bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.