axial fatigue response of AM Inconel 718, along with associated constitutive modeling of the material response exhibited under these mechanical test conditions have been reported. However, in addition to understanding the axial behavioral response exhibited by this material, assessing the role of cyclic shear stresses, through experimental testing and constitutive modeling can provide preliminary insight into the mechanical behavior of AM Inconel 718 under multiaxial loading conditions. This study has presented a novel approach to constitutively model the experimental cyclic shearing deformation of as-built direct metal laser sintered (DMLS) Inconel 718, manufactured along varying build orientations in the xy, yz and xz planes, compared with wrought annealed Inconel 718. Specimens were subjected to completely reversible torsional fatigue tests at room temperature, under angle of twist control. The experimental cyclic shearing response was modeled through the use of the Chaboche model, from which optimized constants are reported with build orientation; and the specimen deformation, under angle of twist control, was captured through a finite-element simulation model of the cylindrical gauge section of the specimens. Overall this study yields a comprehensive understanding of the experimental and modeled cyclic shearing response of an additively manufactured metal, which is vital to develop these components to be conducive for the multiaxial fatigue conditions to which they are subjected to in the gas turbine industry.
Linear Cascade and Wind Tunnel Development for Turbine Blade Tip Heat Transfer Investigations With and Without Film Cooling
Authors: Sampson Michael , Fairbanks Avery , Moseley Jacob , Ligrani Phillip M. , Xu Hongzhou , Fox Michael
Published: November 2019

Currently, there is a deficit of experimental data for surface heat transfer characteristics and thermal transport processes associated with tip gap flows, and a lack of understanding of performance and behavior of film cooling as applied to blade tip surfaces. As a result, many avenues of opportunity exist for development of creative tip configurations with innovative external cooling arrangements. Overall goals of the present investigations are to reduce cooling air requirements, and reduce thermal loading, with equivalent improvements of thermal protection and structural integrity. Described is the development of experimental facilities, including a Supersonic/Transonic Wind Tunnel and linear cascade, for investigations of surface heat transfer characteristics of transonic turbine blade tips with unique squealer geometries and innovative film cooling arrangements. Note that data from past investigations are used to illustrate some of the experimental procedures and approaches which will be employed within the investigation. Of interest is development of a two-dimensional linear cascade with appropriate cascade airfoil flow periodicity. Included are boundary layer flow bleed devices, downstream tailboards, and augmented cascade inlet turbulence intensity. The present linear cascade approach allows experimental configuration parameters to be readily varied. Tip gap magnitudes are scaled so that ratios of tip gap to inlet boundary layer thickness, ratios of tip gap to blade axial chord length, and ratios of tip gap magnitudes to blade true chord length match engine hardware configurations. Ratios of inlet boundary layer thickness to tip gap range from 3 to 5. Innovative film cooling configurations are utilized for one blade tip configuration, and scaled engine components are modelled and tested with complete external cooling arrangements. Blade tip and geometry characteristics are also considered, including squealer depth and squealer tip wall thickness. With these experimental components, results will be obtained with engine representative transonic Mach numbers, Reynolds numbers, and film cooling parameters, including density ratios, which are achieved using foreign gas injection with carbon dioxide. Transient, infrared thermography approaches will be employed to measure spatially-resolved distributions of surface heat transfer coefficients, adiabatic surface temperature, and adiabatic film cooling effectiveness.
Experimental Study on Overall Cooling Effectiveness of Swirl-Stabilized Model Combustor With Effusion Cooling
Authors: Ji Yongbin , Zhang Liang , Jin Ming , Ge Bing , Zang Shusheng , Xin Jianhua , Wu Weiliang , Li Mingjia , Xu Wenyan
Published: November 2019

Application of effusion cooling or effusion based compound cooling in the state of art gas turbine combustor is more and more common, especially in aero-engines. A linearly arranged planar optically accessible three-nozzle lab scale combustor equipped with perforated testing plate for cooling is designed. Overall cooling effectiveness is experimentally examined as the key indicator of cooling performance at non-reacting flow conditions. Main air is electrically heated to about 573K. Temperature of perforated liner is recorded by the short-wave infra camera with careful calibration. Effect of effusion hole inclination angle is investigated by comparing at forward (30°), normal (90°) and backward (150°) cases. Pressure drop across the nozzle is set to be 3%, 4% and 5% respectively and that is 0–2.5% for the effusion plate. The main purpose of this work is to characterize combustor liner effusion cooling capacity at conjugate heat trasnfer conditions, and backward cooling configuration is firstly investigated.

Results clearly show that effusion cooling behavior is strongly influenced by main swirling flow regime near the combustor liner wall. To be specific, three zones as Corner Recirculation Zone (CRZ), Impinging Zone (IZ) and Developing Zone (DZ) can be divided. IZ is the region which we should treat carefully for liner cooling design because it sustains the highest heat load. Generally, inclined holes perform better cooling characteristics than normal ones. The important observation is that backward injections reveal “anti-impinging” ability, which can enhance the cooling effectiveness in upstream CRZ and IZ greatly with high coolant consumption. The potential drawback is that reverse cooling jets may induce intense interactions with main flow. But it is still a good choice for optimizing combustor effusion cooling, especially in swirling impinging regions.