bluuebunny/crossref_metadata_2025 huggingface dataset:
Telemetric Measurement of Heat Transfer Coefficients in Gaseous Flow: First Test of a Recent Sensor Concept in a Rotating Application
Authors: Heinschke Benjamin , Uffrecht Wieland , Günther André , Odenbach Stefan , Caspary Volker
Published: September 2014

Heat transfer coefficients are very important for the design of the various flow paths found in turbomachinery. An accurate measurement of heat transfer is difficult for circumstances of gaseous flow in combination with good thermal conductivity of the boundaries along the flow path. The majority of the measurement methods applied frequently have at least one of the following problems: (1) the measurement system as for instance a heat flux sensor is a thermal barrier in the object of interest, and (2) the sensor introduces for measurement reasons a lot of heat into the object of interest. In both cases the main error results from the modification of the system, which is critical for the investigation of any kind of flow influenced by buoyancy. Furthermore, insufficient fluid reference temperature and/or heat flux with changing sign corrupts any attempt to calculate reliable heat transfer coefficients.

The measurement of heat transfer coefficients becomes even more complicated if the flow path of interest rotates at some thousand rpm as for instance in gas turbines or any other fast rotating machine with fluid flow. This contribution presents a new test rig and an experimental investigation of a setup for the direct telemetric measurement of local heat transfer coefficients in gaseous flow with metallic boundaries. The test rig has a complex instrumentation and the measurements are transferred from the rotating to the stationary frame via newly in house developed telemetry system. The measurements presented are based on a recent measurement/sensor concept tested for the first time in the rotating frame. The measurement setup features miniaturized sensor dimensions and low energy consumption. Therefore, the sensor concept is very well suited for use with telemetry system as necessary for many turbomachinery research applications.

Furthermore, measurements of the radial distribution of the heat transfer coefficient of a rotating free disc are presented. Additionally a comparison with correlations found in literature as well as a discussion of the results is included.
Experimental Investigation of Effects of Leading-Edge Tubercles on Compressor Cascade Performance
Authors: Keerthi M. C. , Kushari Abhijit , De Ashoke , Kumar Arun
Published: September 2014

In the present study, the effectiveness of passive structures called tubercles on an axial compressor blade row is studied experimentally. Tubercles are the modifications to the leading edge of an airfoil in the form of blunt wave-like serrations. Although several studies on the effect of tubercles on isolated blades are available in literature, detailed study of their effect on a cascade of blades, such as in the case of an axial flow turbo-machine is lacking. Such an application in an axial compressor will result in a significant increase in the stall margin. Presently, experiments have been performed on a linear compressor cascade with a blade height of 0.15 m and mean chord of 0.06 m, on a NACA 65209 airfoil profile. The plain and modified blades are fabricated using rapid prototyping to ensure conformity to the required geometry. The cascade is designed in such a way that the incidence (angle of attack) and the stagger can be changed easily. The measurements are taken at the exit plane using a five-hole Pitot probe to obtain three-components of velocity and static pressure data over fine measurement grids. The effect is determined in terms of lift and drag coefficients, lift-to-drag ratio and total pressure loss coefficient. Experiments have been carried out for different pitch and amplitude (serration depth) of tubercles to understand their effect. The stall incidence angle for the best performing blade is found to increase up to 8.6° from that of the unmodified blade of 6.0°. Application of such structures in axial compressor blades may well be adequate to prevent stalling in axial compressors over a wide operating range.
Creep in Interlaminar Shear of a SiC/SiC Ceramic Matrix Composite at Elevated Temperature
Authors: Ruggles-Wrenn M. B. , Pope M. T.
Published: September 2014

Creep behavior in interlaminar shear of a non-oxide ceramic composite with a multilayered matrix was investigated at 1200°C in laboratory air and in steam environment. The composite was produced via chemical vapor infiltration (CVI). The composite had an oxidation inhibited matrix, which consisted of alternating layers of silicon carbide and boron carbide and was reinforced with laminated Hi-Nicalon™ fibers woven in a five-harness-satin weave. Fiber preforms had pyrolytic carbon fiber coating with boron carbon overlay applied. The interlaminar shear properties were measured. The creep behavior was examined for interlaminar shear stresses in the 16–22 MPa range. Primary and secondary creep regimes were observed in all tests conducted in air and in steam. In air and in steam, creep run-out defined as 100 h at creep stress was achieved at 16 MPa. Larger creep strains were accumulated in steam. However, creep strain rates and creep lifetimes were only moderately affected by the presence of steam. The retained properties of all specimens that achieved run-out were characterized. Composite microstructure, as well as damage and failure mechanisms were investigated.
Development of a Novel Axial Compressor Generation for Industrial Applications: Part 2 — Blade Mechanics
Authors: Anding Dirk , Ressing Henning , Hörmeyer Klaus , Pisch Roland , Ziegler Kai
Published: September 2014

Blade vibrations resulting in alternating stresses are often the critical factor in determining blade life. Indeed, many of the failures experienced by turbomachinery blades occur due to high-cycle fatigue caused by blade vibrations. These vibrations can arise either through self-excited oscillations known as flutter or through aerodynamic forcing of the blades from factors such as periodic wakes from up and/or downstream vanes or unsteady flow phenomena such as compressor surge.

The current paper deals with the design and the analytical and experimental verification of the axial blading for a new generation of industrial compressors, a hybrid axial compressor that combines the advantages of conventional industrial compressors — broad operating range and high efficiency — with the advantages of gas turbine compressors — high power-density and high stage pressure ratios. Additionally, the surge robustness of this novel compressor blading has been greatly improved. During the development phase extensive efforts were made to ensure safe operation for future service life. This was achieved by designing blades that will not flutter, do not have high resonance amplitudes throughout their entire operating range and are extremely robust against surge.

This strongly increased robustness of the new compressor blading was achieved by the implementation of a “wide-chord” blade design in all rotor blade rows in combination with a proper tuning of resonance frequencies throughout the entire operating range. For the verification of the new blading well-established methods accepted by industry were used such as CFD and FEA. Furthermore, coupling of the two into a method referred to as Fluid Structure Interaction (FSI) was used to more closely investigate the interaction of flow and structural dynamics phenomena. These analytical techniques have been used in conjunction with extensive testing of a scaled test compressor, which was operated at conditions of dynamic similitude (matching of scaled blade vibration frequencies, flow conditions, and Mach number) with full-scale operational conditions. Strain gauges placed on the blades and a state of the art technique known as “tip timing” were used to verify blade vibrations over a wide range of combinations of guide vane positions and rotational speeds.

No propensity was found of any of the blades to develop high vibration amplitudes at any of the operating conditions investigated in the rig tests. The comparison of non-linear forced response analyses and the rig test results from strain gauges and tip timing showed close agreement, verifying the analysis techniques used.

In conclusion it can be stated that the blade design exhibits a very high level of safety against vibrations within the entire operating range and during surge.
Unsteady RANS Analysis of Particles Deposition in the Coolant Channel of a Gas Turbine Blade Using a Non-Linear Model
Authors: Borello Domenico , Capobianchi Paolo , De Petris Marco , Rispoli Franco , Venturini Paolo
Published: September 2014

The two-phase flow in a geometry representing the final portion of the internal cooling channels of a gas turbine blade is here presented and discussed. In the configuration under scrutiny, the coolant flows inside the duct in radial direction and it leaves the blade through the trailing edge after a 90 deg turning.

An unsteady Reynolds Averaged Navier-Stokes (URANS) simulation of the flow inside such channel was carried out. An original non-linear version of the well-established ζ-f elliptic relaxation model was developed and applied here.

The new model was implemented in the well-validated T-FlowS code currently developed by the authors’ group at Sapienza Università di Roma.

The predictions demonstrated a good accuracy of the non-linear URANS model, clearly improving the results of the baseline linear ζ-f model and of the Launder Sharma k-ε model used as reference.

The obtained unsteady flow field was adopted to track a large number of solid particles released from several selected sections at the inlet and representing the powders usually dispersed (sand, volcanic ashes) in the air spilled from the compressor and used as cooling fluid.

The well-validated particle-tracking algorithm here adopted for determining the trajectories demonstrated to be very sensitive to the flow unsteadiness.

Finally, the fouling of the solid surfaces was estimated by adopting a model based on the coefficient of restitution approach.
Transient Surge Dynamics: A Shock Tube Theory and Experimental Comparison
Authors: Huang Paul Xiubao , Yin JianAn
Published: September 2014

High-speed high-pressure ratio compressor surge is a transient breakdown in compression accompanied by an abrupt momentary reversal of gas flow. It commonly exists in dynamic type turbo compressors, particularly in the axial compressor of modern aero-engines. By Newton’s Laws of Motion, a force is needed to change the state of any motion. So what is the force that can cause such a dramatic motion as surge? What exactly triggers it, and how do we quantify the transient surge phenomenon? This paper attempts to answer these questions and discuss the transient dynamics of surge at its initial stage.

It has generally been accepted that surge is precipitated by the onset of a rotating spike or stall, not only for low speed but for high-speed compressors too. The state of dynamic surge modeling today is best exemplified by the “Greitzer-Moore” model. However, it fails to incorporate the key elements of the transient nature of a surge inception: the extremely short time duration on millisecond scale and the shock wave presence observed experimentally.

An indirect approach is taken in this paper to address the transient dynamics of stall and surge by using an analogy to the shock tube. The link is established based on observations that instant zero net through flow inside stalled cascade cell triggers stall/surge. The results from the analogy reveal that surge initiation simultaneously generates a pair of non-linear compression and expansion waves (CW & EW) and induced reverse fluid flow (IRFF). The dynamic forces for instant flow reversal are the pushing force of upstream propagating CW and the pulling force from downstream travelling EW. Surge Rules are deduced and then compared with experimental findings by previous researchers with good agreements. Moreover, the strength of the transient post-surge components, CW, EW and IRFF, can be estimated analytically or numerically by the shock tube theory from known pre-surge conditions and routes to surge.
CFD Simulation of Single Step and Double Notched Tooth for Labyrinth Seals
Authors: Chougule Hasham H. , Mirzamoghadam Alexander , Ramerth Douglas
Published: September 2014

A variant “Stepped Double Notched Tooth” for conventional sharp teeth of a labyrinth seal has been proposed and investigated by three-dimensional CFD numerical modeling of the flow field. The purpose is to reduce total leakage through the seal. The tooth is numerically tested with both solid and honeycomb lands. CFD assumptions and analysis were validated by comparison with leakage data from stationary labyrinth seal experiments conducted by Stocker [1]. The baseline model considered for comparison study consists of the conventional straight-through four sharp knife shaped teeth in combination with solid and honeycomb land. The variant tooth is also straight having a sharp tip but has a stepped inclined notch opposing the flow at both sides of the tip. CFD analyses revealed that this double notched tooth reduces seal leakage by ∼10.7% when used with solid land and ∼12.5% when used with honeycomb land compared to a conventional baseline tooth.
Reduced Order Transient Disc Temperature Models for Online Health Monitoring
Authors: van Paridon Andrew , Bacic Marko , Ireland Peter T. , Barnes Christopher , Lewis Leo V.
Published: September 2014

Non-uniform temperature distributions in aircraft turbine and compressor discs result in high thermal stresses, particularly during engine transients. This has an important role in limiting disc life and subsequently engine time on wing between overhauls. Typically, and in the absence of specific engine real-time information, disc life is computed and declared at the design stage, for the whole fleet assuming worst case scenarios and flight profiles. This approach potentially leads to conservativeness in disc life prediction for the majority of the engines in the fleet. The purpose of this paper is to present a novel methodology to estimate the transient temperature distribution of such components in real-time, with the ultimate aim of using such information to improve knowledge about disc life consumed on an engine by engine basis. The paper describes a reduced order dynamic model that estimates the disc temperature distribution in real-time using only measured parameters such as spool speed, atmospheric pressure, and compressor exit temperatures. The model presented is a grey box model consisting of dynamic Linear Parameter Varying transfer functions that relate measured air temperatures to the relevant air temperatures in the disc cavities. Heat transfer from air to disc is modelled using rotor-stator aerothermal theory matched to validated computational fluid dynamic analyses. Lumped capacitance models and simplified explicit conduction models are used to simulate the disc temperature distribution. It is shown that this approach gives a scientifically accurate estimate of the temperature distribution both radially and axially, whilst being computationally efficient enough for real-time Engine Health Management implementation.
Study of Unsteady Heat Transfer as a Key Parameter to Characterize Limit Cycle of High Amplitude Pressure Oscillations
Authors: Shahi Mina , Kok Jim B. W. , Roman Casado J. C. , Pozarlik Artur K.
Published: September 2014

The objective of the studies presented in this paper is the numerical prediction of unsteady heat flux and pressure fluctuations during the unstable regime of a combustor. The studied laboratory-scale lean partially premixed combustor was built in the LIMOUSINE project, to explore the mechanisms driving thermo-acoustic instabilities in conditions representative of gas turbine combustors.

Due to the thermal interaction between hot gases and the colder liner wall, and also the correlation between gas temperature, density and speed of sound, prediction of the transient heat transfer rate is of high importance. In this paper analysis of transient heat transfer is conducted by coupling of fluid flow and solid body (liner) in one computational domain and thereby taking into account the thermal convection with the environment around the combustor and also the heat conduction transients within the liner. Conjugate heat transfer modeling can give access to the transient temperature distribution in the structure of the combustor which is important for the dynamic heat storage. Also this can be used to estimate the thermal stresses and creep strain as required to evaluate the lifetime assessment of the combustor. In this work the commercial CFD code ANSYS CFX is used to solve the problem, in which fluid and solid regions are solved simultaneously with a finite volume approach. In the fluid region, three dimensional compressible Reynolds Averaged Navier-Stokes equations are solved, while for the solid region only the enthalpy conservation equation is solved. To remove any interpolation errors, in all cases the skin (interface) mesh cells for both the fluid and solid are similar in resolution on either side of the interface. By comparing heat release and pressure data available from the measurements it follows that this simulation can give more accurate prediction of the amplitudes of thermoacoustic instabilities as compared to the solution with imposed thermal boundary conditions (such as isothermal). In the latter case the time history of heat accumulation in the solid is predicted incorrectly. Because the spatial scales of the solid temperature profiles are different in case of steady state or transient oscillatory heat transfer, care has to be taken in the meshing in these two situations. When meshing for a transient oscillatory heat transfer case, the solid mesh resolution needs to be adapted to the thermal penetration depth of the surface temperature oscillations. Hence for the transient heat transfer in limit cycle combustion oscillations, the meshing strategy and size of the grid in the solid part of the domain will play a very important role in determining the magnitude for the pressure fluctuations.
Experiments on an Axial Fan Stage: Time Resolved Analysis of Rotating Instability Modes
Authors: Pardowitz Benjamin , Tapken Ulf , Neuhaus Lars , Enghardt Lars
Published: September 2014

Rotating Instability (RI) occurs at off-design conditions in axial compressors, predominantly in rotor configurations with large tip clearances. Characteristic spectral signatures with side-by-side peaks below the blade passing frequency are typically referred to RI located in the clearance region next to the leading edge (LE). Each peak can be assigned to a dominant circumferential mode. RI is the source of the clearance noise and an indicator for critical operating conditions. Earlier studies at an annular cascade pointed out that RI modes of different circumferential orders occur stochastically distributed in time and independently from each other, which is contradictory to existing explanations of the RI. Purpose of the present study is to verify the generality with regard to axial rotor configurations.

Experiments were conducted on a laboratory axial fan stage mainly using unsteady pressure measurements in a sensor ring near the rotor LE. A mode decomposition based on cross spectral matrices was used to analyze the spectral and modal RI patterns upstream of the rotor. Additionally, a time-resolved analysis based on a spatial Discrete-Fourier-Transform was applied to clarify the temporal characteristics of the RI modes and their potential interrelations. The results and a comparison with the previous findings on the annular cascade corroborate a new hypothesis about the basic RI mechanism. This hypothesis implies that instability waves of different wavelengths are generated stochastically in a shear layer resulting from a backflow in the tip clearance region.
Deformation Modeling and Lifetime Prediction of Ni-Base Gas Turbine Blade Alloys Under TMF-Conditions
Authors: Grützner Stefan , Fedelich Bernard , Rehmer Birgit , Mosquera Maria
Published: September 2014

Under cyclic thermomechanical loading conditions, various effects such as strain accumulation, creep damage, ageing, fatigue etc. may occur in the material of a gas turbine blade. Depending on the loading conditions, all these effects contribute to reduce the lifetime of the component.

Subject of the present work is the development of a lifetime model able to discriminate between the different damage mechanisms, as well as the development of a material model to describe the mentioned effects and thus providing the input data for lifetime prediction.
CFD Simulation of Incompressible Turbomachinery — A Comparison of Results From ANSYS Fluent and OpenFOAM
Authors: Bothe Franziska , Friebe Christian , Heinrich Martin , Schwarze Rüdiger
Published: September 2014

A numerical investigation of incompressible turbomachinery and the comparison of two CFD packages are presented within this paper. A ducted single rotor fan is simulated with OpenFOAM and ANSYS FLUENT by applying methods as comparable as possible. The characteristic maps and flow fields are analyzed and the results from the CFD codes are compared to examine differences regarding accuracy and efficiency. Additionally the influence of the turbulence model is determined. It is found that the CFD programs show a good agreement especially at the machines design point.

The information about the flow field of this fan is used for the modelling of a high-performance and energy-efficient ducted contra-rotating fan (CRF). Comparing the CRF simulation results to those of the single rotor fan, a doubling of the total pressure rise and a significant reduction of the swirl in the wake flow can be noticed.
Development and Experimental Investigation of a Tubular Combustor for Pyrolysis Oil Burning
Authors: Beran Martin , Axelsson Lars-Uno
Published: September 2014

The growing demand for more economical and environmentally friendly power generation forces the industry to search for fuels that can replace the conventional fossil fuels. This has led to significant developments in the production of alternative fuels during the last years, which have made them a reliable and relatively efficient source of energy. One example of these alternative fuels is the pyrolysis oil. However, higher viscosity, lower heat content, limited chemical stability and its ability to create sediment make pyrolysis oil challenging for gas turbines. The OPRA OP16 gas turbine is an all radial single-shaft gas turbine rated at 1.9 MW. The all radial design, together with the lack of intricate cooling geometries in the hot section, makes this gas turbine suitable for operation on these fuels.

This paper presents an experimental investigation of pyrolysis oil combustion in a tubular combustor developed especially for low-calorific fuels. The experiments have been performed in an atmospheric combustion test rig and the results have been compared to the results obtained from ethanol and diesel combustion. It was found that it was possible to burn pure pyrolysis oil in the load range between 70 to 100% with a combustion efficiency exceeding 99% and without creation of sediments on the combustor inner wall.

It was found that the NOx emissions were similar for pyrolysis oil and diesel, whereas the CO emissions were twice as high for pyrolysis oil. A comparison between the air blast nozzle and the pressure nozzle was performed. The air blast nozzle was found to be more suitable due to its better performance over a wider operating range and that it is more resistant to erosion and abrasion. It was found that the maximum allowed droplet size of the pyrolysis oil spray should be about 50–70% of the droplet size for diesel fuel.
Research and Educational Opportunities in Hardware-in-the-Loop Simulation of Advanced Power Systems: An International Perspective
Authors: Pezzini Paolo , Ferrari Mario L. , Tucker David , Traverso Alberto
Published: September 2014

Hardware-in-the-loop simulation (HiLS) is a specific technique designed in the experimental environment for studying the coupling between different technologies, where simulated and hardware components interact to each other. Two different HiLS facilities used for educational and research purposes are examined in the paper: the Hybrid Performance (Hyper) project facility at the U.S. Department of Energy, National Energy Technology Laboratory (NETL), and the Hybrid system emulator at the Thermochemical Power Group (TPG) facility, run by the University of Genoa in Italy. Since one facility is at a national laboratory and the other one in a university environment, both facilities dedicate considerable resources to the education of students with a different perspective: industrial and experimental approach.

A description of the two configurations, the unique and overlapping attributes of each facility and the experimental results are reported and discussed to show different possibilities for students and researchers. Undergraduates, Postgraduates and Ph.D. students have the opportunity to learn innovative configuration of energy power systems, innovative control strategies applied to hybrid configurations, how to design real hardware components, and how to implementation real-time simulation models. The strong impact of these two laboratories is to show to students the applicability about their knowledge studied during lectures.
Thermal Barrier Coating Validation Testing for Industrial Gas Turbine Combustion Hardware
Authors: Smith Jeffrey , Scheibel John , Classen Daniel , Paschke Scott , Elbel Shane , Fick Kirk , Carlson Doug
Published: September 2014

As gas turbine (GT) temperatures have increased, thermal barrier coatings (TBCs) have become a critically important element in hot section component durability. Ceramic thermal barrier coatings permit significantly increased gas temperatures, reduced cooling requirements, and improve engine fuel efficiency and reliability. TBCs are in use throughout the GT hot section with turbine blades, vanes, and combustion hardware, now being designed with TBCs or upgraded with TBCs during component refurbishment1, 2. While the industry standard 6–9 Wt. % Yttria Stabilized Zirconia (7YSZ) has been the preferred ceramic composition for the past 30+ years, efforts have been underway to develop improved TBCs3, 4. The principal development goals have been to lower thermal conductivity, increase the sintering resistance and have a more stable crystalline phase structure allowing use above 1200° C (2192° F)5, 6. NASA has developed a series of advanced low conductivity, phase stable and sinter resistant TBC coatings utilizing multiple rare earth dopant oxides7. One of the coating systems NASA developed is based on Ytterbia, Gadolinia and Yttria additions to ZrO2 (YbGd-YSZ). This advanced low conductivity (low k) TBC is designed specifically for combustion hardware applications. In addition to lower thermal conductivity than 7YSZ, it has demonstrated thermal stability and sintering resistance to 1650° C (3000° F). The Electric Power Research Institute (EPRI) and Cincinnati Thermal Spray (CTS) have teamed together in a joint program to commercialize the YbGd-YSZ TBC coating system for GT combustion hardware. The program consists of validation of coating properties, establishment of production coating specifications and demonstration of coating performance through component engine testing of the YbGd-YSZ TBC coating system. Among the critical to quality coating characteristics that have been established are a) coating microstructure b) TBC tensile bond strength c) erosion resistance d) thermal conductivity and sintering resistance and e) thermal cycle performance. This paper will discuss the coating property validation results comparing the YbGd-YSZ TBC to baseline production combustor coatings and the status of coating commercialization efforts currently underway.
A Physics-Based Performance Indicator for Gas Turbine Engines Under Variable Operating Conditions
Authors: Hanachi Houman , Liu Jie , Banerjee Avisekh , Chen Ying , Koul Ashok
Published: September 2014

Gas turbines are often used under variable ambient conditions and power demands, which also may be off their design points. Such operating scenarios affect the typical performance parameters, such as thermal efficiency, mass flow and power. As a result, such parameters may fail to accurately indicate the structural degradation of a gas turbine. The objective of this study is to develop a robust physics-based performance indicator for a gas turbine to demonstrate the short term recoverable as well as long term non-recoverable degradation level of the engine, independent of the operating conditions. A comprehensive physics-based thermodynamic model for the gas path of a single shaft gas turbine is developed to accurately predict the cycle parameters based on limited actual operating data. Consequently, for the given ambient condition, demanded power and shaft speed, the model predicts the cycle parameters for the gas turbine in a healthy condition as the baseline. In reality, the measured parameters gradually deviate from the model, which reflects the performance deterioration of the engine caused by degradation mechanisms. In order to capture this performance deterioration, the ratio of the excess exhaust heat power with respect to the design point power, called Excess Heat Ratio (EH) is being proposed as an effective indicator. The effectiveness of the Excess Heat Ratio is examined by using 38-month operating data of an industrial gas turbine between two major overhauls. The trends of EH clearly shows its capability to capture the short term recoverable degradations and subsequent retrievals, arising from compressor fouling and subsequent wash. In addition, EH is also able to capture the trend of the long term non-recoverable degradations. The proposed indicator has the following advantages: 1) only limited data from the operating system of a gas turbine is required without the need of additional instrumentation; 2) the both short and long term degradations of the gas turbine can be quantified by a single indicator that is independent from the operating conditions; and 3) it is practically applicable for real-time monitoring and maintenance planning.
Effects of Platform Misalignment in a 3D Designed 1.5 Stage Axial Turbine
Authors: Kluxen R. , Terstegen M. , Behre S. , Jeschke P. , Guendogdu Y.
Published: September 2014

The effect of hub platform misalignment in the first vane of a 1.5 stage axial test rig turbine on the efficiency is numerically analyzed. An investigation is made into how this misalignment, as caused for example by manufacturing deviation, impacts the intended 3D flow in an endwall-contoured design and how robust the design is compared to a uncontoured turbine. Axial misalignment was created by extending all platforms within the blade row in radial direction by up to 5.5 % of the channel height. In order to create circumferential steps, only every third platform was elevated. The results are based on steady and unsteady simulations with the DLR RANS solver TRACE. In general, both axial and circumferential steps alter the static pressure field and lead to flow separations bubbles. These effects lead to the creation of new vortices which interact with the classic turbine secondary flow. It turns out that increasing the step height generally reinforces the secondary flow intensity. In addition to local detrimental effects, these processes significantly alter the inflow conditions to the subsequent blade rows, leading to increased losses there. A comparison of the results for the uncontoured and the non-axisymmetric endwall shows that the beneficial effects of the latter, which are based mainly on radial homogenization of the outlet flow yaw angle in the first vane, still continue to exist in the presence of platform steps, although the overall efficiency is significantly reduced. An experimental validation of the platform effects is not included in this paper but will follow in the near future.
From Design Aspects Through to Testing of the MAN Diesel and Turbo Subsea Motor-Compressor for the Åsgard Subsea Project
Authors: Büche Dirk , Aho Tuomo , Dettwyler Markus
Published: September 2014

This paper outlines pioneering work in the field of subsea compressor technology. The guiding design principles for the subsea motor-compressor of the authors’ company were operational safety, robustness, reliability, and remote operability. An early demonstrator was realized and tested in collaboration with the end-user upfront and consecutively improved gradually where indicated. This turned out to be beneficial in the phase of project execution since the early knowledge of application specific requirements resulted in an already elaborated overall design basis.

The presented design also draws on extensive top side experience from sealed motor-compressors, where a portion of the process gas is taken directly from an intermediate stage of the compressor and fed back to the suction line after passing through, and thus cooling, the motor and the active magnetic bearings. This minimizes the number of interfaces and required sub-systems.

Various simulations were performed to account for differences between subsea and topside environments. The focus of the work presented in this paper is on the effect of the high heat transfer resulting in an altered overall temperature situation.

At the time of writing, the first units of the discussed subsea motor-compressor have successfully passed Factory Acceptance Testing (FAT) under atmospheric conditions. At the moment, they are being prepared for extended submerged testing with production gas at a test facility of the end-user.
A Theoretical and Experimental Analysis of the Sealing Capability of a Membrane Seal
Authors: Tibos Stacie , Aujla Randhir , Pyzik Przemyslaw , Lewis Martin , Justl Sascha
Published: September 2014

Improvements in turbine performance are increasingly being driven by the need to control leakage both in the main gas path as well as secondary air flow systems. Membrane seals have long been established as a method of sealing in some of the harshest of environments found in gas turbines. The membrane seal has a wide usage in gas turbines for stationary component interface sealing. The geometry is of plate construction with bulbous ends, the seals are assembled vertically and are retained by the component grooves. The grooves allow relative sliding and rotation against their surfaces a necessary feature, since during operation the seal needs to withstand relative movements due to thermal growth, vibratory forces, excitation and assembly loads. However, more accurate leakage estimates are required. Thus, in order to evaluate the complete performance characteristics of the seal for a wide range of working conditions, a theoretical and experimental campaign was undertaken.

The membrane seal performance curves were created based on a series of tests performed in a specially designed rig. The rig utilised an actuation system that allowed for the precise adjustment of the seal’s relative position in two directions while performing the tests at a given working condition. It was noted that not only the movement and deformation of the membrane but also, assembly clearances and surface condition of the components have an impact on the seal’s performance. To assist in the understanding of the influence of the changing parameters on the performance of the seal an FEA study was undertaken employing known data to aid the understanding and improve the knowledge of how the seal behaves under specific engine conditions. The evaluation gives confidence in the experimental test results.
Experiences on Project-Based-Classes for Turbomachine Design in an Aerospace Engineering Undergraduate Program
Authors: Tomita Jesuino Takachi , Barbosa João Roberto , Bringhenti Cleverson
Published: September 2014

At Technological Institute of Aeronautics-ITA, the Flow Machines for Aerospace Applications course deals with turbopumps. It is offered to students of the second professional year in the undergraduate program. The objective of the course is to present enough information for the students to learn about machine preliminary design.

The theory involved in flow machines is multidisciplinary, so that the students must fully understand the principles of fluid mechanics, heat transfer, gas dynamics and thermodynamics, whose complete understanding is vital to start the design of such machine.

Lack of understanding the basic theory due to the problems like difficulty of associating the velocity triangles to blade angles, blade camber, incidence and deviation angles, makes the subject more complex than it really is. This problem is mitigated with hands-on activities during practical classes.

In this work, the syllabus of flow machines design course at ITA is presented, details of how the subjects are taught and the procedures used during the classes are reported, based on real life engineering project. After a period of theory and lab classes the students are requested to do a complete preliminary design of a turbomachine, using adequate numerical tools based on specs of a turbomachine. The instructor follows the class with discussions towards adjustments that could result in operational characteristics improvement. The project starts with meanline calculations to produce the base geometry and proceeds up to 3D CFD calculations to check the performance of the designed turbomachine and to subsidize design modifications. Experience exchanged with students are reported and commented aiming at course improvement.
Self Healing Fusion Welding Technology
Authors: Gontcharov Alexandre , Liburdi Joe , Lowden Paul , Nagy Douglas , Patel Nikesh
Published: September 2014

The properties of laser, microplasma and GTAW welds on representative gas turbine blade materials are disclosed. Proprietary filler materials and technology were used to clad multipass welds onto IN738, RenéN5 and CMSX4 alloys which were then subject to vacuum heat treatment before testing.

It was found that welds with a bulk content of boron up to 0.6 wt. % demonstrated a capability to heal cracks adjacent to the fusion line (HAZ cracks) and they exhibited superior tensile and stress-rupture properties at a temperature of 982°C. Welds that comprised 1.5 to 2% silicon had superior oxidation resistance at a temperature of 995°C. Combined alloying of welds with moderate amount of boron and silicon produced a unique combination of both high mechanical and oxidation properties.

Healing of HAZ cracks took place during post weld heat treatment at a temperature exceeding the solidus temperature of the weld metal eutectics but below of a solidus temperature of the base material. It was found that boron and silicon additives reduced welding pool solidification temperature and increased the solidus–liquidus range. At this temperature a partial re-melt of eutectics occurred allowing healing of HAZ and weld solidification cracks while weld geometry was supported by a continuous framework of high temperature dendrites. This allows the tip repair of turbine blades manufactured of precipitation strengthened superalloys that are normally prone to weld cracking.
Heat Transfer in a Coupled Impingement-Effusion Cooling System
Authors: Miller Mark , Natsui Greg , Ricklick Mark , Kapat Jay , Schilp Reinhard
Published: September 2014

Modern research on gas turbine cooling continues to focus on the optimization of different cooling designs, and better understanding of the underlying flow physics so that cooling schemes can be coupled together. The current study focuses on one particular coupled cooling design: an impingement-effusion cooling system, which combines impingement cooling on the backside of the cooled component and full coverage effusion cooling on the exposed surface.

The goal of this study is to explore a wide range of geometrical parameters outside the ranges normally reported in the available literature. Particular attention is given to the total coolant spent per unit surface area cooled. Through determination of impingement heat transfer, film cooling effectiveness, and film cooling heat transfer on the target wall, a simplified heat transfer model of the cooled component is developed to show the relative impact of each parameter on the overall cooling effectiveness.

The use of Temperature Sensitive Paint (TSP) for data acquisition allows for high resolution local heat transfer and effectiveness results. Impingement arrays with local extraction of coolant via effusion are able to produce higher overall heat transfer, as no significant cross flow is present to deflect the impinging jets. Low jet-to-target-plate spacing produces the highest yet most non-uniform heat transfer distribution; at high spacing the heat transfer rate is much less sensitive to impingement height.

Arrays with high hole-to-hole spacing and high jet Reynold’s number are more effective (per mass of coolant used) than tightly spaced holes at low jet Reynold’s number. On the effusion side, staggered hole arrangements provide significantly higher film cooling effectiveness than their in-line counterparts as the staggered arrangement minimizes jet interactions and promotes a more even lateral distribution of coolant.
Residual Life Assessment of a Critical Component of a Gas Turbine: Achievements and Challenges
Authors: Beres Wieslaw , Zhang Zhong , Dudzinski David , Chen W. R. , Wu X. J.
Published: September 2014

The residual life assessment of a turbine spacer from a gas turbine engine is presented. The spacer has been identified as one of the safety critical components of the engine, therefore the useful life of this component significantly affects economic operation of the fleet.

Numerical analyses of fatigue crack propagation at one critical location of the spacer were performed using both three dimensional (3D) finite element based method and the weight function method. These results combined with the material data allowed for basic assessment of the damage tolerance of this component. Experimental validation of the spacer life was performed in a spin rig facility. During this validation, two sets of spacers were tested and the number of cycles to appearance of a detectable crack was recorded. Moreover, a fractographic study was conducted on the fracture surfaces of two spin rig tested spacers using scanning electronic microscopy techniques. It was found that crack nucleation occurred at multiple sites and crack propagation occurred by a mixed mode of striation formation and faceted fracture. Therefore it was concluded that the mixed mode interaction should be considered in predicting the fatigue life of the spacer.

Finally, the paper describes the challenges and pitfalls encountered during preparation and execution of the analyses and tests, including availability of engine and operational data and also uncertainties in interpretation of the results.
Development of an Innovative Multi-Sensor Waveguide Probe With Improved Measurement Capabilities
Authors: Lenzi Giulio , Fioravanti Andrea , Ferrara Giovanni , Ferrari Lorenzo
Published: September 2014

Currently waveguide probes are widely used in several turbomachinery applications ranging from the analysis of flow instabilities to the investigation of thermoacoustic phenomena. There are many advantages to using a waveguide probe. For example, the same sensor can be adopted for different measurement points, thus reducing the total number of sensors or a cheaper sensor with a lower operating temperature capability can be used instead of a more expensive one in case of high temperature applications. Typically, a waveguide probe is made up of a transmitting duct which connects the measurement point with a sensor housing and a damping duct which attenuates the pressure fluctuations reflected by the duct end. If properly designed (i.e. with a very long damping duct), the theoretical response of a wave guide has a monotone trend with an attenuation factor that increases with the frequency and the length of the transmitting duct. Unfortunately, the real geometry of the waveguide components and the type of connection between them have a strong influence on the behavior of the system. Even the smallest discontinuity in the duct connections can lead to a very complex frequency response and a reduced operating range. The geometry of the sensor housing itself is another element which contributes to increasing the differences between the expected and real frequency responses of a waveguide since its impedance is generally unknown.

Previous studies developed by the authors have demonstrated that the replacement of the damping duct with a properly designed termination could be a good solution to increase the waveguide operating range and center it on the frequencies of interest. In detail, the termination could be used to balance the detrimental effects of discontinuities and sensor presence. In this paper an innovative waveguide system leading to a further increase of the operating range is proposed and tested. The system is based on the measurement of the pressure oscillations propagating in the transmitting duct by means of three sensors placed at different distances from the pressure tap. The pressures measured by the three sensors are then combined and processed to calculate the pressure at the transmitting duct inlet. The arrangement of the sensing elements and the geometry of the termination are designed to minimize the error of this estimation. The frequency response achieved with the proposed arrangement turns out to be very flat over a wide range of frequencies. Thanks to the minor errors in the estimation of pressure modulus and phase the probe is also suitable for the signal reconstruction both in frequency and time domain.
Research on the Structure Design and Flow Field of Supersonic Expander
Authors: Huang Zhenyu , Zhong Jingjun , Yang Ling , Han Ji’ang
Published: September 2014

As a new type of expansion system, compared with conventional axial turbine, the structural traits of the supersonic expander are the use of the thinner strake walls instead of the turbine blades, and the change of the expansion surface shape along the direction of airflow to achieve expansion and acceleration. The expander with three kinds of expansion surface shape has been designed and simulated numerically in this paper. It has been found that the maximum averaged Mach numbers at the exit and the expansion ratio of the expander occur with the linear expansion surface. Because the performance of the expander ties up to the geometric parameters, so taking the expander structure with the linear expansion surface as a foundation, the key geometric parameters which affect the performance of the expander are studied numerically in detail. With the increasing of the strake stagger angle, the expansion ratio of the expander decreases, and the efficiency of the expander increases. And with the increasing of the ratio of the outlet to inlet area, the expansion ratio of the expander increases, and the efficiency of the expander decreases. In order to optimize the overall performance of the supersonic expander, the reasonable compromises should be made between the smaller ratio of the outlet to inlet area and larger strake stagger angle. Under the design and off-design conditions, the flow field and performance of the expander with an optimum performance is further numerically simulated. It has been found that dilatation waves at the entrance of the expansion passage will reduce the static pressure, so as to realize expansion and acceleration of the airflow in the expander passage. Pressure gradient in the direction of the pitch causes the difference of the airflow velocity distribution. The oblique shock waves which near to the outlet brings the rise of the static pressure, thus reduces the airflow velocity of the outlet and increases the flow losses. With increase in the inlet total pressure and rotational speed of the supersonic expander, its expansion ratio and efficiency improves.