bluuebunny/crossref_metadata_2025_split huggingface dataset:
Case Study of User Defined Element Integration in Rotor Dynamics Software
Authors: Mathuria Parag H. , Savela Gregory 
Published: August 2024

Abstract
Gas turbine engine companies often employ home-grown or internally developed computer programs for rotor dynamics design-analysis. Developing, and maturing these sometimes over decades to support day-to-day design execution and some of the more specialized problems in Rotor Dynamics. As some problems now require higher fidelity modeling or visualization, along with the incorporation of more physics-based capabilities, the employment of commercially available, general use software becomes attractive to predict general engine dynamic behavior with these additional features. These are found to be important in predicting rotor dynamic system behavior accurately.
Three case studies are presented in this paper, namely (1) squeeze film dampers with inertia terms in addition to conventional stiffness and damping, (2) speed/thrust dependent bearing stiffness in transient analysis and (3) the explanation of side-banding in the response utilizing transient analysis solutions. The approach described in this paper seeks to make use of already proven general finite-element nonlinear analysis (transient and harmonic analyses) which are available in the market. This process of integration will allow us to include system nonlinearities (particularly at the damper for case #1 and bearings stiffness for case # 2 and 3) appears to be necessary if analytical predictions are to be realistic. The work is applied to Nelson-McVaugh model to validate for squeeze file damper element for harmonic analysis and other two cases for transient analysis. This paper will be useful for the end user for implementing and enhancing the capability in house as well as commercial software where user defined element is possible.
Applicability of Volume of Fluid Method to Two-Phase Flow Turbomachinery Application
Authors: Salpingidou Christina , So Kwok Kai 
Published: August 2024

Abstract
Hydrodynamic bearings, based on lubrication oil, are commonly used in turbomachinery. The understanding and modeling of the air-oil two-phase flows in the bearing casing, piping and drain are important during the design phase. Given the limitations of the analytical methods and experiments, the use of robust and fast numerical methods, which can aid the engineers to assess various designs, is significant. In this paper, the use of VOF method for the air-oil flows for turbomachinery is reviewed. The paper first scrutinizes the use of VOF method for certain flow regimes from the perspective of the underlying VOF numerical method. Then, based on a detailed investigation using test rig observation of the bearing casing of a radial bearing of a turbocharger, the corresponding two-phase flow simulations using VOF are presented. Sensitivity studies are carried-out to understand the role of the key parameters and determine an appropriate CFD model. With the proper numerical setup, the CFD results are in good agreement with the test rig. The numerical setup is further applied to a common use case of air-oil two-phase flows of turbomachinery, namely the oil drain. The CFD model of the oil drain leads to realistic results and illustrates the applicability of the VOF method.
A Simplified Injection Model for Variable Area Turbine Fluidic Throttling
Authors: Spens Alexander , McFadden Evan J. , Westrick Cole D. , Bons Jeffrey P. 
Published: August 2024

Abstract
Previous studies have demonstrated the effectiveness of using fluidic actuators to throttle the flow through a nozzle guide vane, enabling a variable area turbine (VAT) with no moving parts. A simplified model was developed to assess the driving design factors that influence the blocked flow fraction and throttling effectiveness of the actuators. The model approximates slot injection using a simplified stream tube analysis, neglecting mixing with the primary passage flow. Throttling performance is predicted for fluidic actuators with different widths, orientations, streamwise locations, and pressure ratios. This simplified model evaluates these actuators in a constant width straight duct and a variable width duct. Two-dimensional CFD of injection in the nozzle guide vane passage reported strong agreement with the results of the simple model using the variable width duct. Higher injection pressure ratios result in more injected mass flow but not significantly higher throttling effectiveness. Wider slots retain the effectiveness and block much more primary flow. Upstream oriented injection proves best for both effectiveness and blockage capabilities. Finally, there is an optimal injection location relative to the passage throat, which is extracted by both the model and CFD. This model has potential application for optimizing fluidic VAT throttling designs while saving on the cost of high-fidelity testing and production of these configurations.
Undergraduate Hypersonics Research: the Fourth Year of the REU Site HYPER
Authors: Kauffman Jeffrey L. , Gordon Ali P. 
Published: August 2024

Abstract
Progress towards future modes of transportation and energy production has uncovered significant knowledge gaps impeding technical progress. Realizing aircraft that regularly operate in supersonic and even hypersonic regimes and turbomachinery supporting carbon neutrality can be addressed only through multi-disciplinary research. The University of Central Florida (UCF) equips future engineers and scientists for research-oriented careers through a variety of programs and initiatives. One key initiative is a Research Experiences for Undergraduates Site housed within the Center for Advanced Turbomachinery and Energy Research and the Department of Mechanical and Aerospace Engineering. Now hosting its fifth cohort, the site unites multi-disciplinary projects around HYpersonic, Propulsive, Energetic, and Reusable Platforms (HYPER). Beyond graduate-level research with expert faculty, participants engage in a professional development series, industry tours, and computational software training. UCF plays a key role in preparing a workforce of young scientists for research careers in hypersonics. This paper presents data drawn from the four completed cohorts of HYPER participants on how exposing participants to the various disciplines has impacted their self-efficacy, as well as a brief summary of lessons learned along the way. With this site, UCF plays a key role in preparing a workforce of young scientists for research careers in hypersonics.
Dilution Rate Analysis of Repairing 316L Stainless Steel Pump Impeller by Laser Cladding Inconel 625 Powder
Authors: Ahmed Rakan A. , Khan Raja S. , Qahtani Mohammed M. , Alsayoud Abduljabar , Bukhari Abdulhameed S. 
Published: August 2024

Abstract
In the oil and gas industry, critical rotating equipment reliable performance is crucial in the seamless operation of production and processing facilities. This paper uses a pump impeller as the basis for a deep dive into novel repair methods. The impeller retained excessive damage to the wear ring landing area while the wall thickness of the damaged location was critically reduced, making it hard to repair using conventional methods or welding techniques. It is observed that the traditional welding techniques, due to excessive heat, could lead to deformation leading to potential challenges in assembling the pump rotor.
Laser cladding (LC) provides distinct advantages for precision control over the heat input, reducing the deformation and cooling time required. LC technology was crucial to the current study because it caters for intricate, complex geometries and sizes, which is impossible with conventional technologies. The process parameters such as laser power, traverse speed and powder feed rate enable tailored repairs that could mitigate deformation and preserve the mechanical properties of the base metal. The use of Inconel 625 powder with SS 316 base metal is well known to provide superior corrosion resistance and enhanced mechanical properties. While the capability of the technology and powder is well charted, its specific application in pump repairs needs further research and development.
This research takes an experimental approach, focusing on understanding the effect of the process parameters on the base metal from a microstructure point of view. A series of 27 samples were analyzed under microstructural analysis, which helps to decipher the impact of variations in the laser power, powder feed rate, and cladding speed. The study calculates the dilution rate to identify the optimum parameters for repairing the damaged impeller.
Reassessment of the Conventional: Numerical Validation of a 1D Model for the Prediction of Volute Losses
Authors: Ceyrowsky Thomas , Hildebrandt André , Heinrich Martin , Schwarze Rüdiger 
Published: August 2024

Abstract
The flow inside the volute of a centrifugal compressor is complex and three-dimensional. The fluid follows a swirling flow pattern, and under many operating conditions, the flow quantities are highly inhomogeneous in radial and circumferential directions. Despite the complex flow physics, the common one dimensional approach to predict losses inside a volute is simple: The kinetic energy of each velocity component at volute inlet is charged with a loss coefficient. In case of the radial velocity, it is assumed to be constant, while the loss coefficient of the tangential velocity depends on whether the flow inside the scroll is de- or accelerated. In the former case, the loss of a sudden expansion is assumed, while in the latter case, it is presumed to be zero. The loss coefficient of the conical diffuser is also assumed to be equal to that of a sudden expansion. However, considering the complex flow physics inside the volute, it is questionable how valid these assumptions are. In this work, the authors present a comprehensive assessment of these conventional 1D predictions by investigating an extensive database of CFD calculations of one volute as a standalone component. The volute has been supplied with different diffuser widths, and the inlet boundary conditions have been selected to allow for separate investigation of the effects of flow angle and flow rate. The aim is to validate the 1D model against the CFD results across the volute’s entire operating range. Therefore, the CFD-predicted total pressure losses within the two subcomponents of the volute (the scroll and the conical diffuser) are assigned to the respective velocity components at volute inlet, in analogy to the 1D predictions. The results show that the loss coefficient of the radial velocity varies notably across the volute’s loss map, opposing the 1D assumption of a constant loss coefficient. Conversely, the loss coefficient of the tangential velocity inside the scroll agrees well with the CFD results: High matching coefficients (i.e. lower than design flowrates) lead to high loss coefficients, which decrease almost continuously towards low matching coefficients (i.e. higher than design flowrates). The losses inside the conical diffuser depend not only on the matching coefficient but also on the flow angle at volute inlet, contrary to what the 1D model assumes. The fundamental characteristics of the global loss coefficient are predicted satisfactorily by the 1D model, while it generally overpredicts losses. Additionally, the CFD results reveal that the matching coefficient that gives minimum loss coefficients varies with the flow angle, which is not accounted for by the 1D model. Therefore, it is not adequate for assessing volute matching.
An Experimental Study on the Effects of Non-Uniform Vane Spacing on Forced Response Reduction in a Mistuned Rotor Blisk in a Multistage Axial Compressor
Authors: Leng Yujun , Dodda Jhansi R. , Key Nicole L. 
Published: August 2024

Abstract
Stators with non-uniform vane spacing (NUVS) are known to effectively reduce the forced response of adjacent rotors by spreading the primary engine order (EO) excitation at a certain speed to a series of weaker excitations at nearby EOs over a wider speed range. To be used in a real gas turbine engine, it is essential to know the forced response vibratory reduction that can be achieved for a specific NUVS configuration at different operating conditions. The classical estimation method to predict the blade response reduction is to quantify the reduction of the forcing function at a potential resonance crossing by conducting a circumferential Fourier analysis of the asymmetric flow field. However, besides excitation reduction, the blade forced response also depends on other factors, such as damping and blade-to-blade interactions due to mistuning.
To study the blade forced response reduction in a realistic environment, a comprehensive experimental study was conducted in the Purdue 3-stage axial research compressor at three different loading conditions. The vibratory response of the 1st torsion (1T) mode forced response of Rotor 2 was measured by strain gages (SG) for two different upstream Stator 1 configurations: the symmetric 38-vaned Stator 1 configuration and the NUVS Stator 1 configuration with 18–20 vane halves. As expected, the strong 38EO-1T response from the symmetric stator reduced to a series of weaker responses from 35EO to 41EO in the NUVS configuration. The overlap of adjacent EO responses caused considerable beating phenomena in the blade SG time-history data. There was substantial blade-to-blade variation in blade response for both the symmetric and asymmetric Stator 1 configurations due to the inherent non-intentional mistuning in the Rotor 2 blisk. This, in turn, causes a large blade-to-blade variation in the reduction factors. While higher responding blades tend to have larger reduction factors, some blades show almost no forced response reduction when switching to the NUVS stator. In addition, the reduction factors for each blade and the maximum reduction factor for the whole blisk also change significantly with loading conditions. The measured reduction factors and the peak response EO are not well predicted by the classical estimation method. This indicates that both damping and mistuning effects need to be considered in the NUVS reduction factor prediction.
Twofold Adaptive Design Space Reduction for Constrained Bayesian Optimization of Transonic Compressor Blades
Authors: Pretsch Lisa , Arsenyev Ilya , Raponi Elena , Duddeck Fabian 
Published: August 2024

Abstract
As turbomachinery designs become more complex, shape optimization tasks involve computationally expensive simulations and many constraints and design variables. Bayesian optimization (BO) is a class of adaptive surrogate-based methods for global optimization. It can efficiently utilize a small budget of high-fidelity evaluations and handle a large number of constraints. However, it suffers from a hampered convergence rate for problems with a large number of design variables. Adaptive design space reductions via principal component analysis (PCA) and trust region (TR) approaches have been shown to improve the scalability in different phases of the optimization. Extending existing methods, we implement the ability to benefit from parallel high-fidelity evaluations and to handle constraints. We then sequentially combine our PCA-BO and TR-BO in a hybrid method to profit from their respective complexity reduction strategies. We assess the performance of our hybrid algorithm by comparing it to vanilla BO on two problems: a 40D analytical test function and a 55D aerodynamic compressor blade design. The empirical results show that PCA-BO enhances the convergence rate in the initial optimization phase, while TR-BO allows for further improvements in the later iterations. Moreover, the algorithm computation time is more than halved. For the compressor blade case, our approach yields an equally good design as vanilla BO after only 20 instead of 96 iterations. The proposed approach has the potential to extend the good performance of BO to even higher-dimensional constrained problems, including multi-stage turbomachinery optimizations.
Global Stability and Forced Response Analysis of Swirling Flows in Aviation Combustors
Authors: Patki Parth , Emerson Benjamin , Lieuwen Timothy 
Published: August 2024

Abstract
Swirling jets are canonical flow fields used to stabilize flames in many gas turbine combustion systems. These flows amplify background acoustic disturbances and perturb the flame, producing combustion noise and potentially combustion instabilities. Hydrodynamic flow response to acoustic excitations in reacting flows is an important modeling task for understanding combustion noise and combustion instabilities.
This study utilizes a global hydrodynamic stability analysis in a Bi-Global and Tri-Global framework to model the vortical hydrodynamic modes of a reacting, swirling LES mean flow based on a commercial nozzle. After conducting a unforced, natural Bi-Global stability analysis to study the unstable eigenmodes of the flow, linearized equations of motion are used to study flow response of the flow to forcing. An empirical velocity transfer function is constructed by determining the flow response to a harmonically varying 150–1500 Hz u′ velocity disturbance at the inflow boundary. These disturbances are strongly amplified, with amplification factors ranging from about 20 to 50 and peaking at about 1050 Hz, or St = 0.375.
A comparison study with a cartesian, three-dimensional reacting base flow is also performed where the base-flow varies spatially in three-dimensions. The study utilizes a stable, high accuracy, but computationally effective centered finite difference scheme based on a three-dimensional structured mesh. Illustrative results present the qualitative modes and quantitative transfer functions for Bi-Global and Tri-Global stability analyses.
Design Guidelines for Arrays of Closely Spaced Darrieus Turbines
Authors: Mohamed Omar Sherif , Melani Pier Francesco , Soraperra Giuseppe , Brighenti Alessandra , Balduzzi Francesco , Bianchini Alessandro 
Published: August 2024

Abstract
The efficiency gains observed in a pair of closely spaced Darrieus turbines are suggesting the deployment of multiple turbines as an appealing solution for wind and, particularly, hydrokinetic applications, where the inflow direction is constant. The present study develops some design guidelines for closely spaced hydrokinetic Darrieus turbines by analyzing the trends of both power augmentation and wake development within arrays of multiple rotors, including not only an even number of rotors, which is the usual case in the literature, but also an odd one. The analysis is carried out by means of two-dimensional Computational Fluid Dynamics simulations and includes not only the assessment of instantaneous blade forces but also locally sampled flow fields past each blade that allowed the reconstruction of dynamic polar data, contributing to a more comprehensive understanding of the physical mechanisms at play in such compact setups. The study demonstrates a consistent power augmentation mechanism across different layouts, even in the case of an odd number of rotors. This enhancement originates from flow blockage in the mutual interaction areas, favorably altering the inflow angle and subsequently increasing the angle of attack and lift generation. While this mechanism aligns with previous observations on arrays of counter-rotating pairs, its application to multiple turbines introduces complexities due to potential asymmetries in inflow, leading to an uneven power enhancement across turbines within the array. The identified efficiency improvement pattern suggests that maximizing leeward mutual interactions within an array of multiple Darrieus turbines would enhance the overall efficiency of the setup.
Assessment of a Liquid Hydrogen Conditioning System for Retrofitting on Kerosene Designed Turbofan
Authors: Rompokos Pavlos , Kyritsis Vasileios , Mourouzidis Christos , Roumeliotis Ioannis 
Published: August 2024

Abstract
As energy transition to alternative fuels for civil aviation is likely to be gradual, hydrogen’s first entry to service may be implemented on existing gas turbine engines. In this paper a novel liquid hydrogen conditioning system for retrofitting on kerosene designed geared turbofans is assessed in terms of performance and engine rematching. The aim of the analysis is to identify emerging requirements for the design of the fuel and thermal management system within the constraints of a certified engine design. The conditioning system proposed, an LH2 preheater, enables the control of the gaseous hydrogen temperature at combustor entry and consists of a secondary combustor and a heat exchanger. The examined configuration considers various bleed source locations within the engine to supply the preheater system.
For performing the analysis, a kerosene fuelled engine has been designed and suitable integrated models capable to simulate the retrofitted hydrogen fuelled engine as well as the LH2 preheater operation have been developed. The system performance has been analysed for the different bleed source locations identifying operating limits and performance changes. From all the examined bleed source positions, utilizing the bypass duct minimizes the impact on component rematching and engine efficiency. Additionally, through a gas path geometry multi-parametric analysis, it was found that by readjusting the capacity of the high-pressure turbine and the core nozzle area the certified limits can be met for the retrofitted engine.
Implementation of a TBLE-Based Wall Model With Pressure Gradient in a Massively Parallel LES Solver
Authors: Cizeron Mehdi , Odier Nicolas , Duchaine Florent , Gicquel Laurent Y. M. , Nicoud Franck 
Published: August 2024

Abstract
Wall modeling is a common approach to reduce the cost of Large-Eddy Simulations (LES) of high Reynolds number flows. The selection of the wall model is however crucial due to the underlying assumptions made to derive these models. The most frequently employed wall models rely on strong hypotheses such as the absence of pressure gradient, curvature, and the assumption of stationarity. These assumptions are questionable for turbomachinery configurations, which can involve complex phenomena and may result in mispredictions. This work aims to investigate the resolution of a Thin Boundary Layer Equation (TBLE) approach including the pressure gradient effect and evaluate the gain compared to a classical logarithmic law approach. The proposed approach accounts for the pressure gradient directly through a source term. Two configurations are investigated to validate this approach and its performance. First, a planar turbulent channel without pressure gradient is investigated to ensure the model’s ability to accurately predict a turbulent boundary layer. The second case, the periodic hill test case available on the ERCOFTAC database, is used to assess the wall model’s performance on a flow submitted to pressure gradient effects. The conclusions of this work are twofold. First, such wall models can be sensitive to the unsteady pressure gradient fluctuations present in the LES prediction even for cases without mean pressure gradient; temporal averaging can thus be required to reach satisfying results. Second, substantial improvement is found in the periodic hill problem if compared to the algebraic wall model, in terms of mean velocity profiles, recirculation bubble size, reattachment zone, and friction profiles. Promising contributions of such tools can therefore be expected for turbomachinery configurations.