bluuebunny/crossref_metadata_2025 huggingface dataset:
Highly Accurate Delta Efficiency Measurements at the Large Scale Turbine Rig
Authors: Eitenmüller Johannes , Wilhelm Manuel , Gresser Leonhard , Ostrowksi Tom , Leichtfuss Sebastian , Schiffer Heinz-Peter , Lyko Christoph , Naik Shailendra
Published: November 2019

High pressure turbines are nowadays designed to a point where most design enhancements only yield marginal efficiency improvements. This challenges research facilities to reliably resolve ever smaller differences in efficiency caused by individual design changes. In recent years, immense efforts towards such highly accurate delta-efficiency measurements have been undertaken at the Large Scale Turbine Rig (LSTR). This paper comprises an overview of the applied methodology and the achievements on the basis of various validation cases.

By thoroughly controlling the operation point and accounting for all variables affecting the efficiency η, the rig can resolve efficiency-differences Δη of ±0.1 % for a single day measurement. Four benchmark cases are investigated to validate the rig’s capabilities. First, the influence of tip clearance is investigated for a squealer-type geometry for swirling inflow. It is found that for an increase in tip clearance of 1 %, η is decreased by 2.68 %. Then, it is shown that a winglet-type tip geometry may improve the efficiency by Δη 0.33% in comparison to the squealer tip. Third, it is shown that these trends are similar for plain inflow, however swirl decreases efficiency by up to 1.25 % in comparison to plain inflow. Finally, the clocking-position of the combustor-module relative to the nozzle guide vanes is varied leading to efficiency differences of up to 0.52 %.
Quantification of Performance Uncertainty for a Transonic Compressor Rotor Using an Adaptive NIPC Method
Authors: Luo Jiaqi , Xia Zhiheng , Liu Feng
Published: November 2019

Turbomachines are designed and run at specific operational conditions. However, due to some deterministic and stochastic sources of flow variations, especially at the inlet and outlet of turbomachinery blades, the influence of operational condition variations to aerodynamic performance are considerable. The quantification of performance change is one crucial module in robust design of turbomachinery blades. The paper studies the performance impact of stochastic operational condition variations using polynomial chaos. To reduce the computational cost, an adaptive sparse grid technique is employed to construct the adaptive non-intrusive polynomial chaos (NIPC) model. Through statistical evaluations of performance change for a three-dimensional transonic compressor rotor blade, NASA Rotor 67, the response performance of adaptive NIPC is firstly verified by comparing with the direct MCS method and static NIPC. Then the adaptive NIPC is used to statistically evaluate the adiabatic efficiency change of Rotor 67 due to the separate variation of inlet total pressure and outlet back pressure at two operation conditions: near peak efficiency and near stall. It is found that the performance change is nonlinear dependent on the inlet and outlet pressure variations. Besides, the simultaneous effects of inlet and outlet pressure variations to the performance change are investigated. Finally, the statistical results of flow variations along span, on the suction side and blade-to-blade streamsurfaces at different spans are illustrated in detail to demonstrate how the inlet and outlet pressure variations influence the aerodynamic performance change.
Reduced-Order Model of Unsteady Flows in a Turbomachinery Fan Modeled Using a Novel Proper Orthogonal Decomposition
Authors: Krath Elizabeth H. , Carpenter Forrest L. , Cizmas Paul G. A. , Johnston David A.
Published: November 2019

This paper presents a novel, more efficient reduced-order model based on the proper orthogonal decomposition (POD) for the prediction of flows in turbomachinery. To further reduce the computational time, the governing equations were written as a function of specific volume instead of density. This allowed for the pre-computation of the coefficients of the system of ordinary differential equations that describe the reduced-order model. A penalty method was developed to implement time-dependent boundary conditions and achieve a stable solution for the reduced-order model. Rotor 67 was used as a validation case for the reduced-order model, which was tested for both on- and off-reference conditions. This reduced-order model was shown to be more than 10,000 times faster than the full-order model.
Application of Quantitative Monochrome Calibrated Schlieren Technique in Highly-Loaded Turbine Cascade Test
Authors: Zhou Zhihong , Wang Haotian , Liu Huoxing
Published: November 2019

As the load of the turbine components of aircraft engines continuously increases, shock loss becomes the dominant factor of turbine stage loss and has become a hot topic. Schlieren technique is one of the few effective experimental methods to observe and study shock wave and, thus, has been widely used. Nevertheless, limited by camera accuracy and computer image processing technology, quantitative schlieren analysis methods were difficult to achieve in engineering applications. Fortunately, several quantitative schlieren methods have been developed with the help of new digital technology. Applying schlieren technique to the highly-loaded turbine cascade test is of great significance to the study of shock wave in highly-loaded turbine cascades. In this paper, the results of quantitative density field and shock intensity and loss in the cascade are obtained by using a double reflection type monochrome schlieren device. The boundary condition of density field is obtained by pressure test, and MATLAB software is used as image processing calculation tool. The quantitative results of this paper prove the feasibility of applying quantitative schlieren method to highly-loaded turbine cascade tests. Also, the implemented image processing method and density boundary condition acquisition method are suitable and convenient for cascade flow and shock measurement tests.
Structural Integrity Assessment and Engine Test of an Additive Manufactured First Stage Ring Segment of a Siemens Large Gas Turbine
Authors: Rühmer Tobias T. , Gampe Uwe , Fischer Kathrin A. , Wimmer Thomas , Haberland Christoph
Published: November 2019

The first stage ring segment (RS) of a Siemens large gas turbine has been redesigned for Selective Laser Melting (SLM) in order to reduce the cooling air consumption and to increase the gas turbine efficiency. The material is IN939. Cylindrical specimen for uniaxial tensile, cyclic tests and creep rupture tests have been manufactured by SLM to characterize the material by derivation of stress strain and creep rupture curves. The ring segment has been tested in a real gas turbine. The loading conditions as well as measurement data from thermocouples and dynamic strain gages have been taken as input for numerical structural integrity assessment. Permissible service life of the ring segment was evaluated in respect of low cycle fatigue (LCF), high cycle fatigue (HCF) and creep. Results have been compared with the conventional design. Furthermore the hook lock up in the engine was evaluated. The manufacturing quality was ensured through several methods including an optical 3D measuring system and computer tomography, process specimen and flow tests. Post investigations such as cut ups and metallography have also been conducted. The results show that the additive manufactured RS meets the required service lifetime.
Design and Flow Analysis of a Radial Outflow Turbo-Expander
Authors: Wang Xuesong , Sun Jinju , Huo Changjiang , Huo Guilong , Song Peng
Published: November 2019

Radial-outflow turbo-expanders have emerged in the recent years to suit some special applications where complex multi-phase and multi-component flows (like liquid-rich gases and solid particle-laden gases) need to be expanded. This paper presents a systematic study on the design and flow behavior of a single stage radial-outflow turbo-expander, which is to be used in organic Rankine power system to covert the low-temperature heat into shaft power. A mean-line code coupled with the optimization algorithm is developed and used to carry out the one-dimensional preliminary design, where 7 non-dimensional parameters are used as design variables (nozzle velocity coefficient, rotor velocity coefficient, reaction, rotor inlet and outlet flow angles, velocity ratio, and rotor diameter ratio). In comparison with the original design, significant design performance gains are achieved with the matched combination of design parameters. Geometric shape design is further performed for the expander. In consideration of the flow features in nozzle and rotor blade passages being nearly two-dimensional, blade shape design of both rows is conducted on the basis of the airfoils used for conventional axial flow turbines, where a conformal mapping method is used to convert the axial profile into the polar coordinate frame and it is then represented by 11 parameters of mean cylindrical diameter, radial and tangential chord, leading and trailing edge radius, blade inlet and outlet angles, blade inlet wedge angle, number of blades, unguided turning, and throat size. Flow and overall performance are simulated and predicted for the designed expander, where the output shaft power and overall isentropic efficiency is respectively predicted as 87.86 kW and 81.60% at design condition.
Parametric Design of Blisk Repairs by Patching Considering High Cycle Fatigue
Authors: Berger Ricarda , Hofmeister Benedikt , Gebhardt Cristian G. , Rolfes Raimund
Published: November 2019

Advanced repair techniques intended for jet engine parts are continuously under development and improvement. Patching is a high-tech approach towards reduced scrap rates and an extended life of high pressure compressor blisks.

In this work, we contribute to the structural design of patches for compressor blisks with improved high cycle fatigue behaviour. A fully parameterised patch model is developed, which allows the accurate description of the patch geometry. High cycle fatigue is assessed for welding seam positions specified by the patch model. On the basis of this automated process, a multi-objective optimisation is carried out. The fatigue strength and the length of the welding seam are defined as conflicting targets. Pareto-optimal solutions are calculated using a generalised pattern search algorithm. The engineer’s decision for a specific patch geometry can thus be made based on the optimisation results. The application of the new approach to a compressor blisk demonstrates the influence of vibration modes on fatigue strength. We identify sets of optimal suited patch geometries in accordance to the specified damage pattern.
Wet Gas Compressor Model Validation
Authors: Bakken Martin , Bjørge Tor , Bakken Lars E.
Published: November 2019

The continuous demand for oil and gas forces the petroleum industry to develop new and cost-efficient technologies to increase recovery from new fields and enhance extraction from existing fields. Subsea wet gas compression stands out as a promising solution to increase field extraction, utilize remote regions and reduce costs.

Today, a few subsea compressor systems are already operating while several new installations are expected within the next years. This creates a need for dynamic simulation tools to ensure proper system design and facilitate production. This paper presents the model setup for the wet gas compressor test facility at the Norwegian University of Science and Technology (NTNU). The test facility is an open loop configuration consisting of a single shrouded centrifugal impeller, a vaneless diffuser and a circular volute. The fluid is a mixture of ambient air and water. The analysis presented here validates the dynamic model behavior against transient experimental test cases, which include step changes in liquid content and driver trip in both wet and dry conditions. Further, the discharge valve performance has been analyzed in both dry and wet gas flow.

The test reveals that the dynamic model is able to operate in a stable manner while showing a close correspondence to the transient test cases. Care should be taken in utilizing dry gas valve characteristics in multiphase flows as increased liquid content has a distinct impact on the valve performance.
High Temperature Fatigue Assessment of a SiCf/SiC Ceramic Matrix Composite Using Advanced Monitoring Techniques
Authors: Newton Christopher D. , Jordan Steven P. , Bache Martin R. , Gale Louise
Published: November 2019

Laboratory based experiments to assess the “damage tolerance” of any new material system are a pre-requisite to engineering design, especially for aerospace components. In the case of CMCs, macro-scale specimens are preferred containing representative fibre-matrix architectures that support the definition of mechanical properties under service representative stress states.

The combination of complex internal structure and inevitable processing artefacts within CMCs provides numerous sites for damage initiation. Damage then progresses in an inhomogeneous manner prior to ultimate failure at some critical location. Traditional techniques employed for strain measurement (extensometry/strain gauges) prove to be ineffective tools when testing these advanced composites. More complex characterization is essential in order to assess the localised response of the material.

Advanced techniques, specifically digital image correlation and acoustic emission, have been applied to the evaluation of an CVI/MI silicon carbide reinforced/silicon carbide CMC tested at the elevated temperature of 800°C under fatigue loading. The spatial and temporal indications of damage were correlated to the observable forms of damage initiation and progression. Ancillary use of an in-situ SEM loading stage provided insight into the crack opening and closing mechanisms active within this material when under cyclic stress.
Prediction of Low-Engine-Order Excitation due to a Non-Symmetrical Nozzle Ring in a Radial Turbine by Means of the Nonlinear Harmonic Approach
Authors: Kovachev Nikola , Müller Tobias R. , Waldherr Christian U. , Vogt Damian M.
Published: November 2019

Low engine order (LEO) excitation in a turbomachine stage can be induced by non-uniform inflow conditions, manufacturing tolerances or in-service wear. LEOs are known to excite significant forced response vibration amplitudes that can easily cause High Cycle Fatigue (HCF) failure of blades. The accurate prediction of LEO excitation usually requires high-fidelity CFD models of the full annulus of the machine due to the loss of symmetry leading to excessive computational cost.

Previous investigation showed that the aerodynamic excitation stemming from the blade-passing-frequency in a vaned radial inflow turbine can be accurately predicted by using the NonLinear Harmonic (NLH) method at highly reduced computational costs. In the current paper, the feasibility of the NLH method for the prediction of LEO excitation due to geometrical asymmetries is investigated for the same test object. An exact digital replica of the nozzle guide ring is created using measured throat width data. NLH simulations resolving different combinations of frequencies and a time-marching calculation are conducted with the new model involving this digital replica. The results show that a NLH model including small number of certain frequencies is able to predict the occurring LEO excitation sufficiently accurate. By comparing results from subsequent forced response analysis with measured vibration amplitudes, a satisfactory agreement was found confirming this conclusion.
Large Eddy Simulation of the Flow Developing in Static and Rotating Ribbed Channels
Authors: Duchaine Florent , Gicquel Laurent , Grosnickel Thomas , Koupper Charlie
Published: November 2019

In the present work, the turbulent flow fields in a static and rotating ribbed channel representative of an aeronautical gas turbine are investigated by mean of wall-resolved compressible Large Eddy Simulation (LES). This approach has been previously validated in a squared ribbed channel based on an experimental database from Von Karman Institute (Reynolds and rotation numbers of about 15000 and +/− 0.38 respectively). LES results prove to reproduce differences induced by buoyancy in the near rib region and resulting from adiabatic or anisothermal flows under rotation. The model also manages to predict the turbulence increase (decrease) around the rib in destabilizing (stabilizing) rotation of the ribbed channels. On this basis, this paper investigates in more details the spatial development of the flow along the channel and its potential impact on secondary flow structures. More specifically and for all simulations, results on the adiabatic static case exhibits two contra-rotating structures close to the lateral walls of the channel induced by transversal pressure difference created by the ribs. These structures are generated after the first ribs and appear behind all inter rib sections, their relative position being partly affected by rotation. When considering the stabilizing rotating case, two additional contra-rotating structures also develop along the channel from the entrance close to the low-pressure wall (rib-mounted side). These vortices are due to the confinement of the configuration, inflow profile and are the result of Coriolis forces induced by rotation. Görtler vortices also appear on the pressure wall (opposite to the rib-mounted side). In the destabilizing rotating case, these two types of secondary structures are found to co-exist and their migration in the channel is significantly different due to the presence of the ribs on the pressure side. Finally, it is shown that heat transfer affects only marginally the static and stabilized cases while it changes more significantly the flow organization in the destabilizing case mainly because of enhanced heat transfer and increased buoyancy force effects.
Analysis of Thermal Transients for sCO2 Brayton Cycle Heat Exchangers
Authors: Moisseytsev Anton , Sienicki James J.
Published: November 2019

The design of heat exchangers for use in a supercritical carbon dioxide (sCO2) Brayton cycle power converter must provide for acceptable performance for duty cycle events encompassing anticipated transients and postulated accidents. This paper presents the results of a comprehensive analysis of thermal transients for sCO2 cycle heat exchangers, with emphasis on the sodium-to-CO2 heat addition heat exchanger. A range of transients, from normal operation to severe accidents, were simulated with the coupled PDC and SAS4A/SASSYS-1 system level dynamic analysis computer codes. For each transient, the calculated change in the heat exchanger wall temperature is determined as a measure of the thermal loading.
Design and Performance Analysis of Mixed Flow Turbine Rotors With Extended Blade Chord
Authors: Leonard Thomas , Spence Stephen , Filsinger Dietmar , Starke Andre
Published: November 2019

Mixed flow turbines offer additional design freedom compared with conventional radial turbines. This is useful in the automotive turbocharger application to reduce rotor inertia, which can be very beneficial for the transient response of a highly-boosted downsized passenger car powertrain. A previously published study from the authors analysed a series of nine mixed flow turbine rotors with varying blade cone angle and inlet blade angle. This paper reports an extension of that study with two further mixed flow turbine rotors where the chord length of the rotor blade was extended. The aim of this work was to understand both the aerodynamic and mechanical impacts of varying the chord length, particularly for the turbocharger application where off-design performance and transient response are very important. The baseline mixed flow rotor for this study had a blade cone angle of 30° and an inlet blade angle of 30°. Two further variations were produced; one with the TE extended in the downstream direction across the entire blade span. In the second variation the chord was extended at the hub corner only, while the shroud corner of the TE remained unchanged, with the aim of achieving some aerodynamic improvement while meeting mechanical requirements.

When the blade was extended at both the hub and shroud, the inertia and stress levels increased significantly and the blade eigenfrequencies reduced. There was significant improvement in peak efficiency, but the mechanical performance was unfavourable. The improvement in peak efficiency was mainly due to better exhaust diffuser performance and therefore would not be realised in most turbocharger installations.

The blade that was extended at only the hub corner incurred very little additional inertia, and the centrifugal stresses and blade eigenfrequencies were improved. Consequently, it was possible to reduce the blade thickness at the TE in order to achieve a more aerodynamically optimised design. In this case, the mechanical performance was acceptable and there were efficiency improvements of up to 1.1% pts at off-design conditions, with no reduction in peak efficiency or maximum mass flow rate. Therefore, the blade that was extended only at the hub produced some improvement within acceptable mechanical limits. The flow field features were considered for the three rotor geometries to explain the changes in loss and efficiency across the operating range.
Numerical Investigation of the Influence of Flow Deflection at the Upper Hood on Performance of Low Pressure Steam Turbine Exhaust Hoods
Authors: Munyoki Dickson , Schatz Markus , Vogt Damian M.
Published: November 2019

Most of the world’s power is produced by large steam turbines using fossil fuel, nuclear and geothermal energy.

The LP exhaust hoods of these turbines are known to contribute significantly to the losses within the turbine, hence a minor improvement in their performance, which results in a lower backpressure and thus higher enthalpy drop for the steam turbine, will give a considerable benefit in terms of fuel efficiency.

Understanding the flow field and the loss mechanisms within the exhaust hood of LP steam turbines is key to developing better optimized exhaust hood systems. A detailed analysis of loss generation within the exhaust hood was done by the authors [1]. It was found that most losses occur at the upper hood and are caused by the swirling flows, which mostly start at the diffuser outlet, especially for the top diffuser inlet sector flows that have a complex path to the condenser. The authors further numerically investigated the influence of hood height variation on performance of an LP turbine exhaust hood [2], which further contributed to the knowledge of the loss mechanisms.

With the loss mechanisms in exhaust hoods reasonably well understood, flow deflection at the upper hood is investigated in the current paper. The deflection is aimed at minimizing the intensity of the vortices formed thus reducing the exhaust losses. The deflector configurations analyzed are modifications of the walls of the reference configuration’s outer casing. The numerical models of the reference configuration which are based on a scaled axial-radial diffuser test rig operated by ITSM have already been validated by the authors at design and overload operating conditions and three tip jet Mach numbers (0, 0.4 and 1.2)[1].

Deflector configurations investigated are found to re-direct the flow at the upper hood and minimize the intensity of the swirling flows hence leading to improvement in performance of LP steam turbine exhaust hoods. The best performing deflector configuration is found to give a considerable improvement in performance of 20% at design load and 40% at overload both at tip jet Mach number of 0.4 (corresponding to shrouded last stage blades). At design load and tip jet Mach number of 1.2 (corresponding to unshrouded last stage blades), the improvement is found to be moderate. About 7% performance increase is observed.
Simple Contact Stiffness Model Validation for Tie Bolt Rotor Design With Butt Joints and Pilot Fits
Authors: Rimpel Aaron M. , Leopard Matthew
Published: November 2019

Tie bolt rotors for centrifugal compressors comprise multiple shaft components that are held together by a single tie bolt. The axial connections of these rotors — including butt joints, Hirth couplings, and Curvic couplings — exhibit a contact stiffness effect, which tends to lower the shaft bending frequencies compared to geometrically identical monolithic shafts. If not accounted for in the design stage, shaft bending critical speed margins can be compromised after a rotor is built. A previous paper had investigated the effect of tie bolt force on the bending stiffness of stacked rotor assemblies with butt joint interfaces, both with and without pilot fits. This previous work derived an empirical contact stiffness model and developed a practical finite element modeling approach for simulating the axial contact surfaces, which was validated by predicting natural frequencies for several test rotor configurations. The present work built on these previous results by implementing the same contact stiffness modeling approach on a real tie bolt rotor system designed for a high pressure centrifugal compressor application. Each joint location included two axial contact faces, with contact pressures up to five times higher than previously modeled, and a locating pilot fit. The free-free natural frequencies for different amounts of tie bolt preload force were measured, and the frequencies exhibited the expected stiffening behavior with increasing preload. However, a discontinuity in the data trend indicated a step-change increase in the contact stiffness. It was shown that this was likely due to one or more of the contact faces becoming fully engaged only after sufficient tie bolt force was applied. Finally, a design calculation was presented that can be used to estimate whether contact stiffness effects may be ignored, which could simplify rotor analyses if adequate contact pressure is used.
Compound Angle Effects on Shaped Hole Film Cooling
Authors: Gunady Ian E. , Borup Daniel D. , Banko Andrew J. , Elkins Christopher J. , Eaton John K.
Published: November 2019

Diffuser holes are used extensively for film cooling because they dramatically improve film-cooling effectiveness relative to round holes, but there is concern that the drawbacks of a compound angle (CA) may reduce the beneficial effects. This work uses Magnetic Resonance Velocimetry (MRV) to obtain the 3D, 3-component mean velocity field for a shaped hole with a pitch angle of 30 degrees, blowing ratio of unity, and compound angles of 10 and 20 degrees. The data are compared to a previous MRV measurement of an identical hole with zero skew angle. In the 0 and 20 degree cases, a separation bubble is observed on the downstream wall of the diffuser. Streamtubes emanating from the diffuser exit show the asymmetry of the flow as the jet is accelerated to align with the mainstream flow. Streamtube analysis shows evidence of competing effects of CA on film cooling performance: a wider streamtube footprint may increase coverage while a decrease in streamtube thickness may make coverage more susceptible to turbulent mixing. Analysis of the jet trajectory, defined as the streamtube centroid, shows that the realignment of the jet fluid with the freestream direction occurs in the region of the diffuser exit. Although significant qualitative changes in film cooling performance are not expected, some ingestion of mainstream flow may occur due to vortices present in the diffuser below the plane of the blade surface.
A Method for Estimating Profile Loss of Low Pressure Turbine Blades From the Low Speed Cascade Test Data
Authors: Kodama Hidekazu , Funazaki Ken-ichi , Ito Kodai , Ikehata Ryo , Koda Yamato
Published: November 2019

This paper describes the method for accurately estimating profile loss using measured flow parameters in a low speed cascade test. One of the issues of the control volume analysis for obtaining the mixed-out profile loss is to give realistic flow conditions on the control surface at the trailing edge plane. In this paper, the flow conditions at the trailing edge plane are related to the measured velocity distribution on the suction surface from throat to the trailing edge using the concept of circulation.

The validity of the estimation method is verified by using the results of steady Reynolds Averaged Navier-Stokes (RANS) simulation. In this verification, the verification profile loss of the RANS simulation is obtained by using the calculated drag forces of surface pressure and surface shear stress. The verification is conducted for two kinds of blade profiles at three different Reynolds numbers, 57,000, 100,000 and 147,000, for each blade profile. It is found that all the estimations by the current method are in a range between −10% to +6% of the verification profile losses of the RANS simulations.

This method is applied to the data analysis of low speed cascade tests for the two kinds of blade profiles used in the verification. It is shown that the measured pressure loss downstream of the cascade includes an additional loss to the profile loss even in the steady flow.
Jet Propulsion Engine Modelling Using Pseudo Bond Graph Approach
Authors: Göing Jan , Kellersmann Andreas , Bode Christoph , Friedrichs Jens
Published: November 2019

The multidisciplinary performance of a bypass jet propulsion engine is investigated and simulated in this paper by using the pseudo bond graph approach. This theory is applied in the in-house software tool ASTOR (AircraftEngine Simulation of Transient Operation Research) to simulate the different operating points and the system dynamics in transient load cases with high accuracy.

In this paper, the modulation of the V2500-A1 turbofan jet engine in the pseudo bond graph notation is described in detail. The thermodynamic cycle of a steady-state operating point is calculated and a transient load case is investigated to simulate the system performance. The results correspond with the data from a commercial software and with literature. However, some significant discrepancies are detected, which can be explained by the current model simplification.

In a nutshell, ASTOR is able to simulate the dynamic performance of the overall system and can be used to improve the process of the construction or regeneration of a complex capital good such as a jet engine.
Mechanisms and Quantitative Evaluation of Flow Loss Generation in a Multi-Stage Transonic Axial Compressor
Authors: Saito Seishiro , Furukawa Masato , Yamada Kazutoyo , Watanabe Keisuke , Matsuoka Akinori , Niwa Naoyuki
Published: November 2019

Flow structure and flow loss generation in a transonic axial compressor has been numerically investigated by using a large-scale detached eddy simulation (DES). The data mining techniques, which include a vortex identification based on the critical point theory and a limiting streamline visualization with the line integral convolution (LIC) method, were applied to the DES result in order to analyze the complicated flow field in compressor. The flow loss in unsteady flow field was evaluated by entropy production rate, and the loss mechanism and the loss amount of each flow phenomenon were investigated for the first rotor and the first stator. In the first rotor, a shock-induced separation is caused by the detached shock wave and the passage shock wave. On the hub side, a hub-corner separation occurs due to the secondary flow on the hub surface, and a hub-corner separation vortex is clearly formed. The flow loss is mainly caused by the blade boundary layer and wake, and the loss due to the shock wave is very small, only about 1 percent of the total loss amount in the first rotor. However, the shock/boundary layer interaction causes an additional loss in the blade boundary layer and the wake, which amount reaches to about 30 percent of the total. In the first stator, the hub-corner separation occurs on the suction side. Although only one hub-corner separation vortex is formed in the averaged flow field, the hub-corner separation vortex is generated in multiple pieces and those pieces interfere with each other in an instantaneous flow field. The hub-corner separation generates huge loss over a wide range, however, the loss generation around the hub-corner separation vortex is not so large, and the flow loss is mainly produced in the shear layer between the mainstream region and the separation region. The main factors of loss generation are the boundary layer, wake and hub-corner separation, which account for about 80 percent of the total loss amount in the first stator.
On the Importance of Transition Control at Transonic Compressor Blades
Authors: Hergt A. , Klinner J. , Grund S. , Willert C. , Steinert W. , Beversdorff M.
Published: November 2019

The flow through a transonic compressor cascade is characterized by high unsteadiness and a high loss level. This results from the shock waves in the blade cascade and their interaction with the blade suction side boundary layer. In the case of a laminar shock wave boundary layer interaction the loss level is higher due to the occurrence of a laminar separation bubble below the shock wave compared to the shock wave interaction with a turbulent boundary layer. In addition, the oscillation of the shock position in both cases influences the working range concerning the point of stall onset as well as leading to an unsteady interaction with the blade, called buffeting. The reduction of losses and of unsteadiness in the shock wave oscillation, connected to a decrease of the blade buffeting effect, are the aims of the current investigation. Therefore, experimental investigations using a roughness patch as well as air jet vortex generators in order to control the transition in a transonic compressor cascade have been conducted at the transonic cascade wind tunnel of DLR at Cologne. At an inflow Mach number of 1.21 a loss reduction for both transition control cases is achieved. In spite of a nearly uninfluenced fluctuation range of the passage shock wave compared to the reference cascade, the oscillation spectra of the transition control cases show a reduction of the shock movement amplitude at a frequency below 500 Hz and above 1 kHz. In the closing section of the paper a detailed discussion on the reasons for the resulting flow behaviour based on PIV and High Speed Shadowgraphy data is given. The resulting conclusion of the study is that the consideration of transition control at transonic compressor blades is very important in order to reduce losses and flow unsteadiness which directly influences blade buffeting and the numerical prediction quality of the stall onset.
Examining the Effect of Geometry Changes in Industrial Fuel Injection Systems on Hydrodynamic Structures With BiGlobal Linear Stability Analysis
Authors: Kaiser Thomas Ludwig , Oberleithner Kilian , Selle Laurent , Poinsot Thierry
Published: November 2019

Shape optimization with respect to the suppression or enhancement of dynamical flow structures is an important topic in combustion research and beyond. In this paper, we investigate the flow in an industrial fuel injection system by experimental means, as well as Large Eddy Simulation (LES) and Linear Stability Analysis (LSA) for two configurations of the swirler. In the first configuration, the reference geometry, a Precessing Vortex Core (PVC) occurs. In the second configuration, a center body is mounted in the interior of the injector. It is shown by both experiments and LES that the PVC is suppressed in the presence of the center body, while the mean flow remains nearly unaffected. The method of LSA is applied in order to explain the effect of the geometry change. The work shows that LSA is capable of explaining the occurrence or disappearance of coherent structures evolving on the turbulent flows if the geometry is changed. This is an important step in using LSA in the context of shape optimization of industrial fuel injectors.
An Analysis of Civil Aviation Industry Safety Needs for the Introduction of Liquid Hydrogen Propulsion Technology
Authors: Benson C. M. , Ingram J. M. , Battersby P. N. , Mba D. , Sethi V. , Rolt A. M.
Published: November 2019

Over the next few decades air travel is predicted to grow, with international agencies, manufacturers and governments predicting a considerable increase in aviation use. However, based on current fuel type, International Civil Aviation Organization (ICAO) project emissions from aviation are estimated to be seven to ten times higher in 2050 than in 1990. These conflicting needs are problematic and have led to the EU Flightpath 2050 targeting dramatic emissions reductions for the sector (75% CO2, 90% NOX by 2050).

One proposed solution, decreasing carbon emissions without stunting the increase in air travel, is hydrogen propulsion; a technology with clear environmental benefits. However, enabling the safe application of this fuel to aviation systems and industrial infrastructure would be a significant challenge. High-profile catastrophic incidents involving hydrogen, and the flammable and cryogenic nature of liquid hydrogen (LH2) have led to its reputation as a more dangerous substance than existing or alternative fuels. But, where they are used (in industry, transport, energy), with sufficient protocols, hydrogen can have a similar level of safety to other fuels. A knowledge of hazards, risks and the management of these becomes key to the integration of any new technology.

Using assessments, and a gap analysis approach, this paper examines the civil aviation industry requirements, from a safety perspective, for the introduction of LH2 fuel use. Specific proposed technology assessments are used to analyze incident likelihood, consequence impact, and ease of remediation for hazards in LH2 systems, and a gap analysis approach is utilized to identify if existing data is sufficient for reliable technology safety assessment. Outstanding industry needs are exposed by both examining challenges that have been identified in transport and industrial areas, and by identifying the gaps in current knowledge that are preventing credible assessment, reliable comparison to other fuels and the development of engineering systems.

This paper demonstrates that while hydrogen can be a safe and environmentally friendly fuel option, a significant amount of work is required for the implementation of LH2 technology from a mass market perspective.
Experimental and Numerical Investigation on the Flow in a Return Channel of Multistage Centrifugal Compressors
Authors: Dolle B. , Brillert D. , Dohmen H. J. , Benra F.-K.
Published: November 2019

Multistage radial compressors are major components in plenty of industrial applications. Today, compressor downsizing for CAPEX reduction is of utmost importance. Accordingly, the pressure ratio must be increased, accommodated in a most compact design, accepting nearly no penalties in the performance level achieved so far.

In order to investigate the complex flow in stator parts of multistage centrifugal compressors and to increase the confidence level of numerical methods a new test rig is developed and taken into operation. This test rig allows to separate stationary flow effects from time variant effects leading to an in depth insight into the physical flow features. The aim is to investigate the flow in different stator designs in detail for varying flow coefficients. Additive manufacturing techniques are applied to achieve low costs simultaneously with short production time for the tested parts.

In this publucation, the measured flow field in the stator parts is discussed. The experimental results comprise velocity and pressure data from five-hole-probes and unsteady velocity data from single-film hot-film-probes. Using unsteady velocity data, turbulent statistics such as turbulence intensity and the turbulent kinetic energy will be determined. Subsequently, the experimental results are compared to numerical results. Therefore, (U)RANS simulations are performed using a commercial CFD-code. The simulation results are evaluated at planes appropriate to the measuring planes in the test rig to guarantee a directly comparable data base.
A Probabilistic Uncertainty Estimation Method for Turbulence Parameters Measured by Hot Wire Anemometry in Short Duration Wind Tunnels
Authors: Boufidi Elissavet , Lavagnoli Sergio , Fontaneto Fabrizio
Published: November 2019

A robust and complete uncertainty estimation method is developed to quantify the uncertainty of turbulence quantities measured by hot-wire anemometry at the inlet of a short-duration turbine test rig. The uncertainty is categorized into two macro-uncertainty sources: the measurement related uncertainty (the uncertainty of each instantaneous velocity sample) and the uncertainty stemming from the statistical treatment of the time series. The former is addressed by the implementation of a Monte Carlo method. The latter, which is directly related to the duration of the acquired signal, is estimated using the moving block bootstrap method, a non-parametric resampling algorithm suitable for correlated time series. This methodology allows computing the confidence intervals of the spanwise distributions of mean velocity, turbulence intensity, length scales and other statistical moments at the inlet of the turbine test section.
Study of High Pressure Compressor Performances in Windmilling Conditions by Three Complementary Approaches: Experiment, LBM and 1D Modeling
Authors: Nocture Michel , Mery Yoann , Ruiz Domingo Javier , Rochuon Nicolas , Bonnal Benoit , Vanoli Emmanuel , Gopalakrishnan Pradeep , Jammalamadaka Avinash
Published: November 2019

Modeling of the engine behavior in windmilling conditions is an important engineering objective. The relight capability of the engine is mainly associated with the air mass flow rate that passes through the engine high pressure core in those conditions. This is one of the parameters that drive the combustion chamber volume. Predicting the engine behavior is challenging, especially early in the development process. The pressure losses along the core are distributed between the different stages of the compressors and turbines, which are operated extremely far from their design point. Engine manufacturers must anticipate with sufficient margins to ensure that the specifications are met when the engine is finally qualified in flight. This article focuses on the behavior of compressor cascades in such conditions, corresponding to high negative incidences. A recently designed high pressure compressor is studied in windmilling conditions using three complementary approaches. First, engine tests are used to obtain validated 0D data for two flight conditions. Then, state of the art Lattice-Boltzmann Method (LBM) simulations are carried out to have insight in the flow characteristics inside the compressor. They are compared to the available experimental data. Finally, a 1D model using stage by stage Euler equation for turbomachinery is used. This kind of modeling is of particular interest because it can be used early in the design process. The correlations for losses and deviation angle from the literature are modified to account for the particularity of the flow in those conditions. One shows that the three approaches give consistent results.
Effect of Surface Roughness on Aerodynamic Performance of Turbine Rear Structure
Authors: Deshpande Srikanth , Jonsson Isak , Chernoray Valery
Published: November 2019

A turbine rear structure (TRS) is typically used to deswirl the flow from the low pressure turbine (LPT) and hence maximize the axial thrust. It is important to study the effect of surface roughness on aerodynamic performance of TRS.

Numerical simulations with surface roughness are performed and results are compared with the data from experiments. Comparisons show that the trends between the numerical analysis and the experiments are in line with one another. Further understanding of numerical analysis shows that, at higher Reynolds number, the effect of surface roughness is more significant when compared to the effects at low-Reynolds number.

An attempt has been made to study the transition behavior in the presence of surface roughness. Since boundary layer measurements are planned for the rig, this numerical study provides good inputs in order to plan instrumentation.
Modelling and Design of LPC Components With Semi-Analytical Models: Part II — Design of Optimal OGV Cascades
Authors: di Mare Luca , Carnevale Mauro , Rife Max E. , Kulkarni Davendu , Northall Richard
Published: November 2019

The growth in diameter of turbofan engines exacerbates problems related to the interaction of the Outlet Guide Vanes (OGV), pylon and intake because it reduces the ratio between components gaps and disturbance wavelength. The main components of this interaction are the potential fields generated by the intake and by structural components in the bypass, the pylon and the Radial Drive Fairing (RDF). The OGV bladerow and the fan are immersed in these potential fields and suffer performance degradation as well as integrity issues as a result. Simple actuator-disc analysis shows that a uniform OGV cascade amplifies the effect of the pylon potential flow. Therefore, a number of methods have been proposed over the years to compute OGV exit flow angle patterns that result in an approximately circumferentially uniform static pressure field at fan exit. Within actuator disc approximations, the determination of the optimal exit flow angle pattern can be accomplished analytically but little information is obtained on how the geometry of the vanes ought to be modified. Consequently, it is not difficult to generate by this method OGV cascades that stall or choke locally. More recent contributions use CFD computations coupled to optimization methods to determine OGV patterns that reduce the distortion at the fan exit, while minimising some measure of OGV loss. Whilst in principle more rational, these methods encounter practical difficulties due the computational power needed to obtain reliable loss estimates while exploring large design spaces. In this paper the view is taken that the performance of the OGV bladerow can be preserved during the optimization process if the loading distribution of each vane is made to match the loading distribution of the nominal vane (i.e. the aerodynamic design intent with axisymmetric inlet and exit flow). As loading distributions are readily available from inviscid-type analysis, the generation of optimal OGV patterns can be accomplished with very reasonable computational expense using a method based on the model described in part I of this paper.
Numerical Analysis of Lift Generation in a Radial Segmented Gas Seal
Authors: Arghir Mihai , Dahite Samia
Published: November 2019

A radial segmented seal is composed of three or six carbon segments that are assembled by a circumferential (garter) spring that presses them against the rotor. Assembled, they take the form of an annular ring. Each segment has several pads that generate a radial lift force depending on the rotor speed. There are many ways of creating effective lift forces. For example, a pocket on the pad creates a lift force because each pad will act as a Rayleigh step bearing. A groove on the rotating shaft will also create a radial lift force on the pad. However, this latter lift force will be unsteady. The aim of the present work is the numerical study of the lift created by a grooved rotor on a pad. Due to the very small operating radial clearances of radial segmented seals (less than 10 μm), the problem can be simplified by analyzing a single pad and a grooved runner. Previous analysis of gas face seals or thrust bearings always considered grooved pads and a smooth runner, even when the runner was grooved. The peculiarity of this study, which is the first of its kind, is considering the unsteady problem of the moving runner grooves. The analysis was performed for a single pad of a radial segmented seal operating with air.