bluuebunny/crossref_metadata_2025 huggingface dataset:
A Study of Spontaneous Condensation in an LP Test Turbine
Authors: Chandler Kane , Melas Mauro , Jorge Teresa
Published: August 2015

Recent advances in computational fluid dynamics (CFD) offer the possibility to predict condensing flows in 3D LP steam turbine geometries. Correct analysis of wetness losses, droplet deposition and other two-phase effects in LP steam turbines requires accurate prediction of the non-equilibrium flow field and droplet sizes.

The paper compares numerical results from a 3D, polydispersed, condensing flow CFD code to experimental data measured in a scaled model LP turbine for a range of operating conditions. In order to compare the computed efficiencies with the measured values, a method for averaging non-equilibrium flow fields has been developed. Comparisons are made between computational and experimental results for a series of inlet temperature variation tests where the inlet and exit pressures were kept constant. The steady calculations accurately predict the temperature that the primary nucleation zone moves to an upstream row. Furthermore, the mechanism of condensation as nucleation changes rows is explored and it is shown that initially a significant degree of subcooling is maintained in the inter-blade section and, as a result, nucleation occurs at a relatively low rate in a zone that extends far downstream of the blade’s trailing edge. This produces relatively large droplets compared to when nucleation occurs predominantly within the blade passage and is clearly visible in the measured module efficiencies and local flow angles, static pressures and light extinction. The measured variation of efficiency and specific work with inlet temperature is predicted accurately by the computations.

It is concluded that steady condensing flow wet-steam calculations are able to predict the location of nucleation and the variation of flow dynamics and performance with inlet temperature accurately. A description of the condensation process as nucleation moves between rows has been given and is consistent with the numerical and experimental results.
Design of an Aspirated Compressor Stator by Means of DoE
Authors: Siemann Jan , Seume Joerg R.
Published: August 2015

This paper presents the design of an aspirated stator of a four-stage high-speed axial compressor. The aspiration of near-wall fluid at the suction side of the first stator is designed numerically by means of DoE (Design of Experiments). The design objective is a reduction or complete suppression of hub corner separation at off-design conditions. As operating point for the CFD-based design process, the last numerically stable operating point near the stall limit of the reference configuration at 80% of the design speed is chosen. As DoE factors the aspiraton velocity, the chordwise position, and the axial by radial dimensions of the aspiration slot are varied. Their effects on the two target values overall isentropic efficiency and total pressure ratio are investigated. All evaluated configurations show significant improvements in stage performance of all compressor stages be-cause of a reduction of hub corner separation. Based on the DoE correlation factors an optimization is performed. The optimum configuration shows an increase in overall isentropic efficiency Δηis of 1.3% to 90.98% whereas the total pressure ratio π is raised by 0.08 to 2.08.
Phase-Locked Investigation of Secondary Flows Perturbed by Passing Wakes in a High-Lift LPT Turbine Cascade
Authors: Infantino Daniele , Satta Francesca , Simoni Daniele , Ubaldi Marina , Zunino Pietro , Bertini Francesco
Published: August 2015

The present work describes the experimental investigations carried out at the Aerodynamics and Turbomachinery Laboratory of Genoa University aimed at characterizing the unsteady features of the secondary flows in a High-Lift Low Pressure Turbine cascade perturbed by incoming wakes. The investigations have been carried out at the nominal exit flow Reynolds number of 300000 in a 5-blade large-scale linear cascade. Hot-wire phase-locked ensemble-averaging technique has been applied to analyze in depth the time-dependent velocity and turbulence intensity distributions in a downstream tangential plane during a wake period. A multiple rotation technique has been used in order to measure the three velocity components as well as the Reynolds stress tensor terms. Acquired data are presented in terms of the phase-dependent mean velocity, turbulence and vorticity maps in order to distinguish between the contributions due to incoming wake velocity defect and those due to the turbulence carried by wakes on the phase-dependent secondary flow structures. Results clearly highlight a significant distortion and weakening of the passage vortex when the upstream wake passes through the measuring domain. Also an evident displacement of the passage vortex position has been observed in the wake period. This analysis allows understanding the difference in the three dimensional time mean structures of the exit flow field between the steady and unsteady operations.
Effect of Primary Zone Operating Condition for Dilution Mixing Behavior in a Gas Turbine
Authors: Dai Wei , Lin Yuzhen , Xu Quanhong , Zhang Chi , Xue Xin
Published: August 2015

The exit temperature distribution had a great effect on reliability and security in a gas turbine. In this paper, the exit temperature distribution of a small engine reverse-flow combustor with three injectors test module was experimentally obtained to qualitatively analyze the influence of the primary zone operating condition by changing the fuel air ratio at the ambient pressure and temperature condition. Under the nearly identical air condition, there was no obvious difference on the mixing performance with different fuel flow rate. The hot zones occurred at the same position of the combustor exit section, and the temperature declined in the radial direction from the center. It could be seen that the radial temperature profiles in FAR of 0.022–0.03 were almost same. Malvern experimental results showed that the air fuel ratio of swirler cup ranges from 5 to 40 and the droplet distribution index n could not be increased or decreased by the ratio at different air pressure drop. The air fuel ratio of combustor swirl cup had reached more than 5 which fuel particle had been nearly stable and not got some variation by changing the fuel mass rate. As a result, the increase of fuel air ratio had no impact on fuel atomization uniformity in combustor dome. The fuel had been completely atomized when the combustor fuel air ratio ranged from 0.022 to 0.03, and its impact on the droplet size and uniformity of fuel could be neglected. With the uniform fuel spray, a numerical study of the whole combustor had been made to analyze the strong relation between swirl flow and jets of primary holes and dilution holes. The dilution jets had a strong effect on quenching flame and temperature dilution. Along the combustor flow direction, the temperature difference became less and less obvious, the addition of fuel would enhance the combustion intensity mainly in combustion zone, but with an effect of dilution jet, the temperature distributions had little deviation when increasing the fuel air ratio. And it showed a same phenomenon that different fuel air ratio would make the same exit temperature distribution which was found to be in line with the experimental results. In a word, for the primary zone operating condition in the combustor, it almost had no effect on the temperature distribution at the exit of the combustor by changing the fuel air ratio from 0.022 to 0.030 in primary zone at normal pressure and temperature condition.
Optimized Steam Turbine Operation by Controlled Clutch Angle Engagement
Authors: Zimmer Gerta , Pieper Daniel , van Driel Kees , Lacombe Bernd , Daenner Mirko , Bennauer Martin
Published: August 2015

Some single shaft CCPPs are known to display increased vibrations if engaged at certain angles and a very smooth operational behavior if engaged at other angles. Neither the reason nor a mechanical mitigation for this behavior is known.

Roughly, the engagement angles can be clustered into four 90° sectors, one of them is deemed unfavorable and another one is classified as favorable with respect to vibrations of the overall power train shaft. Although the first priority is to have an assembly that runs smoothly at arbitrary engagement angles, an option to engage at a predefined ‘good’ angle provides an I&C back-up solution to avoid undue vibrations.

To meet this requirement a control method was developed to run up the steam-turbine thus that it will engage at a pre specified angle. The basic idea of the developed control algorithm is to increase the acceleration of the steam-turbine during run up if a prediction reveals an engagement angle that would be too small to be within the desired area and, conversely, decrease the acceleration if the anticipated angle would be too large.

A control algorithm to exploit this idea was developed and tested with the aid of a simulation model. The simulation model comprises a detailed thermodynamic model of the steam-turbine, the control valves and their actuators, the steam-turbine shaft and the shift clutch. I&C was modelled with all details relevant to turbine speed control. The gas-turbine/generator unit, however, is cut down to angular velocity and relative angle, respectively.

The performance of the controller was validated to comply with parameter uncertainties, different sampling times and frequency fluctuations of the electrical grid during coupling. In parallel, a high precision angular measurement device was developed and integrated into the existing turbine I&C.

Hardware-in-the-loop tests with simulated turbines and a hardware I&C system implementation also revealed a very satisfactory performance.

On site implementation of a prototype was successfully accomplished and resulted in the predicted accuracy of the preset engagement angle.
Investigations on Transonic Flow of Super-Critical CO2 Through Carbon Ring Seals
Authors: Hylla Eike , Schildhauer Markus , Büssow Richard , Metz Kolja , Klawes Robert
Published: August 2015

This paper gives an overview of numerical and experimental investigations on super-critical CO2 flow through carbon floating ring seals (CRS). The established simulation model considers the real gas effect, temperature deformation and the shaft rotation. For validation extensive measurements of the leakage rates, pressures and temperatures at various positions within the seal were conducted on a compressor prototype. Details of the measurement setup and the test procedure are given. The experimental results are discussed. A comparison of the measured data to the model prediction shows an overall good agreement.
Aerodynamic Investigation of Multi-Swirler Array Utilizing Low and High Swirl Swirler Combinations for a Lean Direct Injection Combustor
Authors: Endicott Derick , Tambe Samir , Jeng San-Mou
Published: August 2015

An experimental study has been carried out to investigate the isothermal aerodynamic behavior and to discern the effects on the flow-field resulting from interactions between low and high-swirl counter-rotating radial-radial air swirlers in three Lean Direct Injection configurations utilizing a 3 × 3 array of radial-radial swirlers. Configurations consisted of varying combinations of two swirlers featuring high and low swirl intensity. Two-dimensional velocity data is presented from the measurement of 37 planes spanning the width of the LDI array. Particle Image Velocimetry (PIV) was used to take velocity field measurements and to study the inter-swirler interactions. Three test cases were studied which utilized a combination of a low and high Swirl Number swirlers: the baseline case utilized 9 low swirl (SN about 0.6) swirlers, the second case used one high swirl (SN about 1.0) swirler in the center of the array, and the third case used 3 high swirl swirlers in a row within the array. The flow field developed by the three experimental cases differed significantly and inter-swirler interaction proved significant and highly complex. The velocity fields developed from swirlers in an array varied from that of the individual swirler, and as such, it should not be expected that the array have the same characteristics of the individual swirler. Placing a high-swirl swirler in a low-swirl array increased swirler interaction and led to substantial favorable changes in velocity fields and the recirculation zones developed downstream of each swirler in comparison to the baseline configuration including the development of a large CTRZ with weakened intensity for increased flame anchoring potential.
Numerical Investigation of Kelvin-Helmholtz Instability in a Centrifugal Compressor Operating Near Stall
Authors: Bousquet Y. , Carbonneau X. , Trebinjac I. , Binder N. , Dufour G.
Published: August 2015

The present works details the occurrence of the Kelvin–Helmholtz instability in a centrifugal compressor operating near stall. The analysis are based on unsteady three dimensional simulations performed on a calculation domain covering the full annulus for the impeller and the vaned diffuser. A detailed investigation of the flow structure is presented, together with its evolution consequent to the mass flow reduction. It is demonstrated that this reduction leads to an enlargement of the low momentum flow region initially induced by the combination of the secondary and leakage flows. When the compressor operates near stall, the shear layer at the interface between the main flow and this low momentum flow becomes unstable and induces a periodic vortex shedding. The frequency of such an unsteady phenomenon is not correlated with the blade passing frequency. Its signature is thus easily isolated from the deterministic rotor/stator interaction. Its detection requires full-annulus simulations with an accurate resolution in time and space, which explains why it has never been previously observed in centrifugal compressors.
Abradable Coating Removal in Turbomachines: A Macroscopic Approach Accounting for Several Wear Mechanisms
Authors: Berthoul Bérenger , Batailly Alain , Legrand Mathias , Stainier Laurent , Cartraud Patrice
Published: August 2015

Abradable materials are widely used as a coating within compressor and turbine stages of modern aircraft engines in order to reduce operating blade-tip/casing clearances and thus maximize the engine energy efficiency. However, recent investigations revealed that the interaction between a blade and these materials may threaten blades structural integrity. Consequently, there is a need for a better understanding of the physical phenomena at play and for an accurate modelling of the interaction in order to predict hazardous events. The cornerstone of related numerical investigations lies in the modelling of the abradable coating removal due to the blade/abradable coating interaction and the associated contact forces along the contact interface. In this context, this article presents a macroscopic model for abradable coating removal accounting for key wear mechanisms including adhesive wear, abrasive wear, micro-rupture wear and machining wear. It is coupled with an in-house numerical strategy for the modelling of full 3D blade/abradable coating interactions within turbomachines and applied to an aircraft engine. Numerical results are compared with respect to existing models and available experimental data. The applicability of the proposed model for 3D interaction simulations is underlined as well as the consistency of the obtained results with experimental observations.
Experimental Spray Structure and Combustion of a Linearly-Arranged 5-Swirler Array
Authors: Kao Yi-Huan , Denton Michael , Wang Xionghui , Jeng San-Mou , Lai Ming-Chia
Published: August 2015

The presented work focuses on the experimental spray structure and the combustion of a linearly-arranged 5-swirler array. The aerodynamics and spray characteristics of a non-reacting single swirler are reported first as a baseline, followed by those of a 5-swirler array to investigate the effect of swirling flow interactions on aerodynamics and combustion. For the baseline single swirler, the smaller droplets follow the air flow more closely and further dispersed away at the exit of swirler. Thus, the mean diameter of droplet increases with the flow developing further downstream. However, in the central portion of a 5-swirler array, the droplet size remains similar. It is attributed to that swirling flow interactions might provide better air/fuel mixing and the additional shear stress to break up droplet continuously and is evident by the higher turbulent intensity in the aerodynamic measurement. Due to the influence of gas phase, the distribution of liquid phase in center toroidal recirculation zone (CTRZ) is non-uniform in a 5-swirler array. The center swirler of a 5-swirler array features a larger CTRZ which is accompanied by two smaller CTRZs from its neighbors. The flame anchored by the center swirler of a 5-swirler array is richer than the other two neighboring flames when the inter-swirler spacing is 2D, where D is the diameter of swirler exit diameter. However, when the inter-swirler spacing is increased to 2.5D, all swirlers feature a similar flame, which is different from what is expected from non-reacting flow studies reported previously. The unexpected result should be attributed to the difference in swirling strength between non-reacting and reacting flows.

Moreover, the high speed imaging is employed to investigate the flame spreading during ignition process for a 5-swirler array. The high-speed movies show that the directional mechanism of flame spreading along lateral direction remains basically the same and is independent of the investigated test parameters including: two inter-swirler spacings, five fuel flow rates, five air pressure drops across swirlers, and five upstream air temperatures. An empirical correlation incorporating normalized inter-swirler spacing, air/fuel ratio, Reynolds number, and normalized air temperature is proposed and validated through a normalization procedure within around ± 10% error. The increase of Reynolds number and normalized air temperature has favorable impact on the flame spreading, which is stated by the empirical correlation.
GE Rapid Response Plant Design: Operational Flexibility and Transient Emissions Control
Authors: Smith Gordon R.
Published: August 2015

The GE Rapid Response plant design is described and compared to conventional combined cycle plant design. Advantages of the Rapid Response improved operational flexibility are explained and compared to conventional combined cycle plants. Improvements include faster power delivery to the grid, more economical plant startup, more profitable plant startup and lower emissions during plant startup.

The capability of a drum type HRSG for the Rapid Response cycling service is explored. Joint studies between GE and HRSG suppliers are highlighted supporting the adoption of drum type HRSGs for this cycling service. Necessary modifications to other plant equipment are explained.

Quantitative comparisons of Rapid Response and conventional combined cycle plant operability are given for electrical energy production and emissions reduction.

An advanced Selective Catalytic Reduction SCR control is shown providing improvements in combined cycle plant transient emissions control. Elements of the new control are explained. Argument is made to designate the new control as a second generation GEN II control compared to all other currently existing controls designated GEN I.

A brief outline of the current state of Rapid Response plant deployment is provided.
Adaptation of Phase-Lagged Boundary Conditions to Large-Eddy Simulation in Turbomachinery Configurations
Authors: Mouret Gaelle , Gourdain Nicolas , Castillon Lionel
Published: August 2015

With the increase in computing power, large eddy simulation (LES) emerges as a promising technique to improve both knowledge of complex physics and reliability of turbomachinery flow predictions. However these simulations are very expensive for industrial applications, especially when a 360° configuration should be considered. The objective of this paper is thus to improve the well-known phase lagged conditions to the LES approach by replacing the traditional Fourier Series Decomposition (FSD) by a compression method which does not make any assumption on the spectrum of the flow. Several methods are reviewed and the Proper Orthogonal Decomposition (POD) is retained. This new method is first validated on a flow around a circular cylinder with rotating downstream blocks. The results show significant improvements with respect to FSD. It is then applied to URANS simulations of a single stage compressor in 2.5D and 3D as a first validation step toward single-passage LES of turbomachinery configuration.
Gas Turbine Integrated Conceptual Design Approach
Authors: Carcasci Carlo , Piola Stefano , Canepa Roberto , Silingardi Andrea
Published: August 2015

In order to improve performance of heavy-duty gas turbines, in terms of power, efficiency and reliability, accurate calculation tools are required. During conceptual design phase, an effective integration of main GT components design into a single modular simulation tool can significantly reduce design iterations and improve the results. Thanks to an innovative modular-structured program for the simulation of air-cooled gas turbines, the one-dimensional design of compressor and turbine flow paths is used to create a complete gas turbine model including a detailed secondary air system and a simplified heat transfer model. This zero-dimensional heat transfer model is applied to each turbine row in order to calculate the cooling flow required to keep turbine blades and vanes metal temperatures below a prescribed threshold. After a description of the air cooled gas turbine modular model, the integrated design approach adopted by Ansaldo Energia is described. The knowledge of technical risks that the designers have to withstand developing advanced technologies during conceptual engine design is fundamental. The inter-disciplinary influence of some disciplines is analyzed and finally it is shown how Ansaldo Energia approach can track expected performance results and provide recovery plans during the conceptual design phase.
Comparison of Supercritical Carbon Dioxide Cycles for Oxy-Combustion
Authors: McClung Aaron , Brun Klaus , Delimont Jacob
Published: August 2015

Advanced oxy-combustion coupled with supercritical carbon dioxide (sCO2) power cycles offers a path to achieve efficient power generation with integrated carbon capture for base load power generation. One commonality among high efficiency sCO2 cycles is the extensive use of recuperation within the cycle. This high degree of recuperation results in high temperatures at the thermal input device and a smaller temperature rise to the turbine inlet. When combined with typical high side pressures ranging from 150 to 300 bar, these conditions pose a non-trivial challenge for fossil fired sCO2 cycles with respect to cycle layout and thermal integration. A narrow thermal input window can be tolerated for indirect cycles such as those used for nuclear power generation and concentrating solar power plants, however, it is at odds with traditional coal or natural gas fired Rankine cycles where the working fluid has been condensed and cooled to near ambient temperatures.

Coal fired sCO2 cycles using oxy-combustion have been examined by Southwest Research Institute and Thar Energy L.L.C. under DOE award DE-FE0009593. Under this project, an indirect supercritical oxy-combustion cycle was developed that provides 99% carbon capture with a 37.9% HHV plant efficiency. This cycle achieves a predicted COE of $121/MWe with no credits taken for the additional 9% of carbon capture, and represents a 21% reduction in cost as compared to supercritical steam with 90% carbon capture ($137/MWe).

Direct fired sCO2 cycles for natural gas or syngas are currently being evaluated by Southwest Research Institute and Thar Energy L.L.C. under DOE award DE-FE0024041. Initial evaluations of direct fired supercritical oxy-combustion cycles indicate that plant efficiencies on the order of 51% to 54% can be achieved with direct fired natural gas oxy-combustion when paired with the recompression cycle with 1,200 °C firing temperatures at 200 bar.

Direct fired natural gas or syngas sCO2 cycles still face significant technology development needs, with the pressurized oxy-combustor a significant component with a low Technology Readiness Level, (TRL) as defined by the DOE. In addition to the combustion system, significant work will be required to prepare the sCO2 turbomachinery for the turbine inlet temperatures required to achieve plant efficiencies greater than 50%.
Large-Eddy Simulation of Turbulent Combustion in Multi Combustors for L30A Gas Turbine Engine
Authors: Hirano Kohshi , Nonaka Yoshiharu , Kinoshita Yasuhiro , Muto Masaya , Kurose Ryoichi
Published: August 2015

When designing a combustor, numerical analysis should be used to effectively predict different performances, such as flame temperature, emission, and combustion stability. However, even with the use of numerical analysis, several problems cannot be solved by investigating single combustors because, in an actual engine, interactions occur between multiple combustors. Therefore, to evaluate the detailed phenomenon in an actual combustor, the interactions between all combustors should be considered in any numerical analysis. On the other hand, a huge amount of computational cost is required for this type of analysis. Here a large-eddy simulation employing a flamelet/progress variable approach is applied to the numerical analysis of industrial combustors. The combustor used for this study is the L30A from Kawasaki Heavy Industries, Ltd. Computations are conducted with a supercomputer (referred to as the “K-computer”) in the RIKEN Advanced Institute for Computational Science. All combustors in the L30A engine (from the compressor outlet to the turbine inlet) are simulated, including the fuel manifold. This engine has eight can combustors that are connected through the fuel manifold and compressed air housing unit. The total number of elements is approximately 140 million. The flow patterns for each combustor are similar in all cans. A swirling flow from the main burner is formed and accelerated by the supplemental burner. There is a high-temperature region before the supplemental burner. The flow field and temperature distribution in an actual combustor interacting with other combustor cans are simulated adequately. The mass flow rate of the air and those of the fuels are distributed equally for each can. Therefore, the outlet temperature difference for each can is also very small.
Turbine Blade Tip Film Cooling With Blade Rotation: Part I — Tip and Pressure Side Coolant Injection
Authors: Tamunobere Onieluan , Acharya Sumanta
Published: August 2015

This is the first in a two-part series of an experimental film cooling study conducted on the tip of a turbine blade with a blade rotation speed of 1200 RPM. In this part of the study, the coolant is injected from the blade tip and pressure side (PS) holes, and the effect of the blowing ratio on the heat transfer coefficient and film cooling effectiveness of the blade tip is investigated. The blade has a tip clearance of 1.7% of the blade span and consists of a cut back squealer rim, two cylindrical tip holes and six shaped pressure side holes. The stator-rotor-stator test section is housed in a closed loop wind tunnel that allows for the performance of transient heat transfer tests. Measurements of the heat transfer coefficient and film cooling effectiveness are done on the blade tip using liquid crystal thermography. These measurements are reported for the no coolant case and for blowing ratios of 1.0, 1.5, 2.0, 3.0 and 4.0. The heat transfer results for the no coolant injection show a region of high heat transfer on the blade tip near the blade leading edge region as the incident flow impinges on that region. This region of high heat transfer extends and stretches on the tip as more coolant is introduced through the tip holes at higher blowing ratios. The cooling results show that increasing the blowing ratio increases the film cooling effectiveness. The tip film cooling profile is such that the tip coolant is pushed towards the blade suction side thereby providing better coverage in that region. The shift in coolant flow profile towards the blade suction side as opposed to the pressure side in stationary studies can primarily be attributed to the effects of the blade relative motion.
Turbine Blade Tip Cooling With Blade Rotation: Part II — Shroud Coolant Injection
Authors: Tamunobere Onieluan , Acharya Sumanta
Published: August 2015

In this paper, blade-tip cooling is investigated with coolant injection from the shroud alone and a combination of shroud coolant injection and tip cooling. The blade rotates at a nominal speed of 1200 RPM, and consists of a cut back squealer tip with a tip clearance of 1.7% of the blade span. The blade consists of tip holes and pressure side shaped holes, while the shroud has an array of angled holes and a circumferential slot upstream of the rotor section. Different combinations of the three cooling configurations are utilized to study the effectiveness of shroud cooling as a complementary method of cooling the blade tip. The measurements are done using liquid crystal thermography. Blowing ratios of 0.5, 1.0, 2.0, 3.0 and 4.0 are studied for shroud slot cooling and blowing ratios of 1.0, 2.0, 3.0, 4.0 and 5.0 are studied for shroud hole cooling. For cases with coolant injection from the tip, the blowing ratios used are 1.0, 2.0, 3.0 and 4.0. The results show an increase in film cooling effectiveness with increasing blowing ratio for shroud hole cooling. The increased effectiveness from shroud hole cooling is concentrated mainly in the tip-region below the shroud holes and towards the blade suction side and the suction side squealer rim. Slot cooling injection results in increased effectiveness on the blade tip near the blade leading edge up to a maximum blowing ratio, after which the cooling effectiveness decreases with increasing blowing ratio. The combination of the different cooling methods results in better overall cooling coverage of the blade tip with the shroud hole and blade tip cooling combination being the most effective. The level of coolant protection is strongly dependent on the blowing ratio and combination of blowing ratios.
Employing Micro-Turbine Components in Integrated Solar-MGT-ORC Power Plants
Authors: Cameretti Maria Cristina , Ferrara Francesco , Gimelli Alfredo , Tuccillo Raffaele
Published: August 2015

The authors propose in this paper the integration of a combined power plant, with a micro gas turbine (MGT) and an ORC system, and a solar field that allows a temperature increase of the air at the MGT recuperator inlet. Consequently, an increase is also obtained for the exhausts and this leads to an enhanced heat recovery in the ORC boiler and a greater availability of thermal energy.

The purpose of the authors’ work is to analyze the effectiveness of the above proposal under several aspects, therefore, under a preliminary thermodynamic study of the plant set-up in CHP mode, the attention is paid to the choice of the organic fluid expander with a low-cost objective. Classical similarity criteria are helpful for a first estimate of the adaptability of a radial flow turbine from the down-sized turbocharger technology to an organic working fluid. A CFD validation of such choice is then carried out and this phase also determines the characteristic curves of the radial flow turbine.

Basing on the availability of the characteristic maps of all the rotating components, a reliable off-design analysis of the solar-assisted CHP plant is performed under several load levels and environmental conditions, the latter strongly influencing the solar irradiance on the parabolic trough collectors.

Finally, since the examples refer to both natural gas and biogas fuelling, a CFD analysis of the reacting flow through the MGT combustor checks the combustion effectiveness under challenging variations of the boundary conditions.
On the Fast Prediction of Open Rotor Tonal Interaction Noise
Authors: Gruber Mathieu , Lonfils Timothée , Dumont Chloé , Vion Laurence , Dubois Adrien , Mc Williams Timothy Delteil
Published: August 2015

This paper discusses the noise prediction of Contra Rotating Open Rotors (CROR) in the context of a multi-disciplinary rotor design. Propeller noise is believed to be one of the dominant sources of noise on CROR engines in all flight conditions that require high thrust. It is therefore important to consider acoustics as early as possible in the design process. At Snecma, blade design is tackled as a multi-disciplinary approach that involves among others; mechanics, dynamics, aerodynamics, acoustics and engine integration constraints. In this context, accurate prediction methods based on unsteady Computational Fluid Dynamics (CFD) cannot be used to predict tonal noise radiation because of the prohibitive time required for convergence. This paper focuses on the prediction of far field tonal interaction noise using the fast prediction platform Sandra, which complies with the timescale of a rotor design project. Sandra is composed of an aerodynamic module and an acoustic module. As a first approximation, the aerodynamic module uses either a lifting-line method or a lifting-surface method to compute the pressure fluctuations on the blades. A map of the flow velocity, which contains the velocity gradients of the wake and of the tip vortex behind the front rotor, is extracted from a Reynolds Averaged Navier-Stokes (RANS) CFD simulation downstream of the front rotor. A quasi-stationary approach, which uses the space and time symmetry of the isolated rotors CFD, allows the flow field to be decomposed along the azimuthal angle. The pressure fluctuations on the rear blade are finally computed for each position. The acoustic propagation is then performed in the time domain using Farassat’s formulation 1A of the Ffowcs Williams and Hawkings equation. It is shown that the physics of the interaction between the front and the rear rotor is well captured. Direct comparisons with the far field noise computed from a uRANS solution, and with experimental data, show very good agreement of the position of the angles of maximum noise radiation for harmonics of order 2 or lower. It is also shown that the relative noise radiation between various rotor geometries is reasonably well captured, which is a requirement to provide a fast and relevant method for multi-disciplinary propeller blade design.
Preliminary Investigations for a Pressure Balanced Back Plate at Low Inclined Brush Seals
Authors: Schwarz H. , Friedrichs J.
Published: August 2015

Within this paper a continuation in brush seal testing for flexible load regimes in a steam turbine is given. Besides the well-known main design parameters of brush seals, e.g. the bristle pack thickness, the bristle diameter or the lay angle of the bristle pack, this paper focuses on the axial inclination of the bristle pack and particularly the affinity of bristle pack oscillations at low inclined bristle packs and small pressure differences. As it was presented in GT2014-26330, the axial inclination of the bristle pack is an important design parameter for brush seals. Along with a clearly increased blow-down capability and a reduced stiffness the seals tend to exhibit an enhanced axial bristle pack width during pressurization. It was previously shown that a low axial inclination of the bristle pack results in a loose package and in bristle pack oscillations until pressure differences of 10 bar. Above pressure drops of 10 bar the resulting higher abrasive behavior stops and a well sealing brush seal with a loose bristle pack is given. Regarding the renewable energy sources for necessary changes in steam turbine operations, a flexible sealing system with an enhanced wide operating range is requested. To capture all positive behaviors of low inclined brush seals for pressure differences until 10 bar, a design to safely avoid bristle pack oscillations is required. With this background low inclined brush seals with a new back plate design were tested at the Institute’s cold air test facility in Braunschweig up to a pressure difference of 4 bar. The facility allows detailed sealing performance investigations including real time bristle pack observations. The present paper shows and discusses overall experimental results of brush seals with different axial inclinations mounted with an adjustable back plate to determine the influence of the back plate design on the bristle pack oscillations. Furthermore, these new results together with older measurements from 2012 were used to develop a theory regarding the changes that result from contact between the bristle pack and the adjusted back plate. Finally, the design for a pressure balanced back plate will be shown.
Numerical Prediction of Stall Inception in Centrifugal Compressor Using Eigenvalue Method
Authors: Yunfei Ma , Xiaohua Liu , Sun Dakun , Xiaofeng Sun
Published: August 2015

This paper is concerned with the prediction of stability inception of centrifugal compressor based on eigenvalue theory. A body force model has been developed to simulate the impellers of the compressor by applying the effect of the blade force on momentum change and energy loss and geometries of blades. Using spectrum method, the stability equations can be precisely transformed into a very large matrix equation due to the compressor configuration. Before computing with spectrum method, it is available to use Jacobi Transform when making a transformation between physical and computational regions. Afterwards, the Singular Value Decomposition is adopted to solve the resultant eigenvalue matrix, the roots of which can conveniently predict whether the flow is stable or not. It is found that the relative error of the computational model is smaller in comparison with CFD steady results, which indicates that the model can be used as a practical and reliable theoretical criterion during the compressor design phase without requiring any experiential formulas and data.
CFD Analysis of Centrifugal Compressor Stage Range Extension Using Internal Flow Recirculation
Authors: Meduri Uday K. , Selvam Kathiravan , Nawrocki Gilles
Published: August 2015

A Centrifugal Compressor is a key component in the Oil and Gas Industry. It is used in all 3 areas of extraction, processing and transportation, namely, upstream, midstream and downstream. Generally a compressor’s life expectancy matches that of the wells it is used on. Barring retrofits and maintenance, a compressor can remain onsite for up to 20 years.

However, at the end of the life of the well or in special conditions with perennial low flow rates, the reduced gas flow rate pushes the compressor to the left of its operating limit. At this point, the compressor surges. In order to bring it back to the normal operating conditions, flow is recirculated via an external circuit involving the anti-surge valve. This drops the flange to flange performance. A simpler method would be to recycle the flow internally, thus removing the losses from the external circuit.

In this paper, internal flow recirculation is studied where flow is extracted from the stage diffuser and recycled back to the upstream return channel. This study was undertaken on a 2D impeller from the lowest flow coefficient stage of an OEM. Using 1D tools and detailed CFD methods to study this novel design, it is shown that the range can be shifted significantly.
Experimental Investigation of the Transition Mechanism From Stable Flame to Flashback in a Generic Premixed Combustion System With High-Speed Micro-PIV and Micro-PLIF Combined With Chemiluminescence Imaging
Authors: Baumgartner Georg , Boeck Lorenz R. , Sattelmayer Thomas
Published: August 2015

Sustainable power generation resulting in low pollutant emissions, such as CO2 and NOx, poses a very challenging task in the near future. Premixed combustion of hydrogen-rich fuels in gas turbines is a promising approach to cope with ever more stringent regulations on emission levels. This method, however, involves the risk of flame flashback from the desired flame position into the premixing section, leading to catastrophic failure of the machine components that are not designed for such high temperatures. The objective of the current study was to visualize and describe the transition from stable flame to flashback in a generic H2-air combustion system and develop a physics-based model for the description of the transition. In order to achieve the high temporal and spatial resolution required for capturing the involved effects, high-speed Particle Image Velocimetry (PIV) and high-speed Planar Laser-Induced Fluorescence (PLIF) were employed. In order to characterize the interaction of the flame with the flow in detail, both measurement techniques were applied to very small fields-of-view using (UV) long-distance microscopes. The repetition rates were 20 kHz for PLIF and 3 kHz for PIV, respectively. During both the PLIF and the PIV measurements, the flame’s OH*-chemiluminescence was captured from a perspective perpendicular to that of the PLIF/PIV camera for further flame characterization. The microscopic measurements revealed that there is negligible influence of the unconfined flame on the incoming burner flow in stable mode. Upon approaching flashback conditions, however, the velocity profile of the burner flow is distinctly distorted by the presence of the flame inside the premixing duct. The flow directly upstream of the flame is retarded and deflected around the leading flame tip. Based on the effects observed in the experiments, a new flashback model is proposed, which identifies the heat transfer to the burner rim and the flame speed as the main drivers for the onset of flashback, whereas the flame backpressure is the governing factor for the subsequent upstream flame propagation.
Numerical Analysis of the Dynamic Flame Response in Alstom Reheat Combustion Systems
Authors: Yang Yang , Noiray Nicolas , Scarpato Alessandro , Schulz Oliver , Düsing K. Michael , Bothien Mirko
Published: August 2015

In the development process of all gas turbines, the thermoacoustic behavior of the combustion system is of crucial importance for the overall performance in terms of lifetime, emissions, and operational flexibility. An efficient design process requires a methodology which is able to analyze this behavior in an early phase. This method is at the same time expected to give insight into the underlying thermoacoustic mechanisms of relevant acoustic modes. Based on an example case for an Alstom reheat combustor relying on the auto-ignition principle, the paper describes such a method for low frequency modes, which is based on unsteady reactive CFD, flame transfer function analysis and acoustic network modeling. Results are validated against full-scale engine measurements. Moreover, physical insight of the coupling mechanisms responsible for the dynamic response of the flame is given.
Experimental Validation of a Curtain Type Fluidic Jet Seal on a Turbine Rotor Shroud
Authors: Hilfer Michael , Hogg Simon , Ingram Grant
Published: August 2015

This paper describes the design and testing of a fluidic “air-curtain” type seal application to reduce tip leakages on a small high-speed single stage axial turbine.

The initial experimental investigations were carried out to demonstrate the application of the fluidic type seal on a “frozen rotor” test of a turbine. The “frozen rotor” test is carried out using an actual turbine rotor in a static test facility without rotation. These preliminary tests provide the first experimental validation of fluidic “air-curtain” type seals working to reduce over-tip leakage in a turbine shroud on a actual turbine geometry.

Ultimately the final stage of the work will be to demonstrate the fluidic seal working in a full rotating facility but these results provide a logical and important step towards that ultimate goal.
Scripted CFD-Tool for the Automated Design of Volutes for Centrifugal Compressors
Authors: Heinrich Martin , Schwarze Rüdiger
Published: August 2015

An automated tool for the design of arbitrary volute geometries is presented in this paper. The shape of the volute geometry is represented by B-splines as a function of the azimuth angle ϕ. Furthermore, the volute and exit cross section areas can be specified as well as the fillet radius.

A volute-only model is used to investigate the influence of the fillet radius and the volute exit area onto the volute performance. Based on the analysis of one hundred randomly generated geometries, a surrogate model is created using the static pressure recovery and the total pressure loss coefficient. This model shows, that there is a large dependency between the exit area and the efficiency of the volute. In contrast, the fillet radius had only minor influence.
Thermodynamic and Economic Analysis and Multi-Objective Optimization of Supercritical CO2 Brayton Cycles
Authors: Zhao Hang , Deng Qinghua , Huang Wenting , Feng Zhenping
Published: August 2015

Supercritical CO2 Brayton cycles (SCO2BC) offer the potential of better economy and higher practicability due to their high power conversion efficiency, moderate turbine inlet temperature, compact size as compared with some traditional working fluids cycles. In this paper, the SCO2BC including the SCO2 single-recuperated Brayton cycle (RBC) and recompression recuperated Brayton cycle (RRBC) are considered, and flexible thermodynamic and economic modeling methodologies are presented. The influences of the key cycle parameters on thermodynamic performance of SCO2BC are studied, and the comparative analyses on RBC and RRBC are conducted. Based on the thermodynamic and economic models and the given conditions, the Non-dominated Sorting Genetic Algorithm II (NSGA-II) is used for the Pareto-based multi-objective optimization of the RRBC, with the maximum exergy efficiency and the lowest cost per power ($/kW) as its objectives. In addition, the Artificial Neural Network (ANN) is chosen to establish the relationship between the input, output, and the key cycle parameters, which could accelerate the parameters query process.

It is observed in the thermodynamic analysis process that the cycle parameters such as heat source temperature, turbine inlet temperature, cycle pressure ratio, and pinch temperature difference of heat exchangers have significant effects on the cycle exergy efficiency. And the exergy destruction of heat exchanger is the main reason why the exergy efficiency of RRBC is higher than that of RBC under the same cycle conditions. Compared with the two kinds of SCO2BC, RBC has a cost advantage from economic perspective, while RRBC has a much better thermodynamic performance, and could rectify the temperature pinching problem that exists in RBC. Therefore, RRBC is recommended in this paper. Furthermore, the Pareto front curve between the cycle cost/ cycle power (CWR) and the cycle exergy efficiency is obtained by multi-objective optimization, which indicates that there is a conflicting relation between them. The optimization results could provide an optimum trade-off curve enabling cycle designers to choose their desired combination between the efficiency and cost. Moreover, the optimum thermodynamic parameters of RRBC can be predicted with good accuracy using ANN, which could help the users to find the SCO2BC parameters fast and accurately.