bluuebunny/crossref_metadata_2025_split huggingface dataset:
Advanced Processing of a Blade Vibratory Response Obtained With Tip Timing Method Using Hyperparameter-Free Sparse Estimation Method
Authors: Kharyton Vsevolod , Zachariah Dave 
Published: September 2021

Abstract
The study presents the application of a sparse estimation method which enables explicit identification of spectrum components of a vibratory signal of a blade obtained by means of blade tip timing measurement. The method exploits the sparse frequency content of the blade vibratory response and uses a data-adaptive weighting to achieve sparsity. In contrast to other approaches, this method obviates the need for any parameter tuning during the identification process and admits an online formulation that renders it capable of real-time data processing.
In the study only experimentally acquired data from either prototype testing or field measurements are used to evoke the method applicability. For some considered test cases there were no strain gauges available, therefore proposed method was the only means to study blades vibratory response.
Experimental Investigation of Gas Turbine Axial Diffuser Performance: Part II — Effect of Inlet Flow Profiles at On- and Off-Design Conditions
Authors: Brown Kenneth , Guillot Stephen , Ng Wing , Iksang Lee , Dongil Kim , Hong Giwon 
Published: September 2021

Abstract
An experimental investigation of the effect of inlet flow conditions and improved geometries on the performance of modern axial exhaust diffusers of gas turbines has been completed. The first article in the two-part series [1] leveraged a scaled model to examine parametric variations in both diffuser geometry and inlet flow conditions with the latter having significant consequences for diffuser performance. This second article pivots on the conclusions of the companion article and offers findings and physical insight on diffuser performance for on- and off-design inlet flow conditions. Using a high-performing diffuser design from the companion article, an experimental investigation is carried out with tailored distributions of inlet Mach distribution, inlet swirl angle, and inlet radial flow angle which are designed to replicate conditions of an industry diffuser at various loads. Six different inlet distributions were investigated including a design condition and five other conditions which feature mass flows both greater than and less than the design condition. The measurements were taken at near full-scale turbine exit Reynolds number (ReH roughly 39% of the value for an H-class diffuser) and at full-scale turbine exit Mach number. The study was accomplished in a blow-down, cold-flow wind tunnel facility, and measurements included 5-hole probe traverses at planes of interest, axial pressure distributions, strut pressure distributions, and oil-flow visualization. Over the range of inlet conditions studied, pressure recovery at the exit varied by up to 68.5% from that of on-design operation. Tracking of performance coefficients along the axial direction suggested the existence of flow phenomena which were in some cases able to be confirmed with on-strut pressure measurements and flow visualization. In addition to physical insight, the results presented here offer an experimental benchmark for the sensitivity of diffuser performance to inlet flow conditions.
Method and Verification for Material Calibration of the Chaboche Plasticity Model for Multiple Material Directions
Authors: Krouse Charles R. , Musgrove Grant O. , Kim Taewoan , Lee Seungmin , Lee Muhyoung , Jeong Seongyong 
Published: September 2021

Abstract
The Chaboche model is a well-validated non-linear kinematic hardening material model. This material model, like many models, depends on a set of material constants that must be calibrated for it to match the experimental data. Due to the challenge of calibrating these constants, the Chaboche model is often disregarded. The challenge with calibrating the Chaboche constants is that the most reliable method for doing the calibration is a brute force approach, which tests thousands of combinations of constants. Different sampling techniques and optimization schemes can be used to select different combinations of these constants, but ultimately, they all rely on iteratively selecting values and running simulations for each selected set. In the experience of the authors, such brute force methods require roughly 2,500 combinations to be evaluated in order to have confidence that a reasonable solution is found. This process is not efficient. It is time-intensive and labor-intensive. It requires long simulation times, and it requires significant effort to develop the accompanying scripts and algorithms that are used to iterate through combinations of constants and to calculate agreement. A better, more automated method exists for calibrating the Chaboche material constants.
In this paper, the authors describe a more efficient, automated method for calibrating Chaboche constants. The method is validated by using it to calibrate Chaboche constants for an IN792 single-crystal material and a CM247 directionally-solidified material. The calibration results using the automated approach were compared to calibration results obtained using a brute force approach. It was determined that the automated method achieves agreeable results that are equivalent to, or supersede, results obtained using the conventional brute force method.
After validating the method for cases that only consider a single material orientation, the automated method was extended to multiple off-axis calibrations. The Chaboche model that is available in commercial software, such as ANSYS, will only accept a single set of Chaboche constants for a given temperature. There is no published method for calibrating Chaboche constants that considers multiple material orientations. Therefore, the approach outlined in this paper was extended to include multiple material orientations in a single calibration scheme. The authors concluded that the automated approach can be used to successfully, accurately, and efficiently calibrate multiple material directions. The approach is especially well-suited when off-axis calibration must be considered concomitantly with longitudinal calibration. Overall, the automated Chaboche calibration method yielded results that agreed well with experimental data. Thus, the method can be used with confidence to efficiently and accurately calibrate the Chaboche non-linear kinematic hardening material model.
Impact of a Centrebody on the Unsteady Flow Dynamics of A Swirl Nozzle: Intermittency of PVC Oscillations
Authors: Gupta Saarthak , Hemchandra Santosh , Shimura Masayasu , Shanbhogue Santosh , Ghoniem Ahmed 
Published: September 2021

Abstract
The precessing vortex core (PVC) is a self-excited flow oscillation state occurring in swirl nozzles. This is caused by the presence of a marginally unstable hydrodynamic helical mode that induces precession of the vortex breakdown bubble (VBB) around the flow axis. The PVC can impact emissions and thermoacoustic stability characteristics of combustors in various ways, as several prior studies have shown. In this paper, we examine the impact of centrebody diameter (Dc) on the PVC in a non-reacting flow in a single nozzle swirl combustor. Time resolved high speed stereoscopic PIV (sPIV) measurements are performed for combinations of two swirl numbers, S = 0.67 and 1.17 and Dc = 9.5 mm, 4.73 mm and 0 (i.e. no centrebody). The bulk flow velocity at the nozzle exit plane is kept constant as Ub = 8 m/s for all cases (Re ∼ 20,000). The centrebody end face lies in the nozzle exit plane. A new modal decomposition technique based on wavelet filtering and proper orthogonal decomposition (POD) provides insight into flow dynamics in terms of global modes extracted from the data. The results show that without a centrebody, a coherent PVC is present in the flow as expected. The introduction of a centrebody makes the PVC oscillations intermittent. These results suggest two routes to intermittency as follows. For S = 0.67, the vortex breakdown bubble (VBB) and centrebody wake recirculation zone (CWRZ) regions are nominally distinct. Intermittent separation and merger due to turbulence result in PVC oscillations due to the de-stabilization of the hydrodynamic VBB precession mode of the flow. In the S = 1.17 case, the time averaged VBB position causes it to engulf the centrebody. In this case, the emergence of intermittent PVC oscillations is a result of the response of the flow to broadband stochastic forcing imposed on the time averaged vorticity field due to turbulence.
In-Stall Compressor Performance and the Effects of Reynolds Number
Authors: Hutchings Jack , Hall Cesare 
Published: September 2021

Abstract
Previous research into axial compressor stall has mainly focused on stall inception and methods to extend the stable operating range. This paper considers the performance of an axial compressor beyond stall and investigates how the characteristics of stall cells depend on Reynolds number. An experimental study has been conducted using a single-stage axial compressor capable of operating across the Reynolds number range of 10,000–100,000. Detailed unsteady measurements have been used to measure the behaviour across a range of install flow coefficients. These measurements have been used to extract the stall hysteresis and to determine the size, speed, number, and spanwise extent of the stall cells. The results show that for the stalled compressor, as Reynolds number increases, the size of the minimum stable stall cell decreases. This means that a larger change in throttle area is needed to reduce the stall cell down to a size where the compressor can recover from stall. At Re = 100,000, the stall hysteresis is six times greater than at Re = 20,000. At the design Reynolds number, the number of stall cells that form transitions from one, to two, and then to four stall cells as the flow coefficient is reduced. At lower Reynolds numbers, the two stall cell state becomes unstable; instead, a single stall cell transitions directly into five cells. In all cases, as the number of stall cells increases, so do the speed of the stall cells and the total size. Further reductions in the flow coefficient cause an increase in the total size of the stall cells and a decrease in the stall cell speed.
Toward Machine Learned Highly Reduced Kinetic Models for Methane/Air Combustion
Authors: Kelly Mark , Dooley Stephen , Bourque Gilles 
Published: September 2021

Abstract
Accurate low dimension chemical kinetic models for methane are an essential component in the design of efficient gas turbine combustors. Kinetic models coupled to computational fluid dynamics (CFD) and chemical reactor networks (CRN) provide quick and efficient ways to test the effect of operating conditions, fuel composition and combustor design compared to physical experiments. However, detailed chemical kinetic models are too computationally expensive for use in computational fluid dynamics (CFD). We propose a novel data orientated three-step methodology to produce compact kinetic models that replicate a target set of detailed model properties to a high fidelity. In the first step, a reduced kinetic model is obtained by removing all non-essential species from the NUIG18_17_C3 detailed model containing 118 species using path flux analysis (PFA). This reduced model is so small that it does not retain fidelity in calculations to the detailed model. Thus, it is numerically optimised to replicate the detailed model’s prediction in two rounds; First, to selected species (OH,H,CO and CH4) profiles in perfectly stirred reactor (PSR) simulations and then re-optimised to the detailed model’s prediction of the laminar flame speed. This is implemented by a purposely developed Machine Learned Optimisation of Chemical Kinetics (MLOCK) algorithm. The MLOCK algorithm systematically perturbs all three Arrhenius parameters for selected reactions and assesses the suitability of the new parameters through an objective error function which quantifies the error in the compact model’s calculation of the optimisation target. This strategy is demonstrated through the production of a 19 species and a 15 species compact model for methane/air combustion. Both compact models are validated across a range of 0D and 1D calculations across both lean and rich conditions and shows good agreement to the parent detailed mechanism. The 15 species model is shown to outperform the current state-of-art models in both accuracy and range of conditions the model is valid over.
The Tip Leakage Vortex Breakdown and its Possible Relationship With Rotating Instability in a Subsonic Compressor Rotor
Authors: Yang Fan , Wu Yanhui 
Published: September 2021

Abstract
The unsteady flow in the compressor at small mass flow rate has an important impact on the safety and efficiency of the compressor. Rotating instability was found in the experiment at near stall condition. Through URANS simulation, the origin of unsteady flow in an isolated subsonic rotor is studied. And the relationship between unsteadiness of tip leakage flow and rotating instability is revealed. With the deepening of the throttle, the flow field in the rotor changes from steady to unsteady. The intermittent spiral type breakdown of tip leakage vortex is considered to be the origin of the unsteady flow. Quantitative analysis of the tip leakage vortex shows the breakdown cycle caused by the interaction of the tip leaked vortex with the adjacent blade. When the tangential velocity and axial velocity of the leakage vortex reach a critical value, the tip leakage vortex will break. A radial vortex called back flow vortex will appear periodically after breakdown happens, which plays an important in rotating instability. The back flow vortex at upstream causes an overflow at adjacent blade leading edge, which results the next breakdown happens at downstream. Due to such feedback, the tip leakage vortex breakdown at two location alternately. A possible cause of RI was proposed: The spiral breakdown of the tip leakage vortex at different positions resulted in a cross-passage structure, which propagates into circumferential direction.
A Mathematical Model for Windmilling of a Turbojet Engine
Authors: Abdulhamitbilal Erkan , Şal Sinan , Jafarov Elbrous M. 
Published: September 2021

Abstract
The transient windmilling characteristic of a modern turbojet engine under different flight conditions and altitudes is obtained with numerous tests conducted at an Altitude Test Facility (ATF). A simple and practical mathematical model for predicting the transient and steady-state rotational speed of a simple turbojet engine in flight has been developed. The method is derived from Froude’s momentum theory or disk actuator theory and implemented to a turbojet engine. A correction factor is introduced to match with test results of KTJ-3200 being indigenously developed by Kale R&D Inc. The present model’s predictions are compared with the test data of Microturbo TRI 60 engine and KTJ-3200 engine. The estimation of the present windmilling model fits very well with test results of two different engines within an error band of ±1.2% for various atmosphere conditions depending on flight speed, altitudes and temperature. The present model is compared with loss modeling windmilling estimation methods described in literature which requires large amount of inputs as blade angle, blade pitch and component efficiencies. The comparison with the available windmilling model at literature shows that both models capture the terminal speed estimation very well. However, the model in literature is not able to capture the transient engine speed, which is important for missile applications as the missile can be fired before the engine reaches to terminal speed. The difference between the test data and the available model during transients is up to 50%. The present model matches perfectly with test data even at transients. It is more practical and much simpler than the available windmilling model in the literature to estimate the both transient and terminal windmilling speed of the turbojet engines.
The agreement between the present model, KTJ 3200 test data, windmilling method available in the literature and test data of Microturbo TRI 60 is very good for most of the ranges investigated.
Experimental Studies on Dry Gas Seals With Time-Resolved Film Thickness Measurements
Authors: Luo Jingjing , Brillert Dieter 
Published: September 2021

Abstract
Dry gas lubricated non-contacting mechanical seals (DGS) are acknowledged as the sophisticated shaft end sealing solution which is most commonly found in turbo-compressors. Especially under demanding conditions where high speed is combined with high pressure, DGS becomes the preferred choice over other sealing alternatives. A reliable operation of DGS, due to the non-contact running between its rotating and stationary rings, is secured by the gas film in the region of a few microns in thickness. This paper presents the measurement method of obtaining the thickness of the running gap in two radial positions, namely the inner and outer diameter of the sealing gap, by integrating the proximity sensors in the stationary ring. The experimental investigations concerning film thicknesses, pressure distributions in the gas film and axial vibrations are carried out in an industry DGS up to 50 bar and 10,000 rpm, whereby a good insight into the dynamic behaviour of the sealing gap is provided. The results demonstrate the practicability of obtaining the gas film parameters in a grooved gas seal, bridging the gap between theory and practice. In combination with the experimental work presented in this paper, the numerical model for simulating the seal performance programmed in MATLAB is compared and validated. The comparisons for various operating conditions and groove profiles are discussed with the focus lying on the hydrodynamic effect in the gas film.
Periodic Unsteady Kinematics of Hub Flows in a Shrouded Multistage Compressor
Authors: Lee Jaehyoung , Lim Sungkyung , Shin Hyoun-Woo , Lee Sungryong , Song Seung Jin 
Published: September 2021

Abstract
Periodic unsteady flow kinematics in a shrouded multistage low-speed axial compressor has been measured for the first time. Data have been acquired at the inlet and exit of a shrouded 3rd-stage stator with a particular focus on the hub flows. The newly found features of the hub flow in a shrouded multistage compressor are different from those at the midspan or in unshrouded (i.e., cantilevered) compressors. First, the merging of the 2nd-stage stator and 3rd-stage rotor wakes causes positive radial migration near the rotor wake pressure surface at the hub of the 3rd-stage stator inlet. Second, the low-momentum labyrinth seal leakage flow of the 3rd-stage stator merges with the 3rd-stage rotor wake to create streamwise vorticity at the 3rd-stage stator inlet hub. Third, contrary to unshrouded stators, suction side hub corner separation in the shrouded 3rd-stage stator reduces rotor wake stretching. Thus, velocity disturbances are attenuated less, and amplitudes of periodic fluctuations in flow angles are larger at the 3rd-stage stator exit hub than at midspan. The positive radial migration of the rotor wake hub flow and wake stretching reduction are expected to decrease efficiency, whereas streamwise vorticity generation is expected to increase efficiency.
Evaluation of Performance Gain by Interstage Injection in a Four-Stage Axial Compressor
Authors: Doerr Tobias , Schuster Sebastian , Brillert Dieter 
Published: September 2021

Abstract
Recently, the energy market has seen a shift towards renewable energies due to changing demands. Gas turbines are used as a transitional technology to cope with grid fluctuations. The changing conditions have increased the interest in applying Wet Compression in order to increase the power output during peak demands.
The novelty of this paper arises from the experimental results of Interstage Injection by analysing the stage and overall pressure ratios at different operating points in the four stage axial compressor “eco.MAC” (“evaporative cooling Multiphase Axial Compressor”). An innovative injection design is realized with twin jet nozzles in the trailing edge of SLM printed stator blades. A variation of water mass fraction, inlet temperature and rotational speed is performed and shows a gain in pressure ratio up to 1.5 %. Moreover, a polynomial approach is used for the dry data to compare wet and dry results at equal air mass flow rates. For the first time, a linear dependency of the pressure gain on the compressor’s gas temperature is experimentally found.
It can be concluded that Interstage Injection is an effective technology to be applied in later stages of axial compressors due to the strong influence of local gas temperatures on the evaporation rate and thus the pressure gain. Furthermore, reducing the local injection rate decreases aerodynamic losses between the liquid and gas phase. Hence, a multiple injection and reduced local injection rates should be targeted.
Robust Design Optimization of an Industrial 1.5 Stage Axial Compressor Under Operational and Geometrical Uncertainties
Authors: Gouttière Alexandre , Wunsch Dirk , Nigro Rémy , Barbieux Virginie , Hirsch Charles 
Published: September 2021

Abstract
A robust design optimization of a 1.5 stage axial compressor with secondary flows from Safran Aero Boosters is investigated. A total of 9 simultaneous operational and geometrical uncertainties are propagated for the nominal design point as well as for two off-design points, close to stall and choke conditions respectively. These uncertainties, including mass flow rates of the secondary flows, tip gap size of the rotor and highly correlated profiles on the inlet condition, are propagated by the Non-Intrusive Probabilistic Collocation method. In order to understand the effects of the uncertainties on the performances and to minimize the computational cost of the robust optimization, a preliminary uncertainty quantification (UQ) study of the original design is performed to identify and rule out less influential uncertainties. Contrary to what was expected, the imposed geometrical uncertainties on the tip gap are identified to have the relatively smallest influence on the performances by means of scaled sensitivity derivatives. The global objective of the robust design optimization is to minimize the standard deviations of the main compressor performances at all three operating points and to preserve the mean values of these performances. Because the objective functions are standard deviations, this study is only possible in a robust optimization setting, by propagating the simultaneous operational and geometrical uncertainties. A total of 9 stochastic objectives and 15 stochastic constraints are taken into account. The best optimal design preserves the mean performances of the compressor, while the standard deviations are minimized compared with the original design, ensuring a more robust operation. This effect is very pronounced in the off-design points.