bluuebunny/crossref_metadata_2025_split huggingface dataset:
Design of a Compact Dry Cooler With an Aluminum Heat Exchanger Core for a Supercritical CO2 Power Cycle Is Evaluated for a Concentrating Solar Power Application
Authors: Katcher Kelsi M. , Amogne Dereje , Patil Abhay 
Published: October 2022

Abstract
As the supercritical CO2 power cycle develops and the component technologies mature, there is still a need to reduce the associated capital and operating costs to maintain a competitive levelized cost of electricity (LCOE) in order to enter the market. When considering concentrating solar power (CSP) coupled with an sCO2 power block and sensible thermal storage, the technology presents a clean source for utility-scale power generation to support baseload or peak-load electrical demand. However, the LCOE of the technology is still considered higher than the competing technologies and should be reduced to better compete in the market; 2030 targets for dispatchable solar plants are 5¢/kWh for baseload CPS and 10¢/kWh for peaker plants, as set by the United States Department of Energy. In response to this need, this study is targeting improvements in the power cycle pre-cooler to reduce power block contribution to LCOE.
This study considers a dry cooler, as CSP plants are sensitive to water consumption because many installations are slated for remote or arid locations where solar irradiance is very high, but water is scarce. Furthermore, the power block footprint for an sCO2 system is quite compact, especially as compared to a steam cycle. Therefore, there is interest in installing a more compact dry cooler that is proportional to the reduced footprint sCO2 power block, while conventional dry coolers are an order of magnitude larger. The competing goals of size, performance, and cost were considered in this study to develop a compact dry cooler that can easily be packaged with the power block, significantly reducing the installation and transport cost compared to the current state of the art, while maintaining or improving upon the heat transfer performance and impact on plant LCOE. This paper details the high-level findings of a large dry cooler sensitivity study for design point selection, design of the compact dry cooler, expected year-round performance for the dry cooler and the power cycle, and the predicted LCOE for a 30-year plant life. It was found that an aluminum heat exchanger core can be suitably designed to meet the pressure and temperature requirements for a pre-cooler in an sCO2 recompression Brayton cycle. The dry cooler assembly was found to have improved heat transfer performance, allowing for increased cycle efficiencies and a reduced plant LCOE. When coupled with a centrifugal blower and compact transition duct, the dry cooler assembly was able to reduce the installation footprint by over 50%.
Unsteady Investigation of the Effect of Purge Air on the Flow Field Inside a Turbine Vane Frame Using Particle Image Velocimetry
Authors: Schien Malte , Hafizovic Asim , Planck Florian , Merli Filippo , Woisetschläger Jakob , Göttlich Emil 
Published: October 2022

Abstract
The urgent need to reduce the emission of greenhouse gases, in combination with high fuel expenses, motivates manufacturers to design more efficient civil aircraft engines. In the case of directly driven jet engines, this is possible through the increased by-pass ratios for high propulsive efficiencies. This tendency implies a change in the operating condition of the low-pressure turbine (LPT) towards lower rotational speeds at larger diameters. Turbine vane frames (TVFs) constitute a new generation of inter-turbine ducts that guide the airflow from the high-pressure turbine (HPT) to the LPT in radial and circumferential direction. The TVF setup integrates turning vanes, and thus removes the need for a separate vane blade-row in the first LPT stage. Consequently, the TVF yields a benefit for overall engine weight and length, resulting in overall efficiency gains. This paper offers new insight into airflow through a TVF duct. Experimental measurements have been conducted at the two-spool test rig at the Graz University of Technology, consisting of a single-stage HPT, the TVF, and the first LPT rotor. Engine-relevant flow conditions are achieved at the TVF inlet, including HPT tip clearance and purge air effects. Particle Image Velocimetry (PIV) was used to capture the flow field in between two struts of the TVF. Inside each strutted segment, splitter vanes are located along the second half of the TVF axial length. This paper presents new results for a TVF based on measurements from a PIV test section located upstream of the splitter vanes in the first half of the TVF duct. Flow data in the area of strong transient interactions between the HPT and the TVF is recorded and discussed in terms of aerodynamic performance. To reveal the unsteady behavior of the fluid, the flow field has been recorded at six serial stator-rotor positions. In addition, two data sets of varying HPT purge flows were obtained and discussed in order to characterize the effect of purge air inside the measurement domain.
Characterization Methods to Evaluate Recrystallization and Weld-Repair in Single Crystal Nickel-Base Superalloys
Authors: Bridges Alex , Shingledecker John , Griscom Eeva , van Esch Hans , Pietersen Stijn , Zuber Robert , Greaves Wayne 
Published: October 2022

Abstract
Single crystal (SX) nickel-base superalloys have been extensively used for the highest temperature gas turbines blades. In power generation turbines, these alloys are often exposed to high temperatures and stresses for extended periods of time and microstructural evolution occurs. Rejuvenation heat treatments and numerous repair methods can be successfully utilized to extend the life of components manufactured from SX alloys. These repair methods may include surface modifications such as shot-peening and welding along with subsequent heat-treatments. These repair processes may lead to recrystallization in the SX materials, and the presence and extent of grain boundaries can have deleterious effects on local high-temperature mechanical properties.
The research in this paper focuses on characterization methods for evaluating recrystallization in SX nickel-base superalloys during the repair process. Micro hardness mapping, micro x-ray fluorescence (μXRF) and several different scanning electron microscopy (SEM) tools were used to evaluate recrystallization and microstructural features in both weld repairs and shot peened samples subjected to various heat-treatments. Simulated weld repairs consisted of both SX castings in Rene N4 and Rene N5 that were welded with Haynes 230 and Rene 80 filler metals using a gas tungsten arch welding process. The effect of recrystallization from shot peening was also evaluated on both alloys. Additionally, various samples were given either a full solution, partial solution or stress relief heat treatment to evaluate microstructural changes which may be used to the repair/rejuvenation process.
The findings in this research show that several different characterization tools can be effectively used to evaluate recrystallization in SX nickel-base superalloys. Micro hardness and μXRF mapping showed local changes in hardness and chemical composition across the weld metal, heat affected zone and base metal as a function of weld metal selection. Electron backscattered diffraction SEM based techniques was particularly effective in identifying changes in recrystallization due to various processing methods. The research shows that filler metal selection, shot-peening control, and heat-treatment conditions all need to be carefully considered in the development of repair processes to minimize recrystallization effects.
Vane-Probe Interactions in Transonic Flows
Authors: Torre A. F. M. , Patinios M. , Lopes G. , Simonassi L. , Lavagnoli S. 
Published: October 2022

Abstract
In this paper, a numerical investigation of the effect of a miniaturized five-hole probe downstream of a transonic low-pressure turbine vane row is presented.
Firstly, a numerical calibration of the probe was performed in uniform flow conditions, as is the case for any traditional calibration, for a wide range of Mach number, yaw and pitch angle conditions.
The effect of the probe on the general flow-field throughout the turbine vane segments was then evaluated by performing a comparison between a set-up with vanes-only (no probe) and with vanes and probe. It was found that, as the probe traverse downstream the vane, the probe impact on the vane isentropic Mach number depends on the probe circumferential position. The highest impact was observed when the probe is located at the upper mid passage (θ = 0.5), consisting on a relatively small reduction of the isentropic Mach number on the vane suction side of just 0.02.
To assess the accuracy of the quantities ‘measured’ by the probe, the probe-determined flow-field was compared to the flow-field of the vanes-only set-up.
A non-negligible modification of the probe-determined local distributions of Mach number, yaw and pitch angle is revealed with respect to the undisturbed flow. Further investigation involving stagnation point tracking showed that the artificial high circumferential variation of the yaw angle is not caused by a modification of the vane outlet flow angle, but is induced by non-uniform flow conditions downstream of the vanes.
With knowledge of the above, a two-step correction is used to account for the effects of the non-uniformity of the flow and its impact is evaluated on 2D and 3D flow regions.
A significative effect of the correction was found on the probe-determined yaw angle, in which the difference from the vanes-only data was reduced to below 1 degree, except near the endwalls where larger discrepancies remain due to probe-endwall interactions. A shortfall of the correction was instead observed on the probe-determined Mach numbers.
Finally, the pitch-wise averaged quantities were evaluated. It was observed that the highest differences between probe-determined and undisturbed data occur where radial gradients of total pressure are stronger and that the two-step correction had almost negligible impact on the pitch-wise averaged quantities.
A Comparison of Static and Rotordynamic Characteristics for Three Types of Impeller Front Seals in a Liquid Oxygen Turbopump
Authors: Jin Zhihong , Li Zhigang , Li Jun 
Published: October 2022

Abstract
Annular seals are widely used to minimize the leakage, improve efficiency and rotordynamic stability in turbomachinery. In a liquid oxygen turbopump, the operating conditions of annular seals are harsher with the high-pressure cryogenic propellant. Researches show that the primary leakage of a liquid oxygen turbopump is from the front and rear shoulder seals of the impeller. Moreover, the impeller shoulder seal sustains the largest pressure drop and highest swirl velocity in machine. Therefore, the shoulder seal plays an important role in rotor stability and successful full load operation of the turbopump, due to the significant seal fluid response forces.
Previous literature shows that the hole-pattern seal has excellent performance in rotordynamic characteristics, and its leakage rate shows a very weak sensitive to the rotating speed. For helical-groove seal, however, the leakage shows a significant decrease with the increasing rotating speed and the roughness on stator surface can enhance the “pump effect” of helical-groove. The static and rotordynamic characteristics of annular seals with cryogenic liquid oxygen are limited in the previous literature.
To make use of the advantages of both types of seals and address the sealing challenge in liquid oxygen turbopump, three types of liquid annular seals were designed for the front shoulder seal of a liquid oxygen turbopump, which include a hole-pattern seal (HPS), a double helical-groove seal (DHG), and a hybrid damper seal (HDS, with hole-pattern on stator and helical-groove on rotor). To assess and compare the leakage and rotordynamic characteristics of the present three types of annular seals under the liquid oxygen medium, a steady three-dimensional (3D) CFD method was developed to predict the seal leakage, based on the Frozen Rotor interface model. A transient 3D CFD-based perturbation method was also proposed to predict the seal rotordynamic characteristics, based on the subdomain method, mesh deformation technique and multiple-frequency elliptical-orbit whirling model. The accuracy and reliability of the present numerical methods were demonstrated based on the experimental data of leakage rates and rotordynamic coefficients for an experimental hole-pattern seal and an experimental helical-groove seal using water as working fluid. The leakage rate and rotordynamic coefficients of these three types of annular seals were calculated and compared under six variable load operating conditions of a liquid oxygen turbopump, focusing on the seal leakage rate, effective stiffness and damping. The numerical results show that compared with the traditional hole-pattern seal and helical-groove seal, the novel hybrid damper seal possesses the much less leakage flow rate and much better rotordynamic characteristics, so is a desired seal scheme for the impeller shoulder seal.
Detailed Design and Optimization of the First Stage of an Axial Supercritical CO2 Compressor
Authors: Ha Matthew , Holder Justin , Ghimire Saugat , Ringheisen Adam , Turner Mark G. 
Published: October 2022

Abstract
Advancement in energy storage technology is critical in the transition to increased renewable energy sources. The thermodynamic properties of S-CO2 allow for high thermal efficiency and power density potential in turbomachinery design. Relative to the Steam Rankine and Air Brayton cycles, S-CO2 cycles benefit in performance, size, and cost.
As S-CO2 gains acceptance in the industry, research must be conducted to understand the potentials and limitations of this new technology; this is key to the eventual commercial viability of S-CO2 applications. Currently, applications of S-CO2 in turbomachinery are limited to centrifugal design due to the complex fluid properties and flow interactions.
Advancements in compressor design now allow for the intelligent navigation of this complex design space. Optimization tools are utilized to evaluate parametrically defined blades in S-CO2 working fluid to explore advanced, high-performance geometries.
The first axial S-CO2 compressor is designed using this optimization based methodology. This design is the scaled 9 MW 3 stage version of a larger 100 MW 9 stage compressor that will be used for an energy storage application. The adiabatic efficiency of the first stage design is estimated at 91.6% with 3.14 MW of power at 19,800 rpm. The blade height at the rotor leading edge is 3.28 cm.
The first stage of the scaled 9 MW 3 stage compressor will be tested at the University of Notre Dame Turbomachinery Lab; testing of the complete 3 stage machine will follow the single stage testing.
Stage one design drawings have been finalized and submitted for manufacturing. The IGV and Stator 1 have been manufactured and received by the University of Notre Dame Turbomachinery Lab for assembly and testing in the Fall of 2022.
Fluid-Dynamics of Turbine Rim Seal Structures: A Physical Interpretation Using URANS
Authors: De Cosmo Giove , Scobie James A. , Lock Gary D. , Sangan Carl M. , Carnevale Mauro 
Published: October 2022

Abstract
Unsteady Reynolds-Averaged Navier-Stokes modelling (URANS) is a valuable and cost-effective tool for Computational Fluid Dynamics (CFD), including the investigation of mainstream-cavity interaction in turbines. Despite the gap in accuracy with higher order CFD methodologies, URANS is among the few simulation strategies of industrial interest suitable for predicting ingress/egress over a wide range of conditions.
This paper presents a numerical study of the flow-field in the upstream double-radial seal of a 1.5 stage turbine. Various configurations are tested, including non-purged and purged conditions. Rigour of the approach is ensured by a set of sensitivity analyses, allowing the delineation of a best practice on the use of URANS in rim seal simulations: this includes an assessment of the effects of sector size, cavity domain size and blade count.
Time-averaged and time-resolved flow predictions capture coherent structures in the rim gap. An association between the 3D morphology of these structures and different ingress/egress mechanisms is proposed. Regions of enhanced radial activity are identified to correspond with the blade leading edges. A frequency analysis of unsteady pressure signals probed in the rim gap leads to a calculation of the structure number and speed.
The structures are synchronous with the disc rotation for non-purged cases but rotate at slower speed when purge is introduced. The relative number of blades and vanes directly influences the structure count and velocity. The configuration with no blades is characterised by the slowest structures. The calculations have been conducted at three different flow coefficient for the annulus flow. There is a reduction in radial activity and structure speed at lower flow coefficient, fundamentally related to the reduced pressure asymmetry and gradient of swirl across the rim seal.
Development of Translucent Design Philosophy for the Cyclic Pattern Design of Fan Outlet Guide Vanes
Authors: Kulkarni Davendu Y. , di Mare Luca 
Published: October 2022

Abstract
The fan systems of typical high bypass civil engines encounter strong flow distortions originating in the intake and in the bypass ducts and its bifurcations. These flow distortions cause the fan stage operation point to vary from its design intent, thus reducing the fan stage performance and increasing low engine-order fan blade forcing. A cyclic pattern design for the fan Outlet Guide Vanes (OGV) can be effectively used to recover the fan stage performance and to control its system-level aeromechanical behaviour.
This paper presents the development of a OGV pattern design philosophy using numerical experimentation technique. Multiple fan-intake unsteady CFD computations are conducted by clocking the circumferential pressure profile at fan exit to understand its effect on fan rotor efficiency and 1EO fan forced response. The study revealed that a mild, low-harmonic fan back pressure field with a suitable clocking position is able to improve the fan efficiency and reduce the fan forcing simultaneously. Such a pattern can be generated by designing a cyclic OGV pattern that allows the bifurcation potential fields of controlled intensity and phase to pass through the OGV blade row. The notion of deliberately generating a clocked 1EO intra-stage static pressure field by means of cyclic OGV pattern design is termed as the translucent design philosophy.
Further, a sensitivity study is performed to assess the effects of simultaneous distortions upstream and downstream of the fan in two flight conditions. The study showed that a correctly clocked intra-stage static pressure field can effectively counter the fan upstream flow distortions and at the same time improve the fan rotor performance and fan system aeromechanical behaviour. The implementation of the proposed translucent design philosophy in a new OGV pattern design tool is discussed.
A Novel Decomposition Approach Preventing Spurious Entropy Generation in Hybrid Thermoacoustic Stability Computations
Authors: Heilmann Gerrit , Liu Tong , Romero Vega Pedro , Sattelmayer Thomas 
Published: October 2022

Abstract
Prominent approaches for the computation of thermoacoustic stability are hybrid methods like the linearized Navier-Stokes equations (LNSE) or the linearized Euler equations (LEE). The transient fluctuations around a precomputed steady-state mean flow field solved with these sets of equations naturally include the energy transition between acoustic, vortical and entropic modes. It is common practice to account for flame-acoustic interactions by applying measured or computed flame transfer functions (FTF) as a volumetric source term proportional to the mean heat release rate in the energy equation. However, the underlying assumption of a static flame is the root-cause of spurious entropy production, which may ultimately falsify the thermoacoustic stability predictions. In the present paper, a methodology to include arbitrary flame movement in the governing set of equations is presented. The procedure makes use of an Arbitrary Lagrangian-Eulerian (ALE) description of conservation equations and is demonstrated for the Euler equations. The resulting set of linear perturbation equations is then applied to two test cases. First, the frequency response of a one-dimensional premixed air-methane flame is evaluated. Secondly, the frequency response of the first longitudinal eigenmode of an experimental premixed, swirl-stabilized combustor is computed. To demonstrate the reduction of spurious entropy waves, the results are compared to those of the classic LEE.
Improved Modeling and Experimental Evaluation of a Micro Gas Turbine for Solar-Hybrid Application
Authors: Fenner Chaz , van der Spuy Sybrand J. 
Published: October 2022

Abstract
This study contributes to the ongoing research to develop a turbocharger based dual-shaft Micro Gas Turbine (MGT) for a commercialized solar-hybrid system. The work in this study developed an improved model to predict the performance of the MGT which comprises of two turbochargers, with one turbocharger representing the gas generator turbine and the other, bigger turbocharger used as the power turbine unit. It did so by including the effects of heat transfer through a One-Dimensional Thermal Resistance Network (1-D TRN) to determine diabatic outlet temperatures and by accounting for the supposed incomplete combustion. Overall, the model’s temperature estimations were found to be within a maximum deviation of 5 % of the measured values and, 8 % for pressure. Combustor outlet temperature estimates were substantially improved to within 4 % of the measured value, which is a 15 % improvement on previous work. Despite the increased accuracy, the model was only validated for the smaller gas generator turbine. The larger power turbine was reasoned to have not reached thermal equilibrium as temperature estimates had substantially increased levels of deviation from the measured values. A subsequent energy audit of the facility demonstrated the utility of the 1-D TRN. The results of which were used to determine the scale of the heat transfer. It showed that the power turbine is in fact operating outside of its optimal range which resulted in the heat loss rate of the gas through the turbine being greater than the power it produced. The usefulness of the combustion model is also highlighted as a technique to estimate the combustor outlet temperature with acceptable levels of accuracy and with a rapid turn-around time due to its simplicity. The 1-D TRN was shown to estimate heat flows in the MGT accurately despite employing correlations for the heat transfer coefficients that were not developed for the machines. A combustor designed for solarized operation was benchmarked against a standard unit and the results indicated the significance of reducing parasitic pressure losses as a means to improve MGT performance.