bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
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.
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.
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.
Experimental and Numerical Investigation of the Flow Field in the Radial Inlet of a Centrifugal Compressor
Authors: Han Fenghui , Qi Datong , Tan Jiajian , Wang Li , Mao Yijun 
Published: July 2013

This paper presents an experimental and numerical study of the flow field in a typical geometry of a centrifugal compressor radial inlet. A five-hole probe system, which makes the probe calibration and the data acquisition automatically controlled by computer, was developed and used to measure the pressure, velocity and flow angle distributions inside the radial inlet. The testing portion consists of the entrance and exit of the radial inlet, the outlet section of the suction nozzle and the exit of the plenum, including 46 sampling holes and 923 measuring points. In parallel with the experiment, a computational analysis was also carried out to simulate the internal flow of the radial inlet with a commercial CFD Code. The numerical results are compared with the experimental data. It shows a good agreement between CFD and the measurement on most sections.
Based on the experiment and simulation, this study reveals the detailed flow conditions in a radial inlet, which helps to figure out how the complex flow pattern in a radial inlet forms and develops as well as the influences on the downstream components. It yields an improved understanding of the principle of flow phenomena in radial inlets, and gives recommendations for optimizing the structure design of the radial inlet of centrifugal compressors.
Experimental Investigation of Purge Flow Effects on a High Pressure Turbine Stage
Authors: Regina K. , Kalfas A. I. , Abhari R. S. 
Published: July 2013

In the present paper an experimental investigation of the effects of hub purge flow on the performance of a high pressure axial turbine stage is presented. The test configuration consists of a one-and-a-half stage, unshrouded, highly loaded axial turbine, with a blading representative of high pressure gas turbines. The test configuration has the capability of integrating purge flow from the cavity under the rotor/stator platform.
Efficiency measurements for various purge flow injection levels have been carried out with pneumatic probes at the exit of the rotor and show a reduction of isentropic total-to-total efficiency of 0.8 % per percent of injected mass flow.
For three purge flow conditions the unsteady aerodynamic flow field at rotor inlet and rotor exit has been measured with the in-house developed Fast Response Aerodynamic Probe (FRAP): one condition is with sucking at a mass flow fraction of −0.1 % and two conditions are with injection at a mass flow fraction of 0.8 % and 1.2 %. The time-resolved data shows the unsteady interaction of the purge flow with the secondary flows of the main flow and the impact on the radial displacement of the rotor hub passage vortex.
Steady measurements at off-design conditions show the impact of the rotor incidence and of the stage flow factor on the resulting stage efficiency and the radial displacement of the rotor HPV.
A comparison of the effect of purge flow and of the off-design conditions on the rotor incidence and stage flow factor shows that the detrimental effect of the purge flow on the stage efficiency caused by the radial displacement of the rotor hub passage vortex is dominated by the increase of stage flow factor in the hub region rather than by the increase of negative rotor incidence.
Numerical Investigation of the Behavior of Tip Leakage Flow in a Low-Speed Axial Compressor Rotor at Near-Stall Condition
Authors: Duan Zhenzhen , Liu Yangwei , Lu Lipeng 
Published: July 2013

In the present work, time-accurate simulations were performed to investigate the unsteady flow fields in the tip region of a low-speed large-scale axial compressor rotor at near-stall condition. Firstly, the steady performance characteristic of the rotor was obtained by steady simulations. Secondly, a series of unsteady simulations were carried out to investigate the physical processes as the rotor approaching stall and the role of complex tip flow mechanism on flow instability in the rotor.
The characteristics of tip leakage vortex were compared between design condition and near-stall condition. Detailed analyses were then employed to emphasize the development of stall inception and the comprehensions of the internal flow field. Two flow phenomena, spillage at the leading edge and backflow at the trailing edge, are found beyond the flow solution limit, which are both linked to the tip leakage flow. And the breakdown of the tip leakage vortex has been captured.
The flow visualization and the quantification of passage blockage expose that the tip leakage vortex and corner vortex contribute most to the total passage blockage. Therefore, they are considered to be the key flow structures contributing to the rotating stall. Further analyses indicate that, in the current rotor, the interaction of the tip leakage flow and the corner vortex is clarified to be the key factor that leads to the rotating stall.
In addition, the very initial disturbances of stall inception are discussed. And the interaction of the boundary layer migration on the blade suction side and the tip leakage vortex also plays a significant role in the stall inception.
Full Design of a Highly Loaded Fan by Multi-Objective Optimization of Through-Flow and High-Fidelity Aero-Mechanical Performances
Authors: Joly Michael , Verstraete Tom , Paniagua Guillermo 
Published: July 2013

An innovative design methodology for axial flow compressors is developed utilizing a multi-objective optimization. The full design of a highly-loaded fan is considered, including through-flow and high-fidelity performance evaluations. To augment the explored design space and smoothen the whole process, optimization techniques are integrated into the different steps in the design.
As an alternative to the traditional parametric studies performed for the flow path design, an optimization of the through-flow configuration is performed to initiate the aerodynamic design of the fan. To bypass two-dimensional sub-optimal results, the detailed design of the fan rotor geometry is then directly processed with a three-dimensional optimization, including several section profiles along the span, as well as lean and sweep. The multi-objective algorithm enables one to consider fluid and structure performances simultaneously. High-fidelity CFD (Computational Fluid Dynamics) and CSM (Computational Structural Mechanics) methods are used to guarantee the flow efficiency and the structural integrity of the finalized design. This methodology is applied to the design of a transonic fan achieving a pressure ratio of 2.1.
Numerical and Experimental Investigations of Steady and Unsteady Characteristics of a Counter Rotating Fan Model With Thickened Blades of Working Wheel
Authors: Mileshin Victor , Brailko Igor , Stepanov Alexander , Korzhnev Vladimir 
Published: July 2013

Under VITAL Project funded by the European Community, Snecma as a project leader developed a counter rotating low-speed fan concept for a high bypass ratio engine [1–4].
At first, a counter rotating fan model (hereinafter referred to as CRTF1) with solid titanium blades was designed, manufactured and tested in CIAM’s C-3A anechoic chamber. The CRTF1 fan model had blades with a conventional thickness distribution in order to provide optimal mechanical properties and weight characteristics [1, 2]. To simulate blades made of composite materials, CRTF2a [3] and CRTF2b [4] counter-rotating fan models were designed with thickened blades (by 20–40%) as compared with the CRTF1 fan model to ensure mechanical properties.
The CRTF2a counter-rotating fan model with thickened blades to simulate blades made of a composite material was tested in CIAM’s C-3A anechoic chamber. Fan local and integral performances within rotational speeds from ncor = 40% to ncor = 100% were measured.
The numerical investigations were based on 3DFS software package developed for RANS and URANS solutions. The solution procedure is based on a modified S.K. Godunov’s scheme of implicit finite-difference second-order approximation [5].
The numerical investigations were subdivided into three stages corresponding to various problem definitions. Numerical investigations at the first stage and second stages were carried out without flow nonuniformity at the CRTF inlet. The first stage meets the requirements of the stationary problem definition. CRTF performances at this stage were calculated in the “mixing plane” approximation and compared with test data.
Numerical investigations at the second stage were completed for non-stationary problem definition without flow nonuniformity at the inlet (the same as at the first stage). Calculations at this stage were carried out for the problem definition with a common period corresponding to calculations covering 5 blade channels in Rotor 1 (R1) and 7 blade channels in Rotor 2 (R2). Results of non-stationary calculations at the second stage were in good agreement with computed data at the first stage (the stationary calculation).
The third stage of numerical investigations was in line with the numerical simulation of CRTF operation with total pressure nonuniformity at the inlet. At this stage the numerical investigations were carried out for non-stationary problem definition for all blade channels in Rotor 1 and Rotor 2 (10 and 14, respectively). The computed data were in good agreement with test results for CRTF integral characteristics as well as for local flow characteristics at the CRTF outlet (instantaneous and averaged by time values of flow parameters distributed in radial and circumferential directions).