bluuebunny/crossref_metadata_2025_split huggingface dataset:
High-Frequency Acoustic Mode Identification of Unstable Combustors
Authors: Kim J. , Lieuwen T. , Emerson B. , Acharya V. , Wu D. , Mckinney R. , Wang X. , Isono M. 
Published: November 2019

Abstract
High frequency thermoacoustic instabilities are becoming increasingly problematic in modern combustion systems. Understanding which acoustic mode is being excited is important for understanding potential mechanisms and control approaches — for example, influence of a helical shear layer mode on the flame has profoundly different effects on the first tangential acoustic mode, than a higher order axial mode of similar frequency. Nonetheless, the modal density increases with frequency and it becomes increasingly difficult to determine which acoustic mode is self-excited, based upon frequency calculations alone. Moreover, access issues and cost usually limit the number of pressure probes that can be distributed axially and azimuthally in the combustor. This paper presents a methodology for identifying the acoustic mode by using high temperature pressure transducers flush mounted in a combustion chamber. Modal identification is demonstrated with a siren under non-reacting conditions. The siren is mounted on the chamber to excite longitudinal and azimuthal waves. Five acoustic sensors at different axial and azimuthal locations measure the pressure fluctuations simultaneously. Given the forcing frequency and the speed of sound, the pressure distribution in the combustor is reconstructed in the time domain from the measured data by using a least squares method to determine its mode shapes. In addition, the finite element method (FEM) solver is used to provide the eigenfrequencies and corresponding mode shapes. The test results demonstrate that the mode shapes from the reconstructed data and corresponding frequencies are consistent with those predicted from the FEM, which validates the methodology in this study. In addition, the methodology is extended to practical reacting cases without the siren to determine the acoustic mode shapes of naturally occurring instabilities. In these cases, the modal features have strong stochastic features, such as what appear to be stochastic variations in overall amplitude and relative amplitudes of clockwise and counterclockwise waves.
Transonic Turbine Vane Endwall Film Cooling Using PSP Measurement Technique
Authors: Shiau Chao-Cheng , Sahin Izzet , Ullah Izhar , Han Je-Chin , Mirzamoghadam Alexander V. , Riahi Ardeshir , Stimpson Curtis 
Published: November 2019

Abstract
This work focuses on the parametric study of film cooling effectiveness on turbine vane endwall under various flow conditions. The experiments were performed in a five-vane annular sector cascade facility in a blowdown wind tunnel. The controlled exit isentropic Mach numbers were 0.7, 0.9, and 1.0, from high subsonic to transonic conditions. The freestream turbulence intensity is estimated to be 12%. Three coolant-to-mainstream mass flow ratios (MFR) in the range 0.75%, 1.0%, and 1.25% are studied. N2, CO2, and Argon/SF6 mixture were used to investigate the effects of density ratio (DR), ranging from 1.0, 1.5 to 2.0. There are 8 cylindrical holes on the endwall inside the passage. Pressure-sensitive paint (PSP) technique was used to capture the endwall pressure distribution for shock wave visualization and obtain the detailed film cooling effectiveness distributions. Both the high-fidelity effectiveness contour and the laterally (spanwise) averaged effectiveness were measured to quantify the parametric effect. This study will provide the gas turbine designer more insight on how the endwall film cooling effectiveness varies with different cooling flow conditions including shock wave through the endwall cross-flow passage.
The Effect of Blade Deflections on the Torsional Dynamic of a Wind Turbine
Authors: Jauregui Juan , Cárdenas Diego , Morales Luis , Martinez Miguel , Basaldua Jovan 
Published: November 2019

Abstract
The dynamic behavior of a wind turbine comprises three major parts: the external torque produced by the wind, the mechanical elements and the grid. For the aerodynamic response, there is three type of models: constant aerodynamic torque for Type I and Type IV turbines, a pseudo aerodynamic model for Type I and II, and linearized aerodynamic model for Type III. The drivetrain has been model either as a single-mass shaft model or as a double-mass shaft model. Most of the dynamic models of wind turbines consider the wind torque only as a function of the wind velocity, and they neglect the vibrations of the blades as an excitation torque. Therefore, a dynamic model that includes the aerodynamic power, the torque produced by the deflection of the blades, the vortex-induced vibrations of the blades and the torque caused by the eccentricity of the center of mass represents the excitation torque. The dynamic model of the wind turbine is a multibody dynamic model with six degrees of freedom. The blades are represented as a two lumped-masses, the torsional response of the main rotor is described as a single torsional mass, which is connected to the electric generator by a gearbox. The gearbox is represented as a double-shaft model, and the gear mesh is simulated with a nonlinear torsional stiffness. The generator is described as another torsional mass. The torque produced by the wind is calculated using QBlade for different pitch angles. The dynamic parameters of the blade were determined experimentally, and it was found that the blade has only two dominant vibration modes. For this reason, the blades were modeled as two lumped-masses. It was found that the vortex-induced vibrations modify the torsional vibrations of the generator and they are an extra source of perturbations for the electric generation, and they depend on the wind velocity and the pitch angle.
Design and Experimental Assessment of Bladeless Turbines for Axial Inlet Supersonic Flows
Authors: Braun James , Paniagua Guillermo , Falempin Francois , Le Naour Bruno 
Published: November 2019

Abstract
Supersonic inlet flow is usually considered to be detrimental to the performance of turbine systems. This paper demonstrates an effective manner to harness power from supersonic axial inflow without swirl. The bladeless axial turbine allows for power extraction from harsh environments with minimal maintenance costs. In a first step, a baseline bladeless turbine is designed and the power extraction is analyzed. The bladeless turbine surface is parametrized in Matlab and subsequently imported into Hexpress (Numeca) to mesh an unstructured grid. The first layer thickness is kept below one for all the simulations. The unstructured mesh is loaded into CFD++ (Metacomp) to solve the three dimensional steady Reynolds Averaged Navier Stokes equations. Second, the work extraction principle is broken down from a three-dimensional unsteady problem into a two-dimensional steady phenomenon. An experimental campaign is outlined and test details are discussed. Finally, after the experimental characterization, the operational envelope and scaling of the bladeless turbine is described for several reduced mass flows, reduced speeds and geometrical features of the turbine (amplitude of the wavy surface, helix angle, hub radius and length of the axial turbine).
Topology Optimization of Serpentine Channels for Minimization of Pressure Loss and Maximization of Heat Transfer Performance As Applied for Additive Manufacturing
Authors: Ghosh Shinjan , Kapat Jayanta S. 
Published: November 2019

Abstract
Gas Turbine blade cooling is an important topic of research, as a high turbine inlet temperature (TIT) essentially means an increase in efficiency of gas turbine cycles. Internal cooling channels in gas turbine blades are key to the cooling and prevention of thermal failure of the material. Serpentine channels are a common feature in internal blade cooling. Optimization methods are often employed in the design of blade internal cooling channels to improve heat-transfer and reduce pressure drop. Topology optimization uses a variable porosity approach to manipulate flow geometries by adding or removing material. Such a method has been employed in the current work to modify the geometric configuration of a serpentine channel to improve total heat transferred and reduce the pressure drop. An in-house OpenFOAM solver has been used to create non-traditional geometries from two generic designs. Geometry-1 is a 2-D serpentine passage with an inlet and 4 bleeding holes as outlets for ejection into the trailing edge. Geometry-2 is a 3-D serpentine passage with an aspect ratio of 3:1 and consists of two 180-degree bends. The inlet velocity for both the geometries was used as 20 m/s. The governing equations employ a “Brinkman porosity parameter” to account for the porous cells in the flow domain. Results have shown a change in shape of the channel walls to enhance heat-transfer in the passage. Additive manufacturing can be employed to make such unconventional shapes.
Transcritical / Supercritical CO2 Recompression Brayton Cycle Using a Novel Rotary Liquid Piston Compressor
Authors: Thatte Azam 
Published: November 2019

Abstract
This paper presents a transcritical / supercritical CO2 (sCO2) recompression Brayton cycle using a novel rotary liquid piston compressor (LPC). This new type of multi-phase compressor utilizes a pumped motive fluid that interfaces with sCO2 in a rotating ducted cylinder for efficient CO2 compression at lower hardware costs. The energy required to pump the motive fluid can be significantly lower than that required to compress CO2 in a traditional compressor. The compressor utilizes a low compressibility, low diffusivity, low solubility liquid as the motive fluid to pressurize process fluid (sCO2) stream. Its use as a replacement for the main compressor in a recompression sCO2 Brayton cycle is expected to reduce compression power by more than 10% while maintaining robust operation over a wide range of ambient temperatures and CO2 densities that are typical for dry-cooled sCO2 cycles in arid climates. The new rotary liquid piston compressor also eliminates the need for gas lubricated bearings & dry gas seals, thus providing added advantage of rotordynamic stability, mechanical robustness & life over traditional compressors. Thermodynamic cycle analyses and 1D compressible flow analysis of multi-phase compression inside the rotary LPC is presented. An advanced 3D multi-phase flow model is developed to study fundamental physics of multi-species transport, diffusion & mixing of species and liquid-supercritical interface compression & decompression. This 3D model is used to validate some of the assumptions made in the 1D model. Various performance curves are developed to study the effect of lead flow, rotational speed and compressor inlet temperature on CO2 exit mass flow rate, % mixing of the two species, compression power requirements and overall compression efficiency. Optimization study on above system variables is carried out and a set of guidelines for use of rotary LPC in sCO2 compression is established.
Evaluation of Film Cooling Superposition Predictions Using Shaped Holes on the Suction Side of a Blade Model
Authors: Yoon Christopher , Moore Jacob , Bogard David 
Published: November 2019

Abstract
Film cooling is often used for turbine airfoil cooling, and there are numerous studies of the performance of a single row of holes. In actual application there will typically be multiple rows of holes which interact. Consequently there is a need to develop techniques to predict film cooling performance with multiple rows of coolant holes using superposition of single row cooling effectiveness. Although there have been many studies of superposition techniques for predicting film cooling effectiveness with multiple rows of cylindrical holes, there have been very few in which shaped holes were used with a typical turbine airfoil model. In this study, film effectiveness was measured on the suction side of a turbine blade model using two rows of shaped coolant holes. Measurements were made with each row independently and with both rows combined. This provided the experimental data for superposition predictions and to evaluate these predictions. Each row had 7-7-7 shaped holes with pitch to diameter ratio of 6, and the two rows were more than 40 diameters apart. The experiments were run using two different upstream blowing ratios, and a wide range of downstream blowing ratios. The superposition predictions of film effectiveness were reasonably accurate when the upstream row of holes were operated at a high blowing ratio with a corresponding smaller film effectiveness (due to jet separation). However, when the upstream coolant holes were operated at the optimum blowing ratio, and hence maximum film effectiveness downstream, the superposition analysis predicted film effectiveness levels slightly lower than actual levels. These results show that there was an interaction between jets that resulted in higher film effectiveness than was accounted for with a superposition prediction.
Secondary Flows in the Return System of a Centrifugal Compressor Stage
Authors: Rossbach T. , Bisping J. , Grates D. R. , Jeschke P. , Hildebrandt A. , Franz H. 
Published: November 2019

Abstract
This Paper presents an analysis of the flow in the return system of a centrifugal compressor with a flow coefficient of 0.15. Based on detailed experimental and numerical data, the areas of high losses and potentials for improving the return system geometry are revealed. Special emphasis is placed on the interaction of the flow in the return system components, including the U-bend, the vaned return channel and the final L-bend. Strong flow redistribution occurs due to the sharp curvature of the U-bend, forming a blockage area at the hub near the vane leading edge. This causes a strong passage vortex, which is further intensified by the pressure gradient induced by the L-bend. Additionally, the flow near the shroud accelerates due to the large blockage area near the hub at the exit of the U-bend, resulting in high friction losses. To identify the main causes of loss, a method was evolved. It was validated and supplied by pneumatic measurement data. On this basis analytical approaches were taken to quantify the total pressure losses due to friction, secondary flows, incidence and trailing edge flow. As a result, approximately 60 % of the return system losses arise due to friction. Another 30–40% are caused by secondary flows. It can be concluded that the results of the investigation contribute to the understanding of the secondary flow structures inside a centrifugal compressor return system of high mass flow rates. By combining the knowledge acquired in respect to the sources of highest losses with the experimental data, a well-founded basis for future optimization and the validation of numerical approaches is possible.
Identification of Poorly Ventilated Zones in Gas-Turbine Enclosures With Machine Learning
Authors: Corsini Alessandro , Delibra Giovanni , Giovannelli Marco , Lucherini Gabriele , Minotti Stefano , Rossin Stefano , Tieghi Lorenzo 
Published: November 2019

Abstract
Ventilation systems are used in gas turbine packages to control the air temperature, to protect electrical instrumentation and auxiliary items installed inside the enclosure and to ensure a proper dilution of potentially dangerous gas leakages. These objectives are reached only if the ventilation flow is uniformly distributed in the whole volume of the package, providing a good air flow quality as prescribed by international codes such as ISO 21789. To evaluate the effectiveness of the ventilation design, numerical computations are performed for several purposes, one of which is the identification of poorly ventilated portions of the enclosure. In fact, it is essential to accurately detect the regions which are less ventilated, since they could be prone to the accumulation of an accidental fuel gas leak. There are different approaches to identify these portions, such as decay regression or inlet source analysis, that require unsteady simulations of the flow field inside the package. The present work discusses the implementation of a new methodology using machine learning and artificial neural networks (ANN) to detect the poorly ventilated regions where a gas cloud can accumulate. The concentration of fuel gas is estimated starting from a steady-state computation without running a more expensive unsteady computation. The entire process is built around an accurate training of the ANN using a proper set of simpler test-cases that have been identified to match the characteristics of the gas turbine enclosure. During the training phase accuracy and overfitting of the ANN were monitored to ensure robustness of the method. The procedure is then applied to a real case scenario and the results are presented in this paper highlighting the main advantages of this approach respect to a conventional use of CFD analysis. Computations of the flow fields are carried out using OpenFOAM with RANS and U-RANS approaches, while the ANN is developed and trained in Python.
Modelling of Sonic Jets for Gas Leak Applications
Authors: Minotti Stefano , Corsini Alessandro , Delibra Giovanni , Lucherini Gabriele , Rossin Stefano , Tieghi Lorenzo , Traldi Stefania 
Published: November 2019

Abstract
Design of gas turbine packages is subjected to safety issues and the related guidelines are provided by ISO-21789. According to this code, the ventilation system shall guarantee a good and safe dilution in case of an unexpected gas leakage from components of the fuel gas system inside the enclosure. The evaluation of the dilution is commonly carried out by CFD simulations and the ISO-21789 indicates the criteria to evaluate the danger of a gas leak by estimating the cloud volume of the explosive mixture. To follow this prescription and to properly calculate the exact volume cloud, it is fundamental to accurately reproduce the fuel gas leak, which is always a supersonic jet of fuel gas into an air-ventilated domain. The main criticality is to simulate a supersonic jet into a complex domain such as the gas turbine package, considering the industrial goals in terms of accuracy and time constraints. The complexity is due to the geometry of the package and to the multiple locations where the leakage could occur. In such context, it is preferable to develop an advanced modeling of the phenomenon rather than simply improve the detail of the CFD, that could turn out to be unfeasible for industrial goals.
For this reason, the authors present a series of simulations of under-expanded jets at high pressure ratios carried out to investigate the applicability of the sonic source approach to not-round jets.
Turbine Cascade Profile Loss Sensitivity to Incoming Wake Parameters: Effects of Reduced Frequency, Wake Momentum Defect and Axial Gap
Authors: Simoni D. , Yepmo V. , Zunino P. , Ubaldi M. , Lengani D. , Bertini F. 
Published: November 2019

Abstract
In the present work the profile losses of a highly loaded low pressure turbine cascade, operating under realistic unsteady conditions, have been measured for different incoming wake parameters. A moving bar system has been used for wake generation, allowing the variation of bar diameter, bar count and axial gap between the bars and the cascade leading edge. The overall test matrix spans three different bar diameters, three different reduced frequencies and two axial gaps, for a total of 18 different conditions tested. For each of them, the time-dependent cascade inflow has been characterized by means of phase-locked hot-wire measurements in order to determine the effects of the wake parameter modification on the turbulence intensity peak and on the incoming wake momentum deficit, that are well known to affect the generation of losses in the downstream cascade. The procedure recently developed by the authors based on the simultaneous acquisition of the signals of two kiel probes, located upstream and downstream of the cascade, has been used to accurately quantify the profile losses for each condition, identifying the contribution due to the wake bowing, tilting and dilation process into the cascade channel and that due to the wake-boundary layer interaction. Additionally, Proper Orthogonal Decomposition (POD) has been applied to the ensemble data matrix constructed from the loss coefficient distributions in the pitchwise direction, measured for the different conditions, with the aim of highlighting the loss trend vs the design space parameter variation. The POD modes obtained from the cross-correlation matrix provide a direct information on the flow region where losses are prevalently produced, while the corresponding POD coefficients give the weight of each parameter in the loss generation. The paper shows the potentiality of this procedure in providing a rapid identification of the main causes of losses, and the dominant parameter affecting the process of loss generation.
Evaluation of Turbulent Spot Production Rate in Boundary Layers Under Variable Pressure Gradients for Gas Turbine Applications
Authors: Dellacasagrande M. , Lengani D. , Simoni D. , Ubaldi M. , Zunino P. 
Published: November 2019

Abstract
The paper presents an experimental data base on transitional boundary layers developing on a flat plate installed within a variable area opening endwall channel. Measurements have been carried out by means of time-resolved PIV. The overall test matrix spans 3 Reynolds numbers, 4 free-stream turbulence intensity levels and 4 different flow adverse pressure gradients. For each condition, 16000 instantaneous flow fields have been acquired in order to obtain high statistical accuracy. The flow parameters have been varied in order to provide a gradual shift of the mode of transition from a bypass process occurring with mild adverse pressure gradients at high free-stream turbulence, to separated flow transition, occurring with low Reynolds number, low free-stream turbulence intensity and elevated adverse pressure gradient. In order to quantify the influence of the flow parameter variation on the boundary layer transition process, the transition onset and end positions, and the turbulent spot production rate have been evaluated with a wavelet based intermittency detection technique. This post-processing technique is in fact able to identify the vortical structures developing within the boundary layer, the intermittency function is then automatically evaluated for each tested condition counting the number of such structures and defining the cumulative probability function.
The by-pass transition mode has the longest transition length that decreases with increasing the Reynolds number. The transition length of the separated flow case is smaller than the by-pass one, and the variation of the flow parameters has a similar impact. Similarly, the dimensionless turbulent spot production rate reduces when the Reynolds number is increasing. The variation of the inlet turbulence intensity has a small influence on this parameter except for the condition at the highest turbulence intensity, that always shows the lowest turbulent spot production rate because a by-pass type transition occurs. This large amount of data has been used to develop new correlations used to predict the spot production rate and the transition length in attached and separated flows.