bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Application of the Arbitrary-Order Galerkin Reduction Method to the Dynamic Analysis of a Rotor With a Preloaded Single-Pad Foil-Air Bearing
Authors: Ghalayini Ibrahim , Bonello Philip 
Published: October 2022

Abstract
The compressible Reynolds Equation (RE) is typically integrated within a fully-coupled dynamical foil-air bearings (FABs)-rotor system via spatial discretisation transformation e.g. Finite Difference (FD), Finite Element (FE). An alternative way of integrating the RE is through Galerkin Reduction (GR). The motivation for using GR is the computational benefit coming from the drastic condensation of the problem due to the elimination of the two-dimensional grid used for the air film in FD or FE. This paper presents a novel application of arbitrary-order GR to both nonlinear and linearised analyses of rotor systems supported by single-pad FABs with variable radial clearance (preload). Simulations using FD gave close correlation with those using GR for all preloads, with discrepancies increasing as the preload approaches the nominal clearance (c). The simulations show that the preload has to exceed a certain level in order to delay the onset of instability speed (OIS), and significant delay in OIS and suppression of sub-synchronous vibration is possible when the preload is comparable to c. Experimental validation is provided.
Modeling of Flashback With Different Blends of CH4 and H2 by Using Finite Rate Chemistry With Large Eddy Simulation
Authors: Verma Ishan , Yadav Rakesh , Ansari Naseem , Orsino Stefano , Li Shaoping , Nakod Pravin 
Published: October 2022

Abstract
Due to its clean combustion characteristics, hydrogen fuel is gaining attention in power generation. New designs of engine systems and components are being explored to allow blending with the increasing amount of hydrogen in natural gas. Adding H2 increases the probability of flashback and often is one of the main constraints in using high H2 blends in premixed combustors. There are several mechanisms of flashback like boundary layer flashback, combustion induced vortex break down, turbulence in the flow, fluctuations in equivalence ratio, etc. Semi-empirical models, based on non-dimensional numbers and flame speed, have successfully predicted flashback propensity for a given operating condition. The semi-empirical models are computationally very efficient; however, they lack generality. A typical combustor can have multiple flashback mechanisms. The relative importance of each mechanism can change with a change in the combustor design or even with a difference in the operating conditions for the same combustor. Since prediction of flashback requires accurate modeling of highly transient chemistry phenomena and the impact of heat loss on chemistry, a viable detailed chemistry solution is preferred to model flashback.
This paper describes the use of a finite rate chemistry model to predict flashbacks in a turbulent premixed combustor in this work. The configuration used is a swirl stabilized combustor (SimVal) from National Energy Technology Laboratory. The current computations are done with Finite Rate Chemistry (FRC) and Large Eddy Simulations (LES). Simulations are carried out for a varied percentage of CH4/H2 blends, ranging from 0% H2 to 100% H2 at a fixed equivalence ratio and inlet mass flow. As the percentage of H2 is increased in the fuel, flame speed also increases. With this, the propensity for flashbacks also increases. A 28-species reduced mechanism for CH4/H2 blend flames is used to keep the simulations computationally tractable. The simulations with the reduced mechanism are performed by considering non-adiabatic effects from heat loss near the walls and multi-component property considerations. This improves the accuracy of the FRC-LES simulations to capture the onset of boundary layer flashback towards the inlet. The simulations from FRC-LES suggest a fine mesh in the boundary layer for an accurate prediction that makes the simulations expensive. Therefore, an Adaptive Mesh Refinement (AMR) approach has been used for different CH4/H2 blends to accurately model the flashback without any loss in generality as the AMR criteria used here are applicable for a wide range of conditions. The FRC-based solution strategy proposed in this work provides a framework to model flashback for different blends without any case-specific tuning.
Nonlinear Dynamic Analysis of the Pressure Signals on a Swirl-Stabilized Atmospheric LDI Burner Across Different Operating Conditions
Authors: Torregrosa Antonio , Broatch Jacobi Alberto , García-Tíscar Jorge , Rodríguez Pastor Marc 
Published: October 2022

Abstract
Lean Direct Injection (LDI) burners are a promising technology aimed at reducing NOx emissions in new generation aeroengines. However, one of the main drawbacks of this technology is the appearance of combustion instabilities at certain operating conditions. In order to investigate these issues, a confined, atmospheric, swirl-stabilized LDI burner has been set up at the Institute CMT-Motores Térmicos. In this configuration, air mass flow, temperature, and fuel mass flow rate, which is controlled by the injection pressure, can be independently modified to reach different combustion states. In this paper, a parametric study of the equivalence ratio (0.3 ≤ Φ ≤ 0.8), air temperature (50, 100, 150 °C) and fuel mass flow rate (200, 250, 300, 335, 370 mg/s) has been performed to assess their influence on the dynamics of the system through the evaluation of the pressure signals inside the chamber. These signals have been acquired with two piezoresistive sensors flush-mounted to the combustor wall at the same axial distance but in opposite sides of the chamber. Large-amplitude unsteady oscillations are detected for some combinations of the variables of interest. Equivalence ratio variations are shown to affect deeply the dynamic features of the pressure signal, obtaining more stable configurations either close to the lean limit (Φ = 0.3) or at the richest condition tested (Φ = 0.8). Mid-range equivalence ratio values (0.4 ≤ Φ ≤ 0.7) are shown to display the most unstable behavior, featuring large pressure oscillations that remain nearly constant over time (quasi-periodic states) or signals that experience sudden variations in their amplitude (intermittent states). Since turbulent swirl-stabilized spray flame combustors may experience complex flow-flame interactions that could lead to nonlinear behavior of these combustion regimes, several signal processing techniques such as three-dimensional phase space reconstruction or recurrence plots have been applied to the experimental data in order to obtain better insight into these highly dynamic features.
Analytical Methods for Transonic Compressor Rotor Blade Tip Clearance Measurements Using Capacitive Probes
Authors: Magno David , Gannon Anthony , Smith Walter , Hobson Garth 
Published: October 2022

Abstract
A method is presented to improve the capability of proximity sensing capacitive probes used in rotor blade tip clearance (BTC) measurements. This research presents the development and result of a post-processing method used to calibrate capacitive probe instrumentation that will be used to passively analyze BTC of a transonic axial fan under high-speed and high-transient loading. The method attempts to address limitations currently placed on BTC measurements due to poor a SNR. Each revolution’s raw capacitive probe signal is uniformly resampled to a synchronizing once-per-revolution signal, normalizing the data. This reduces timing inaccuracies in the sampling frequency inherent to the data acquisition system and transfers data into a spatial domain removing time dependence and rotational speed variance, which in turn improves the SNR. A Fast Fourier Transform (FFT) is used to identify acceptable lowpass filter passbands that are then adaptively applied to this resampled data based on tip clearance distance. This produces increased precision and dynamic range in capacitive probe calibration compared to existing BTC calibration methods. Use of the proposed method gives the potential ability to operate capacitive probes at larger ranges and in poor SNR environments and gives a possible application in monitoring rotor blade integrity, at a low, additional computation time cost.
An Integrated Creep Damage Analysis Method of Turbine Blades Based on the Service History
Authors: Shi Duoqi , Cheng Muwei , Yang Xiaoguang , Fan Yongsheng 
Published: October 2022

Abstract
The creep fracture life of turbine blades is a limitation of the whole engine life because of its high operating temperature. Thus, developing an analysis approach of creep damage based on complex service history is of significant importance for the safe operation and economic overhaul. Within this content, an integrated creep damage analysis method is constructed, which can be used to calculate the accumulation of creep damage in real time once obtaining the service history. This approach first gets some critical parameters such as rotor speed and turbine forward temperature of the turbine blades through thermodynamic performance model of the engine. Then the stress and temperature states of the turbine blade is obtained by the thermal-fluid-solid coupling analysis. Based on the numerical results, a train of surrogate models from engine operating state to the detail load states including temperature, thermal stress and centrifugal stress are established. The classical Rabotnov-Kachanov creep model is selected to calculate the creep damage accumulation. This integrated damage analysis method has been carried out by a turbofan engine’s turbine blades. The results show that this method works well and quickly when faced with a large number of flight record data with only once numerical simulation under the typical service state. The blades damage accumulation changes reasonably as flight profile. The proposed method decreases the time cost by the developed surrogate models when flight profile changes, which has the potential to be used to monitor individual engine life and to extend to study the other damage types of turbine blades under different flight loads.
Crossflow Effect on Heat Transfer and Flow Characteristics of Simplified Double Wall Cooling Structure
Authors: He Juan , Deng Qinghua , Xiao Kun , Feng Zhenping 
Published: October 2022

Abstract
Double wall cooling is regarded as one of the advanced cooling technologies of modern gas turbines, but its internal cooling is always confronted with crossflow effect. To reveal the conjugate heat transfer characteristics under different crossflow configurations, this paper utilized ANSYS CFX to numerically simulate a double wall cooling model with staggered impingement holes and film holes. CFX numerically solves steady three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations. Both the overall cooling and internal heat transfer performance of four different crossflow mass flow ratios (CMFR = 0, 0.25, 0.5, 0.75) under four impingement jet Reynolds numbers (Rej = 15,000, 25,000, 35,000, 45,000) are compared in detail. The calculated results show that the CMFR has significant influence on double wall cooling performance. The averaged blowing ratio increases with the increase of jet Reynolds number under the same crossflow configuration, and it decreases with the increase of CMFR under the same impingement jet Reynolds number. The area-averaged Nusselt number decreases with the increase of CMFR at the CMFR ranging from 0.25 to 0.75, but the area-averaged overall cooling effectiveness increases with the increase of CMFR since better film coverage plays a dominated role in the enhancement effect of double wall cooling. In addition, the influence of solid thermal conductivity is also taken into consideration. It is revealed that solid thermal conductivity has great influence on double wall cooling. Under all crossflow configurations, the overall cooling effectiveness increases with the increase of solid thermal conductivity, but the increase rate slows down with the increase of thermal conductivity.
Developing a Scalar Flux Model Solely Based on Mean Flow Quantities for the Film Cooling Jet Flow
Authors: Shi Bo , Li Xueying , Ren Jing 
Published: October 2022

Abstract
Previous studies showed that the Reynolds-averaged Navier Stokes simulation (RANS) which used gradient diffusion hypothesis (GDH) severely under-predicts the scalar diffusion downstream the film cooling jet flow. Scalar flux models of different types have been developed throughout the years. Of particular interest is the algebraic model, which is easy to implement and has a low computational cost. Well-known algebraic models include the generalized gradient diffusion hypothesis (GGDH) and the high-order generalized gradient diffusion hypothesis (HOGGDH). However, due to the dependence on the Reynolds stress, GGDH and HOGGDH may suffer from a lack of scalar prediction along with RANS, because the Boussinesq core of which will lead to a loss of anisotropy. In a previous study [1], we revealed the mechanism of turbulent scalar transport in the shear layers of the film cooling jet based on the analysis of the flow and scalar field predicted by the large eddy simulation (LES). Upon the mechanism revealed, this paper aims to develop a scalar model that only depend on mean flow quantities, including mean velocity, turbulent kinetic energy and turbulent viscosity. It is our hope that the model can be comparable or surpass the GGDH and HOGGDH concerning the ability of scalar prediction, while not be dependent on the Reynolds stress. Scalar transport equation was solved with the mean flow data provided by the previous LES. The prediction of an inclined cylindrical hole with VR = 0.46 using GGDH, HOGGDH and current model (namely SLR) were compared and analyzed.
Interaction Mechanism of Impeller and Diffuser Stall in a Centrifugal Compressor
Authors: Fujisawa Nobumichi , Naitou Momoko , Ohta Yutaka 
Published: October 2022

Abstract
The interaction mechanism of impeller and diffuser stall in a centrifugal compressor with a vaneless diffuser was investigated by experimental and computational analyses. This study focuses on the effect of impeller stall on the diffuser stall behavior. Impeller stall rotated at 58% of the impeller rotational speed was generated inside the impeller. Two-cell diffuser stalls (with each of the cells rotating at 25%–30% of the impeller rotational speed) were generated inside the diffuser. The diffuser stall fluctuations were observed at 180° from the cutoff. The magnitudes of the diffuser stall fluctuations gradually increased near the volute tongue. The diffuser stall fluctuations were generated near both the shroud and hub sides. Finally, the diffuser stall cell vanishes when it passes the cutoff because mass flow recovery occurs. The numerical results revealed that boundary layer separation occurred near the hub side at 45°–90° of the diffuser because of the circumferential adverse pressure gradient. Subsequently, the low-velocity region discharged from the impeller caused by impeller stall merged into the boundary layer separation, which was generated near the hub side at 45°–90°. Diffuser stall was initiated by the hub-side boundary layer separations, which were caused by the impeller stall. The diffuser stall cell was then further developed by the boundary layer separation accumulation and the induced low-velocity area. The boundary separation was further developed by merging the wake from the impeller stall passage.
Parametric Design of Radial Guide Vanes for Power Augmentation of Darrieus-Type Vertical-Axis Wind Turbines
Authors: Melani Pier Francesco , Balduzzi Francesco , Ferrara Giovanni , Bianchini Alessandro , Bissanti Roberto , Bissanti Palmiro 
Published: October 2022

Abstract
Among proposed solutions for power augmentation of Darrieus turbines, one of the most promising is represented by Radial Guide Vanes (RGVs) which can potentially increase both the velocity magnitude and the swirl of the incoming flow, without losing omni-directionality like in the case of diffusers. The main drawback of this technology is the increase in the dimension of the wind energy converter, which however comes together with reasonable cost (only static parts are added) and additional benefits like a higher safety and lower noise.
The study presents an extensive parametric analysis aimed at investigating the impact of some key design parameters of a RGV cascade on the performance of a medium-size industrial Darrieus rotor. Focus is given to vanes angle and length. Simulations are carried out by means of the two-dimensional Actuator Line Model developed by some of the authors for the commercial ANSYS® FLUENT® 20.2 solver. The hybrid simulation approach has been validated against blade-resolved unsteady CFD RANS simulations of the machine in both open- and vaned-rotor configurations. The use of high-fidelity techniques comes indeed with a non-negligible calculation cost, but it can solely provide the needed accuracy in modeling the physics related to the interaction of the flow with both static and rotating blades. Different turbine operating points and inlet flow angles are considered, so that the effective omni-directionality of the RGV concept could be verified. Tested configurations are compared in terms of power coefficient and blade loading azimuthal profile. Overall, results prove that — if the correct design is chosen — RGVs can provide notable improvements in the performance of a Darrieus VAWT, opening interesting prospects for their future application in industrial installation.
Modification of Pump Turbine Characteristics With Fluid Injection in Pump Operating Mode
Authors: Deniz Sabri , In Albon Simon 
Published: October 2022

Abstract
The requirements of a stable and reliable pump turbine operation under continuously expanding operating ranges, challenges the design of pump turbines and demand new developments. This paper presents the results of experimental (model pump turbine at the test rig) and numerical (CFD) investigations of the instabilities of a low specific speed (nq = 25) pump turbine in pump operating mode.
During the operation at off-design conditions, not only performance penalties but also flow instabilities may occur, limiting the operating range of the pump turbines. Although unstable behavior can be observed during the part load operation in turbine mode (i.e., draft tube vortex rope) and during the turbine mode operation near runaway speed (speed no load conditions), the focus of this paper is on the pump operating mode, the so-called hump instability at part load operation, when the head vs. flow rate characteristics of the pump has a positive slope. The pump mode dimensionless head vs. flow rate characteristics are measured for different diffuser opening angles, DA. Using the data of the unsteady pressure measurements, flow instabilities in the low-specific speed model pump turbine are analyzed in pump operating mode.
Flow control with fluid injection in the vaneless space (between the runner and the diffuser) on a model pump turbine during pump mode operation was applied for different diffuser angles at HSLU (Lucerne University of Applied Sciences, Switzerland) in order to modify the pump mode, head vs. flow rate characteristics and to eliminate the regions with positive slopes in the characteristics. Water-injection is first applied using an external energy source (pump) with discrete nozzles that are circumferentially distributed in the vaneless space. Later water injection is also implemented without an external energy source using a bypass, which is connecting the discharge of the pump with the vaneless space. With fluid injection, the pump head vs. flow rate characteristics are modified so that there are no more positive slope regions, meaning an improvement in the stability behavior and extension of the operating range of the pump mode operation. After the implementation of flow control in the laboratory, CFD simulations were carried out to calculate the pump head vs. flow rate characteristics with and without fluid injection. CFD simulations with the BSL EARSM (Baseline Explicit Algebraic Reynolds Stress) turbulence model are able to predict the experimentally determined pump head vs. flow rate characteristics with- and without water injection.
Carbon Capture Performance Assessment Applied to Combined Cycle Gas Turbine Under Part-Load Operation
Authors: Verhaeghe Antoine , Dubois Lionel , Bricteux Laurent , Thomas Diane , Blondeau Julien , De Paepe Ward 
Published: October 2022

Abstract
The growing share of renewable energies in our electricity production, together with the still lacking storage capacity, strongly reinforces the need for more flexible electricity production units. In this context, Combined Cycle Gas Turbines (CCGTs) have a role to play, both in the current and future electricity production system due to their high efficiency, high load flexibility, and low CO2 emissions compared to other conventional thermal power plants. Nevertheless, bearing in mind our current challenges concerning climate change, the CO2 emissions of these CCGTs need to be reduced drastically. The amine-based absorption Carbon Capture (CC) process is currently the most mature and applicable CC technology. This process is known to require a considerable amount of thermal energy, degrading plant performance. However, to back-up renewable production, CCGTs will operate most of the time under part-load conditions. The impact of these part-load operations on the CC is still relatively unknown. Within this framework, this study aims to assess the performance of the CC process applied to a typical CCGT under part-load operation using specific simulation models. The CC plant model has been successfully validated against experimental data from a pilot-scale capture facility. Then, the CC plant has been scaled-up to the CCGT scale and the process has been optimized for each operating condition. The simulation results show that the specific reboiler duty increases for part-load operation, while the specific cooling requirements decrease. Moreover, the analysis of the yearly CCGT operation highlights a relative increase in CC energy penalty of 21% for an annual CCGT load factor of 0.5, impacting significantly plant performance. The next step will involve reducing this energy penalty.
CFD Analysis of the Forces on a Steam Turbine Balance Seal Packing Ring
Authors: Bianchini Cosimo , Da Soghe Riccardo , Bertini Davide , Mazzei Lorenzo , Arcangeli Lorenzo , Cosi Lorenzo 
Published: October 2022

Abstract
In high-pressure single flow Steam Turbines, sealing of the radial gap between rotating and stationary parts in the front end of the turbine is a known design challenge. A traditional solution to control and reduce the leakages between the stationary and rotating parts in that area is to implement spring-backed labyrinth packings. The operating position of such packings, which affects the effective clearance and in turn the leakage flow, is determined by the equilibrium of the forces exerted by the steam and the spring load applied on the back. In order to select the adequate spring and guarantee the desired clearance, it is hence of paramount importance to precisely predict the forces acting on the packing ring during the design stage.
This paper describes a computational analysis aimed at characterizing the forces on the packing ring. A full 3D model of a single packing ring, assuming periodic flow in the tangential direction, including both the labyrinth seal on the bottom side, the packing ring chamber on top and the gap between consecutive packing rings was developed. Different clearances between the packing ring and the surrounding casing as a result of manufacturing tolerances are considered both in the axial and tangential direction.
The analysis showed that the radial force varies quite significantly with such clearances. The analysis also permitted to highlight that 2D modelling of the labyrinth seals, being intrinsically insensitive to such clearances, is not capable to estimate with sufficient accuracy the radial force on the packing ring.