bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Investigation of Dual-Swirl Spray Flame in a Fuel Staged Optical Model Combustor With Laser Diagnostics
Authors: Yang Siheng , Wang Jianchen , Wang Zhichao , Han Meng , Lin Yuzhen , Wang Yexin
Published: September 2021

Lean premixed prevaporized combustors often feature staged combustion with a premixed main flame anchored by the nonpremixed pilot flame to obtain a wide operating range. Interaction between pilot flame and main flame is complex. The present article investigates the flame topologies and flame-fuel interactions in separated stratified swirl flames under various operating conditions (fuel to air ratio FAR and fuel stage ratio α) and injector designs (main stage swirl number Sm and fuel injection angle JA). Experiments are carried out in the centrally staged optical model combustor at inlet pressure P3 = 0.49–0.7 MPa and inlet temperature T3 = 539 K. At first, the flame structures obtained from OH-PLIF are investigated and discussed for the baseline injector (Sm = 0.9, JA = −50°). The V-shaped flame is stabilized in the inner shear layer (ISL) with the flame attachment point located at the lip for the pilot flame mode (α = 1). Dual flame is observed in the combustor for the fuel staged combustion (α < 1): the main flame stabilized in the outer shear layer (OSL) and the pilot flame stabilized in the inner shear layer (ISL). For increasing α from 0.15 to 0.25, gaps between the main flame and pilot flame are decreased, indicating a stronger interaction between the two flames. The flame structure for different injector geometries is then investigated. It is found that the higher main stage swirl number induces a larger flame opening angle, decreasing the interaction between two flames. Fuel injected into crossflow (JA = −50°) is found to generated a more separated flame, decreasing the flame interactions. Finally, fuel distribution measured by kerosene-PLIF is analyzed with the correlation to flame structure. Results show that the existence of a good mixing of fuel and fresh air in ISL and OSL provide favorable conditions for chemical reaction with high heat release. The OH distribution is highly correlated to fuel distribution. The fuel zone is located at the inner side of high OH region, indicating the reaction and heat release take place after the mixing of preheating of fuel-air mixture.
Effect of Tip Vortex Reduction on Air-Cooled Condenser Axial Flow Fan Performance: An Experimental Investigation
Authors: Pretorius J. P. , Erasmus J. A.
Published: September 2021

Large diameter axial flow fans are used in Air-cooled Condenser (ACC) systems of modern power stations. Efficiency improvements on these fans can significantly reduce the ACC power consumption and increase the net sent-out power to the grid. This study targets fan performance enhancement through blade tip vortex reduction. Experimental investigations are performed on a representative ACC scale fan, where tests consider the effects of tip clearance and two new tip endplate designs on fan performance. Test results confirm the findings of previous studies, showing the negative effect of increasing tip clearance on performance. Despite testing limitations, results from tests incorporating endplates show fan static pressure coefficient and efficiency increases over large ranges of flow coefficient compared to the datum fan. These outcomes agree with observations from literature and warrants further exploration. Future work is recommended to provide confirmation on the presented trends.
Endwall Boundary Layer Development in a Multistage Low-Speed Compressor With Tandem Stator Vanes
Authors: Hopfinger Michael , Gümmer Volker
Published: September 2021

The development of viscous endwall flow is of major importance when considering highly-loaded compressor stages. Essentially, all losses occurring in a subsonic compressor are caused by viscous shear stresses building up boundary layers on individual aerofoils and endwall surfaces. These boundary layers cause significant aerodynamic blockage and cause a reduction in effective flow area, depending on the specifics of the stage design. The presented work describes the numerical investigation of blockage development in a 3.5-stage low-speed compressor with tandem stator vanes. The research is aimed at understanding the mechanism of blockage generation and growth in tandem vane rows and across the entire compressor. Therefore, the blockage generation is investigated as a function of the operating point, the rotational speed and the inlet boundary layer thickness.
Binary Repetitive Model Predictive Active Flow Control Applied to an Annular Compressor Stator Cascade With Periodic Disturbances
Authors: Fietzke Benjamin , King Rudibert , Mihalyovics Jan , Peitsch Dieter
Published: September 2021

Novel pressure gain combustion concepts invoke periodic flow disturbances in a gas turbine’s last compressor stator row. This contribution presents studies of mitigation efforts on the effects of these periodic disturbances on an annular compressor stator rig. The passages were equipped with pneumatic Active Flow Control (AFC) influencing the stator blade’s suction side, and a rotating throttling disc downstream of the passages inducing periodic disturbances. For steady blowing, it is shown that with increasing actuation amplitudes Cμ, the extension of a hub corner vortex deteriorating the suction side flow can be reduced, resulting in an increased static pressure rise coefficient Cp of a passage. The effects of the induced periodic disturbances could not be addressed intrinsically, by using steady blowing actuation, Considering a corrected total pressure loss coefficient ζ*, which includes the actuation effort, the stator row’s efficiency decreases with higher cμ due to the increasing costs of the actuation mass flow. Therefore, a closed-loop approach is presented to address the effects of the disturbances more specifically, thus lowering the actuation cost, i.e., mass flow. For this, a Repetitive Model Predictive Control (RMPC) was applied, taking advantage of the periodic nature of the induced disturbances. The presented RMPC formulation is restricted to a binary control domain to account for the used solenoid valves’ switching character. An efficient implementation of the optimization within the RMPC is presented, which ensures real-time capability. As a result, Cp increases in a similar magnitude but with a lower actuation mass flow of up to 66%, resulting in a much lower ζ* for similar values of cμ.
Adaptive Geometry Representation of Turbine Vane Frames for Use in Optimization
Authors: Riebl Sebastian F. , Wakelam Christian , Niehuis Reinhard
Published: September 2021

Turbine Vane Frames (TVF) are a way to realize more compact jet engine designs. Located between the high pressure turbine (HPT) and the low pressure turbine (LPT), they fulfill structural and aerodynamic tasks. When used as an integrated concept with splitters located between the structural load-bearing vanes, the TVF configuration contains more than one type of airfoil with sometimes pronouncedly different properties. This system of multidisciplinary demands and mixed blading poses an interesting opportunity for optimization. Within the scope of the present work, a full geometric parameterization of a TVF with splitters is presented. The parameterization is chosen as to minimize the number of parameters required to automatically and flexibly represent all blade types involved in a TVF row in all three dimensions. Typical blade design parameters are linked to the fourth order Bézier-curve controlled camber line-thickness parameterization. Based on conventional design rules, a procedure is presented, which sets the parameters within their permissible ranges according to the imposed constraints, using a proprietary developed code. The presented workflow relies on subsequent three dimensional geometry generation by transfer of the proposed parameter set to a commercially available CAD package. The interdependencies of parameters are discussed and their respective significance for the adjustment process is detailed. Furthermore, the capability of the chosen parameterization and adjustment process to rebuild an exemplary reference TVF geometry is demonstrated. The results are verified by comparing not only geometrical profile data, but also validated CFD simulation results between the rebuilt and original geometries. Measures taken to ensure the robustness of the method are highlighted and evaluated by exploring extremes in the permissible design space. Finally, the embedding of the proposed method within the framework of an automated, gradient free numerical optimization is discussed. Herein, implications of the proposed method on response surface modeling in combination with the optimization method are highlighted. The method promises to be an option for improvement of optimization efficiency in gradient free optimization of interdependent blade geometries, by a-priori excluding unsuitable blade combinations, yet keeping restrictions to the design space as limited as possible.
Influence of Stator Hub Cavities on the Forced Response Behaviour of an Embedded Compressor Rotor
Authors: Hegde Shreyas , Kielb Robert , Zori Laith , Campregher Rubens
Published: September 2021

This paper focuses on the impact of hub labyrinth seal leakage flows on the aeromechanical behavior of an embedded compressor rotor. End wall flows are critical in determining the performance of gas turbine engine compressors, particularly the hub leakage flows that can contribute to a significant reduction in performance due to the loss in efficiency induced by the leakage. While the current literature does contribute extensively to the understanding of the influence of this leakage flow on the steady compressor performance, no attention has been given to its impact on the multi-row unsteady aeromechanical influence. The authors of this paper have talked about the multi-row influence at various modes and operating condition using models without the hub cavities included [11–12;33–34]. The embedded compressor rotor utilized for this study is a part of a 3.5 stage subsonic rig located at the Zucrow Laboratory at Purdue University. The current paper first addresses the steady aerodynamics of a multi-row compressor with hub cavities and talks in detail about the effect of cavities on the performance at both the torsional mode and a higher order mode. Next the influence on the forcing function utilizing both 3-row (S1/R2/S2) and 4-row (S1/R2/S2/R3) simulations at both the Peak Efficiency (PE) and the High Loading (HL) operating conditions is determined. To reduce the computational domain significantly, the time transformation (TT) method was utilized within ANSYS CFX. The first part of the paper describes the multi-row influence of two neighboring stators having the same vane count, which excites the embedded rotor at the same resonant frequency; the second part shows the influence of having physical waves reflecting from a rotating row downstream (R3).

The results show the significance of modelling the stator hub cavities and the drastic improvement in the modal force prediction with the cavities included. However, the authors observed that the impact tends to be more significant when the computational domain is small, i.e., fewer rows are included. As the number of rows are increased the influence of hub cavities diminish. Some of the conclusions drawn from this study are: 1) The presence of hub cavities changes the angle of incidence to the stators thereby reducing flow separation at the hub. The influence of these propagate throughout the domain i.e., a change in the angle of incidence in the first stage has an effect even at a downstream row. 2) The modal force prediction improved by ∼10% for the 3-row case and 1% for the 4-row case and the values moved closer to the experimental values in both cases. 3) The influence of hub cavities is more significant at torsional modes compared to higher order modes.
Design and Development of Biogas Venturi Mixture for Stationary Diesel Engine Using Analytical and CFD Approach
Authors: Salave H. S. , Desai A. D.
Published: September 2021

The major problem to use biogas as an alternative fuel in diesel engines is the modification needed for converting the current diesel engine into an enriched biogas engine. The fuel intake system is one of the major modifications required for the diesel engine. To overcome this problem, a new biogas venturi mixture has been designed by using an analytical and Computational Fluid Dynamics (CFD) approach. With the new fuel intake system, the engine runs effectively and properly using enriched biogas as an alternative fuel. It has been observed that simple modifications are required in the fuel intake system such that convergent divergent angle, throat diameter, etc. for uniform mixing of enriched biogas and air for complete combustion of fuel for improving engine performance and efficiency. This paper focuses on the design and development of a biogas venturi mixture with different convergent angles (20°, 24° & 28°, etc.) and different throat diameters (22 mm, 21mm, 20mm, 18mm & 16 mm etc.) used in a 3.5 kW, 661CC, 4-stroke stationary diesel engines using an analytical and CFD approach. This paper concludes that 16 mm throat diameter and 24° convergent angle, the maximum pressure drop and maximum velocity observed in a uniform and homogenous mixture. Better mixing can affect combustion, which leads to improved volumetric efficiency, brake thermal efficiency with reduced emission.
A Kinematic Study of Individual Rotating Detonation Engine Waves Using K-means Algorithm
Authors: Rezzag Taha , Burke Robert , Ahmed Kareem
Published: September 2021

The current research is concerned with studying the instantaneous properties of the detonation waves in a RDRE by tracking each individual wave and recording its position, velocity, and peak intensity as it travels around the annulus. This information is retrieved by a non-intrusive method consisting of using a data mining technique, the k-means algorithm, to distinguish each detonation from each other in a particular frame. An algorithm was then developed to match the detonations of a current frame to the ones of a previous frame. The code was validated against results found from the back-end imaging method developed by the Air Force Research Laboratory with excellent agreement. Results for two and three-wave mode cases show that the instantaneous detonation wave speeds oscillate around the mode locked average wave speed computed from a detonation surface. Moreover, the investigation of the relationship of the detonation’s peak light intensity with the azimuthal position revealed to also be oscillatory but more distinct.
Dynamic Analysis of a Coupled Dual-Rotor With Squeeze Film Damper Considering Sudden Unbalance
Authors: Cui Ying , Huang Yuxi , Yang Guogang , Wang Yongliang , Zhang Han
Published: September 2021

A nonlinear multi-degree-of-freedom dynamic model of a coupled dual-rotor system with an intershaft bearing and uncentralized squeeze film damper is established by using finite element method. Based on the model, the critical speed characteristic diagram and vibration modes of the system were calculated. The steady-state unbalance response is obtained by using Newmark-β algorithm. The numerical results show the effect of SFD position in the dual-rotor system on response amplitude. It is found that with the decrease of radial clearance and the increase of length-diameter ratio and lubricating oil viscosity, the damping effect of SFD is enhanced and the bistable state phenomenon can be suppressed. The transient response of the system in case of sudden unbalance occurring at the fan was simulated by applying a step function. It is demonstrated that the SFD can effectively reduce the duration and maximum amplitude of the transient process, but at certain speeds, the SFD will increase the amplitude after the system returns to steady state, the damping effect on the transient response is also enhanced with the increase of length-diameter and the decrease of radial clearance, and with the increase of the sudden unbalance value, the response is more likely to stabilized at the high amplitude state of the bistable state.
On the Creep-Fatigue Design of Double Skin Transpiration Cooled Components Towards Hotter Turbine Cycle Temperatures
Authors: Skamniotis Christos G. , Cocks Alan C. F.
Published: September 2021

The need for better aeroengine efficiency and fuel burn savings can be addressed by increasing turbine cycle temperatures. New cooling technologies such as emerging double skin transpiration (DST) systems, are essential for preserving the integrity of metallic parts if operating temperatures are to be increased beyond current levels. Their implementation, however, requires complex architectures with detailed features such as inclined film holes that raise local stresses. Our aim is to accelerate the implementation of DST systems in turbomachines, by providing an understanding of their implications on thermal stresses and the creep-fatigue failure processes. By using geometric, temperature field and nickel alloy material property idealizations, we generate both theoretical and Finite Element (FE) solutions for the thermal stress field and the critical cyclic strain range. Theoretical stress analysis and a local approach to failure lead to life predictions that are in reasonable agreement with inelastic cycle-by-cycle FE analysis, suggesting that analytical approaches can be useful for immediately identifying the significance of the various geometric features and thermal loading parameters. Film hole locations are predicted to fail under low cycle fatigue, suggesting that optimizing hole inclination, hole shape and other important geometric features is critical.
Experimental Determination of Heat Transfer Coefficient on Impingement Cooled Gear Flanks: Validation of the Evaluation Method
Authors: Ayan Emre , von Plehwe Felix C. , Keller Marc C. , Kromer Christian , Schwitzke Corina , Bauer Hans-Jörg
Published: September 2021

Understanding the heat transfer characteristics of impingement cooling of high-speed high-power gears is essential to design a reliable gearbox for a new generation of jet engines. However, experimental data on the impingement cooling of gears is limited in the literature. The experimental setup at the Institute of Thermal Turbomachinery aims at closing this gap. It includes a rotating gear instrumented with thermocouples. The measured temperatures are used to determine a spatially resolved heat transfer coefficient distribution on the gear tooth. The iterative evaluation approach applied in the post-processing of the experimental data is validated with two reference cases. First, it is shown that the interpolation of temperature data between thermocouple locations leads to inaccurate results and would not be valid for the evaluation of the experiments, even if the number of thermocouples were increased. The iterative evaluation approach can reproduce the reference heat transfer coefficient distributions very accurately even with a low spatial resolution of temperature data. A new iterative method based on the Levenberg-Marquardt algorithm is implemented within this study. The new method generally converges faster than the existing method. The difference in required computational time is negligible in the easy to evaluate high heat transfer case, whereas a speed-up of up to three times is observed in the relatively cumbersome evaluation of the low heat transfer case.
Internal Aerodynamic Performance Evaluation of Double Entrance S-Duct Intake at Moderately High Subsonic Mach Number
Authors: Sidhu Satpreet , Asghar Asad , Allan William D. E. , Stowe R. A. , Pimentel R.
Published: September 2021

Inlets are an essential element of aircraft propulsion systems. Aircraft with fuselage-embedded engines require intake ducts with bends to direct oncoming air into the engine. Consequently they often experience flow separation, losses, total pressure distortion, and swirling flow near the engine faces, all of which are detrimental to engine stability and performance. In some aircraft, double-entrance ducts are used to meet geometric constraints and maintain the required airflow. The present paper investigated aerodynamic performance of a bifurcated Y-duct with S-bends in both horizontal and vertical planes. Intake performance was evaluated at inlet Ma = 0.63 by measuring the surface static pressure along the four stream-wise rows of pressure taps and total pressure and 3D velocities using 5-hole probe across the exit plane of the intake duct. The data were used to determine the static and total pressure recovery, together with associated radial and circumferential distortion coefficients and swirl intensity. This work provides a rare experimental data-set for a twin-entrance, moderately high-subsonic, double S-duct intake. It compared reasonably with the most similar work published, that of single-entrance ducts at higher Mach number. Pressure recovery was on par while swirl was noted to be reduced when compared with those geometries. Complementary computational fluid dynamics was useful in the qualitative comparisons as well.
Heat Transfer in Rotating, Trailing Edge, Converging Channels With Full and Partial Height Strip-Fins
Authors: Sahin Izzet , Chen I-Lun , Wright Lesley M. , Han Je-Chin , Xu Hongzhou , Fox Michael
Published: September 2021

A wide variety of pin-fins have been used to enhance heat transfer in internal cooling channels. However, due to their large blockage in the flow direction, they result in an undesirable high pressure drop. This experimental study aims to reduce pressure drop while increasing the heat transfer surface area by utilizing strip-fins in converging internal cooling channels. The channel is designed with a trapezoidal cross-section, converges in both transverse and longitudinal directions, and is also skewed β = 120° with respect to the direction of rotation in order to model a trailing edge cooling channel. Only the leading and trailing surfaces of the channel are instrumented, and each surface is divided into eighteen isolated copper plates to measure the regionally averaged heat transfer coefficient. Utilizing pressure taps at the inlet and outlet of the channel, the pressure drop is obtained. Three staggered arrays of strip-fins are investigated: one full height configuration and two partial fin height arrangements (Sz = 2mm and 1mm). In all cases, the strip fins are 2mm wide (W) and 10mm long (Lf) in the flow direction. The fins are spaced such that Sy/Lf = 1 in the streamwise direction. However, due to the convergence the spanwise spacing Sx/W, was varied from 8 to 6.2 along the channel. The rotation number of the channel varied up to 0.21 by ranging the inlet Reynolds number from 10,000 to 40,000 and rotation speed from 0 to 300rpm. It is found that the full height strip-fin channel results in a more non-uniform spanwise heat transfer distribution than the partial height strip-fin channel. Both trailing and leading surface heat transfer coefficients are enhanced under rotation conditions. The 2mm height partial strip-fin channel provided the best thermal performance, and it is comparable to the performance of the converging channels with partial length circular pins. The strip-fin channel can be a design option when the pressure drop penalty is a major concern.
Aeromechanical Optimization of Scalloping in Mixed Flow Turbines
Authors: Elliott Matthew , Spence Stephen , Seiler Martin , Geron Marco
Published: September 2021

Scalloping of radial and mixed flow turbocharger turbine rotors has been commonplace for many years as a means of inertia reduction and stress relief. The interest in turbine rotor inertia reduction is driven by transient loading requirements of turbocharged internal combustion engines, as this is a key factor in the time taken to meet transient engine torque requirements. Due to the high density materials used in turbine rotors, any material removal from the turbine wheel has a significant impact on turbocharger inertia, and thus the transient response of the engine.

It is well known that scalloping not only reduces inertia, but also efficiency. This study aimed to identify if it was possible to produce a new scallop design which reduced the scalloping efficiency penalty without increasing inertia, or compromising mechanical constraints. This was carried out with the aim of developing design recommendations for scalloping where a complete minimization of inertia is not the design goal.

A multipoint, multi-physics numerical optimization, with constraints on inertia and back disc stress, was carried out to determine what efficiency benefit could be realized by aerodynamically designing mixed flow turbine scalloping. An efficiency benefit was identified across the entire turbocharger operating line, with increased benefit at low engine load, whilst not exceeding the design constraints. Scalloping losses for the baseline design were found to be greatest at low engine load, where the turbine experienced low expansion ratio, mass flow and speed. This explains why an aerodynamic redesign yields the greatest benefit under those operating conditions. These performance predictions were experimentally validated on the cold flow test rig at Queen’s University Belfast, with good agreement between simulated and measured data.

To conclude the study, a detailed loss audit was carried out to identify key loss generating flow structures, and to understand how changes in geometry affected the formation and development of these flow structures throughout the passage. A large vortex which entered the passage from the scalloped region and interacted with the tip leakage vortex along the suction surface of the blade was identified as the main source of loss due to scalloping. The optimized design was found to better control the location of entry of this vortex into the blade passage, thus reducing the associated loss, and facilitating a performance improvement. Geometric design guidelines were then proposed based on these findings.
Data Selection and Feature Engineering for the Application of Machine Learning to the Prediction of Gas Turbine Trip
Authors: Losi Enzo , Venturini Mauro , Manservigi Lucrezia , Ceschini Giuseppe Fabio , Bechini Giovanni , Cota Giuseppe , Riguzzi Fabrizio
Published: September 2021

A gas turbine trip is an unplanned shutdown, of which the consequences are business interruption and a reduction of equipment remaining useful life. Therefore, detection and identification of symptoms of trips would allow predicting its occurrence, thus avoiding damages and costs.

The development of machine learning models able to predict gas turbine trip requires the definition of a set of target data and a procedure of feature engineering that improves machine learning generalization and effectiveness.

This paper presents a methodology that focuses on the steps that precede the development of a machine learning model, i.e., data selection and feature engineering, which are the key for a successful predictive model.

Data selection is performed by partitioning units into homogeneous groups according to different criteria, e.g., type, region of installation, and operation. A subsequent matching algorithm is applied to rotational speed data of multiple gas turbine units to identify start-ups and shutdowns so that the considered units can be partitioned according to their operation, i.e., base load or peak load.

Feature engineering aims at creating features that improve machine learning model accuracy and reliability. First, the Discrete Fourier Transform is used to identify and remove from the time series the seasonal components, i.e., patterns that repeat with a given periodicity. Then, new features are created based on gas turbine domain knowledge in order to capture the complex interactions among system variables and trip occurrence.

The outcomes of this paper are the definition of a set of target examples and the identification of a meaningful set of features suitable to develop a machine learning model aimed at predicting gas turbine trip.
Prediction of Gas Turbine Trip: a Novel Methodology Based on Random Forest Models
Authors: Losi Enzo , Venturini Mauro , Manservigi Lucrezia , Ceschini Giuseppe Fabio , Bechini Giovanni , Cota Giuseppe , Riguzzi Fabrizio
Published: September 2021

A gas turbine trip is an unplanned shutdown, of which the most relevant consequences are business interruption and a reduction of equipment remaining useful life. Thus, understanding the underlying causes of gas turbine trip would allow predicting its occurrence in order to maximize gas turbine profitability and improve its availability.

In the ever competitive Oil & Gas sector, data mining and machine learning are increasingly being employed to support a deeper insight and improved operation of gas turbines. Among the various machine learning tools, Random Forests are an ensemble learning method consisting of an aggregation of decision tree classifiers.

This paper presents a novel methodology aimed at exploiting information embedded in the data and develops Random Forest models, aimed at predicting gas turbine trip based on information gathered during a timeframe of historical data acquired from multiple sensors. The novel approach exploits time series segmentation to increase the amount of training data, thus reducing overfitting.

First, data are transformed according to a feature engineering methodology developed in a separate work by the same authors. Then, Random Forest models are trained and tested on unseen observations to demonstrate the benefits of the novel approach. The superiority of the novel approach is proved by considering two real-word case-studies, involving filed data taken during three years of operation of two fleets of Siemens gas turbines located in different regions.

The novel methodology allows values of Precision, Recall and Accuracy in the range 75–85 %, thus demonstrating the industrial feasibility of the predictive methodology.
Studying the Effect of Porosity of Porous Layer Coating on the Performance of the Horizontal Tubular Falling Film Evaporator
Authors: Ibrahim Alaa Adel , Elgamal Hassan , Elmekawy Ahmed M. Nagib
Published: September 2021

Through the recent decades, many studies have focused on finding efficient methods to enhance the heat transfer performance in heat exchangers. Therefore, using porous media attracted many researchers, as it is such a simple, efficient, and low-cost technique in enlarging the surface contact area of heat transfer through the fluid pass. Nevertheless, there is little work associated with using porous media to enhance the thermal performance of falling film evaporators. The present study seeks to discuss numerically the liquid flow behaviour over falling film evaporator tubes in the case of bare tubes and tubes with porous layer coating. The two-dimensional multi-phase numerical simulations are also carried out in order to investigate the effect of the porosity ratio of the porous medium added to the tubes in the heat transfer performance. Furthermore, deducing the way to select a decent porosity ratio to be used to get the best thermal performance is demonstrated through the study. Time-averaged results gained from the numerical simulations have been compared to those of bare-tube falling film evaporator to observe much higher heat transfer performance represented in the average surface Nusselt number (Nu) which increased by 3 times.
On the Forced Response Predictions and Life Improvements of an Industrial Axial Compressor Rotor Blade
Authors: Krishnababu Senthil , Bruni Giuseppe , Frach Agnieszka
Published: September 2021

Improvements made to the high cycle fatigue life of an industrial compressor rotor blade for tip active modes through aerodynamic design changes and aero-mechanical assessments are presented in this paper. Typical aero-mechanical computations involved utilising an in-house linear-harmonic solver to compute the aero damping. In parallel, a novel hybrid model with whole-anulus domain for the blade rows of interest followed by a single passage domain for the rest of the compressor was used to compute the modal forcing. In addition to the standard blade passing resonances, low engine order excitations due to vane number differences, were analysed. This was achieved within a time frame consistent with the product design cycle by using TurboStream, a GPU based non-linear time domain unsteady flow solver. The excitation due to low engine order resonance was found to be influenced by a harmonic of upstream blade passing frequency. When considering a design change targeting HCF life, the calculated reserve factors showed significant improvements for the tip modes of interest. The subsequent engine tests carried out with tip timing agreed closely with the predictions thus validating not only the design but also the forced response prediction process.
Investigation on Mode Characteristics of Rotating Instability and Rotating Stall in an Axial Compressor
Authors: Yang Zeyuan , Wu Yadong , Ouyang Hua
Published: September 2021

Rotating instability (RI) and rotating stall (RS) are two types of aerodynamic instability in axial compressors. The former features the side-by-side peaks below the blade passing frequency (BPF) in frequency spectra, and the latter represents one or more stall cells rotating in the compressor. This paper presents an experimental on the nearfield pressure and farfield acoustic characteristics of RI phenomenon in a low-speed axial compressor rotor, which endures both RI and RS at several working conditions. In order to obtain the high-order modes of RI and other aerodynamic instability, a total of 9 or 20 Kulites are circumferentially mounted on the casing wall to measure the nearfield pressure fluctuation using a mode order calibration method. Meantime in the farfield 16 microphones are planted to measure the acoustic mode order using the compressive sensing method. Through calibration the experiments acquire the mode orders generated by RI and the interaction between RI and BPF, which is higher than the number of transducers. As for RS, the mode decomposition shows a mode order of 1, indicating one single stall cell rotating in the compressor. This experiment also shows that amplitude of RI modes is decreased when RS occurs, but RS modes and RI modes will both be enhanced if the flow rate is further reduced. This experiment reveals that RI experiences three stages of “strengthen-weaken-strengthen”, and hence RI may not be regarded only as “prestall” disturbance.
Composite UHBR Fan for Forced Response and Flutter Investigations
Authors: Eggers Torben , Friedrichs Jens , Goessling Jan , Seume Joerg R. , Natale Nunzio , Flüh Jan Peter , Paletta Nicola
Published: September 2021

In the CA3ViAR (Composite fan Aerodynamic, Aeroelastic, and Aeroacoustic Validation Rig) project, a composite low-transonic fan is designed and tested. The aim is a scaled ultra-high bypass ratio (UHBR) fan with state-of-the-art aerodynamic performance and composite rotor blades, which features aeroelastic phenomena, e.g. forced response by inlet distortions and flutter, under certain operating points within the wind tunnel. In this paper, the aerodynamic and aeroelastic design process starting from the overall performance specifications to a threedimensional numerical model is described. A target of eigen-frequency and twist-to-plunge ratio is specified such that flutter occurs at desired operating conditions with a sufficient margin with respect to the working line. Different materials and layups of the composite blade are analyzed to reach the structural target. The fan should serve as an open test case to advance the future research on aerodynamic, aeroelastic, and aeroacoustic performance investigations in a wide range of operating conditions. A preliminary fan stage design is presented in this paper.
Design and Analysis of an Aircraft Thermal Management System Linked to a Low-Bypass Ratio Turbofan Engine
Authors: Clark Robert A. , Shi Mingxuan , Gladin Jonathan , Mavris Dimitri
Published: September 2021

The design of an aircraft thermal management system (TMS) that is capable of rejecting heat loads into the bypass stream of a typical low-bypass ratio turbofan engine, or a ram-air stream, is investigated. The TMS consists of an air cycle system (ACS), which is similar to the typical air cycle machines (ACMs) used on current aircraft, both military and commercial. This system turbocharges compressor bleed air and uses heat exchangers in a ram air stream or the engine bypass stream to cool the engine bleed air prior to expanding it to low temperatures suitable for heat rejection. In this study, a simple low-bypass ratio afterburning turbofan engine was modeled in NPSS to provide boundary conditions to the TMS system throughout the flight envelope of a typical military fighter aircraft. The engine was sized to produce sea level static (SLS) thrust roughly equivalent to that of an F-35-class engine. Two different variations of the TMS system, a ram air cooled and a bypass air cooled, were sized to handle a given demanded aircraft heat load, which might include environmental control system (ECS) loads, avionics cooling loads, weapons system loads, or other miscellaneous loads. The architecture and modeling of the TMS is described in detail, and the ability of the sized TMS to reject these demanded aircraft loads throughout several key off-design points was analyzed, along with the impact of ACS engine bleeds on engine thrust and fuel consumption. A comparison is made between the cooling capabilities of the ram-air stream versus the engine bypass stream, along with the benefits and drawbacks of each cooling stream. It is observed that the maximum load dissipation capability of the TMS is tied directly to the amount of engine bleed flow, while the level of bleed flow required is set by the temperature conditions imposed by the aircraft cooling system and the heat transfer fluid used in the ACS thermal transport bus. Furthermore, the higher bypass stream temperatures significantly limit the thermodynamic viability and capability of a TMS designed with bypass air as the ultimate heat sink.

The results demonstrate the advantage that adaptive, variable cycle engines (VCEs) may have for future military aircraft designs, as they combine the best features of the two TMS architectures that were studied here.
Low-Order Modeling of Can-Annular Combustors
Authors: Fournier Guillaume J. J. , Meindl Max , Silva Camilo F. , Ghirardo Giulio , Bothien Mirko R. , Polifke Wolfgang
Published: September 2021

Heavy-duty land-based gas turbines are often designed with can-annular combustors, which consist of a set of identical cans, acoustically connected on the upstream side via the compressor plenum, and, downstream, with a small annular gap located at the transition with the first turbine stage. The modeling of this cross-talk area is crucial to predict the thermo-acoustic modes of the system. Thanks to the discrete rotational symmetry, Bloch wave theory can be exploited to reduce the system to a longitudinal combustor with a complex-valued equivalent outlet reflection coefficient, which models the annular gap. The present study reviews existing low-order models based purely on geometrical parameters and compares them to 2D Helmholtz simulations. We demonstrate that the modeling of the gap as a thin annulus is not suited for can-annular combustors and that the Rayleigh conductivity model only gives qualitative agreement. We then propose an extension for the equivalent reflection coefficient that accounts not only for geometrical but also flow parameters, by means of a characteristic length. The proposed model is in excellent agreement with 2D simulations and is able to correctly capture the eigenfrequencies of the system. We then perform a Design of Experiments study that allows us to explore various configurations and build correlations for the characteristic length. Finally, we discuss the validity limits of the proposed low-order modeling approach.
Numerical Investigation of Air-Oil Two-Phase Flow Pattern Transition in the Scavenge Line of an Aeroengine
Authors: Sekrani Ghofrane , Dick Jean-Sebastien , Poncet Sébastien , Nallamothu Sravankumar
Published: September 2021

Since most research investments in aeroengines have been targeted at the hot and cold sections, the oil system has remained an area poorly understood. Optimum sizing of the oil system can directly reduce the engine’s weight and specific fuel consumption while maximizing service life. The understanding of air/oil interaction in scavenge lines is required to influence the design of the oil systems and achieve those objectives.

The challenge is in the existence of numerous possible flow regimes and phase interactions. In scavenge lines, a complex two-phase flow results from the interaction of sealing airflow and lubrication oil. Scavenge lines can have bends, junctions and sudden area changes which complicates their modeling by amplifying pressure gradients and turbulence generation, and causing the flow to change morphology (annular, slug, stratified, bubbly, mist, etc.).

Several multiphase flow approaches have been developed to model two-phase flow in straight scavenge lines. However, up until now, no methodology is preferred by the community for simulating two-phase flow in such application. There are still many unknowns regarding the modeling of turbulence, phase interaction and the compressibility of immiscible mixtures such as air and oil.

The present study compares the performance of two numerical models: Volume of Fluid (VOF) and Algebraic Interfacial Area Density (AIAD), for simulating the air/oil flow in a suddenly expanding scavenge line against the experimental data of Ahmed et al. [1–2]. The AIAD model is a two-fluid Eulerian approach newly implemented on Ansys Fluent. Discrepancies between the two models for predicting pressure loss and void fraction are evaluated and discussed into details. The flow regime before and after the sudden expansion is identified using iso-surfaces of the void-fraction and compared against visual data. Based on the results presented, recommendations are formulated for further work regarding the calibration of AIAD modeling parameters.
Rubbing Of a Bladed Disk Considering Coriolis Effect: A Reduced Model Based on Complex Modal Analysis
Authors: Chen Dawei , Zhang Jiguo , Xiao Jiaguangyi , Chen Yong
Published: September 2021

Due to the high demands of aerodynamic efficiency in modern aero-engines, tip clearances between blades and casings are becoming smaller. This increases the possibility of rubbing between rotating bladed disks and their surrounding casings. Rotational effects exhibit increased significance in the latest generation of fans, which currently have relatively long blade and elongated cantilevered shaft. Previous studies on the rotor dynamics during rub impact have mainly focused on simplified models. However, it is necessary to take both realistic blades and Coriolis effect into account. Based on an open-source bladed disk model, the impact of the Coriolis effect on rub-induced responses is investigated. A two-step model reduction method is adopted by combining the fixed interface reduction and cyclic symmetry reduction. Both centrifugal and gyroscopic effects are incorporated in the numerical model. Complex modal analysis, based on classical Craig-Bampton method, is used to improve the model reduction of the gyroscopic system. The response of a flexible bladed disk to a simplified pulse rubbing force is investigated. With the time and space Fourier transform, a Coriolis-induced frequency split is observed on some nodal diameter lines, which indicates the significance of the Coriolis effect in rub-induced responses. A complex model reduction has been successfully applied to the rub-impact problem of cyclic symmetric bladed disks. Compared with the classical model reduction, the numerical results obtained by complex modal analysis are more reasonable. This lays a solid foundation for further rub-impact research considering rotor dynamics.
Effect of Accelerating Convergence in Adjoining 1D Domains Having Large Difference in Thermal Time Scales
Authors: Kaushik Tanvi , Wang Liangyu , Basani Jaydeep , Xu Fang
Published: September 2021

Combustor liners are subjected to high operating temperatures and high temperature gradients, which have an adverse effect on the durability of liners. Accurate prediction of liner wall temperature distribution can provide better insight into the design of effective cooling systems that have the potential to improve liner structure life.

When compared to RANS (Reynolds averaged Navier Stokes), LES (Large eddy simulation) framework provides better accuracy in resolving the large range of temporal and spatial scales of turbulent flow inside combustors. In simulations in which an unsteady LES fluid solver is interacting with an unsteady solid thermal solver, it would be impractical to advance and synchronize fluid and solid domains in physical time, due to a large difference between small fluid time scales set by turbulence and large solid time scales set by the thermal inertia of the solid. By advancing the fluid and solid solvers with different time step sizes, or by loosely coupling fluid and solid solvers such that they communicate at a defined frequency, convergence can be artificially accelerated. The convergence of the predicted temperature field solution is dependent on the implementation methodology of the acceleration techniques.

A combustor liner is subjected to hot turbulent gases on one side of its boundary and relatively colder air on the other side. This scenario is analyzed to understand the effect of accelerating convergence on the temperature field in a simplified 1D linear framework. A representative polychromatic temperature wave that a combustor liner is subjected to, is used in defining the boundary condition of a 1D implicit unsteady heat conduction solver.
Ignition Delay Time Correlation of C1 – C5 Natural Gas Blends for Intermediate and High Temperature Regime
Authors: Mohamed A. Abd El-Sabor , Sahu Amrit Bikram , Panigrahy Snehasish , Bourque Gilles , Curran Henry
Published: September 2021

New ignition delay time (IDT) data for stoichiometric natural gas (NG) blends composed of C1 – C5 n-alkanes with methane as the major component were recorded using a high pressure shock tube (ST) at reflected shock pressures (p5) and temperatures (T5) in the range 20–30 bar and 1000–1500 K, respectively. The good agreement of the new IDT experimental data with literature data shows the reliability of the new data at the conditions investigated. Comparisons of simulations using the NUI Galway mechanism (NUIGMech1.0) show very good agreement with the new experimental results and with the existing data available in the literature. Empirical IDT correlation equations have been developed through multiple linear regression analyses for these C1 – C5 n-alkane/air mixtures using constant volume IDT simulations in the pressure range pC = 10–50 bar, at temperatures TC = 950–2000 K and in the equivalence ratio (φ) range 0.3–3.0. Moreover, a global correlation equation is developed using NUIGMech1.0, to predict the IDTs for these NG mixtures and other relevant data available in the literature. The correlation expression utilized in this study employs a traditional Arrhenius rate form including dependencies on the individual fuel fraction, TC, φ and pC.