bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Analysis of Particle Deposition in an Aircraft Engine Compressor Cascade
Authors: Casari Nicola , Altmeppen Johannes , Koch Christian , Pinelli Michele , Staudacher Stephan , Suman Alessio , Vulpio Alessandro 
Published: January 2021

Abstract
Solid particles dispersed in the air represent a real hazard for gas turbines in both heavy-duty and aero-propulsion applications. Particles impacting the inner surfaces of the machine can stick to such surfaces or erode them. The geometry modifications related to such occurrences entail aerodynamic surface degradation. As the severity of the problem increases, the performance reduction can increase, demanding engine shut-down and off-line washing or refurbishing.
Numerical modeling is one of the techniques employed for understanding and predicting the particle deposition problem. Multiple numerical studies investigated the influences of these phenomena. However, the basic challenge of modeling the particle wall-interaction with sufficient accuracy remains. In this work, a cascade exposed to a particle-laden flow is numerically investigated. The numerical analysis is devoted to investigate a test rig designed to be representative of aircraft engine compressor blading and exposed to an accelerated deposition process.
Firstly, the relation between flow structures and particle trajectory is investigated. Then, a computational analysis is carried out considering different particle-wall interaction models of varying complexity levels (e.g. pure adhesion, presence of humidity or the influence of surface roughness) in order to identify advantages and disadvantages of each model and their ability to include different phenomena. The results are discussed by taking into account measurement data from a cascade test rig. The deviation between experimental data and the investigated model is evaluated, showing the increasing reliability that derives from successive model refinement. This work is proposed to be a test case for the numerical analyses of compressor fouling applications and a first step towards a general physical based particle-wall interaction model.
A State-of-the-Art CFD Setup for Axial Compressors: Details and Validation
Authors: Cozzi Lorenzo , Rubechini Filippo , Arnone Andrea , Depalo Savino , Astrua Pio , Schneider Andrea , Benvenuto Marcello 
Published: January 2021

Abstract
The overall fraction of the power produced by renewable sources in the energy market has significantly increased in recent years. The power output of most of these clean sources is intrinsically variable. At present day and most likely in the upcoming future, due to the lack of inexpensive and reliable large energy storage systems, conventional power plants burning fossil fuels will still be part of the energy horizon. In particular, power generators able to promptly support the grid stability, such as gas turbines, will retain a strategic role. This new energy scenario is pushing gas turbine producers to improve the flexibility of their turbomachines, increasing the need for reliable numerical tools adopted to design and validate the new products also in operating conditions far from the nominal one.
Especially when dealing with axial compressors, i.e. machines experiencing intense adverse pressure gradients, complex flow structures and severe secondary flows, CFD modelling of offdesign operation can be a real challenge.
In this work, a state-of-the art CFD framework for RANS analysis of axial compressors is presented. The various aspects involved in the whole setup are discussed, including boundary conditions, meshing strategies, mixing planes modelling, tip clearance treatment, shroud leakages and turbulence modelling. Some experiences about the choice of these aspects are provided, derived from a long-date practice on this kind of turbomachines. Numerical results are reported for different full-scale compressors of the Ansaldo Energia fleet, covering a wide range of operating conditions. Furthermore, details about the capability of the setup to predict compressor performance and surge-margin have been added to the work.
In particular, the setup surge-margin prediction has been evaluated in an operating condition in which the turbomachine experiences experimental stall. Finally, thanks to several on-field data available at different corrected speeds for operating conditions ranging from minimum to full load, a comprehensive validation of the presented numerical framework is also included in the paper.
Interpretation of Low-Pressure Turbine Profile Loss Generation Mechanisms From a Viewpoint of Blade Drag Forces
Authors: Kodama Hidekazu , Funazaki Ken-ichi 
Published: January 2021

Abstract
This paper describes the interpretation of a generation mechanism of profile loss of low pressure turbine (LPT) blades from a viewpoint of blade drag forces. On the analogy of profile drag of an isolated body, the profile loss of a cascade blade is subdivided into two components, the loss due to friction drag and the loss due to pressure drag. The friction drag is equal to the integral of all axial component of shearing stresses taken over the surface of the blade. The pressure drag, which does not exist in an inviscid flow, is due to the fact that the presence of the boundary later modifies the pressure distribution on the blade.
The losses due to friction drag and pressure drag are evaluated for two kinds of blade profiles using the results of steady incompressible Reynolds Averaged Navier-Stokes (RANS) simulations at three different Reynolds numbers (Re), 57,000, 100,000 and 147,000. It is found that the trend of the total profile loss with Reynolds number is mainly determined by the trend of the loss due to pressure drag with Reynolds number. A rise in the total profile loss of the blade with a laminar separation bubble on the suction surface at low Reynolds number is mainly attributed to the increase in the pressure drag due to thickened suction surface boundary layer by the enlarged separation bubble.
The friction drag and the pressure drag are also estimated for the measured data of low speed linear cascade tests with a moving-bar mechanism. In the estimation, the pressure drag is derived from the estimated total profile loss and the estimated friction drag by using boundary layer integral equations. It is found that the trend of total profile loss with incoming wake passing frequency is almost determined by the trend of the loss due to pressure drag with the wake passing frequency.
Development of New Single and High-Density Heat-Flux Gauges for Unsteady Heat Transfer Measurements for a Rotating Transonic Turbine
Authors: Celestina Richard , Sperling Spencer , Christensen Louis , Mathison Randall , Aksoy Hakan , Liu Jong 
Published: January 2021

Abstract
This paper presents the development and implementation of a new generation of double-sided heat-flux gauges at The Ohio State University Gas Turbine Laboratory (GTL) along with heat transfer measurements for film-cooled airfoils in a single-stage high-pressure transonic turbine operating at design corrected conditions. Double-sided heat flux gauges are a critical part of turbine cooling studies, and the new generation improves upon the durability and stability of previous designs while also introducing high-density layouts that provide better spatial resolution. These new customizable high-density double-sided heat flux gauges allow for multiple heat transfer measurements in a small geometric area such as immediately downstream of a row of cooling holes on an airfoil. Two high-density designs are utilized: Type A consists of 9 gauges laid out within a 5 mm by 2.6 mm (0.20 inch by 0.10 inch) area on the pressure surface of an airfoil, and Type B consists of 7 gauges located at points of predicted interest on the suction surface.
Both individual and high-density heat flux gauges are installed on the blades of a transonic turbine experiment for the second build of the High-Pressure Turbine Innovative Cooling program (HPTIC2). Run in a short duration facility, the single-stage high-pressure turbine operated at design-corrected conditions (matching corrected speed, flow function, and pressure ratio) with forward and aft purge flow and film-cooled blades. Gauges are placed at repeated locations across different cooling schemes in a rainbow rotor configuration. Airfoil film-cooling schemes include round, fan, and advanced shaped cooling holes in addition to uncooled airfoils. Both the pressure and suction surfaces of the airfoils are instrumented at multiple wetted distance locations and percent spans from roughly 10% to 90%. Results from these tests are presented as both time-average values and time-accurate ensemble averages in order to capture unsteady motion and heat transfer distribution created by strong secondary flows and cooling flows.
Numerical Sensitivity Study on the Design of a Transonic Aeroelastic Compressor Rig
Authors: Tian Simeng , Gutierrez Salas Mauricio 
Published: January 2021

Abstract
In modern transonic compressors, forced response can occur at high-order modes and at high-reduced frequencies. To understand this phenomenon, a new cascade test-rig is being built to provide configurations and validations for the forced response simulations of transonic compressors. With the aid of Computation Fluid Dynamics (CFD) optimizations, the test section shape was roughly determined before. The purpose of this paper is to provide the finalization process of the cascade test-rig design including a transonic nozzle and blade tip gaps. Hence, the steady and unsteady simulations are employed based on three different geometries: test section, test rig with nozzle, and test rig with 1% tip gap. The simulation results show that the unsteadiness in the test rig is related mainly to the oscillation performance of the shock waves in the passage. The comparison in the test rig with and without tip gap confirms that tip gap can reduce the unsteady pressure. The unsteady pressure reflection due to the tailboards, especially on the bottom tailboards, indicates this problem needs to be thoroughly considered in the installation and testing.
Aerodynamic Performance Prediction of Transonic Axial Multistage Compressors Based on One-Dimensional Meanline Method
Authors: Zhang Yingying , Zhang Shijie , Xiao Yunhan 
Published: January 2021

Abstract
The one-dimensional meanline method is of great importance for the design and performance prediction of multistage axial compressors. The models adopted in it, such as incidence, deviation and loss, considering real-fluid effects, determine whether the compressors’ operating behavior can be simulated accurately or not.
This paper describes an improved meanline stage-stacking approach for the modelling of modern transonic axial multistage compressors. The improvement embodied in this study is mainly focused on deviation and surge margin prediction, which is the result of a combination of the previous models and models’ correction. One of the coefficients in the deviation angle model is corrected. A new surge model, different from the well-known maximum static pressure rise method of Koch and Smith, is introduced into this program and its advantage lies in higher accuracy and direct calculation instead of proposing a judgment criterion. Three well-documented NASA axial transonic compressors are calculated by this meanline method, and the speedlines and aerodynamic parameters are compared with the experimental data to verify the method presented in this paper. A discussion of the result then follows.
Experimental Investigation on a 3 kW Air Tesla Expander With High Speed Generator
Authors: Renuke Avinash , Reggio Federico , Silvestri Paolo , Traverso Alberto , Pascenti Matteo 
Published: January 2021

Abstract
Tesla bladeless turbomachines are recently being investigated due to many advantages such as its simple design and ease of manufacturing. If an efficient design is achieved, this will be a promising machine in the area of small-scale power generation and energy harvesting. This paper focuses on the experimental performance investigation of 3 kW (rated power) Tesla bladeless expander. The Tesla expander and electric generator are housed in a single casing making it first of its kind being tested with such configuration. The expander is fed with air and operated at high rotational speeds up to 40000 rpm. The test is carried out with different number of nozzles to understand its effect on the performance. Results show that the peak efficiency for two nozzles is better than one nozzle and four nozzle configurations for the same inlet pressure conditions. Experimental tests revealed that this turbine is most efficient Tesla turbine till now with air as a working fluid. Furthermore, one of the most important losses in Tesla turbomachines, nozzle loss, is experimentally characterized. Specific vibrational tests were carried out to obtain complete machine dynamical characterization. The vibrational response characterization of the turbine enabled us to recognize a disk mode family solicited by the air flow and to perform a proper machine maintenance and balancing aiming to reduce the energy of its operational vibration.
Multi-Point Optimization Design of High Pressure-Ratio Centrifugal Impeller Based on Machine Learning
Authors: Cheng Hongliang , Yi Weilin , Ji Luchen 
Published: January 2021

Abstract
The traditional optimization method on turbomachinery has the problem as time-consuming and difficult to solve well multi-parameter optimization in a short time. So an accurate surrogate model that is used to estimate the functional relationship between the independent variable and objective value is important to accelerate computationally expensive CFD-based optimization. Many of them had been developed and proven their reliability, such as the Kriging model, Back Propagation Neural Network (BPNN), Artificial Neural Network (ANN) and Support Vector Regression (SVR), etc.
Because SVR is based on the principle of structural risk minimization, it has advantages in dealing with a small database, high dimensional and non-linear problems. The reliability of SVR is depended on its kernel parameter and penalty factor, and it can be improved by getting optimal parameters with some optimization algorithms.
In this paper, a machine learning model based on SVR combined with a multi-point genetic algorithm (MPGA) is applied to the optimization of a centrifugal impeller with 41 parameters. The optimization objectives are to maximize efficiency at design point and pressure-ratio at near stall point and to minimize the variation of choked mass flow. Results show that (1) time costs reduced significantly. (2) The maximum efficiency increases by 1.24%. (3) It is verified that the reliability of the SVR-MPGA model for multi parameters optimization by comparing to the results of the traditional optimization method — Design 3D.
The efforts of this study expand the application of machine learning and provide an idea for multi-point optimization of turbomachinery as well.
Effect of Axial Short Slot Casing Treatment and its Center Deviation on Stability of a Transonic Axial Flow Compressor
Authors: Zhang Sha , Chu Wuli , Yang Jibo 
Published: January 2021

Abstract
In order to increase the stability margin of axial compressor with low efficiency losses, this paper studies the influence of axial short slot casing treatment and its axial position on compressor performance. A transonic axial compressor rotor, NASA rotor37, is taken as the research object, and the solid wall case and three axial slot casing treatments with different axial positions are studied by numerical simulation. The results show that the configuration with a center deviation of 0 (CT _C) has the best effect, with a margin improvement of 7.6% and an efficiency reduction of 0.09%; the configuration with an upstream positioned axial slot (CT_L) is the second, with a margin improvement of 5.4% and an efficiency reduction of 0.28%; the configuration with a downstream positioned axial slot (CT_T) is the worst, with a margin improvement of 3.6% and an efficiency reduction of 0.3%. A shift of the slot in downstream direction is not effective because it only affects the extent of boundary layer separation and has little effect on the development of the tip leakage flow. The upstream positioned axial slot with unsatisfactory effect affects the tip leakage flow trajectory and weakens the radial vortex at the blade tip, but it cannot affect the subsequent development of the leakage vortex. The short slot casing treatment in the central position effectively inhibits the development of the vortex. At the same time, it affects the development of the boundary layer to some extent and ensures the lower efficiency reduction while obtaining better stability margin.
Towards Primary Breakup Simulation of a Complete Aircraft Nozzle at Realistic Aircraft Conditions
Authors: Warncke Katharina , Sadiki Amsini , Staufer Max , Hasse Christian , Janicka Johannes 
Published: January 2021

Abstract
Predicting details of aircraft engine combustion by means of numerical simulations requires reliable information about spray characteristics from liquid fuel injection. However, details of liquid fuel injection are not well documented. Indeed, standard droplet distributions are usually utilized in Euler-Lagrange simulations of combustion. Typically, airblast injectors are employed to atomize the liquid fuel by feeding a thin liquid film in the shear zone between two swirled air flows. Unfortunately, droplet data for the wide range of operating conditions during a flight is not available.
Focusing on numerical simulations, Direct Numerical simulations (DNS) of full nozzle designs are nowadays out of scope. Reducing numerical costs, but still considering the full nozzle flow, the embedded DNS methodology (eDNS) has been introduced within a Volume of Fluid framework (Sauer et al., Atomization and Sprays, vol. 26, pp. 187–215, 2016). Thereby, DNS domain is kept as small as possible by reducing it to the primary breakup zone. It is then embedded in a Large Eddy Simulation (LES) of the turbulent nozzle flow. This way, realistic turbulent scales of the nozzle flow are included, when simulating primary breakup. Previous studies of a generic atomizer configuration proved that turbulence in the gaseous flow has significant impact on liquid disintegration and should be included in primary breakup simulations (Warncke et al., ILASS Europe, Paris, 2019).
In this contribution, an industrial airblast atomizer is numerically investigated for the first time using the eDNS approach. The complete nozzle geometry is simulated, considering all relevant features of the flow. Three steps are necessary: 1. LES of the gaseous nozzle flow until a statistically stationary flow is reached. 2. Position and refinement of the DNS domain. Due to the annular nozzle design the DNS domain is chosen as a ring. It comprises the atomizing edge, where the liquid is brought between inner and outer air flow, and the downstream primary breakup zone. 3. Start of liquid fuel injection and primary breakup simulation. Since the simulation of the two-phase DNS and the LES of the surrounding nozzle flow are conducted at the same time, turbulent scales of the gas flow are directly transferred to the DNS domain.
The applicability of eDNS to full nozzle designs is demonstrated and details of primary breakup at the nozzle outlet are presented. In particular a discussion of the phenomenological breakup process and spray characteristics is provided.
Influence of Geometrical Parameters and Reynolds Number on Flat Plate Film Cooling Effectiveness
Authors: Rouina S. , Abdeh H. , Perdichizzi A. , Barigozzi G. , Odemondo V. , Abba L. , Iannone M. 
Published: January 2021

Abstract
In the present paper the influence of geometrical deviations, related to the manufacturing process or to a different hole positioning over the vane surface, and of coolant Reynolds number on flat plate film cooling through shaped holes are experimentally investigated. Hole geometrical parameters, such as the length of the cylindrical section, hole injection angle, lateral and forward expansion angles were varied and tested for blowing ratio M values between 1.0 and 2.0, also changing the coolant Reynolds number. The dual-luminophore Pressure Sensitive Paint (PSP) technique was used for measuring the adiabatic film cooling effectiveness distribution. Compared with the standard geometry, the V-shaped hole was shown to produce a better thermal protection, especially in the near hole region. Effectiveness is strongly affected by relatively small changes in the hole geometry, like the length of the cylindrical section and the forward expansion angle. A critical coolant Reynolds number was also identified, whose value changes depending on the hole geometry.
Dynamic Identification of 280mm Diameter Tilting Pad Journal Bearings: Test Results and Measurement Uncertainties Assessment of Different Designs
Authors: Ferraro Riccardo , Innocenti Alice , Libraschi Mirko , Barsanti Michele , Ciulli Enrico , Forte Paola , Nuti Matteo 
Published: January 2021

Abstract
Tilting pad journal bearings (TPJBs) are crucial elements in turbomachinery applications providing stiffness and damping characteristics that determine rotor system dynamic behavior. Hence, a correct design and an accurate dynamic properties prediction is fundamental for the successful industrial operation of rotating machinery. Current design trends in turbomachinery aiming at higher efficiency and power through weight optimization and higher operating speeds determine the development of large flexible rotors that are particularly important from the rotordynamic standpoint. The dynamic feasibility of this type of machine relies on bearing stiffness and damping characteristics that must be predicted with a certain level of confidence in order to increase the accuracy of the expected rotordynamic behaviour and avoid unpredicted vibration issues when rotors are operated. Furthermore, large centrifugal compressors commonly used in Liquified Natural Gas (LNG) applications make the bearings operate at very high peripheral speed where the transition from laminar to turbulent regime occurs, increasing the necessity of predictions accuracy.
In this paper a test campaign on different large TPJB solutions operating in turbulent lubrication regime has been performed on a dedicated test rig designed for investigations on large size high-performance oil bearings.
In the present work both static performance and dynamic identification of the tested TPJB solutions are presented and compared to numerical model predictions. The results of an uncertainty quantification, performed to validate the experimental results, are also shown.