bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flow Field Instability and Rotordynamic Impedances for an Open Impeller Centrifugal Pump in Transient Four-Quadrant Regimes
Authors: Ali Md Shujan , Mortazavi Farzam , Palazzolo Alan 
Published: January 2021

Abstract
The American Petroleum Institute (API) level 2 rotordynamic stability analysis requires determination of possible destabilization forces on a compressor or pump impeller. Dynamic forces in transient regimes are often excluded although a turbomachine impeller may experience transient operation intentionally or accidentally. The centrifugal pump head, flow direction, rotation and torque can be both positive and negative in transient regimes. For example, in a renewable energy application, pump flow direction and rotation are reversed to generate power from the imposed fluid head. The complete characteristics of a centrifugal pump correspond to all four quadrants (4Q) of operation, to encompass all possible operating conditions. It is required to understand centrifugal pump impeller dynamic forces and rotordynamic responses for all 4Q for design, fault diagnostic, instability analysis, upset conditions (such as water hammer, surge etc.) and for reliable operation of high energy density machines. In the open literature, whirling impeller rotordynamic analyses appears only for normal pump operation. Centrifugal pump dynamic forces, rotordynamic impedances and flow instabilities of an open impeller are reported for 4Q operating regimes in this paper. A transient Computational Fluid Dynamics (CFD)-based model is implemented which is applicable to nonaxisymmetric turbomachinery components, such as with a volute and/or vaned diffuser. Whirling motion of the impeller is modeled by imposing mesh deformation at the impeller walls. A phase modulated multi-frequency mesh deformation method is imposed for better numerical efficiency. Reynolds Averaged Navier-Stokes (RANS) equations with the Shear Stress Transport (SST) turbulence model along with a transitional bypass turbulence model are employed for the CFD solution. The results show the underlying flow field instability and stall cells responsible for the impedance shapes. Furthermore, the model is employed for determining the dependence of the outputs on specific speed to extract rotordynamic forces more efficiently. Impeller dynamic forces are found to scale with the size of the impeller for the same eccentricity ratio and the same flow coefficient. Strength of impeller rotating stalls has dependence on whirl frequency ratio.
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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 &lt; Rez &lt; 5.14 × 105, 1.65 × 106 &lt; Reθ &lt; 3.16 × 106, 0.10 &lt; Ro &lt; 0.60 and 3.40 × 1011 &lt; Gr &lt; 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

Abstract
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

Abstract
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

Abstract
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

Abstract
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 &lt; S/C &lt; 0.5 and S/C &lt; −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

Abstract
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.