bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preliminary Study of a Centrifugal Compressor With Counter-Rotating Impellers: Design and Performances Study
Authors: Cheikh Brahim Abed , Sofiane Khelladi , Michael Deligant , Abdel El Marjani , Bakir Farid 
Published: January 2021

Abstract
Turbomachinery with double counter-rotating impellers offer more degrees of freedom in the choice of design and control parameters compared to conventional machines. For these innovative machines, the literature review shows that more published works are available concerning axial type turbomachines than centrifugal ones. This work deals with a preliminary design and performance analysis applied to two counter-rotating impellers of a centrifugal compressor. We present here the design practice developed based on 0D/1D models, also coupled with optimization and stream-curvature through-flow methods to satisfy the selected design-criteria. An analyze of aerodynamic performances results are made and compared to those available experimental and numerical data of a baseline configuration, composed of one centrifugal-impeller and a volute. The compressor studied here includes a first conventional impeller with an axial inlet and a mixed or centrifugal outlet. The second impeller is designed parametrically and can be considered as a rotating-diffuser with a radial or mixed inlet and outlet. Ultimately, the numerical simulation results of a selection of candidate solutions are discussed.
A Novel Sensor for Improving Flame Stability of Gas Fired Gas Turbine by Continuously Monitoring Fuel Gas Quality
Authors: Flot Patrice , Duval Alexis , Digneton Mathias 
Published: January 2021

Abstract
Gas networks are interconnected and strategically linked to multiple sources. Because of this, the quality of gas can change rapidly at a given location when switching from one source to another. When this occurs, these rapid changes can result in flashback or flame extinction.
To overcome combustion issues and instabilities of gas fired gas turbines due to the variability of gas incoming gas quality, a new sensor called NIRIS NG has been designed which analyzes the natural gas composition at the inlet of the turbine burners. The design of the NIRIS NG sensor boasts a short response time (less than one second), easy installation, simple maintenance, and low cost. This is primarily because unlike other gas quality sensors, the NIRIS NG sensor is based on spectrometry technology and the sensor has been specifically engineered for installation on turbine applications. By employing spectrometry, the NIRIS NG sensor is performing a technological breakthrough by using low cost optical components and proprietary signal treatment software within robust packaging that can sustain the vibration and heat over extended periods. The gas-pipe-plugged sensor provides fast response times and transmits the data to the turbine controller using CAN protocol. This paper will describe in detail the sensor hardware and software technologies, validation testing that has been completed to date, and the expected advantages on industrial gas fired gas turbines.
Numerical Investigations on the Effect of Pivot Shapes in Part Clearance Flow Field of Variable Area LP Turbine Nozzle Vane
Authors: Bhavsar Hardikkumar , Mistry Chetan S. 
Published: January 2021

Abstract
The performance of the gas turbine engines deteriorates under off-design conditions with the change of required power demand. The performance of the engine can be improved by actively controlling the mass flow rate through the engine turbine section using the variable area nozzle turbine (VANT). However, to implement VANT, vanes of the turbine nozzle need to be rotated, which demands part clearance to be provided near both the hub and tip region. In order to keep constant part clearance during vane turning, endwalls are modified to spherical shapes in such a way that distance between vane and upstream as well downstream rotor remains unaffected. Also, vanes are rotated about its pivot, which creates a blockage to the leakage flow in the part clearance. As pivot creates a blockage to the leakage flow, the shape of the pivot need to be selected in such a way that leakage losses can be reduced effectively. Hence, to analyze the effect of different pivot shapes on leakage losses, two different shapes of the pivot i.e., circular and elliptic, are explored in the present study. Also, three vane turning angles are analyzed to observe the effectiveness of these pivot shapes. The effect of the pivot is analyzed by entropy contours and total pressure loss coefficient in the exit plane, and it is found that the elliptic pivot performs better than a circular pivot as an elliptic pivot provides more blockage to the leakage flow and hence minimizing the overall losses.
The Limit Inlet Temperature of Refrigeration Centrifugal Compressor to Avoid Phase Change
Authors: YaFei Duan , YongHong Tang , ZhiHong Jin , HanSen Zou , Guang Xi 
Published: January 2021

Abstract
From the polytropic compression work formula, we can find that the consumed polytropic work will reduce with the decrease of inlet temperature while compressing the refrigerant to the same compression ratio. However, the refrigerant may condense if the inlet temperature is low enough. Though the principle that the acceleration of fluid may result in condensation has been proved by numerical simulations and experiments, and the liquid formation inside the supercritical carbon dioxide (SCO2) centrifugal compressor has been widely studied, there is still not a user-friendly method to predict whether the inlet condition may cause liquid formation inside the compressor.
The fluid flow in the space near the blade suction face of the leading edge (SNSL) is assumed to the similar flow in a converging nozzle when the mass flow is larger enough; the fluid impinges on the suction surface of blades, and the absolute velocity of fluid will not be greater than sound velocity. The fluid turns to impinge on the pressure surface with the decrease of mass flow rate, which is similar to the flow in a converging-diverging nozzle, and the maximum absolute velocity in the SNSL may be greater than the sound speed.
A method is proposed to predict the lowest inlet temperature of refrigeration centrifugal compressor to avoid phase change, which is called the limit temperature. The predicted lowest temperature shares the same trend with the numerical results. The condensation will occur inside the compressor when the inlet temperature is lower than the limit inlet temperature. The lowest temperature will first increase and then decrease as the mass flow increases, which should be taken into account while designing a refrigeration centrifugal compressor or adjusting the operating condition.
Influence of Blade Tip Fillet Structure on Aerodynamic Performance of a Compressor Rotor
Authors: Wang Haohao , Zhao Lei , Gao Limin , Li Yongzeng , Ma Chi 
Published: January 2021

Abstract
This paper deals with the numerical simulation of a passive control technology to increase the performance of the first rotor in a counter-rotating axial compressor. The objective is to extend the stable operating range of an axial compressor rotor using blade tip fillet structure that located on the blade tip pressure side. Firstly, the behavior of the tip leakage flow is investigated for the compressor rotor without passive treatment. The simulations show the loading of blade tip increases as the mass flow rate decreases, which pushed the location of tip leakage vortex and tip separation vortex forward to leading edge. A blockage in the rotor blade passage is also observed at near stall conditions. Then, a rotor blade tip fillet structure (TFS) is tested in order to control leakage flow in the tip region. Steady calculations were conducted to investigate the impact of TFS on the performance of the compressor rotor. The results show that TFS could extend the operating range with no penalty for efficiency when the fillet structure located on the blade tip pressure side. The flow control mechanisms of tip leakage flow are that TFS has a good ability to weaken the tip separation vortex and make the tip leakage vortex closer to the blade suction surface compared to origin rotor blade. It is founded that TFS may lead to a increase of leakage flow mass rate near tip clearance region that resulted in the addition of mixing loss. It is significant to obtain a balance between the benefits of weakening the tip separation vortex and the damage of mixing loss.
Development and Validation of a Model for Centrifugal Compressors in Reversed Flow Regimes
Authors: Powers Katherine H. , Kennedy Ian J. , Brace Chris J. , Milewski Paul A. , Copeland Colin D. 
Published: January 2021

Abstract
Turbochargers are widely used to help reduce the environmental impact of automotive engines. However, a limiting factor for turbochargers is compressor surge. Surge is an instability that induces pressure and flow oscillations that often damages the turbocharger and its installation.
Most predictions of the surge limit are based on low-order models, such as the Moore-Greitzer model. These models tend to rely on a characteristic curve for the compressor created by extrapolating the constant speed lines of a steady-state compressor map into the negative mass flow region. However, there is little validation of these assumptions in the public literature.
In this paper, we develop further the first-principles model for a compressor characteristic presented in Powers et al. [1], with a particular emphasis on reverse flow. We then perform experiments using a 58mm diameter centrifugal compressor provided by Cummins Turbo Technologies, where we feed air in the reverse direction though the compressor while the impeller is spinning in the forwards direction in order to obtain data in the negative mass flow region of the compressor map.
This demonstrated experimentally that there is a stable operating region in the reverse flow regime. The recorded data showed a good match with the theoretical model developed in this paper We also identified a change in characteristic behaviour as the impeller speed is increased which, to the authors knowledge, has not been observed in any previously published experimental work.
High Firing Temperature GT36 H-Class Low NOx Combustor Engine Validation and Performance
Authors: Granet V. , Sierra Sanchez P. , Cuquel A. , Günster P. , Wickström A. , Pennell D. , Singla G. , Früchtel G. 
Published: January 2021

Abstract
In order to minimize the footprint of human activities on the environment, technologies to reduce greenhouse gases while meeting constantly growing electricity demands are critical. Amongst the various sources of energy production, Gas Turbines (GT) are an efficient way to stabilize the grid with regards to renewable sources like wind and solar energies. The demand for higher efficiency, higher power output while reducing emission levels (especially NO and NO2) at high loads, and for higher flexibility within the H-class Gas Turbine market is thereby a natural consequence. The development and validation of a two-stage sequential combustor, so-called Constant Pressure Sequential Combustion (CPSC) system, to achieve these goals has been accomplished by Ansaldo Energia. The CPSC consists of a premix burner system (First Stage) and of a sequential burner (SB) in series within a can combustor. At the 2017 and 2019 ASME conferences, high pressure test rig validation results of the CPSC were introduced. The advantages with regards to fuel flexibility, hydrogen combustion and low emissions at high firing temperature were presented [1,2,3,4,5]. This article focuses on the validation of the combustor performance in Ansaldo Energia’s Validation Power Plant located in Birr, Switzerland, which includes detailed validation from ignition to full speed no load, part load operation and full load over various ambient and engine thermal state conditions. To allow for detailed validation, dedicated fully instrumented combustor cans were installed in the GT. Detailed validated air distribution and emission models support the results obtained on the engine. Ignition and ramps up to full speed no load have been validated with large variations of the first combustor stage firing temperature to minimize power consumption and start-up time. The potential of the CPSC with regards to turndown capability, with minimum environmental load (MEL) below 25% GT load while keeping CO levels low has been confirmed. The MEL can be kept low over a wide range of ambient temperature and fuel compositions by adjusting the inlet temperature of the sequential burner. Low NOx values were achieved at baseload and peak firing temperature. The operational flexibility and stability of the premixed first stage combustor over the load range and over a large variation of combustor inlet plenum pressures was as well validated along with the operation concept of the gas turbine.
Numerical Modeling of Centrifugal Compressors With Heterogeneous Incoming Flow due to Low Pressure Exhaust Gas Recirculation
Authors: Galindo José , Serrano José Ramón , Navarro Roberto , García-Olivas Guillermo 
Published: January 2021

Abstract
Low pressure EGR (LP-EGR) has become recently one of the most investigated technique in the field of internal combustion engines. When LP-EGR is active, two streams with different psychrometric conditions are mixed at the compressor inlet, i.e. fresh air (considered as cold and dry) and EGR (humid and warm). The main objective of the present work is to assess the impact of the inlet flow heterogeneity, associated with LP-EGR systems, in the performance of centrifugal compressor using 3D CFD simulations. Two intake configurations will be studied, namely a standard straight duct providing the compressor with a homogeneous flow and T junction with a mixing of air and EGR streams. 9 operating points using an EGR rate of 15% (or equivalent inlet conditions for the single duct) are explored. The temporal treatment is firstly assessed, comparing steady RANS simulations against unsteady ones for both intakes, discussing their behavior in terms of global variables and in mean flow field too. These studies show how the steady approach is not enough accurate for predicting the heterogeneity of the flow field in LP-EGR applications. After that, the comparison in global variables between the T-junction inlet and the standard inlet shows slightly differences in terms of compression ratio (around 0.5%) and isentropic efficiency (around 1%). However, in terms of local differences, the case with the standard inlet is clearly not able to predict the temperature heterogeneity of the case with a T-joint. Despite these issues, for an EGR rate of 15%, the global parameters of the compressor are not affected by the T-junction when equivalent operating points are considered in a single duct intake, so this approach can be employed to still use the standard compressor map for LP-EGR applications.
Design Space Exploration of Turbine Blade Shroud Interlock for Flutter Stability
Authors: Larrieta Olatz , Alonso Roberto , Escobar Óscar Pérez , Eryilmaz Ibrahim , Pachidis Vassilios 
Published: January 2021

Abstract
The geared turbofan engines bring the potential to rotate the fan at lower speed and allow an increase in diameter, which in turn leads to an increase in propulsive efficiency through high by-pass ratio. The low-pressure turbine stages driving the fan can also rotate at high speed resulting in fewer stages when compared to traditional turbofans. However, when operating at high speed, pressure fluctuations due to self-excited vibrations increase and may provoke flutter instabilities.
In a geared architecture, to deliver the high power required by the fan and the intermediate-pressure compressor, the low-pressure turbine system operates at higher temperatures compared to its predecessors. This phenomenon requires structural materials with higher heat resistance, which carries the inconvenience of poor welding suitability. That is the reason why alternative non-welded blade shroud joint techniques are so important, techniques as the blade interlock mechanism studied in this work.
This manuscript examines the effects of different design parameters of a low-pressure turbine blade shroud interlock on flutter stability, to make future recommendations for geared engines. The shrouded turbine rotor blades feature blade interlocks, which enhances the dynamic stability by providing stiffness to the rotor blade row. To assess the stability of the system, a parametric design of a turbine blade-disk assembly was prepared. In the parametric model the design variables that define the blade interlock are the interlock angle, interlock axial position, interlock contact length and height, knife seal position and pre-twist angle.
After parametrization, a finite element model of the turbine blade and disk assembly was prepared with cyclic symmetry boundary condition. The stresses caused by rotation were calculated in a static structural analysis and these were used as pre-stress boundary conditions in modal analysis. The modal results were afterwards exchanged with an aerodynamic model to obtain the aerodynamic damping for different blade interlock design configurations.
In the present work, the dynamic response of the first three excitation modes was analyzed. It was found that the third mode was stable for all the design points, whereas first and second modes were unstable at least for the reference design point. Among the considered six different parameters that define the blade interlock geometry, the interlock contact position turned to be the most influential parameter for modal response and for flutter stability. Moving the interlock contact position towards the trailing edge gave the most beneficial results. On the other hand, the interlock angle showed the least influence on both, the modal analysis and flutter behavior. The accomplished Design of Experiments and subsequent optimization process also conclude that there exists an interdependency between the studied parameters.
Quantification of Variation in Combustion Instability Amplitude in a Multi-Nozzle Can Combustor
Authors: Westfall Seth , Sekulich Olivia , Culler Wyatt , Peluso Stephen , O’Connor Jacqueline 
Published: January 2021

Abstract
In this work, we quantify the level of variation in unstable combustion oscillation amplitudes and identify the source of this variation in a multi-nozzle can combustor. At conditions where pollutant emissions are reduced, lean-premixed combustors can undergo thermoacoustic instability when pressure and heat release rate oscillations couple. A commonly used method for suppressing instability is fuel staging, which is a method where fuel is unevenly distributed between nozzles in a multi-nozzle combustor. Our work follows others who have characterized the effect of fuel staging on combustion instability and the mechanisms by which it works during both steady-state and transient operation. One of the outcomes from our previous work was that certain instability operating points display a high level of pressure oscillation amplitude variation. Instead of oscillating at a constant limit-cycle amplitude, the pressure oscillation amplitude varies significantly in time. In this work, we use the concept of permutation entropy to quantify the level of variation in the pressure fluctuation amplitude. We correlate the level of variation with a number of state variables over a range of operating conditions, 291 test cases in all. These state variables include mixture equivalence ratio; transient timescale, amplitude, and direction; hardware temperatures; gas temperatures; and thermoacoustic damping and growth rates. Significant pressure oscillation amplitude variation occurs when the thermoacoustic damping rate is low. The damping and growth rates can be low for a number of reasons, but they are highly correlated with the metal temperature of the centerbody, where the flames are anchored; lower temperatures result in lower damping rates during stable operation and lower growth rates during unstable operation. These results show the importance of the thermal boundary condition on the time-dependent behavior of the thermoacoustic instability.
Simulation of Premixed and Partially Premixed Jet-in-Crossflow Flames at High-Pressure
Authors: Stiehl Bernhard , Otero Michelle , Genova Tommy , Worbington Tyler , Reyes Jonathan , Ahmed Kareem , Martin Scott , Velez Carlos 
Published: January 2021

Abstract
In this paper we explore the operational map of a lean axial-staged combustor of premixed and partially premixed reacting jet-in-crossflow flames at high-pressure (5 atm). This study attempts to expand the data to relatively high pressure and could significantly aid scaling to real gas turbine engine conditions at 20–30 atm. High speed camera, PIV, CH* chemiluminescence, temperature and pressure measurements were taken and processed to allow accurate reconstruction of six operating points relative to CFD simulations under minimal adjustments. Variation of lean main stage (φ = 0.575 and 0.73) and rich jet (φ = 1.1, 4 and 8) equivalence ratio has been investigated for a four mm axial jet. The fully premixed flames were found to be controlled by the crossflow temperature before ignition and the crossflow oxygen content during combustion. Analysis of flame shape and position for the partially premixed operating points describes a lee stabilized as well as a more unsteady windward flame branch. Adjustment of added jet fuel and crossflow temperature along with its corresponding oxygen level is required to attain a compact flame body. The risk of delaying combustion progress is significantly increased at a richer jet φ = 8 and an overshooting, spatially divided flame was attained with a main stage φ = 0.73. Control towards a compact flame body is critical to allow combustion at reasonable reaction rate.