bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Novel Vortex Identification Technique Applied to the 3D Flow Field of a High-Pressure Turbine
Authors: Pátý Marek , Lavagnoli Sergio 
Published: November 2019

Abstract
The efficiency of modern axial turbomachinery is strongly driven by the secondary flows within the vane or blade passages. The secondary flows are characterized by a complex pattern of vortical structures that origin, interact and dissipate along the turbine gas path. The endwall flows are responsible for the generation of a significant part of the overall turbine loss because of the dissipation of secondary kinetic energy and mixing-out of non-uniform momentum flows. The understanding and analysis of secondary flows requires a reliable vortex identification technique to predict and analyse the impact of specific turbine designs on the turbine performance. However, literature shows a remarkable lack of general methods to detect vortices and to determine the location of their cores and to quantify their strength.
This paper presents a novel technique for the identification of vortical structures in a general 3D flow field. The method operates on the local flow field and it is based on a triple decomposition of motion proposed by Kolář. In contrast to a decomposition of velocity gradient into the strain and vorticity tensors, this method considers a third, pure shear component. The subtraction of the pure shear tensor from the velocity gradient remedies the inherent flaw of vorticity-based techniques which cannot distinguish between rigid rotation and shear. The triple decomposition of motion serves to obtain a 3D field of residual vorticity whose magnitude is used to define vortex regions.
The present method allows to locate automatically the core of each vortex, quantify its strength and determine the vortex bounding surface. The output may be used to visualize the turbine vortical structures for the purpose of interpreting the complex three-dimensional viscous flow field, as well as to highlight any case-to-case variations by quantifying the vortex strength and location.
The vortex identification method is applied to a high-pressure turbine with three optimized blade tip geometries. The 3D flow-field is obtained by CFD computations performed with Numeca FINE/Open. The computational model uses steady-state RANS equations closed by the Spalart-Allmaras turbulence model. Although developed for turbomachinery applications, the vortex identification method proposed in this work is of general applicability to any three-dimensional flow-field.
Steam Turbine Hot Standby: Electrical Pre-Heating Solution
Authors: Kostenko Y. , Veltmann D. , Hecker S. 
Published: November 2019

Abstract
Growing renewable energy generation share causes more irregular and more flexible operational regimes of conventional power plants than in the past. It leads to long periods without dispatch for several days or even weeks. As a consequence, the required pre-heating of the steam turbine leads to an extended power plant start-up time [1].
The current steam turbine Hot Standby Mode (HSM) contributes to a more flexible steam turbine operation and is a part of the Flex-Power Services™ portfolio [2].
HSM prevents the turbine components from cooling via heat supply using an electrical Trace Heating System (THS) after shutdowns [3]. The aim of the HSM is to enable faster start-up time after moderate standstills. HSM functionality can be extended to include the pre-heating option after longer standstills.
This paper investigates pre-heating of the steam turbine with an electrical THS. At the beginning, it covers general aspects of flexible fossil power plant operation and point out the advantages of HSM. Afterwards the technology of the trace heating system and its application on steam turbines will be explained. In the next step the transient pre-heating process is analyzed and optimized using FEA, CFD and analytic calculations including validation considerations. Therefor a heat transfer correlation for flexible transient operation of the HSM was developed. A typical large steam turbine with an output of up to 300MW was investigated. Finally the results are summarized and an outlook is given.
The results of heat transfer and conduction between and within turbine components are used to enable fast start-ups after long standstills or even outages with the benefit of minimal energy consumption. The solution is available for new apparatus as well as for the modernization of existing installations.
LDV Characterization of Unsteady Vaned Diffuser Flow in a Centrifugal Compressor
Authors: Gooding William J. , Fabian John C. , Key Nicole L. 
Published: November 2019

Abstract
Modern turbomachinery faces increased performance demands in terms of efficiency, compactness, and pressure-rise. Advancements in computational technology have allowed numerical methods to become the backbone of design development efforts. However, the unique complexities of centrifugal compressor flow-fields pose difficult computational problems. As such, advanced experimental methods must be used to obtain high-quality datasets to further inform, improve, and validate computational methods in complex flow regimes.
Recent experimental work on a high-speed centrifugal compressor has provided detailed, unsteady, three-component velocity data using Laser Doppler Velocimetry. A passage vortex is present and its nascent tied to the increased incidence at mid-span associated with impeller wake flow. This vortex begins in the hub-pressure side corner and grows to fill the passage and become temporally stable. The vortex development is unsteady in nature and the unsteady effects persist 40% downstream of the throat. Distinct jet and wake flow patterns from the impeller also do not agglomerate until 40% downstream of the throat. Additionally, the critical impact of the unsteady flow development on the time-averaged flow-field is explained.
Evaluation of the Numerical Modelling of a High Pressure Turbine Test Rig
Authors: Luquet David , Julienne Francois , Arntz Aurélien , Lippinois Eric 
Published: November 2019

Abstract
To improve the fuel efficiency demanded by airlines and regulations, the turbomachinery industry is required to steadily enhance engine performances and numerical prediction capabilities. One of the solutions is the lean burn combustor which dramatically reduces NOx levels compared to rich one. However, one drawback of this technology is its impact on the High-pressure turbine due to large swirl and reduced cooling airflow, inducing large spatial and temporal variations in the turbine inlet condition. This can drastically change the operation of the turbine and our ability to model it using standard practice, usually RANS computation. To investigate this combustor-turbine interaction, the European Commission-funded project FACTOR (Full Aerothermal Combustor-Turbine interactiOns Research) was launched several years ago. A test rig of a combustor simulator coupled with a 1.5 stage turbine was built at a DLR facility. An extensive test campaign comprising 5 holes probes and infrared imaging was performed. These produced an array of aerodynamic quantities at different points of interest along the machine axis. With this project reaching its term by the end of 2017, results have been disseminated to the partners. This allows a comparison of measurements with RANS modeling on this configuration. The present paper deals with this analysis using several RANS computations and the results of the test campaign. First, single row computation of the Nozzle Guide Vane and rotor blade were performed. To impose the boundary conditions, the experimental map were azimuthally averaged to obtain profiles of total temperature, total pressure and flow angles. Second, the impact of some geometrical features was investigated. This was done using the recent addition of unstructured mesh capability in the elsA solver. Finally, multi-stage computations, both steady (mixing plane) and unsteady (sliding mesh) give an insight on the relative accuracy of these interstage models. All these computations were then used to investigate the behavior of this particular turbine. In addition to classical analysis using profiles of averaged data, the loss sources were identified by computing the viscous and thermal entropy production. This paves the way for a better understanding of the possibilities and limitations of our simulation capabilities.
A Third-Generation Swirl-Venturi Lean Direct Injection Combustor With a Prefilming Pilot Injector
Authors: Tacina K. M. , Podboy D. P. , Dam B. , Lee F. P. 
Published: November 2019

Abstract
This paper presents experimental results for a low-NOx aero gas turbine combustor, in particular, a third-generation swirl-venturi lean direct injection (SV-LDI-3) combustor concept called V4. The purpose of testing was three-fold. First, to evaluate the combustor against the 80% NOx reduction goal set by NASA’s AATT project. Second, to compare V4 to a previous SV-LDI-3 combustor concept called V3, especially at low power conditions. Third, to examine the accuracy of a type of correlation equation frequently used by engine systems analysis groups to estimate NOx emissions. All three testing goals were met. For the first testing goal, with an estimated NOx reduction of 85%–90%, SV-LDI-3 V4 surpassed the AATT goal. For the second goal, however, V4 did not perform better than V3 at low power conditions. For the third goal, it was found that a major assumption of the correlation equations — a simple dependence on combustor inlet pressure — did not hold.
Static Stiffness Measurements for a Thrust Collar Used in an Integrally Geared Compressor
Authors: Kerr Thomas , Delgado Adolfo , Childs Dara 
Published: November 2019

Abstract
This paper presents a comparison of predicted and measured axial stiffness of an oil-lubricated thrust collar (TC) for use in an integrally geared compressor (IGC). The test rig used to measure the stiffness closely resembles a TC that would be used in a production IGC. Separate motors spin two shafts at predetermined spin speeds, and a pneumatic loader applies an axial load to the pinion shaft. The load is transmitted from the pinion shaft through the TC and onto the bull gear shaft. The relative deflection between the faces of the TC is measured as the axial load is increased. Tests were conducted at pinion spin speeds of 5, 7.5, and 10 krpm, and the axial load was varied from 75 to 2,600 N (1 to 32 bar specific load). A custom curve fit describes the load-deflection plot. The slope of the equation is the stiffness coefficient, kz. The measured kz values increase versus axial load, and decrease versus spin speed. Measured and predicted values agree in trend and magnitude. Predicted kz values slightly overestimate the measured results. The power loss from the lubricated area is measured from VFD power outputs. Power loss increases with spin speed and the measured power loss tends to be twice as high as predictions. These results are useful in validating the predictions made by Cable et. al.[1] The results are also useful to IGC original equipment manufacturers (OEMs) or end-users who desire to model their machines.
Effect of Annulus Flow Conditions on Turbine Rim Seal Ingestion
Authors: Palermo Donato M. , Gao Feng , Chew John W. , Beard Paul F. 
Published: November 2019

Abstract
A systematic study of sealing performance for a chute style turbine rim seal using URANS methods is reported. This extends previous studies from a configuration without external flow in the main annulus to cases with a circumferentially uniform axial flow and vane generated swirling annulus flow (but without rotor blades). The study includes variation of the mean seal-to-rotor velocity ratio, main annulus-to-rotor velocity ratio, and seal clearance. The effects on the unsteady flow structures and the degree of main annulus flow ingestion into the rim seal cavity are examined. Sealing effectiveness is quantified by modeling a passive scalar, and the timescales for the convergence of this solution are considered. It has been found that intrinsic flow unsteadiness occurs in most cases, with the presence of vanes and external flow modifying, the associated flow structures and frequencies. Some sensitivities to the annulus flow conditions are identified. The circumferential pressure asymmetry generated by the vanes has a clear influence on the flow structure but does not lead to higher ingestion rates than the other conditions studied.
A Numerical Study on the Effect of Hole Inclination Angle With Imperfection on Film Cooling Effectiveness
Authors: Rezzag Taha , Jubran Bassam A. 
Published: November 2019

Abstract
The present study numerically evaluates the influence of hole inclination angle with a hole imperfection on film cooling performance. Here, the hole imperfection due to laser percussion drilling is modelled as a half torus. Three hole inclination angles were investigated: 35°, 45° and 55°. Furthermore, every case was evaluated at three blowing ratios: 0.45, 0.90 and 1.25. Each case is compared to a baseline case where the hole imperfection is absent. The results indicate that the hole inclination angle has a strong influence on the film effectiveness performance when a hole imperfection is present. Centerline effectiveness plots reveal a maximum effectiveness deterioration of 89% for a blowing ratio of 0.90 in the vicinity of the hole exit. Dimensionless temperature contours show that the jet produced in the presence of an imperfection is much more compact causing the counter rotating vortex pair to be closer to each other. This enhances the jet to lift off from the plate.
Computational Analysis of the Equalization Behavior of Thrust Bearings With Regular and Modified Leveling Plates
Authors: Gokaltun Seckin , DeCamillo Scan 
Published: November 2019

Abstract
In this work, a Finite Element Analysis (FEA) model has been developed that represents the interaction between the thrust bearing components under the influence of a misaligned rotor. The FEA model represents the contact between bearing components such as the pads and leveling plates and calculates the forces and moments created, as well as capturing the elastic deformation caused by the load imposed by the runner. The current analysis excludes the existence of the fluid film between the runner and the pads; therefore, the loads and misalignments created represent a static loading condition. It was observed that the bearing equalization system is still functional for design modification cases such as material removal at the outer diameter of the lower leveling plates, while the equalization performance is reduced slightly.
Reducing Blade Force Response in a Radial Turbine by Means of Jet Injection
Authors: Netzhammer Stephan , Vogt Damian M. , Kraetschmer Stephan , Leweux Johannes , Blackburne Jennifer 
Published: November 2019

Abstract
Radial turbines consisting of a spiral volute inlet casing, such as those found in turbochargers, are subject to excitations caused by the inlet flow. In the absence of inlet guide vanes, the asymmetries from the volute are accentuated and lead to Low Engine Order (LEO) excitations. These excitations can be particularly troublesome as they are likely to resonate with the first bending mode (M1) at high rotational speeds, causing large vibration displacement amplitudes which will result in High Cycle Fatigue (HCF). It is therefore imperative to ensure these vibration amplitudes are low enough to make certain blade failure will not occur.
This paper deals with the possibility of actively influencing the excitation pressure pattern on the blades such that the amplitude and phase of the forcing is affected. This active influence is through the use of an air jet injection at the tip of the turbine blade and has the potential to substantially reduce the blade vibrations caused by the LEO excitations. This theory of using air jets to alter the blade vibration amplitude is investigated in this paper both experimentally, using standard turbine housing equipped with a rotatable device with a single jet nozzle, and numerically, using Computation Fluid Dynamics (CFD) software ANSYS CFX.
The tests yielded positive results indicating that a single air injection was able to significantly decrease, as well as increase, the blade vibration amplitude. At certain jet injection locations, decreases in blade vibration amplitude of 70% were measured which was backed up by numerical results. To numerically calculate these differences in the vibration amplitude, the generalized force approach was used successfully. The positive results obtained from this study show real potential for this method to become a useful tool in keeping blade vibration to a safe level and avoiding failures in turbomachines.
CH Kinetics Measurements and Their Importance for Modeling Prompt NOx Formation in Gas Turbines
Authors: Cooper Sean P. , Mulvihill Clayton R. , Mathieu Olivier , Petersen Eric L. , Crofton Mark W. , Lam King Y. 
Published: November 2019

Abstract
Recent work by the authors and others has uncovered the need for further chemical kinetic-related modeling and experiments, specifically for NOx kinetics at engine conditions. In particular, data on CH formation at realistic combustion conditions are needed for further refinement of the prompt-NOx kinetics. To this end, a series of shock-tube experiments to obtain CH concentration time histories at elevated temperatures was performed behind reflected shock waves at The Aerospace Corporation using a tuneable laser. This Ti-Sapphire laser was operated in the near infrared at about 854 nm; blue light at 426.9 nm was obtained using an external, frequency-doubling crystal. The resulting light was used in a differential absorption setup with common-mode rejection to measure CH time histories. New measurements in CH4-C2H6-O2 mixtures highly diluted in argon were performed at temperatures between 1890 K and 2719 K. These new data are compared to several modern, detailed chemical kinetics mechanisms with updated NOx submechanisms. Sensitivity and rate of production analyses at the shock-tube conditions along with a gas turbine model are used to elucidate the current state of affairs in CH prediction by the literature models and its effect on NOx production, particularly through the prompt mechanism. A brief discussion of the chemical kinetics for an important reaction in the production of CH is also presented to emphasize the need for further study and refinement of reactions leading to CH production.
Dynamics of a Rod-Fastened Rotor Considering the Bolt Loosening Effect
Authors: Li Pu , Yuan Qi , Zhao Bingxi , Gao Jin 
Published: November 2019

Abstract
Rod-fastened rotors are widely applied in heavy duty gas turbines and aircraft engines due to a good stiffness-to-weight behavior compared to conventional forged rotors. In order to achieve a continuous and stable power output, it is critical to guarantee the mechanical integrity. Therefore, the clamping force is of great importance which influences the distribution of the contact pressure. In an extreme condition, the bolt loosening resulting in an additional bending moment entails a different dynamic response. In this paper, the dynamics of a rod-fastened rotor subjected to the unbalance force, combined loads from the residual bow as well as the bolt loosening will be analyzed. First of all, an accurate rod-fastened rotor model is generated incorporating 1D beam element and zero-length joint element. Next, the mode superposition method is applied to derive the equations of motion and the analytical solution of the rod-fastened rotor will be achieved. Furthermore, experimental results are used to verify the simulations. It has demonstrated that the rod loosening yields a remarkably different behavior compared to the normal rotor after balancing. The dynamic response is also closely dependent on the unbalance as well as the relative phase angle between the location of unbalance and rod loosening. This paper provides a fundamental insight into the steady response of the rod-fastened rotor and may be used for fault identification as well as balancing of combined rotors.
Numerical Study on Flow and Heat Transfer Characteristics of Discrete Film Cooling Holes of the Sinusoidal Longitudinal Corrugated Heat Liner
Authors: Xu Zhi-peng , Zhu Hui-ren , Wang Ya-zhou , Bian Xinyu 
Published: November 2019

Abstract
To understand film cooling flow fields and heat transfer characteristics of the longitudinal corrugated surface on afterburner heat liner, the numerical simulation was performed in approximate actual boundary conditions. The single hole and full film holes on the corrugated surface were investigated under different boundary conditions to study the heat transfer and discharge coefficient. The adverse pressure gradient on the leeward results in spanwise expansion of the airflow, while the favorable pressure gradient on the windward keeps the shape of the jet constant. The different hole spacing and hole row spacing in different positions of the corrugated surface should be considered due to the film covering characteristics. The film cooling holes at the same height on the leeward and windward share the similar laterally average effectiveness. The flow rate and discharge coefficient increase from crest to trough. Cross-flow has a negative influence on the discharge coefficient especially the inlet cross-flow. The cross-flow and discharge coefficient can be correlated with each other by a logarithmic function. The jet discharge coefficient on the windward surface is higher than that on the leeward surface, which is contrary to previous cognition. The reason is that the jet blocking causes the downstream pressure zone to advance, which counteracts and enhanced the siphon effect on the leeward and windward side respectively. As the inlet pressure of coolant increases, the film cooling effectiveness on the windward side is greatly improved in full film condition. However, it changes little on the leeward side.