bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigations of Unsteady Aerodynamics of an Offshore Floating Wind Turbine With Platform Motions Using Dual-Sliding Method
Authors: Wang Xiaodong , Ye Zhaoliang , Chen Ziwen , Guo Yize , Qiao Yujun 
Published: January 2021

Abstract
Offshore wind energy developed rapidly in recent years. Due to the platform motions causing by ocean waves, the aerodynamics of floating offshore wind turbines (FOWT) show strong unsteady characters than onshore wind turbines. The widely used methods to investigate the unsteady aerodynamic performance of wind turbine are Blade Element Momentum (BEM) and Free-Vortex Wake (FVW) methods. The accuracy of these two methods strongly depend on empirical formula or correction models. However, for dynamics motions of wind turbine, there is still a lack of accurate models. CFD simulations using overset or dynamic mesh methods also have been used for FOWT aerodynamic investigations. However, the mesh deforming or reconstruction methods are usually suitable for small movement of wind turbine blade. In this paper, a dual-sliding mesh method is employed to simulate the unsteady aerodynamic characters of an offshore floating wind turbine with supporting platform motions using Unsteady Reynolds Averaged Navier-Stokes (URANS) simulations. Both rotor rotation and platform motions are treated as rigid angular motions. The relative motion and data exchange were simulated using sliding mesh method. The NREL 5MW reference wind turbine with platform pitching and rolling motions are considered. The pitching and rolling motions of floating platform are simplified in the form of a prescribed sinusoidal function. Different conditions with two amplitudes and two frequencies of pitching and rolling motions were investigated. URANS were performed with full structured mesh for wind turbine rotor using commercial software FLUENT. The platform motions were set using User Defined Function (UDF). Transitional Shear Stress Turbulence (T-SST) model was employed.
The simulation results were compared with BEM method and FVW method results. Both steady status and dynamic pitching processes are investigated. The variations of wind turbine aerodynamic load, as well as the aerodynamic character of airfoils at different spanwise positions, were obtained and analyzed in detail. The simulations results show that the platform pitching introduce remarkable influence on the wind turbine aerodynamic performance. The platform pitching has much larger influence on the wind turbine power and thrust than the platform rolling. The dual-sliding mesh method shows potentials to investigation the dynamic process with multiple rigid motions.
Investigation on the Fluctuations of the Spray Angle Generated From Pressure-Swirl Atomizers
Authors: Wang Xiwei , Huang Yong , Sun Lei 
Published: January 2021

Abstract
The unsteady characteristic of the pressure-swirl atomization system was studied experimentally in this paper. It was found that the fluctuations of the spray can be divided into two modes: high and low frequency mode, among which the frequency of the high mode is within the range of 500–1100Hz, and the low mode is 100–400Hz. The low mode depends on the turbulent exchange of momentum between the liquid and the surrounding stagnant gas. While the high mode depends on the comprehensive effect of the turbulent vortex generated by the liquid flowing through the atomizer and the natural frequency of the atomizer. Experiments show that the peak frequency of the low mode increases but the peak frequency of the high mode decreases when the pressure drop of the atomizer increases. When the atomizer outlet area size increases, both the peak frequency of the low mode and the high mode decrease. When the deflection angle of the swirl chamber increases, the peak frequency of the low mode increases, while the peak frequency of the high mode decreases first and then increases, reaching the minimum at 60°, and the value at 45° is basically the same as at 80°.
Reliable Calculation of Thermoacoustic Instability Risk Using an Imperfect Surrogate Model
Authors: Guo Shuai , Silva Camilo F. , Polifke Wolfgang 
Published: January 2021

Abstract
One of the fundamental tasks in performing robust thermoacoustic design of gas turbine combustors is calculating the modal instability risk, i.e., the probability that a thermoacoustic mode is unstable, given various sources of uncertainty (e.g., operation or boundary conditions). To alleviate the high computational cost associated with conventional Monte Carlo simulation, surrogate modeling techniques are usually employed. Unfortunately, in practice it is not uncommon that only a small number of training samples can be afforded for surrogate model training. As a result, epistemic uncertainty may be introduced by such an “inaccurate” model, provoking a variation of modal instability risk calculation. In the current study, using Gaussian Process (GP) as the surrogate model, we address the following two questions: Firstly, how to quantify the variation of modal instability risk induced by the epistemic surrogate model uncertainty? Secondly, how to reduce the variation of risk calculation given a limited computational budget for the surrogate model training? For the first question, we leverage on the Bayesian characteristic of the GP model and perform correlated sampling of the GP predictions at different inputs to quantify the uncertainty of risk calculation. We show how this uncertainty shrinks when more training samples are available. For the second question, we adopt an active learning strategy to intelligently allocate training samples, such that the trained GP model is highly accurate particularly in the vicinity of the zero growth rate contour. As a result, a more accurate and robust modal instability risk calculation is obtained without increasing the computational cost of surrogate model training.
Large Eddy Simulation of the 7-7-7 Shaped Film Cooling Hole at Axial and Compound Angle Orientations
Authors: Tracy Kevin , Lynch Stephen P. 
Published: January 2021

Abstract
Shaped film cooling holes are used extensively for film cooling in gas turbines due to their superior performance in keeping coolant attached to the surface, relative to cylindrical holes. However, fewer studies have examined the impact of the orientation of the shaped hole axis relative to the main flow direction, known as a compound angle. A compound angle can occur intentionally due to manufacturing, or unintentionally due to changes in the main flow direction at off-design conditions. In either case, the compound angle causes the film cooling jet to roll up into a strong streamwise vortex that changes the lateral distribution of coolant, relative to the pair of vortices that develop from an axially oriented film cooling hole. In this study, Large Eddy Simulation (LES) using the Wall-Adapting Local Eddy Viscosity (WALE) model was performed on the publicly available 7-7-7 shaped film cooling hole, at two orientations (0°, 30°) and two blowing ratios (M = 1, 3). Laterally-averaged film effectiveness was largely unchanged by a compound angle at a blowing ratio of 1, but improved at a blowing ratio of 3. For both blowing ratios, the lateral distribution of film was more uniform with the addition of a 30° compound angle. Both wall normal and lateral turbulent convective heat transfer was increased by the addition of a compound angle at both blowing ratios.
Heat Transfer in Rotating, Trailing Edge, Converging Channels With Smooth Walls and Pin-Fins
Authors: Sahin Izzet , Chen I-Lun , Wright Lesley M. , Han Je-Chin , Xu Hongzhou , Fox Michael 
Published: January 2021

Abstract
The heat transfer and pressure drop characteristics of a rotating cooling channel that has an angled trapezoidal cross-section and converges from the hub to tip in both the streamwise and spanwise directions are experimentally investigated. The channel is oriented 120° with respect to the direction of rotation to model the geometry of an internal, trailing edge cooling passage. Both the leading and trailing sides of the channel are divided into three and six regions in the spanwise and streamwise directions, respectively. The copper plate method is used to obtain regionally averaged heat transfer coefficients. The pressure drop is measured utilizing pressure taps placed at the inlet and outlet of the channel. Experiments were conducted with the inlet Reynolds number ranging from 10,000 to 40,000. The rotational speed varies from 0 rpm to 300 rpm, resulting in the highest rotation number of 0.21. The effects of full pin-fins on the heat transfer and pressure drop characteristics are obtained and compared to the smooth surface converging channel results. The impact of the convergence, which causes variations of flow and geometric parameters through the passage, such as aspect ratio, Reynolds number, and rotation number, on the heat transfer coefficients and pressure drop are addressed. Results show that due to the 120° channel orientation, rotation has a positive impact on the leading and trailing surface heat transfer. Furthermore, the convergence decreases the aspect ratio while increasing Reynolds number. The convergence significantly enhances heat transfer on both the leading and trailing surfaces along the streamwise and spanwise directions. The convergence also reduces the rotation effect in the streamwise direction for a given mass flow rate.
Steady and Unsteady Temperature Measurements in the Wake of a Linear Cascade With Heated Airfoils
Authors: Aberle-Kern Svenja , Ripplinger Thomas , Niehuis Reinhard 
Published: January 2021

Abstract
Understanding basic aerodynamic and thermodynamic processes in engine components is critical to achieving higher efficiencies and lower fuel consumption in aircraft engines. To aid in this process, a linear compressor cascade was investigated in the high-speed cascade wind tunnel of the Institute of Jet Propulsion to quantify the influence of heat transfer on the temperature distribution in the wake and, finally, the profile loss. For this purpose, a patented five-hole probe with an integrated thermocouple was developed and applied for steady measurements. Additionally, a hot-wire measurement set-up was implemented to receive temperature fluctuations via the constant current mode as well as velocity fluctuations via the constant temperature mode. A novel method for a two-way temperature and velocity correction for the two types of hot-wire measurement is presented. Good agreement between the measurement data of the five-hole probe and averaged data from hot-wire anemometry was found. The temperature distribution indicates the occurrence of energy separation which in some cases is overlain with the effects of heat transfer. In addition, the analysis of unsteady fluctuations of temperature and velocity give more detailed information about the vortex shedding in the wake, including the size of the vortices. Finally, this is the first discussion of energy separation at a compressor cascade combined with overlain effects of heat transfer on the blade surface.
Control of the Aero-Engine Nacelle Intake Flow Separation Caused by Crosswind Condition Using Plasma Actuation
Authors: Zhang Haideng , Wu Yun , Yu Xianjun , Li Yinghong , He Qikun 
Published: January 2021

Abstract
To develop active flow control technique which can suppress the nacelle intake flow separations caused by crosswind effectively, microsecond plasma actuation is used to control the flow separations of a typical nacelle intake model. Both experimental and numerical investigations have been implemented to uncover the corresponding flow control effects. The plasma actuation is installed near the inception point of the nacelle intake flow separations. According to the experimental and numerical results, the nacelle intake flow separations caused by crosswind are suppressed by the plasma actuation. The frequency of the plasma actuation as well as the scale of the flow separation are influential to the flow control effects. The compressive wave induced by the plasma actuation will act on the separated flow as well as the interface between the flow separation zone and the mainstream zone. This is the mechanism behind the suppression of nacelle intake flow separations using microsecond plasma actuation.
Theoretical Assessment of Turbocharged Pulse Detonation Engine Performance at Various Flight Conditions
Authors: Nageswara Reddy Pereddy 
Published: January 2021

Abstract
A typical Pulse Detonation Engine (PDE) cycle of operation includes three basic processes: initiation and propagation of detonation wave in the Detonation Chamber (DC); a quasi-steady exhaust of detonation products from the DC at varying pressure through the supersonic nozzle; and a steady exhaust of remained detonation products at constant pressure through the nozzle while filling the DC with fresh air. In the present work, a novel method of Turbo-charging is proposed to increase the inlet pressure/density of fresh air fed into the DC in each cycle so as to increase the thrust developed per unit area of DC. The thermodynamic cycle of operation of Turbocharged Pulse Detonation Engine (TPDE) is analyzed based on quasi-steady state one dimensional formulation, and a computer code is developed in MATLAB to simulate the cycle performance at different compressor pressure ratios. Thrust per unit area of DC, the specific thrust and the fuel-based specific impulse are estimated at various flight conditions at different pressure ratios by considering C2H4/air as the fuel-oxidizer. The net thrust developed per unit area of DC increases with an increase in compressor pressure ratio, up to the pressure ratio of 4.0, at all flight conditions. The compressor pressure ratio of about 2.0 is observed to be optimum pressure ratio as TPDE develops nearly the same air-based specific thrust at this pressure ratio irrespective of flight operating conditions.
Dynamic Gas Turbine Condition Monitoring Scheme With Multi-Part Neural Network
Authors: Li Zhouzheng , Feng Kun , Yan Binbin 
Published: January 2021

Abstract
Gas turbines are high value industrial assets with significant roles in various kinds of industrial processes, health management systems are therefore important for helping maintaining gas turbines’ stability in long-term operations. With more and more performance data able to be collected by sensors and the new machine learning methods developed, researchers are able to build more powerful digital models to monitor the gas turbine.
This paper introduces a performance parameters alarm scheme for gas turbine using an adaptive state following model. The proposed scheme consist of 3 parts: Part 1, a dynamically adaptive multi-part neural network trained using performance data that can simulate different parts of gas turbine and output “normal” sensor data to make comparison with the actual data collected; Part 2, a group of thresholds set according to system noise that flags sudden failures by sensing performance parameter outliers, this also decides which data should be used to update the neural network; Part 3, a recorder for “reference point” outputs that can reflect change of the gas turbine’s status and detect long-term degradation.
Unlike traditional approaches, the proposed adaptive states following model separates long term degradation and short term sudden failure, therefore both faults can be detected more accurately. The core of the proposed method is that physical properties are embedded into the neural network as constraints to regulate training and make the model more interpretable. In our scheme, a gas turbine is divided into 4 parts referencing the equipment’s physical mechanism, they are simulated digitally by 4 sub corresponding networks, which are then combined into the proposed integrated network. The proposed scheme achieves an overall pleasing result and shows potential in gas turbine fault analysis.
A Sector-Cascade Test Rig for Measurements of Heat Transfer in Turbine Center Frames
Authors: Jagerhofer Patrick R. , Patinios Marios , Erlacher Gerhard , Glasenapp Tobias , Göttlich Emil , Farisco Federica 
Published: January 2021

Abstract
The turbine center frame (TCF) is an inherent component of turbofan aircraft engines and is used for connecting the high-pressure turbine (HPT) to the low-pressure turbine (LPT). Its position immediately downstream of the HPT makes it susceptible to the extremely high temperatures of future engines. Despite this, fundamental knowledge of heat transfer in TCFs and the influencing factors is still missing.
This paper presents a new 45° sector-cascade test rig specifically designed for fundamental studies of film cooling effectiveness and heat transfer coefficient in TCFs and for the development and validation of a measurement technique involving infrared thermography and heating foils.
Measurements of heat transfer coefficient in the TCF were taken for two purge-to-mainstream mass flow ratios corresponding to the case of no purge and nominal (to engine operation) purge. The magnitude of the heat transfer coefficients on the hub and strut surfaces was highly influenced by the various flow structures in the passage and by the velocity variation of the mainstream flow due to the “aggressive” design of the TCF. Heat transfer on the surface of the strut was mainly governed by boundary layer behavior (laminar near the leading edge and turbulent for the rest of the strut) augmented by the effect of the secondary flow structures.
Measurements of film cooling effectiveness were also taken for the single case of nominal purge. A region of high film cooling effectiveness was observed, extending from the purge cavity exit to about 40% of the passage axial length. In this region, the effectiveness decreased with increasing axial length. On the surface of the struts and fillet radii the film cooling effectiveness was found to be zero. This was attributed to the effect of the horse-shoe vortex which sweeps the purge flow away from the strut surface and dilutes it by continuously entraining hot mainstream flow.
Hybrid Model-Based and Data-Driven Diagnostic Algorithm for Gas Turbine Engines
Authors: Fentaye Amare , Zaccaria Valentina , Rahman Moksadur , Stenfelt Mikael , Kyprianidis Konstantinos 
Published: January 2021

Abstract
Data-driven algorithms require large and comprehensive training samples in order to provide reliable diagnostic solutions. However, in many gas turbine applications, it is hard to find fault data due to proprietary and liability issues. Operational data samples obtained from end-users through collaboration projects do not represent fault conditions sufficiently and are not labeled either. Conversely, model-based methods have some accuracy deficiencies due to measurement uncertainty and model smearing effects when the number of gas path components to be assessed is large. The present paper integrates physics-based and data-driven approaches aiming to overcome this limitation. In the proposed method, an adaptive gas path analysis (AGPA) is used to correct measurement data against the ambient condition variations and normalize. Fault signatures drawn from the AGPA are used to assess the health status of the case engine through a Bayesian network (BN) based fault diagnostic algorithm. The performance of the proposed technique is evaluated based on five different gas path component faults of a three-shaft turbofan engine, namely intermediate-pressure compressor fouling (IPCF), high-pressure compressor fouling (HPCF), high-pressure turbine erosion (HPTE), intermediate-pressure turbine erosion (IPTE), and low-pressure turbine erosion (LPTE). Robustness of the method under measurement uncertainty has also been tested using noise-contaminated data. Moreover, the fault diagnostic effectiveness of the BN algorithm on different number and type of measurements is also examined based on three different sensor groups. The test results verify the effectiveness of the proposed method to diagnose single gas path component faults correctly even under a significant noise level and different instrumentation suites. This enables to accommodate measurement suite inconsistencies between engines of the same type. The proposed method can further be used to support the gas turbine maintenance decision-making process when coupled with overall Engine Health Management (EHM) systems.
Numerical Investigation of Inlet Turbulence Intensity Effect on a Bluff-Body Stabilized Flame at Near Flame Blow-Off Conditions
Authors: Ali Montakhab Amir , Akih Kumgeh Benjamin 
Published: January 2021

Abstract
This paper investigates the effects of the inlet turbulence intensity (ITI) on the dynamics of a bluff-body stabilized flame operating very close to its blow-off condition. This work is motivated by the understanding that more stringent regulations on combustion-generated emission have forced the industry to design combustion systems that operate at very fuel-lean conditions. Combustion at very lean conditions, however, induces flame instability that can ultimately lead to flame extinction. The dynamics of the flame at lean conditions can therefore be very sensitive to boundary conditions. Here, a numerical investigation is conducted using Large Eddy Simulation method to understand the flame sensitivity to inlet turbulence intensity. Combustion is accounted for through the transport of chemical species. The sensitivity to inlet turbulence is assessed by carrying out simulations in which the inlet turbulence is varied in increments of 5%. It is observed that while the inlet intensity of 5% causes blow-off, further increased to 10% preserves a healthy flame on account of greater heat release arising from greater and balanced entrainment of combustible mixtures into the flame zone just behind the bluff-body. This balanced stabilization is again lost as the inlet turbulence intensity is further increased to 15%. Since experimental data pertaining to the topic of this paper are rare, the reasonableness of the combination of models is first checked by validating Volvo propane bluff-body flame, whereby reasonable agreement is observed. This study will advance our understanding of the sensitivity of bluff-body flames to boundary conditions specifically to the inlet turbulent boundary condition at near critical blow-off flame conditions.