bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Study of Thermal Performance and NOx Emission for An Ammonia-Fuelled Micro-Combustor With Ring-Shaped Ribs in Lean Combustion
Authors: Ni Siliang , Zhao Dan 
Published: September 2021

Abstract
As a renewable energy source, ammonia is regarded as one of the ideal gases that can replace fossil fuels and has been extensively studied in large-scale combustion. However, studies on energy conversion efficiency and NOx emission in microscale are still inadequate. In this work, ammonia/oxygen premixed cylindrical micro-combustors with inner ribs under condition of lean combustion is numerically investigated. The key geometrical parameters of the ribs and the ammonia/oxygen equivalence ratio are evaluated based on thermal performance and NOx emission performance. Finally, the sensitivity analysis of NO and related reaction pathways are analyzed under different equivalence ratios. The results show that increasing the height of the rib and decreasing the distance between the first rib and the inlet can effectively inhibit the generation of NO. Among all cases, the combustor with U-shaped ribs is observed the minimum mole fraction of NO at the outlet under the same working condition, which is 16% less comparing to the rectangular-shaped one. Besides, the mean wall temperature shows a weak correlation with NO emission. Increasing the equivalence ratio can help gain higher mean wall temperature, but at the same time promotes NOx production. This study is helpful to the design and improvement of micro-combustors fuelled by ammonia.
Experimental and Numerical Investigation of Vaned Hub and Shroud Wall Contoured Diffusers Designed to Improve Flexibility and Efficiency of an Open Impeller Centrifugal Compressor Stage
Authors: Hermann Daniel , Wirsum Manfred , Robinson Douglas , Jenny Philipp 
Published: September 2021

Abstract
State-of-the-art centrifugal compressor stages are required to provide both a flexible and a highly efficient operation. To extend the stable operating range and to improve the design-point polytropic total-to-total efficiency of an open impeller centrifugal compressor stage, three vaned contoured diffusers characterized by geometric modifications of the hub and shroud wall in the vaneless space upstream the diffuser vanes and within the diffuser passages were designed. In this paper, a shroud wall, a hub wall and a hub and shroud wall contoured diffuser and a state-of-the-art baseline diffuser are experimentally examined. For the hub-contoured diffuser an operating range extension of 5.3% was measured at design stage Mach number. For the shroud-contoured diffuser an improvement of polytropic total-to-total efficiency by up to 0.3% is observed. The experimental data including normalized total-to-static pressure ratio and 5-hole-probe data is utilized to validate the numerical setup. By means of the CFD simulations the hub- and the shroud-contoured diffuser designs are analyzed and the hub-contoured diffuser’s effect on the local flow at diffuser vane leading edge is investigated. The results illustrate the local effect of the hub-contoured diffuser design on the flow field in the examined centrifugal compressor stage.
Steam Turbine Overspeed Scenarios: Comparison Between API Energy Method and Dynamic Simulation
Authors: Piras Fabrizio , Bucciarelli Federico , Checcacci Damaso , Ingrasciotta Filippo 
Published: September 2021

Abstract
In turbomachinery applications the possibility to reduce size and costs of main flow-path components, by increasing shaft rotating speed, has always been appealing. The technological challenge in increasing this power density capability is typically related to performance prediction, to operating stress in blades and shafts, as well as to the need for a more accurate rotor-dynamic analysis. Yet another aspect, often reduced to standard assessments in less demanding applications, is related to the analysis of overspeed scenarios where, following a sudden loss of load and/or driven inertia, the turbomachine shall maintain its mechanical integrity.
Especially in steam turbines applications, where the behavior of the machine is strongly affected by the plant conditions, valves intervention time and connected volumes, the reduction of the rotor inertia, against comparable power, may produce overspeed scenarios that can become a primary design constraint and, if overlooked, may have both availability and safety implications.
In this paper several approaches to the analysis of overspeed scenarios are discussed, with increasing level of detail. The energy-based overspeed analysis method, as required by API612, is first discussed against practical design cases. A more accurate dynamic model is then presented, and its results compared with those of the energy-based approach. Finally, the sensitivity analysis of the overspeed peak value with respect to critical design parameters is discussed. With respect to previous works, mostly based on load rejection scenarios, the main focus is on the scenario of sudden coupling loss.
Surface Heater Fabrication Using Micro-Lithography for Transpiration Cooling Heat Transfer Coefficient Measurements
Authors: Min Zheng , Parbat Sarwesh , Wang Qing-Ming , Chyu Minking K. 
Published: September 2021

Abstract
Transpiration cooling is able to provide more uniform coolant coverage than film cooling to effectively protect the component surface from contacting the hot gas. Due to numerous coolant ejection outlets within a small area at the target surface, the experimental thermo-fluid investigation on transpiration cooing becomes a significant challenge. Two classic methods to investigate film cooling, the steady-state foil heater method and the transient thermography technique, both fail for transpiration cooling because the foil heater would block numerous coolant outlets, and the semi-infinite solid conduction model no longer holds for porous plates. In this study, a micro-lithography method to fabricate a silver coil pattern on top of the additively manufactured polymer porous media as the surface heater was proposed. The circuit was deliberately designed to cover the solid surface in a combination of series connection and parallel connection to ensure the power in each unit cell area at the target surface was identical. With uniform heat flux generation, the steady-state tests were conducted to obtain distributions of a pair of parameters, adiabatic cooling effectiveness, and heat transfer coefficient (HTC). The results showed that the adiabatic cooling effectiveness could reach 0.65 with a blowing ratio lower than 0.5. Meanwhile, the heat transfer coefficient ratio (hf/h0) of transpiration cooling was close to 1 with a small blowing ratio at 0.125. A higher HTC ratio was observed for smaller pitch-to-diameter cases due to more turbulence intensity generated at the target surface.
Transient Analysis of Supercritical Carbon Dioxide Air Cooler With Using IDAES Model
Authors: Gentile Russell , Vesely Ladislav , Goyal Vipul , Kapat Jayanta S. 
Published: September 2021

Abstract
The supercritical CO2 (sCO2) power cycle is a promising system for meeting future electricity grid demands. Its main advantage over Brayton cycles with other working fluids is its high net efficiency. To maintain this efficiency, the compressor must operate close to the critical point of CO2 (7.32 MPa and 31 °C). Maintaining a near constant inlet temperature is crucial, posing a design and operations challenge. In this study, we simulate the air cooler in an sCO2 power plant using a dynamic model with a focus on transient analysis. This was done for a 100 MWe sCO2 power cycle molten salt application (solar and nuclear reactors). For transient analysis, step changes in ambient temperature were simulated. A parametric study was also conducted using the model in steady-state. The model was implemented using the Institute for the Design of Advanced Energy Systems (IDAES) Process Systems Engineering (PSE) framework, an open-source software package. A brief description of the software architecture is given. Model applications and its overall fit in the digital twin landscape are also discussed.
Assessment of Profile Transformation for Turbomachinery Large Eddy Simulations - From Academic to Industrial Applications
Authors: Gout Clovis , Papadogiannis Dimitrios , Dombard Jérôme , Duchaine Florent , Gicquel Laurent , Odier Nicolas 
Published: September 2021

Abstract
Large Eddy Simulation (LES) of turbomachinery stages has been recently brought to attention due to its potential increased prediction fidelity and its reduced dependency to modeling. Such simulations are however often very CPU intensive, with potentially long return times and only possible for reduced periodic sectors. For real applications, such limitations are prohibitive for a daily use in a design phase. Indeed, most industrial turbomachinery applications rely on designs where at least one of the blade rows has a prime number of blades. Full 360° simulations are in such a case required for appropriate flow dynamics predictions, which implies prohibitive computational costs although recent demonstrations prove these feasible. To make LES affordable in an industrial context, it is clearly necessary to find ways to reduce its cost and return time, one approach being the reduction of the computational domain size.
The Profile Transformation Approach (PTA) is one of such specific methods that allows to simulate down to a single blade passage per blade row, thus decreasing the domain size of the problem and its CPU cost. PTA has been devised and validated in a URANS context and its limits are well known in this specific context. In terms of development and implementation in a code, PTA essentially consists in re-scaling the flow field at the rotor/stator interface to comply with the geometrical constraints on both sides of the interface since these often have different angular extents. Thanks to this flow re-scaling, periodic flow conditions can be applied on the azimuthal limits of both domains while retaining only one passage per row. In the following, the method is assessed in the context of fully unsteady LES simulations in an attempt to identify generated approximations and errors. This LES approach is then used to address a set of cases of increasing complexity ranging from the academic problem focusing first on the convection of a vortex across an interface and finishing with simulations of industrial relevance.
Development of a Harmonic Balance Method-Based Numerical Strategy for Blade-Tip/Casing Interactions: Application to NASA Rotor 37
Authors: Colaïtis Yann , Batailly Alain 
Published: September 2021

Abstract
In this study, a frequency-domain approach based on the harmonic balance method coupled to a predictor-corrector continuation algorithm is implemented for the qualitative analysis of blade-tip/casing contacts in aircraft engines. Unilateral contact and dry friction are taken into account through a regularized penalty law. To enhance the robustness of the methodology, particular attention is paid to the mitigation of the Gibbs phenomenon. To this end, the employed Alternating Frequency/Time scheme features a Lanczos σ-approximation so that spurious oscillations of the computed nonlinear contact forces become negligible. This approach is applied in combination with a model reduction technique on an industrial compressor blade: NASA rotor 37. In order to assess the influence of both the contact law regularization and the Lanczos σ-approximation, obtained results are thoroughly compared to an existing time integration-based numerical strategy relying on a Lagrange multiplier-based approach for contact treatment and that was previously confronted to experimental results. Presented results underline the very good agreement between the proposed methodology and the reference time integration numerical strategy. The proposed developments thus complement existing results on blade-tip/casing contact adding a much needed qualitative understanding of the interaction and an accurate assessment of the contact stiffening phenomenon.
A Non-Compact Effective Impedance Model for Can-to-Can Acoustic Communication: Analysis and Optimization of Damping Mechanisms
Authors: von Saldern Jakob G. R. , Orchini Alessandro , Moeck Jonas P. 
Published: September 2021

Abstract
Can-annular combustors can feature azimuthal instabilities even if the acoustic coupling between the individual cans is weak. Recently, various studies have focused on modeling the acoustic communication between adjacent cans in can-annular systems. In this study, a coupling model is presented that, in contrast to previous models, includes the effect of density fluctuations, mean flow, and dissipative effects at the connection gaps. By assuming plane acoustic waves inside each can and exploiting the discrete rotational symmetry of the can-annular system, the acoustic can-to-can interaction can be represented by an effective Bloch-type impedance. A single can modeled with the effective impedance at the downstream end emulates the acoustic response of the entire can-annular arrangement. We then propose the idea of installing a liner just upstream of the first turbine stage to damp azimuthal instabilities. By using the proposed can-to-can coupling model, we discuss in detail the effect that the impedance of the liner has on the effective reflection coefficient for different Bloch wavenumbers. In the low-frequency limit, we derive an analytical condition for achieving maximum damping at a specific Bloch-number. We show that the damping of azimuthal modes depends on the porosity of the liner, mean flow parameters and the Bloch-structure of the mode. These results suggest the possibility of targeting the damping of modes of certain azimuthal order by geometric variations of the liner or of the connection gap. As an exemplary application of the theory, we set up a network model of a generic industrial 12-can combustor and investigate a cluster of acoustic and thermoacoustic eigenvalues for a varying liner porosity. The findings of this study provide a deeper understanding of the mechanisms that drive the can-to-can acoustic communication, and open the path for devising passive damping strategies aimed at stabilizing specific modes in can-annular combustors.
Determining Total Pressure Fields From Velocimetry Measurements in a Transonic Turbine Flowfield
Authors: Rusted Alexander , Lynch Stephen 
Published: September 2021

Abstract
This work describes a method for calculating pressure fields from temperature and velocity data in non-adiabatic compressible flows, such as the flow around a cooled turbine vane. Prior studies have demonstrated the ability to use particle image velocimetry methods to estimate the pressure gradient in the momentum equation, which is subsequently integrated to produce pressure fields. Due to changes in total temperature for non-adiabatic compressible flows, pressure fields cannot be computed from velocity measurements alone and temperature data must also be provided. In this work, a benchmarked steady 3D RANS simulation is used to generate velocity, temperature, and pressure fields in the transonic flow around a high-pressure turbine inlet guide vane. A procedure for solving the momentum equation and integrating for pressure is developed for non-adiabatic flows. Error is assessed by comparing calculated pressure to CFD predicted pressure, and the effects of PIV spatial resolution and measurement error are considered. The accuracy of the method on non-adiabatic flows is assessed using a vane with extensive film cooling. A clear benefit of incorporating temperature measurements in the pressure determination method is demonstrated, offering opportunities for deeper understanding of aerodynamic losses and entropy generation in cooled turbine flowfields.
A Dynamic Systems Based Approach to Estimate Cyclic and Creep Damage of a Power Turbine Blade Subjected to a Random Transient Operation
Authors: Dua Dipankar , Le Quang , Saladino Anthony , Thirumurthy Deepak , Singh Jaskirat 
Published: September 2021

Abstract
The Paper presents a novel computationally efficient physics based framework for continuous assessment of cyclic and time dependent damage consumption for Siemens Aeroderivative power turbine components based on actual engine operation.
The framework discussed in paper provides the capability for Siemens’ customers to move away from fixed overhaul schedule to a customized schedule which is based on a given gas turbines actual operation and inspection findings. This customized overhaul schedule enables the customers a flexibility to maximize the unit availability and minimize operating costs.
Semi-empirical framework discussed in this paper, utilizes dynamic systems theory-based approach to estimate the cyclic & creep damage as a response to transient engine operation; characterized by relevant installed engine instrumentation data from the Engine Health Monitoring system.
To estimate damage response through any given complex transient operating cycle, algorithm solves a set of ordinary differential equations (ODEs), that have been calibrated to the engine control and safety instrumentation parameters such as shaft speed, turbine temperatures, pressures etc. by pre-analyzed operating envelope cases.
The framework can be setup for predicting accumulated cyclic and creep damage for all type of turbine components (Aerofoils, disks, casings, diffusers etc.), transient stress state complexity (in-phase, out-of-phase, uniaxial, multiaxial stress profiles) and is capable to handle unit specific ramp rates, start-up times, restart/cooldown effects specific and random changes in load, history.
The framework for discussion in this paper has been demonstrated as applied to the stage-1 blade of an A-35 RT62 power turbine as an example.
Heat Transfer in a Rotating, Blade-Shaped, Two-Pass Cooling Channel With a Variable Aspect Ratio
Authors: Chen I-Lun , Sahin Izzet , Wright Lesley M. , Han Je-Chin , Krewinkel Robert 
Published: September 2021

Abstract
This study features a rotating, blade-shaped, two-pass cooling channel with a variable aspect ratio. Internal cooling passages of modern gas turbine blades closely follow the shape and contour of the airfoils. Therefore, the cross-section and the orientation with respect to rotation varies for each cooling channel. The effect of passage orientation on the heat transfer and pressure loss is investigated by comparing to a planar channel design with a similar geometry. Following the blade cross-section, the first pass of the serpentine channel is angled at 50° from the direction of rotation while the second pass has an orientation angle of 105°. The coolant flows radially outward in the first passage with an aspect ratio (AR) = 4:1. After a 180-degree tip turn, the coolant travels radially inward into the second passage with AR = 2:1. The copper plate method is applied to obtain the regionally-averaged heat transfer coefficients on all the interior walls of the cooling channel. In addition to the smooth surface case, 45° angled ribs with a profiled cross section are also placed on the leading and trailing surfaces in both the passages. The ribs are placed such that P/e = 10 and e/H = 0.16. The Reynolds number varies from 10,000 to 45,000 in the first passage and 16,000 to 73,000 in the second passage. The rotational speed ranges from 0 to 400 rpm, which corresponds to maximum rotation numbers of 0.38 and 0.15 in the first and second passes, respectively. The blade-shaped feature affects the heat transfer and pressure loss in the cooling channels. In the second passage, the heat transfer on the outer wall and trailing surface is higher than the inner wall and leading surface due to flow impingement and the swirling motion induced by the blade-shaped tip turn. The rotational effect on the heat transfer and pressure loss is lower in the blade-shaped design than the planar design due to the feature of angled rotation. The tip wall heat transfer is significantly enhanced by rotation in this study. The overall heat transfer and pressure loss in this study is higher than the planar geometry due to the blade-shaped feature. The heat transfer and pressure loss characteristics from this study provide important information for the gas turbine blade internal cooling designs.
Enhanced Film Cooling Effect Downstream of a Cylindrical Hole Using SDBD and DBD-VGs Plasma Actuations
Authors: Huang Yuefeng , Zhang Zihan , He Kun , Yan Xin 
Published: September 2021

Abstract
Effects of SDBD and DBD-VGs plasma actuations on film cooling performance of a plain wall were numerically investigated based on the RANS solutions and linearized body force model. With a user defined function (UDF), the plasma actuation forces were implemented into the momentum equations as the source terms in the commercial CFD solver ANSYS Fluent. With the experiment data and referenced numerical results, reliabilities of the linearized body force model and numerical methods were validated. At a range of dimensionless actuation strengths and frequencies, the film cooling effectiveness on the wall surface and flow structure development in the near-wall regions were analyzed and compared with the plasma-off case. The results show that both SDBD and DBD-VGs plasma actuations are beneficial for reducing the development of kidney vortex pair downstream of the cooling hole, thus significantly improving the film cooling effect on the wall surface. With SDBD plasma actuation, the streamwise velocity gradient in near-wall region is increased compared with the plasma-off case, resulting in delayed coolant flow lifting-off downstream of the cooling hole. However, with DBD-VGs plasma actuation, the development of anti-kidney vortex pair is intensified, which in turn weakens the development of kidney vortex pair and widens the coolant coverage on the wall surface along lateral direction. As the actuation strength and frequency increase, the film cooling effectiveness on the wall surface is enhanced along both streamwise and lateral directions. Compared with the plasma-off case, the area-averaged film cooling effectiveness for DBD-VGs plasma actuation case is increased by 331% at dimensionless actuation frequency of 2.5 and dimensionless actuation strength of 30, whereas for SDBD plasma actuation case the area-averaged film cooling effectiveness is only increased by 42.8% at dimensionless actuation frequency of 2.5 and dimensionless actuation strength of 60. With the same actuation parameters, compared against the SDBD case, a higher film cooling effectiveness is achieved on wall surface for the DBD-VGs plasma actuation case, and the coolant coverage along the lateral direction is significantly improved by DBD-VGs plasma actuation.