bluuebunny/crossref_metadata_2025 huggingface dataset:
Probabilistic Minimum-Creep-Strain-Rate and Stress-Rupture Prediction for the Long-Term Assessment of IGT Components
Authors: Hossain Md Abir , Stewart Calvin M.
Published: January 2021

Time-dependent creep induced failure is a major concern for structural components (i.e. IGT components, Gen IV nuclear reactor components) operating at elevated temperature. The likelihood of a failure is aggravated by randomness in several sources of uncertainty. Creep rupture data shows expanding scatter bands for long-duration creep tests where uncertainty can span multiple logarithmic decades of life. This experimental uncertainty is exacerbated by the uncertainties that exist during service. The continuum damage mechanics (CDM) based creep-damage model readily available in literature does not consider the uncertainty effect while predicting the long-term reliability of the components; rather the problem is tackled deterministically. Introduction of probabilistic phenomena into the existing model to predict the minimum-creep-strain-rate (MCSR) and stress-rupture (SR) would present a pathway for estimation of effect of uncertainty ensuing high reliability in the assessment.

The objective of this paper is to develop a probabilistic model for MCSR and SR that is capable of predicting experimental uncertainty and extrapolating the expanded scatter bands observed in long-duration creep data. The Sine-hyperbolic (Sinh) CDM model is selected. Multi-isotherm MCSR and SR data for 304 (18Cr-8Ni) and 316 (18Cr-12Ni-Mo) stainless steel are gathered from the NIMS material database. A deterministic calibration is performed where the optimal material constants are obtained with no initial damage and perfect loading conditions. Probabilistic calibration begins with adding ASTM-specified temperature and stress tolerances (± X°C, ±Y% MPa) to capture a portion of the experimental uncertainty. The initial damage tolerances is then calibrated to capture the remaining uncertainty in the data. Probability distribution functions (pdfs) are assigned to each uncertainty parameter. Monte Carlo simulations are performed over a range of stress and temperature. The probabilistic Sinh model is shown to predict the expanding scatter band observed in long-term MCSR and SR data. Parametric simulations are performed where service condition uncertainty is added to the probabilistic model. It is determined that service condition uncertainties further degrade the creep resistance of a material.
Design of Heat Shield for Compressor Case of Industrial Gas Turbine to Meet Clearance Requirement
Authors: Malavade Prashant , Babu Santhana G. , Frosini Luca , Marchetti Simone
Published: January 2021

In Gas Turbine design key important role was to establish proper clearance between rotating and statoric parts during operating conditions which controls the performance, cooling flow requirements, part performance etc., These clearances must be optimized to meet product requirements. Too tight clearance at assembly condition causes excessive rubbing during starting or shutdown of gas turbine which could cause excessive heat generation and damage rotating and statoric parts. In some case, rubbing can cause tip liberations and damages to flow path causing aero dynamic losses. Similarly, if clearance is large at assembly condition causes aerodynamic losses. In this paper describes the experience of Baker Hughes, in design of compressor case wherein different design options in casing design with and without considering external features / components are considered to have adequate clearance between rotating and statoric parts. It also describes the Heat shield design iterations which was provided on a compressor case to establish proper thermal response during transient operating conditions. This helps in providing adequate clearance without causing excessive rubs or too large clearance avoiding aerodynamic losses. During development of heat shield design, challenges encountered considering clearance, manufacturing aspects, assembly feasibility and part life capabilities like low cycle fatigue, high cycle fatigue requirements are discussed in the paper. Also heat shield was subjected to high thermal gradient due to temperature difference, this makes heat shield to have constrained growth. This restriction in growth provides huge stresses beyond the material limit causing it to fail before product requirement time period. To avoid constrained growth, this paper describes how the heat shield was connected to casing by different means are mentioned. It also describes the impact on frequency margin if there is not adequate fixity in heat shield design. Some of the design parameters like circumferential & axial ribs and intermittent stiffeners and its influence on stress by comparing against yield and on frequency margin with reference to potential driver are also discussed in this paper. It also incorporates the methods to control intersegment leakages and design features to avoid interface interference. Feasibility study of heat shield design was done using finite element modeling techniques using ANSYS tool and its best practices would also be dealt in this paper.
Introduction to Multi-Point Design Strategies for Aero Engines
Authors: Sielemann Michael , Coïc Clément , Hübel Moritz , Zhao Xin , Kyprianidis Konstantinos
Published: January 2021

Classic gas turbine design relies on the definition of a design point, and the subsequent assessment of the design on a range of off-design conditions. On the design point, both component sizing (e.g., in terms of physical dimensions or in terms of map scaling parameters) and a solution to the off-design governing equations are established. With this approach, it is however difficult to capture the contradicting requirements on the full operating envelope. Thus, practical design efforts rely on various multi-point design approaches. This paper introduces a simplified notation of such multi-point approaches via synthesis matching tables. It then summarizes two academic state-of-the-art multi-point design schemes using such tables in a comprehensible fashion. The target audience are students and engineers familiar with the basics of classic cycle design and analysis looking for a practical introduction to such multi-point design approaches. Application examples are given in terms of a simple turbojet and a typical geared turbofan as modeled in state-of-the-art academic cycle design and analysis efforts. The results of the classic design point approach are compared to those of multi-point approaches.
Performance of a Low Speed Axial Fan Under Distortion: An Experimental Investigation
Authors: Tambe Sumit , Bartolomé Oseguera Ugaitz , Rao Arvind Gangoli
Published: January 2021

In the pursuit of reducing the fuel burn, future aircraft configurations will feature several types of improved propulsion systems, e.g. embedded engines with boundary layer ingestion, high-bypass ratio engines with short intakes, etc. Depending on the design and phase of flight, the engine fan will encounter inflow distortion of varying strength, and fan performance will be adversely affected. Therefore, investigation of the flow phenomena causing performance losses in fan and distortion interaction is important.

This experimental study shows the effect of varying distortion index on four aspects of fan performance: distortion topology, upstream redistribution, performance curve, and flow unsteadiness. A low speed fan is tested under 60° circumferential distortion of varying strength, generated using distortion screens. The flow field in the upstream redistribution region is measured using PIV (planar and stereo). The fan performance is obtained using total pressure measurements. The noise spectra measured by a microphone are used to quantify the unsteadiness in the flow field. The distortion index (DC60) varies linearly with the grid porosity at constant wall thickness and aspect ratio of the grid cells. However, the distortion topology is significantly different as a stream-wise vortex pair appears in distorted flow at higher DC60. The vortices are stronger at higher DC60, but their order of magnitude is much lower than the circulation corresponding to fan itself. The spinner, distortion index and topology significantly affect the upstream redistribution mechanism. The vortex pair redistributes the flow which results in lower asymmetry in the symmetry plane. With increasing distortion, the performance is reduced and the unsteadiness is increased.
Unsteady Modeling of Turbochargers for Automotive Applications by Means of a Quasi-3D Approach
Authors: Montenegro Gianluca , Tamborski Matteo , Della Torre Augusto , Onorati Angelo , Marelli Silvia
Published: January 2021

This work describes the development and the application of a quasi-3D method for the simulation of turbochargers for automotive applications under unsteady flow conditions. The quasi-3D approach is based on the solution of conservation equations for mass, momentum and energy for unsteady flows and applied to 0D and 1D elements arbitrarily oriented in the space. The compressor is divided into different regions, each one treated numerically in a different way. For the impeller region a relative reference system has been used and the presence of a centrifugal force field has been introduced both in the momentum and energy conservation equation. The direction of the ports at the inlet and outlet of the impeller are used to determine the design flow angles and therefore the deviation during off-design conditions. Conversely in the vaneless diffuser the conservation of the angular momentum of the flow stream has been imposed in the tangential direction and then combined with the solution of the momentum equation in the radial direction. The model has been validated against measurements carried out on the test bench of the University of Genoa both in diabatic and adiabatic conditions.
Experimental Investigation on NO Pollutant Formation in High-Pressure Swirl-Stabilized Kerosene/Air Flames Using NO-, OH- and Kerosene-PLIF and PIV Laser Diagnostics
Authors: Salaün E. , Frindt F. , Cabot G. , Renou B. , Richard S. , Cazalens M. , Malbois P. , Grisch F.
Published: January 2021

A Lean Premixed injection system (LP) was experimentally investigated at elevated pressure and air inlet temperature, corresponding to engine conditions, i.e. with high swirl number and elevated fresh gases velocities. OH-PLIF, NO-PLIF and kerosene-PLIF laser diagnostics were used to study the flame structure and the NO formation within the primary zone. These experimental studies were complemented with PIV measurements. The acquired data allows the evaluation of the coupling of aerodynamics with the flame structure. Starting from there, the combustion process governing the formation of NO pollutant into the flame was analyzed with high spatial resolution. The Zeldovich pathway has been found to control the NO formation in the inner recirculation zone while the nitrous oxide pathway is found to be important especially in the regions in which the residence time of burnt gases is small. Effect of pressure and FAR also produced significant changes in the NO production. It does appear, however that no universal behavior can be found for the pressure dependence of NO.
Heat Transfer Analysis in a Rotating Cavity With Axial Through-Flow
Authors: Puttock-Brown M. R. , Long C. A.
Published: January 2021

This paper presents local Nusselt numbers computed from experimental measurements of surface temperature of compressor discs in a multiple rotating cavity test rig with axial through-flow. A validated 2D steady state heat conduction analysis methodology is presented, using the actual test geometry, and 95% confidence intervals calculated using Monte Carlo simulation. Sensitivity of the solution to curve fitting types, geometric simplification and surface instrumentation are explored.

The results indicate that polynomial curves fits, whilst computational simple, are unsuitable especially at higher orders. It is shown that geometric simplifications, that typically simplify the algorithmic implementation, may also omit significant variation in heat flux at critical stress relieving locations. The effect of reducing measurement points in the analysis is to both over-predict heat transfer and increase the uncertainty of the results. Finally, the methodology is applied to previously published thermal data from the University of Sussex, facilitating qualitative discussion on the influence of the governing parameters.

Whilst this study does not overcome the inherent uncertainty associated with inverse solutions it is intended to present a methodology that is readily available to the wider community for the analysis of thermal test data and suggests some guidelines at the planning and post-processing stages.

The range of experiment reported here covers: 1.13 × 105 < Rez < 5.14 × 105, 1.65 × 106 < Reθ < 3.16 × 106, 0.10 < Ro < 0.60 and 3.40 × 1011 < Gr < 1.25 × 1012.
Stability Analysis of the Morton Effect of Rigid and Flexible Rotors
Authors: Zhang Silun , Hassini Mohamed Amine , Arghir Mihai
Published: January 2021

This paper presents a stability analysis of the Morton effect. The analysis is an extension of the Murphy and Lorenz method [11] and is based on better estimates of three influence coefficients linking the phenomena contributing to the Morton effect: the total response to the rotor unbalance, the temperature difference on the rotor surface induced by synchronous vibrations and the thermomechanical deformation of the rotor.

The models used in the present work are more complex and accurate because they are based on the non-linear unbalance response (large amplitude vibrations) of the rotor, on the non-isothermal analysis of the journal bearing flow and on a three-dimensional thermos-elastic analysis of the rotor. The results obtained with the original stability analysis of Murphy and Lorenz and with the modified one are compared with original experimental data obtained for a short (rigid) and long (flexible) rotor guided by a ball bearing and by a cylindrical bearing and presented in a previous work [20]. Both methods confirm the experimental results obtained for a short (rigid) rotor. They show that this rotor is not subject to instabilities generated by the Morton effect. However, the results obtained for a long (flexible) rotor are different. The simplified method of Murphy and Lorenz shows a stable behavior while the modified method presented in this work confirms the findings of [20] and indicates that the rotor could be subject to a Morton effect at rotational speeds close to the experimental conditions. The improvements obtained by using the modified stability analysis are therefore clearly underlined, as well as its inherent limitations.
Pseudo Bond Graph System Modelling of Electric Air Compressors With Energy Recovery for Fuel Cell Applications
Authors: Lück Sebastian , Göing Jan , Bode Christoph , Friedrichs Jens
Published: January 2021

In this paper, the novel machine type of an electric air compressor (EAC) for fuel cell applications is investigated and simulated using a Pseudo Bond Graph (PBG) approach. Initially, the system along with its miscellaenous components is derived in the Pseudo Bond Graph notation. Subsequently, the multiphysical connections of fluid, thermal and electrical domains are highlighted. In addition, a derivation for an extended definition of the Pseudo Bond Graph theory’s inertia I element is presented. In contrast to the previous formulation, it takes into account the effects of compressibility which were previously neglected. The simulations are carried out using in-house simulation tool ASTOR (AircraftEngine Simulation for Transient Operation Research) and feature different transient acceleration and deceleration manoeuvres with varying manoeuvre duration. It is shown that manoeuvre duration significantly influences transient performance such as the surge margin which is found to decrease by up to 9% in comparison to the steady operating line. In addition, deceleration is identified as the most critical operating condition.
Improved Delayed Detached Eddy Simulation (IDDES) of a 1.5 Stage Axial Compressor Non-Synchronous Vibration
Authors: Patel Purvic , Yang Yunchao , Zha Gecheng
Published: January 2021

This paper utilizes the Improved Delayed Detached Eddy Simulation (IDDES) to investigate the non-synchronous vibration (NSV) mechanism of a 1.5 stage high-speed axial compressor. The NSV occurs at a part speed in the rig test. A low diffusion E-CUSP approximate Riemann solver with a third order Weighted Essentially Non-Oscillating (WENO) scheme for the inviscid flux and a second order central differencing scheme for the viscous flux are employed to solve the 3D time accurate Navier-Stokes equations. The fully conservative sliding boundary condition is used to preserve the wake-propagation. The aerodynamic instability in the tip region induces two alternating low pressure regions near the leading and the trailing edge on the suction side of the rotor blade. It is observed that the circumferential tip vortex motion in the rotor passage above 75 % span and its coupling forces cause NSV at the operating speed. This instability moves in the counter-rotating direction in the rotational frame. The NSV results using URANS simulation is also presented for comparison. The predicted frequency with the IDDES and URANS using rigid blades agrees well with the measured frequency in the rig test. In addition to the NSV, the IDDES solver also captures the dominant engine order frequencies. The tip flow structures show the vortex filament with one end on the suction side of the rotor blade and other side terminating on the casing or the pressure side of the rotor blade.
Film Cooling and Heat Transfer Performance of a Fully-Cooled Turbine Vane at Varied Density Ratios and Mass Flow Ratios
Authors: Yao Chun-yi , Zhu Hui-ren , Liu Cun-liang , Zhang Bo-lun , Li Xin-lei
Published: January 2021

A number of experimental studies have been performed to study the effect of geometric and aerodynamic parameters on the film cooling performance on the flat plate and turbine blade, however, the experimental investigations on a fully-cooled turbine vane is limited, especially at different density ratios. Consequently, an experiment on a fully-cooled turbine vane with multi-row film cooling holes was carried out to investigate the effect of mass flow ratio and density ratio on the film cooling performance, in which the film cooling effectiveness and heat transfer coefficient was measured by transient liquid crystal. The mainstream inlet Reynolds number based on the inlet velocity and the true chord length is 120000 and the mainstream turbulence intensity is 15%, three mass flow ratios of 5.5%, 8.4% and 11% and two density ratios of 1.0 and 1.5 were tested. The air was selected as the mainstream, the air and carbon dioxide were independently selected as secondary flow to produce two density ratios of 1.0 and 1.5. The test vane is similar in geometry to a first stage turbine vane of a normal aeroengine. Two cavities were manufactured in the test vane to feed 18 rows of film cooling holes.

Results show that with the mass flow ratio increasing for DR = 1.0 and 1.5, the film cooling effectiveness on pressure side gradually increases, however, that on the suction side gradually decreases. Generally, increased density ratio produces higher film cooling effectiveness because the injection momentum was reduced, however, the film cooling effectiveness on the suction side for DR = 1.5 is lower than that for DR = 1.0. The coolant outflow significantly enhances the surface heat transfer coefficient for 0 < S/C < 0.5 and S/C < −0.5. The heat transfer coefficient in the leading edge is less affected by the density ratio, however, the increase in density ratio reduces the heat transfer coefficient ratio in other regions, especially for large mass flow ratios.
Research on Dynamic Characteristics and Control Method of Propelling Nozzle Based on MATLAB/AMESim Integrated Simulation
Authors: Wang Zhitao , Liu Shuoshuo , Li Tielei , Li Shuying
Published: January 2021

In this paper, the integrated simulation method is used to study the dynamic characteristics and control methods of propelling nozzle when it is coupled with the gas generator. The overall simulation model of the double-shaft hybrid exhaust turbofan engine was established by the volume inertia method under MATLAB/Simulink platform. A simulation model of the propelling nozzle hydraulic actuator was established under the AMESim platform. These two models are transmitted through the “Propelling Nozzle Throat Kinematics Simulation Module”, thus achieving the construction of the integrated simulation model. Then, based on the integrated model, a fuzzy self-tuning PI controller is developed. The quantization factor is obtained through optimization to further optimize the coupled dynamic response of the propelling nozzle.

The simulation results show that the integrated simulation model captures the special change of aerodynamic force during the nozzle area adjustment process, which can more realistically show the working condition of the actuator. Controller design based on integrated simulation model is more reasonable. The fuzzy self-tuning PI controller used in this paper corrects the PI parameters online according to the fuzzy control rules, so that the hydraulic actuator of the nozzle formed by numerical simulation has faster response, and good dynamic characteristics. It has certain guiding significance for follow-up research.
Numerical Calculation of Seal Clearance Change in Installation Process of a 1000MW Nuclear Steam Turbine HIP Casing
Authors: Ji Daohui , Mei Ziyue , Jiang Wei , Xiang CaiYan , Xie Danmei , Yue Yanan
Published: January 2021

During installation process, most of 1000MW-class nuclear power steam turbines will undergo certain deformations due to their own big size and heavy weight, which will change seal clearances in the steam passage. The clearance change will affect steam turbine’s efficiency, and may cause rubbing faults and even strong abnormal vibration, affecting the safety of the steam turbine. Moreover, limited by the complex structure and measurement method, it is difficult to measure deformation and seal clearance accurately, so it is necessary to study the change tendency of the clearance in the installation process.

In this paper, a HIP (High and Intermediate Pressure) casing of a 1000MW nuclear steam turbine was taken as the research object, and its 3D geometry model is established based on Pro/E software. By using ANSYS WORKBENCH, we calculated the deformation of the HIP casing during installation with five steps, which are named as: ① lower casing with lower diaphragms, ② step ① + upper diaphragms, ③ step ② + upper casing, ④ step ③ + bolting, and ⑤ replacing the support. Then we analyzed the change of the seal clearance during the installation process by deformation differences of some points under different conditions.

The calculation results show that the maximum deformation of the HIP Casing during the installation process occurs in the middle of casing close to the IP (Intermediate Pressure) casing. The relative change of the clearance during the whole process is 0.6–0.8 mm. The change of seal clearance is largest at the first-stage of IP casing, and it can be 0.8mm during replacement of the support.
Modeling Superposition of Flat Plate Film Cooling Under Complicated Conditions Using Recurrent Neural Networks
Authors: Yang Li , Wang Qi , Rao Yu
Published: January 2021

Film Cooling is an important and widely used technology to protect hot sections of gas turbines. The last decades witnessed a fast growth of research and publications in the field of film cooling. However, except for the correlations for single row film cooling and the Seller correlation for cooling superposition, there were rarely generalized models for film cooling under superposition conditions. Meanwhile, the numerous data obtained for complex hole distributions were not emerged or integrated from different sources, and recent new data had no avenue to contribute to a compatible model. The technical barriers that obstructed the generalization of film cooling models are: a) the lack of a generalizable model; b) the large number of input variables to describe film cooling. The present study aimed at establishing a generalizable model to describe multiple row film cooling under a large parameter space, including hole locations, hole size, hole angles, blowing ratios etc. The method allowed data measured within different streamwise lengths and different surface areas to be integrated in a single model, in the form 1-D sequences. A Long Short Term Memory model was designed to model the local behavior of film cooling. Careful training, testing and validation were conducted to regress the model. The presented results showed that the method was accurate within the CFD data set generated in this study. The presented method could serve as a base model that allowed past and future film cooling research to contribute to a common data base. Meanwhile, the model could also be transferred from simulation data sets to experimental data sets using advanced machine learning algorithms in the future.
Computational and Experimental Studies of Cellular Samples Manufactured Using Additive Methods for Use in Advanced Lightweight Designs of Engine Parts
Authors: Magerramova Liubov , Volkov Michael , Volgin Oleg , Kolos Pavel
Published: January 2021

The use of cellular structures is one way to reduce the weight of engine parts. Cellular structures are used to provide rigidity and strength for parts subject to compression, bending, and shock loads. Failure of the individual elements of a lattice/cell structure does not result in the destruction of the entire part; this stands in contrast to the structure of a conventional homogeneous metal object, in which cracks will continue to increase with increasing load, causing the destruction of the entire part. Lattice/cell structures have relatively high characteristics of rigidity and strength, excellent thermal insulation properties, energy absorption characteristics, and high fatigue resistance. The use of this type of structure in engine part construction opens up new opportunities for advanced aviation applications.

However, the deformation behavior of porous and metallic structures differs significantly from that of conventional homogeneous materials. Samples with cellular and porous structures are themselves designs. Therefore, procedures for strength testing and interpretation of experimental results for cellular and porous structures differ from those for samples derived from homogeneous materials. The criteria for determining the properties of cellular structures include density, stiffness, ability to accumulate energy, etc. These parameters depend on the configuration of the cells, the size of each cell, and the thickness of the connecting elements. Mechanical properties of cellular structures can be established experimentally and confirmed numerically.

Special cellular specimens have been designed for uniaxial tensile, bending, compression, shear, and low-cycle fatigue testing. Several variants of cell structures with relative densities ranging from 13 to 45% were considered. Specifically, the present study examined the stress-strain states of cell structures from brands “CobaltChrome MP1” powder compositions obtained by laser synthesis on an industrial 3D printer Concept Laser M2 Cusing Single Laser 400W.

Numerical simulations of the tests were carried out by the finite element method. Then, the most rational cellular structures in terms of mass and strength were established on the basis of both real and numerical experiments.
Short-Term Optimization of a Combined Cycle Power Plant Integrated With an Inlet Air Conditioning Unit
Authors: Mantilla Weimar , García José , Guédez Rafael , Sorce Alessandro
Published: January 2021

Under new scenarios with high shares of variable renewable electricity, combined cycle gas turbines (CCGT) are required to improve their flexibility, in terms of ramping capabilities and part-load efficiency, to help balance the power system. Simultaneously, liberalization of electricity markets and the complexity of its hourly price dynamics are affecting the CCGT profitability, leading the need for optimizing its operation. Among the different possibilities to enhance the power plant performance, an inlet air conditioning unit (ICU) offers the benefit of power augmentation and “minimum environmental load” (MEL) reduction by controlling the gas turbine inlet temperature using cold thermal energy storage and a heat pump. Consequently, an evaluation of a CCGT integrated with this inlet conditioning unit including a day-ahead optimized operation strategy was developed in this study.

To establish the hourly dispatch of the power plant and the operation mode of the inlet conditioning unit to either cool down or heat up the gas turbine inlet air, a mixed-integer linear optimization (MILP) was formulated using MATLAB, aiming to maximize the operational profit of the plant within a 24-hours horizon. To assess the impact of the proposed unit operating under this dispatch strategy, historical data of electricity and natural gas prices, as well as meteorological data and CO2 emission allowances price, have been used to perform annual simulations of a reference power plant located in Turin, Italy. Furthermore, different equipment capacities and parameters have been investigated to identify trends of the power plant performance. Lastly, a sensitivity analysis on market conditions to test the control strategy response was also considered.

Results indicate that the inlet conditioning unit, together with the dispatch optimization, increases the power plant’s operational profit by achieving a wider operational range, particularly important during peak and off-peak periods. For the specific case study, it is estimated that the net present value of the CCGT integrated with the ICU is 0.5% higher than the power plant without the unit. In terms of technical performance, results show that the unit reduces the minimum environmental load by approximately 1.34% and can increase the net power output by 0.17% annually.
Influence of Key Design Parameters on the Aerodynamic Performance of a Centrifugal Compressor Volute for Turbocharger Applications
Authors: Melani Pier Francesco , Balduzzi Francesco , Bianchini Alessandro , Ferrara Giovanni , Hoffer Pierre-Alain , Montesino Stephane , Brenner Mattia
Published: January 2021

A centrifugal compressor volute should ideally collect the pressurized flow at the diffuser outlet and convey it to the outlet piping as efficiently as possible. The total pressure loss related to the conversion of a radial flow into an axial one, however, is often not negligible, especially for applications where severe dimensional constraints are given, such as in turbochargers applications. Having a reliable tool for the performance prediction of the volute, flexibly adaptable to external constraints, is then pivotal in the design phase of new prototypes.

Within this context, a fully parametric tool has been developed. Based on few geometrical inputs, it allows an automatic generation of both the CAD model of the volute and the numerical setup for the CFD calculation. The shape of the volute cross-section can be fully customized and automatically adapted to the azimuthal distributions of the area and centroid radius given in input by the user. The volute tongue can be also freely modified in terms of shape, azimuthal position and width.

An extensive parametric analysis was then carried out, aimed at investigating the influence of key design parameters needed to define the shape of the volute on the internal fluid dynamics. Particular attention was paid to the tongue modelling strategy and shape, being it the critical feature for the volute flow performance.

As a result, some annotated indications are given to define the first layout of a volute when approaching a new design.
Overall Cooling Effectiveness of Effusion Cooled Can Combustor Liner Under Reacting and Non-Reacting Conditions
Authors: Ahmed Shoaib , Ramakrishnan Kishore Ranganath , Ekkad Srinath , Singh Prashant , Liberatore Federico , Ho Yin-Hsiang
Published: January 2021

Emphasis on lean premixed combustion in modern low NOx combustion chambers limits the availability of air for cooling the combustion liner. Hence the development of optimized liner cooling designs is imperative for effective usage of available coolant. Effusion cooling (also known as full-coverage film cooling) is a common method to cool the combustor liner, which involves uniformly spaced holes distributed throughout the liner curved surface area. This paper presents findings from an experimental study on the characterization of overall cooling effectiveness of an effusion-cooled liner wall, which was representative of a can combustor under heated flow (non-reacting) and lean-combustion (reacting) conditions. The model can-combustor was equipped with an industrial swirler, which subjected the liner walls to engine representative flow and combustion conditions. Inline and staggered arrangement of effusion holes have been studied. These configurations were tested for five different blowing ratios ranging from 0.7 to 4, under both reacting and non-reacting conditions. The experiments were carried out at a constant Reynolds number (based on combustor diameter) of 12,500. Infrared Thermography (IRT) was used to measure the liner outer surface temperature and detailed overall effectiveness values were determined under steady-state conditions. Under non-reacting conditions, the staggered configuration was found to be 9–25% more effective compared to inline configuration. Under reacting conditions, the staggered configuration was be 4–8% more effective compared to inline configuration. It is clear that the coolant-flame interaction for the reacting cases had a significant impact on the liner cooling effectiveness as compared to the non-reacting cases and results in less variation between inline and staggered configurations.
Significance of the Direct Excitation Mechanism for High-Frequency Response of Premixed Flames to Flow Oscillations
Authors: Acharya Vishal , Lieuwen Tim
Published: January 2021

Premixed flames are sensitive to flow disturbances, which can arise from acoustic or vortical fluctuations. For transverse instabilities, it is known that a dominant mechanism for flame response is “injector coupling”, whereby pressure oscillations associated with transverse waves excite axial flow disturbances. These axial flow disturbances then excite heat release oscillations. The objective of this paper is to consider another mechanism — the direct sensitivity of the unsteady heat release to transverse acoustic waves, and to compare its significance relative to the induced axial disturbances, in a linear framework. The rate at which the flame adds energy to the disturbance field is quantified using the Rayleigh criterion and evaluated over a range of control parameters, such as flame length and swirl number. The results show that radial modes induce heat release fluctuations that always add energy to the acoustic field, whereas heat release fluctuations induced by mixed radial-azimuthal modes can add or remove energy. These amplification rates are then compared to the flame response from induced axial fluctuations. For combustor centered flames, these results show that the direct excitation mechanism has negligible amplification rates relative to the induced axial mechanism for radial modes. For transverse modes, the fact that the nozzle is located at a pressure node indicates that negligible induced axial velocity disturbances are excited; as such, the direct mechanism dominates. For flames that are not centered on pressure nodes, the direct mechanism for mixed-modes, dominates for certain nozzle locations and flame angles.
Performance of Darrieus Wind Turbine Using Slotted Blades With Gurney Flap
Authors: Elbaz Ahmed M. R. , Ibrahim Ahmed A. , Mohamed Omar S. , Etman Ahmed K.
Published: January 2021

VAWT such as the Darrieus turbine, could effectively be used in urban spaces. However, the poor self-starting of this type has been considered as a major drawback which limits its application. This also hinders the turbine’s operation at low wind speeds. While the wind energy research community have been lately focusing on augmenting the power coefficient of the Darrieus machines, the enhancement of self-starting capabilities has not attract much attention. In this research, some modifications were applied to the Darrieus type VAWT blades in order to improve its self-starting capability. This entails the application of slotted and Gurney flapped airfoils. The proposed modifications were tested using computational fluid dynamics (CFD) tools. The commercial software ANSYS FLUENT© was used to solve the unsteady Reynolds-averaged Navier–Stokes (URANS) in two dimensions, using two different techniques: the first one is by setting a constant rotational speed for the turbine, and the second one is using the Six Degrees of Freedom (6DOF) solver to calculate the rotational speed during starting due to generated aerodynamic torque on the blades. The proposed airfoil modifications using slot and Gurney flap were applied on Darrieus type VAWT. In a previous study by the authors, the slotted airfoil was shown to enhance the starting torque capabilities, however, the maximum power coefficient decreased, compared to the baseline airfoil turbine. Adding the Gurney flap to the slotted airfoil shows a significant enhancement of the power coefficient throughout the operating range of the turbine. Moreover, the maximum power coefficient of the proposed turbine is also higher than that of the baseline turbine. Further, the self-starting capabilities of the slotted-flapped airfoil turbine has also been remarkably augmented compared to the baseline turbine.
Novel Cyclo-Non-Stationary Indicators for Monitoring of Rotating Machinery Operating Under Speed and Load Varying Conditions
Authors: Mauricio Alexandre , Helm Dustin , Timusk Markus , Antoni Jerome , Gryllias Konstantinos
Published: January 2021

Condition monitoring arises as a valuable industrial process in order to assess the health of rotating machinery, providing early and accurate warning of potential failures and allowing for the planning and effective realization of preventative maintenance actions. Nowadays machinery (gas turbines, wind turbines etc.) manufacturers adopt new business models, providing not only the equipment itself but additionally taking on responsibilities of condition monitoring, by embedding sensors and health monitoring systems within each unit and prompting maintenance actions when necessary. Among others, rolling element bearings are one of the most critical components in rotating machinery. In complex machines the failure indications of an early bearing damage are weak compared to other sources of excitations (e.g. gears, shafts, rotors etc.). Vibration analysis is most widely used and various methods have been proposed, including analysis in the time and frequency domain. In a number of applications, changes in the operating conditions (speed/load) influence the vibration sources and change the frequency and amplitude characteristics of the vibroacoustic signature, making them nonstationary. Under changing environments, where speed and load vary, the assumption of quasi-stationary is not appropriate and as a result a number of time-frequency and time-order representations have been introduced, such as the Short Time Fourier Transform and the Wavelets. Recently an emerging interest has been focused on modelling rotating machinery signals as cyclostationary, which is a particular class of non-stationary stochastic processes. The classical cyclostationary tools, such as the Cyclic Spectral Correlation Density (CSCD) and the Cyclic Modulation Spectrum (CMS), can be used in order to extract interesting information about the cyclic behavior of cyclostationary signals, only under the assumption that the speed of machinery is constant or nearly constant. Global diagnostic indicators have been proposed as a measure of cyclostationarity under steady operating conditions. In order to overcome this limitation a generalization of both SCD and CMS functions have been proposed displaying cyclic Order versus Frequency as well as diagnostic indicators of cyclo-non-stationarity in order to cover the speed varying operating conditions. The scope of this paper is to propose a novel approach for the analysis of cyclo-non-stationary signals based on the generalization of indicators of cyclo-non-stationarity in order to cover the simultaneous and independently varying speed and load operating conditions. The effectiveness of the approach is evaluated on simulated and real signals captured on a dedicated test rig.
The Effects of Specific Heat and Viscosity on Film Cooling Behavior
Authors: Wiese Connor J. , Rutledge James L.
Published: January 2021

For many years, there has been interest in evaluating the effect of density differences between the coolant and the freestream in terms of the cooling effectiveness. Numerous experiments have been conducted with different cooling gases or different temperature gases to evaluate the effect of the density ratio. With little agreement on the best way to scale the density ratio effect, it has become commonplace for some researchers to insist upon matching the density ratio for experimental work.

Unfortunately, the density is not the only property that differs between the various coolant gases used in experiments, and it is certainly not the only property difference between the coolant and the freestream in actual engines. In the present work, we isolate some of these effects through film cooling experiments with carefully selected and conditioned coolant gases at near identical densities but exhibiting other property differences. Most significantly, coolant specific heat varied, but subtle viscosity and thermal conductivity effects were present. Through measurements of the adiabatic effectiveness from a film cooling hole on a leading edge model, we are able to show that the specific heat effect is just as important as the density effect, providing more evidence that effects in prior research attributed to density differences, are actually a combination of density and other property differences.
Generating Laminar Flame Speed Libraries for Autoignition Conditions
Authors: Puduppakkam Karthik V. , Modak Abhijit U. , Wang Cheng , Hodgson Devin , Naik Chitralkumar V. , Meeks Ellen
Published: January 2021

With advanced gas turbine combustor and internal combustion engine designs, autoignition can happen alongside flame propagation. Laminar flame speeds are required to model flame propagation. Determining laminar flame speeds using simulation assumes flames are freely propagating, an assumption that is not valid when autoignition does occur. From a CFD modeling viewpoint however, it is useful to have extrapolated laminar flame-speed values over a wide range of conditions, to allow CFD to operate smoothly and avoid discontinuities while calculating flame-propagation properties. In this work we focus on developing an approach for generating laminar flame-speed libraries under both nonigniting and autoigniting conditions. Following a test of whether autoignition occurs, laminar flame speeds are either modeled or extrapolated. The details of the approach implemented and its validation are explained. We assess the accuracy of the extrapolation employed by calculating relevant coefficients based on flame speeds from nearby operating points. Recommendations are made for the time scales to be used in determining autoignition occurrence. Fuel effects are also explored in this context.
Secondary Flow Response to Endwall Jets in a Low Pressure Turbine
Authors: Fletcher Nathan , Marks Christopher R. , Donovan Molly H.
Published: January 2021

Due to the significant losses contributed by the secondary flow features, an active flow control system was implemented in a low-pressure turbine linear cascade which consisted of localized endwall jets with small mass ratios to perturb the dominant passage vortex. Benefits included significant area-averaged total pressure loss reduction and improved exit angle deviations which help to open the design envelope to application of high-lift front-loaded blades. This report looks to reveal the impact of steady and pulsed endwall blowing on the secondary flow dynamics. High-speed stereoscopic particle image velocimetry for an in-passage measurement plane was utilized to investigate the time-dependent behavior of key flow features such as the passage vortex. At baseline conditions, the passage vortex is characterized by time-varying oscillatory motion in the pitchwise direction, streamwise undulation, bursting, and fluctuating strength. Upon actuation of endwall jets, some of these defining dynamics of key flow features were greatly affected. A complementary investigation of the endwall jets mounted outside of a turbine environment in order to study the emitted structures at varying conditions was used to explain the observations found in the turbine passage. Insights into the secondary flow responsiveness demonstrated that loss reduction was realized by inducing reduced coherence of the passage vortex. Despite pulsed blowing at discrete frequencies associated with the passage vortex, there was no indication that instability excitation was exploited. Rather, the endwall jets acted as a periodic shape-change to the endwall which weakened the passage vortex and forced it closer to the suction-surface.
A Numerical Approach to Centrifugal Compressor Stage Flow Path Design Synthesis and Optimization
Authors: Goldenberg Vlad , Gorman John M. , Simon Terrence , Sparrow Ephraim M.
Published: January 2021

This paper proposes geometry parameterization of a complete single centrifugal compressor stage and applies CFD-driven optimization using artificial neural networks and a Kriging surrogate model. Kinematic velocity triangle analysis is used to arrive at an initial design, which is then improved by using automated optimization algorithms and fundamental flow physics using CFD simulation. By allowing the design to evolve, guided by CFD, new and untested optimum designs are possible. This work deals specifically with design and optimization of the flow path. Design for structural aspects such as vibration, rotor dynamics and other mechanical aspects is outside the scope of this work.

The CAD parameterization enables robust specification of the flow path geometry while maintaining a sufficiently small set of parameters for practical design space exploration. The parameterization includes an impeller with optional splitter blades, a vaneless diffuser and volute. Steady-state, RANS-based CFD is employed in the analysis of both the rotationally-periodic components and the volute geometry.

Direct optimization and response surface optimization are demonstrated for rotationally periodic components to maximize design-point efficiency of the flow path using a multi-objective genetic algorithm (MOGA). Improvements in total-total isentropic efficiency of between 4 and 5 percent are achieved.

Optimization of the flow path of the volute is likewise demonstrated. In the case of the volute, a Kriging response-surface model is used and a 1.4 percentage point improvement is shown. Further research in the utilization various implementations of Artificial Intelligence (AI) machine learning techniques in conjunction with parameterized turbomachinery flow paths to enable enhanced designs to be generated effectively is proposed.