bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Freestream Turbulence Intensity, Turbulence Length Scale, and Exit Reynolds Number on Vane Endwall Secondary Flow and Heat Transfer in a Transonic Turbine Cascade
Authors: Li Zhigang , Bai Bo , Liu Luxuan , Li Jun , Mao Shuo , Ng Wing , Xu Hongzhou , Fox Michael 
Published: January 2021

Abstract
In gas turbine engines, the first-stage vanes usually suffer harsh incoming flow conditions from the combustor with high pressure, high temperature and high turbulence. The combustor-generated high freestream turbulence and strong secondary flows in a gas turbine vane passage have been reported to augment the endwall thermal load significantly.
This paper presents a detailed numerical study on the effects of high freestream turbulence intensity, turbulence length scale, and exit Reynolds number on the endwall secondary flow pattern and heat transfer distribution of a transonic linear turbine vane passage at realistic engine Mach numbers, with a flat endwall no cooling. Numerical simulations were conducted at a range of different operation conditions: six freestream turbulence intensities (Tu = 1%, 5%, 10%, 13%, 16% and 20%), six turbulence length scales (normalized by the vane pitch of Λ/P = 0.01, 0.04, 0.07, 0.12, 0.24, 0.36), and three exit isentropic Mach number (Maex = 0.6, 0.85 and 1.02 corresponding exit Reynolds number Reex = 1.1 × 106, 1.7 × 106 and 2.2 × 106, respectively, based on the vane chord). Detailed comparisons were presented for endwall heat transfer coefficient distribution, endwall secondary flow field at different operation conditions, while paying special attention to the link between endwall thermal load patterns and the secondary flow structures.
Results show that the freestream turbulence intensity and length scale have a significant influence on the endwall secondary flow field, but the influence of the exit Reynolds number is very weak. The Nusselt number patterns for the higher turbulence intensities (Tu = 16%, 20%) appear to be less affected by the endwall secondary flows than the lower turbulence cases. The thermal load distribution in the arc region around the vane leading edge and the banded region along the vane pressure side are influenced most strongly by the freestream turbulence intensity. In general, the higher freestream turbulence intensities make the vane endwall thermal load more uniform. The Nusselt number distribution is only weakly affected by the turbulence length scale when Λ/P is larger than 0.04. The heat transfer level appears to have a significant uniform augmentation over the whole endwall region with the increasing Maex. The endwall thermal load distribution is classified into four typical regions, and the effects of freestream turbulence, exit Reynolds number in each region were discussed in detail.
Numerical Study on Film Effectiveness and Heat Transfer Characteristics of Aero-Engine Nose Cone With Hot Air Film
Authors: Yang Tao , Zhang Li , Zhu Hui-Ren , Wang Xing-Ming 
Published: January 2021

Abstract
When the aircraft works in an environment containing supercooled water droplets, it is easy to cause the engine inlet nose cone on the windward side to freeze, which not only affects the performance of the engine, but also leads to flight accidents. Therefore, it is necessary to research the anti-icing technology of aero-engine nose cone components. At present, the air intake cone of the aircraft mainly forms a thermal anti-icing system by means of hot film anti-icing and heating impingement anti-icing.
In this paper, the effects of blowing ratio, film hole pitch, hole shape and film hole arrangement method on film heating effectiveness and heat transfer characteristics are studied by numerical simulation methods for the hot film anti-icing system of the nose cone. The results show that with the increase of the blowing ratio, the film heating effectiveness in the downstream area quickly decreases first and then increases, and the range of change aggrandizes. Under the given condition, as the pitch between the film holes decreases, the area covered by the film extends, and the heating effectiveness improves significantly. In the case of high blowing ratio, the advantage of film heating effectiveness of waist-shaped film hole is more apparent. The laterally-averaged film heating effectiveness of the staggered film holes is much higher than that of the aligned film holes. For the characteristics of film heat transfer, the hole pitch and hole shape has little effect on the heat transfer characteristics at low blowing ratio. In the case of high blowing ratio, the heat transfer effect will be greatly weakened when the hole pitch is increased, moreover the heat transfer efficiency of the waist-shaped hole is better. In the region near the exit of the secondary row film hole, the heat transfer characteristics of the staggered structure is stronger than that in the aligned structure. In addition, it is found that the high heat transfer region for staggered arrangement shows W–shaped.
Reynolds Number and Roughness Effects on Turbocompressor Performance: Numerical Calculations and Measurement Data Evaluation
Authors: Dietmann Fabian , Casey Michael , Vogt Damian M. 
Published: January 2021

Abstract
Further validation of an analytic method to calculate the influence of changes in Reynolds number, machine size and roughness on the performance of axial and radial turbocompressors is presented. The correlation uses a dissipation coefficient as a basis for scaling the losses with changes in relative roughness and Reynolds number. The original correlation from Dietmann and Casey [6] is based on experimental data and theoretical models. Evaluations of five numerically calculated compressor stages at different flow coefficients are presented to support the trends of the correlation. It is shown that the sensitivity of the compressor performance to Reynolds and roughness effects is highest for low flow coefficient radial stages and steadily decreases as the design flow coefficient of the stage and the hydraulic diameter of the flow channels increases.
Introduction of a Novel Parameter Model to Analyze the Geometric Variation of Airfoil Edges of Ex-In-Service Compressor Airfoils
Authors: Voigt Paul , Voigt Matthias , Mailach Ronald , Abu-Taa Kimon , Rostamian Mirco 
Published: January 2021

Abstract
The leading and trailing edge shapes of high pressure compressor (HPC) airfoils have a high impact on their aerodynamic performance. Typically, the shape of these airfoil edges are designed symmetrically as half circles or half ellipses. Due to manufacturing scatter and operational effects, the edges of real HPC airfoils deviate from the design intent. Especially the change in shape of the airfoil edges due to erosion can lead to a reduction of the aerodynamic efficiency and operability range.
This paper introduces a novel and intuitive parametrization approach to describe the occurring airfoil edge shapes. The introduced parametric model has been applied to a set of postservice airfoils with a variety of airfoil edge shapes. For this purpose, just above 1000 of used HPC airfoils from different engines with different operational conditions and runtimes were digitized by means of a structured light 3D scanner. The high precision of the scanning system enables accurate capturing of the sensitive airfoil edge shapes.
Subsequently, the extracted parameters were used for a statistical evaluation of the leading edge (LE) shape geometry. It turned out that the LEs of the investigated post-service compressor airfoils exhibit a thinner LE shape characteristics compared to the design intent LE shape. Furthermore, in nearly all cases, more material is missing on the suction sided LE of the investigated airfoils. This result is rather contrary compared to the findings of relevant literature, where the LE pressure side is missing more material due to erosion.
Nevertheless, the generated results suggest that the developed method is suitable for a sufficient qualitative and quantitative description of HPC LE shapes. In future work, the introduced parametric model can be used as the basis of a prospective evaluation of the correlation between the geometric variation of airfoil edges and manufacturing scatter as well as engine operational condition.
Unsteady Steam Turbine Optimization Using High Fidelity CFD
Authors: Iranidokht Vahid , Papagiannis Ilias , Kalfas Anestis , Abhari Reza , Senoo Shigeki , Momma Kazuhiro 
Published: January 2021

Abstract
This paper presents the computational methodology, and experimental investigations accomplished to enhance the efficiency of a turbine stage by applying non-axisymmetric profiling on the rotor hub wall. The experimental setup was a two-stage axial turbine, which was tested at “LISA” test facility at ETH Zurich. The 1st stage was considered to create the flow history for the 2nd stage, which was the target of the optimization. The hub cavity of the 2nd stage was designed with large dimensions as a requirement of a steam turbine. The goal was to optimize the interaction of the cavity leakage flow with the rotor passage flow to reduce the losses and increase efficiency.
The computational optimization was completed using a Genetic Algorithm coupled with an Artificial Neural Network on the 2nd stage of the test turbine. Unsteady time-accurate simulations were performed, using in-house developed “MULTI3” solver. Besides implementing all geometrical details (such as hub and tip cavities and fully 3D blade geometries) from the experimental setup into the computational model, it was learned that the unsteady upstream effect could not be neglected. A novel approach was introduced by using unsteady inlet boundary conditions to consider the multistage effect while reducing the computational cost to half. The importance of this implementation was tested by performing a steady simulation on the optimized geometry. The predicted efficiency gain from steady simulations was 4.5 times smaller (and negligible) compared to the unsteady approach. Excluding the cavity geometry was also assessed in a different simulation setup showing 3.9% over-prediction in the absolute efficiency value.
Comprehensive steady and unsteady measurements were performed utilizing pneumatic, Fast Response Aerodynamic (FRAP), and Fast Response Entropy (FENT) probes, on the baseline and profiled test cases. The end-wall profiling was found to be successful in weakening the strength of the hub passage vortex by a 19% reduction in the under-over turning. As a result, the blockage was reduced near the hub region leading to more uniform mass flow distribution along the span. The flow angle deviations at the higher span position were also corrected due to better control of the flow angles. Furthermore, the improvements were confirmed by reductions in entropy, Secondary Kinetic Energy, and pressure unsteadiness. The accurate computational implementations led to an excellent agreement between the predicted and measured efficiency gain.
A Comparison of VOF and Euler-Euler Approaches in CFD Modelling of Two-Phase Flows With a Sharp Interface
Authors: Bertolotti Luc , Jefferson-Loveday Richard , Ambrose Stephen , Korsukova Evgenia 
Published: January 2021

Abstract
In aero-engines, it is important to predict the behavior of shear flows in the different parts such as bearing chambers or gearboxes. In bearing chambers, the thickness distribution of wavy films is well studied as two-phase flows are still very hard to predict depending on the case. Experimental studies remain very expensive to carry out and Computational Fluid Dynamics (CFD) still struggles with two-phase flow prediction especially when a sharp interface between the two phases must be modelled. CFD is used to predict the oil film thickness distribution and interface velocity at different engine operating conditions. Currently Reynold-Averaged Navier-Stokes (RANS) CFD uses a semi-empirical method of turbulence damping, which is inaccurate for wavy films and so impacts the modelling of bearing chambers and gearboxes. With the objective of improving RANS models from Large Eddy Simulation (LES) methods, the Volume of Fluid (VOF) and Euler-Euler methods for two-phase flow modelling are investigated in this study. The Volume of Fluid (VOF) approach assumes a single set of momentum equations for the two phases and volume fractions are 1 or 0 everywhere except in the interface region. An alternative to VOF, is the Euler-Euler method with interface sharpening for shear flows. This approach assumes one set of momentum equations per phase but a shared field of pressure. The VOF and Euler-Euler approaches are compared in this study using LES with the CFD code OpenFOAM v6. The case study is based on experimental work investigating stratified flow in a horizontal channel that will be further detailed in the paper. In this study, a simplified 3D periodic channel filled with two distinct phases: air and water is used. A flow regime is studied in which flows are fully developed and the water phase has a much smaller velocity than the air phase in order to obtain a shear flow. Numerical results are compared with experimental measurements from the literature. With OpenFOAM, the VOF solver used for the study is interFoam and the Euler-Euler solver used is reacting-MultiphaseEulerFoam. Velocity profiles, shear-stress profiles and kinetic energy profiles are compared with experimental measurements for the assessment of the two flow solvers. Maps of vorticity magnitude are also provided to support the comparisons between the Euler-Euler and the VOF approaches as well as an appropriate vortex identification method.
Transonic Axial Compressors Loss Correlations: Part I — Analysis and Update of Loss Models
Authors: Manfredi Marco , Fontaneto Fabrizio 
Published: January 2021

Abstract
The quest for greener, more efficient aircraft engines is the main driver for the development of innovative compression system designs. Reduced order design tools rely nevertheless on semi-empirical loss models, whose validity range is often not net or in general not verified. The present work aims at defining a set of loss correlations, which could readily be employed in the analysis and design process of modern transonic axial compressors. In part I, the main entropy generation mechanisms are described together with a review of the most commonly employed modelling approaches. Selected loss models are then deeper investigated and updated to increase both their range of validity and the accuracy of their predictions. In Part II, the effectiveness of the investigated models will be tested for one specific low aspect ratio axial compressor stage.
A Multi-Timescale Approach for the Prediction of Temperatures in a Gas Turbine Combustor Liner
Authors: Karalus Megan , Brandt Dustin , Brown Alistair , Lister Vincent 
Published: January 2021

Abstract
The desire for increased engine efficiencies is driving higher firing temperatures. But this increases the risk for hot spots in solid components which can lead to durability issues. These may not be discovered until late in the design process through expensive and time consuming thermal paint tests. Historically, conjugate heat transfer simulations to predict solid temperatures have been done with steady RANS. However, Large Eddy Simulation (LES) is now being used in the early design process for gas turbine engines to account for the multiphysics of reacting flows. Incorporating the solid into these simulations poses a new challenge: the physical response time of the solid components can be orders of magnitude larger than the reacting gas phase. Running a fully coupled unsteady conjugate heat transfer analysis is therefore not tractable, but the high fidelity of the LES reacting solution is still desired.
The objective of this paper is to demonstrate a multi-timescale simulation approach for conjugate heat transfer (CHT) in Simcenter STAR-CCM+ 2019.3. The combustor is solved using LES, including all relevant physics, while steady state conduction is determined in the metal liner and thermal barrier coating. Time averaged boundary conditions are transferred from the combustor to the solids, and temperature is returned through multiple exchanges until the solid temperatures reach a stable solution. A simplified case is used to verify the approach, and then results from a test combustor are compared against data. The investigation compares results obtained with PISO and SIMPLE numerical schemes.
Nonlinear Vibration by Asynchronous Excitation Force in Friction Damper of Turbine Blade
Authors: Umehara Ryuichi , Shiraishi Haruko , Onozato Naoki , Shimmyo Tetsuya 
Published: January 2021

Abstract
Turbine blades are now being used under increasingly severe conditions in order to increase the thermal efficiency of gas turbines. Friction dampers are often used to reduce the vibration of the blade and improve the plant reliability. This is a general study dealing with resonance passing where the natural frequency of the turbine blade coincides with the frequency of specific harmonic excitation forces while increasing the turbine rotation speed. Asynchronous components of excitation forces are also considered in addition to the synchronous components caused by specific harmonic excitation forces. In this study, a new method for predicting the characteristics of nonlinear vibration under excitation force including both synchronous and asynchronous force components is developed. In order to investigate the effect of additional asynchronous loading, time history response analyses considering nonlinear vibration using simulated turbine blades were conducted. Results showed that friction damper slip can be induced by the presence of the additional asynchronous excitation force components even for low values of synchronous excitation force. It is shown that it is possible to use a calibration factor to predict vibration characteristics considering friction slipping by estimating the ratio of the total excitation force to the single harmonic excitation force. To verify the effect of asynchronous excitation force and the validity of the proposed correction method, verification tests were conducted experimentally. The experimental results show that friction slipping occurred under small harmonic excitation force when there was asynchronous excitation force and show good agreement with the numerical results. Moreover, the validity of the proposed method which corrects the dynamic characteristics obtained using of the first order harmonic balance method is confirmed.
Aeroelastic Stability of Axial Compressor Blades Under Different Operating Conditions
Authors: Fang Mingchang , Wang Yanrong 
Published: January 2021

Abstract
Flutter is one of the important issues in turbomachinery analysis. There are four common types of flutter, including sub/transonic stall flutter, choke flutter, supersonic stall flutter, and supersonic non-stall flutter. Flutter may occur under many different operating conditions. Therefore, it is important to study the aeroelastic stability of blades when the compressor operates under different conditions.
Based on the energy method proposed by Carta [1], this paper studied the aeroelastic stability of the second-stage rotor blade of an axial compressor under different operating conditions. It is found that the aerodynamic damping of the blade under the near-stall operating point of the compressor is negative. Three typical operating points are selected to study the differences in flutter mechanism between different operating conditions.
The 90% span section is selected as the reference section to analyze the variation of the aerodynamic work at different operating points. The influence of reduced frequency, modal component, and tip clearance on aerodynamic damping are analyzed under three operating points.
Performance of a Turbine Rim Seal Subject to Rotationally-Driven and Pressure-Driven Ingestion
Authors: Bru Revert Anna , Beard Paul F. , Chew John W. , Bottenheim Sebastiaan 
Published: January 2021

Abstract
This experimental study considered the performance of a chute rim seal downstream of turbine inlet guide vanes (but without rotor blades). The experimental set up reproduced rotationally-driven ingestion without vanes and conditions of pressure-driven ingestion with vanes. The maximum rotor speed was 9000 rpm corresponding to a rotational Reynolds number of 3.3 × 106 with a flow coefficient of 0.45. Measurements of mean pressures in the annulus and the disc rim cavity as well as values of sealing effectiveness deduced from gas concentration data are presented. At high values of flow coefficient (low rotational speeds), the circumferential pressure variation generated by the vanes drove relatively high levels of ingestion into the disc rim cavity. For a given purge flow rate, increasing the disc rotational speed led to a reduction in ingestion, shown by higher values of sealing effectiveness, despite the presence of upstream vanes. At Uax/(Ωb) = 0.45, the sealing effectiveness approached that associated with purely rotationally-driven ingestion. A map of sealing effectiveness against non-dimensional purge flow summarises the results and illustrates the combined rotational and pressure-driven effects on the ingestion mechanism. The results imply that flow coefficient is an important parameter in rim sealing and that rotational effects are important in many applications, especially turbines with low flow coefficient.
Full Annulus Analysis of Inlet Distortion Effects on the Performance of a Compressor
Authors: Cao Dongming , Wang Dingxi , Huang Xiuquan 
Published: January 2021

Abstract
The paper presents a numerical investigation of inlet distortion effects on the performance of a whole compressor. The compressor system consists of three and a half stages: a fan stage, an axial stage, a mixed-flow stage and an outlet guide vane. There are two bypasses after the fan stator. The following two and a half stages are in the core flow. The inlet distortion is generated by blocking part of the upstream inlet duct using a plate. The inlet distortion breaks up the original axisymmetric flow feature, thus a whole annulus computational domain has to be employed throughout the numerical unsteady analyses. The commercial GPU-based software of Turbostream is used to conduct all the analyses on several GPU workstations. The purpose of the numerical analysis is to understand how the inlet distortion propagates within this compressor and how the performance of each stage and the whole compressor is affected by the inlet distortion qualitatively and quantitatively. To achieve this goal, two separate numerical analyses have been performed for the compressor with and without inlet distortion at an interested operation point. For these two simulations, we do DFT analysis for the total pressure distribution at three spans of several different axial positions, such as the inlet and outlet of each stage, to get the spatial harmonic characteristic of each stage. The finding provides the insight needed to redesign the relevant stage to increase the surge margin.