bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.
An Understanding of Stress and Pretension Behavior of Aero Engine Rotor Bolted Joint
Authors: Mogullapally Venkateshwarlu , Jyoth Shine , Kumar Sanju , Rao Rashmi , B. A. Rajeevalochanam 
Published: September 2021

Abstract
Bolted joints in gas turbines are used commonly to connect the parts of dissimilar materials to facilitate assembly, dis-assembly, and also to achieve modularity for advanced aero engines. In gas turbine engine, there are many rotating and stationary parts that are subjected to an extreme working environment. Bolted joints should have sufficient strength to support the mating parts such as safety critical fan/turbine discs, drums, and shaft assembly. Bolted joints are designed to avoid flange separation and slippage. This paper attempts to understand the challenges faced in designing a typical fan disc rotor plain flange type bolted assembly and structural integrity aspects under various thermo-mechanical operating loads. The understanding of stiffness of the bolt and joint members is necessary to evaluate the performance of the joint assembly. Based on literature, different approaches are used for estimating member stiffness to compare with finite element results. The effect of external loads such as thermo-mechanical loads on pretension behavior of bolted joint is studied with the help of standard commercial software platform ANSYS. Bolted joint preload loss has been assessed via the standard analytical method and validated with 3D finite element approach. This paper enables designer a quick understanding of rotor bolted joint behavior for finalization of gas turbine rotor layout, before going into complex and time consuming 3D finite element modelling and nonlinear stress analysis.
Turbocharger Radial Turbine Response to Pulse Amplitude
Authors: Mosca Roberto , Lim Shyang Maw , Mihaescu Mihai 
Published: September 2021

Abstract
Under on-engine operating conditions, a turbocharger turbine is subject to a pulsating flow and, consequently, experiences deviations from the performance measured under continuous flow. Furthermore, due to the high exhaust gas temperatures, heat transfer further deteriorates the turbine performance. The complex interaction of the aerothermodynamic mechanisms occurring inside the hot-side, and consequently the turbine behavior, is largely affected by the shape of the pulse, which can be parameterized through three parameters: pulse amplitude, frequency, and temporal gradient. This paper investigates the hot-side system response to the pulse amplitude via a Detached Eddy Simulation (DES) approach of a radial turbocharger turbine system including exhaust manifold. Firstly, the computational model is validated against experimental data obtained under gas stand continuous flow conditions. Then, two different mass flow pulses, characterized by a pulse amplitude difference of ≈ 5%, are compared. An exergy-based post-processing approach shows the beneficial effects of increasing pulse amplitude. An improvement of the turbine power by 1.3%, despite the increment of the heat transfer and total internal irreversibilities by 5.8% and 3.4%, respectively, is reported. As a result of the higher maximum speed, internal losses by viscous friction are responsible for the growth of the total internal irreversibilities as pulse amplitude increases.
High Efficiency Active Damping on a Fan Rotor Blade in Case Of Resonant Vibrations by Means of Piezoelectric Actuators
Authors: Rossi Andrea , Botta Fabio , Giovannelli Ambra , Belfiore Nicola Pio 
Published: September 2021

Abstract
Severe resonant vibration is one of the main roots of turbomachinery blades failure. Forced response issues arise when the blades work in non-uniform flow fields. As a result unsteady aerodynamic pressures occur on the surfaces of the blade. If the frequency of the aerodynamic excitation matches an eigenfrequency of the blade, the vibration level may considerably increase and a drop in the life-cycle of the component could be entailed. The resonant vibration conditions could be identified at the design level by means of the Campbell diagram. Unfortunately, it is not possible to avoid all the resonant conditions, hence the mitigation of vibration has always been of the utmost importance for turbomachinery designers. Moreover an active damping system based on piezoelectric (PZT) actuators which is capable of tuning its behavior according to the resonant excitation, may be considered very attractive. In this work the forced response of a fan rotor blade, due to a stationary inlet flow distortion resulting from the presence of upstream struts, is taken into account. Some resonant conditions have been analyzed by means of Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) simulations. Thereafter a novel approach based on a proper distribution of the potential supplied to the electrodes of each PZT pair, in order to maximize the damping efficiency, is applied to the case of a plausible fan blade. The outcomes show that the proposed system is able to efficiently damp each resonant excitation and enhance the structural integrity of the blade.
Vortex Breakdown and Recirculation Bubble Formation in Counter Swirl Flows
Authors: Bompelly Ravi K. , Ponduri Sai Phani Keerthan , Maddila Sriharsha 
Published: September 2021

Abstract
For achieving better fuel-air mixing within a short distance or for improved atomization of liquid fuels counter rotating swirler designs are preferred in gas turbine engine combustors. In this study, vortex breakdown phenomenon is investigated in co and counter rotating swirlers using CFD. The swirler assembly consists of two axial swirlers, an inner and an outer swirler both with straight vanes. Swirler vane angles are varied from 30° to 60° in steps of 10° while keeping inner and outer swirler vane angles equal. CFD simulations are performed with air at ambient conditions as the working fluid at a constant mass flow rate. It is observed that strong shear layers are created in counter swirl flows due to the opposite flow rotation. The shear layers result in rapid decay of inner swirler tangential velocities for the counter swirlers compared to the co-swirlers. The tangential velocity decay is characterized with a parameter named tangential velocity integral (TVI). TVI was observed to decay faster for the counter swirl flows compared to the co-swirl flows. The faster decay in TVI for the counter swirlers is found to result in a stronger adverse pressure gradient in the axial direction at the center. The strong adverse pressure gradient resulted in higher pressure excess ratios (PER) for the counter swirlers. The higher PERs are observed to induce vortex breakdown in counter swirlers even at low vane angles whereas in co-swirlers vortex breakdown is not observed except for the highest vane angle. It is demonstrated that vortex breakdown could be suppressed in counter swirlers using a converging mixer passage. The converging mixer passage creates a favorable pressure gradient that counters the adverse pressure gradient due to swirl decay, resulting in breakdown suppression.
Effects on Film Cooling Performance in the Showerhead From Geometric Parameterization of Shaped Hole Designs
Authors: Moore Jacob D. , Easterby Christopher C. , Bogard David G. 
Published: September 2021

Abstract
The high heat loads at the leading-edge regions of turbine vanes and blades necessitate the most robust thermal protection, typically accomplished via a dense array of film cooling holes, nicknamed the “showerhead.” Although research has shown that film cooling using shaped holes provides more reliable thermal protection than that using cylindrical holes, the effects on cooling performance from varying the geometric details of the shaped hole design are not well characterized. In this study, adiabatic effectiveness and off-the-wall thermal field measurements were conducted for two shaped hole geometries designed as successors to a baseline hole geometry presented in a previous study. One geometry with a 40% increase in area ratio exhibited only a marginal improvement in adiabatic effectiveness (∼10%). A second design with a 12° forward and lateral expansion angle with a breakout area 40% larger performed marginally worse than its matched area ratio counterpart (∼15% lower), suggesting a negative sensitivity to breakout area. Such changes in performance for different shaped hole designs were small compared to the boost in performance gained by switching from a cylindrical hole to a shaped hole, which suggests cooling performance is insensitive to specific shaped hole details provided the exterior coolant flow is well-attached.
Aerodynamic Prediction on the Off-Design Performance of a S-CO2 Turbine Based on Deep Learning
Authors: Wang Yuqi , Liu Tianyuan , Zhang Di 
Published: September 2021

Abstract
The research on the supercritical carbon dioxide (S-CO2) Brayton cycle has gradually become a hot spot in recent years. The off-design performance of turbine is an important reference for analyzing the variable operating conditions of the cycle. With the development of deep learning technology, the research of surrogate models based on neural network has received extensive attention. In order to improve the inefficiency in traditional off-design analyses, this research establishes a data-driven deep learning off-design aerodynamic prediction model for a S-CO2 centrifugal turbine, which is based on a deep convolutional neural network. The network can rapidly and adaptively provide dynamic aerodynamic performance prediction results for varying blade profiles and operating conditions. Meanwhile, it can illustrate the mechanism based on the field reconstruction results for the generated aerodynamic performance. The training results show that the off-design aerodynamic prediction convolutional neural network (OAP-CNN) has reduced the mean and maximum error of efficiency prediction compared with the traditional Gaussian Process Regression (GPR) and Artificial Neural Network (ANN). Aiming at the off-design conditions, the pressure and temperature distributions with acceptable error can be obtained without a CFD calculation. Besides, the influence of off-design parameters on the efficiency and power can be conveniently acquired, thus providing the reference for an optimized operation strategy. Analyzing the sensitivity of AOP-CNN to training data set size, the prediction accuracy is acceptable when the percentage of training samples exceeds 50%. The minimum error appears when the training data set size is 0.8. The mean and maximum errors are respectively 1.46% and 6.42%. In summary, this research provides a precise and fast aerodynamic performance prediction model in the analyses of off-design conditions for S-CO2 turbomachinery and Brayton cycle.
A Study on Fundamental Combustion Properties of Oxymethylene Ether-2
Authors: Ngugi John N. , Richter Sandra , Braun-Unkhoff Marina , Naumann Clemens , Köhler Markus , Riedel Uwe 
Published: September 2021

Abstract
Oxymethylene ethers (OMEn, n = 1–5) are a promising class of synthetic fuels that have the potential to be used as additives or substitutes to diesel in compression ignition engines. A comprehensive understanding of their combustion properties is required for their safe and efficient utilization. In this study, the results of a combined experimental and modeling work on oxidation of OME2 are reported: (i) Ignition delay time measurements of stoichiometric OME2 / synthetic air mixtures diluted 1:5 with nitrogen using the shock tube method at pressures of 1, 4, and 16 bar, and (ii) laminar flame speeds of OME2 / air mixtures using the cone angle method at ambient and elevated pressures of 3 and 6 bar. The experimental data sets obtained have been used for validation of a detailed reaction mechanisms of OME2. The results of ignition delay times showed that OME2 exhibits a two-stage ignition in the lower temperature region. There is a good match of the measured data compared to the predicted ones using three reaction mechanisms from the literature. The mechanism from Cai et al. (2020) best predicted the temperature and pressure dependence of ignition delay times. For laminar flame speeds, the experimental data were well matched by the mechanism from Ren et al. (2019) at p = 1, 3, and 6 bar and for all equivalence ratios considered. From sensitivity analyses calculations, it was observed that chain reactions involving small radicals, i.e., H, O, OH, HO2, and CH3 control the oxidation of OME2. The comparison of the results of this work and our previous work (Ngugi et al. (2021)) on OME1 show that these two fuels have similar oxidation pathways.
The results obtained in this work will contribute to a better understanding of the combustion of oxymethylene ethers, and thus, to the design and optimization of burners and engines as well.
A Comprehensive Model for Cetane Number Prediction Using Machine Learning
Authors: Abdul Jameel Abdul Gani 
Published: September 2021

Abstract
Machine learning based predictive models are being extensively applied for predicting combustion properties like derived cetane number (DCN), which is the measure of a fuels ignition quality. In the present work, a comprehensive model was developed using artificial neural networks (ANN) that can predict the DCN of fuels containing a large number of chemical classes like paraffins, iso-paraffins, olefins, naphthenes, aromatics, alcohols, ethers, aldehydes, ketones and esters. Experimental DCN’s of 275 fuels was used as a dataset and the composition of the fuels expressed in the form of twelve functional groups and two structural parameters namely, branching index (BI) and molecular weight were used as the input features for the model. A feed forward neural network with two hidden layers with 40 neurons in each layer was developed using Levenberg-Marquardt algorithm. The developed model was validated with 15% of the data points that were randomly generated and kept aside for validation. A regression coefficient (R2) of 0.99 was observed between the predicted and the experimental values along with an average absolute error of 1.1. The results showed that the developed model was successful in predicting the DCN of fuels and can be applied to pure compounds, blends and real fuels containing diverse chemical functionalities.
Performance of a Long Smooth Multiphase Pump Seal in Different Flow Regimes
Authors: Zhang Min , Childs Dara W. 
Published: September 2021

Abstract
Demanding for multiphase pumps introduces new challenges to the pump design. To prevent machine failures, the performance of the pump (non-contact) annular seal under multiphase conditions needs to be studied. The air addition into the oil flow not only changes the properties of the fluid but also can change the flow status in the seal clearance. The flow status can significantly affect the performance of the pump seal and thereby impact the pump vibration performance. Within the seal annulus, the axial direction flow is dominated by the pressure drop through the seal and can be considered as a Poiseuille flow. The circumferential direction flow is driven by the rotor rotation and can be considered as a Couette flow. The regime of the flow in the seal is controlled by the axial Reynolds number and the circumferential Reynolds number. Published test results on the boundaries between the laminar, transitional, and turbulent regimes in an annular seal are scant. This paper will first draw these boundaries based on the test data for long smooth pump seals. Then, this paper will show the performance of the long smooth pump seal in different flow regimes. Predictions will also be presented to compare with test results under different flow conditions.