bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improvement of Turboshaft Restart Time Through an Experimental and Numerical Investigation
Authors: Ferrand Antoine , Bellenoue Marc , Bertin Yves , Marconi Patrick 
Published: January 2021

Abstract
Inflight shutdown of one engine for twin-engine helicopters has proven beneficial for fuel consumption. A new flight mode is then considered, in which one engine is put into sleep mode while the second engine runs at nominal load. The ability to restart the engine in sleep mode is then critical for safety reasons. Indeed, the certification of this flight mode involves ensuring a close-to-zero failure rate for in-flight restarts and a fast restart capability of the shutdown engine (focus of this paper). Fast restart capability is necessary in case of a failure of the operating engine. Indeed, there is no more power available, and the helicopter can lose up to 15–20 meters per second during autorotation. The restart time becomes a critical parameter to limit the loss of altitude. The aim of the paper is to assess the potential restart time saving using an approach combining test rig data analysis and numerical results generated by a thermodynamic model able to simulate at low rotational speed. It is important to understand the detailed phenomenology of the startup process and the various subsystems involved, first to highlight the influencing parameters and then to establish an exhaustive listing of the possible time optimizations. The results of this study show that a fast restart going from sleep mode to max power speed can be up to 60% faster than a conventional restart going from sleep mode to idle speed, which is significantly faster.
Simulation and Experimental Investigation of a New Type of Combined Seal Structure
Authors: Li Jin , Fu Xiaoli , Yan Shenglin 
Published: January 2021

Abstract
Based on the study of leakage characteristics of labyrinth seal structure (LSS), a new type of combined seal structure (CSS) consisting of the labyrinth structure and the nozzle structure has been proposed. The sealing characteristics of CSS and LSS are compared by means of numerical simulation and experiments, and the effects of the internal resistance of the device, structural geometric parameters and other factors on the leakage characteristics of CSS are studied. The results illustrate the following conclusions: (a) When the inlet flow is 12 m3/h and the internal resistance of the device is 2000–4000 Pa, the leakage rate of CSS decreases by 30%–40% in comparison with that of LSS, which indicates that the performance of CSS is much better than that of LSS. (b) The leakage rate increases as the internal resistance of the device increases. When the internal resistance of the device increases from 2000 Pa to 8000 Pa, the leakage rate increases from 26% to 72%. (c) When the internal resistance of the device is constant, the larger the inlet flow, the smaller the leakage rate. (d) The choice of nozzle radius in structural geometric parameters is more important for the leakage rate than the tooth height and teeth numbers. When the nozzle radius decreases, ΔPAB (pressure difference between the labyrinth structure and the nozzle structure) and the leakage rate decrease accordingly.
Investigation of Endwall Heat Transfer in Staggered Pin Fin Arrays
Authors: Otto Marcel , Gupta Gaurav , Tran Patrick K. , Ghosh Shinjan , Kapat Jayanta S. 
Published: January 2021

Abstract
Arrays of staggered pin fins are a typical geometry found in the trailing edge region of modern airfoils. If coolant is supplied by bleeding from the mid-section of the airfoil instead of provided through the root, the channel length is insufficiently long to reach a fully developed flow which is commonly found from the fifth row downstream. This present study focuses on the developing section (four rows) of a staggered array with a height-to-diameter ratio of 2 and a spanwise and streamwise spacing of 2.5, respectively. Measurements are conducted at Reynolds numbers of 10,000 and 30,000 based on the maximum velocity and pin diameter. Stereoscopic particle image velocimetry (PIV) is used to describe the flow field and turbulence characteristics in the wake of the first and third row pin. It is found that the dominating vortical structures depend highly on the Reynolds number. A transient thermochromic liquid crystal (TLC) technique is used to obtain local heat transfer coefficients on the endwall which are then discussed in the context with the vortical structures. The structure of the horseshoe vortex and the transient wake shedding behaves differently in the first and third row. The interaction of both vortex systems affects directly the endwall heat transfer. The results are supplemented by a thorough discussion of TLC and PIV uncertainty.
A Review of Journal Bearing Induced Nonlinear Rotordynamic Vibrations
Authors: Kim Sitae , Shin Dongil , Palazzolo Alan B. 
Published: January 2021

Abstract
Nonlinear elements found in fluid film journal bearings and their surrounding structures are known to induce sub- and super-synchronous, chaos and thermally induced instability responses in rotor-bearing systems. The current review summarizes the literature on journal bearing induced nonlinear, rotordynamic forces, and responses. Nonlinear, thermo-elasto-hydrodynamic (TEHD) aspects of journal bearings has become increasingly important in high-performance turbomachines. These have significant influence on bearing dynamic performance and thermally induced, rotordynamic instability problems. Techniques for developing TEHD bearing models are discussed in the second section. Nonlinear solution methodology, including bifurcation determination and time and frequency domain methods such as harmonic balance, shooting and continuation, etc., is presented in the third section. Numerical tools to determine nonlinear vibration responses, including chaos, along with examples of bearing induced nonlinear vibrations are presented in the fourth and fifth sections, respectively.
Performance Analysis of Solar-Powered Organic Rankine Cycle With Energy Storage in Different Climate Zones in the United States
Authors: Hemmati Hadis , Zhang Jian , Spayde Emily , Mago Pedro J. , Cho Heejin 
Published: January 2021

Abstract
Solar-powered organic Rankine cycle (ORC) is considered a promising technology and has the potential to provide clean electric energy. Extensive studies on the design of ORC systems have been conducted and reported in the literature. However, few studies have presented the influence of climate zones on the performance of a solar-powered ORC, especially for an integrated ORC and energy storage system. This paper presents an analysis to determine the performance of solar-powered ORCs with electric energy storage (EES) systems to supply electricity to buildings in different climate zones in the United States. The building type evaluated in this paper is a large office, and the energy consumption of the facility in each climate location was determined using EnergyPlus. The ORC-EES operational strategy used in this investigation is described as follows: when solar irradiation is adequate to produce power, the ORC charges the EES. Then, when there is no solar energy available, the EES provides power to the building. The ORC-EES is evaluated based on the potential to reduce the operational cost, the primary energy consumption, and the carbon dioxide emission. Furthermore, the influence of the number of solar collectors and the EES size on the performance of the ORC-EES system is investigated.
Vibration Analysis and Methods of Dry Friction Damping of Tubed Vortex Reducer
Authors: Chen Siyuan , Wang Yanrong , Wei Dasheng , Luo Yanbin , Gao Shimin 
Published: January 2021

Abstract
The tubed vortex reducer is a new structure of aero-engine, which is widely used in advanced large bypass ratio high performance turbofan engines. It is usually installed between the rear two-stage discs of the high-pressure compressor, and reduces the generation of free vortex by restricting the flow path of the cooling airflow, thereby reducing the pressure loss of the cooling airflow and improving the engine efficiency. In this paper, vibration analysis of tubed vortex reducer is carried out by experiments and numerical simulations. Using the finite element method, the natural vibration characteristics of the vortex reducer are calculated with ANSYS. The sensitivity analysis of the impact of design parameters on the vibration characteristics is carried out. In addition, the vibration test bench of the vortex reducer is set up, and the vibration test of the vortex reducer is conducted by means of frequency sweeping and hammer hitting respectively. The experimental results satisfactorily reproduce the simulation results. Then the theoretical model of dry friction damping of vortex reducer is established. Based on the dynamic model of the complex contact system composed of vortex reducer and damping sleeve, the relationship between energy dissipation in different directions is derived. And a method evaluating the performance of vibration reduction is presented for calculating its equivalent damping ratio. Finally, the influence of the key design parameters and different installation methods on the damping ratio is analyzed. Overall, this work can provide reference for vibration reduction design and optimization of vortex reducer.
Size and Reynolds Number Effects on Compressor Performance and Scaling
Authors: Chen Hua 
Published: January 2021

Abstract
Performance of small turbocharger compressors is greatly affected by their size and size related Reynolds number. Although the effect of Reynolds number on compressors’ efficiency is well known, the effects of Reynolds number have on other performance and design parameters of these compressors are little recognized in open literature. This paper reports the effects of Reynolds number and size on peak efficiency and surge flow of turbocharger compressors, studies the influences of Reynolds number on optimum compressor blade count. Test results show that when a compressor is scaled up (Reynolds number increases), its stability is generally reduced, and vice versa when scaled down. How this feature can be utilised in compressor design is discussed, and an example is given to show how compressor efficiency and flow range may be improved when scaling down by employing a more stable vaneless diffuser and reducing impeller blade number. Finally, the effect of Reynolds number on blade number selection for different sizes of a compressor is studied through CFD and test, and based on these experiences and the theory of flow on flat plate, a design guide line is proposed for the optimum blade numbers in compressor scaling for both impellers with and without splitter.
Large Eddy Simulation of Wake-Shear Layer Interactions Over a Multi-Element Aerofoil
Authors: Naskar Souvik , Sarkar S. 
Published: January 2021

Abstract
Modern commercial airliners use multi-element aerofoils to enhance take-off and landing performance. Further, multielement aerofoil configurations have been shown to improve the aerodynamic characteristics of wind turbines. In the present study, high resolution Large Eddy Simulation (LES) is used to explore the low Reynolds Number (Re = 0.832 × 104) aerodynamics of a 30P30N multi-element aerofoil at an angle of attack, α = 4°. In the present simulation, wake shed from a leading edge element or slat is found to interact with the separated shear layer developing over the suction surface of the main wing. High receptivity of shear layer via amplification of free-stream turbulence leads to rollup and breakdown, forming a large separation bubble. A transient growth of fluctuations is observed in the first half of the separation bubble, where levels of turbulence becomes maximum near the reattachment and then decay depicting saturation of turbulence. Results of the present LES are found to be in close agreement with the experiment depicting high vortical activity in the outer layer. Some features of the flow field here are similar to those occur due to interactions of passing wake and the separated boundary layer on the suction surface of high lift low pressure turbine blades.
Transfer Function Based Optimization of Film Hole Sizes With Conjugate Heat Transfer Analysis
Authors: Dutta Sandip , Smith Reid 
Published: January 2021

Abstract
With the improvements of 3D metal printing of turbine components, it is now feasible to produce ready to use production quality parts without casting and conventional machining. This new manufacturing technique has opened new frontiers in cooling optimizations that could not be practiced before. For example, it is now or in-the-near-future possible to have unconventional diameters of film holes. This paper seeks to optimize each film hole diameter at the leading edge of a turbine to achieve an optimum thermal objective. The design technique developed uses a transfer function-based learning model and can be used for both stationary and rotating airfoils. Proposed optimization procedure will also work on other parts of an airfoil; but our current analysis is limited to the leading-edge region. To apply this work on other critical regions, the corresponding heat transfer coefficients need to be implemented while building the transfer functions suitable for that specific component; however, the underlying optimization technique stays the same for any other component. Any optimization technique needs cost and benefit criteria. Cost is minimized in optimization to get maximum benefit with given constraints. In gas-turbine heat transfer, there is a ceiling constraint on maximum temperature that must be satisfied. This study minimizes the coolant flow with satisfying the constraints on average metal temperature and metal temperature variations that limit the life of turbine components. Proposed methodology provides a scientific basis for the sizing of film holes and is expected to decrease developmental cost of efficient thermal designs.
Circumferential Combustor Cavity Flow Fields With Decreasing Core Flow
Authors: Bohan Brian T. , Polanka Marc D. , Goss Larry P. 
Published: January 2021

Abstract
Prior research into Ultra Compact Combustors (UCC) showed an axial length savings compared to traditional gas-turbine combustors. This savings is achieved by swirling the reactants circumferentially in a recessed cavity around the outside diameter of the engine. A similar circumferential combustor is envisioned for a new engine configuration that positions the combustor outboard of a radial compressor and an inflow turbine. This configuration will offer an axial length savings for the entire engine, not just the combustor. The new engine configuration will not utilize a core flow path and thus requires all engine air from the compressor to pass through, or around, the combustor cavity. This report characterizes the cavity flow behavior as the core flow quantity was reduced from 80% of the total engine mass flow rate down to zero, representing the new engine configuration, while maintaining constant cavity mass flow rates. Velocity profiles were obtained with particle-shadow image velocimetry (PSV) in cold flow and with particle streak emission velocimetry (PSEV) in reacting flow experiments. The cold flow results showed that the core flow produced a suction and removed fluid from the circumferential cavity resulting in a lower cavity mass flow rate. This behavior resulted in lower circumferential velocities at higher core flow percentages and the fastest cavity velocity with zero core flow. Reacting flows produced a similar result with the fastest cavity velocities achieved at reduced, but non-zero core flows, and the slowest velocities at the highest and zero core flows. Overall, it was found that there was no negative impact on performance from the removal of the core flow that would prohibit development of the new engine.
Experimental Study on the Wear-in Behaviour of Brush Seals
Authors: Hildebrandt Manuel , Munz Oliver , Schwitzke Corina , Bauer Hans-Jörg 
Published: January 2021

Abstract
Although some investigations on the wear behaviour of brush seals can be found in the literature, not all aspects are yet understood during the wear-in process of the seal in operation. However, it is important to understand all aspects in order to ensure a long service life of the seal. The present paper gives an overview of the procedure, the results and the knowledge gained through the long-term rub tests carried out with a tungsten carbide coated rotor with the aim of determining the time required to wear the seal in (“time-on-condition”). The total test duration of the cyclic tests was approx. 100 h. The measurements have shown that on the basis of the applied test procedure the initial wear-in phase is completed after approx. 40 cumulated operating hours and only very little wear occurs afterwards. Furthermore, it could be shown that the major part of the wear occurred within a short period of time within these 40 h and that the properties of the test cycle have a great influence on the wear-in time. The coupling of the rubbing intensity with time is achieved by measuring the transient rotor temperatures during rubbing.
The tests carried out have also shown that the influence of the concentricity properties of the rotor can resulting in rotor temperature deviations over the circumference (“hot spots”).
Measurements of Multiple Pure Tone Propagation From a High Bypass Turbofan Rotor in an Internal Flow Facility
Authors: Bozak Richard F. 
Published: January 2021

Abstract
An important noise source in modern high bypass ratio turbofans is from multiple pure tones produced by the fan during takeoff. An experiment conducted on a 1.5 pressure ratio fan in an internal flow facility provided dynamic pressure measurements to investigate multiple pure tone generation and propagation. Since multiple pure tones are generated by blade shock variation primarily due to the fan’s blade stagger angle differences, the blade stagger angles were measured with an array of over-the-rotor dynamic pressure transducers. Multiple pure tone measurements were made with 30 wall-mounted dynamic pressure transducers from 0.4 to 1.1 diameters upstream of the rotor. Measured blade stagger angle differences correspond to the the shock amplitude variation measured upstream. The acoustic field was extracted from the dynamic pressure signals using principal component analysis as well as duct mode beamforming. Shocks traveling out the inlet were found to couple to duct modes propagating at similar angles. Over-the-rotor acoustic liners appear to reduce rotor shock variation resulting in a reduction of sub-harmonic multiple pure tone sound pressure levels by 3–4 dB.
Methods for Measuring and Computing the Adiabatic-Wall Temperature
Authors: Peck James , Liu Jason , Bryden Kenneth M. , Shih Tom I-P. 
Published: January 2021

Abstract
For convective heat transfer involving multiple sources of different temperatures in the flow field such as in film cooling, the adiabatic-wall temperature, Tad, is used as the reference temperature to define the heat-transfer coefficient (HTC). Studies based on computational Fluid Dynamics (CFD) have always obtained Tad by requiring the cooled or heated surface to be adiabatic. Similarly, most experimental studies that measured Tad have sought to mimic adiabatic wall by using solids with very low thermal conductivity. Other experimental studies have obtained Tad by making two assumptions: (1) Tad at any given point on the cooled or heated surface is independent of the surface temperature, Ts, and the surface heat flux, qs″, at that point and (2) the HTC, had, which equals qs″/(Ts – Tad), depends only on the ratio of qs″ to Ts – Tad. With these two assumptions, measuring qs″ at two different Ts or vice versa at a point yields Tad and had at that point. In this study, CFD simulations, based on steady RANS, were performed to assess the assumptions invoked by CFD and experimental studies that seek to obtain Tad and had. The assessment was made by studying film cooling of a flat plate with an adiabatic wall and with isothermal walls, where the temperature of the isothermal wall, Ts, ranged from the lowest to the highest temperatures in the flow. Results from this study show Tad obtained by enforcing an adiabatic wall does not satisfy the requirement: where and when Ts – Tad = 0, qs″ = 0. Therefore, had approaches infinity where Ts – Tad is either zero or nearly zero, but qs″ ≠ 0. Also, obtaining Tad and had by measuring two sets of (Ts, qs″) was found to yield non-unique values that depended strongly upon the pair of (Ts, qs″) chosen. To overcome the shortcomings of existing methods, a new method was developed in this study to obtain Tad that does satisfy the requirement: Ts – Tad = 0 where and when qs″ = 0. Also, the method developed yields an had that is continuous across Ts – Tad = 0. By using the new method developed, errors in Tad and had obtained by existing methods were assessed.
Complex Energy Networks Optimization: Part I — Development and Validation of a Software for Optimal Load Allocation
Authors: Ancona M. A. , Bianchi M. , Branchini L. , De Pascale A. , Melino F. , Peretto A. , Rosati J. 
Published: January 2021

Abstract
The growing diffusion of the distributed generation systems, due to the European and national legislations which impose the fossil fuel and greenhouse gas emissions reduction and the renewable sources exploitation, have led to an increase in the complexity of the existing energy networks.
The main issue of the complex energy grids is their management, which consists in the resolution and optimization of the load allocation problem by minimizing the primary energy consumption and, thus, improving the overall efficiency.
In this context, the aim of this paper is to develop and validate a non-linear algorithm suitable for the resolution of the load allocation problem. In detail, the software COMBO, which has been developed by the University of Bologna, is based on a non-heuristic algorithm and allows to optimize a complex energy network — characterized by electrical, thermal, cooling and fuel fluxes — by evaluating all the possible combinations of solutions. The objective function of the software consists in the minimization of the total cost of energy production, including not only the variable costs, but also the costs related to the environmental impact of the energy systems. In this paper the mathematical model of the algorithm at the basis of the software COMBO is presented and described in detail.
Furthermore, the software has been validated by its application to a case study and comparing the results with the ones obtained with a previously developed software based on a genetic algorithm (heuristic non-linear method).
Improving the Safety of Power Plants by Developing a Digital Twin and an Expert System for Adaptive-Predictive Analysis of the Operability of Gas Turbine Units
Authors: Polyakov Roman , Paholkin Eugenii , Kudryavcev Igor , Krupenin Nikolay 
Published: January 2021

Abstract
The article describes general approaches to creating an intelligent system for monitoring and diagnosing the operability of energy supply facilities. The general concept of the adaptive-predictive analysis system and the construction of an artificial neural network for its use in the predictive module for predicting the type and time of failure occurrence is given. The basic principles of training a neural network for recognizing various types of failures are also given. Critical remarks of the concept of creating a digital twin of such a complex object for modeling as energy-generating equipment are given.