bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Swirl Distribution on Blade Shape and Performance of a Centrifugal Impeller
Authors: Cui Qin , Qin Guoliang , Li Lei , Jia Cheng , Wang Yi
Published: January 2021

All-over-controlled vortex method is an effective tool to inversely design the 3D impeller of a centrifugal compressor. In this method, swirl distribution is treated as a significant input parameter to control the blade shape, impeller flow field, and compressor performance. It is acknowledged that swirl distribution is prescribed by designers mostly relying on the personal experience at the beginning of design. So how to specify the swirl distribution is still a big challenge for impeller designers. Of the most interest in this paper is to provide a theoretical technique that can be readily applied to specify swirl distribution and reduce the dependence on the designers experience. A judgement criterion rCθ – ωr2 is proposed to design the swirl distribution. Based on the streamline curvature method, a 3D centrifugal impeller design program is developed to design centrifugal impeller. The scale and uniformity of rCθ – ωr2 along flow direction are discussed theoretically to conduct the specifying of swirl distribution. The theoretical analysis is verified by a specific centrifugal compressor case. Then commercial CFD software is used to predict the flow field and the performance of the impeller. The results demonstrate that the scale and distribution uniformity of rCθ – ωr2 have a significant effect on the blade shape and the flow field within the impeller, and possible loss can be reduced. For the new designer, it is possible to preliminarily recognize and eliminate the infeasible swirl distribution, and adjust the unsatisfactory swirl distribution using rCθ – ωr2. Proper blade shape and good impeller performance can be achieved with the help of the judgement criterion rCθ – ωr2.
The Thermo-Hydrodynamic Analysis of the Plain Journal Bearing With Centered Circumferential Groove: Numerical Simulation vs. Experiment
Authors: Zhang Guanghui , Yu Shubo , Liu Zhansheng , Xu Kefan , Li Yu
Published: January 2021

In order to increase the reliability of the oil lubricated journal bearing, the thermal characteristics of the plain journal bearing are investigated and optimized. In this paper, the steady state thermo-hydrodynamic analysis of the plain journal bearing with centered circumferential groove is studied by numerical simulation and experiments. The diameter of the journal bearing is 190mm, and the load of the bearing is 6150N, which is operated with the rotating speed of 5560 r/min. The flow characteristics including the temperature distribution in the clearance of the bearing are simulated by ANSYS CFX, where the Walther viscosity temperature relation and the cavitation effect are considered. The test rig for measuring the pressure and temperature distributing in established, which is driven by electrical motor and certain bearing load can be exerted on it. In the experiments, the temperature distribution of the bearing is measured by 10 temperature sensors, which is arranged on three cross sections along the axial direction. The temperature of the lubricating oil is obtained by the sensors on the shell of the bearing, which is installed in the Babbitt metal. In order to obtain the circumferential distribution of the temperature, the sensors locate at different circumferential angles. The influence of geometrical parameters on the temperature distribution is studied, including the bearing clearance, the bearing length and the groove width by numerical simulation and experiment. The bearing clearance ratios of 1.8‰ and 2.5‰ are compared, and as the increment of the bearing clearance ratio, the temperature of the bearing decreased, which is benefit from the flow mass into the bearing increases. For the bearing length increasing from 90mm to 94mm, the maximum temperature decreases about 3K. For the groove width varying from 20mm to 19mm and 18mm, the temperature of the bearing decreases. The comparison of the numerical results and experiments are presented, and they show similar tendency for the temperature distribution, but the difference of temperature values exists. Based on the results from variation of bearing clearance ratio, bearing length and groove width, the optimized parameters of the bearing are proposed by determining the groove width with 18mm, bearing length with 94mm and the bearing clearance ratio with 2.1‰. The thermo-hydrodynamic analysis from the CFD and the experiments for the optimized bearing are carried out. The results indicate that the thermal performance of the bearing is improved. Compared with original design of the bearing, the maximum temperature is reduced by approximately 5K for optimized design of the bearing.
Development and Application of an Internal Heat-Transfer Measurement Technique for Cooled Real Engine Components
Authors: Ali Asif , Cocchi Lorenzo , Picchi Alessio , Facchini Bruno , Cubeda Simone
Published: January 2021

The aim of this work is to present the development and application of a measurement technique that allows to record internal heat transfer features of real components. In order to apply this method, based on similar approaches proposed in previous literature works, the component is initially heated up to a steady temperature, then a thermal transient is induced by injecting cool air in the internal cooling system. During this process, the external temperature evolution is recorded by means of an IR camera. Experimental data are then exploited to run a numerical procedure, based on a series of transient finite-element analyses of the component. In particular, the test duration is divided into an appropriate number of steps and, for each of them, the heat flux on internal surfaces is iteratively updated as to target the measured external temperature distribution. Heat flux and internal temperature data for all the time steps are eventually employed in order to evaluate the convective heat transfer coefficient via linear regression.

This technique has been successfully tested on a cooled high-pressure vane of a Baker Hughes heavy-duty gas turbine, which was realised thanks to the development of a dedicated test rig at the University of Florence, Italy. The obtained results provide sufficiently detailed heat transfer distributions in addition to allowing to appreciate the effect of different coolant mass flow rates. The methodology is also capable of identifying defects, which is demonstrated by inducing controlled faults in the component.
Prediction of Non-Linear Mechanical Behavior With Deep Neural Network: Application on Low Pressure Turbine Disc
Authors: Jin Yuan , Li Weichen , Yang Zheyi , Jung Olivier
Published: January 2021

Thanks to the increase of computational capacity and the diversification of computational means, deep learning techniques have shown great successes in learning representations from data in the past decade. Following this trend, efforts have been made in the literature to apply Deep Neural Network (DNN) as surrogate model. Common practice consists in utilizing a single DNN to predict a certain physical property given input design parameters, and the DNN is trained by corresponding simulation results. However, most of the complex high-fidelity simulations involve nonlinear physical laws, e.g. elasto-plasticity, which cannot be explicitly depicted by the applied single DNN model. In the present work, static mechanical simulation with nonlinear constitutive law is addressed with a novel approach in a deep learning framework. We approximate the displacement and the nonlinear constitutive law by two deep neural networks. The first DNN acts as a prior on the unknown displacement field, while the second network aims at describing the nonlinear strain-stress relationship. The dependence of the strainstress relationship on the strain level is taken into consideration by taking the first order derivative with respect to spatial coordinates of the first DNN as an input of the second network. A new loss model combining the error in displacement field prediction and constitutive law description is proposed to train the two DNNs together. We demonstrate the effectiveness of the proposed framework on a low pressure turbine disc design problem.
Comparative Assessment of Fouling Scenarios in an Axial Flow Compressor
Authors: Templalexis Ioannis , Pachidis Vasilios , Hasani Azamar
Published: January 2021

It is commonly accepted that fouling degrades severely axial compressor performance. Deposits build up throughout the compressor’s operating life, causing a decrease in its delivery pressure, efficiency and flow capacity. Researchers have also concluded that the presence of wet contaminants and/or high air humidity, plus the quality of air filtration systems, have a far greater impact on fouling rates, than engine specific fouling susceptibility factors [1]. The size of airborne particles ingested into the engine is primarily controlled by the presence of a filtration system. On the other hand, the particle deposition rate and the fouling patterns formed on the blade surfaces are greatly affected by the “stickiness” of the blade surfaces which in turn is affected by the moisture level of the incoming air. Compressor geometry, size and operating point would affect far less the rate of contaminants built up on the wetted surfaces and they would affect even less the exact location on compressor walls and blade surfaces.

The current study identifies four basic operating scenarios which refer to the same compressor, in order to put forward a comparative assessment as to how the factors mentioned above, affect the compressor performance through the fouling mechanism. Scenarios were formed out of the possible combinations regarding the presence of a filtration system and the level of humidity. These were: i) Filtered - dry air, ii) Filtered - humid air, iii) Unfiltered - dry air, and iv) Unfiltered - humid air. These scenarios will eventually reproduce four completely different situations regarding the quality of the incoming air and subsequently, four different fouling regimes for the compressor operating downstream. Data to support the impact of each reported incoming air condition on compressor wetted surfaces, are based on experimental findings collected from a thorough literature review. A fixed operating period was set for all cases.

Prescribed requirements of the computational tool selected to build the compressor model were; i) low computational power since several runs had to be performed in order to cover the assumed time period, and ii) ability to introduce the imprint of various fouling patterns on compressor blades, into the performance of the compressor. SOCRATES, an in-house two-dimensional, streamline curvature-based, through-flow computational tool, meets these requirements and it was used for this study. A fully customizable empirical model, recently introduced in the code, takes into account various aspects of fouling such as the surface roughness level, the flow blockage and the altered deviation angle at the exit of the blade row. A coverage factor was introduced which takes into account the location and the extent of fouling onto the blade surfaces.
Development of Web-Based Short Courses on Control, Diagnostics, and Instrumentation
Authors: Aslanidou Ioanna , Zaccaria Valentina , Fentaye Amare D. , Kyprianidis Konstantinos G.
Published: January 2021

As a consequence of globalization and advances in digital tools, synchronous or asynchronous distance courses are becoming an integral part of universities’ educational offers. The design of an online course introduces more challenges compared to a traditional on campus course with face to face lectures. This is true especially for engineering subjects where problem or project-based courses may be preferred to stimulate critical thinking and engage the learners with real-life problems. However, realizing this with distance learning implies that a similar study pace should be kept by the learners involved. This may not be easy, since individual pace is often a motivation for choosing a distance course. Student engagement in group projects, collaborations, and the proper design of examination tasks are only some of the challenges in designing a distance course for an engineering program.

A series of web-based courses on measurement techniques, control, and diagnostics were developed and delivered to groups of learners. Each course comprised short modules covering key points of the subject and aimed at getting learners to understand both the fundamental concepts that they do not typically learn or understand in the respective base courses and to build on that knowledge to reach a more advanced cognitive level.

The experience obtained in the courses on what strategies worked better or worse for the learners is presented in this paper. A comparison between the courses provides an interesting outlook on how the learners reacted to slightly different requirements and incentives in each course. The results from the evaluation of the courses are also used as a base for discussion.

The background and availability of the learners is closely linked to how a course should be designed to optimally fit the learning group, without compromising on the achievement of the learning outcomes. This series of courses is a good example of continuous professional development courses in the field of control, diagnostics, and instrumentation (CDI), and brings with it a number of challenges and opportunities for the development of online courses.
Non-Uniform Source Term Model for Film Cooling With the Internal Cross Flow
Authors: Zhang Zhen , Chen Ziyu , Su Xinrong , Yuan Xin
Published: January 2021

The source term model is an effective way to reduce the calculation consumption in predicting film cooling performance. The aim of this work is to develop a new source term model to consider the non-uniform in-hole flows. The internal cross flow that occurs in air-cooled blades and vanes has been shown to distinctly affect the cooling performance. In this work, the in-hole flow mechanism with the presence of the internal cross flow is studied. A topological model that divides in-hole flows into three parts and several regions is put forward. It is shown that, compared with the parallel ones, the perpendicular internal cross flows dominate the cooling performance. What is more, flows within the cooling hole are not affected by the main flow, especially in the region under a certain plane (named the R plane). This feature makes it possible for a source term model to work under various main flow conditions. Based on these understandings, a non-uniform source term model is established. It models and solves the three-dimensional in-hole flows by a two-dimensional transient solver and describes the effect of the internal cross flow as initial conditions using a vortex model. The result of the transient solver is then transformed into the axial velocity distribution at the R plane and is used as the source term. The prediction of the source term model is compared with full CFD under various VR, VRi and β, showing the ability of this model to predict the effect of the internal cross flow with discrepancy increasing with VR. Accurate modeling of the three-dimensional in-hole flows is the key point in this source term model and needs further development.
Comparison of Radiation and Convection-Based Calibration of Fast-Response Heat Flux Sensors
Authors: Huber Konstantin , Rödiger Tim
Published: January 2021

In this study, the static calibration of different heat flux sensors in radiation- and convection-based procedures are compared. First, three heat flux sensors based on different principles: ALTP (based on the Transverse Seebeck Effect), HFM8E (differential-layer device) and a TG-2000 (circular-foil gage) are calibrated in a laser-based radiation setup and compared to the manufacturers calibration. In a second step, all three heat flux sensors are compared with standard temperature-based, robust heat flux measurement techniques (coaxial thermocouple and slug-calorimeter) within a newly built convection-dominated facility based on stagnation-point measurments of an impinging hot air jet. The obtained results show measurement principle depending divergences indicating that a sensitivity transfer between a radiative calibrated sensor used in a mainly convective environment is not always possible and can lead to significant, systematic errors. By comparing the time signal behavior of temperature based heat flux measurement techniques, benefits for direct heat flux measurement techniques are detected.
Innovative Design, Structural Optimization and Additive Manufacturing of New-Generation Turbine Blades
Authors: Amedei Andrea , Meli Enrico , Rindi Andrea , Romani Benedetta , Pinelli Lorenzo , Vanti Federico , Arnone Andrea , Benvenuti Gianluigi , Fabbrini Marco , Morganti Nicolò
Published: January 2021

The need for high performances is pushing the complexity of mechanical design at very high levels, especially for turbomachinery components.

In this field, structural topology optimization methods together with additive manufacturing techniques for high resistant alloys are considered very promising tools, but their potentialities have not been deeply investigated yet for critical rotating components like new-generation turbine blades.

In this framework, this research work proposes a methodology for the design, the optimization and the additive manufacturing of extremely stressed turbomachinery components like turbine blade-rows. The presented procedure pays particular attention to important aspects of the problems as fluid-structure interactions (forced response and flutter phenomena) and fatigue of materials, going beyond the standard structural optimization approaches found in the literature. The new design strategy enables a substantial reduction of the component mass, limiting the maximum stress and improving the vibrational behaviour of the system in terms of eigenfrequencies, modal shapes and fatigue life.

Furthermore, the numerical procedure shows robustness and efficiency, making the proposed methodology a good tool for rapid design and prototyping, and for reducing the design costs and the time-to-market typical of this kind of mechanical elements.

The procedure has been applied to a low-pressure turbine rotor to improve the aeromechanical behavior while keeping the aerodynamic performance. From the original geometry, mode-shapes, forcing functions (due to rotor/stator interactions) and aerodynamic damping have been numerically evaluated and are used as input data for the following topological optimization. Finally, the optimized geometry has been verified in order to confirm the improved aeromechanical design.

After the structural topology optimization, the final geometries provided by the procedure have been then properly rendered to make them suitable for additive manufacturing. Some prototypes of the new optimized turbine blade have been manufactured from aluminum to be tested mechanically and in terms of fatigue.
Experimental Investigations on the Pressure Fluctuations in the Sealing Gap of Dry Gas Seals With Embedded Pressure Sensors
Authors: Luo Jingjing , Brillert Dieter
Published: January 2021

Dry gas lubricated non-contacting mechanical seals (DGS), most commonly found in centrifugal compressors, prevent the process gas flow into the atmosphere. Especially when high speed is combined with high pressure, DGS is the preferred choice over other sealing alternatives. Even though the non-contacting seal is proved reliable; the ultra-thin gas film can still lead to a host of potential problems due to possible contact.

In order to investigate the flow field in the sealing gap and to facilitate the numerical prediction of the seal performance, a dedicated test facility is developed to carry out the measurement of key parameters in the gas film. Gas in the sealing film varies according to the seal inlet pressure, and the thickness of gas film depends on this fluctuated pressure. In this paper, the test facility, measurement methods and the first results of static pressure measurements in the sealing gap of the DGS obtained in the described test facility are presented. An industry DGS with three-dimensional grooves on the surface of the rotating ring, where experimental investigations take place, is used. The static pressure in the gas film is measured, up to 20 bar and 8,100 rpm, by several high frequency ultraminiature pressure transducers embedded into the stationary ring. The experimental results are discussed and compared with the numerical model programmed in MATLAB [1], the characteristic and magnitude of which have a good agreement with the numerical simulations. It suggests the feasibility of measuring pressure profiles of the standard industry DGS under pressurized dynamic operating conditions without altering the key components of the seal and thereby affecting the seal performance.
Life Prediction Modeling of Combined High-Cycle Fatigue and Creep
Authors: Bouchenot Thomas , Patel Kirtan , Gordon Ali P. , Shinde Sachin
Published: January 2021

Industrial gas turbine blades are subjected to high temperatures and an array of mechanical and dynamic loads, making creep and high-cycle fatigue critical aspects of turbine blade design. The combination of creep and high-cycle fatigue produces a synergistic interaction effect whose explicit consequence to turbine life has been the subject of very little research. This interaction remains unaccounted for by current, decoupled life prediction models, which traditionally incorporate such interactions into conservative design safety factors. Improved lifing models capable of capturing these effects are now needed in order to maintain current reliability standards in next-generation operating conditions.

This research identifies the life-limiting aspect of a combined high-cycle fatigue and creep response in conventionally cast Alloy 247 LC, and captures the interaction of the two loads in a novel life prediction model. The proposed model is created from a comprehensive collection of experimental data obtained using an unconventional two-part test method, where test specimens pre-deformed to a prescribed creep strain are fatigue loaded at an elevated temperature and high frequency until failure. A variety of temperatures, creep strains, and fatigue loading conditions are explored to ensure that the resulting model is applicable to the myriad of potential turbine blade operating conditions. Rigorous metallographic assessments accompanying each test are leveraged to create a microstructurally-informed combined life prediction model.
Quality Key Numbers of Gas Turbine Combined Cycles
Authors: Wettstein Hans E.
Published: January 2021

The most relevant quality key numbers for the largest and most efficient Gas Turbine Combined Cycles (GTCC) are not (only) the data published by the original engine manufacturers OEM’s. Additional numbers are here evaluated with educated guesses based on published data of the latest announcements of the “big four OEM’s” [8]. Such data are of interest for potential customers but also for nailing down the current state-of-the-art for all kind of further cycle studies using turbomachinery components and also as a contemporary history record.

Making educated guesses means thermodynamic 1D simulation based on additional assumptions for pressure losses and other cycle data, which have a limited influence on the (unpublished) target quality numbers, such as:

• Mixed turbine inlet temperature Tmix. This is a key value describing the technology level. It can be derived independently of the (unpublished) TCLA value. It is a quality number for the general cooling design and for the secondary air systems.

• Polytropic efficiency of the compressor blading. This number describes the aerodynamic quality of the compressor blading.

• Polytropic efficiency of the turbine blading. It describes the quality level of both the blading aerodynamics and of the open air cooling design.

• Distribution of the exergy losses within the GT and in the bottoming cycle. The exergy losses describe the remaining opportunities for further improvements in the thermodynamic cycle design. But they also indicate its limits.

However already the determination of the Tmix is tricky. It depends on the analysis method and on the fluid data applied. The polytropic efficiency of the turbine blading and the exergy losses will depend both on the used methods and on the Tmix found. Achieving a trustable result therefore requires a transparent and reproducible method. In case of application of the found results for performance prediction of similar cycles the same method has to be applied in order to avoid mistakes.

In this paper real gas data with consideration of dissociation in equilibrium are used, while the polytropic efficiencies are determined with an incremental method based directly on the classic definitions of Stodola [3] and Dzung [4]. Therefore the still most used method using semi-perfect gas properties and corresponding formulas is bypassed.

In order to keep it as simple as possible the evaluation is limited to base load at ISO ambient condition (15°C, 60% relative humidity, sea level). The fuel is limited to pure methane according to the practice in current catalogue data.

The main focus is on the gas turbine with its components. The steam bottoming cycle is captured with its effect on the overall exergy and energy balance of the GTCC, which identifies exhaust and condensation losses.
Correlating and Updating Finite Element Models of Different Fidelity Using an Energy-Based Approach
Authors: Hardenberg Alexander , Kühhorn Arnold , Fanter Maren
Published: January 2021

Building finite element models of complex structures requires the engineer to make various simplifying assumptions. While there exists no unique way of modeling, the resulting model depends to a level on experience and engineering judgment. The inherent model uncertainties can be subdivided into three categories: idealization errors, discretization errors and parameter errors. Understanding the effect of different modeling assumptions and minimizing these uncertainties is key for creating efficient and physical meaningful finite element models. In this paper the effects of different modeling assumptions are analyzed by comparing finite element models of an aero engine turbine casing. Various models of different fidelity are created reaching from simple shell element representations neglecting geometric features like bosses, fixings and holes, to higher fidelity mixed dimensional models using coupled shell and three-dimensional elements. To quantify their impact on the stiffness and mass properties, the different models are correlated with a high-fidelity three-dimensional finite element model using numerical modal data. A novel method is proposed based on the strain and kinetic energy distribution to assess the effect of different modeling assumptions on the model structure. This is done by splitting the discretized model into multiple sections of interest and calculating the deviation of energies within the related splits. The derived strain and kinetic energy deviations are then used in addition to other correlation criteria like the modal assurance criteria or the relative difference in eigenfrequencies to analyze the impact of the different modeling assumptions. Having quantified the differences, the difficulties of error localization using modal data are discussed in the context of the correlation results. Finally, the effectiveness of the derived deviation values are demonstrated by updating a finite element model of an aero engine turbine casing in the presence of structural simplifications using an evolutionary optimization algorithm and comparing the model updating strategy to the standard sensitivity-based updating approach. If the resulting updated model is used to predict structural modifications or untested loading conditions, the updated parameters might lose their physical meaning when altering regions of the model not in error. Therefore, it is important to examine the physical significance of the updated parameters. It is shown, how the energy-based model updating can help to address this problem. All in all, the proposed energy-based approach can be used to compare various modeling strategies in order to build efficient finite element models as well as assist in the choice of parameters for subsequent model updating to validate the numerical model against test data.
The Impact of Various Modelling Decisions on Flow Field Predictions in a Centrifugal Compressor
Authors: Gooding William J. , Meier Matthew A. , Key Nicole L.
Published: January 2021

Computational tools have become increasingly important in design and research applications in recent years due to increasing computational resources. In most cases, model geometry and flow-physics are simplified to reduce the complexity of the computational model. While this was necessary historically, modern computational tools are capable of including realistic features such as fillets, surface roughness, and heat transfer.

This work presents extensive and systematic numerical results from a simulation of a centrifugal compressor stage for an aero-engine application. Numerical results are compared to detailed experimental data to investigate the effect of various modelling decisions, including turbulence models, on the predicted aerodynamics developing through the diffuser passage. Roughness and the inclusion of fillets significantly impact the flow development, especially with the SST turbulence model.

This approach leads to the conclusion that the BSL-EARSM model is best able to predict the experimentally determined diffuser flow profiles and overall performance trends with the inclusion of the previously mentioned model features. Additionally, the misleading conclusions can be reached if modelling decisions are based on merely matching overall performance values. Finally, frozen rotor simulations are used to roughly approximate the impact of unsteadiness on the flow field. The results show a significant impact and also that the inclusion of approximate unsteady effects tends to further improve the predictive capability of the computational models that were considered.
Infrared Temperature Measurements of the Blade Tip for a Turbine Operating at Corrected Engine Conditions
Authors: Christensen Louis , Celestina Richard , Sperling Spencer , Mathison Randall , Aksoy Hakan , Liu Jong
Published: January 2021

A high-speed infrared camera is used to measure the temperature of blade tips in a cooled high-pressure turbine operating at corrected engine conditions in The Ohio State University short duration Turbine Test Facility. These experiments create a challenging problem for infrared imaging since the rotor turns at over 13,000 rpm with tip speeds on the order of 300 m/s, and the surface temperature of the airfoils is on the order of 350 K. This means that the camera needs to capture a low intensity signal in a very short time period. This paper will review the design and operation of a measurement procedure to accomplish this difficult task along with the post-processing steps necessary to extract useful data. Raw infrared images are processed by deblurring the images using a non-blind Wiener filter and mapping the two-dimensional data onto the three-dimensional blade.

This paper also describes experiments covering a range of cooling flow rates and main flow temperatures. In addition, several tests with no main flow and only cooling flow were performed at lower speeds to reduce motion blur and enable the separation of internal and external heat transfer information. Results show that the infrared data is consistent and can provide quantitative comparisons of cooling performance even at the high rotation speed. This paper presents the lessons learned for high-speed infrared measurement along with representative data to illustrate the repeatability and capability of the measurement scheme as well as suggested improvements to guide further development.
3D Multi-Solver Coupled Simulation of Combustor-Turbine Interaction in an Aero-Engine
Authors: Zhang Yufang , Lei Kai
Published: January 2021

Generally, combustor and turbine components of aeroengine are designed in a relatively isolated manner and simplified boundary conditions from experiment or numerical simulation are commonly used at the interface. However, the hot gas at combustor exit is characterized by high non-uniformity of temperature, pressure, and flow distribution which may significantly affect turbine performances and reliability. Moreover, the presence of high-pressure turbine guide vanes also affects combustor flow field. The coupled simulation of combustor and turbine can describe the interaction between them more accurately.

Combustor and turbine components are generally simulated with different flow solvers since they are working at different Mach number range with different flow and physical characteristics. In this work, a 3D multi-solver coupled simulation system is developed where multiple flow solvers are coupled by using two different coupling approaches. In the first approach, a 2D interface is used to connect the computational domains of combustor and turbine, the data extracted from combustor exit (including total pressure, total temperature, velocity profile and turbulent quantities) is sent to turbine guide vane inlet and the static pressure profile at combustor exit is defined by turbine. In the second approach, the computational domains have a 3D overlap region where virtual body forces are added in combustor simulation in order to enforce the 3D velocity, temperature and turbulence profiles which is provided by the turbine simulation. Moreover, data from combustor simulation is also extracted and interpolated onto the turbine inlet and vice versa in the second approach.

The validation from a swirling jet case shows that the coupling system works well and the second approach provides more accurate results. Then a coupled simulation of aeroengine combustor and turbine are performed. Isolated simulation is also done for comparison. Results of these simulations are compared. It can be seen that the non-uniformity of temperature and flow distribution at combustor exit and hot streaks transport are successfully captured by the coupled simulation. The features have an important influence on the temperature distribution of turbine. Besides, the influence of turbine guide vanes on combustor flow field is mainly at the region close to combustor exit. The multi-solver coupled simulation system could be useful for designer to fully consider the interaction between combustor and turbine and gain more precise engine performance and improved turbine cooling design.
Study on the Influence of Inlet Asymmetry on Aerodynamic Noise of Cooling Fan
Authors: Tian Jie , Sun Zonghan , Chai Pengfei , Ouyang Hua
Published: January 2021

Experimental and numerical studies on the aerodynamic noise characteristics of a variable-speed axial fan commonly used for electronic device heat dissipation were conducted. First, the far-field noise spectrum of the fan was measured using a microphone array on the contour plane of the fan axis. The spectral analysis indicated that the discrete single-tone noise energy ratio was high, which indicates that it was the dominant aerodynamic noise. Afterwards, the double-uniform sampling point mode correction technique, which is based on the circumferential acoustic mode measurement method, was used to obtain the modal distribution on the inlet and outlet sides of the cooling fan. The influence of inlet unevenness on the cooling fan was identified. The traditional Tyler-Sofrin rotor-stator interaction formula was modified to account for the non-axisymmetric shape of the fan inlet bellmouth. The validity of the modified formula was verified by measuring the circumferential acoustic modes of three cooling fans with different rotor and strut counts. Furthermore, a CFD numerical study was conducted using Fluent to understand the influence of uneven inlet flow. The results showed that uneven inlet flow significantly affects the size and distribution of unsteady pulses on the rotor blades, which cause regular, periodic changes as the rotor blades rotate. Interactions between rotor blades and inlet unevenness were observed via the POD method as well. The discussion of the circumferential modes from aerodynamic noise of an axial flow cooling fan can act as a reference for further cooling fan noise reduction measures.
Large Eddy Simulation of Periodic Wake Impact on Boundary Layer Transition Mechanisms on a Highly Loaded Low-Pressure Turbine Blade
Authors: Winhart Benjamin , Sinkwitz Martin , Schramm Andreas , Post Pascal , di Mare Francesca
Published: January 2021

In the proposed paper the transient interaction between periodic incoming wakes and the laminar separation bubble located on the rear suction surface of a typical, highly loaded LPT blade is investigated by means of highly resolved large-eddy simulations. An annular, large scale, 1.5-stage LPT test-rig, equipped with a modified T106 turbine blading and an upstream rotating vortex generator is considered and the numerical predictions are compared against hot film array measurements. In order to accurately assess both baseline transition and wake impact, simulations were conducted with unperturbed and periodically perturbed inflow conditions. Main mechanisms of transition and wake-boundary layer interaction are investigated utilizing a frequency-time domain analysis. Finally visualizations of the main flow structures and shear layer instabilities are provided utilizing the q-criterion as well as the finite-time Lyapunov exponent.
Steady State Modeling of Unsteady Wake Induced Transition Effects in a Multistage Low Pressure Turbine
Authors: Führing Alexander , Kožulović Dragan , Bode Christoph , Franke Matthias
Published: January 2021

As low pressure turbine blade rows can operate at fairly low Reynolds numbers, long laminar boundary layers and transitional separation bubbles are not unusual in conventional blade design. Upstream wakes interact with the boundary layer in multistage low pressure turbine applications in a way that can alter the engine performance. In order to provide quick turnaround times, industrial applications mainly involve steady state computations which do not accurately model the unsteady wake effects. In this study, a low-pressure turbine cascade with periodic unsteady inflow as well as a two-stage low pressure turbine are computed at various Reynolds numbers using unsteady and steady RANS methods in the flow solver TRACE by DLR and MTU Aero Engines AG. A quasi-unsteady wake model working together with the γ – ReΘt model by Langtry and Menter is applied to the steady state simulation in another step in order to improve the prediction accuracy of low cost simulations utilizing mixing plane interfaces. The steady state results with and without wake model are compared to the time-resolved reference solution and the computation time is evaluated in order to show that the additional model is able to improve steady state mixing plane simulation results without sacrificing the low computational effort provided by the status quo.
Uncertainty Evaluation on Multi-Hole Aerodynamic Pressure Probes
Authors: Notaristefano Andrea , Gaetani Paolo , Dossena Vincenzo , Fusetti Alberto
Published: January 2021

In the frame of a continuous improvement of the performance and accuracy in the experimental testing of turbomachines, the uncertainty analysis on measurements instrumentation and techniques is of paramount importance. For this reason, since the beginning of the experimental activities at the Laboratory of Fluid Machines (LFM) located at Politecnico di Milano (Italy), this issue has been addressed and different methodologies have been applied.

This paper proposes a comparison of the results collected applying two methods for the measurement uncertainty quantification to two different aerodynamic pressure probes: sensor calibration, aerodynamic calibration and probe application are considered. The first uncertainty evaluation method is the so called “Uncertainty Propagation” method (UPM); the second is based on the “Monte Carlo” method (MCM).

Two miniaturized pressure probes have been selected for this investigation: a pneumatic 5-hole probe and a spherical fast response aerodynamic pressure probe (sFRAPP), the latter applied as a virtual 4-hole probe. Since the sFRAPP is equipped with two miniaturized pressure transducers installed inside the probe head, a specific calibration procedure and a dedicated uncertainty analysis are required.
Criteria for the Stability Limit Prediction of High Speed Centrifugal Compressors With Vaneless Diffuser: Part II — The Development of Prediction Criteria
Authors: Cravero Carlo , Marsano Davide
Published: January 2021

The challenge to be able to predict the stability limit in high speed centrifugal compressor is particularly strategic in an initial design phase. Furthermore, to be able to predict the limit massflow rate through the use of simplified numerical models (which does not require excessive computational resources) is very important. In the literature there are several methods to predict the chocking condition, while there is a lack as regards the surge condition. The authors have already presented a criterion to predict the surge line valid for centrifugal compressors with vaned diffuser. Instead those with vaneless diffuser have a very different behavior. For this reason, in the first paper an in-depth fluid dynamic analysis has been carried out, in order to identify the main phenomena linked to the trigger of instability in this type of compressors. This analysis has allowed understanding that the rotational speed is a discriminating factor in the phenomenology. In this second part, using the previous information, different criteria to predict the limit massflow rate for centrifugal compressors with vaneless diffuser are described. All the criteria are based on different simplified CFD approaches that can be routinely used during the design phase.
Effect of a Vortex Distortion on the Operability of an Ultra High Bypass Ratio Fan
Authors: Awes Amaury , Brosse Alexandre , Dufour Guillaume , Carbonneau Xavier , Godard Benjamin
Published: January 2021

Inlet distortion can significantly impact turbofan operability. In the present contribution, the focus is on vortex ingestion, which is a type of distortion that has received less attention in the literature for high-bypass-ratio fans of civil engines than inlet separation or boundary layer ingestion. Due to the unsteady and non-axisymmetric nature of the inflow, full annulus computations are performed, using an unsteady RANS approach with a sliding mesh interface between the rotor and the stator. The goal is to provide a detailed analysis and understanding of the mechanisms responsible for operability loss when a vortex is ingested by the fan. To that end, a simplified model of vortex is derived from previous simulations in crosswind conditions including the presence of the ground plane. The study test case is a turbofan demonstrator representative of modern turbofans. Simulations are run with and without vortex at several operating points until rotating stall is observed. The global results show that the vortex ingestion induces a stall margin loss of up to 8%. Modal analysis indicates a stall pattern with 10 cells rotating at somewhere between 52 and 67% of the shaft speed. A comparison of the two configurations shows that the stall inception mechanism is similar with and without distortion. In particular, examining the incidence at the fan blade, a similar critical angle is observed for the two configurations, which is leveraged to establish a stall criterion valid for vortex ingestion cases.
A Machine-Learning Approach to Assess Aircraft Engine System Performance
Authors: Tong Michael T.
Published: January 2021

Machine learning and big data have become the most disruptive technologies for organizations to improve workplace efficiency and productivity. This work explored the application of machine learning-based predictive analytics that would enable aircraft engine designers to estimate engine system performance quickly during the conceptual design stage. Supervised machine-learning algorithm was employed to study patterns in an open-source database of one-hundred-eighty-three production and research turbofan engines, and built predictive analytics for use in predicting system performance of new turbofan designs. Specifically, the author developed deep-learning analytics to predict turbofan system weight, using turbofan design parameters as the input. The predictive analytics were trained and deployed in Keras, an open-source neural networks API (application program interface) written in Python, with TensorFlow (an open-source Google machine learning library) serving as the backend engine. The current engine-weight prediction results, together with those for the TSFC (thrust specific fuel consumption) and core-size predictions that were studied previously by the author, show that machine learning-based predictive analytics can be an effective, time-saving tool for assessing aircraft engine system performance (TSFC, weight, and core size) during the conceptual design stage. It would enable expeditious identification of the best engine design amongst several candidates.
Analysis of Thermoacoustic Modes in Can-Annular Combustors Using Effective Bloch-Type Boundary Conditions
Authors: von Saldern Jakob G. R. , Orchini Alessandro , Moeck Jonas P.
Published: January 2021

Heavy-duty gas turbines are commonly designed with canannular combustors, in which all flames are physically separated. Acoustically, however, the cans communicate via the upstream located compressor plenum, or at the downstream gaps found at the transition to the turbine inlet. In the present study, a coupling condition that is based on a Rayleigh conductivity and acoustic flux conservation is derived. It enables acoustic communication between adjacent cans, in which one-dimensional acoustic waves propagate. In addition, because can-annular systems commonly feature a discrete rotational symmetry, the acoustic field can be expressed as a Bloch-periodic wave in the azimuthal direction. We demonstrate how the coupling conditions resulting in a combustion system with N cans can be expressed as an effective impedance for a single can. By means of this Bloch-type boundary condition, the thermoacoustics of a can-annular system can be analyzed considering only one can, thus reducing the size of the problem by a factor of N. Using this method, we investigate in frequency domain the effect of the coupling strength of a generic can-annular combustor consisting of 12 identical cans, which are connected at the downstream end. We describe generic features of can-annular systems that can be efficiently addressed with this framework and derive results on the frequency response of the cans at various Bloch numbers in the low-frequency and high-frequency limits. Furthermore, the formation of eigenvalue clusters with eigenvalues of close frequency and growth rate, but very different mode shapes is discussed.