bluuebunny/crossref_metadata_2025_split huggingface dataset:
Integrated Control Design for a Partially Turboelectric Aircraft Propulsion System
Authors: Simon Donald L. , Bianco Santino J. , Horning Marcus A. 
Published: September 2023

Abstract
Electrified Aircraft Propulsion (EAP) holds great potential for reducing aviation emissions and fuel burn. A variety of EAP architectures have been proposed including partially-turboelectric configurations that combine turbofan engines with motor-driven propulsors. Such architectures exhibit coupling between subsystems and thus require an integrated control solution. To address this need, this paper presents an integrated control design strategy for a commercial single-aisle partially-turboelectric aircraft concept consisting of two wing-mounted turbofan engines and an electric motor driven tailfan propulsor. Within this architecture the turbofans serve the dual purpose of generating thrust and supplying mechanical offtake power used to generate electricity for the tailfan motor. The propulsion control system is tasked with coordinating turbofan and tailfan operation under both steady-state and transient scenarios. The paper introduces a linear state-space representation of the architecture reflecting the coupling between the turbofan and tailfan subsystems along with loop transfer functions reflecting open- and closed-loop system dynamics. Also discussed is an applied strategy for scheduling the tailfan setpoint command based on the average sensed fan speed of the two turbofans. This approach ensures synchronized operation of the turbofan and tailfan subsystems while also allowing the turbofan fuel control design to be simplified. Performance of the integrated control design is assessed through a real-time hardware-in-the-loop test conducted at the NASA Electric Aircraft Testbed. During this test a scaled version of the electrical system and turbomachinery shaft dynamics were implemented in electrical machine hardware and evaluated under closed-loop control. Results from this facility test are presented to illustrate the efficacy of the applied integrated control design approach under steady-state and transient scenarios including a full-flight mission profile.
A Numerical Investigation of the Design Point Performance for a Centrifugal Compressor With a Parameterized Volute
Authors: McLaughlin Laura , Stuart Charles , Spence Stephen , Rusch Daniel , Geron Marco , So Kwok Kai , Kreiselmaier Erich 
Published: September 2023

Abstract
The volute component of a centrifugal compressor is a complex three-dimensional geometry used to collect the diffuser outflow and discharge it to a single point of delivery. Volute design has a significant impact on the overall dimensions of the entire compressor stage and it’s performance. By reducing the extent of the compressor housing in the radial direction, without sacrificing performance, the compressor will be less expensive to manufacture, lighter in weight and could be suitable for a wider range of applications. The volute can only be designed to achieve optimal performance at one operating point per compressor constant speed line. Away from this operating point, the flow will either accelerate or decelerate through the volute component and will generate increased losses.
The current investigation considered an existing state-of-the-art high pressure ratio, centrifugal compressor coupled with a new vaned diffuser component. The new diffuser incorporated a diverging endwall that reduced its length by 15% in the radial direction and consequently discharged a significantly different flow field to the volute inlet. Hence, the existing volute was no longer optimally designed for the diffuser outflow. This study targeted the design of a new volute that took advantage of the reduced diffuser diameter and matched the outlet flow field of the new diffuser. This study considered the compressor design operating point and implemented a fixed 15% radial reduction to the radial extent of the volute component. The volute spiral was carefully parameterized and a Design of Experiments investigation was set up to quantify the impact of these parameters on the performance of the volute and the upstream components. The resulting analysis generated understanding of the underlying flow physics responsible for the performance changes.
The study found that a 15% reduction could be applied to the volute geometry while achieving 99.9% of the baseline compressor total-total efficiency at design point. Detailed flow field analysis has shown the impact of different volute geometry parameters on compressor performance. For example, the area under the volute tongue was demonstrated to significantly impact the losses generated in the volute as well as the circumferential flow uniformity at the diffuser outlet. Although this investigation considered design point only, the improvement to circumferential flow uniformity suggests that the highest efficiency radially reduced design may achieve an extension to the compressor operating map width. Overall, the combination of the diverging endwall diffuser and the new volute design achieved a 15% reduction in the radial extent of the compressor stage downstream of the impeller (from the impeller trailing edge radius to the outer radius of the volute casing).
Implementation of a Central Upwind Scheme in Unsteady Compressible Flow Simulation of Multi-Stage Axial-Centrifugal Compressor
Authors: Jing Zhenhao , Neumeier Yedidia , Prasad J. V. R. , James Darrell K. 
Published: September 2023

Abstract
This work investigates the merits of converting the KT central scheme into a central-upwind scheme for simulating the compressible, unsteady flow in a multi-stage axial-centrifugal compressor. The conversion from a pure central scheme to an upwind scheme is very simple, and it follows the basic idea of the original KT scheme. The paper investigates the quality of shock capturing, artificial mass generation, and execution time. The results suggest that, compared to the KT scheme, the central-upwind scheme produces a thinner shock structure, reduced numerical error even for cases involving drastic variations of flow field geometry, and a higher tolerance for CFL number &gt; 0.5.
Direct Numerical Simulation of Riblets Applied to Gas Turbine Compressor Blades at On- and Off-Design Incidences
Authors: Kozul Melissa , Nardini Massimiliano , Przytarski Pawel J. , Solomon William , Shabbir Aamir , Sandberg Richard D. 
Published: September 2023

Abstract
Any realizable increase in gas turbine efficiency has significant potential to reduce fuel burn and environmental impact. Streamwise micro-groove surfaces (‘riblets’) are well-known as a passive surface treatment to reduce drag, which may be useful in the context of increasing overall gas turbine efficiency. This paper presents the first direct numerical simulation of potentially performance-enhancing riblets on an axial flow high pressure compressor blade, where the micro-geometry of the riblets is fully resolved. The midspan section of a NACA6510 profile is considered at an engine-relevant true chord Reynolds number of 700,000 and Mach number 0.5 based on inlet conditions. Fixed triangular (or sawtooth) riblets are considered in the present numerical campaign. The current high-fidelity computational method permits the extraction of data such as the wall shear stress directly from the riblet surface. At the design incidence, the riblets tend to promote earlier transition to a turbulent flow over the suction side, yet significantly reduce the skin friction over the entire downstream chord to the trailing edge. The riblets reduce the viscous force over the blade by up to 18% at this nominal inflow incidence. Thus the current dataset permits new insight into the action of the riblets, since most studies of riblets on turbomachinery blades have been conducted experimentally where direct measurements of skin friction are not possible. The riblets are also able to reduce the skin friction over the high pressure compressor blade at off-design incidences, a promising result given axial flow compressors must cope with variable operating conditions.
Constitutive Model Based Efficient Creep-Fatigue Damage Computation Technique for Steam Turbine Rotors to Enhance Flexible Operational Capabilities
Authors: Sen Suvadeep , Almstedt Henning 
Published: September 2023

Abstract
In the new era of renewable energy, flexible operation of conventional power plants is inevitable, causing high creep-fatigue life consumption. Conventional life assessment methods are deemed to be conservative to address the current requirements. The use of unified constitutive models for the analysis of damage evolution in steam turbine rotors in the past decade has shown promising results and closely relate to experimental data. However, identification of large number of material constants and high computational efforts hinder the widespread use of such models. In this paper, the latter is addressed using a novel representative input cycle (RIC) concept together with the non-iterative asymptotic numerical method (ANM). Various start-up shutdown sequences of a typical steam turbine rotor are studied using a unified constitutive model based on Chaboche’s kinematic hardening including the damage parameter, Chaboche-Rousselier’s isotropic hardening model including the damage parameter, Norton’s viscoplastic flow model, Lemaitre’s damage potential function and Kachanov-Rabotnov’s creep damage law. First, a conventional FEM technique is used and then the proposed RIC method is used to study the evolution of inelastic variables. The reduction in computational efforts and the compromise in accuracy using the proposed method is studied.
Effects of Fuel Composition on Azimuthal Combustion Instabilities in an Annular Combustor Equipped With Spray Injectors
Authors: Latour Véranika , Durox Daniel , Rajendram Soundararajan Preethi , Renaud Antoine , Candel Sébastien 
Published: September 2023

Abstract
In a context where the aviation sector is actively looking into replacing standard jet fuels with sustainable aviation fuels (SAFs), examining the effects of fuel composition on combustion dynamics is of current interest. There are indeed indications that the chemical composition may notably impact the location of the unstable operating points and the amplitude and frequency of thermo-acoustic oscillations. The fuel composition effect is hence investigated in this article by considering the case of binary fuel mixtures composed of heptane and dodecane, two fuels presenting very different volatilities (Tboil = 380 K for heptane and Tboil = 480 K for dodecane). The blends composition is varied between pure heptane and pure dodecane, and the corresponding dynamical behavior is observed in an annular combustor equipped with swirl spray injectors. It is shown that the composition changes the location, extent, and geometry of the unstable domain. The frequency of the instability also depends on fuel composition. The differences in behavior observed for the different blends are then characterized by measuring flame describing functions (FDFs). These functions are determined in a separate burner representing a sector of the annular chamber in which the air flow is modulated from the upstream side. It is found that the FDF gain and phase curves change with the fuel blend. These data, combined with a reduced-order thermo-acoustic model, are used to interpret the experimental observations. From a more practical standpoint, this study indicates that it is important to examine the dynamical behavior of combustors that will use novel fuels like SAFs.
Experimental Vibroacoustic Measurements of a Centrifugal Compressor Stage for Oil & Gas Applications
Authors: Santoni Andrea , Zuccherini Martello Nicolò , Grimaldi Roberto , Mori Francesco , Fausti Patrizio , Chiari Simone , Carmicino Carmine , Ferrini Marcello , Rossin Stefano 
Published: September 2023

Abstract
Designing adequate noise mitigations on centrifugal compressors for Oil & Gas applications to meet the noise regulation requirements for industrial plants requires an accurate prediction of the radiated noise. Further investigation of centrifugal compressors’ noise emission is still needed to develop predictive sound models, which require a thorough understanding of all noise generation mechanisms involved. This paper presents the results of an experimental vibroacoustic analysis conducted on a centrifugal compressor equipped with one closed impeller. Vibroacoustic measurements were performed in three different operating conditions at various working points, aiming to characterize the noise emission of the compressor stage. The results identified the main tonal components of the compressor stage and the noise generated by auxiliary machinery under different working conditions. Consistent with findings from other studies from the literature, a strong influence of the rotational impeller speed on the radiated sound pressure is observed. Moreover, the results propose an experimental comparison between vaned and vaneless diffuser configurations, highlighting higher sound pressure levels radiated with a vaneless impeller design. The paper concludes by highlighting the difficulties related to the experimental testing of such machinery and the significant influence of noise emitted by auxiliary equipment.
Probabilistic Life Estimation of Turbine Shaft Bolted Joints Considering the Effect of Nonlinear Stress Gradients on Crack Growth Rates
Authors: Tümergin Özge , Ertekin Şevket , Kara Aliyye , Giz Ayşe Su , Kula Topak Emel , Ozturk Umud Esat , Muğan Ata 
Published: September 2023

Abstract
Crack growth in mechanical components is determined by initial crack size and fracture toughness that have probabilistic distributions. With a focus on a turbine shaft bolted joint made of Inconel 718, fracture damage was examined during a test cycle while crack size and fracture toughness were random variables. A finite element model of a turbine was created to calculate the stress field in turbine components. Following, stress distribution around the potential crack zones was included in calculating the crack growth. Proposed approach was verified by making comparisons with the results of Nasgro. Probabilistic distribution of crack depth and length, expected life and probability of detecting a crack was included in crack growth analyses. Probability of failure of the stub shaft was calculated via Monte-Carlo simulations. Comparisons were made with the crack growth results of Nasgro to verify the developed methodology. Effect of inspection period on probability of detecting the cracks before failure was determined.
Investigation on the Influence of Surface Roughness of Rotating Microchannel on Flow Conditions
Authors: Rusin Krzysztof , Wróblewski Włodzimierz , Rulik Sebastian , Pahlavanzadeh Mohammadsadegh , Hasani Malekshah Emad 
Published: September 2023

Abstract
This paper presents numerical and experimental investigations of the flow in a rotating microchannel whose walls’ roughness covers a substantial part of the channel height. The roughness can intensify the momentum and heat transfer but also increase the drag force. An intentionally designed roughness may contribute to the improvement in the effectiveness of different processes, especially in turbomachinery, where additional effects that accompany the rotation are of great importance. The methods of assessing the roughness impact in the rotating microchannels constitute a scientific gap and are discussed in this research.
The experimental part was carried out on the Tesla turbine, whose rotor consists of multiple disks spaced by a sub-millimetre distance. The investigations were performed for two sets of disks. In the first case, the surfaces of the disks were polished to obtain a hydraulically smooth flow regime, and in the second case, they were roughened with the use of a tracing wheel.
In the numerical part of the study, the impact of the roughness on the momentum transfer was modelled with the use of the turbulence boundary conditions imposed on the surfaces of the disks. The numerical and experimental results were compared and the validity of the method was assessed.
Cooling Effectiveness of Additive-Manufactured Internal Structure Within a Double Wall Cooling System
Authors: Song Ho Seop , Park Hee Seung , Kim Taehyun , Choi Seungyeong , Moon Hee-Koo , Cho Hyung Hee 
Published: September 2023

Abstract
An internal structure that additively manufactured (AM) within a double-wall cooling system for gas turbine applications was proposed and evaluated for its ability to increase cooling efficiency. Polymer AM specimens were fabricated using a Biot number similarity approach with actual gas turbine materials. Three types of double wall specimens were manufactured: a standard double wall cooling (baseline) case, a double wall cooling with pin-fin structure (pin), and a double wall cooling with a cube lattice structure(cube). Flow pattern analysis was conducted to examine the effect of the cube lattice on the internal structure of the double wall cooling system, and static pressure was measured in each chamber. An infrared thermography method was used to measure overall cooling effectiveness on the specimen surface, and each case was tested at blowing ratios (M = 0.4, 0.6, and 0.8). Compared to the baseline case, the cube lattice structure improved cooling effectiveness by 3.36% at M = 0.4, the most significant improvement of 4.33% at M = 0.6, and 2.71% at M = 0.8. These findings suggest that the use of a cube lattice structure that produced by AM can effectively enhance the cooling performance in double wall cooling system for gas turbine hot parts.
Learning RANS Model Parameters From LES Using Bayesian Inference
Authors: Hemchandra Santosh , Datta Anindya , Juniper Matthew P. 
Published: September 2023

Abstract
We propose a formal mathematical approach to assimilate LES data into values of RANS model parameters combined with some prior knowledge of the expected RANS parameter values. This is achieved using Bayesian inference to determine parameter values that maximize their posterior probability and is known as maximum a posteriori (MAP) estimation. We apply this approach to a premixed turbulent methane-air round jet flame using unburnt mixture equivalence ratio and bulk flow velocity as design parameters. The k-ε model is used for turbulence closure and the eddy dissipation concept (EDC) model is used to model combustion. Three dimesional LES data for six design cases are computed and upto three of these are used for MAP estimation. The likelihood of RANS solutions is evaluated using flow field statistics from LES at training data points. The results show significant improvement in agreement between LES and RANS solutions, computed using MAP estimate parameters for species mass fraction and temperature fields at design points not in the training set. Marginal improvement is observed for velocity fields. This is most likely due to the absence of production terms in the RANS model that capture the three-dimensional nature of the flow being modelled. The marginal likelihood of the RANS model when assimilating both k-ε and EDC model parameters is significantly higher than the case that leaves out the EDC model parameters. This suggests that the former approach is more likely to yield reliable RANS parameters. These results demonstrate the viability of MAP estimation as a means to improving the reliability of turbulent reacting flow RANS simulations for engineering design and optimization applications.
An Apparatus for Tensile and Fatigue Testing of Metallic Materials Involving Miniature Specimens
Authors: Pal Ritam , Garikipati Shashank , Banks Andrew , Basak Amrita 
Published: September 2023

Abstract
Mechanical testing under tensile and fatigue loading is ubiquitous. Such testing often requires expensive equipment and peripherals. During the development stages of any new material or manufacturing processes, it is often desired to perform quick evaluations to optimize the material composition or the manufacturing process parameters to achieve the desired properties. To address this requirement, this paper designs, develops, and deploys a low-cost custom testing apparatus capable of performing both tensile and fatigue testing to investigate the failure characteristics of a candidate material system, e.g., cold-rolled Al7075-T6. The apparatus consists of a linear actuator, a load cell, a polycarbonate sleeve, and a data acquisition system. The apparatus is additionally integrated with a high-speed video imaging system to investigate the failure evolution. The experiments are performed through a custom MATLAB® code. The resulting data are processed to extract the relevant mechanical properties such as the yield strength, the ultimate tensile strength, and the fatigue life. The results demonstrate that the apparatus can reliably characterize the tensile and fatigue properties of Al7075-T6. Throughout its use, the apparatus is found to be robust, resilient, and easy to assemble/disassemble. In conclusion, this apparatus can serve as a low-cost testing equipment to understand tensile and fatigue failure characteristics of metallic specimens during the qualification stages.
Effect of Leading-Edge Inlet Models on the Performance of Gas Bearings Operating in Highly Compressible Flow Regimes
Authors: Prabhakar Arvind , Kim Daejong 
Published: September 2023

Abstract
Reynolds equation has been widely used in modelling lubrication flow and load carrying performance prediction of fluid flow within gas bearings for a number of years. However, the underlying assumption of negligible fluid inertia is not a reasonable design approach philosophy as the operating speeds of such bearings become extremely high. In this paper, A 3D thermos hydrodynamic (THD) model is presented to show effects of leading-edge inlet models on pressure profile predictions of gas films for a rigid 3d bearing film, operating in high speed and highly compressible flow regimes.
The model solves full 3-dimensional Navier-Stokes equations in laminar form coupled along with the gas film energy equation for gas temperature throughout the gas film. Results are also compared with a classical Reynolds equation-based 3D thermos-hydrodynamic model to show impact of choice of boundary condition treatments on performance and pressure profile predictions of such bearings, along with impacts of including inlet dead volume (IDV) region modeling on gas film properties. Further, some more results are discussed from solutions of 3-dimensional Navier-Stokes equations coupled with Peng-Robinson equation of state (EOS), to illustrate impacts on flows and pressure profiles when considering highly compressible real gas effects for typical high density refrigerant flows within such bearings.