bluuebunny/crossref_metadata_2025 huggingface dataset:
SS-OCT and FD-OCT System Prototyping Using LabVIEW FPGA
Authors: Olson Zach
Published: July 2013

Optical coherence tomography (OCT) techniques have opened up a number of new medical imaging applications in research and clinical applications. Key application areas include cancer research, vascular applications such as imaging arterial plaque, and ophthalmology applications such as pre and post-operative cataract surgery imaging. Emerging Technologies in galvo control, light sources, detector technologies, and parallel hardware-based processing are increasing the quality and performance of images, as well as reducing the cost and footprint of OCT systems. The parallel computing capabilities of field programmable gate arrays (FPGAs), multi-core processors, and graphics processing units (GPUs) have enabled real-time OCT image processing, which provides real-time image data to support surgical procedures.
Strategies for Building an Arterial Flow Phantom
Authors: Kargar Soudabeh , Bridges Loren , Bardot Dawn M.
Published: July 2013

Flow phantoms are used to simulate and study the cardiovascular system, associated disease states and boundary conditions. A flow phantom reproduces the flow and pressure of a portion of the vascular system for use in bench top studies of the effect of different changes or devices on the pressure response and deformation of the vessels.
A Finite Element Approach for Evaluating the Risk of Endograft Migration
Authors: Prasad Anamika , Zarins Christopher K. , Figueroa C. Alberto
Published: July 2013

Evaluating the risk of endograft migration is important for long-term durability of endovascular aneurysm repair (EVAR) technique. In this paper we apply a step-wise coupled finite element approach to evaluate the risk of endograft migration in representative aorta models subjected to in-vivo hemodynamic displacement forces. Device stability is observed to be a strong function of aortic geometry (tortuosity, proximal fixation) with increased tortuosity or lower proximal fixation leading to greater risk of device migration.
Control of a Brain-Computer Interface Using Intracranial Electrodes
Authors: Krusienski Dean J. , Shih Jerry J.
Published: July 2013

A brain-computer interface (BCI) is a device that uses brain signals to provide a non-muscular communication channel [1], particularly for individuals with severe neuromuscular disabilities. One of the most promising signals for controlling a BCI are event-related potentials (ERPs) such as the P300. The P300 event related potential is an evoked response to an external stimulus that has been traditionally observed in scalp-recorded electroencephalography (EEG). The scalp-recorded P300 response has proven to be a reliable signal for controlling a BCI using the P300 Speller paradigm [2]. Recent studies have demonstrated that the P300 Speller has the potential to serve as an effective communication device for persons who have lost or are losing the ability to write and speak.
Multi-Disciplinary Optimization of Mid-Span Shroud Ring Structure: A Multi-Parameter Geometry Study Case
Authors: Wu Yuan-Ting , Le Moine Jerome , Hsu Pei-feng , Funk Christian K. , Subramanian C. , Campbell Christian X. , Miller Sam R. , Marra John J.
Published: July 2013

In modern industrial high-output, high-efficiency engines, long turbine blades can require the use of a mid-span or partial-span damping ring for damping vibrations. However, the inclusion of a mid-span damping shroud, or “snubber,” can have negative effects on the aerodynamic performance of the gas turbine stage and engine. Therefore, a method of coupling two independent computational fluid dynamics and finite element structure software tools under an optimization environment was applied to minimize the drag force caused by the snubber, while maximizing the structural life of the blade.

Following the earlier two-parameter (the shroud width and taper ratio) shroud geometry study by the authors, this study extends to the five-parameter geometry model to approach a higher performance design with controllable computational time as well. For the optimized turbine blade shroud in this case, 14.5% reduction of the maximum material stress and 22.6% decrease in the drag force from original snubber design has been accomplished.
A Spectral Study of a Moderately Loaded LPT Airfoil: Part 2—Effects of Turbulence Intensity and Reynolds Number on Frequencies Affecting By-Pass Transition
Authors: Graveline J. R. S. , Sjolander S. A.
Published: July 2013

A single wire, hot-wire, probe is used to examine the airflow in, and in close vicinity to, the shearlayer of a Low-Pressure Turbine (LPT) airfoil. The experiment was performed with varying turbulence intensities (Tu) and Reynolds numbers (ReBx); in this work, Re is based on the cascade inflow velocity and axial chord length. In part 1 of the present study [1], the methodology used to identify the key frequencies in the free shearlayer using a combination of statistical and spectral measures of the airflow was first discussed. Here, the focus is on the effects of ReBx and Tu on the spectral results. The frequencies and location in the shearlayer of the Tollmien-Schlichting (TS) waves and Kelvin-Helmholtz (KH) instabilities are shown to be affected by both Tu and ReBx. Additionally, the KH instabilities are shown to undergo pairing.
Numerical Investigation of High-Pressure Turbine Environment Effects on the Prediction of Aerothermal Performances
Authors: Wlassow Fabien , Leboeuf Francis , Leroy Gilles , Gourdain Nicolas , Boum Ghislaine Ngo
Published: July 2013

Aerothermal prediction for the high-pressure turbine is challenging because of the complex environment that interacts with the turbine: hot-streak migration, unsteady flow phenomena, fluid/solid thermal coupling and technological details (squealer tip, coolant ejections, fillets, etc.). There is a need to compare their relative impacts on the blade temperature and turbine efficiency prediction. This is the main purpose of this paper. URANS simulations of the flow have been performed with a structured flow solver in a one stage high-pressure turbine. The baseline simulation takes into account the squealer tip and an inlet condition representative of a hot streak generated by the combustion chamber. Other technological details (coolant ejections and fillets) and fluid/solid thermal coupling on the rotor blade are alternatively considered in the simulation in order to quantify their relative contribution. The Chimera technique is used to ease the integration of technological details. The conjugate heat transfer (CHT) problem is solved by means of a code coupling where fluxes and temperatures are exchanged at the blade surface between the fluid dynamics solver and the solid thermal code. Results shows that rotor blade fillets have a little impact on both the blade temperature and the turbine efficiency (less than 1%). On the contrary, taking into account external cooling leads to a modification of radial distribution of loss and loading coefficients and reduces the efficiency by 2%. The blade temperature is also impacted, mainly on the suction side where differences of several per cent with the baseline case are observed. Fluid/solid coupling mainly affects the blade temperature prediction by homogenizing it which induces differences around 3% with the baseline case. To complete the analysis, a post-processing that includes a computation of local entropy production terms is used. It shows that the entropy production is mainly due to turbulent dissipation and allows to identify the reduction of efficiency of the case with cooling as an additional production of entropy where the cooling flow mixes with the main flow.
Experimental Analysis of the Interaction Between Rim Seal and Main Annulus Flow in a Low Pressure Two Stage Axial Turbine
Authors: Schrewe Sebastian , Werschnik Holger , Schiffer Heinz-Peter
Published: July 2013

The spoiling effects of rim seal flow are studied at the Large Scale Turbine Rig (LSTR) at Technische Universität Darmstadt. Detailed flow field measurements and efficiency measurements were performed for various ingress and egress setups and will be presented in this paper.

Efficiency measurements show an efficiency decrease as the rim seal mass flow is increased. Five hole probe measurements upstream and downstream of the second stator row show that an increasing rim seal mass flow leads to an increased pressure loss across the stator, to altered incidence angles and to an intensification of secondary flow structures within the lower 50 % span. Static pressure taps at the stator profile primarily show alternated aerodynamic loading with increased rim seal air. In addition, the endwall profile pressure was measured at the stator 2 hub. It can be seen that seal air injection causes increased pressure fluctuations on the platform. Temperature measurements with a temperature difference between rim seal and main annulus flow show that rim seal air primarily enters the passage vortex.
Numerically Optimizing an Annular Diffuser Using a Genetic Algorithm With Three Objectives
Authors: Cerantola David J. , Birk A. M.
Published: July 2013

A genetic algorithm was implemented to determine preferential solutions of a short annular diffuser exhaust system of length 1.5Do (outer annulus diameters). Five free variables defined the centre body shape and two variables determined the outer wall profile. Diffuser performance was evaluated using three objectives—(i) diffuser pressure recovery, (ii) outlet velocity uniformity, and (iii) total pressure loss—that were calculated from steady state solutions obtained using the computational fluid dynamics software FLUENT 13.0 with the realizable k-ε turbulence model and enhanced wall treatment. Inlet conditions were ReDh = 8.5 × 104 and M = 0.23. After thirty-five generations, a paraboloid-shaped centre body with length 0.74Do and initial annular expansion of approximately 14° produced preferential solutions. A configuration with a converging outer wall above the centre body developed greater outlet flow uniformity and lower total pressure loss whereas a straight outer wall followed by the solid diffuser generated more static pressure recovery.
Through Flow Flange-to-Flange Turbine and Diffuser Analysis
Authors: Granovskiy Andrei , Kostege Mikhail , Krupa Vladislav , Rudenko Sergey
Published: July 2013

At the present time an important aspect of power generation in combined cycle power plants is to keep part load performance of heavy duty gas turbines sufficiently high. Therefore it is a matter of importance to ensure the aerodynamic alignment between the turbine and exhaust diffuser, allowing potential increase in both turbine efficiency and diffuser pressure recovery. The benefit of such alignment could be noticed at numerical analysis accuracy of part-load conditions in particular due to the change in gas flow angle downstream of the turbine and resulting in an incidence on the diffuser struts. This incidence, in its turn, often causes local flow separation and an associated loss increase.

This paper presents an integrated approach of the turbine and diffuser aerodynamic design by means of use of a single 3D Navier-Stokes CFD model. This model explores an automatic interface between the turbine and diffuser calculation domains.

Furthermore, whilst gas turbine part load performance has been improved thanks to last stage turbine blade redesign, the above-mentioned integrated turbine & diffuser numerical modelling was used as working instrument to reach the optimal solution in terms of flange-to-flange efficiency in a broad operation range. Following test results, comparison against the numerical prediction fully proved the validity of chosen analytical approach.
Investigation of Separating and Utilizing the Influences of Up- and Downstream Blade Rows
Authors: Zhao Ben , Yang Ce , Hu Liangjun , Zhou Mi , Li Du
Published: July 2013

The superimposed influences of the blade rows in multistage compressor are important, because different matching status of upstream and downstream blades can result in significant differences in unsteady pressure fluctuations. Numerical investigation of the unsteady pressure distributions on axial stator blade, which affect by the axial rotor in the upstream and the radial rotor in the downstream, was performed in an axial-radial combined compressor. Unsteady pressure fluctuation was investigated. When rotors have equal blade numbers, the unsteady pressure fluctuates periodically versus time within T time. On contrast, it fluctuates irregularly within T time when they have different blade numbers. A model-split subtraction method to separate the influences of the individual blade rows on the profile pressure distribution of the axial stator was presented. Analysis from the rotor-stator configuration showed that the unsteady pressure fluctuation response caused by the upstream rotor. For the rotor-stator-rotor configuration, the unsteady pressure fluctuations were influenced by up- and downstream blade rows. With the model-split subtraction method, the up- and downstream influences on the unsteady pressure could be clearly separated and quantified. High amplitudes were observed when the influences from up- and downstream moving rows were superimposed with “positive peak-positive peak” type wave. In contrast, the amplitudes were decreased by the opposite superimposition phase (“positive peak-negative peak” type wave). Clocking investigations were carried out for two goals. One is to show the isolated influence from up- or downstream rotor by eliminating down- or upstream influence components. This is called clocking subtraction method. The other one is to change the relative superimposed phase of influences from the surrounding blade rows. Thus, the physical mechanism of the unsteady pressure fluctuation amplitude modulation by means of clocking was put forward.
Influence of the Swirling Flow in the Side Cavities of a High-Pressure Centrifugal Compressor on the Characteristics of Excited Acoustic Modes
Authors: Petry N. , König S. , Benra F.-K.
Published: July 2013

Previous experimental investigations revealed the existence of acoustic modes in the side cavities of a high-pressure centrifugal compressor. These modes were excited by pressure patterns which resulted from rotor/stator-interactions (often referred to as Tyler/Sofrin-modes). The acoustic modes were significantly influenced by the prevailing flow in the side cavities. The flow field in such rotor/stator-cavities is characterized by a high circumferential velocity component. The circumferential velocity of the flow and the phase velocity of the acoustic eigenmode superimpose each other, so that the frequencies of the acoustic eigenmodes with respect to the stator frame of reference follow from the sum of both velocities. In the previous study the circumferential velocity was estimated based on existing literature and the phase velocities of the acoustic modes were calculated via an acoustic modal analysis. Based on these results the rotational speeds of the compressor, where acoustic modes were excited in resonance, were determined.

The present paper is based on these results and focuses on the influence of the swirling flow and the coupling of the excited acoustic modes between the two side cavities. Such a coupling has been predicted in previous numerical studies but no experimental evidence was available at that time. In this study the circumferential velocities of the flow are determined by measuring the actual radial pressure distribution in the side cavities and assuming radial equilibrium. The determined values are directly used for the prediction of the rotational speeds at resonance. The values for the rotational speeds at resonance predicted that way are compared to the resonance speeds found in the experiments. Further on, simultaneously measured pressure fluctuations in the shroud and hub side cavities with respect to the rotor frame of reference give evidence about the coupling of the acoustic modes between the two side cavities in case of resonance.

If the experimentally determined swirling flow velocity is accounted for in the prediction of acoustic resonances, the calculated rotational speeds of resonance are in good agreement with the experimental findings in most cases. Neglecting the flow in the cavities, however, leads to large deviations between calculated and experimentally determined rotational speeds. Varying the operating point of the compressor results in changes of the circumferential velocities in the side cavities and, therefore, in changes of the rotational speeds of resonance.

Contrary to the acoustic modes calculated via a Finite Element Analysis by the authors of this paper in previous studies the excited acoustic modes in the experiments are mostly not coupled between the two side cavities, but are localized to one of both cavities. This finding is assumed to be caused by the flow field in the compressor.
Experimental Study of the Effect of the Tip Clearance to the Diffuser Flow Field and Stage Performance of a Centrifugal Compressor
Authors: Jaatinen Ahti , Turunen-Saaresti Teemu , Grönman Aki , Röyttä Pekka , Backman Jari
Published: July 2013

The effect of tip clearance to the centrifugal compressor diffuser flow fields and stage overall performance are studied experimentally. The relative tip clearance (tip clearance divided by the impeller exit blade height) is increased by shimming the shroud side casing of a high-speed variable speed driven industrial centrifugal compressor. Four different relative tip clearances are studied: 0.027, 0.053, 0.082, and 0.106. The stage efficiency and pressure ratios are measured, as well as the diffuser flow fields. The diffuser flow fields are measured both at the diffuser inlet and outlet. The total pressure and flow angle are measured with a cobra probe, and the total pressure and temperature with three Kiel probes. Static pressures are measured adjacent to the probe measurements. As expected, increasing the tip clearance leads to lower stage efficiency and pressure ratios. The decrement in the efficiency due to the increasing of the tip clearance is higher with higher mass flows, and at lower rotational speeds. Increasing tip clearance increases the size of the secondary flow region present at the impeller outlet near the shroud.
Design and Development of a 14-Stage Axial Compressor for Industrial Gas Turbine
Authors: Ikeguchi Takuya , Matsuoka Akinori , Sakai Yusuke , Sakano Yoshinobu , Yoshiura Kenichiro
Published: July 2013

A 14-stage axial flow compressor was newly designed and tested for developing an advanced industrial gas turbine. In order to achieve a high thermal efficiency required for the new gas turbine, the compressor needed to have a significantly higher pressure ratio and higher efficiency than those of existing engines.

The new design methodology used to this compressor design was based on an automated airfoil geometric optimization system combined with a 3D-CFD analysis, which resulted in arbitrary shaped airfoil design in most blade rows. A multi-stage CFD analysis was used effectively in order to adjust a loading distribution along stages and to obtain a proper stage matching.

Before the full development of the gas turbine, an approximately two-thirds scaled compressor rig tests were conducted to verify the aerodynamic design and the structural reliability. The test results of the first build indicated a satisfactory level of efficiency and mass flow, but with a lack of sufficient stall margin. The second build with the re-staggered vanes was tested and its result showed improvements both in stall margin and in efficiency.

The prototype test of developing an industrial gas turbine also had been conducted. The measured performance of the compressor which was scaled up from the second build rig compressor achieved the design target. Consequently, the aerodynamic design which considered the scale effects of the compressor was successful.
Three-Dimensional Flow Through a Compressor Cascade With Circulation Control
Authors: Fischer S. , Müller L. , Saathoff H. , Kožulović D.
Published: July 2013

A compressor cascade with active circulation control at the trailing edge of the blades is presented. The main objective of the current work is to investigate the influence of the active blowing on the three dimensional flow field. Furthermore the estimation of the blowing efficiency is of great interest and will be considered in detail. Navier-Stokes simulations have been conducted and compared to low-speed wind tunnel measurements. With the particular measurement techniques (five-hole-probe measurements and particle image velocimetry) significant three-dimensional flow details are accessible. Further details near the trailing edge are analysed by PIV-measurements at different spanwise positions. These measurements show a good jet quality over the blade span.
Detailed Measurements of Spike Formation in an Axial Compressor
Authors: Weichert Stephanie , Day Ivor
Published: July 2013

This paper presents new experimental measurements of spike-type stall inception. The measurements were carried out in the single stage Deverson compressor at the Whittle Laboratory. The primary objective was to characterize the flow field in the tip clearance gap during stall inception using sufficient instrumentation to give high spatial and temporal resolution. Measurements were recorded using arrays of unsteady pressure transducers over the rotor tips and hot-wires in the tip gap. Pre-stall ensemble averaged velocity and pressure maps were obtained as well as pressure contours of the stall event. In order to study the transient inception process in greater detail, vector maps were built up from hundreds of stalling events using a triggering system based on the stalling event itself. The results show an embryonic disturbance starting within the blade passage and leading to the formation of a clear spike. The origins of the spike and its relation to the tip leakage vortex are discussed. It has also been shown that before stall the flow in the blade passage which is most likely to stall is generally more unsteady, from revolution to revolution, than the other passages in the annulus.
An Object-Oriented CFD Code for Optimization of High Pressure Ratio Compressors
Authors: Gröschel Elmar , Rembold Benjamin , Mangani Luca , Casartelli Ernesto
Published: July 2013

The flow fields and performances of different transonic radial compressors of varying geometries and conceptual designs have been studied numerically. All the simulations were performed with a modified in-house 3D RANS solver based on an object-oriented open-source library. The solver uses an All-Mach algorithm with a special treatment for the pressure corrector equation to deal with highly compressible flows. The 3D flow field structures, the characteristics and integral quantities have been compared to the results of established, state-of-the-art commercial solvers as well as to measurements whenever possible. This paper demonstrates for various configurations that the main flow features and the flow characteristics have been captured by the new solver. Furthermore, the new solver is also capable of computing the delta variations of similar designs. This is an essential step for the broad application of the new solver for optimization design cycles.
Numerical Study of Cavitating Behavior in a Cryogenic Liquid Turbine
Authors: He Zhilong , Ge Yunzheng , Sun Jinju , Wang Ke
Published: July 2013

The cryogenic liquid turbine is used in the internal compression air-separation unit to replace the Joule-Thomson valve for the purpose of energy-saving. Evaporation of the liquefied air must be reduced to a minimum to increase gas production of the air-separation unit and simultaneously prevent cavitation damage to the turbine structure during throttling process. In the present study, cavitation behavior in the liquid turbine is investigated and some influential factors are identified. A numerical flow model is established in a turbine stage environment, which includes an asymmetrical volute, variable geometry nozzle, impeller, and diffuser. The simulation is conducted by using the ANSYS-CFX, where an iterative model is incorporated to update the liquefied gas properties at local temperature, and the Rayleigh-Plesset model is used for describing cavitation behavior. The cavitation model is validated first by experimental data of a hydrofoil in liquid nitrogen and its suitability for cryogenic fluid flow has been justified. Both steady and unsteady simulations are conducted respectively and the results are compared. At the design condition, the vapor fraction in the impeller produced by the unsteady simulation is similar to that obtained by the steady simulation. At off-design condition, the turbine flow behavior is far from the steady assumption. The influence of the diffuser duct cone angle on cavitation behavior is also investigated, which demonstrate that geometry modification of diffuser duct is effective to suppress the cavitation flow.
Numerical Investigation of a Banki Turbine in Transient State: Reaction Ratio Determination
Authors: Croquer Sergio D. , de Andrade Jesus , Clarembaux Jorge , Jeanty Freddy , Asuaje Miguel
Published: July 2013

Cross-Flow Turbines (CFT) also known as Banki Turbines, are often considered for small scale hydroelectric generation. They are known for their simple construction, maintenance and operation, which means they incur in lower CAPEX and OPEX when compared to other types of turbines. However, they also tend to have a modest efficiency (82% [1–3]), hence they are not considered for big scale operations. Little is known about the flow characteristics inside the runner of the CFT. The objective of this investigation is to better understand the flow inside CFTs using Computational Fluid Dynamics (CFD) tools. Steady and Transient State simulations were performed for a CFT at an specific speed NS = 45. SST and κ–ε turbulence models were compared in terms of simulation requirements and obtained results. A proposed runner-nozzle interface, considering real CFT existent gap between these two components (free space) was evaluated as well. Results were compared to available experimental data. Maximum, numerically calculated efficiency deviation from reported experimental global efficiency was 15%. Pressure and velocity profiles along nozzle outlet, energy transfer stages location and CFT reaction ratio values were addressed. Results were compared in terms of runner-nozzle interface (gap vs no-gap), turbulence model (SST vs κ–ε) and calculation regime (steady vs transient regime). Only calculation state (steady vs transient) was found to have major influence over results. Transient state calculations better representing complex flow inside the CFT. Obtained degrees of reaction (no runner-nozzle gap, SST, transient state) were 0.12 and 0.08, for 1st and 2nd stages respectively. Hence the CFT is defined, according to this numerical models, as an impulse turbine.
Large-Eddy Simulation of Flow in a Low-Pressure Turbine Cascade
Authors: Medic Gorazd , Sharma Om
Published: July 2013

Flow over three low-pressure turbine airfoils presented in [1] is analyzed for a range of Reynolds numbers (30,000 to 150,000) by means of large-eddy simulation. Baseline computational grid for these 2D linear cascade configurations consisted of 35 millions cells, and additional finer grids of 70 millions cells were used for grid sensitivity studies. For these low Reynolds number flows, this represents a quasi-DNS resolution which minimizes the role of the subgrid-scale model — however, WALE subgrid-scale model [7] was still employed. The configurations were analyzed for low free-stream turbulence intensity, as well as for 4% turbulence intensity at free-stream.

Laminar separation exists on the suction side, and, depending on the Reynolds number, the flow at the outer edge of the separation either transitions, and the separation closes before the trailing edge, or not. Detailed comparisons to measurements are presented for computed surface pressure and total pressure losses over the range of Reynolds numbers for all three airfoils; these show that LES analyses are able to capture the main trends across all three geometries.
Quantification of the Numerical Solution Sensitivity to Unknown Parameters: Application to Compressor and Turbine Flows
Authors: Gourdain Nicolas , Dewandel Karl
Published: July 2013

Due to complexity, the numerical simulations of flows in real gas turbine configurations usually consider geometries and flows that are different from the reality (ill-defined boundary conditions, inaccuracy of the geometry, etc.). Unfortunately, these differences can significantly affect the accuracy of the numerical solution. The aim of this paper is thus to apply a method to turbomachinery test cases, in order to estimate the influence of unknown/uncertain parameters on the numerical solution. The approach, based on a Stochastic-Collocation (SC) method, is first validated against the classical Monte-Carlo (MC) method (that uses random sample points to describe the space of parameters). The computational cost required to evaluate the sensitivity to two parameters is reduced by a factor 30 with the SC method compared to MC. The SC method is then applied to an inlet guide vane of a high-pressure turbine and a three and a half stage compressor. For the turbine case, the results quantify the sensitivity of the wall heat transfer to inlet turbulent intensity, inlet turbulent Reynolds number and outlet Mach number. The analysis also points out a bifurcation phenomenon related to the position of the boundary layer transition point along the vane suction side, which is the main parameter that influences the wall heat transfer. For the compressor case, the study shows the dependence of the overall performance (pressure ratio, efficiency and stability) to the dimension of the rotor tip clearances. In the present case, the study shows that the influence of a tip clearance variation increases when the operating point moves closer to the stability limit (surge line). The compressor stability is also more affected by a variation of the tip clearance in the second rotor than in the third rotor.
The Impact of Compressor Exit Conditions on Fuel Injector Flows
Authors: Ford C. L. , Carrotte J. F. , Walker A. D.
Published: July 2013

This paper examines the effect of compressor generated inlet conditions on the air flow uniformity through lean burn fuel injectors. Any resulting non-uniformity in the injector flow field can impact on local fuel air ratios and hence emissions performance. The geometry considered is typical of the lean burn systems currently being proposed for future, low emission aero engines.

Initially, RANS CFD predictions were used to examine the flow field development between compressor exit and the inlet to the fuel injector. This enabled the main flow field features in this region to be characterized along with identification of the various stream-tubes captured by the fuel injector passages. The predictions indicate the resulting flow fields entering the injector passages are not uniform. This is particularly evident in the annular passages furthest away from the injector center-line which pass the majority of the flow which subsequently forms the main reaction zone within the flame tube. Detailed experimental measurements were also undertaken on a fully annular facility incorporating an axial compressor and lean burn combustion system. The measurements were obtained at near atmospheric pressure/temperatures and under non-reacting conditions. Time-resolved and time-averaged data were obtained at various locations and included measurements of the flow field issuing from the various fuel injector passages. In this way any non-uniformity in these flow fields could be quantified. In conjunction with the numerical data, the sources of non-uniformities in the injector exit plane were identified. For example, a large scale bulk variation (+/−10%) of the injector flow field was attributed to the development of the flow field upstream of the injector, compared with localized variations (+/−5%) that were generated by the injector swirl vane wakes. Using this data the potential effects on fuel injector emissions performance can be assessed.
Investigation of the Wake Effect From the Centrifugal Splitter Impeller Blade to the Vaned Diffuser
Authors: Li Xuechen , Xi Guang , Hua Jiang , Gong Wuqi
Published: July 2013

In this paper, the unsteady wake effect from an unshrouded centrifugal impeller with splitter blades was numerically and experimentally investigated. The numerical simulated detail flow characteristics of two stations, respectively placed at the impeller outlet and the diffuser inlet, were compared with the measured data. The “jet-wake” flow pattern was observed at the exit of the impeller. And the investigation showed that the wake effect of the splitter was weaker that of the main blade. But both the main blade and the splitter blade wake could affect the diffuser performance at a range of whole-chord length and they provoked the pressure side profile pressure fluctuating intensely from 10% chord to 50% chord, while the suction side pressure varying rapidly at the range from 60% chord to 80% chord.
Modeling of the Hub Cavity Leakage Flows in Axial Compressors
Authors: Chougule Hasham H. , Dhamarla Anand , Goswami Shraman , Mansour Mahmoud L.
Published: July 2013

Computational analyses are carried out to predict the effect of the hub leakage flow from the inner banded stator cavities on the overall performance of an axial high pressure compressor. The results of a full fidelity simulation model, which includes cavities, sealing and main flow, is compared with models without the hub leakage flow. The CFD prediction confirms a significant effect from the hub leakage on the performance of the multistage axial compressor. A simpler and faster CFD modeling technique is explored and discussed for the modeling of the effect of the hub cavity leakage. In this approach, costly details of the stator cavities are ignored. Transfer functions or correlations are derived from the 1.5 stage (IGV-Rotor1-Stator1) of a multistage compressor having inner banded stator cavity. These correlations are used as boundary conditions to the primary flow path of the compressor while carrying out the simplified CFD models for the complete 4 stage compressor model. A MINITAB study is conducted to understand the most influencing parameters and their interactions in deriving the correlations. Analyses are then carried out using the simplified model with the hub leakage boundary conditions derived from these correlations. The CFD results of the full fidelity simulation and the simplified models are compared in this paper.
Robust Design Strategies for Heavy Duty Axial Compressor Inlet Strut
Authors: Cioffi Marco , Puppo Enrico , Silingardi Andrea , Macciò Mauro
Published: July 2013

Novel procedures for the robust optimization of compressor blades are here presented and applied to the optimal design of the inlet duct struts of an heavy duty, multistage axial compressor. Different approaches can be adopted to properly define the struts actual inlet flow boundary conditions, which can be affected by spatial non-uniformity or uncertainness: suitable deterministic and stochastic approaches are therefore introduced. A number of blade solutions are computed and discussed. The presented procedures are able to find new struts geometries giving improved performances with respect to a reference strut, mainly with an air mass flow increase. In particular the proposed stochastic procedure seems to be quite appropriate for a large class of design problems with parameters fluctuation or to properly analyze the statistical effect of changing operative conditions occurrence in power plants.
A Comparison of Three Low Pressure Turbine Designs
Authors: Wakelam Christian T. , Niehuis Reinhard , Hoeger Martin
Published: July 2013

As part of the current research, three LPT geometries — which were designed with a common pitch, axial chord, inlet angle, and exit Mach number and to create the same nominal level of turning — are compared. Each of the LPT cascades was investigated under a range of Reynolds numbers, exit Mach numbers, and under the influence of a moving bar wake generator.

Profile static pressure distributions, wake traverses at 5% and 40% axial chord downstream of the trailing edge and suction side boundary layer traverses were used to compare the performance of the three designs. The total pressure losses are strongly dependant on both the maximum velocity location as well as the diffusion on the suction surface. The importance of the behavior of the pressure surface boundary layer turned out to be negligible in comparison.

Cases with equivalent operating Reynolds number and suction side diffusion level are compared in terms of the total pressure losses that are generated. It is shown that a relationship between loss and suction side maximum velocity location exists. An optimum suction side maximum velocity location depends on the Reynolds number, diffusion factor, and wake passing frequency.
Recent Advances in Manufacturing of Riblets on Compressor Blades and Their Aerodynamic Impact
Authors: Lietmeyer Christoph , Denkena Berend , Kling Rainer , Krawczyk Thomas , Overmeyer Ludger , Reithmeier Eduard , Scheuer Renke , Vynnyk Taras , Wojakowski Bodo , Seume Joerg R.
Published: July 2013

Since Oehlert et al. (2007), significant improvements in the manufacturing processes of riblets by laser-structuring and grinding have been achieved. In the present study, strategies for manufacturing small-scale grooves with a spacing smaller than 40 μm by metal bonded grinding wheels are presented. For the laser-structuring process, significant improvements of the production time by applying diffractive optical elements were achieved. Finally, strategies for evaluating the geometrical quality of the small-scale surface structures are shown and results obtained with two different measuring techniques (SEM and confocal microscope) are compared with each other.

The aerodynamic impact of the different manufacturing processes is investigated based upon skin friction reduction data obtained on flat plates as well as the profile-loss reduction of riblet-structured compressor blades measured in a linear cascade wind tunnel. Numerical simulations with MISES embedded in a Monte Carlo Simulation (MCS) were performed in order to calculate the profile-loss reduction of a blade structured by grinding to define further improvements of the riblet-geometry. A numerical as well as experimental study quantifying the relevant geometrical parameters indicate how further improvements from the present 4 % reduction in skin friction can be achieved by an additional decrease of the riblet tip-diameter and a more trapezoidal shape of the groove in order to realize the 8 % potential reduction.
Development and Applications of a Stage Stacking Procedure
Authors: Kulkarni Sameer , Celestina Mark L. , Adamczyk John J.
Published: July 2013

The preliminary design of multistage axial compressors in gas turbine engines is typically accomplished with mean-line methods. These methods, which rely on empirical correlations, estimate compressor performance well near the design point, but may become less reliable off-design. For land-based applications of gas turbine engines, off-design performance estimates are becoming increasingly important, as turbine plant operators desire peaking or load-following capabilities and hot-day operability. The current work develops a one-dimensional stage stacking procedure. This includes a newly-defined blockage term, which is used to estimate the off-design performance and operability range of a 13-stage axial compressor. The new blockage term is defined to give mathematical closure on static pressure, and values of blockage are shown to collapse to a curve as functions of stage inlet flow coefficient and corrected speed. Utility of the stage stacking procedure is demonstrated by estimation of the minimum corrected speed which allows stable operation of the compressor. Further utility of the stage stacking procedure is demonstrated with a bleed sensitivity study, which estimates a bleed schedule to expand the compressor’s operating range.
Three-Dimensional Pressure Controlled Vortex Design of a Turbine Stage
Authors: Deng Qingfeng , Zheng Qun , Yue Guoqiang , Zhang Hai , Luo Mingcong
Published: July 2013

A three-dimensional (3D) Pressure Controlled Vortex Design (PCVD) method for turbine stage design is proposed and discussed in this paper. The concept is developed from conventional Controlled Vortex Design (CVD) via pressure control approach and CVD technology. By specifying the static pressure and axial velocity distributions, the spanwise pressure gradient incorporated with pressure gradient in streamwise and azimuthal directions is moderated. Not only can profile loss profit from pressure control approach, but also secondary flow can be managed. The reasons for CVD are derived from stream surface thickness and stream surface twist. Through modifying stream surface thickness and inducing large stream surface twist, the secondary flow migrations are controlled properly and orderly. The relations of pressure control approach and CVD technology complement one another and finally lead to a well-posed flow pattern in turbine stage. The first stage redesign of a well-designed low pressure turbine demonstrates this technique application. A significant reduction of secondary flow losses and a corresponding increase of stage efficiency have achieved.
Influence of Low-Solidity Cascade Diffuser on Spike Stall Inception in a Centrifugal Compressor
Authors: Joukou Satoshi , Shinkawa Yasushi , Kanno Toshio , Nishida Hideo , Nishioka Takahiro , Hiradate Kiyotaka
Published: July 2013

Stall inception patterns for three low-solidity cascade diffusers were experimentally investigated to extend the operating range of centrifugal compressor. Pressure fluctuations on the wall and flow distributions at the diffuser inlet were measured, and static pressure-rises across the diffuser vane were also measured to clarify the mechanism of rotating stall inception. In the case of the original diffuser (LSD_O), which had the radius ratio between the impeller outlet and the diffuser vane inlet of 1.10 and a flat plate wing section, a short length-scale stall cell known as a spike first appeared in the positive slope of the diffuser static pressure-raise (after the flat slope was maintained), and then a surge occurred as flow-rate decreased. The propagation speed of short length-scale stall cell was about 13% of the impeller rotation speed. The measured flow distribution at the inlet of the LSD_O suggested that the flow separation occurred in the vaneless space and this separation influenced the rotating stall. In the case of the LSD_A, which had the radius ratio of 1.10 and the NACA 63 wing section, a short length-scale stall cell that was smaller than that of LSD_O was appeared in the positive slope of the diffuser static pressure-raise (without the flat slope). A surge also occurred as further flow-rate decreased. The propagation speed of short length-scale stall cell was about 13% just prior to surge point. In contrast, in the case of LSD_B, which had the radius ratio of 1.05 and the NACA 63 wing section, a small disturbance appeared without spike just prior to surge point and rotating stall did not occur. The small disturbance did not propagate in the circumferential direction. Moreover, the flow separation did not occur in the semi-vaneless space. At the stall inception point of LSD_O and LSD_A, the averaged absolute flow angle at the diffuser inlet agreed with the onset flow angel of rotating stall in vaneless diffuser predicted by Senoo. Therefore, it was considered that the flow separation also occurred in the vaneless space and this separation influenced the rotating stall in the case of LSD_A. Moreover, it was considered that the difference of two stall cell patterns between LSD_O and LSD_A depended on the static pressure-rise characteristic of diffuser determined by the design specifications in case of that the rotating stall occurred in the vaneless space. In contrast, at the point of the small disturbance appeared of LSD_B, the averaged absolute flow angle at the diffuser inlet is smaller than that predicted by Senoo. Therefore, in case of small the radius ratio, the reverse flow in vaneless diffuser is suppressed, and the rotating stall is also suppressed.
Multiobjective Optimization for Duct and Strut Design of an Annular Exhaust Diffuser
Authors: Schaefer Philipp , Hofmann Willy H. , Gieß Peter-Anton
Published: July 2013

This paper describes the aerodynamic optimization of a typical exhaust diffuser for a heavy duty gas turbine. The objective is to maximize diffuser performance and, in this way, pressure recovery by optimizing the geometry for two given inlet conditions.

To validate and adjust the numerical set-up, experimental data from measurements on the test model is used. The numerical results obtained by using TRACE compares with the experimental results.

An optimization process is applied using the framework AutoOpti developed by DLR, which combines evolutionary strategies with surrogate models in order to select optimal geometric parameters. Finally, the differences between the baseline and several optimized designs are discussed and the impact of different parameters on diffuser performance is demonstrated.
Design of Compressor Blades Considering Efficiency and Stability Using CFD Based Optimization
Authors: Ellbrant Lars , Eriksson Lars-Erik , Mårtensson Hans
Published: July 2013

To design a highly loaded axial transonic compressor several objectives need to be considered simultaneously. From an aerodynamic perspective, one of the major requirements is high efficiency at a specific operating condition where the fuel consumption is of main interest. Furthermore, the compressor needs to have a sufficient stall-margin along the entire flight envelope to ensure a stable operating range.

This work is focused on creating an efficient design method which produces a trade-off between high stall margin and high efficiency. The design method is based on an automatic multiobjective optimization process divided into two steps. In the first step, 2D blade profiles are optimized where both efficiency and stall margin are considered. Once the optimization is finished the selected profiles are stacked together to be further optimized in 3D. When going to the second step, i.e. a 3D optimization, one can focus on a smaller set of design variables thereby reducing the time to get what is considered the optimal solution.

The results show that it is possible to rate designs with potential of having high stall margin and high efficiency both in the 2D and 3D optimization. The main contribution in this work is the design method, which offers an efficient way of designing robust blades where the designer can decide the best trade off between stall margin at part speed and efficiency at the design point.