bluuebunny/crossref_metadata_2025_split huggingface dataset:
Assessing the Sensitivity of Stall-Regulated Wind Turbine Power to Blade Design Using High-Fidelity CFD
Authors: Sanvito A. G. , Persico G. , Campobasso M. S. 
Published: November 2019

Abstract
This study provides a novel contribution towards the establishment of a new high–fidelity simulation–based design methodology for stall–regulated horizontal axis wind turbines. The aerodynamic design of these machines is complex, due to the difficulty of reliably predicting stall onset and post–stall characteristics. Low–fidelity design methods, widely used in industry, are computationally efficient, but are often affected by significant uncertainty. Conversely, Navier–Stokes CFD can reduce such uncertainty, resulting in lower development costs by reducing the need of field testing of designs not fit for purpose. Here, the compressible CFD research code COSA is used to assess the performance of two alternative designs of a 13–meter stall–regulated rotor over a wide range of operating conditions. Validation of the numerical methodology is based on thorough comparisons of novel simulations and measured data of the NREL Phase VI turbine rotor, and one of the two industrial rotor designs. An excellent agreement is found in all cases. All simulations of the two industrial rotors are time–dependent, to capture the unsteadiness associated with stall which occurs at most wind speeds. The two designs are cross-compared, with emphasis on the different stall patterns resulting from particular design choices. The key novelty of this work is the CFD–based assessment of the correlation among turbine power, blade aerodynamics, and blade design variables (airfoil geometry, blade planform and twist) over most operational wind speeds.
Flow Instabilities in Gas Turbine Chute Seals
Authors: Horwood Joshua T. M. , Hualca Fabian P. , Wilson Mike , Scobie James A. , Sangan Carl M. , Lock Gary D. , Dahlqvist Johan , Fridh Jens 
Published: November 2019

Abstract
The ingress of hot annulus gas into stator-rotor cavities is an important topic to engine designers. Rim-seals reduce the pressurised purge required to protect highly-stressed components. This paper describes an experimental and computational study of flow through a turbine chute seal. The computations — which include a 360° domain — were undertaken using DLR TRACE’s time-marching solver. The experiments used a low Reynolds number turbine rig operating with an engine-representative flow structure. The simulations provide an excellent prediction of cavity pressure and swirl, and good overall agreement of sealing effectiveness when compared to experiment.
Computation of flow within the chute seal showed strong shear gradients which influence the pressure distribution and secondary-flow field near the blade leading edge. High levels of shear across the rim-seal promote the formation of large-scale structures at the wheel-space periphery; the number and speed of which were measured experimentally and captured, qualitatively and quantitatively, by computations.
A comparison of computational domains ranging from 30° to 360° indicate that steady features of the flow are largely unaffected by sector size. However, differences in large-scale flow structures were pronounced with a 60° sector and suggest that modelling an even number of blades in small sector simulations should be avoided.
Use of Vector Autoregressive Model for Anomaly Detection in Utility Gas Turbines
Authors: Goyal Vipul , Xu Mengyu , Kapat Jayanta 
Published: November 2019

Abstract
This study is based on time-series data from the combined cycle utility gas turbines consisting of three-gas turbine units and one steam turbine unit. We construct a multi-stage vector autoregressive model for the nominal operation of powerplant assuming sparsity in the association among variables and use this as a basis for anomaly detection and prediction. This prediction is compared with the time-series data of the plant-operation containing anomalies. Granger causality networks, which are based on the associations between the time series streams, are learned as an important implication from the vector autoregressive modelling. Anomaly is detected by comparing the observed measurements against their predicted value.
A Computational Technique to Evaluate the Relative Influence of Internal and External Cooling on Overall Effectiveness
Authors: Bryant Carol E. , Rutledge James L. 
Published: November 2019

Abstract
Gas turbine hot gas path components are protected via coolant that travels through internal passageways before being ejected as external film cooling. Modern computational approaches facilitate simulation of the conjugate heat transfer that takes place within turbine components, allowing prediction of the actual metal temperature, usually nondimensionalized in the form of the overall effectiveness. Efforts aimed at improving cooling are often focused on either only the internal cooling or the film cooling; however, the common coolant flow means the internal and external cooling schemes are inextricably linked and the coolant holes themselves provide another convective path for heat transfer to the coolant. The relative influence of internal cooling, external cooling, and convection through the film cooling holes on overall effectiveness is not well understood.
Computational fluid dynamics (CFD) simulations were performed in order to isolate each cooling mechanism, and thereby determine their relative contributions to overall effectiveness. The conjugate CFD model was a flat plate with five staggered rows of shaped film cooling holes. Unique boundary conditions were used to isolate the cooling mechanisms. The internal cooling was modeled with and without heat transfer on the internal surface in order to isolate the effects of plenum cooling. Convection through the coolant holes was isolated by making the inside of the film cooling holes adiabatic. This was done in order to evaluate the influence of the internal cooling provided by the cooling holes themselves. The effect of film cooling was removed through the novel use of an outlet boundary condition at the exit of each hole that allowed unaltered internal coolant flow without external coolant ejection.
Application of Multi-Scale Methodology for Transonic Turbine Blade Tip Cooling Design
Authors: Duan P. H. , He L. 
Published: November 2019

Abstract
In recent research the cooling flow at transonic turbine tip is found to have several unique flow features such as strong interaction with the base flow, acceleration at divergent duct, strong shock-boundary layer interaction and weak correlation between the aerodynamic loss and the heat transfer. These flow features require the cooling design to be considered together with the tip geometry shaping. However due to the large disparity of the length scales between the cooling holes and the turbine blade, the combination of the cooling design and tip geometry shaping tends to be too computationally expensive to be employed. In this study the multi-scale method is implemented in a commercial solver to provide a fast and accurate solution for the turbine tip cooling design. The method uses source terms added on the coarse mesh to generate the solution that is rather close to the solution obtained with a well resolved mesh. The source terms are found to present not only the influence of mesh resolution but also the flow injection. The computed results have been validated against the experimental data and the fine mesh results. The good agreement shows a great potential for this multi-scale method to be used in cases with large length scale disparity.
Development of High Speed and High Temperature Atomic Layer Thermopiles
Authors: Bhatnagar Lakshya , Paniagua Guillermo 
Published: November 2019

Abstract
This work aims to provide a technique with which high frequency heat flux measurement data can be acquired in systems with high operational temperatures and high-speed flows with quantifiable and accurate uncertainty estimates. This manuscript presents the detailed calibration and application of an atomic layer thermopile, for heat fluxes with a frequency bandwidth of 0 to 1MHz. Two calibration procedures with a detailed uncertainty analysis. The first procedure consists using a laser to deliver radiation heat flux, while the second consists of a convective heat blowdown experiment. The use of this probe is demonstrated in a high-speed environment at Mach 2. The sensor effectively captures the passage of the normal shock wave and the values are compared with those computed using surface temperature measurement. Finally, a numerical study is carried out to design a cooling system that will allow the sensor to survive in high temperature conditions of 1273K while the sensor film is maintained at 323K. A two-dimensional axisymmetric conjugate heat transfer analysis is carried out to obtain the desired geometry.
Airfoil Optimization for a Wind Turbine Operating in a Particle-Laden Environment
Authors: Diab Aya , Hossam El-Din Ahmed 
Published: November 2019

Abstract
Dust may be challenging to the blades of wind turbines deployed in the harsh environment of the Sahara. In this paper, the airfoil sections of a wind turbine have been customized for low sensitivity to surface roughness at the wind conditions prevailing in Hurghada—Egypt to avoid serious power degradation. To this end, a two-dimensional a computational model is developed using ANSYS-FLUENT 15.0 to understand the distinguishing features that govern the specific behavior of NACA-63-215 (root section) and NACA-63-415 airfoils (midspan and tip sections) with respect to dust deposition and sand erosion. Subsequently, a two-objective genetic algorithm is developed in MATLAB 16.0 and used to customize the airfoil geometry, enhancing the lift-to-drag ratio while simultaneously minimizing the deposition and erosion rates. The whole optimization process is realized through coupling MATLAB 16.0 with ANSYS-FLUENT 15.0 via the ICEM meshing tool to predict the optimum blade shape based on its aerodynamic performance in a dust-loaded environment. The optimization process enhanced the aerodynamic performance for the aforementioned airfoils under particle laden conditions with up to 38.34% higher lift-to-drag coefficients ratio in addition to 70 % and 99.267 % drop in dust deposition and sand erosion, repectively.
Preliminary Design and Performance Assessment of an Underwater CAES System (UW-CAES) for Wind Power Balancing
Authors: Astolfi Marco , Guandalini Giulio , Belloli Marco , Hirn Adriano , Silva Paolo , Campanari Stefano 
Published: November 2019

Abstract
A key approach to large renewable power management is based on implementing storage technologies, including batteries, power-to-gas and compressed air energy storage (CAES). This work presents the preliminary design and performance assessment of an innovative type of CAES, based on underwater storage volumes (UW-CAES) and intended for installation in the proximity of deep water seas or lakes. The UW-CAES works with constant hydrostatic pressure storage and variable volumes. The proposed system is adiabatic, not using any fuel to increase the air temperature before expansion; a sufficient TIT is instead obtained through a thermal energy storage system which recovers the compression heat.
The system includes (i) a set of turbomachines (modular multi-stage compressor, with partial intercooling; expansion turbine); (ii) a thermal energy storage (TES) system with different temperature levels designed to recover a large fraction of the compression heat, allowing the subsequent heating of air prior to the expansion phase; (iii) an underwater modular compressed air storage, conceived as a network of rigid but open tanks lying on the seabed and allowing a variable-volume and constant pressure operation. The compressor operates at variable loads, following an oscillating renewable power input, according to strategies oriented to improve the overall system dispatchability; the expander can be designed to work either at full load, thanks to the stability of the air flow rate and of the TIT guaranteed by the thermal storage, or at variable load.
The paper first discusses in detail the sizing and off-design characterization of the overall system; it is then simulated a case study where the UW-CAES is coupled to a wind farm for peak shaving and dispatchability enhancement, evaluating the impact of a realistic power input on performances and plant flexibility.
Although the assessment shall be considered preliminary, it is shown that round trip efficiency in the range of 75%–80% can be obtained depending on the compressor section configuration; making the UW-CAES a promising technology compared to electrochemical and pumped-hydro storage systems. The technology is also applied to perform peak-shaving of the electricity production from a wind park; annual simulations considering part load operation result in global round trip efficiency around 75% with a 10 to 15% reduction in the average unplanned energy injection in the electric grid. The investigated case study provides an example of the potential of this system in providing power output peak shaving when coupled with an intermittent and non-predictable energy source.
Design Procedure and Performance Analysis of a Microturbine Combustor Working on Biogas for Power Generation
Authors: Bazooyar Bahamin , Darabkhani Hamidreza Gohari 
Published: November 2019

Abstract
Design of the combustor is of high priority in microturbine generators (MTG) due to the small and compact configuration of these type of generators and high range of the shaft revolution (normally over 100k rpm). Design process of the MTG components including the micro combustor and turbomachinery also require accurate description of the combustion phenomena, heat transfer, emission level and performance analysis of the system. Design of combustors for renewable fuels such as biogas has several complications including overcoming the lower heating value of the biogas (normally 1/3 of the natural gas), combustion instabilities and corrosion effects of burning these types of fuels. The main benefit of burning a carbon neutral fuel (e.g., biogas), however will be in reducing the carbon emission by avoiding fossil fuels and achieving the environmental targets (e.g., Paris Agreement). The tubular combustors are in the centre of attention in design and operations of the microturbines due to their low cost and the level of emission. This research work presents the design procedure and CFD modelling of a tubular combustor for a biogas burnt microturbine engine assembly. The biogas is generated from anaerobic digestions of agriculture waste and include a 57% and 43% mixture of methane and CO2 respectively. All the combustor parts are designed with empirical and practical equations and dimensions are optimised by CFD simulations. Operation of the combustor is then analysed in terms of its gaseous emissions. Finally, the operation of the new combustor in a closed heat and power cycle was verified and compared with conventional combustor of the microturbine burning diesel fuel, and as a result all the benefits and considerations for the application of biogas in microturbine assembly are carefully remarked and discussed.
The Effects of Exit Boundary Condition on Precessing Vortex Core Dynamics
Authors: Mason Danielle , Clees Sean , Frederick Mark , O’Connor Jacqueline 
Published: November 2019

Abstract
Many industrial combustion systems, especially power generation gas turbines, use fuel-lean combustion to reduce NOx emissions. However, these systems are highly susceptible to combustion instability, the coupling between combustor acoustics and heat release rate oscillations of the flame. It has been shown in previous work by the authors that a precessing vortex core (PVC) can suppress shear layer receptivity to external perturbations, reducing the potential for thermoacoustic coupling. The goal of this study is to understand the effect of combustor exit boundary condition on the flow structure of a swirling jet to increase fundamental understanding of how combustor design impacts PVC dynamics. The swirling jet is generated with a radial-entry, variable-angle swirler, and a quartz cylinder is fixed on the dump plane for confinement. Combustor exit constriction plates of different diameters are used to determine the impact of exit boundary condition on the flow field. Particle image velocimetry (PIV) is used to capture the velocity field inside the combustor. Spectral proper orthogonal decomposition, a frequency-resolved eigenvalue decomposition that can identify energetic structures in the flow, is implemented to identify the PVC at each condition in both energy and frequency space. We find that exit boundary diameter affects both the structure of the flow and the dynamics of the PVC. Higher levels of constriction (smaller diameters) force the downstream stagnation point of the vortex breakdown bubble upstream, resulting in greater divergence of the swirling jet. Further, as the exit diameter decreases, the PVC becomes less energetic and less spatially defined. Despite these changes in the base flow and PVC coherence, the PVC frequency is not altered by the exit boundary constriction. These trends will help inform our understanding of the impact of boundary conditions on both static and dynamic flame stability.
Large Eddy Simulation of Bypass Transition in Vane Passage With Freestream Turbulence
Authors: Kanani Yousef , Acharya Sumanta , Ames Forrest 
Published: November 2019

Abstract
High Reynolds flow over a nozzle guide-vane with elevated inflow turbulence was simulated using wall-resolved large eddy simulation (LES). The simulations were undertaken at an exit Reynolds number of 0.5×106 and inflow turbulence levels of 0.7% and 7.9% and for uniform heat-flux boundary conditions corresponding to the measurements of (Varty, J. W., and Ames, F. E., 2016, ASME Paper No. IMECE2016-67029). The predicted heat transfer distribution over the vane is in excellent agreement with measurements. At higher freestream turbulence, the simulations accurately capture the laminar heat transfer augmentation on the pressure surface and the transition to turbulence on the suction surface. The bypass transition on the suction surface is preceded by boundary layer streaks formed under the external forcing of freestream disturbances which breakdown to turbulence through inner mode secondary instabilities. Underneath the locally formed turbulent spot, heat transfer coefficient spikes and generally follows the same pattern as the turbulent spot. The details of the flow and temperature fields on the suction side are characterized and first and second order statistics are documented. The turbulent Prandtl number in the boundary layer is generally in the range of 0.7–1, but decays rapidly near the wall.
Experimental Demonstration of Inverse Heat Transfer Methodologies for Turbine Applications
Authors: Cuadrado David G. , Lozano Francisco , Paniagua Guillermo 
Published: November 2019

Abstract
Gas turbines operate at extreme temperatures and pressures, constraining the use of both optical measurement techniques as well as probes. A strategy to overcome this challenge consists of instrumenting the external part of the engine, with sensors located in a gentler environment, and use numerical inverse methodologies to retrieve the relevant quantities in the flowpath. An inverse heat transfer approach is a procedure used to retrieve the temperature, pressure or mass flow through the engine based on the external casing temperature data.
This manuscript proposes an improved Digital Filter Inverse Heat Transfer Method, that consists of a linearization of the heat conduction equation using sensitivity coefficients. The sensitivity coefficient characterizes the change of temperature due to a change in the heat flux. The heat conduction equation contains a non-linearity due to the temperature-dependent thermal properties of the materials. In previous literature, this problem is solved via iterative procedures that however increase the computational effort. The novelty of the proposed strategy consists of the inclusion of a non-iterative procedure to solve the non-linearity features. This procedure consists of the computation of the sensitivity coefficients in function of temperature, together with an interpolation where the measured temperature is used to retrieve the sensitivity coefficients in each timestep. These temperature-dependent sensitivity coefficients, are then used to compute the heat flux by solving the linear system of equations of the Digital Filter Method.
This methodology was validated in the Purdue Experimental Turbine Aerothermal Lab (PETAL) annular wind tunnel, a two minutes transient experiment with flow temperatures up to 450K. Infrared thermography is used to measure the temperature in the outer surface of the inlet casing of a high pressure turbine. Surface thermocouples measure the endwall metal temperature. The metal temperature maps from the IR thermography were used to retrieve the heat flux with the inverse method. The inverse heat transfer method results were validated against a direct computation of the heat flux obtained from temperature readings of surface thermocouples. The experimental validation was complemented with an uncertainty analysis of the inverse methodology: the Karhunen-Loeve Expansion. This technique allows the propagation of uncertainty through stochastic systems of differential equations. In this case, the uncertainty of the inner casing heat flux has been evaluated through the simulation of different samples of the uncertain temperature field of the outer casing.