bluuebunny/crossref_metadata_2025 huggingface dataset:
Turbomachinery Loss Analysis: The Relationship Between Mechanical Work Potential and Entropy Analyses
Authors: Leggett John , Zhao Yaomin , Richardson Edward S. , Sandberg Richard D.
Published: September 2021

Physics-based loss analysis methods have been developed to interpret the detailed three-dimensional and time-dependent predictions of turbomachinery CFD simulations. This paper contrasts two analysis methods for assessing loss: entropy loss analysis (Zhao & Sandberg, GT2019-90126) and mechanical work potential analysis (Miller, GT2013-95488). The two individual analyses are applied to high-fidelity simulation data for linear high-pressure compressor and high-pressure turbine cascades. The results show each analysis captures the loss generating processes in different ways, corresponding to different terms in their equations. The key loss generation processes are shown to be turbulent and mean viscous dissipation in the mechanical work potential analysis, and mean viscous dissipation and turbulence production in the entropy loss analysis. A relationship between the two approaches is derived rigorously, providing a means to convert between the results of the two approaches, enabling designers to assess individual stage performance using the entropy-based analysis and multiple stages in terms of mechanical work potential, by using the same reference pressure.
On the Challenge of Determining the Surge Limit of Turbocharger Compressors: Part 1 – Experimental and Numerical Analysis of the Operating Limits
Authors: Dielenschneider T. , Ratz J. , Leichtfuß S. , Schiffer H.-P. , Eißler W.
Published: September 2021

The surge limit of compressors is one key parameter in the design process of modern turbocharger compressors for automotive applications. Since the compressor is operated close to the surge limit, the determination of the surge limit is of high importance. Unfortunately, the determination of the surge limit with any numerical method with high accuracy is still an unsolved challenge. The numerical surge limit is often determined by the operating point with the minimum converged mass flow rate. But, as this investigation will clearly show, this cannot be used as a surge limit of the investigated compressor configuration. In this paper it will be shown that a more differentiated approach is required when it comes to operating limits. Especially, two different operating limits can be determined. A methodology for the determination of each limit will be presented. One is based on the system approach defined by Greitzer and the other one is based on the analysis of the low momentum fluid in the shroud region of the compressor wheel. Finally, experimental data will be used as benchmark data for both limits. The determination of the experimental surge limit is based on the analysis of transient experimental pressure signals. This is achieved through a fourier analysis of the unsteady compressor outlet pressure signal for transient surge runs.
A Stochastic Model for Nanoparticle Deposits Growth
Authors: Suman Alessio , Vulpio Alessandro , Casari Nicola , Pinelli Michele
Published: September 2021

Natural events and human activities are responsible for the generation and transport of large amounts of micro-sized particles, which could contaminate several engineering devices like solar panels, wind turbines, and aero-engines. In industrial processes, systems as heat exchangers, fans, and dust collectors are continuously affected by nanoparticles’ interaction. For several applications, the adhesion of such nanoparticles is detrimental, generating safety and performance issues. Particle-to-particle and particle-to-surface interactions are well known, even if a general explanation of nanoparticle deposit growth is still unknown.

In the present paper, an interpretation of deposit growth due to nanoparticle deposition can predict particle adhesion, and layer accretion is proposed. A statistical model and a set of coefficients are used to generalize nanoparticle deposits’ growth by an S-shaped function. In particular, the nanoparticle deposits grow analogously to a typical autonomous population settlement in a virgin area following statistical rule, which includes the initial growth, the successive stable condition (development), and catastrophic events able to destroy the layer. This approach generalizes nanoparticle adhesion/deposition behavior, overpassing the constraints reported in common deposition models, mainly focused on the mechanical aspect of the nanoparticle impact event. The catastrophic events, such as layer detachment, are modeled with a Poisson’s distribution, related to material characteristics and impact conditions.

This innovative approach, analogies, and coefficients applied to common engineering applications may be the starting point for improving the prediction capability of nanoparticle deposition.
Progresses in Particle-Laden Flows Simulations in Multistage Turbomachinery With OpenFOAM
Authors: Oliani Stefano , Friso Riccardo , Casari Nicola , Pinelli Michele , Suman Alessio , Carnevale Mauro
Published: September 2021

Numerical simulations of particle-laden flows have received growing attention in the last decade, due to the broad spectrum of industrial applications in which discrete phases prediction is of interest. Among these, ingestion of particles by turbomachinery is an area that is seeing vivid research and studies. The most common technique to tackle this kind of problem is the Eulerian-Lagrangian method, in which individual particles are tracked inside the domain. At the same time, in multi-stage turbomachinery simulations interfaces are needed to couple the flow solution in adjacent domains in relative motion. In this work, an open-source extension for Lagrangian simulations in multistage rotating machines is presented in the foam-extend environment. Firstly, a thorough discussion of the implementation is presented, with particular emphasis on particle passage through General Grid Interfaces (GGI) and mixing planes. Moreover, a mass-conservative particle redistribution technique is described, as such a property is requested at interfaces between Multiple Reference Frame (MRF). The peculiarities of the algorithm are then shown on a relevant test-case. Eventually, three turbomachinery applications are presented, with growing complexity, to show the capabilities of the numerical code in real-life applications. Simulation results in terms of erosion and impacts on aerodynamic surfaces are also presented as examples of possible parameters of interest in particle-laden flow computations.
A Novel Energy Storage System Based on Carbon Dioxide Unique Thermodynamic Properties
Authors: Astolfi Marco , Rizzi Dario , Macchi Ennio , Spadacini Claudio
Published: September 2021

This paper focuses on the thermodynamic performance and techno-economic assessment of a novel electrical energy storage technology using carbon dioxide as working fluid. This technology, named CO2 battery and recently patented by Energy Dome SpA., addresses to an energy market which has great need of energy storage solutions able to handle the increasing share of non-dispatchable renewable energy sources like photovoltaic and wind energy. After a brief introduction, the present study presents the concept of CO2 batteries and their operation. Then the detailed numerical model developed for the accurate calculation of system round trip efficiency is presented with the adopted assumptions and the optimization routine description. Results on the reference case and following sensitivity analysis confirm a RTE of around 77% (±2%) which makes CO2 batteries a very promising technology with respect to other energy storage systems based on thermodynamic cycles like compressed air and liquid air energy storage thanks to the high performance and the easiness of installation. Finally, calculation of system footprint, capital investment cost and levelized cost of storage are discussed.
A Rapid Viscous-Inviscid Interaction Method for the Preliminary Design of S-Shaped Transition Ducts
Authors: Veyrat A. , Carrotte J. F. , Walker A. D. , Hall C. , Simpson H.
Published: September 2021

For preliminary design of compressor transition ducts, knowledge-based tools for the rapid assessment of aerodynamic performance of S-shaped ducts are not currently available in the open literature. This is due to the highly complex flow developing under the combined influence of pressure gradients and streamline curvature. This paper presents a new approach enabling an agile design process avoiding premature use of time-consuming high-fidelity CFD calculations. The features of a 2D axisymmetric incompressible steady flow field are captured with a semi-analytical viscous inviscid interaction method. A potential core, based on streamline curvature and implicit velocity profile by parametric spline reconstruction, is coupled to an integral method predicting the turbulent boundary layer growth up to separation. The shear stress distribution is generated by a modified mixing length model for strongly curved flows and wall shear stress closure is performed by inverse calculation of a composite law-of-the-wall. When compared to CFD, the aerodynamic loading is generally predicted to within ±3% but convergence is achieved 20 times faster.
Hot Turbine Guide Vane Performance Improvement With Metal Additive Manufacturing at Siemens Energy
Authors: Fedorov Ilya , Barhanko Dikran , Hallberg Magnus , Lindbaeck Martin
Published: September 2021

Additive manufacturing (AM) of gas turbine components has been suggested as a measure to improve performance and create other value additions in several research papers. This paper focuses on application of AM for gas turbine performance improvement considering industrial scale of this activity at Siemens Energy.

Efficient cooling designs, made possible by AM, are considered not only from the standpoint of cooling characteristics, but also inherent challenges, arising in the complete chain of manufacturing processes: from powder removal to coating. Practical limitations of cooling scheme complexity are discussed and the benefits of in-wall cooling, enabled by AM, are described. It is shown that thin cooled trailing edges, enabled by the AM, provide considerable reduction of losses. It is demonstrated that production challenges can be successfully overcome, and the components can be manufactured with the required quantity and according to the original design intent.

The sequence and progress of AM components long-term validation in the field engines are discussed and illustrated with actual operation experience. The development of the AM vane was executed in line with the roadmap of AM portfolio development in Siemens Energy and supports the strategy of commercial validation and full commercial release of AM components..
Impact of Mistuned Underplatform Dampers on the Nonlinear Vibration of Bladed Disks
Authors: Quaegebeur Samuel , Chouvion Benjamin , Thouverez Fabrice
Published: September 2021

Before the final experimental validation and certification of a turboengine, designers perform a numerical simulation of its vibratory properties, among other things, in order to estimate its lifespan and adjust the design in an optimization process. One possible practical solution to decrease the vibratory response is to add underplatform dampers to the system. These components dissipate energy by friction and are widely employed in turbomachinery. However, a specific underplatform damper is usually efficient only for a specific mode. The purpose of this work is to investigate the possibility of adding different kinds of underplatform dampers to the cyclic structure in order to decrease the vibratory energy over a larger panel of modes. Different methods exist to determine the vibrations of nonlinear cyclic symmetric systems, but creating a robust methodology to account for the additional effect of mistuning remains a big challenge in the community. In this paper, the structure is mistuned through the friction coefficient of the dampers and not by altering its geometry, as is usually done in the literature. First, assuming a cyclic symmetric structure, the performance of the dampers is assessed for specific modes. Then, employing a method recently developed, the efficiency of an intentional mistuning pattern of underplatform dampers is studied and an optimal pattern proposed.
Steam Turbine Casing Analyses to Determine Pressure and Temperature Limits
Authors: Smith Paul T. , Griffin Daniel J.
Published: September 2021

To ensure safe and reliable operation, steam turbine casings must have acceptable stresses and maintain sealing when subjected to internal pressures and temperatures. To show turbine casings acceptable, analysts conduct structural evaluations using finite element analysis (FEA) techniques. This paper outlines the analytical methods used to perform these types of analyses, provides analysis examples, and summarizes the process to create pressure and temperature limit maps.

Finite element models of the main casing and steam chest are used to determine stresses and sealing of the casing horizontal split line and steam chest cover during normal operation. The sealing evaluations consider the sealing capabilities of the bolted joints when the casing is subjected to internal steam pressure and consider the effects of bolt stress relaxation at elevated temperatures, joint contact surface separation, and penetration of the internal pressure into the sealing surface. The acceptance criteria for the bolted joint sealing is based on the minimum width of the contacting surface and the minimum joint contact pressure.

A series of analyses were conducted on the various models to create pressure and temperature limit maps, so that the design can be applied for the appropriate conditions. These maps plot maximum allowable working pressure (MAWP) versus maximum allowable working temperature (MAWT), and allow an application engineer to easily determine the acceptability of the casing for a particular application. An explanation of the process used to create the limit maps is presented.
The EPRI Gas Turbine Digital Twin – a Platform for Operator Focused Integrated Diagnostics and Performance Forecasting
Authors: Lim Jamie , Perullo Christopher A. , Milton Joe , Whitacre Rachel , Jackson Chris , Griffin Chris , Noble David , Boche Lea , Seachman Steve , Angello Leonard , Maley Susan , Lieuwen Timothy C.
Published: September 2021

EPRI has been developing a digital twin of simple and combined cycle gas turbines over the last 5+ years to provide owners and operators with improved capabilities that typically reside in the expert domain of OEMs and 3rd party service providers. The digital twin is a digital model, a physics-based representation of the actual asset. The model is thermodynamic and is created with the intent to support 5 M&D areas:

• Integrate with existing M&D tools such as advanced pattern recognition (APR)

• Power plant performance prediction and trending such as day, week, and month ahead performance prediction for capacity and generation planning

• Health Monitoring and Fault Diagnostics to support asset management with additional health scores and virtual instrumentation enabled by the digital twin model

• Monitoring and prediction of both base and part-load performance. Many gas turbine tools have been simplified to work only at full load conditions. To be useful and to improve utilization of collected data, part-load conditions should also be considered.

• Outage and repair impacts, including “what-if” capability to understand and quantify potential root causes of less than expected performance improvement or recovery after outage and repairs.

This paper presents current progress in creating an EPRI Digital Twin applicable to gas turbines. The formulation, methodology, and real-world use cases are presented. To date, digital twins have been created and tested for both E and F class frames. This paper describes the process of generating closed-form equations capable of transforming existing, measured historian data into the health parameters and virtual sensors needed to better track unit health and monitor faulted performance. These equations encapsulate the digital twin physical model and provide end-users with a methodology to calibrate to their specific unit and efficiently use their choice of monitoring software. Tests have been performed using operator data and have shown good accuracy at detecting anomalous operation and predicting week ahead performance with excellent accuracy. Post-outage impact analysis is also assessed.

Real-world application cases for the digital twin are also presented. Examples include using the digital twin to identify causes of post-outage emissions and performance issues, expected impact of degradation and fault conditions, and simulating improvements to operation through part repair and upgrades.
Performance and Emission Assessment on a 3kW Micro Gas Turbine: Comparison of RANS and LES Predictions
Authors: Pappa Alessio , Nicolosi Francesco F. , Verhaeghe Antoine , Bricteux Laurent , Renzi Massimiliano , De Paepe Ward
Published: September 2021

Computational fluid dynamics represent a powerful tool to assess the performance of a combustor and identify possible issues/instabilities, helping thus e.g. to investigate the impact of advanced cycle modifications on the combustion in mGTs. The steady Reynolds-averaged Navier-Stokes (RANS) approach is still mostly used in this framework. With growing computational power, Large Eddy Simulation (LES) has gained more interest. LES provides higher details concerning flow structures and can better predict possible instabilities, specifically needed for advanced cycle modelling. On the other hand, LES remain rather challenging for real industrial applications. This work aims at providing an answer whether the advantages of LES justify the much higher computational costs. The objective of the present study is thus to assess the combustion performance and emissions of a typical small-scale 3.2 kWe micro gas turbine (mGT), using steady RANS and LES for various fuels. In this framework, a comparison of RANS and LES approaches (two levels of fidelity) is performed on a typical industrial case, to point out the strengths and weakness of each method with regard to industrial and research needs. The results show that both RANS (at a reduced cost) and LES can accurately predict the time-averaged trends of the main performance parameters, like temperature levels and emissions, also using various non-conventional inlet conditions. For the accurate prediction of the instabilities, the LES approach stands out as this approach takes into account the time-variation of the different quantities. Finally, a significant discrepancy has been observed between the CO levels provided by RANS and LES approaches where LES is overestimating the level of CO in the exhaust gases. Whereas it is difficult for LES to compete with convincing results provided by RANS, especially in the prediction of global emissions at reduced simulation cost, the LES strengths come out especially in flame and combustion stability analysis.
Comparing Environmental Impacts of Additive Manufacturing vs. Investment Casting for the Production of a Shroud for Gas Turbine
Authors: Serra Angela , Malarco Martina , Musacchio Alessandro , Buia Giulio , Bartocci Pietro , Fantozzi Francesco
Published: September 2021

Additive manufacturing (AM hereinafter) is revolutionizing prototyping production and even small-scale manufacturing. Usually it is assumed that AM has lower environmental impact, compared to traditional manufacturing processes, but there have been no comprehensive environmental life-cycle assessment studies confirming this, especially for the gas turbines (GT hereinafter) and turbomachinery sector. In this study the core processes performed at Baker Hughes site in Florence are considered, together with the powder production via atomization process to describe the overall environmental impact of a GT shroud produced through additive manufacturing and comparing it with traditional investment casting production process. Particular attention is given to materials production and logistics. The full component life cycle starts from the extraction of raw materials during mining, their fusion and, as said, the atomization process, the powders are transported to the gas turbines production site where they are used as base material in additive manufacturing, also machining and finishing processes are analyzed as they differ for a component produced by AM respect to one produced by traditional investment casting. From the analysis of the data obtained, it emerges that the AM process has better performances in terms of sustainability than the Investment casting (IC hereinafter), highlighted above all by a decrease in greenhouse gas emissions (GHG hereinafter) of over 40%.
Assessment of CFD Models for Multiphase Heat Transfer in Different Boiling Regimes
Authors: Bianchini Cosimo , Da Soghe Riccardo , Mazzei Lorenzo , Caggiano Giuseppe , Angelucci Maddalena
Published: September 2021

Cryogenic propellant rockets, designed to exploit the high energy densities of liquid hydrogen and liquid oxygen, are equipped with turbopumps that deliver liquid fuel to the engine at high pressure levels. Due to the very low saturation temperature of the cryogenic propellant, it is common during the transient operation to have portion of pump walls that achieve boiling conditions. The effect of boiling on the heat transfer between the solid and the fluid needs to be well characterized in order to correctly predict the pump metal temperature evolution and the necessary amount of propellant.

This paper presents an investigation about the capabilities of currently available CFD models for boiling to reproduce correctly the phenomenon under various flow conditions. The analysis, conducted with Ansys Fluent CFD solver, focuses on the Eulerian multiphase approach coupled with the mechanistic nucleate boiling model extended to consider the wall boiling regime transition from the nucleate boiling to the critical heat flux regime (CHF).

Several test cases are presented to cover the full range of boiling regimes and flow characteristics: the first test focuses on nucleate boiling of sub-cooled water in an upward heated cylindrical pipe, second one deals with 3D boiling water in a rectangular-sectioned duct, the third one considers again nucleate boiling but with a different fluid, namely the R-113 refrigerant, whereas the last investigates the critical heat flux and post dry-out regimes in vertical pipes. Selected tests span over different operating conditions and consider alternative fluids in order to provide a preliminary validation propaedeutic for future investigations focused on more complex applications representative of cryogenic turbopumps.
Vortex Tracking of Purge-Mainstream Interactions in a Rotating Turbine Stage
Authors: Mesny Alex W. , Glozier Mark A. , Pountney Oliver J. , Scobie James A. , Li Yan Sheng , Cleaver David J. , Sangan Carl M.
Published: September 2021

The use of purge flow in gas turbines allows for high turbine entry temperatures, which are essential to produce high cycle efficiency. Purge air is bled from the compressor and reintroduced in the turbine to cool vulnerable components. Wheel-spaces are formed between adjacent rotating and stationary discs, with purge air supplied at low radius before exiting into the mainstream gas-path through a rim-seal at the disc periphery. An aerodynamic penalty is incurred as the purge flow egress interacts with the mainstream. This study presents unparalleled three-dimensional velocity data from a single-stage turbine test rig, specifically designed to investigate egress-mainstream interaction using optical measurement techniques.

Volumetric Velocimetry is applied to the rotating environment with phase-locked measurements used to identify and track the vortical secondary flow features through the blade passage. A baseline case without purge flow is compared to experiments with a 1.7% purge mass fraction; the latter was chosen to ensure a fully sealed wheel-space. A non-localised vortex tracking function is applied to the data to identify the position of the core centroids. The strength of the secondary-flow vortices was determined by using a circulation criterion on rotated planes aligned to the vortex filaments.

The pressure-side leg of the horseshoe vortex and a second vortex associated with the egress flow were identified by the experimental campaign. In the absence of purge flow the two vortices merged, forming the passage vortex. With the addition of purge flow, the two cores remained independent to 40% of the blade axial chord, while also demonstrating an increased radial migration and intensification of the passage vortex. The egress core was shown to remain closer to the suction-surface with purge flow. Importantly, where the vortex filaments demonstrated strong radial or tangential components of velocity, the circulation level calculated from axial planes underpredicted the true circulation by up to 50%.
System Level Analysis of Compressor Eye-Labyrinth Seal Rotordynamic Forces: A Computational Fluid Dynamics Approach
Authors: Ali Md Shujan , Mortazavi Farzam , Palazzolo Alan
Published: September 2021

Accurate characterization of compressor rotordynamic coefficients during the design phase reduces the risk of sub-synchronous vibration (SSV) problems occurring in the field. Although rotordynamists extensively investigate discrete compressor components (such as seals and front shrouds) to tackle instability issues, integrated or system-level analysis of compressor rotordynamics is rare. In reality, the impeller, eye labyrinth seal, and the front shroud heavily influence one another; and the collective dynamic behavior of the system differs from the sum of the dynamic behavior of isolated components.

To further investigate, a CFD-based approach is taken to evaluate the dynamic behavior of the system as a whole. The geometry and operating conditions in this work are based on the recent experimental study of Song et al. (2019) on compressor seal and front shroud stiffness values. The compressor impeller is redesigned utilizing turbomachinery design software CFturbo. The commercial CFD code CFX 19.0 is used to resolve Reynolds Averaged Navier-Stokes (RANS) equations to quantify eye labyrinth seal and front cavity stiffness, damping, and added mass, while the whole compressor stage is modeled to uncover the coupled behavior of the components, and assess the stability of the whole system instead of any discrete components. The coupled system is constructed by modeling the interacting upstream and downstream components to accurately capture key rotordynamic parameters such as damping, axial pressure, and pressure distribution evolution inside the cavities. Effect of turbulence is captured utilizing the shear stress transport (SST) k-ω model. In the current work, three CFD approaches, namely quasi-steady, transient static eccentric, and transient mesh deformation technique are tested, and predictions are made on stiffness, damping, and virtual mass. Effectiveness of each CFD method is evaluated by comparison with the experimental data. CFD results provide the non-axisymmetric pressure perturbation for the shroud and seal surfaces. Furthermore, rotordynamic coefficients are derived utilizing correlations from the literature, and compared with CFD based and experimental results.
Combustion of Hydrogen-Methane-Air-Mixtures in a Generic Triple Swirl Burner: Numerical Studies
Authors: Vishnoi Neha , Valera-Medina Agustin , Saurabh Aditya , Kabiraj Lipika
Published: September 2021

Ever-increasing energy demand, limited non-renewable resources, requirement for increased operational flexibility, and the need for reduction of pollutant emissions are the critical factors that drive the development of next generation fuel flexible gas turbine combustors. The use of hydrogen and hydrogen-rich fuels such as syngas helps in achieving decarbonisation. However, high temperatures and flame speeds associated with hydrogen might increase the NOx emissions. Humidified combustion presents a promising approach for NOx control. Humidification inhibits the formation of NOx and also allows for operating on hydrogen and hydrogen-rich fuels. The challenge in the implementation of this technology is the combustor (burner) design, which must provide a stable combustion process at high hydrogen content and ultra-wet conditions. In the present work, we investigate the flow field and combustion characteristics of a generic triple swirl burner running on humidified and hydrogen enriched methane-air mixtures.

The investigated burner consists of three co-axial co-rotating swirling passages: outer radial swirler stage, and two inner concentric axial swirler stages. Reynold’s Averaged Navier-Stokes (RANS) simulation approach has been utilized here for flow description within the burner and inside the combustor. We present the flow fields from isothermal and lean pre-mixed methane-air reactive simulations based on the characterization of velocity profiles, streamwise shear layers, temperature fields and NOx emissions. Subsequently, we investigate the effect of combustion on flow fields, and flame stabilization for hydrogen enriched methane-air mixtures as a function of hydrogen content. We also investigate the effect of humidified combustion on methane-hydrogen blends and present comparison of temperature estimations and NOx emissions.
Cost Effective Options of Closed CO2 Cycles for CSP Applications
Authors: Maccarini Simone , Traverso Alberto , Pesatori Emanuel
Published: September 2021

Electrical power production from CSP is worldwide still limited in its diffusion by a higher LCOE with respect to other renewable sources, nevertheless it offers some unique features such as the possibility of a reliable energy storage capability. Among the most interesting, emerging-to-industrial ready technologies, CO2 power cycles seem to have the potential to provide a major step toward the average plant efficiency and equipment cost levels needed to achieve the marketability. Today, in most cases, supercritical CO2 power loops are seen as an opportunity to achieve a major step in thermodynamic efficiencies if applied in supercritical condition and with a quite complicated cycle configurations (e.g. Recompressed and ReHeated, or other combined solutions), with cycle maximum temperature above 650°C. Current cycle configurations are affected by a relative complexity of the power block, including non-negligible technological uncertainties with respect to simpler Brayton cycle solutions, possibly causing delay in the commercial application of the CO2 power block, at least for CSP applications. The aim of this article is to present some possible CO2 power closed cycle solutions, including supercritical as well as transcritical options, in order to propose cost-effective alternatives to current state-of-the-art steam power block of CSPs, highlighting that relatively simple CO2 cycle arrangements can enhance CSP competitiveness, representing a valid intermediate step towards next more advanced sCO2 cycles.
Thermal Performance of Double-Sided, Partial Height Strip Fin Arrays in a High Aspect Ratio, Rectangular Channel
Authors: Tracy Nathaniel J. , Wright Lesley M. , Han Je-Chin
Published: September 2021

Friction loss and heat transfer enhancement measurements were obtained for double-sided, partial height, strip fin arrays within a high aspect ratio (AR = 8), rectangular channel. Fins were arranged in a staggered array configuration with channel height to fin thickness ratio H/W = 9.6, spanwise spacing distance to fin thickness ratio S/W = 8.0, and streamwise spacing distance to fin length ratio X/L = 1.0. Shortened strip fins of equal length are positioned directly opposite of each other on the upper and lower channel surfaces with three gap size to channel height ratios considered G/H = 0.2, 0.3, and 0.4. The thermal performance of each fin configuration is determined from the measured pressure drop across the array and regionally averaged heat transfer coefficients at flow Reynolds numbers ranging from Re = 20,000–80,000. The partial height strip fin results are compared to baseline cases of strip fins spanning the full height of the channel and the smooth channel without roughness elements. Linear correlations of friction loss and power correlations of the heat transfer enhancement and thermal performance are provided as functions of flow Reynolds numbers for all cases. Strip fins spanning the full height of the channel provide the greatest heat transfer enhancement of all cases but introducing a gap size can significantly reduce friction losses. Full height strip fins provide the greatest thermal performance for Reynolds numbers ranging from Re = 20,000–30,000, and partial height strip fins with the gap size of G/H = 0.3 provide the greatest thermal performance for flow Reynolds numbers ranging from Re = 40,000–80,000.
Effect of Pin Fins on Jet Impingement Heat Transfer on A Rotating Disk
Authors: Bhansali Pratik S. , Ramakrishnan Kishore Ranganath , Ekkad Srinath
Published: September 2021

Heat transfer on rotating surfaces is a predominant phenomenon in rotating machinery as in the case of the gas turbine disk. The gas turbine disk needs to be cooled as well as protected from the ingress of hot turbine gases in the stator-rotor cavity. In the current study, an experimental investigation of the heat transfer of an impinging air jet on a surface rotating at low rotational Reynolds number has been carried out. Addition of pin-fins on the disk surface is an effective way to enhance the heat transfer between the disk and the jet of cooling air. The effect of addition of an inline array of square pin fins on the rotating disk heat transfer has been investigated in this study. Steady state measurements have been carried out using thermocouples embedded at different locations in an aluminum disk with an array of square pin-fins rotating in a large space. Experiments have been conducted at rotational Reynolds numbers (ReR) of 5,487–12,803 based on the disk diameter (D) and jet Reynolds numbers (Re) of 5,000–18,000 based on the jet diameter (d). Two different ratios of jet to nozzle spacing and jet diameter (z/d) of 2 and 4 and three different impingement locations – at eccentricities (ε) – 0, 0.33 and 0.67 have been considered. The diameter of the impinging jet has been kept constant in order to maintain an equal jet footprint across all the cases. The area averaged Nusselt number over the surface with pin fins has been compared with a smooth rotating disk of equal diameter. Results indicate that for the smooth surface, ε and ReR have negligible effect on Nu. However, addition of pin fins enhance Nu by a factor between 1.5 and 3.9 in the present study. Qualitative visualization of flow field has been performed using the commercial simulation package Ansys Fluent to further understand the heat transfer trends.
Rapid Defect Detection and Classification in Images Using Convolutional Neural Networks
Authors: Warren Peter , Ali Hessein , Ebrahimi Hossein , Ghosh Ranajay
Published: September 2021

Several image processing methods have been implemented over recent years to assist and partially replace on-site technician visual inspection of both manufactured parts and operational equipments. Convolutional neural networks (CNNs) have seen great success in their ability to both identify and classify anomalies within images, in some cases they do this to a higher degree of accuracy than an expert human. Several parts that are manufactured for various aspects of turbomachinery operation must undergo a visual inspection prior to qualification. Machine learning techniques can streamline these visual inspection processes and increase both efficiency and accuracy of defect detection and classification. The adoption of CNNs to manufactured part inspection can also help to improve manufacturing methods by rapidly retrieving data for overall system improvement. In this work a dataset of images with a variety of surface defects and some without defects will be fed through varying CNN set-ups for the rapid identification and classification of the flaws within the images. This work will examine the techniques used to create CNNs and how they can best be applied to part surface image data, and determine the most accurate and efficient techniques that should be implemented. By combining machine learning with non-destructive evaluation methods component health can be rapidly determined and create a more robust system for manufactured parts and operational equipment evaluation.
Rotating Mechanism of Diffuser Stall in a Centrifugal Compressor With Vaneless Diffuser
Authors: Fujisawa Nobumichi , Agari Yuki , Yamao Yoshifumi , Ohta Yutaka
Published: September 2021

The rotating mechanism of diffuser stall in a centrifugal compressor with a vaneless diffuser is investigated via experimental and computational analyses. Diffuser stall is generated as the mass flow rate decreases, and it rotates at 25%–30% of the impeller rotational speed. First, a diffuser stall cell emerges at 180° from the cutoff by the hub-side boundary layer separation. Subsequently, the diffuser stall cell develops further owing to boundary layer separation accumulation and an induced low-velocity area. The low-velocity region forms a blockage across the diffuser passage span. The diffuser stall cell expands owing to the boundary layer separations that occurred on the shroud and hub wall by turns. Finally, the diffuser stall cell vanishes when it passes the cutoff because mass flow recovery occurred. Furthermore, the static pressure ahead of the rotating stall decreases because of the merging of the impeller discharge flow and the reverse flow from the casing. Accordingly, a reverse flow occurred owing to the evolution of the separation vortex at the diffuser exit. In addition, the flow angle decreases by the merging of the impeller discharge flow and reverse flow from the casing. Therefore, boundary layer separations start occurring on the shroud and hub wall ahead of the stall cell. The rotating mechanism of the diffuser stall is induced by the reverse flow development and a decrease in the flow angle ahead of the stall cell.
Development of a Lifetime Pressure Sensitive Paint Procedure for High-Pressure Vane Testing
Authors: Aye-Addo Papa Aye N. , Paniagua Guillermo , Cuadrado David G. , Bhatnagar Lakshya , Castillo Sauca Antonio , Braun James , Gomez-Gomez Mateo , Meyer Terrence , Bloxham Matthew
Published: September 2021

Optical measurements based on fast response Pressure Sensitive Paint (PSP) provide enhanced spatial resolution of the pressure field. This paper presents laser lifetime PSP at 20 kHz, with precise calibrations, and results from a demonstration in an annular vane cascade. The laser lifetime PSP methodology is first evaluated in a linear wind tunnel with a converging-diverging nozzle followed by a wavy surface. This test section is fully optically accessible with maximum modularity. A data reduction procedure is proposed for the PSP calibration, and optimal pixel binning is selected to reduce the uncertainty. In the annular test section, laser lifetime PSP was used to measure the time-averaged static pressure field on a section of the suction surface of a high-pressure turbine vane. Tests were performed at engine representative conditions in the Purdue Big Rig for Annular Stationary Turbine Analysis module at the Purdue Experimental Turbine Aerothermal Lab. The 2-D pressure results showed a gradual increase of pressure in the spanwise and flow directions, corroborated with local static pressure taps and computational results. The variation in PSP thickness was measured as a contribution to the uncertainty. The discrete Fourier transform of the unsteady pressure signal showed increased frequency content in wind-on conditions compared to wind-off conditions at the mid-span and 30% span. Compared to the mid-span region, the hub end wall region had an increase in frequencies and pressure amplitude. This result was anticipated given the expected presence of secondary flow structures in the near hub region.
Comparison Study on Stage Performance of Centrifugal Compressors With Shrouded and Unshrouded Impellers
Authors: Xi Guang , Zhao Chenxi , Tang Yonghong , Wang Zhiheng
Published: September 2021

The shrouded and unshrouded impellers are two typical kinds of impellers, which are widely utilized in centrifugal compressors of various applications. Centrifugal compressors with unshrouded impellers are generally recognized to display inferior performance to the shrouded impellers with the same geometry. In this paper, a comparative experiment shows some results inconsistent with conventional cognition. Measured performance indicates that the peak efficiency of the centrifugal compressor with an unshrouded impeller is higher than the shrouded one, where the two impellers have the same geometry of meridional profile and blade central plane, and matched the same vaneless diffuser and volute. In order to explore the causes of this divergence, the effects of factors such as blade thickness, surface roughness of components, tip clearance and sealing leakage characteristics on performance are analyzed by CFD code. Numerical results show that reasonable reduction in the blade thickness and improvement on the surface quality of the impeller could effectively increase the peak efficiency and the choke mass flow rate of the shrouded impeller. The unshrouded impeller with arbitrary blade surfaces would be deformed under the action of centrifugal force to achieve a small tip clearance during operation, and then obtains higher efficiency at design speed. The research results are helpful to evaluate the performance potential and sensitive design parameters of shrouded and unshrouded impellers.
Impact of Dry Cooler Air-Side Performance on a sCO2 Power Cycle for a CSP Application
Authors: Katcher Kelsi M. , Amogne Dereje
Published: September 2021

Uncertainty around the design and control of the supercritical CO2 power cycle must be reduced before this technology can be implemented for large-scale grid support. To better understand the day-to-day performance of an sCO2 cycle, off-design performance calculations must be included for all power block components, and performance assumptions must be removed. This study has expanded the modeled scope to include the air-side performance for the dry cooler and has incorporated discretized heat transfer calculations for both streams through the pre-cooler to better predict off-design performance. This study considered a recompression Brayton cycle in a concentrating solar power application. The cycle model utilized fixed sCO2 turbomachinery maps for the main compressor, recompressor, and expander operating to supply approximately 10 MW gross at the design point. Fixed vendor-supplied fan curves were used to calculate the air-side performance of the dry cooler. The primary heater was modeled considering both the sCO2 and heat transfer fluid streams. Off-design performance was predicted for an ambient temperature range of 0–55°C, a HTF temperature range of 705–735°C, and a HTF mass flow range of 50–105% of the design point value. To understand the importance of modeling the air-side performance, the cycle off-design performance was also calculated using a constant CO2 outlet temperature assumption and a constant approach temperature assumption for the dry cooler. Results show that using these assumptions can significantly alter the power output and cycle efficiency predictions.
Optimization of a Primary Heat Exchanger for FLiBe Molten Salt Nuclear Reactor With sCO2 Power System
Authors: Gabriel-Ohanu Emmanuel , Khadse Akshay , Vesely Ladislav , Raju Nandhini , Otto Marcel , Kapat Jayanta S. , Harris Kurt
Published: September 2021

One of the concepts being investigated for Generation IV nuclear reactors is the Molten Salt Reactor (MSR), with designs utilizing molten salts as both fuels and/or coolants. Historic development focused on large reactors, but contemporary efforts are likely to be small and modular, with this analysis considering 30 MWth per reactor unit For both cases, the use of a supercritical carbon dioxide (sCO2) Brayton cycle is being considered for power conversion. Compatibility of sCO2 power cycles with high turbine inlet temperature among several other advantages allows for several nuclear applications.

This paper sought to optimize heat exchange between an MSR heat source and an sCO2 power cycle by thermalhydraulically optimizing a salt-heat exchanger sCO2 (HEX). This is accomplished using a one dimensional (1D) heat transfer code that solves for the geometry of a single pass shell-and-tube HEX, as well as pressure loss. Input to the HEX code are derived from a MSR technology assessment and from an optimized recuperated recompression (RRC) sCO2 power cycle. The HEX designs comprise of single shell and tubes with molten salt 2LiFBeF2 (FLiBe) flowing in the shell and sCO2 in the tubes. Hastelloy N is chosen for HEX material due to its tested compatibility with in nuclear application with FLiBe. Shell diameter and number of tubes are varied to optimize length of the HEX. Initial estimate for the weight of the HEX is then compared against the heat transfer area to further converge on an optimized design.
Efficiency Maximization of Allam Cycle at a Given Combustion Temperature
Authors: Haseli Yousef
Published: September 2021

This study analyzes an Allam cycle by means of analytical modeling. In a recent ASME Turbo Expo Conference (Turbo Expo 2020), an analytical formulation was presented for the net power output of a natural gas fired Allam cycle with an uncooled turbine. An algebraic expression was derived for optimum turbine inlet temperature (TIT) maximizing the cycle efficiency. In practice, TIT is constrained by durability of the turbine blade material with a maximum allowable temperature of 860 °C as reported by the cycle developers. The objective here is to determine optimum turbine inlet and exhaust pressures by maximization of the cycle efficiency subject to a fixed temperature at the combustor outlet. To avoid complexity of the analysis, reasonable simplifications are considered including negligible temperature and pressure drops between adjacent components. Analytical expressions are obtained for optimum pressure of the combustion gases at the inlet and outlet of the turbine meaning that the net cycle efficiency can be twice optimized. The optimum turbine exhaust pressure is found to be a function of (TITηtηc/Tc) where Tc denotes a cycle minimum temperature and η is the isentropic efficiency. The new expressions are used to calculate the optimum turbine inlet pressure, exhaust pressure, and maximum cycle efficiency for a practical range of the combustion temperature and varying pressure at the exit of the CO2 compressor. The relations derived in this study provide (i) a solid foundation for those unfamiliar with Allam cycle, and (ii) a useful tool for engineers to roughly estimate optimum operational regime of the cycle without a need for complex calculations.