bluuebunny/crossref_metadata_2025_split huggingface dataset:
Assessment of Unsteadiness Modelling for Transient Natural Convection
Authors: Fadl M. , He L. , Stein P. , Marinescu G. 
Published: August 2017

Flexible operations of steam turbines with faster startups and shutdowns are required to accommodate emerging renewable power generations, needing more advanced prediction tools for transient thermal design and analysis. A major challenge is the time scale disparity. For a natural cooling, the physical process is typically in hours or tens of hours, but on the other hand, the time step sizes typically usable tend to be very small (in seconds or sub-seconds) due to the numerical stability requirement for natural convection as often observed. A general issue to be addressed is what time step sizes can be and should be used in terms of stability as well as accuracy.
In the present work, the impact of the temporal gradient in unsteady flow and its modelling is examined in relation to numerical stability and modelling accuracy for natural convectio n. A source term based dual timing for mulation is adopted and implemented in a commercial code, which is shown to be numerically stable for very large time steps for natural convection analysis. Furthermore, a loosely coupled partitioned procedure is developed to combine this enhanced flow solver together with a solid conduction solver for solving transient conjugate heat transfer problems for natural convection. This allows very large computational time steps to be used without any stability issues, and thus enables to assess the impact of using different time step sizes entirely in terms of the temporal accuracy requirement. Computational case studies demonstrate that the present method is more stable at a markedly shortened computational time than the baseline solver. The method is also shown to be more accurate than the commonly adopted quasi-steady methods when unsteady effects are non-negligible.
Turbulent Energy Budget in a Tip Leakage Flow: A Comparison Between RANS and LES
Authors: Monier Jean-François , Boudet Jérôme , Caro Joëlle , Shao Liang 
Published: August 2017

An academic configuration of a single airfoil and a flat casing with clearance, put in the potential core of a jet at Rec = 9.3 × 105, is studied in order to analyse the turbulence modelling. A zonal large-eddy simulation (ZLES), validated against experimental results, is considered as a reference to evaluate two steady Reynolds-averaged Navier-Stokes (RANS) simulations. Both RANS simulations use the original Wilcox k-ω model. They differ on the constitutive relation: one uses the classical Boussinesq constitutive relation, while the other relies on the quadratic constitutive relation (QCR).
The analysis focuses on the mean velocities, the Reynolds stresses and a term-to-term decomposition of the turbulent kinetic energy budget on a plane through the clearance. RANS represents quite well the mean velocities, but under-estimates the Reynolds stresses, thus under-estimates every turbulent kinetic energy budget term. The QCR has little effect on the flow and the turbulent quantities. The method allowed a fine analysis of the physics of the turbulence.
Managing Gas Turbine Combustion System Fuel Manifold Distress Through Ultrasonic Inspections and Calibrated Fracture Analyses
Authors: Keller Scott , Mohammed Afzal Pasha , Oumejjoud Khalid 
Published: August 2017

One of the common issues within the industrial gas turbine fleet is the susceptibility of a can-annular combustors’ fuel manifold cover (support housings) to develop embedded cracks. These cracks, located in the assembly joint of cover plates that create internal passages for fuel delivery to the combustion system, have enough of a driving force to propagate to the surface of the component. Once a crack propagates to the surface, gas has the potential to leak into the enclosure, posing a potential fire and safety risk. Furthermore, cracked fuel manifold covers are prone to increased NOx levels and excessive dynamics. Consequently, operators have the potential for a forced outage due to the failure of the fuel manifold. Currently, the existing solution is to replace the support housings with new or refurbished housings, with prior analyses requiring near perfect fusion.
An ultrasonic inspection procedure has been developed to inspect a combustor’s fuel manifold cover for embedded cracks, which are not currently detectable with FPI or X-ray methods. Through this method, the amount of fusion in the assembly joint is readily obtained, including the ability to understand if the crack is partial-thickness or through-thickness. Parametric fracture analyses, utilizing experimental material test data calibrated to service-exposed components, are conducted to predict the residual life. Coupled with the engine operating data, including the use of cold- or heated-fuels, a recommendation for the remaining useful operation of the support housings can be provided. Ultimately, by completing the ultrasonic inspection and analysis on the support housing/fuel manifold, both the risk of an unplanned outage in the future and the lifecycle management cost to the operator is reduced.
The Use of Air-Measured Profile Data for Application in a High Pressure Steam Turbine
Authors: Britz Marcus , Jeschke Peter , Brunn Oliver , Polklas Thomas 
Published: August 2017

This paper investigates the validity of the current industrial procedure of measuring optimized blade profiles in a wind tunnel under air condition although they are applied in a steam turbine. Therefore, it is important to analyze the possibility of using air-measured profile data for optimizing steam turbine blades. To this end, experimental data is collected using the cylindrical datum blade of a steam turbine in a three-stage high pressure steam turbine and in an annular air cascade wind tunnel. Three-dimensional CFD simulations are separately performed for both setups and show a good agreement with the experimental data. The numerical simulations can therefore be assumed to represent the real flow conditions.
Firstly, for analyzing aerodynamic transferability, two optimized profiles are measured in the annular air cascade wind tunnel at Reynolds number of 6 × 105. These profile sections are designed for high and intermediate pressure applications by employing an optimizer. The optimization is performed with the focus on reducing the profile loss for steam conditions. The experimental data verifies that the losses of the optimized profiles are reduced significantly compared to the datum blade profile measured in the same air rig. Secondly, the air-measured optimized blade profiles are used to design a 3D-optimized blade. In a numerical investigation, this optimized blade is analyzed in the steam turbine by applying steam conditions. The outlet Reynolds number of the 2nd stage is 8 × 105. This configuration is compared with the numerical results of the datum blade profile simulations.
The relative isentropic total-to-total efficiency is increased by 0.6% due to the use of the optimized rotor blades. The benefit persists also for a maximum outlet Reynolds number of 9 × 106.
Analysis of a Tilted Turbine Housing Volute Design Under Pulsating Inlet Conditions
Authors: Lee Samuel P. , Jupp Martyn L. , Nickson Ambrose K. , Allport John M. 
Published: August 2017

Radial inflow turbines are widely used in the automotive turbocharger industry due to the greater amount of work that can be extracted per stage and their ease of manufacture compared with equivalent axial designs [1]. The current industry trend towards downsized engines for lower emissions has driven research to focus on improving turbine technologies for greater aero-thermal efficiency. Consequently, mixed flow turbines have recently received significant interest due to a number of potential performance benefits over their radial counterparts, including reduced inertia and improved performance at low velocity ratios.
This paper investigates the performance of a tilted volute design compared with that of a radial design, under steady state and pulsating flow conditions. The tilted volute design was introduced in an attempt to improve inlet flow conditions of a mixed flow turbine wheel and hence improve performance. The investigation is entirely computational and the approach used was carefully validated against gas stand test results.
The results of the study show that under steady state conditions the tilted volute design resulted in stage efficiency improvements of up to 1.64%. Under pulsating flow conditions, the tilted housing design resulted in a reduction in incidence angle and a maximum cycle averaged rotor efficiency improvement of 1.49% while the stage efficiencies resulted in a 1.23% increase. To assess the loss mechanisms within the rotor, the entropy flux generation through the blade passage was calculated. The tilted housing design resulted in reductions in leading edge suction and shroud surface separation resulting in the improved efficiency as observed.
Complete Characterization of a Highly Loaded Low Pressure Compressor at Different Reynolds Numbers for CFD Simulations
Authors: Hadavandi Ruzbeh , Fontaneto Fabrizio , Desset Julien 
Published: August 2017

CFD is nowadays extensively used for turbomachinery design and performance prediction. Nevertheless, compressors numerical simulations still fail in correctly predicting the stall inception and the post-stall behavior. Several authors address such a lack of accuracy to the incomplete definition of the boundary conditions and of the turbulence parameters at the inlet of the numerical domain. The aim of the present paper is to contribute to the development of compressors CFD by providing a complete set of input data for numerical simulations.
A complete characterization has been carried out for a state-of-art 1.5 stage highly loaded low pressure compressor for which previous CFD analyses have failed to predict its behavior. The experimental campaign has been carried out in the R4 facility at the Von Karman Institute for Fluid Dynamics. The test item has been tested in different operative conditions for two different speed lines (90% and 96% of the design speed) and for two different Reynolds numbers. Stable and unstable operative conditions have been investigated along with the stalling behavior, its inception and the stall-cell flow field. Discrete hot-wire traverses have been performed in order to characterize the span-wise velocity field and the turbulence characteristics.
Ported Shroud Flow Processes and Their Effect on Turbocharger Compressor Operation
Authors: Sharma Sidharath , Jupp Martyn L. , Nickson Ambrose K. , Allport John M. 
Published: August 2017

The ported shroud (PS) self-recirculating casing treatment is widely used to delay the onset of the surge by enhancing the aerodynamic stability of the turbocharger compressor. The increase in the stable operation region of the turbocharger compressor is achieved by recirculating the low momentum fluid that blocks the blade passage to the compressor inlet through a ported shroud cavity. While the ported shroud design delays surge, it comes with a small penalty in efficiency.
This work presents an investigation of the flow processes associated with a ported shroud compressor and quantifies the effect of these flow mechanisms on the compressor operation. The full compressor stage is numerically modelled using a Reynolds Averaged Navier-Stokes (RANS) approach employing the shear stress transport (SST) turbulence model for steady state simulations at the design and near surge conditions. The wheel rotation is modelled using a multiple reference frame (MRF) approach. The results show that the flow exits the PS cavity at the near surge condition in the form of three jet-like structures of varying velocity amplitudes. Net entropy generation in the compressor model is used to assess the influence of the ported shroud design on the compressor losses, and the results indicate a small Inlet-PS mixing region is the primary source of entropy generation in the near surge conditions. The analysis also explores the trends of entropy generation at the design and the near surge condition across the different speed lines. The results show that the primary source of entropy generation is the impeller region for the design condition and the inlet-PS cavity region for the near surge condition.
The Effect of Fuel Staging on the Structure and Instability Characteristics of Swirl-Stabilized Flames in a Lean Premixed Multi-Nozzle Can Combustor
Authors: Samarasinghe Janith , Culler Wyatt , Quay Bryan D. , Santavicca Domenic A. , O’Connor Jacqueline 
Published: August 2017

Fuel staging, or fuel splitting, is a commonly used strategy for the suppression of combustion instabilities in gas turbine engines. In multi-nozzle combustor configurations, this is achieved by varying the fuel flow rate to the different nozzles. The effect of fuel staging on flame stabilization and heat release rate distribution (referred to as flame structure), and self-excited instability characteristics is investigated in a research can combustor employing five small-scale lean-premixed industrial nozzles. The nozzles are arranged in a “four-around-one” configuration and fuel staging is achieved by injecting additional fuel to the middle nozzle. An operating condition was identified where all five nozzles were fueled equally and the combustor was subject to a self-excited instability. At the operating condition considered, the self-excited instabilities are suppressed with fuel staging: this is true for cases where overall equivalence ratio is increased by staging (by only increasing the fuel flow rate to the middle nozzle) as well as cases where overall equivalence ratio is kept constant while staging (by simultaneously decreasing the fuel flow rate of the outer nozzles while increasing the fuel flow rate to the middle nozzle).
Fuel staging causes variations in the distribution of time-averaged heat release rate in the regions where adjacent flames interact. The locations of highest heat release rate fluctuation are not altered with increased fuel staging but the fluctuation amplitude is reduced. A breakup in the monotonic phase behavior that is characteristic of convective disturbances is observed with increased fuel staging, resulting in a lower pressure fluctuation amplitude. In particular, the monotonic variation in phase in the middle flame and the region where adjacent flames interact is out-of-phase with that of the outer flames, resulting in a cancellation of the global heat release rate oscillations. The distribution of local Rayleigh integral within the combustor shows that during a self-excited instability, the regions of highest heat release rate fluctuation are in phase-with the pressure fluctuation. When staging fuel is introduced, these regions fluctuate out-of-phase with the pressure fluctuation, further illustrating that fuel staging suppresses instabilities by altering the phase relationship of convective disturbances that travel along the flame front.
Leading-Edge Slots for Improving the Aerodynamic Performance of Cambered Airfoils in Horizontal Axis Wind Turbine Blades
Authors: Amano Ryoichi S. , Beyhaghi Saman 
Published: August 2017

In the present work, a narrow span-wide rectangular channel (referred to as a slot) is introduced and drilled near the leading edge of a finite-span cambered airfoil to study its impact on the overall aerodynamic performance. These slots are proposed to have two legs, where the first leg starts from the vicinity of the leading edge, and the second leg exits from the pressure-side of the airfoil. NACA 4412 is used as the baseline airfoil profile, and the influence of several geometrical parameters of the slots at different angles of attack (AoAs) ranging from 0 to 16 degrees are investigated on the lift and drag coefficients. The influence of slot’s length, width, and exit angles are studied, and it is demonstrated that longer and narrower slots that exit more aligned with the pressure-side streams are generally more suitable, and can result in better performance over the entire range of AoA. For the best case considered, a lift coefficient improvement as large as 15% is observed, while the drag penalty is insignificant.
Furthermore, the inlet angle and the vertical position of slots are independently varied within reasonable ranges to characterize the slots further. Computational fluid dynamics (CFD) is used for modeling and analysis. Simulations are performed at the chord-based Reynolds number of 1.6E6. Results are validated against published data and the results from a set of wind-tunnel experiment.
Quantification of X-Ray Measurement Uncertainty Based on Optical Measurement Data of Turbine Blades
Authors: Högner Lars , Knebel Sebastian , Voigt Matthias , Mailach Ronald , Meyer Marcus 
Published: August 2017

Probabilistic design approaches taking geometric variation due to manufacturing scatter or wear into account reflect a relevant part of today’s design process in turbomachinery. This process is characterized by a high degree of multidisciplinarity involving complex geometric features, which demands high standards to incorporate geometric variability. The significance of the employed probabilistic approaches considering real geometry effects is based on the information about the existing variability including distributions, correlations as well as the respective uncertainty of employed measurement techniques.
Within the scope of mechanical probabilistic analysis of cooled turbine blades, the variability of the internal geometry is of particular interest since this in combination with the external geometry variation leads to a change in wall thickness, which may influence stress and life significantly. Computed tomography (CT) represents a non-destructive technology that enables the detection of internal geometric features.
The present paper address the uncertainty quantification (UQ) of CT for a high-pressure turbine (HPT) blade. Measurement data derived by optical techniques are used by way of comparison. A parametric turbine blade model is employed to quantify the deviations between optical and tomographic measurement data. Furthermore, five blades were cut open by wire erosion, which enables a comparative investigation in terms of wall thickness. The observed deviations are related to inherent sources of uncertainties in CT.
Fabrication and Characterization of Additive Manufactured Nickel-Based ODS Coating Layer for High Temperature Application
Authors: Min Zheng , Parbat Sarwesh Narayan , Yang Li , Kang Bruce , Chyu Minking K. 
Published: August 2017

Increasing turbine inlet temperature (TIT) is important for improving the efficiency of gas turbine engine. Elevated thermal load causes severe oxidation and corrosion for base alloy in turbine airfoils. To survive in this extreme high temperature and harsh oxidation environment, both outside protection like thermal barrier coatings (TBC) and inside air cooling have been applied to turbine blades. Significantly more protection can be achieved if the cooling channels are embedded near surface, constructed partially by the coating system and partially by the superalloy substrate. However, neither the ceramic coating layer nor the metallic bond coating layer in current TBC system can provide structural support to such internal cooling channels. Development of structural bond coating layers consequently becomes one of the key technologies to achieve this goal.
Present study proposed a method to fabricate structural coating layers on top of turbine blades with the aid of additive manufacturing (AM) and oxide dispersion strengthened (ODS) nickel based alloy. ODS powder comprised of evenly distributed host composite particles (Ni, Al, Cr) with oxide coating layers (Y2O3) was subjected to a direct metal laser sintering (DMLS) process to fabricate a desirable structural coating layer above Nickel based superalloy substrates. Systematic experimental tests were carried out focusing on the interface adhesion, mechanical strength, microstructure and surface finish of the ODS coating layer. Based on characterization results from indentation tests and microscopy observations, an optimal coating quality was obtained under ∼250W laser power.
The selected samples were then characterized under isothermal conditions of 1200 °C for 2000 hours. SEM observations and Energy-dispersive X-ray spectroscopy (EDX) analysis were conducted in different stages of the oxidation process. Results indicated a formation of Al2O3 scale on top of the ODS coating layer at early stage, which showed long term stability throughout the oxidation test. The formation of a stable alumina scale is acting as a protective layer to prevent oxygen penetrating the top surface. Spallation of part of nickel oxide and chromium oxide is observed but the thickness of oxide scale is almost no change. In addition, the observed adhesion between ODS coating layer and substrate was tight and stable throughout the entire oxidation test. Present study has provided strong proof that additive manufacturing has the capability to fabricate structural and protective coating layers for turbine airfoils.
Investigation of In-Stall Behavior in a Transonic Compressor Rotor
Authors: Lang Jinhua , Chu Wuli , Zhang Haoguang , Ma Shan , Chen Xiangyi 
Published: August 2017

This paper shows the results of three-dimensional multi-passage numerical simulations on a transonic compressor, NASA compressor Rotor 37. The aim is to investigate the unsteady flow on the stall condition and elucidate the dynamic evolution mechanism of the rotating stall. Three-dimensional Reynolds-averaged Navier-Stokes equations with the Spalart-Allmaras turbulence model were solved to analyze the fluid flow in the transonic axial compressor. Before the study of the stall flow, grid independence and data correctness were well validated.
A new parameter B is defined to assess the blockage effect during the stall development. As shown in the results, with the development of the rotating stall, the blockage effect increases slowly before the 18th revolution in unsteady numerical simulation, and then increases dramatically in the following revolutions. Thus, the whole process of stall evolution can be divided into two stages, i.e. stall stage I and stall stage II. The stall stage I is the first 18th revolutions, while the stall stage II refers to the period after the18th revolution.
Further analyses of the instantaneous flow field show that the interaction between the tip leakage flow and the detached shock wave induces the breakdown of the leakage vortex. As the broken leakage vortex moves downstream, the low energy flow is rolled up. At the middle of the channel, the trajectory of the vortex core inclines to the PS of adjacent blade under the influence of the adverse pressure gradient, and an obvious new vortex is formed. During the development process of the rotating stall, the blockage is primarily induced by the tip leakage vortex and the new vortex. In the stall stage I, the evolution of the blockage area near the tip is periodic affected by the self-sustaineed process of tip leakage vortex. The self-sustained phenomenon will be illustrated in detail later. In the stall stage II, the whole passage is blocked at 99% blade span, and the spillage flow is observed throughout the whole stage. These flow charicteristics are regarded as signs of a rapid deterioration of the flow field. A vicious cycle is seen as the main reason for the rapid deterioration of the flow field, and the vicious cycle will be explained in detail later.