bluuebunny/crossref_metadata_2025_split huggingface dataset:
Design of a Tip Appendage for the Control of Tip Leakage Vortices in Axial Flow Fans
Authors: Meyer Thomas O. , van der Spuy Sybrand J. , Meyer Christiaan J. , Corsini Alessandro 
Published: January 2021

Abstract
This paper reports on numerical investigations of passive control techniques used for the performance enhancement of a large diameter axial flow cooling fan through modification of the blade tip geometry. Using open-source software, a novel meshing strategy is developed to carry out both steady and unsteady numerical computations of a periodic section of an axial flow fan. Analysing the flow near the blade tip with a reduction in tip clearance, two predominant flow phenomena are identified. These two flow phenomena are further investigated with the aim of controlling them through implementation of a tip appendage design. Both introduced end-plate designs indicate effective control of each relevant flow phenomena. The constant thickness (CT) end-plate design is found to increase all fan performance characteristics at lower than design point (DP) flow rates while increasing the fan’s peak efficiency plateau towards the rotor stall margin. However, none of the CT end-plate designs are able to improve the fan’s performance characteristics at its DP. The introduction of a novel trailing edge (TE) end-plate design is found to increase all fan performance characteristics across the entire evaluated stable operating range, with an indicated increase of 37.3 percent in total-to-static pressure rise and a 2.9 percentage point increase in total-to-static efficiency at the fan’s DP flow rate. The aerodynamic performance results attest to the associated benefits of the investigated passive control techniques.
The Effects of Incidence and Deviation on the CFD-Based Throughflow Analysis
Authors: Li Jian , Wu Dongrun , Teng Jinfang , Zhu Mingmin , Qiang Xiaoqing 
Published: January 2021

Abstract
A major concern in the Computational Fluid Dynamics (CFD)-based throughflow calculation is the treatment of the incidence and deviation. This paper investigates the effects of the incidence and deviation on the CFD-based throughflow analysis by a time-marching throughflow model. The model is realized by solving complete Navier-Stokes equations with a single grid in the g-wise direction. The inviscid blade force is determined by calculating a pressure difference between the pressure and suction surfaces. The losses are introduced by imposing a blade surface skin friction factor converted from the pressure loss coefficient. And the flow discontinuity problem at the leading and trailing edges is resolved by modifying the mean blade surface to accommodate the incidence and deviation. The sensitivity of the throughflow results to the modification strategy of the mean blade surface is studied through response surface method. And the Kriging-assisted genetic algorithm (GA) is applied to determine the optimal distributions of incidence and deviation in the streamwise direction for NASA Rotor 37. Finally, four examples are provided to validate the throughflow model and to demonstrate the effects of incidence and deviation on CFD-based throughflow analysis at off-design conditions.
Accuracy Assessment of the Sellers Model in Predicting the Multi-Row Film Cooling Performance
Authors: Chen Ziyu , Li Yifei , Su Xinrong , Yuan Xin 
Published: January 2021

Abstract
Multi-row film cooling is widely applied in modern gas turbine cooling designs. However, there are few effective methods to predict local cooling effectiveness and the Sellers model based on the existing 1-D correlation is popular in the community but its prediction accuracy is questionable in some cases. The primary work of the current study is to analyze the prediction error of the Sellers model and to reveal the underlying flow mechanism. Considering the lateral uniformity assumption of the 1-D Sellers model, the effect of pitchwise row-to-row misalignment can hardly be included and the 2-D Sellers model is, therefore, proposed. Numerical simulations under density ratio near 1.0 are conducted on the double-row film cooling. Configurations of inline and staggered arrangements and blowing ratios from 0.5 to 2.0 are included. Cooling effectiveness can be theoretically decomposed into two parts contributed by separate rows, and this method has been validated. The footprint of coolant can, therefore, be tracked. Based on vortical interaction analysis, conclusions are obtained that pitchwise row-to-row spacing determines the overestimation or underestimation of the model-predicted result and the blowing ratio affects the absolute value of the prediction error. By comparing prediction accuracy of the two rows, the conclusion can be drawn that the prediction error is, to a greater extent, contributed by the row #2 because it is more likely to be affected by the row-to-row interaction.
Hybrid Method Based on FV Concept for Lean Blowout Limits Predictions for Aero Engine Combustors With Low Inlet Temperature
Authors: Lei Sun , Yong Huang , Xiang Feng 
Published: January 2021

Abstract
Lean blowout (LBO) limit is one of the most important parameters for aero engines. The LBO must be avoided during the whole flight envelope and modes. Thus the LBO limit should be predicted accurately during the research and development (R&D) process of an aero engine combustor. Some prediction models had been proposed by the previous studies. Lefebvre’s LBO model is widely used among these models due to its good accuracy and generality. Based on Lefebvre’s LBO model, the flame volume (FV) model is proposed to improve the prediction accuracy as well as keep the good generality. However, an additional equation is needed when the FV model is applied to predict the LBO limit. Based on our previous studies, the volume in the combustor liner enclosed by the iso-surface whose temperature is 900K could be chosen as the flame volume. The flame volume could be served as the additional equation and further makes the FV model available for the LBO limit prediction. This method could be named as the hybrid method based on the FV concept in this paper. On the other hand, the LBO limit at high altitude is attracting more and more attentions due to the extension of the flight envelope and modes in the recent years. Low inlet temperature is one of the most typical characteristics for the operating condition at high altitude. The temperature could reach less than −40 °C at high altitude. Compared with the normal condition, the characteristics of flow, atomization and combustion are different at the low temperature condition. In this paper, the hybrid method based on the FV concept is applied to predict the LBO limits of 11 combustors with low inlet temperature. The inlet temperature is 236.2K (corresponding to the altitude of 8km). The results show that the flame volumes obtained by the numerical simulation vary near linearly with the fuel/air ratio when the fuel/air ratio is close to the LBO limits. For all these 11 combustor configurations, the LBO limits with low inlet temperature (236.2K) obtained from the hybrid method based on the FV concept are significantly larger than those with normal inlet temperature (300K) obtained from experiments. The maximum and minimum increases are 29% and 2%, respectively. The LBO limits increases are more than 20% and 10% for 6 out of the 11 combustors and 9 out of the 11 combustors, respectively. The reasons for the increase of the LBO limits at low temperature include the decreasing of chemical reaction rate and evaporation rate, the increasing of the mean drop size.
Considerations on Axial Compressor Bleed for Sub-Idle Performance Models
Authors: Roig Tió Ferran , Ferrer-Vidal Luis E. , Azamar Aguirre Hasani , Pachidis Vassilios 
Published: January 2021

Abstract
The trend towards increased bypass ratio and reduced core size in civil aero-engines puts a strain on ground-start and relight capability, prompting renewed interest in sub-idle performance modelling. While a number of studies have looked at some of the broad performance modelling issues prevalent in this regime, the effects that bleed can have on sub-idle performance have not been addressed in the literature. During start-up and relight, the unknown variation in bleed flows through open handling bleed valves can have a considerable impact on the compressor’s operating line. This paper combines experimental, numerical and analytical approaches to look at the effect that sub-idle bleed flows have on predicted start-up operating lines, along with their effect on compressor characteristics. Experimental whole-engine data along with a purpose-built core-flow analysis tool are used to assess the effect of bleed model uncertainty on engine performance models. An experimental rig is used to assess the effects of reverse bleed on compressor characteristics and measurements are compared against numerical results. Several strategies for the generation of sub-idle maps including bleed effects are investigated.
Optimization Design of Turbine Blade Cooling Structure Based on Conjugate Heat Transfer
Authors: Wang Mingrui , Zhu Huiren , Xu Yang 
Published: January 2021

Abstract
Conjugate heat transfer (CHT) has been widely used in the analysis on flow field and heat transfer of turbine blades. In this paper, a baseline design of turbine rotor blade is selected. By improving the arrangement of film holes, turning cylindrical holes into laid back fan-shaped holes in the pressure surface (PS) and suction surface (SS), and reducing the radially inclined angle of film holes on the leading edge (LE), an optimized design (OPT) is created. Grid independence validation is conducted by comparing the pressure and temperature distributions adopting three different numbers of grids. In order to select a suitable turbulence model, experiment is performed and its values are compared with the calculation results of three different turbulence models. The distributions of static pressure, static temperature, overall cooling effectiveness and streamlines of cooling flow are compared between the OPT and baseline design by the numerical calculation results of CHT. Furthermore, the adiabatic film cooling effectiveness is calculated and the cooling performances between cylindrical holes and laid-back fan-shaped holes are compared. At last, the flow and heat transfer mechanisms are analyzed and the forming causes of low or high temperature regions on the blade are explained.
Calculation results show that compared with the baseline design, the area average temperature drops by 2.6% on the PS and by 3.7% on the SS. The area average overall cooling effectiveness increases by 9.3% on the PS and by 14.1% on the SS. The cooling performances are promoted greatly on the PS and SS but change little on the LE and TE. Obviously, the improvements are successful.
Experimental Investigation of Film Cooling Performance on Blade Endwall With Diffusion Slot Holes and Stator-Rotor Purge Flow
Authors: Yu Zhiqiang , Liu Jianjun , Li Chen , An Baitao , Xu Guangyao 
Published: January 2021

Abstract
This paper focuses on the influences of the discrete hole shape and layout on the blade endwall film cooling effectiveness. The effect of upstream purge slot injection on the film cooling performance of the discrete hole was also investigated. The diffusion slot hole was first applied to the blade endwall. As a comparison, the cooling performance of the fan-shaped hole was also measured. Totally, six discrete-hole cooling configurations (2 hole shapes × 3 layouts) were investigated. Experiments were performed in a seven-blade linear cascade with the exit Reynolds number of 2.64 × 105. The average blowing ratios (BR) of the discrete holes changed from 0.5 to 2.5, and the coolant mass flow ratio of the purge slot (MFR) was fixed at MFR = 1.5%. The distributions of the cooling effectiveness on the blade endwall were measured by the pressure sensitive paint technique. Results indicate that the diffusion slot hole significantly increases the film cooling effectiveness on the blade endwall compared to the fan-shaped hole, especially at high blowing ratio. The maximum relative increment of the cooling effectiveness is over 40%. The layout with the discrete holes arranged lining up with the tangent direction of the blade profile offset curves exhibits a comparable film cooling effectiveness with the layout with the discrete holes arranged according to the cross-flow direction. The film cooling effectiveness on the pressure surface corner is remarkably enhanced by deflecting the hole orientation angle towards the pressure surface. The combination of purge slot and diffusion slot holes supplies a full coverage film cooling for the entire blade endwall at MFR = 1.5% and BR = 2.5. In addition, the slot injection leads to a non-negligible influence on the cooling performance of the discrete holes near the separation line.
Durable Abrasive Tip Design for Single Crystal Turbine Blades
Authors: Nagy Douglas , Tollett Robert 
Published: January 2021

Abstract
In order to create and maintain peak efficiency in turbine stages, it is useful to minimize hot air leakage over blade tips. For unshrouded blades, this means creating minimal clearance over the airfoil tip with rub-tolerate zero-gap materials systems. In this study, a refractory abrasive tip material was developed and applied to a plain turbine blade tip to work in conjunction with an abradable coating on the tip-shoe. Process development efforts resulted in abrasive material that could be as much as 2mm thick. Further, the abrasive media included imbedded grits that would remain in back-up until such time as they were exposed and were pressed into service. Application methods of both furnace brazing and induction brazing were explored as were pre and post consolidation net shaping. Evaluation testing included compatibility for the application process onto single-crystal blades. Performance testing included rub-rig testing and long-term oxidation testing. Service testing included commercial engine operation for 14,000 hours followed by metallurgical re-evaluation. Service performance was mechanically successful, although some material transfer from the tip-shoe was observed which decreased the abrasive nature of the tip. Metallurgically, some intergranular oxidation was observed, but the grits themselves were well retained and were sufficiently refractory to avoid microstructural or oxidation degradation. A production implementation of the coating by an induction heating process is shown.
Impact of the Stabilized Finite Element Method on Acoustic and Vortical Perturbations in Thermoacoustic Systems
Authors: Hofmeister Thomas , Hummel Tobias , Sattelmayer Thomas 
Published: January 2021

Abstract
This paper seeks to advance linear stability analyses of thermoacoustic systems conducted with the stabilized Finite Element Method (sFEM). Specifically, this work analyzes and quantifies the impact of the Streamline-Upwind-Petrov-Galerkin (SUPG) artificial diffusion scheme on (eigen)mode shapes and damping rates of the isentropic Linearized Euler Equations (LEE) in frequency space. The LEE (eigen)mode shapes are separated into acoustic and vortical perturbation components via a Helmholtz decomposition and their sensitivity on the employed stabilization scheme is investigated separately. The regions where numerical stabilization mainly acts on the perturbation types are identified and explanations for the observations are provided. A methodology is established, which allows the quantification of the impact of artificial diffusion on the acoustic field in terms of a damping rate. This non-physical damping rate is used to determine the physically meaningful, acoustic LEE damping rate, which is corrected by the contribution of artificial diffusion. Hence, the presented method eliminates a main shortcoming of LEE eigen-frequency analyses with the sFEM and, as a result, provides more accurate information on the stability of thermoacoustic systems.
Experimental Two-Phase Flow Analysis Inside a Laboratory Scale Jet-Engine Combustion Chamber Using PIV
Authors: von Langenthal Thomas , Zarzalis Nikolaos , Loukou Alexandra 
Published: January 2021

Abstract
The characterization of the two-phase kerosene/air flow near the nozzle of an aero engine combustor is important in order to understand the combustion characteristics of the burner. Typically, Particle Image Velocimetry (PIV) or Laser Doppler Velocimetry (LDV) is used to measure velocities inside aero engine combustors. However, these measurement techniques rely on tracer particles to visualize the flow field and are usually only able to measure the velocity field of one phase at a time. In the case of PIV measurements both the flow tracers and the kerosene droplets scatter the laser light and thus, appear on the PIV recordings. Depending on droplet size and flow velocity, these kerosene droplets do not necessarily follow the airflow leading to errors in the derived velocity field. This work presents a method on how to separate kerosene droplets from flow tracers depending on their optical characteristics in the PIV recording. This phase separation enables the independent measurement of the flow fields of both the gaseous and liquid phase at the same time using a standard PIV setup. The method is demonstrated on a laboratory scale aero engine combustor operated at atmospheric conditions. The test rig features liquid kerosene combustion with realistic inlet temperatures and pressure drop as well as good access for optical measurement techniques. The phases are separated by filtering the images with noise reduction filters for suppressing the signal of the flow tracers, and edge detection filters to detect the kerosene droplets. The detected kerosene droplets are removed from the PIV pictures and the pictures are evaluated using standard PIV cross-correlation. Afterwards the liquid phase images are evaluated using Particle Tracking Velocimetry (PTV). This phase separation can lead to errors in the derived velocity fields because of incorrect and incomplete particle detection or due to errors in the cross correlation at the edges of detected particles. These errors in the phase separation are quantified by evaluating artificial two-phase flow PIV pictures with similar optical properties to the actual two-phase PIV pictures, and comparing the derived velocity fields to the results calculated using the original, unaltered pictures. The obtained results show, that in the setup under investigation, gaseous and liquid phase can have significantly different flow fields with kerosene droplets moving in the opposite direction of the recirculating airflow. The influence of essential parameters like seeding and spray density are discussed and at positions with a sufficient data rate, the instantaneous slip velocity between droplets and gaseous flow is calculated. Generally, the presented method appears to be suitable for studying combustion with liquid kerosene injection.
Application of Spectral Method for Vibration-Induced High-Cycle Fatigue Evaluation of an HP Turbine Blade
Authors: Ubulom Iroizan 
Published: January 2021

Abstract
A method of fluid-structure interaction coupling is implemented for a forced-response, vibration-induced fatigue life estimation of a high-pressure turbine blade. Two simulations approaches; a two-way (fully-coupled) and one-way (uncoupled) methods are implemented to investigate the influence of fluidsolid coupling on a turbine blade structural response. The fatigue analysis is performed using the frequency domain spectral moments estimated from the response power spectral density of the two simulation cases. The method is demonstrated in light of the time-domain method of the rainflow cycle counting method with mean stress correction. Correspondingly, the mean stress and multiaxiality effects are also accounted for in the frequency domain spectral approach. In the mean stress case, a multiplication coefficient is derived based on the Morrow equation, while the case of multiaxiality is based on a criterion which reduces the triaxial stress state to an equivalent uniaxial stress using the critical plane assumption. The analyses show that while the vibration-induced stress histories of both simulation approaches are stationary, they violate the assumption of normality of the frequency domain approaches. The stress history profile of both processes can be described as platykurtic with the distributions having less mass near its mean and in the tail region, as compared to a Gaussian distribution with an equal standard deviation. The fully-coupled method is right leaning with positive skewness while the uncoupled approach is left leaning with negative skewness. The directional orientation of the principal axes was also analyzed based on the Euler angle estimation. Although noticeable differences were found in the peak distribution of the normal stresses for both methods, the predicted Euler angle orientations were consistent in both cases, depicting a similar orientation of the critical plane during a crack initiation process. It is shown that the fatigue life estimation was conservative in the fully-coupled solution approach.
Heat Transfer and Pressure Loss in a Two-Pass, Rectangular Channel Featuring a Reduced Cross-Sectional Area After the 180-Degree Tip Turn With Different Turning Vane Configurations
Authors: Alsaleem Sulaiman M. , Wright Lesley M. , Han Je-Chin 
Published: January 2021

Abstract
Serpentine, varying aspect ratio cooling passages, are typically used in cooling advanced gas turbine blades. These passages are usually connected by sharp, 180-deg bends. In the open literature, most of the internal cooling studies use a fixed cross-sectional area for multi-pass channels. Studies that use varying aspect ratio channels, along with a guide (turn) vane to direct the flow with turning, are scarce. In general, studies show that the incorporation of turning vanes in the bend region of a multi-pass channel keeps the heat transfer rate high while reducing pressure loss. Therefore, the current study investigates the effect of using different guide (turn) vane designs on both the detailed heat transfer distribution and pressure loss in a multi-pass channel with an aspect ratio of (4:1) in the entry passage and (2:1) in the second passage downstream of the vane (s). The first vane configuration is one solid-vane with a semi-circular cross-section connecting the two flow passages. The second configuration has three broken-vanes with a quarter-circular cross-section; two broken vanes are located downstream in the first passage (entering the turn), and one broken vane is upstream in the second passage (exiting the turn). For a Reynolds number range 15,000 to 45,000, detailed heat transfer distributions were obtained on all surfaces within the flow passages by using a transient liquid crystal method. The results show that the turning vane configurations have large effects on the heat transfer, in the turning bend and second passage, and the overall pressure drop. Results show that including the semi-circular vane in the turning region of a multi-pass channel enhanced the overall heat transfer by around 29% with a reduction in pressure loss by around 20%. Moreover, results show that the quarter-circular vane design provides higher overall averaged heat transfer enhancement than the semi-circular vane design by around 9% with penalty of higher pressure drop by 6%, which yields higher thermal performance by 7%, over the Reynolds number range.