bluuebunny/crossref_metadata_2025 huggingface dataset:
Rotor System Mathematical Model Substructure-Based Reduction and Updating Using Experimental Modal Analysis
Authors: Semenov Sergey , Nikhamkin Mikhail , Sazhenkov Nikolai
Published: August 2018

Modeling of rotor dynamics is one of the most important parts of gas turbine engine creation process. But the need to understand the system response to design predictable, low maintenance, cost-effective, and optimal systems has driven rotor dynamics to large-order complex rotor system models. These models contain more intricate geometric complexities, bearings, seals, and attached components such as disks, blades, fans, and couplings. All this makes vibration processes more complicated and so they require more calculation resources. That makes such iterative procedures as model updating and optimization difficult.

Possible solution for this problem is substructuring. Partitioning of the model to substructures opens up a possibility to verify and update parts of the model independently using modern modal analysis experimental techniques like 3D scanning vibrometry. And then they can be condensed using reduction methods to simplify the whole model.

This work demonstrates the possible way of rotor system model updating based on experimental modal analysis via 3D scanning vibrometry and reduction using CMS method. Demonstration of the method is made on a special rotor test rig. The quality of updating and reduction is evaluated by comparing of critical speeds obtained numerically and experimentally. The comparison shows that proposed method is adequate for rotor system model creation and simplification but for constructions with a lot of connections updating procedure should be improved.
Effectiveness Testing of an Inverse Method for Balancing Nonlinear Rotordynamic Systems
Authors: Torres Cedillo Sergio G. , Bonello Philip , Al-Ghazal Ghaith Ghanim , Cortés Pérez Jacinto , Reyes Solis Alberto
Published: August 2018

Modern aero-engine structures typically have at least two nested rotors mounted within a flexible casing via squeeze-film damper (SFD) bearings. The inaccessibility of the HP rotor under operational conditions motivates the use of a non-invasive inverse problem procedure for identifying the unbalance. Such an inverse problem requires prior knowledge of the structure and measurements of the vibrations at the casing. Recent work by the authors reported a non-invasive inverse method for the balancing of rotordynamic systems with nonlinear squeeze-film damper (SFD) bearings, which overcomes several limitations of earlier works. However, it was not applied to a common practical configuration wherein the HP rotor is mounted on the casing via just one weak linear connection (retainer spring), with the other connections being highly nonlinear SFDs. The analysis of the present paper considers such a system. It explores the influence of the condition number and how it is affected as the number of sensors and/or measurement speeds is increased. The results show that increasing the number of measurement speeds has a far more significant impact on the conditioning of the problem than increasing the number of sensors. The balancing effectiveness is reasonably good under practical noise level conditions, but significantly lower than obtained for the previously considered simpler configurations.
Rotating Annulus Component Performance Characterisation Based on CFD Analyses
Authors: Yuan Youming , Hunt David
Published: August 2018

FloMASTER is a 1-D thermo-fluids system simulation tool and its component models depend on the characterisation data of the component performance. Such performance data is mainly based on data banks established from extensive tests exemplified by the books like “Internal Flow” by Miller [1] and “Handbook of Hydraulic Resistance” by Idelchik [2].

One of the key components of the gas turbine secondary air system is the rotating annulus. However, reliable data and correlations for performance characteristics like pressure loss coefficient, torque coefficient, windage and heat transfer for this component are rare and non-existent in the open literature for the case of both walls rotating simultaneously, which is becoming more common in today’s multi-spool military aero engines.

To overcome this challenge of lack of reliable performance data and correlations, in this paper the Mentor Graphics 3D CFD tool “FloEFD” is used to model both inner wall rotating and outer wall rotating annulus flow, and to verify the 3D CFD results of performance data in terms of pressure loss coefficient and torque coefficient versus some published test data in the open literature. It is shown that the CFD gives results on pressure loss and torque coefficients that are in good agreement with test data based correlations used in FloMASTER. This demonstrates that 3D CFD can be used as a powerful tool for verifying the existing 1D model, extending the 1D model performance data range and generating new performance data for developing new components where such data is not available from open literature. A future project is to extend this approach to provide performance data for rotating annuli with both walls rotating. Such data will form the basis for developing a new component model for a rotating annulus with both walls rotating.
Reduction of Heat Transfer on the Endwall in the Upstream Junction Region of a Symmetric Airfoil With Vortex Generator Pair
Authors: Hussain Safeer , Liu Jian , Wang Lei , Sundén Bengt
Published: August 2018

Heat transfer on the endwall upstream of the junction of the stator vane/rotor blade with the hub becomes very high due to the vortices generated as a result of an adverse pressure gradient. Control of this high heat transfer is very vital for safe operation of gas turbines. In the present experimental study, a pair of vortex generators is employed to reduce the high heat transfer on the endwall close to the junction region. A pair of winglet vortex generators upstream of a symmetric airfoil have been employed. The steady state liquid crystal thermographic method is used to measure the surface temperature of the endwall. Different cases are studies depending on various lateral gaps of the vortex generator pair while keeping the yaw angle and streamwise position relative to the airfoil constant. It is found from the experiments that all positions of the vortex generators reduce the heat transfer on the junction region of the endwall compared to the base case. The level of reduction and local distribution of heat transfer is dependent on the position of vortex generators. The aerodynamic performance of a stator vane/rotor blade is the main objective in gas turbines, therefore the pressure drop is also measured experimentally and results show that pressure loss is recovered with the installation of vortex generator compared to the airfoil without the vortex generator.
Effect of Compressor Inlet Pressure on Cycle Performance for a Supercritical Carbon Dioxide Brayton Cycle
Authors: Clementoni Eric M. , Cox Timothy L.
Published: August 2018

Supercritical carbon dioxide (sCO2) Brayton power cycles take advantage of the high density of CO2 near the critical point to reduce compressor power and increase cycle efficiency. However, thermophysical properties of CO2 vary drastically near the critical point. Concerns of large property variations and liquid formation within the compressor can result in sCO2 cycle designers selecting compressor inlet operating conditions substantially above the critical point, thereby reducing cycle performance. The Naval Nuclear Laboratory has built and tested the 100 kWe Integrated System Test (IST) to demonstrate the ability to operate and control an sCO2 Brayton power cycle over a wide range of conditions. Since the purpose of the IST is focused on controllability, the design compressor inlet conditions were selected to be 8.2°F (4.6°C) and 270 psi (18.4 bar) above the critical point to reduce the effect of small variations in compressor inlet temperature and pressure on density. This paper evaluates the effect of design compressor inlet pressure on cycle efficiency for a simple recuperated Brayton cycle and the performance of an operating Brayton power cycle with a fixed design over a range of compressor inlet pressures.
Automated Aerodynamic Optimization of an Aggressive S-Shaped Intermediate Compressor Duct
Authors: Stürzebecher T. , Goinis G. , Voss C. , Sahota H. , Groth P. , Hammer S.
Published: August 2018

As bypass-ratio in modern aero engines is continuously increasing over the last decades, the radial offset between low pressure compressor (LPC) and high pressure compressor (HPC), which needs to be overcome by the connecting s-shaped intermediate compressor duct (ICD), is getting higher. Due to performance and weight saving aspects the design of shorter and therefore more aggressive ducts has become an important research topic. In this paper an already aggressive design (with respect to current aero engines) of an ICD with integrated outlet guide vane (OGV) is used as a baseline for an aerodynamic optimization. The aim is to shorten the duct even further while maintaining it separation free. The optimization is broken down into two steps. In the first optimization-step the baseline design is shortened to a feasible extent while keeping weak aerodynamic restrictions. The resulting highly aggressive duct (intermediate design), which is shortened by 19 % in axial length with respect to the baseline, shows separation tendencies of low momentum fluid in the strut/hub region. For the second step, the length of the optimized duct design is frozen. By implementing new design features in the process of the optimizer, this optimization-step aims to eliminate separation and to reduce separation tendencies caused by the aggressive shortening. In particular, these features are: a nonaxisymmetric endwall contouring and parametrization of the strut and the OGV to allow for changes in lift and turning in both blade designs. By comparison of the three designs: Baseline, intermediate (separating flow) and final design, it can be shown, that it is possible to decrease length of the already aggressive baseline design even further, when adding a nonaxisymmetric endwall contouring and changes in blade shape of the strut and OGV. Flow separation can be eliminated while losses are kept low. With a more aggressive and therefore shorter duct the engine length and weight can be reduced. This in turn leads to lighter aircrafts, less fuel consumption and lower CO2 and NOx emissions.
Numerical Investigations of an Axial Exhaust Diffuser Coupling the Last Stage of a Generic Gas Turbine
Authors: Mihailowitsch Marius , Schatz Markus , Vogt Damian M.
Published: August 2018

It is well known that the last stage of a turbine and the subsequent diffuser should be viewed at and designed as a coupled system rather than as single standalone components. The turbine outlet flow imposes the inlet conditions to the diffuser, whereas the recovered dynamic pressure in the diffuser directly controls the turbine back pressure.

With changing operating point, the turbine outflow can vary significantly. This results consequently in large variations of the diffuser performance. A major role in the coupled system of turbine and diffuser can be attributed to the tip leakage flow. While it is desirable to minimize the tip leakage with regard to the turbine, a higher leakage mass flow can often be beneficial for the diffuser performance. As there is currently a trend towards aggressive and hence shorter diffusers which are particularly prone to separation, the question arises where the optimum for this tradeoff problem lies.

To investigate the performance in the coupled turbine/diffuser system, a generic last stage with shrouded rotor and axial exhaust diffuser have been designed. The components are representative for heavy duty stationary gas turbine applications. Results are presented for three different operating points representing part-load, design-load and over-load condition. Three different seal gap widths are taken into account to control the leakage flow. The results indicate that an operating point dependent optimum gap width can be found for the coupled system efficiency whereas the maximimum turbine performance is always achieved with a minimum gap width.
Source Term Based Modeling of Rotating Cavitation in Turbopumps
Authors: Vermes A. G. , Lettieri C.
Published: August 2018

The recent growth of private options in launch vehicles has substantially raised price competition in the space launch market. This has increased the need to deliver reliable launch vehicles at reduced engine development cost, and has led to increased industrial interest in reduced order models.

Large-scale liquid rocket engines require high-speed turbopumps to inject cryogenic propellants into the combustion chamber. These pumps can experience cavitation instabilities even when operating near design conditions. Of particular concern is rotating cavitation, which is characterized by an asymmetric cavity rotating at the pump inlet, which can cause severe vibration, breaking of the pump and loss of the mission. Despite much work in the field, there are limited guidelines to avoid rotating cavitation during design and its occurrence is often assessed through costly experimental testing.

This paper presents a source term based model for stability assessment of rocket engine turbopumps. The approach utilizes mass and momentum source terms to model cavities and hydrodynamic blockage in inviscid, single-phase numerical calculations, reducing the computational cost of the calculations by an order of magnitude compared to traditional numerical methods. Comparison of the results from the model with experiments and high-fidelity calculations indicates agreement of the head coefficient and cavity blockage within 0.26% and 5% respectively. The computations capture rotating cavitation in a 2D inducer at the expected flow coefficient and cavitation number. The mechanism of formation and propagation of the instability is correctly reproduced.
Performance Assessment of an Integrated Gasification Combined Cycle Under Flexible Operation
Authors: Ravelli S. , Perdichizzi A.
Published: August 2018

In this paper a simulation tool (Thermoflex®) has been setup to model an entire Integrated Gasification Combined Cycle (IGCC) on the basis of the report entitled “Cost and Performance of PC and IGCC Plants for a Range of Carbon dioxide Capture” by DOE/NETL [1]. The investigated layout has no water-gas-shift (WGS) reactor and does not allow for any CO2 capture. Two gasification islands are included, each of which consists of Air Separation Unit (ASU), GEE radiant-only gasifier, quench and syngas scrubber as well as syngas cleanup. Two advanced GE’s F-class gas turbines (2 × 232 MW), coupled with two heat recovery steam generators and one steam turbine (276 MW) constitute the power block.

In the IGCC simulation, the base model of the GE 7F.05 gas turbine has been adapted to burn syngas. Mass and energy balances were carefully computed on design condition to validate the proposed modelling procedure against the IGCC performance data contained in the above mentioned report: the net power output of 622 MW was underestimated by about 5% whereas the net electric efficiency was slightly overpredicted. The off-design behavior of the syngas turbine was then simulated as dependent on ambient temperature and partial load, in preparation for modelling flexible operation of the whole power plant. The variation in IGCC net efficiency and power output was assessed in a load following operational strategy, thus reducing the load factor and varying the number and slope of ramps in a typical day. The IGCC net efficiency goes down from 42.5% to 32.8% when the load is reduced from 100% to 40% of the design rate.
Flow Analysis of an Operational Natural Gas Turbo Expander
Authors: Huo Changjiang , Sun Jinju , Sun Shan , Song Peng , Zhao Guizheng , Pan Ben
Published: August 2018

The paper focuses on an operational gas expander being used in a natural gas plant for over 10 years, whose recent realtime monitoring shows that the impeller back-side gap pressure is excessively low. To ensure the safe operation, an insight into the complex internal flow of the expander is demanded. The reverse engineering is firstly conducted to reconstruct the flow passage data from the used impeller and nozzle. The physical model includes the main flow domain components (nozzle ring, impeller, and diffuser duct), and the leakages and seal chambers (the impeller front and back-side toothed gaps, shaft seal chamber, and seal gas inlet). Two-phase flow simulation is conducted with the homogeneous multiphase mixture equilibrium model, which is used to allow for the phase change in terms of condensation. Flow analysis is performed based on the obtained numerical results. At the concerned operating point, the expander outlet wetness fraction is about 16.0%, and evident condensation is encountered in the main flow domain and its back-side gap around the pressure tap, which is thought to be responsible for the abnormal pressure reading. The condensed small droplets may grow to block the pressure tap leading to a lower gauge reading. At the operating speed and different flow rates, the flow simulation is conducted for the expander: condensation in the expander is encountered locally at all flow rates and the overall isentropic efficiency closely associated with the overall wetness fraction.
Steady-State Characteristics of a Dual-Rotor System With Intershaft Bearing Subjected to Mass Unbalance and Base Motions
Authors: Chen Xi , Liao Mingfu
Published: August 2018

A dual-rotor system with an intershaft bearing subjected to mass unbalance and base motions is established. Using Lagrange’s principle, equations of motion for dual-rotor system relative to moving base are derived. Rotary inertia, gyroscopic inertia, transverse shear deformation, mass unbalance, and six components of deterministic base motions are taken into account. Using state-space vector, steady-state characteristics of dual-rotor system are analyzed through dual-rotor critical speed map, mode shapes, unbalance responses considering base rotations, frequency responses due to base motions, and shaft orbits.

The results show that base translations just add external force vectors, while base rotations bring on parametric system matrices and additional force vectors. Base rotations not only change natural frequencies of dual-rotor system, but also break the symmetry of dynamic characteristics in the case of base lateral rotation. Excited by base harmonic translation, resonant frequencies correspond to whirl frequencies. The orbit remains circular under base axial rotation, while it becomes elliptical with a static offset under lateral rotation and then a complicated curve due to harmonic translation. When harmonic frequency of base translation gets close to dual-rotor excitation frequencies, obvious beat vibration appears. Overrall, this flexible approach can ensure calculation accuracy with high efficiency and good expandability.
Influence of Rotor-Stator Interaction and Reflecting Boundary Conditions on Compressor Forced Response
Authors: Mao Zhiping , Hegde Shreyas , Pan Tianyu , Kielb Robert E. , Zori Laith , Campregher Rubens
Published: August 2018

This paper focuses on the rotor forced response behavior in a 3.5-stage compressor rig. The aim is to provide an accurate prediction of forced response with the less computational effort. Previous research indicates that by reducing the computation domain from 7-row to a 3-row stator-rotor-stator (S1-R2-S2) configuration, the forcing function is over-predicted by 60%. To address this over prediction, an investigation of boundary conditions and a study with additional rows are conducted. The influence of reflecting boundary conditions on the blade modal force is studied by preventing wave reflection. Additionally, a 5-row simulation is studied to take an extra source of excitation force, the IGV row with the same blade count as the other stators, into consideration. Three conclusions were drawn from this study: 1) boundary reflection has a significant influence on unsteady simulation and the modal force, thus should be avoided by using mesh treatment up and down stream; 2) the IGV wake contributes to the forcing function and cannot be ignored; 3) the clocking feature of IGV, S1, and S2 leads to a transfer of energy from 1st harmonic to other higher harmonics. This research provides a guidance of forced response modeling and can be employed for industrial forced response analysis.
Modeling of the Cavity Response to Rapid Transient Considering the Effect of Heat Transfer
Authors: Ding Shuiting , Yu Hang , Qiu Tian , Liu Chuankai
Published: August 2018

The internal air system, as one of the important subsystems of the aeroengine, is used to cooling and sealing, and plays a vital role in the safe operation of the engine. Especially in rapid transients, the complex dynamic response in air system may impose hazardous transition state loads on engine. Cavity is a component with pretty evident characteristics of transient in the air system due to the storage and release effects on the air. The flow and heat transfer characteristics of cavity should be made clear to precisely quantify the performance of the air system. The traditional study on cavity is based on the adiabatic assumption. However, the assumption is applicable to the transient of millisecond time scales physical phenomena in the air system, which is not usually common. Generally, the actual transition process is not instantaneous. Great discrepancies exist in the process of transition predicted by the adiabatic hypothesis compared with the practical process. The objective of this work is to propose a feasible method to solve the heat transfer issue throughout the transient process, which has not been settled by a proper method before, and develop a model for simulating the transient responses of the cavity with consideration of the heat transfer effect on the basis of the method. The model can predict transient responses under different thermal boundary conditions. Experiments have been developed for investigation of the charging process of the cavity. The thermal boundary can be controlled in the experiment, and the pressure and temperature responses of the cavity under different thermal boundary conditions have been analyzed. The non-dimensional numbers related to heat transfer characteristics were deduced by dimensional analysis, and the empirical formula of characteristics was proposed based on the experimental results. The non-adiabatic low-dimensional transient model of the cavity was established based on the heat transfer characteristics correlation. Results of transient responses calculated by non-adiabatic model were compared with the experimental data. It is found that both the transient responses of pressure and temperature agree well, with the maximum relative errors less than 2%. By comparison, the relative errors of pressure and temperature calculated by adiabatic model are about 8% and 12%, respectively. Meanwhile, the tendency of temperature response deviates from the actual process. Thus, the modeling method proposed is feasible and high-precision. The present work provides a technical method for establishing a low-dimensional model to describe the transient responses of the cavity with high accuracy, and supports the component-level modeling of the transient air system.
Turbine Vane Endwall Film Cooling Comparison From Five Film-Hole Design Patterns and Three Upstream Leakage Injection Angles
Authors: Shiau Chao-Cheng , Sahin Izzet , Wang Nian , Han Je-Chin , Xu Hongzhou , Fox Michael
Published: August 2018

The effects of upstream leakage injection angle on film cooling effectiveness of a turbine vane endwall with various endwall film-hole designs were examined by applying PSP measurement technique. As the leakage flow from the slot between the combustor and the turbine vane is not considered an active source to protect the vane endwall in certain engine designs, discrete cylindrical holes are implemented near the slot to create additional controllable upstream leakage flow to cool the vane endwall. Three potential leakage injection angles were studied: 30°, 40°, and 50°. To explore the optimum endwall cooling design, five different film-hole patterns were tested: axial row, cross row, cluster, mid-chord row, and downstream row. Experiments were conducted in a four-passage linear cascade facility in a blowdown wind tunnel at the exit isentropic Mach number of 0.5 corresponding to inlet Reynolds number of 380,000 based on turbine vane axial chord length. A freestream turbulence intensity of 19% with an integral length scale of 1.7 cm was generated at the cascade inlet plane. Detailed film cooling effectiveness for each design was analyzed and compared at the design operation conditions (coolant mass flow ratio 1% and density ratio 1.5). The results are presented in terms of high-fidelity film effectiveness contours and laterally (spanwise) averaged effectiveness. This paper will provide the gas turbine designers valuable information on how to select the best endwall cooling pattern with minimum cooling air consumption over a range of upstream leakage injection angle.
Fretting Fatigue and Wear of Ti-6Al-4V With HVOF Sprayed Stellite Coating on Contact Surfaces of Shrouds and Stubs of Turbine Blades
Authors: Asai Kunio , Ishizawa Shuichi , Isobe Nobuhiro
Published: August 2018

High velocity oxygen fuel (HVOF) sprayed stellite coating is often adopted on contact surfaces of the shrouds and stubs of titanium turbine blades, in order to increase fretting fatigue strength and reduce fretting wear. To confirm the effectiveness of the sprayed stellite coating, we conducted friction-type fretting tests originally developed to simulate the load condition of shrouds and stubs, vibratory force was carried only by friction force. We also investigated the fretting fatigue mechanism of coated materials by observing non-propagating cracks in the tested specimens and analyzed crack propagation behavior at the interface using fracture mechanics.

The fretting fatigue tests confirmed that the sprayed stellite coating could double the fretting fatigue strength of Ti-6A1-4V. The fretting fatigue mechanism of Ti-6A1-4V with a sprayed stellite coating was revealed as follows: Final fracture was led by a newly initiated micro-crack at the interface as cracks initiated on the coating surface did not continuously propagate into the substrate but mainly propagated along the interface. The micro-crack propagation at the substrate depends on the length of interface crack. The longer interface crack delays micro-crack propagation to the substrate because the lines of force are less concentrated at the crack tip. Hence, the interface crack makes the fretting fatigue strength of coated Ti-6A1-4V higher than that of uncoated specimens. This finding was supported by the cross-sectional observations of non-propagating cracks in the tested specimens, and by FE analysis which revealed that ΔK of the substrate crack initiated at the interface decreases with an increase in delaminated crack length. Ti-6A1-4V with a sprayed stellite coating offers better wear resistance than uncoated Ti-6A1-4V because the coating’s friction coefficient is lower than that of Ti-6Al-4V, although the wear rates of coated and uncoated materials against the consumption energy per cycle were almost the same.
Aeroelastic Analysis of Last Stage LP Steam Turbine Rotor Blades With Exhaust Hood for Various Non-Nominal Regimes
Authors: Rzadkowski Romuald , Gnesin Vitaly , Kolodyazhnaya Lubov , Szczepanik Ryszard
Published: August 2018

Presented here are the numerical calculations of the 3D transonic flow of an ideal gas through an LP steam turbine last stage with exhaust hood, taking into account blade oscillations. The approach is based on a solution to the coupled aerodynamic-structure problem for 3D flow through a turbine stage using the partially integrated method. The blade oscillations and loads acting on the blades are a part of the solution. An ideal gas flow through the stator and moving rotor blades with periodicity on the whole annulus is described by unsteady Euler conservation equations, integrated with the Godunov-Kolgan explicit monotonous finite-volume difference scheme and a moving hybrid H-H rotor blade grid. The structural analysis uses the modal approach and a 3D finite element model of a blade. The proposed algorithm allows for the calculation of turbine stages with an arbitrary pitch ratio of stator and rotor blades, taking into account unsteady-load induced blade oscillations. The pressure distribution behind the rotor blades was non-uniform on account of the exhaust hood. As a result of the fluid-structure interaction and exhaust hood induced nonsymmetrical pressure distribution behind the rotor blades, the first blade mode was no longer bending but bending-torsion.
Jet-Oscillation-Induced Combustion Dynamics in a Multi-Nozzle FLOX® Combustor
Authors: Yin Zhiyao , Kutne Peter , Boxx Isaac , Meier Wolfgang
Published: August 2018

A 12-nozzle FLOX® combustor is used to generate a full-premixed methane-air flame at ϕ = 0.86 at atmospheric pressure. Combustion stability is examined using 5-kHz simultaneous stereo Planar Image Velocimetry (PIV), OH Planar Laser-induced Fluorescence (OH PLIF) and OH chemiluminescence imaging. Proper Orthogonal Decomposition (POD) of the PIV results from various measurement planes reveals that slow jet oscillations with a characteristic Strouhal number of 0.012 are the dominant fluctuations in the flow field. Jet impingement on and detachment from the walls during jet oscillations are shown to cause the liftoff heights of the flames to increase and decrease. Such changes in flame lift-off heights are also primarily asymmetric among geometrically-symmetric flame pairs. In addition, direct flame-flame interactions are observed as jets collide during oscillations. Dynamic Mode Decomposition (DMD) of the same flow fields is shown able to capture not only the same low-frequency jet-oscillation mode, but also a series of modes spanning the whole resolvable spectrum, which are potential origins of higher-frequency peaks observed in the power spectra of integrated OH chemiluminescence signals.
Numerical Investigation of the Compressible Flow Through a Turbine Center Frame Duct
Authors: Chen Li-Wei , Wakelam Christian , Ong Jonathan , Peters Andreas , Milli Andrea , Michelassi Vittorio
Published: August 2018

Numerical investigation of the compressible flow in the Turbine Center Frame (TCF) duct was carried out using a Reynolds-averaged Navier-Stokes (RANS) method, and a Hybrid RANS/Large Eddy Simulation (HLES) method, i.e. Stress-Blended Eddy Simulation (SBES).

The reference Reynolds number based on the TCF inlet condition is 530,000, and the inlet Mach number is 0.41. It is found that the boundary layer flow behavior is very sensitive to the incoming turbulence characteristics, so the upstream grid used to generate turbulence in the experiment is also included in the computational domain.

Results have been validated carefully against experimental data, in terms of static pressure distribution on hub and casing walls, total pressure and Mach number profiles on the TCF measurement planes, as well as over-all pressure loss coefficient. Further, various fundamental mechanisms dictating the intricate flow phenomena, including concave and convex curvature effects, interactions between inlet turbulent structures and boundary layer, and turbulent kinetic energy budget, have been studied systematically.

The current study is to evaluate the performance of HLES method for TCF flows and develop a further understanding of unsteady flow physics in the TCF duct. The results obtained in this work provide physical insight into the mechanisms relevant to the turbine intercase or TCF duct flows subjected to complex inlet disturbances.
Influence of Scaling Parameters and Gas Properties on Overall Effectiveness on a Leading Edge Showerhead
Authors: Wiese Connor J. , Bryant Carol E. , Rutledge James L. , Polanka Marc D.
Published: August 2018

Testing new turbine cooling schemes at engine conditions becomes increasingly cost prohibitive as the desired gas-path temperatures increase. As a result, the turbine component is simulated in a laboratory with a large-scale model that is sized and constructed out of a selected material so that the Biot number is matched between the laboratory and engine conditions. Furthermore, the experimental temperatures are lower, so the surface temperature that the metal component would experience in the engine is scaled via the overall cooling effectiveness, ϕ.

Properly measuring ϕ requires that the relevant flow physics must be matched, thus the relevant Reynolds numbers be matched-both those of the freestream and the coolant, as well as the other scaling parameters, such as the mass flux, momentum flux, and velocity ratios. However, if the coolant-to-freestream density ratio does not match that of the engine condition, the mass flux, momentum flux, coolant and freestream Reynolds numbers, and coolant-to-freestream velocity ratios cannot be matched simultaneously to the engine condition. Furthermore, the coolant thermal transfer properties are unaccounted for in these parameters, despite their large influence on the resultant overall effectiveness. While a good deal of research has focused on the effects of the coolant-to-freestream density ratio, this study specifically examines the influence of other thermodynamic properties, in particular the specific heat, which differ substantially between experimental and engine conditions. This study demonstrates the influence of various coolant properties on the overall effectiveness distribution on a leading edge by selectively matching M, I, and ACR with air, argon and carbon dioxide coolants.
Steam Flow and Heat Transfer in the Intermediate Pressure Cylinder of the Ultra-Supercritical Steam Turbine
Authors: Sun Chong , Zhou Daiwei , Zhu Xiaocheng , Du Zhaohui
Published: August 2018

The cooling protection of the hot end is the key technique for ultra-supercritical steam turbine. Tangential direction cooling chamber has a simple form and stable cooling effectiveness. The influence of inlet Mach number, turbulent Prandtl number, rotational speed, and inlet turbulence intensity on cooling effect of the structure in ideal air model have been made by previous work. The cooling mechanism and the flow characteristic in the ideal air chamber were investigated.

In this paper, the focus of the study is to investigate the flow and heat transfer characteristics of the tangential direction cooling chamber in the real steam model. The cooling chamber coupled with the whole steel shaft are simulated. Different boundary condition are compared. The heat transfer coefficients of the hub are acquired at some different rotational speeds and different hub conditions. The distribution of heat transfer coefficients and wall temperature are mainly affected by the viscous force and the velocity gradient near the hub.
Influences of Tip Leakage Flows Discharged From Main and Splitter Blades on Flow Field in Transonic Centrifugal Compressor Stage
Authors: Kaneko Masanao , Tsujita Hoshio
Published: August 2018

A transonic centrifugal compressor impeller is generally composed of the main and the splitter blades which are different in chord length. As a result, the tip leakage flows from the main and the splitter blades interact with each other and then complicate the flow field in the compressor. In this study, in order to clarify the individual influences of these leakage flows on the flow field in the transonic centrifugal compressor stage at near-choke to near-stall condition, the flows in the compressor at four conditions prescribed by the presence and the absence of the tip clearances were analyzed numerically. The computed results clarified the following noticeable phenomena. The tip clearance of the main blade induces the tip leakage vortex from the leading edge of the main blade. This vortex decreases the blade loading of the main blade to the negative value by the increase of the flow acceleration along the suction surface of the splitter blade, and consequently induces the tip leakage vortex caused by the negative blade loading of the main blade at any operating points. These phenomena decline the impeller efficiency. On the other hand, the tip clearance of the splitter blade decreases the afore mentioned acceleration by the formation of the tip leakage vortex from the leading edge of the splitter blade and the decrease of the incidence angle for the splitter blade caused by the suction of the flow into the tip clearance. These phenomena reduce the loss generated by the negative blade loading of the main blade and consequently reduce the decline of the impeller efficiency. Moreover, the tip clearances enlarge the flow separation around the diffuser inlet and then decline the diffuser performance independently of the operating points.
A Sobol' Sequence Parametric Analysis of Rotor Thermal Bow in Gas Turbines
Authors: Smith Evan O. , de Baar Jouke H. S. , Neely Andrew J.
Published: August 2018

After a jet engine is shut down, hot air rising inside the compressor disc cavities, secondary air systems, and the gas path annulus will result in a vertical temperature gradient. As the compressor rotor cools and contracts in the presence of this thermal gradient, it will bend, in a phenomenon known as thermal rotor bow. Starting an engine under bowed conditions can result in rubbing of the rotor and stator seals, adding heat to the rotor, exacerbating the rotor bow. This causal sequence of rubbing and bending is called the Newkirk Effect.

In this study, 30 simulations of simplified compressor geometries have been run in three-dimensional unsteady conjugate heat transfer computational fluid dynamics coupled with finite element modelling, using a Sobol’ quasi-random sequence coupled with kriging interpolation to study the effects of three important geometric parameters on the thermal bow response of an engine. The three parameters, rotor length, rotor diameter, and compressor case wall thickness, were selected based on a similar screening test analysis performed by authors in a previous study.

The results include response maps of each parameter with respect to rotor bow and clearance reduction onset time, duration, and severity, and show that length and case wall thickness exhibit linear responses due to their effect on stiffness, whereas diameter exhibits a non-linear response, due to the conflicting and competing effects on stiffness and vertical temperature difference.
Influence of Hole-Pattern Stator on Leakage Performance of Labyrinth Seals
Authors: Yan Xin , Dai Xinbo , Zhang Kang , Li Jun , He Kun
Published: August 2018

The honeycomb seal shows promising characteristics in many turbine machines for the leakage control and rotor stability enhancement. However, the cost of honeycomb seal is relative high due to its complexities in manufacture and installation process. The hole-pattern seal has a very close leakage and rotordynamic performance with honeycomb seal, and also the manufacture and installation of hole-pattern seal are easier than the honeycomb seal, which attract the researchers and designers in recent years. In the published literature, there have been many papers dealt with the rotordynamic coefficients measurements, but very few researchers concentrated on the leakage control performance for the labyrinth seal with hole-pattern land. In this paper, the experimental tests were carried out to obtain the leakage rates versus pressure ratios at four clearances for the straight-through labyrinth seal with smooth stator, straight-through labyrinth seal with hole-pattern stator, stepped labyrinth seal with smooth stator and the stepped labyrinth seal with hole-pattern stator. The flow fields in the seal chambers were also visualized at different clearances and pressure ratios. Moreover, the CFD tool was also implemented to predict the leakage performance in labyrinth seals, and the numerical results were compared with the measurements. The results show that, the stepped labyrinth seal with hole-pattern land performs better leakage control characteristic than the straight-through labyrinth seal with hole-pattern land, and the stepped labyrinth seal with smooth land performs better leakage control than the straight through labyrinth seal with smooth land. For the stepped labyrinth seal, holes in the stator increase the effective clearance thus increase the leakage rate in seal. However, the straight-through labyrinth seal with hole-pattern land almost has the identical leakage performance with the smooth configuration.
Optimization of the Straight-Through Labyrinth Seal With a Smooth Land
Authors: Wróblewski Włodzimierz , Frączek Daniel , Szymański Artur , Bochon Krzysztof , Dykas Sławomir , Marugi Krzysztof
Published: August 2018

The primary goal of this study was to develop and experimentally validate the methodology of labyrinth seals optimization concerning leakage. The problem was investigated using the ANSYS CFX commercial software.

This paper presents the methodology and results of the optimization of a straight-through labyrinth seal with two inclined fins against smooth-land. The optimization was performed using commercial tools implemented in the ANSYS Workbench environment, such as Goal-Driven Optimization (GDO). The response surfaces were created based on Latin hypercube samples found from CFD calculations. The CFD solver — Ansys CFX, using a steady-state scheme with the k-omega Shear Stress Transport turbulence model, was applied. The CFD model was previously validated concerning spatial discretisation and turbulence modelling. A screening algorithm was used to find the best candidates on the response surfaces. The objective function adopted in the labyrinth seal optimization was the minimization of the discharge coefficient value. A wide range of parameters of the fins position and shape, such as the angles, heights and widths, were taken into account, with physically justified degrees of freedom. The leakage reductions being the effect of the optimization were considerable. The cuts in the discharge coefficient significantly exceed the uncertainties of the CFD model and the test rig accuracy. The factors that have the strongest impact on the leakage reduction in are the inclination, thickness of the fin tips, and the distance between fins.

The optimization results were supported with the results of an in-house experiment performed on a stationary, linear test rig. The specimens tested experimentally were on the same scale (1:1) as the optimised ones. The test rig was fed by a high-capacity vacuum air blower, which made it possible to reach critical pressure ratios, with high-precision hot wire anemometry (HWA) mass flow evaluation. The measuring system also enabled assessment of the pressure distribution along the labyrinth structure. The experimental testing results were compared to the CFD calculations and the optimization effects, highlighting some specific tendencies in the labyrinth seal flow behaviour. Good agreement was obtained between the optimization results and the experimental data, which proves that the presented methodology is sufficient for the labyrinth seal optimization. The same methods will also be applied to more sophisticated sealing structures.
Applying Machine Learnt Explicit Algebraic Stress and Scalar Flux Models to a Fundamental Trailing Edge Slot
Authors: Sandberg R. D. , Tan R. , Weatheritt J. , Ooi A. , Haghiri A. , Michelassi V. , Laskowski G.
Published: August 2018

A form of supervised machine learning was applied to highly resolved large-eddy simulation (LES) data to develop non linear turbulence stress and heat flux closures with increased prediction accuracy for trailing-edge cooling slot cases. The LES data were generated for a thick and a thin trailing-edge slot and shown to agree well with experimental data, thus providing suitable training data for model development. A Gene Expression Programming (GEP) based algorithm was used to symbolically regress novel nonlinear Explicit Algebraic Stress Models (EASM) and heat-flux closures based on either the gradient diffusion or the generalized gradient diffusion approaches. Following a-priori assessment, the new models were used for steady RANS calculations of both thin and thick trailing-edge slot geometries, testing their performance and robustness. Overall, the best agreement with LES data was found when training the RANS model in the near wall region where high levels of anisotropy exist and using the mean squared error of the anisotropy tensor as cost function. In the case of the thin lip geometry, combining an improved EASM model with the standard eddy-diffusivity model predicted the adiabatic wall effectiveness in good agreement with the LES and experimental data. Crucially, the obtained model was also applied to different blowing ratios of the thin lip geometry and a significant improvement in the predictive accuracy of adiabatic wall effectiveness was observed for those cases not previously seen in the training process. For the thick lip case the match with reference values deteriorated due to the presence of large-scale, relative to the slot height, vortex shedding. The machine-learning algorithm was therefore also used to ‘learn’ an appropriate closure for the turbulent heat flux vector. The constructed scalar flux model, in conjunction with a trained RANS model, was found to have the capability to further improve the prediction of the adiabatic wall effectiveness.
Axial Turbine Design for a Twin-Turbine Heavy-Duty Turbocharger Concept
Authors: Anton Nicholas , Genrup Magnus , Fredriksson Carl , Larsson Per-Inge , Christiansen-Erlandsson Anders
Published: August 2018

In the process of evaluating a parallel twin-turbine pulse-turbocharged concept, the results considering the turbine operation clearly pointed towards an axial type of turbine. The radial turbine design first analyzed was seen to suffer from sub-optimum values of flow coefficient, stage loading and blade-speed-ratio. Modifying the radial turbine by both assessing the influence of “trim” and inlet tip diameter all concluded that this type of turbine is limited for the concept. Mainly, the turbine stage was experiencing high values of flow coefficient, requiring a more high flowing type of turbine.

Therefore, an axial turbine stage could be feasible as this type of turbine can handle significantly higher flow rates very efficiently. Also, the design spectrum is broader as the shape of the turbine blades is not restricted by a radially fibred geometry as in the radial turbine case.

In this paper, a single stage axial turbine design is presented. As most turbocharger concepts for automotive and heavy-duty applications are dominated by radial turbines, the axial turbine is an interesting option to be evaluated for pulse-charged concepts.

Values of crank-angle-resolved turbine and flow parameters from engine simulations are used as input to the design and subsequent analysis. The data provides a valuable insight into the fluctuating turbine operating conditions and is a necessity for matching a pulse-turbocharged system.

Starting on a 1D-basis, the design process is followed through, resulting in a fully defined 3D-geometry. The 3D-design is evaluated both with respect to FEA and CFD as to confirm high performance and durability.

Turbine maps were used as input to the engine simulation in order to assess this design with respect to “on-engine” conditions and to engine performance.

The axial design shows clear advantages with regards to turbine parameters, efficiency and tip speed levels compared to a reference radial design. Improvement in turbine efficiency enhanced the engine performance significantly.

The study concludes that the proposed single stage axial turbine stage design is viable for a pulse-turbocharged six-cylinder heavy-duty engine. Taking into account both turbine performance and durability aspects, validation in engine simulations, a highly efficient engine with a practical and realizable turbocharger concept resulted.