bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Approach for Real Gas Simulations: Part I — Tabular Fluid Properties for Real Gas Analysis
Authors: Moraga Francisco , Hofer Doug , Saxena Swati , Mallina Ramakrishna 
Published: August 2017

Recently there has been increased interest in the use of carbon dioxide (CO2) in closed loop power cycles. As these power cycles capitalize on the non-ideal gas behavior of CO2, their analysis both at the system level and at the detailed component level requires an advanced equation of state. Commonly used analytical equations of state as BWRS (BenedictWebbRubin equation of State) or Peng-Robinson are known to have high errors near the critical point and are thus unsuitable for the analysis of cycles or components where the flow conditions approach the critical point. An accurate equation of state is required at all phases of the development process from high level cycle calculations to the detailed component CFD. The NIST RefProp software package provides accurate CO2 fluid properties across the thermodynamic space but suffers from high computational over-head.
This study is presented in two parts. Part I (this part) of this paper describes an approach to creating a tabular representation of the equation of state that is applicable to any fluid. This approach is applied to generating an accurate, fast and robust tabular representation of the RefProp CO2 properties and an error analysis is performed to meet the accuracy requirements. The paper also discusses two approaches used to define speed of sound in the two-phase region and their sensitivity analysis on the 3D compressor flow. Part II of the paper details the numerical simulations of a supercritical CO2 centrifugal compressor using the tabular approach.
This paper shows that table resolution can be tailored to match the accuracy requirements while minimizing the time used to evaluate the tabulated thermo-physical functions. Error analysis are shown to demonstrate the level of accuracy possible with this approach.
A Semantic Differential for Evaluating the Sound Quality of Fan Systems
Authors: Feldmann Carolin , Carolus Thomas , Schneider Marc 
Published: August 2017

Fans are main components e.g. in heating, ventilating and air conditioning systems for vehicles or buildings, cooling units of engines and electronic circuits, and household appliances such as kitchen exhaust hoods or vacuum cleaners. End-users increasingly demand a high sound quality of their system or device. The overall objective of a recent research project at the University of Siegen is a multidimensional assessment of fan sound quality.
In a first step an advanced novel semantic differential for the assessment of fan-related sounds is established with the aid of carefully designed jury tests. Eventually, this semantic differential is employed for sound quality jury tests of fans in kitchen exhaust hoods, heat pumps and air purifiers as a first case. Finally, a prediction model is suggested, which relates the outcome from the jury tests to objective metrics.
A principal component analysis is carried out and yields five main assessment criteria with 23 relevant adjective scales. The results show that the perceived sound quality of fan systems is mainly determined by the loudness and tonality of the sound. The spectral content (represented by the sharpness) as well as the time structure (represented by the roughness) have no significant impact on perceived sound quality of the fan systems investigated.
Influence of Nozzle Design Upon the Primary Jet Breakup of High-Viscosity Fuels for Entrained Flow Gasification
Authors: Müller Thomas , Dullenkopf Alexa , Habisreuther Peter , Zarzalis Nikolaos , Sänger Alexander , Jakobs Tobias , Kolb Thomas 
Published: August 2017

The research work of the present study is focused on the influence of design parameters of twin-fluid nozzles used for the atomization of high-viscosity fuels with respect to the primary breakup of the liquid jet. Two external mixing twin-fluid nozzles, which have already been investigated in previous studies [1, 2], were chosen as basic design. Based on the previous findings the web thickness between fuel and oxidizer supply was varied. In addition both designs were extended by a channel for internal mixing of gas and liquid with a length to diameter ratio of one. Moreover one of the basic nozzles was scaled by decrease of the effective areas in a way that momentum flux ratio as well as gas to liquid mass flow ratio was kept constant.
The newly designed atomizers were subsequently investigated with regard to the influence of the changes upon the primary jet breakup using CFD simulations. The numerical simulations were conducted by means of the open source package OpenFOAM. The Volume of Fluid method was used for the determination of the gas-liquid interface. These simulations were then compared with experimentally validated simulations of the basic nozzle designs with regard to the breakup morphology of the jet and the mode of the primary surface instability. In addition, the liquid structure was examined by comparison of breakup length and frequency.
The results of these simulations showed that small changes in the atomizer design heavily influence the primary breakup, which in turn influences the overall performance of the atomizer (e.g. SMD).
Moreover, these findings will contribute to a better understanding of the physics of the breakup of high-viscosity liquid jets and as well to create an experimentally validated CFD based tool for future burner development and optimization.
Facing the Challenges in CFD Modelling of Multistage Axial Compressors
Authors: Cozzi Lorenzo , Rubechini Filippo , Marconcini Michele , Arnone Andrea , Astrua Pio , Schneider Andrea , Silingardi Andrea 
Published: August 2017

Multistage axial compressors have always been a great challenge for designers since the flow within these kind of machines, subjected to severe diffusion, is usually characterized by complex and widely developed 3D structures, especially next to the endwalls. The development of reliable numerical tools capable of providing an accurate prediction of the overall machine performance is one of the main research focus areas in the multistage axial compressor field.
This paper is intended to present the strategy used to run numerical simulations on compressors achieved by the collaboration between the University of Florence and Ansaldo Energia. All peculiar aspects of the numerical setup are introduced, such as rotor/stator tip clearance modelling, simplified shroud leakage model, gas and turbulence models. Special attention is payed to the mixing planes adopted for steady-state computations because this is a crucial aspect of modern heavy-duty transonic multistage axial compressors. In fact, these machines are characterized by small inter-row axial gaps and transonic flow in front stages, which both may affect non-reflectiveness and fluxes conservation across mixing planes. Moreover, the high stage count may lead to conservation issues of the main flow properties form inlet to outlet boundaries. Finally, the likely occurrence of partspan flow reversal in the endwall regions affects the robustness of non-reflecting mixing plane models.
The numerical setup has been validated on an existing machine produced and experimentally tested by Ansaldo Energia. In order to evaluate the impact on performance prediction of the mixing planes introduced in the steady-state computation, un-steady simulations of the whole compressor have been performed at different operating conditions. These calculations have been carried out both at the compressor design point and close to the surge-line to evaluate the effect of rotor/stator interaction along the compressor working line.
On Boundary Layer Relaminarization in an Highly Accelerated High Pressure Turbine Stator Flow
Authors: Bader Pascal , Sanz Wolfgang 
Published: August 2017

The boundary layer represents the thin layer between the wall and the free stream. Although this zone is small in respect to the free stream its state — whether it is laminar or turbulent — has a high impact on wall parameters like skin friction but also on the free stream.
The state of the boundary layer is influenced by free stream parameters like free stream turbulence intensity or acceleration. Transition can occur from laminar to turbulent, but also from turbulent to laminar. The latter process is called relaminarization.
Transition and relaminarization has already been detected in laboratory conditions but also occur in real-life flow around aeroplane wings, but also in turbomachines. In this work a high pressure stator of a two-spool, two-stage turbine is analyzed numerically regarding transition and relaminarization to show how the boundary layer flow along casing and blade is influenced by these phenomena.
It is found out in this work, that the boundary layer along the blade, hub and shroud undergoes transition and also relaminarization despite the high free stream velocities and turbulence levels inside the machine. The differences between a transitional and fully turbulent simulation regarding loss generation by wall friction are given.
Fast Optimisation of a Three-Dimensional Bypass System Using a New Aerodynamic Design Method
Authors: Barbarossa F. , Rife M. E. , Carnevale M. , Parry A. B. , Green J. S. , di Mare L. 
Published: August 2017

The propulsive efficiency of civil aviation power plants can be effectively improved by increasing the bypass ratio. Higher bypass ratios, however, exacerbate issues of performance, stability and integrity due to the interaction between the engine pylon, the outlet guide vanes (OGV) and the fan. These issues are due to the distortion of the static pressure field at fan exit due to the presence of the pylon and its transmission through the OGV bladerow and are more pronounced the closer the components of the low pressure compression (LPC) system are. These issues make a rational and effective design of the LPC system of paramount importance for the success of very high-bypass ratio engines.
At the preliminary design phase, methods that utilise computational fluid dynamics (CFD) are prohibitively expensive, particularly if they are used as part of optimisation processes involving highly three dimensional, non-axisymmetric OGV designs. An alternative method is being developed exploiting the simplicity and the accuracy of surface singularity element methods to investigate the sensitivity of the bypass system to changes in the design variables. Although the singularity method is based on simplified assumptions of inviscid, incompressible flow, it still performs remarkably well when combined with a tailored optimisation technique. This paper discusses the optimisation framework in detail, including the underlying mathematical models that describe the three-dimensional aerodynamic flowfield as well as the optimisation tools, variables and cost functions used within the optimisation process. The results show that the proposed approach can be used to explore quickly and efficiently a far wider design space than attempted so far in literature. Furthermore, the proposed method leads to non-axysymmetric cascade designs whereby every vane has the same load as the nominal vane whilst greatly reducing the static pressure distortion at fan exit.
The Design of a Large Diameter Axial Flow Fan for Air-Cooled Heat Exchanger Applications
Authors: Wilkinson Michael B. , van der Spuy Johan , von Backström Theodor W. 
Published: August 2017

An axial flow fan design methodology is developed to design large diameter, low pressure rise, rotor-only fans for large air-cooled heat exchangers. The procedure aims to design highly efficient axial flow fans that perform well when subjected to off design conditions commonly encountered in air-cooled heat exchangers. The procedure makes use of several optimisation steps in order to achieve this. These steps include optimising the hub-tip ratio, vortex distribution, blading and aerofoil camber distributions in order to attain maximum total-to-static efficiency at the design point.
In order to validate the design procedure a 24 ft, 8 bladed axial flow fan is designed to the specifications required for an air-cooled heat exchanger for a concentrated solar power (CSP) plant. The designed fan is numerically evaluated using both a modified version of the actuator disk model and a three dimensional periodic fan blade model. The results of these CFD simulations are used to evaluate the design procedure by comparing the fan performance characteristic data to the design specification and values calculated by the design code. The flow field directly down stream of the fan is also analysed in order to evaluate how closely the numerically predicted flow field matches the designed flow field, as well as determine whether the assumptions made in the design procedure are reasonable.
The fan is found to meet the required pressure rise, however the fan total-to-static efficiency is found to be lower than estimated during the design process. The actuator disk model is found to under estimate the power consumption of the fan, however the actuator disk model does provide a reasonable estimate of the exit flow conditions as well as the total-to-static pressure characteristic of the fan.
Development of Reliable NARX Models of Gas Turbine Cold, Warm and Hot Start-Up
Authors: Bahlawan Hilal , Morini Mirko , Pinelli Michele , Spina Pier Ruggero , Venturini Mauro 
Published: August 2017

This paper documents the set-up and validation of nonlinear autoregressive exogenous (NARX) models of a heavy-duty single-shaft gas turbine. The considered gas turbine is a General Electric PG 9351FA located in Italy.
The data used for model training are time series data sets of several different maneuvers taken experimentally during the start-up procedure and refer to cold, warm and hot start-up. The trained NARX models are used to predict other experimental data sets and comparisons are made among the outputs of the models and the corresponding measured data.
Therefore, this paper addresses the challenge of setting up robust and reliable NARX models, by means of a sound selection of training data sets and a sensitivity analysis on the number of neurons. Moreover, a new performance function for the training process is defined to weigh more the most rapid transients. The final aim of this paper is the set-up of a powerful, easy-to-build and very accurate simulation tool which can be used for both control logic tuning and gas turbine diagnostics, characterized by good generalization capability.
A Numerical Investigation of the Impact of Part-Span Connectors on the Flow Field in a Linear Cascade
Authors: Brüggemann C. , Schatz M. , Vogt D. M. , Popig F. 
Published: August 2017

This paper presents a numerical investigation of the impact of different part-span connector (PSC) configurations on the flow field in a turbine passage. For this purpose a linear cascade based on a profile section of a typical reaction blade used in industrial steam turbines was modeled and 3D simulations with varying size, shape, axial position and yaw incidence angle of the PSC were performed. Air modeled as ideal gas was chosen as the working fluid.
Apart from a sensitivity study of the above mentioned parameters on the losses incurred by PSCs based on the numerical results, a detailed investigation of the flow field was carried out to highlight the interaction with the incoming flow. Moreover, the variation of the flow field behind the cascade was examined to assess the impact on the subsequent blade row. It is shown that depending on the geometry and the position of the PSC, different vortex structures are established in the wakes. These wakes interact with the main flow in the passage, thus influencing both dissipation and the downstream flow field. Major changes of the wake flow character and extent could be observed.
Comparisons of the CFD results against commonly used analytical loss correlations for PSC revealed large differences, especially as certain parameters such as the yaw incidence angle are generally not considered by the latter. As a consequence, the analytical models need to be improved and extended. The results of this study indicate that the possibility of reducing the losses incurred by PSC by careful selection of design parameters within the design space dictated by its mechanical constraints.
Effect of Vortex Shedding on the Performance of Scoop Based Lubrication Devices
Authors: Prabhakar Arun , Abakr Yousif Abdalla , Simmons Kathy 
Published: August 2017

In civil aircraft aeroengine bearing chambers it is sometimes difficult to feed oil to bearings using the traditional under-race or targeted jet approaches. In such situations one proposed solution is that of a scoop delivery system. Published experimental investigations into scoop performance show that scoop collection efficiency (the percentage of oil delivered by the scoop system to its destination compared to that supplied by the feed jet) is a function of many operational and geometric parameters. However even with high speed imaging it is impossible to experimentally determine in detail the factors that most contribute to reduction in collection efficiency and it is here particularly that a computational fluid dynamics (CFD) investigation has value.
In the work reported here a commercial CFD code (ANSYS Fluent) is used to investigate vortex formation at the scoop tips and the effect these structures have on scoop collection efficiency. The computational domain, a 2D slice through the chosen scoop system, is discretized utilizing ANSYS Meshing. A Volume of fluid (VOF) method is used to model the multiphase flow of oil and air in the system and the RNG k-ε turbulence model is employed.
The results obtained show that the formation of vortices from the tip of the rotating scoops leads to a reduction in pressure in the region near the tip of the oil jet, subsequently causing part of the jet to divert upwards away from the scoop creating a plumed tip. The pluming effect reduces capture efficiency because the oil plume moves outwards under centrifugal effects and this oil is not captured. The frequency of vortex shedding from the scooped rotor was investigated and the Strouhal numbers obtained were around 0.132. This compares well to 0.15 for an inclined flat plate. Two potential methods to reduce the jet pluming effect are investigated one in which the sharp tip of the scoop is blunted and the other in which the jet direction is reversed. The blunt tip increased capture efficiency by almost 2%. Reversing the jet orientation reduces jet pluming but also significantly reduces capture efficiency; it was found to be 10% lower for the case investigated.
The Impact of the Multiple Reference Frame Interface on Modelling the Interaction Between IGVs and the Impeller in Turbocharger Compressors
Authors: Li Xiangjun , Spence Stephen 
Published: August 2017

In this paper numerical investigations are presented of how the axial position of the multiple reference frame (MRF) stator-rotor interface between the inlet guide vanes (IGVs) and the impeller would influence the predicted flow field for a turbocharger centrifugal compressor when simulated by the steady RANS method. In the first step, a total of three different axial positions of the MRF IGV-impeller interface were considered and compared with the results of an unsteady simulation to evaluate their accuracy. The results showed that the choice of the MRF interface location significantly influenced the predicted overall performance. At the lower rotational speed, the peak efficiency varied by 1.3% and the corresponding total pressure ratio varied by 0.022. At the high rotational speed, the different axial locations of the MRF interface varied the predicted choke point by 0.012 normalized mass flow rate. The mass flow rate of the near surge (NS) point was over estimated at both the high and low rotational speed by at least 0.038 normalized mass flow rate.
Consideration of the flow field suggested that the MRF interface between the IGV and the impeller should be placed towards the upstream side of the available region to avoid being unphysically influenced by its interaction with the non-uniform pressure in the downstream subsonic flow field and to enable a more accurate prediction of the extent of the inducer shock in transonic operating situations. Based on this understanding, a further improvement was made for the setting of the MRF interface by employing a polyline interface. This achieved a more accurate numerical result for the NS operating point at low rotational speeds. The position of the MRF interface for modelling IGVs in a turbocharger compressor should be suitably chosen according to the objectives of the numerical study.
Transient Simulation of Critical Flow With Thermal-Hydraulic System Analysis Code for Supercritical CO2 Applications
Authors: Kim Min Seok , Oh Bong Seong , Kwon Jin Su , Jung Hwa-Young , Lee Jeong Ik 
Published: August 2017

As a part of Sodium-cooled Fast Reactor (SFR) development, the supercritical CO2 (S-CO2) Brayton cycle is considered as an alternative power conversion system to eliminate sodium-water reaction (SWR) from the current conventional steam Rankine cycle is utilized with SFR. The leakage flow of S-CO2 from turbo-machinery via seal becomes one of important issues since not only it influences the cycle efficiency due to parasitic loss but also it is important for evaluating the system safety under various operating conditions. Thus, a transient simulation for estimating the critical flow in a turbo-machinery seal is essential to predict the leakage flow rate and calculate the required total mass of working fluid in a S-CO2 power system.
This paper briefly reviews the advantages of supercritical CO2 Brayton cycle relative to a typical steam Rankine cycle used in the Sodium-cooled Fast Reactor. In addition, this paper describes the test data using a CO2 critical flow experimental facility with three orifice configurations to model the flow resistance of a rotating shaft labyrinth seal. This data is used for validation of an existing transient analytical tool developed for transient hydraulic system analysis. Contained within this code is the analysis approach of Henry/Fauske from 1971 for two phase critical flow of one-component mixtures. This paper presents prediction of transient pressure, temperature, and flow profiles for critical and sub-critical flows of CO2 relative to blowdown test data to show that reasonable results are obtained. Similar analyses relative to test results of three orifice configurations are conducted and it shows that multiple orifices increase the time to equalize pressure in the blowdown system and therefore equates to higher flow resistance and lower leakage.