bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multall: An Open Source, CFD Based, Turbomachinery Design System
Authors: Denton John D. 
Published: August 2017

Turbomachinery design systems are usually the jealously guarded property of large companies, the author is not aware of any for which the source code is freely available. The present paper is aimed providing a freely available system that can be used by individuals or small companies who do not have access to an in-house system.
The design system is based on the 3D CFD solver Multall, which has been developed over many years. Multall can obtain solutions for individual blade rows or for multi-stage machines, it can also perform quasi-3D blade-to-blade calculations on a prescribed stream surface and axisymmetric throughflow calculations. Multall is combined with a one-dimensional mean-line program, Meangen, which predicts the blading parameters on a mean stream surface and writes an input file for Stagen. Stagen is a blade geometry generation and manipulation program which generates and stacks the blading, combines it into stages, and writes an input file for Multall.
The system can be used to design the main blade path of all types of turbomachines. Although it cannot design complex features such as shroud seals and individual cooling holes these features can be modeled and their effect on overall performance predicted. The system is intended to be as simple and easy to use as possible and the solver is also very fast compared to most CFD codes. A great deal of user experience ensures that the overall performance is reasonably well predicted for a wide variety of machines.
This paper describes the system in outline and gives an example of its use. The source codes are written in FORTRAN77 and are freely available for other users to try.
Low Load Operation Range Extension by Autothermal On-Board Syngas Generation
Authors: Baumgärtner Max H. , Sattelmayer Thomas 
Published: August 2017

The increasing amount of volatile renewable energy sources drives the necessity of flexible conventional power plants to compensate for fluctuations of the power supply. Gas turbines in a combined cycle power plant (CCPP) adjust the power output quickly but a sudden increase of CO and UHC emissions limit their turn-down ratio. To extend the turn-down ratio, part of the fuel can be processed to syngas, which exerts a higher reactivity. An autothermal on-board syngas generator in combination with two different burner concepts for natural gas and syngas mixtures are presented in this study.
A mixture of natural gas, water vapor and air reacts catalytically in an autothermal reactor test rig to form syngas. At atmospheric pressure, the fuel processor generates syngas with a hydrogen content of ∼30 vol% and a temperature of 800 K within a residence time of 200 ms.
One concept for the combustion of natural gas and syngas mixtures comprises a generic swirl stage with a central lance injector for the syngas. The second concept includes a central swirl stage with an outer ring of jets. The combustion is analyzed for both concepts by OH*-chemiluminescence, lean blow out (LBO) limit and gaseous emissions.
The central lance concept with syngas injection exhibits an LBO adiabatic flame temperature that is 150 K lower than in premixed natural gas operation. For the second concept an extension of almost 200 K with low CO emission levels can be reached. This study shows that autothermal on-board syngas generation is feasible and efficient in terms of turn-down ratio extension and CO burn-out.
Modeling Capability for Cavity Flows in an Axial Compressor
Authors: Mahmood Syed Moez Hussain , Turner Mark G. 
Published: August 2017

Seal-teeth cavity leakage in a shrouded stator blade deteriorates the performance of an axial compressor. This impact of shrouded stator seal-teeth cavity flows on compressor performance is demonstrated by presenting a sensitivity study with different seal-teeth clearances. A parametric definition of the cavity geometry (including the seal teeth) is created for an axial compressor, which allows for variation in seal teeth design, clearance and cavity shape. One and a half subsonic stages (rotor-stator-rotor) of a 10 stage axial compressor derived from the EEE design is considered to perform a computational fluid dynamic study. A NLH calculation is performed to account for the unsteady effects across the rotor-stator interface. Accuracy of the NLH calculations is determined by a comparison with time-marching results. For mixing plane calculations the location of the rotor-stator interface relative to the upstream and down-stream cavity connections is crucial. Comparison for mixing plane calculation at different rotor-stator interface is made with NLH results.
For this configuration the low momentum leakage flow through the cavities gets entrained in the power stream upstream of the stator which increases the near hub blockage for the stator. Excessive near hub blockage alters the outlet flow conditions for the stator which changes the incoming flow for the down-stream rotor. A vortical flow structure exists at the upstream and downstream cavity connections which changes with the increase in clearance and defines the flow going into and coming out of the cavity. An increase in seal-teeth cavity clearance is shown to deteriorate compressor efficiency up to 0.86% for the largest clearance analyzed. The parametric design and simulation process presented represents the first step in a design optimization process that accounts for cavity flows and seal leakage. The seal-teeth cavity should be modeled correctly to account for the correct blockage and loss distribution. It should also be integrated into the airfoil design at an early stage.
Frequency Analysis Performed on Compressor Blades of Two Types of Gas Turbines Using Campbell and SAFE Diagrams
Authors: Bab Saeed , Behzadi Mohsen , Ahmadi Ahmad , Ramesh Ali , Shahrabi Ali Reza , Fathi Sola Jalal 
Published: August 2017

This paper investigates the results of a frequency analysis performed on the blades of the last three compressor stages of two different gas turbines (Case A and B). The axial compressors in A and B have ten and eleven stages, respectively. The studied stages have identical number of blades in both compressors. However turbine B has higher number of upstream vanes before each rotating stage. Turbine B is actually a modified version of A with higher power output. The manufacturer provides acceptable ranges for several natural frequencies of blades of stage No.8 to 10 in case A. One of the purposes of this study is to figure out the logic behind the abovementioned ranges.
FEM has been used in order to determine the natural frequencies of a single blade (for Campbell diagram) and bladed disk (for SAFE diagram). By surveying the results of the Campbell diagrams for blades of case A’s mentioned stages, it is concluded that the manufacturer has obtained the acceptable ranges by considering a 10% difference (at least) between single blade natural frequencies and excitation frequencies (upstream vane passage frequencies (VPF)).
On the other hand, according to Campbell diagram, there is no resonance for these blades within the operational speed while SAFE diagrams show the existence of one resonance mode within the same range. The reason of this contradiction is found to be ignoring the disk stiffness effect on the blades frequencies. A same procedure was also followed to study the critical frequencies of the blades of the last three stages of turbine B’s compressor by SAFE diagrams.
By checking the critical modes, it is concluded that these modes in case B are transferred to one or two modes higher in comparison to A which results in a much better vibrational behavior. This has been acquired by increasing the number of the upstream vanes.
In addition, in case A’s compressor, the blades of the stage No.10 have been designed with far thicker airfoils (approximately 50%) when compared to stage No.8 and 9, even though their other dimensions are almost identical. But, this fault has been corrected in turbine B and the airfoils of all three stages almost have the same thickness. To sum up, although the design of mentioned blades in turbine B looks better and more logical than A, still a more precise look at its stages bladed disk SAFE diagrams reveals another issue. In some references there are some hints that low number of critical nodal diameter (veering region) might cause high level of blade vibration due to mistuning and this means that even in turbine B the design might not be optimal. A cure could be an increase or decrease in the number of upstream vanes in order to have a higher critical nodal diameter.
An Experimentally Derived Model to Predict the Water Film in a Compressor Cascade With Droplet Laden Flow
Authors: Neupert Niklas , Harbeck Janneck Christoph , Joos Franz 
Published: August 2017

In recent years overspray fogging has become a powerful means for power augmentation of industrial gas turbines. Despite the positive thermodynamic effect on the cycle droplets entering the compressor increase the risk of water droplet erosion and deposition of water on the blades leading to an increase of required torque and profile loss. Due to this detailed information about the structure and the amount of water on the surface is key for compressor performance.
Experiments were conducted with a droplet laden flow in a transonic compressor cascade focusing on the film formed by the deposited water. Two approaches were taken. In the first approach the film thickness on the blade was directly measured using white light interferometry. Due to significant distortion of the flow caused by the measurement system a transfer of the measured film thickness to the undisturbed case is not possible. Therefore, a film model is adapted to describe the film flow in terms of height averaged film parameters.
In the second approach experiments were conducted in an undisturbed cascade setup and the water film pattern was measured using a non-intrusive quantitative image processing tool. Utilizing the measured flow pattern in combination with findings from literature the rivulet flow structure is resolved. From continuity of the water flow a film thickness is derived showing good agreement with the previously calculated results. Using both approaches a 3D reconstruction of the water film pattern is created giving first experimental results of the film forming on stationary compressor blades under overspray fogging conditions.
Experimental Investigation on the Tip Vortex of a Wind Turbine With and Without a Slotted Tip
Authors: Liu Pengyin , Chen Jinge , Xin Shen , Zhu Xiaocheng , Du Zhaohui 
Published: August 2017

In this paper, a slotted tip structure is experimentally analyzed. A wind turbine with three blades, of which the radius is 301.74mm, is investigated by the PIV method. Each wind turbine blade is formed with a slots system comprising four internal tube members embedded in the blade. The inlets of the internal tube member are located at the leading edge of the blade and form an inlet array. The outlets are located at the blade tip face and form an outlet array. The near wake flow field of the wind turbine with slotted tip and without slotted tip are both measured. Velocity field of near wake region and clear images of the tip vortex are captured under different wake ages.
The experimental results show that the radius of the tip vortex core is enlarged by the slotted tip at any wake age compared with that of original wind turbine. Moreover, the diffusion process of the tip vortex is accelerated by the slotted tip which lead to the disappearance of the tip vortex occurs at smaller wake age. The strength of the tip vortex is also reduced indicating that the flow field in the near wake of wind turbine is improved. The experimental data are further analyzed with the vortex core model to reveal the flow mechanism of this kind of flow control method. The turbulence coefficient of the vortex core model for wind turbine is obtained from the experimental data of the wind turbine with and without slotted tip. It shows that the slotted tip increases the turbulence strength in the tip vortex core by importing airflow into the tip vortex core during its initial generation stage, which leads to the reduction of the tip vortex strength.
Therefore, it is promising that the slotted tip can be used to weaken the vorticity and accelerate the diffusion of the tip vortex which would improve the problem caused by the tip vortex.
Analytical Study of Low-Frequency Helmholtz Mode Oscillation in a Model Combustor
Authors: Zhang Man , Lin Yuzhen , Tao Wenjie 
Published: August 2017

The “growl” mode combustion instability is one of the most destructive phenomenon occurring in the lean burn aeroengine combustor at low power condition. This topic is widely investigated these years focusing on the mechanism of flame structures, oscillation modes and the development of prediction methods. Recently, an analytical prediction method which based on the linear solution of Helmholtz equation was successfully used to predict the inception of the growl instability. In this model, the flame tube and the inflow duct are modeled as individual cavities and connected through a swirler acting as the neck of Helmholtz resonators. However, in many applications, the inflow duct has more complex geometry and thus complex acoustic boundary condition. So there is the need to extend this approach in a more universal form. This is the motivation of the current work.
This paper firstly presents the measured dynamic pressure and the flame motions in a single sector combustor. By changing the cross section area of the inflow duct, self-excited combustion instability was observed. This combustion instability mainly occurred at the frequency of 350HZ∼400Hz. The test results showed that flame front moves with the bulk flow in the axial direction while the pressure fluctuations in the inflow duct show a harmonic feature. It confirms that the combustion instability corresponds to the Helmholtz mode. This phenomenon was next analyzed with a new low-order linear acoustic method developed in this paper. The method integrates the model of Helmholtz resonator within harmonic oscillation (also called IM2H), and is validated by comparing with experimental data. By considering Helmholtz oscillation in the flame tube, the predicted frequency and mode agree well with experiments. The results show that the stability of the system is more sensitive to the geometry design parameter than the aerodynamics parameters.
Identification of Torsional Natural Frequencies and Damping As Well As Prediction of Stress Amplitudes at a Nuclear Power Train
Authors: Grein Roland , Ehehalt Ulrich , Balkowski Ingo 
Published: August 2017

As the landscape of energy production in Europe and other developed countries undergoes a rapid shift towards renewable energies, such as offshore wind, the use of HVDC (High-Voltage Direct Current) technology is increasing. HVDC converter stations have been reported to potentially cause sub-synchronous torsional interaction (SSTI) with turbo-generators in the grid. This phenomenon implies a negative electrical damping at the turbo-generator which may result in non-attenuating torsional vibrations. This is especially an issue in power grids where the close proximity of the power stations to the HVDC converter stations cannot be avoided. Therefore, in order to ensure safe and stable operation, monitoring of torsional vibrations is required.
In this article, a proof-of-concept study of touchless torque sensing at a nuclear power train in Gösgen, Switzerland, is presented. All three sub-synchronous natural frequencies were detected by the torque sensor during a load rejection test and show very good agreement with theoretical predictions based on finite element calculations. Possibilities to devise monitoring and eventually protection systems for torsional vibrations based on this technology are also discussed.
Optimization of Coupled System Components Using Approximations of Interface Quantities
Authors: Lockan Michael , Bestle Dieter , Janke Christian , Meyer Marcus 
Published: August 2017

Optimization of complex systems like jet engines is a process where discipline experts from several departments or even different companies have to work together. Thus, a complete system analysis code usually does not exist preventing an overall system optimization. Therefore, the system is typically split into components, and interface parameters between components are decided and fixed in early design stages based on low-fidelity information. Finally the components are optimized separately according to these fixed settings which, however, may prohibit an overall optimal system behavior even if sophisticated subsystem optimization is performed. Consequently, interface parameters should be varied in an overall coupled system optimization process and adapted to subsystem needs.
This may be supported by utilizing collaborative optimization strategies. Basically there are two types of such optimization approaches: global strategies with nested optimization loops and local subsystem optimization strategies supported by sensitivity-based approximations of other subsystems. The multidisciplinary optimization approach presented here combines the benefits of both strategies: efficient global optimization and approximations of subsystem quantities without the need of sensitivity information. It starts with an initial design of experiments for each component by varying all input parameters and evaluating the associated outputs. Due to the fact that these quantities consist of shared design parameters and outputs of other components, not all of the used input parameter combinations are feasible for the coupled system. In order to enforce consistency for the entire system, the interface regions are characterized by feasibility criteria acting as approximated constraints for further component optimizations. Beside that an approximation of the overall system objective is provided to all components to drive component design towards an overall optimal system performance.
The developed approach is demonstrated by an application to a jet engine turbine consisting of a high and low pressure part where the goal is to maximize the overall turbine efficiency. On the one hand the turbine is optimized with the proposed approach by splitting it into two coupled components; on the other hand the turbine is optimized as a complete system. It turns out that the proposed approach yields equally good results in much shorter time than overall optimization.
Experimental Study on Pressure Losses in Circular Orifices With Inlet Cross Flow
Authors: Feseker Daniel , Kinell Mats , Neef Matthias 
Published: August 2017

The cooling air in the secondary air system of gas turbines is controlled and metered by numerous restrictors, mainly in the shape of orifices. The ability to understand and predict the associated pressure losses are important in order to improve the air flow in the secondary air system. This experimental study investigates the behavior of the discharge coefficient for circular orifices with inlet cross flow which is a common flow case in gas turbines. Examples of this are at the inlet of a film cooling hole or the feeding of air to a blade through an orifice in a rotor disc.
Measurements were conducted for a total number of 38 orifices, covering a wide range of length-to-diameter ratios, including short and long orifices with varying inlet geometries. Up to five different chamfer-to-diameter and radius-to-diameter ratios were tested per orifice length. Furthermore, the static pressure ratio across the orifice was varied between 1.05 and 1.6 for all examined orifices.
The results of this comprehensive investigation demonstrate the beneficial influence of rounded inlet geometries and the ability to decrease pressure losses, which is especially true for higher cross flow ratios where the reduction of the pressure loss in comparison to sharp edged holes can be as high as 54%. With some exceptions, the chamfered orifices show a similar behavior as the rounded ones but with generally lower discharge coefficients. Nevertheless, a chamfered inlet yields lower pressure losses than a sharp edged inlet. The obtained experimental data was used to develop two correlations for the discharge coefficient as a function of geometrical as well as flow properties.
Investigation of Advanced Lifetime Calculation Procedure for Steam Turbines in Flexible Operation
Authors: Jarmowski Dennis , Capozzi Paolo , Vogt Jan , Helbig Klaus 
Published: August 2017

At high intermittent renewable energy share, plants are forced to operate more flexible beyond their original design intent. Many plants are older than 30 years with only limited residual lifetime. Decreasing energy prices and capacity factors will further enforce older plants to more transient operation with steeper gradients. Steam Turbine (ST) protections systems on site often are not designed for such flexible operation and therefore do not properly supervise the resulting impact on lifetime consumption.
Therefore precise lifetime management concepts are required to increase plant reliability and flexibility, mitigate risks for new implemented operation modes like faster start-ups and extended turn down.
The prerequisite for properly managing a plants lifetime is the accurate knowledge of the current state of consumed lifetime, which is evaluated in a lifetime assessment (LTA). This includes a standardized process for the calculation of creep and fatigue damage. For this long-term field operation data is used as input. The current LTA procedure typically limits the analysis to transient operation during start-up and shut-down. Other types of transient operation such as improved turn-down also need to be considered in order to take all relevant operation modes into account.
Therefore dedicated, new advanced methods are required for the precise estimation of the lifetime impact due to new operation modes with higher requirements compared to an assessment based on known current procedure. These methods will allow optimizing asset lifetime. In order to maintain power plant competitiveness, operation and maintenance cost must be reduced despite the demand for improved turn-down and more frequent start-up procedures.
This paper presents results of ST lifetime studies combining long-term operation data (including improved turn-down operation), FEM calculations and simplified and advanced constitutive material models.
In a first investigation, the rotor is modelled with FEM and thermal boundary conditions during isolated transient operation are derived from measurement data combined with generically elaborated new turn-down profiles.
The impact of the start-stop (enclosing cycle) and turndown cycle (sub-cycle) on the lifetime consumption is evaluated. For this, sub-cycles are considered in combination with the enclosing cycle and as isolated cycle.
In a second investigation, the above described calculation model is fed with 2 years of continuous operation data. Postprocessing is performed with common rain-flow methods and compared to an accumulative start-stop cycle assessment.
Based on the input of the calculation with the advanced constitutive material model further fracture mechanic investigations are performed.
The paper closes with an outlook on opportunities arising from digitalization of power generation equipment.