bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanism of Blockage Generation in Transonic Centrifugal Compressor at Design and Off-Design Conditions
Authors: Kaneko Masanao , Tsujita Hoshio 
Published: August 2015

In a transonic centrifugal compressor, the loss generation is intensified by the formation of the shock wave and consequently the blockage is expected to increase. The blockage is considered to influence not only the flow rate and the increase of the static pressure but also the stall inception. However, the detailed mechanism of the blockage generation in the transonic centrifugal compressor has not been fully clarified.
In this study, in order to clarify the mechanisms of loss and blockage generations in the transonic centrifugal compressor which are expected to be strongly influenced by the operating condition, the flows in the compressor at the off-design condition as well as at the design condition were analyzed numerically. The verifications of the computed results were carried out by comparing with available experimental results. The computed result clarified that the loss generation near the impeller inlet at design condition was mainly caused by the interactions of the shock wave with the tip leakage vortex appearing from the leading edge of the main blade as well as the boundary layer on the suction surface of the main blade. Moreover, these interactions were intensified by the decrease of the flow rate, and consequently enhanced the blockage effects by the tip leakage vortex from the leading edge of the main blade and resulted in the increase of the aerodynamic loss especially along the shroud surface in the impeller passage. On the other hand, the decrease of the blockage effects by the tip leakage vortex from the main blade with the increase of the flow rate formed the shock wave on the suction surface of the splitter blade at near-choke condition. This shock wave interacted with the tip leakage vortex from the splitter blade and consequently increased the aerodynamic loss.
Heat Transfer Implications of Acoustic Resonances in HP Turbine Blade Internal Cooling Channels
Authors: Selcan C. , Cukurel B. , Shashank J. 
Published: August 2015

In an attempt to investigate the acoustic resonance effect of serpentine passages on internal convection heat transfer, the present work examines a typical high pressure turbine blade internal cooling system, based on the geometry of the NASA E3 engine. In order to identify the associated dominant acoustic characteristics, a numerical FEM simulation (two-step frequency domain analysis) is conducted to solve the Helmholtz equation with and without source terms. Mode shapes of the relevant identified eigenfrequencies (in the 0–20kHz range) are studied with respect to induced standing sound wave patterns and the local node/antinode distributions. It is observed that despite the complexity of engine geometries, as a first order approximation, the predominant resonance behavior can be modeled by a same-ended straight duct.
Therefore, capturing the physics observed in a generic geometry, the heat transfer ramifications are experimentally investigated in a scaled wind tunnel facility at a representative resonance condition. Focusing on the straight cooling channel’s longitudinal eigenmode in the presence of an isolated rib element, the impact of standing sound waves on convective heat transfer and aerodynamic losses are demonstrated by liquid crystal thermometry, local static pressure and sound level measurements. The findings indicate a pronounced heat transfer influence in the rib wake separation region, without a higher pressure drop penalty. This highlights the potential of modulating the aero-thermal performance of the system via acoustic resonance mode excitations.
Numerical Investigation of Contrasting Flow Physics in Different Zones of a High-Lift Low Pressure Turbine Blade
Authors: Cui J. , Nagabhushana Rao V. , Tucker P. G. 
Published: August 2015

Using a range of high fidelity large eddy simulations, the contrasting flow physics on the suction surface, pressure surface and endwalls of a low pressure turbine blade (T106A) was studied. The current paper attempts to provide an improved understanding of the flow physics over these three zones under the influence of different inflow boundary conditions. These include: (a) the effect of wakes at low and high turbulence intensity on the flow at mid-span and (b) the impact of the state of the incoming boundary layer on endwall flow features.
On the suction surface, the pressure fluctuations on the aft portion significantly reduced at high Free-Stream Turbulence (FST). The instantaneous flow features revealed that this reduction at high FST is due to the dominance of ‘streak-based’ transition over the ‘Kelvin-Helmholtz’ based transition. Also, the transition mechanisms observed over the turbine blade were largely similar to those on a flat plate subjected to pressure gradients.
On pressure surface, elongated vortices were observed at low FST. The possibility of the co-existence of both the Görtler instability and the severe straining of the wakes in the formation of these elongated vortices was suggested. While this was true for the cases under low turbulence levels, the elongated vortices vanished at higher levels of background turbulence.
At endwalls, the effect of the state of the incoming boundary layer on flow features has been demonstrated. The loss cores corresponding to the passage vortex and trailing shed vortex were moved farther from the endwall with a turbulent boundary layer when compared to an incoming laminar boundary layer. Multiple horse-shoe vortices, which constantly moved towards the leading edge due to a low-frequency unstable mechanism, were captured.
Low NOx SEV Lean Premix Reheat Combustion in Alstom GT24 Gas Turbines
Authors: Guyot Daniel , Tea Gabrielle , Appel Christoph 
Published: August 2015

Reducing gas turbine emissions and increasing their operational flexibility are key targets in today’s gas turbine market. In order to further reduce emissions and increase the operational flexibility of its GT24 (60Hz) and GT26 (50Hz), Alstom has introduced an improved SEV burner and fuel lance into its GT24 upgrade 2011 and GT26 upgrade 2011 sequential reheat combustion system.
Sequential combustion is a key differentiator of Alstom GT24 engines in the F-class gas turbine market. The inlet temperature for the GT24 SEV combustor is around 1000 degC and reaction of the fuel/oxidant mixture is initiated through auto-ignition. The recent development of the Alstom sequential combustion system is a perfect example of evolutionary design optimizations and technology transfer between Alstom GT24 and GT26 engines. Better overall performance is achieved through improved SEV burner aerodynamics and fuel injection, while keeping the main features of the sequential burner technology.
The improved SEV burner/lance concept has been optimized towards rapid fuel/oxidant mixing for low emissions, improved fuel flexibility with regards to highly reactive fuels (higher C2+ and hydrogen content), and to sustain a wide operation window. In addition, the burner front panel features an improved cooling concept based on near-wall cooling as well as integrated acoustics damping devices designed to reduce combustion pulsations thus extending the SEV combustor’s operation window even further. After having been validated extensively in the Alstom high pressure sector rig test facility, the improved GT24 SEV burner has been retrofitted into a commercial GT24 field engine for full engine validation during long-term operation.
This paper presents the obtained high pressure sector rig and engine validation results for the GT24 (2011) SEV burner/lance hardware with a focus on reduced NOX and CO emissions and improved operational behavior of the SEV combustor. The high pressure tests demonstrated robust SEV burner/lance operation with up to 50% lower NOX formation and a more than 70K higher SEV burner inlet temperature compared to the GT24 (2006) hardware.
For the GT24 engine with retrofitted upgrade 2011 SEV burner/lance all validation targets were achieved including an extremely robust operation behavior, up to 40% lower GT NOX emissions, significantly lower CO emissions at partload and baseload, a very broad operation window (up to 100K width in SEV combustor inlet temperature) and all measured SEV burner/lance temperatures in the expected range. Sector rig and engine validation results have confirmed the expected SEV burner fuel flexibility (up to 18%-vol. C2+ and up to 5%-vol. hydrogen as standard).
Impact of High Exhaust Back Pressure on Power Turbine Secondary Flows and Disc Thermals
Authors: Thirumurthy Deepak 
Published: August 2015

Industrial and aeroderivative gas turbines use exhaust systems for flow diffusion and pressure recovery. The downstream balance-of-plant systems such as heat recovery steam generators or selective catalytic systems require, in general, a steady, uniform flow out of the exhaust system. One detrimental effect of having these downstream systems is the increased back pressure. These combined-cycle systems increase the back pressure on the free power turbine which results in decreased power output and efficiency.
Aeroderivative gas turbines for mechanical drive application have a wide operational envelope. In general, at baseload, the exhaust back pressure ranges from 1.5 to 2.5 kPa above ambient pressure. Increased exhaust back pressure results in changes to power turbine secondary flows by changing the cavity flow dynamics, sealing flows, and rim seal ingestion. This impacts the thermal characteristics of turbine rotor discs and their lives.
The primary motivation for this research and development work was to develop solution for secondary air system and investigate the impact of high exhaust back pressure on power turbine disc thermals. At first, 1-D system-level power turbine secondary flow analyses were carried out with normal back pressure (3.0 kPa) and with high back pressure (11.37 kPa). In addition, 3-D computational fluid dynamic simulations were performed to understand the cavity flow dynamics and disc heat transfer coefficient variations. These results were used in a high-fidelity 2-D thermal modeling of the power turbine to study the impact of back pressure on turbine disc thermal characteristics and their lives.
The fluid and thermal predictions were validated using normal back pressure full-scale full-load test results. Cooling mass flow rate, static pressure, air temperature, and metal temperature predictions are compared with test results over a wide operating range. The numerical predictions are in good agreement with test results.
A Comparison of a Mono, Twin and Double Scroll Turbine for Automotive Applications
Authors: Walkingshaw Jason , Iosifidis Georgios , Scheuermann Tobias , Filsinger Dietmar , Ikeya Nobuyuki 
Published: August 2015

As a means of meeting ever increasing emissions and fuel economy demands car manufacturers are using aggressive engine downsizing. To maintain the power output of the engine turbocharging is typically used. Due to the miss-match of the mass flow characteristics of the engine to the turbocharger, at low engine mass flow rates, the turbocharger can suffer from slow response known as “Turbolag”. Mono-scroll turbines are capable of providing good performance at high mass flow rates and in conjunction with low inertia mixed flow turbines can offer some benefits for transient engine response. With a multi-entry system the individual volute sizing can be matched to the single mass flow pulse from the engine cylinders. The exhaust pulse energy can be better utilised by the turbocharger turbine improving turbocharger response, while the interaction of the engine exhaust pulses can be better avoided, improving the scavenging of the engine.
The behaviour of a mono-scroll turbocharger with the engine using engine simulation tools has been well established. What requires further investigation is the comparison with multi-entry turbines. CFD (Computational Fluid Dynamics) has been used to examine the single admission behaviour of a twin and double scroll turbine. Turbocharger gas stand maps of the multi-entry turbines have been measured at full and single admission. This data has been used in a 0D engine model. In addition, the turbine stage has been tested on the engine and a validation of the engine model against the engine test data is presented. Using the validated engine model a comparison has been made to understand the differences in the sizing requirements of the turbine and the interaction of the mono-scroll and multi-entry turbines with the engine. The impact of the different efficiency and mass flow rate trends of the mono and multi-entry turbochargers are discussed and the trade-offs between the design configurations regarding on engine behaviour are investigated.
Effects of Flow Path Height of Impeller Exit and Diffuser on Flow Fields in a Transonic Centrifugal Compressor
Authors: Tomita Isao , Ibaraki Seiichi , Wakashima Koji , Furukawa Masato , Yamada Kazutoyo , Kanzaki Dai 
Published: August 2015

Today turbocharging has become a fundamental technology to realize engine downsizing, which is an attractive strategy for low carbon emissions. High efficiency and wide operating range are strongly required for the automotive turbochargers. Especially centrifugal compressors for automotive turbochargers are requested to operate with high efficiency from the surge limit to the choke limit. The internal flow in a centrifugal compressor is however three dimensional and shows very complex unsteady flow phenomena like a rotating stall and a surging, which have yet to be elucidated fully.
In this study the effect of flow path height of impeller and diffuser on flow fields in a transonic centrifugal compressor has been investigated both numerically and experimentally. Detached Eddy Simulation (DES) has been applied and revealed the reduction of impeller exit flow path affects the accumulation of low momentum flow at impeller inlet as well as impeller exit. Also it has been confirmed experimentally the 15% reduction of the impeller exit flow path height can halve the surging flow rate with same choking capacity at pressure ratio of 2.6.
Aeroelastic Investigation of an Annular Transonic Compressor Cascade: Numerical Sensitivity Study for Validation Purposes
Authors: Chenaux Virginie Anne , Grüber Björn 
Published: August 2015

The accuracy of flutter or forced response analyses of turbomachinery blade assemblies strongly depends on the correct prediction of the unsteady aerodynamic loads acting on the vibrating blades.
This paper presents the aeroelastic numerical results of an annular transonic compressor cascade subjected to harmonic oscillation conditions. The measurements associated were performed in an annular test facility for non-rotating cascades.
The aim of this investigation is to get a deeper understanding of the specific characteristics of this test facility as well as improving the flutter prediction procedure and accuracy.
For a subsonic and a transonic flow condition, the steady-state blade surface pressure distributions were predicted with two mesh configurations and results were compared to the experimental results. The first configuration omits the geometrical complexity of the experimental model and only models the blade passage. The second mesh configuration includes the cascade’s detailed geometry and cavities. The presence of leakage flows arisen due to the cascade’s slits and cavities are identified and their impact on the main flow field is analyzed and discussed.
For the flutter computations, two mesh resolutions were investigated. The global damping predicted with a fine and a coarse mesh was compared, as well as the local pressure amplitudes and phases predicted with both configurations.
Results show that even though similar global damping curves are predicted with both mesh resolution, for some IBPAs, local differences exist on the pressure amplitudes and phases. This highlights that only comparing the global damping coefficient, is not sufficient for code validation.
Experimental Analysis of Floating Ring Annular Seals and Comparisons With Theoretical Predictions
Authors: Mariot Antoine , Arghir Mihai , Hélies Pierre , Dehouve Jérôme 
Published: August 2015

Floating ring annular seals represent one of the solutions for controlling leakage in high speed rotating machinery. They are generally made of a carbon ring mounted in a steel ring for preserving their integrity. Low leakage is ensured by the small clearance of the annular space between the carbon ring and the rotor. Under normal operating conditions, the ring must be able to “float” on the rotor in order to accommodate its vibration. Impacts between the carbon ring and the rotor may occur when the annular seal is locked up against the stator and the amplitude of rotor vibrations are larger than the radial clearance. This situation is prohibited because it rapidly leads to the destruction of the carbon ring.
The present work presents experimental results obtained for floating ring annular seals of 38 mm, tandem mounted in a buffer seal arrangement. The rotation speed was comprised between 50 Hz and 350 Hz and maximum pressure drop was 7 bar. For these operating conditions the floating ring follows the rotor vibrations without any impacts.
Comparisons were made with a theoretical model based on the equations of motion of the floating ring driven by mass inertia forces, hydrostatic forces in the (main) annular seal and by friction forces on its radial face (also named the “nose” of the seal). The friction coefficient on the nose of the floating ring was estimated from Greenwood and Williamson’s model for mixed lubrication. The present analysis validates the theoretical model used for predicting the dynamic response of the floating ring for a given rotor motion.
Implementation of Explicit Density-Based Unstructured CFD Solver for Turbomachinery Applications on Graphical Processing Units
Authors: Romanelli G. , Mangani L. , Casartelli E. , Gadda A. , Favale M. 
Published: August 2015

For the aerodynamic design of multistage compressors and turbines Computational Fluid Dynamics (CFD) plays a fundamental role. In fact it allows the characterization of the complex behaviour of turbomachinery components with high fidelity.
Together with the availability of more and more powerful computing resources, current trends pursue the adoption of such high-fidelity tools and state-of-the-art technology even in the preliminary design phases. Within such a framework Graphical Processing Units (GPUs) yield further growth potential, allowing a significant reduction of CFD process turn-around times at relatively low costs.
The target of the present work is to illustrate the design and implementation of an explicit density-based RANS coupled solver for the efficient and accurate numerical simulation of multi-dimensional time-dependent compressible fluid flows on polyhedral unstructured meshes. The solver has been developed within the object-oriented OpenFOAM framework, using OpenCL bindings to interface CPU and GPU and using MPI to interface multiple GPUs.
The overall structure of the code, the numerical strategies adopted and the algorithms implemented are specifically designed in order to best exploit the huge computational peak power offered by modern GPUs, by minimizing memory transfers between CPUs and GPUs and potential branch divergence occurrences. This has a significant impact in terms of the speedup factor and is especially challenging within a polyhedral unstructured mesh framework. Specific tools for turbomachinery applications, such as Arbitrary Mesh Interface (AMI) and mixing-plane (MP), are implemented within the GPU context.
The credibility of the proposed CFD solver is assessed by tackling a number of benchmark test problems, including Rotor 67 axial compressor, C3X stator blade with conjugate heat transfer and Aachen multi-stage turbine. An average GPU speedup factor of approximately S ≃ 50 with respect to CPU is achieved (single precision, both GPU and CPU in 100 USD price range). Preliminary parallel scalability test run on multiple GPUs show a parallel efficiency factor of approximately E ≃ 75%.
Influence of Fuel Characteristics in a Correlation to Predict Lean Blowout of Bluff-Body Stabilized Flames
Authors: Huelskamp Bethany C. , Kiel Barry V. , Gokulakrishnan Ponnuthurai 
Published: August 2015

This study employed experimental data collected at the Air Force Research Laboratory (AFRL) as well as data from a review of past literature to develop a correlation for predicting lean blowout through the use of a least-squares curve-fit method. Combining data from the literature with data from AFRL allowed significant variations within the dataset with regard to velocity, flameholder diameter and shape, pressure, temperature, and fuel. Gaseous, single-component fuels as well as multi-component jet fuels were included in the study. The study reports new jet fuel blowout data. The laminar flame speed and ignition delay time calculated using detailed chemical kinetics mechanisms were used in the correlations to determine the chemical timescales relevant to lean blowout.
The correlation presented here indicates that the lean blowout of bluff-body stabilized flames is dependent on the Damköhler number, with fuel variation being a significant factor. The ratio of the flameholder diameter to the lip velocity was found to influence the lean blowout. This ratio represents the fluid-mechanic timescale in the Damköhler number. Pressure, temperature, and the hydrogen-to-carbon ratio of the fuel affect the reactivity of the mixture, contributing to the chemical timescale in the Damköhler number. For a limited dataset, the ignition delay time is an adequate representation of the chemical timescale.
Stochastic Methods for Nonlinear Rotordynamics With Uncertainties
Authors: Peradotto Edoardo , Panunzio Alfonso M. , Salles Loïc , Schwingshackl Christoph 
Published: August 2015

The calculated dynamic response of an excited rotating system can be significantly affected by uncertainties in its mechanical properties, such as mass, stiffness, geometrical imperfections, or loadings. For this reason, it is essential to understand and quantify the influence of uncertain parameters on the predicted rotor response.
This paper aims to optimize the propagation of random input uncertainties for a rotordynamic problem and assess their influence on the dynamic behaviour of an unbalanced rotor. The Harmonic balance method (HBM) and a non-intrusive Polynomial Chaos Expansion (PCE) are used to evaluate the stochastic response of a finite element rotor. The proposed stochastic approach is based on a numerical quadrature calculation of integrals for finding the coefficients of the PCE.
The method is initially applied to evaluate the stochastic response of a linear rotodynamic system, leading to the original concept of stochastic Campbell diagram and further extended to nonlinear rotordynamic problems, using the Asymptotic Numerical Method (ANM).