bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Fluid-Structure Interaction Tool Using a Van der Pol Based Reduced-Order Model for Buffet and Non-Synchronous Vibrations
Authors: Hollenbach Richard , Kielb Robert , Hall Kenneth 
Published: October 2022

Abstract
This paper builds upon a two-degree-of-freedom Van der Pol oscillator based Reduced-Order Model for studying the mechanisms around Non-Synchronous Vibrations (NSV) in turbomachinery. One degree tracks the fluid motion utilizing a combination of a traditional Van der Pol Oscillator and a Duffing Oscillator; the other degree of freedom is a mass on a spring and a damper, in this case a cylinder. Thus, this model can be considered one of fluid-structure interaction. The cubic stiffening from the Duffing Oscillator proved to improve the match to experimental data. Using this model to study the time-history of the fluid and the structure oscillation, additional parameters are extracted to understand the underlying mechanisms of frequency lock-in and limit cycle oscillation. First, the phase shift between the vortex shedding and the structural motion is calculated when it locks-in then unlocks. Second, the work done per cycle is analyzed from the contributions of the mass, spring, and damping forces to determine the dominant contributor when locking-in versus unlocking. Third, the phase portrait is plotted on a Poincare Map to further study the locked-in versus unlocked responses.
This model is then validated against not only experimental data, but also computational simulation results and previous reduced-order models. The finalized model can now serve as a preliminary design tool for turbomachinery applications. For more realistic and accurate modeling, a third degree-of-freedom in the form of an airfoil pitching motion will be added in a separate paper as well.
PDA Laser Measurements of Droplet-Laden Flows in a Four Stage Axial Compressor
Authors: Doerr Tobias , Schuster Sebastian , Brillert Dieter 
Published: October 2022

Abstract
Droplet-laden flows play a significant role in the development of turbomachinery. For example, fine water droplets are injected into the flow path of axial compressors to increase the power output of gas turbines by making use of evaporation cooling, often referred to as Wet Compression. Another example is the ingestion of rain droplets in aircraft engines. Therefore, thermodynamic and aerodynamic measurements of air and liquid are indispensable in order to better predict the following behaviour of the droplets in the gas flow.
This paper presents a new PDA measurement setup for a droplet-laden four-stage axial compressor in order to analyse the droplet behaviour in swirled flows. To reduce optical disturbances of the laser beam path, liquid films at the casing are suppressed by a boundary layer air injection. Supplementary investigations with this treatment show a negligible influence on the compressor behaviour. In order to minimize refraction effects of the laser beams at the casing window, the laser device with the optical probes can be translated and rotated, thus having 4 degrees of freedom. Furthermore, the collected droplet data is compared with a mathematical description of velocity slip in superimposed air flows.
For the first time, it can be shown experimentally that droplets smaller than 10 μm attain the velocity of air one stage after injection. For larger droplets, however, deviations from the air Mach number of up to 0.05 remain. In addition, detached liquid films behind the trailing edge of the stator blades with low velocities can be clearly detected.
Sound Generation in Multicomponent Nozzle Flows With Dissipation
Authors: Jain Animesh , Magri Luca 
Published: October 2022

Abstract
Low emission aircraft engines burn in a lean regime, which makes the combustor susceptible to unsteady combustion. Along with improper mixing and air cooling, the unsteady combustion process gives rise to flow inhomogeneities. The acceleration of these inhomogeneities in the nozzle downstream of the combustor generates indirect combustion noise. If the acoustic waves that are reflected off the nozzle are sufficiently in phase with the heat released by the flame, thermoacoustic instabilities can occur. The generation and transmission of sound through the nozzle guide vane are typically modelled with a compact and isentropic nozzle model. Because the flow is non-isentropic due to losses from wall friction and recirculation zones, in the literature, a mismatch is observed between experimental and theoretical predictions in subsonic-choked regimes. In this work, we propose a low-order physical model to predict indirect noise in a multi-component nozzle flow with dissipation using conservation laws whilst modelling non-isentropicity using a friction factor. The model is generalized for finite-length (non-compact) arbitrary geometry nozzles. We show that the friction factor can account for wall friction and two (or three) dimensional effects, such as flow recirculation in a cross-averaged sense. We analyse the model numerically for both subsonic and supersonic nozzles, emphasizing the importance of non-isentropic and non-compact assumptions with compositional inhomogeneities. Further, we show the effect of the nozzle geometry. The results are validated with existing experimental data from the literature.
Plume Model for Buoyancy-Induced Flow and Heat Transfer in Closed Rotating Cavities
Authors: Tang Hui , Owen J. Michael 
Published: October 2022

Abstract
The radial clearance between the rotating blades and stationary casing of a gas turbine compressor depends on the radial growth of the rotating discs to which the blades are attached, and this growth depends on the buoyancy-induced flow and heat transfer in the air-filled cavities between adjacent discs. In some engines, the cavities are sealed, which creates a closed rotating cavity. A theoretical model has been developed to calculate the radial distribution of the temperature of the disc in a closed rotating cavity. The principal assumptions are that the convective heat transfer from the hot shroud to the cold hub of the cavity is via plumes of fluid in which the cold fluid moves radially outward, and the hot fluid inward, inside an inviscid quasi-axisymmetric core of rotating fluid. The fluid core is surrounded by boundary layers on all rotating surfaces, with free-convection layers on the surfaces of the shroud and hub and laminar Ekman layers on the surface of the discs. In addition to the convection, heat is transferred by one-dimensional radial conduction in the rotating discs. Using the model, equations have been derived to calculate the radial distribution of temperature in the discs and fluid core. These equations reveal that the non-dimensional temperatures for the disc and core, θd and θc, are controlled by three independent non-dimensional parameters: Reϕ, βΔT and χ, the rotational Reynolds number, the buoyancy parameter, and the compressibility parameter, respectively. The compressibility parameter is defined as χ=defMa2/βΔT where Ma is a Mach number, and χ is shown to strongly affect the radial distribution of the core temperatures. There will be a critical value of χ at which the core temperature equals that of the heated shroud. For a closed cavity with adiabatic discs and xα = 0.5, the critical value is 6.7. Above this critical value, stratification is expected to occur and heat transfer from the shroud to the core will be by conduction rather than by convection. The theoretical model predicts radial distributions of temperatures in the discs and fluid core that are in good agreement with the experimentally derived values in a companion paper.
Estimation of Dynamical Thermoacoustic Modes Using an Output Only Observer Kalman Filter-Based Identification (O3KID) Algorithm
Authors: Balasubramanian Nikhil , Rouwenhorst Driek , Hermann Jakob 
Published: October 2022

Abstract
Thermoacoustic instabilities have plagued the operation of gas turbine engines for years and significant research is being conducted in detecting and understanding them. In this paper, an output only identification technique is employed for a noise induced dynamical system representing combustion dynamics. Background turbulent flow in a combustor has a significant influence on combustion dynamics. In general, this flow noise is referred to as background noise, whose characteristics are unknown apriori. Identification of combustion dynamics with output only identification becomes challenging since the system dynamics and background noise dynamics are indistinguishable. To simplify the problem and identify both deterministic and stochastic components, a two-step identification using state space modelling is implemented. The data is transformed to accommodate an observer, which predicts the current state of a system from its previous states. The observer takes the form of a Kalman filter and in solving for the Kalman filter gain would solve the original problem yielding all the system matrices of the state space model. This approach is called the Output only Observer Kalman filter identification (O3KID) and its first step solves for least squares from a set of algebraic equations constructed from just the measured output. The least squares solution gives the Markov parameters (impulse response) and the output residuals. The subsequent step takes the Markov parameters or the residuals to solve for the system matrices using any deterministic sub-space identification method. In this paper, classical methods such as the Eigenvalue Realization Algorithm (ERA) using the Markov parameters is employed to solve for the system matrices. In using this direct non-iterative two-step algorithm, it is possible to estimate the eigenmodes and damping coefficients from output measured data. To validate the algorithm, a system of independent harmonic oscillators, excited by random noise is used to generate surrogate data representing pressure oscillations in a combustor prior to an instability. The O3KID algorithm could identify the eigenmodes with exactly the degrees of freedom required to define it i.e., a system with three harmonic oscillators could be defined with a 6-order model, which implies 6 coefficients. The same method was applied to pressure fluctuations data from a laboratory burner. The estimation of the most energetic modes was accurate with as few as 10 modes. This fast direct approach could be used to provide an early warning indicator in industrial gas turbines by tracking the rate of damping of dominant eigenmodes. Additionally, saving the state space parameters periodically can serve as a data-lean option to track changes of the dynamics and across a gas turbine fleet.
An Optimization Methodology for Turbines Driven by Pulsed Detonation Combustors
Authors: Asli Majid , Stathopoulos Panagiotis 
Published: October 2022

Abstract
A step-change in efficiency of gas turbine technology and, subsequently, an emissions reduction from this technology requires conceptual changes. Substituting conventional combustion chambers with pressure gain combustion in the form of pulsed detonation combustion (PDC) is one of the promising methods that can reduce gas turbine emissions significantly. Nevertheless, the component matching for the respective systems and specifically that of turbine expanders working with the exhaust flow of PDC tubes is still not solved. The unsteady nature of PDC exhaust flow makes 3D-CFD simulations too expensive to be applied in optimization loops in early design stages. To address this question, the present paper introduces a new cost-effective but reliable methodology for turbine analysis and optimization, based on the unsteady exhaust flow of pulsed detonation combustors. The methodology unitizes a robust unsteady one-dimensional solver, a meanline performance analysis, and an adaptive surrogate optimization algorithm. A two-stage axial turbine is optimized considering all unsteady flow features of a hydrogen-air PDC configuration with five PDC tubes. A threedimensional URANS simulation is performed for the optimized geometry and the baseline to evaluate the methodology. The results showed that the optimized turbine produces 16% lower entropy than the original one. Additionally, the turbine output power is increased by 14% by the optimized design. Based on the results, it is concluded that the approach is fast and reliable enough to be applied in optimizing any turbine working with unsteady flows, more specifically in PDC applications.
Large Eddy Simulations of a Transonic Airfoil Cascade
Authors: Priebe Stephan , Wilkin Daniel , Breeze-Stringfellow Andy , Mousavi Arash , Bhaskaran Rathakrishnan , d’Aquila Luke 
Published: October 2022

Abstract
The tip region of transonic blades in turbomachinery involves complex flow physics including shock wave/boundary layer interactions (SBLI). SBLI can lead to flow separation, transition from laminar to turbulent flow, and unsteadiness, which can affect the overall performance of the blade. In this paper, we present wall-resolved large eddy simulations (LES) of a transonic rotating cascade that is modeled after the tip region of a transonic diffusing blade. The calculations were performed using GENESIS, a high-order unstructured large eddy simulation solver. The convergence of the LES solution is assessed by varying the polynomial order of the solution from low to high order. LES simulations for a total of five operating conditions are presented, which cover the range of operation from unique incidence low operating line to stall and the associated shock wave/boundary layer interaction physics. The overall aerodynamics of the transonic passage airfoil are described based on the LES solutions as well as providing a detailed analysis of the boundary layer behavior. The changes in shock structure, boundary layer interaction physics, and associated losses with operating condition are highlighted. A low-frequency SBLI unsteadiness is observed in the cases where the boundary layer into the shock is laminar, and a scaling of the frequency is proposed. The scaling is based on the time scale of turbulent structures convecting from the shock to the trailing edge and acoustic disturbances then traveling back upstream.
Impact of Inlet Conditions on TVF Exit Flow Field
Authors: Graiff Mattia , Staggl Marian , Wakelam Christian , Heitmeir Franz , Göttlich Emil 
Published: October 2022

Abstract
The drive towards lightweight, more efficient engine architectures leads to the development and improvement of key aircraft engine components. The Turbine Vane Frame (TVF) can be seen as an evolution of the Turbine Center Frame (TCF), combining its structural and aerodynamic purposes with the function otherwise provided by the first stage turbine inlet guide vanes. Therefore, the TVF needs to smoothly guide the flow over the radial offset between high-pressure and low-pressure turbine stages, provide shrouded paths for oil lines, and impart to the flow the turning required by the following low pressure turbine stage. The expected beneficial effects on the engine include reduced weight, cost, and fuel burn. The key relevance of this component makes a broad, low-tier approach to its study highly desirable. The HighSpeed Wind Tunnel (HSWT) at the Technical University of Graz delivers excellent opportunities to explore the design space for Turbine Vane Frames. This paper deals with the impact of several important design parameters on the TVF. An engine relevant TVF configuration is replicated in an annular sector cascade test rig. The test rig is operated at relevant Mach number and turbulence level. Representative inlet flow is achieved through flow conditioning. Aerodynamic data is collected with five-hole probe and hot wire anemometry techniques. The insights offered by flow visualization and numerical computations are furthermore leveraged. Particular attention is given to the flow features at the TVF exit.
Interplay of Clusters of Acoustic and Intrinsic Thermoacoustic Modes in Can-Annular Combustors
Authors: Fournier Guillaume J. J. , Schaefer Felicitas , Haeringer Matthias , Silva Camilo F. , Polifke Wolfgang 
Published: October 2022

Abstract
Thermoacoustic systems can exhibit self-excited instabilities of two nature, namely cavity modes or intrinsic thermoacoustic (ITA) modes. In heavy-duty land-based gas turbines with canannular combustors, the cross-talk between cans causes the cavity modes of various azimuthal order to create clusters, i.e. ensembles of modes with close frequencies. Similarly, in systems exhibiting rotational symmetry, ITA modes also have the peculiar behavior of forming clusters. In the present study, we investigate how such clusters interplay when they are located in the same frequency range. We first consider a simple Rijke tube configuration and derive a general analytical low-order network model using only dimensionless numbers. We investigate the trajectories of the eigenmodes when changing the downstream length and the flame position. In particular, we show that ITA and acoustic modes can switch nature and their trajectories are strongly influenced by the presence of exceptional points. We then study a generic can-annular combustor. We show that such configuration can be approximated by an equivalent Rijke tube. We demonstrate that, in the absence of mean flow, the eigenvalues of the system necessarily lie on specific trajectories imposed by the upstream conditions.
Modelling and Optimization of a Hospital Gas Turbine-Based Cogeneration System
Authors: Zini Marco , Carcasci Carlo , Sodini Roberto 
Published: October 2022

Abstract
Hospitals are among the most energy-intensive commercial buildings in the service industry and their energy demand is characterized by specific features, being operative 24 hours a day, 365 days a year. Moreover, several activities performed inside the building require strict control of the indoor climate conditions to ensure comfort and security standards. Often, they present complex HVAC systems that need various energy forms like electricity and thermal energy in the form of hot water, chilled water and steam. Consequently, hospitals and healthcare facilities are ideal application to exploit the cogeneration systems potential. Indeed, the number of hospitals using CHP systems has grown steadily in past years. Hospitals that use CHP take advantage of favourable rate structures and protect themselves from rising electricity prices. Since CHP uses waste heat to produce thermal energy for heating and cooling, hospitals using CHP systems are more energy-efficient, leading also to a reduction of the global emissions connected to the hospital activity. The present study involves the development of a numerical model of the gas turbine-based cogeneration system installed in a hospital facility. The realized model has been used to define the system management strategies that enabled two achievements. The minimization of the main global emissions parameters of the system as CO and NOx and the maximization of operational CHP parameters as total efficiency and primary energy saving (PES). The present work describes in detail the realized model and its exploitation, leading to define the optimal system management strategy based on control parameters applicable to the real test case management system.
Roughness-Resolved LES of Additive Manufacturing-Like Channel Flows
Authors: Meynet Serge , Barge Alexis , Moureau Vincent , Balarac Guillaume , Lartigue Ghislain , Hadjadj Abdellah 
Published: October 2022

Abstract
In the last decade, progresses in additive manufacturing (AM) have paved the way for optimized heat exchangers whose disruptive design will heavily rely on predictive numerical simulations. However, due to typical roughness induced by AM, current wall models used in steady and unsteady 3D Navier-Stokes simulations do not take into account such characteristics. For the development and assessment of novel wall models for AM, a high-fidelity roughness-resolved Large-Eddy Simulation (RRLES) database is built. This article describes the numerical setup and the methodology used for conducting RRLES, from surface generation to post-processing. In addition, three different cases representing two printing directions plus a streamwise and spanwise isotropic case are investigated. While the roughness distributions are the same in the three cases, the effective slope (ES) is very different and the impact of this parameter on turbulence and heat transfer is analyzed at different Reynolds numbers.
Design and Commissioning of the Constant Condition Dynamic Test Rig
Authors: Pearce Robert , Tombs Michael , Hussain Zahid 
Published: October 2022

Abstract
This paper presents details and data from a new facility designed, constructed and commissioned at the Oxford Thermofluids Institute. The constant condition dynamic test rig is designed primarily to test aero-engine butterfly valves under a wide range of representative conditions. A novel strategy of actively controlled downstream valves placed between the test section and vacuum tank is used to provide a tightly controlled constant pressure drop across the test section. This strategy effectively synthesises a much larger volume than the physical size of the available downstream tank, providing long test times under true steady state conditions. Full experimental test rig details are given in this paper with an overview of the control strategy and verification of the test conditions obtained in this novel rig configuration. Primary data outputs of discharge and torque coefficients for the test valve are presented for static points across the full range of valve opening with RANS CFD data included for verification of the experimental data. This initial commissioning data is presented at a low pressure ratio of approximately 1.05. Localized pressure data are presented for analysis of local flow fields around the valve and for further validation. Finally, a modified discharge coefficient formulation is presented to account for cross-sectional area changes in the test rig and to ensure the experimental data is directly transferable to practical engine cases.
Analysis of a Multi-Generation Renewable Energy System with Hydrogen-Fueled Gas Turbine
Authors: Bahlawan Hilal , Losi Enzo , Manservigi Lucrezia , Morini Mirko , Spina Pier Ruggero , Venturini Mauro 
Published: October 2022

Abstract
It is now universally established that the use of fossil fuels is responsible for environmental issues such as global warming. Among the different renewable energy sources, solar energy is considered one of the most affordable resources for meeting current energy demands and mitigating environmental problems. However, the exploitation of solar energy is challenging because of both diurnal and seasonal variations. Power-to-Hydrogen technologies can play a key role to counterbalance the variation of solar irradiance. Moreover, hydrogen-fueled gas turbines are considered promising technologies to decarbonize the electricity sector.
To tackle these concerns, this paper presents a multi-generation energy system operated in island mode in which a hydrogen-fueled gas turbine is coupled with a solar photovoltaic plant, an electrolyzer, an absorption chiller, electric and thermal energy storage, as well as a hydrogen storage. Therefore, the energy system is 100% based on renewable energy. The sizes of the components and the respective energy management strategy are optimized by maximizing the exploitation of renewable energy sources, while the supply of electricity from the national grid must be null. Moreover, the effect of ambient conditions on the optimal sizing is also investigated by considering the thermal, cooling and electrical energy demands of two case studies located in two different climatic zones. The paper demonstrates that the adoption of hydrogen-fueled gas turbines coupled with Power-to-Hydrogen technologies can effectively support the transition towards a clean energy supply. Moreover, this study provides a procedure for the optimal sizing of a multi-generation energy system fully based on solar energy, by also demonstrating that both PV panel area and hydrogen storage volume are feasible, if compared to the considered district layout.