bluuebunny/crossref_metadata_2025 huggingface dataset:
Large Eddy Simulations of a Transonic Airfoil Cascade
Authors: Priebe Stephan , Wilkin Daniel , Breeze-Stringfellow Andy , Mousavi Arash , Bhaskaran Rathakrishnan , d’Aquila Luke
Published: October 2022

The tip region of transonic blades in turbomachinery involves complex flow physics including shock wave/boundary layer interactions (SBLI). SBLI can lead to flow separation, transition from laminar to turbulent flow, and unsteadiness, which can affect the overall performance of the blade. In this paper, we present wall-resolved large eddy simulations (LES) of a transonic rotating cascade that is modeled after the tip region of a transonic diffusing blade. The calculations were performed using GENESIS, a high-order unstructured large eddy simulation solver. The convergence of the LES solution is assessed by varying the polynomial order of the solution from low to high order. LES simulations for a total of five operating conditions are presented, which cover the range of operation from unique incidence low operating line to stall and the associated shock wave/boundary layer interaction physics. The overall aerodynamics of the transonic passage airfoil are described based on the LES solutions as well as providing a detailed analysis of the boundary layer behavior. The changes in shock structure, boundary layer interaction physics, and associated losses with operating condition are highlighted. A low-frequency SBLI unsteadiness is observed in the cases where the boundary layer into the shock is laminar, and a scaling of the frequency is proposed. The scaling is based on the time scale of turbulent structures convecting from the shock to the trailing edge and acoustic disturbances then traveling back upstream.
Impact of Inlet Conditions on TVF Exit Flow Field
Authors: Graiff Mattia , Staggl Marian , Wakelam Christian , Heitmeir Franz , Göttlich Emil
Published: October 2022

The drive towards lightweight, more efficient engine architectures leads to the development and improvement of key aircraft engine components. The Turbine Vane Frame (TVF) can be seen as an evolution of the Turbine Center Frame (TCF), combining its structural and aerodynamic purposes with the function otherwise provided by the first stage turbine inlet guide vanes. Therefore, the TVF needs to smoothly guide the flow over the radial offset between high-pressure and low-pressure turbine stages, provide shrouded paths for oil lines, and impart to the flow the turning required by the following low pressure turbine stage. The expected beneficial effects on the engine include reduced weight, cost, and fuel burn. The key relevance of this component makes a broad, low-tier approach to its study highly desirable. The HighSpeed Wind Tunnel (HSWT) at the Technical University of Graz delivers excellent opportunities to explore the design space for Turbine Vane Frames. This paper deals with the impact of several important design parameters on the TVF. An engine relevant TVF configuration is replicated in an annular sector cascade test rig. The test rig is operated at relevant Mach number and turbulence level. Representative inlet flow is achieved through flow conditioning. Aerodynamic data is collected with five-hole probe and hot wire anemometry techniques. The insights offered by flow visualization and numerical computations are furthermore leveraged. Particular attention is given to the flow features at the TVF exit.
Interplay of Clusters of Acoustic and Intrinsic Thermoacoustic Modes in Can-Annular Combustors
Authors: Fournier Guillaume J. J. , Schaefer Felicitas , Haeringer Matthias , Silva Camilo F. , Polifke Wolfgang
Published: October 2022

Thermoacoustic systems can exhibit self-excited instabilities of two nature, namely cavity modes or intrinsic thermoacoustic (ITA) modes. In heavy-duty land-based gas turbines with canannular combustors, the cross-talk between cans causes the cavity modes of various azimuthal order to create clusters, i.e. ensembles of modes with close frequencies. Similarly, in systems exhibiting rotational symmetry, ITA modes also have the peculiar behavior of forming clusters. In the present study, we investigate how such clusters interplay when they are located in the same frequency range. We first consider a simple Rijke tube configuration and derive a general analytical low-order network model using only dimensionless numbers. We investigate the trajectories of the eigenmodes when changing the downstream length and the flame position. In particular, we show that ITA and acoustic modes can switch nature and their trajectories are strongly influenced by the presence of exceptional points. We then study a generic can-annular combustor. We show that such configuration can be approximated by an equivalent Rijke tube. We demonstrate that, in the absence of mean flow, the eigenvalues of the system necessarily lie on specific trajectories imposed by the upstream conditions.
Modelling and Optimization of a Hospital Gas Turbine-Based Cogeneration System
Authors: Zini Marco , Carcasci Carlo , Sodini Roberto
Published: October 2022

Hospitals are among the most energy-intensive commercial buildings in the service industry and their energy demand is characterized by specific features, being operative 24 hours a day, 365 days a year. Moreover, several activities performed inside the building require strict control of the indoor climate conditions to ensure comfort and security standards. Often, they present complex HVAC systems that need various energy forms like electricity and thermal energy in the form of hot water, chilled water and steam. Consequently, hospitals and healthcare facilities are ideal application to exploit the cogeneration systems potential. Indeed, the number of hospitals using CHP systems has grown steadily in past years. Hospitals that use CHP take advantage of favourable rate structures and protect themselves from rising electricity prices. Since CHP uses waste heat to produce thermal energy for heating and cooling, hospitals using CHP systems are more energy-efficient, leading also to a reduction of the global emissions connected to the hospital activity. The present study involves the development of a numerical model of the gas turbine-based cogeneration system installed in a hospital facility. The realized model has been used to define the system management strategies that enabled two achievements. The minimization of the main global emissions parameters of the system as CO and NOx and the maximization of operational CHP parameters as total efficiency and primary energy saving (PES). The present work describes in detail the realized model and its exploitation, leading to define the optimal system management strategy based on control parameters applicable to the real test case management system.
Roughness-Resolved LES of Additive Manufacturing-Like Channel Flows
Authors: Meynet Serge , Barge Alexis , Moureau Vincent , Balarac Guillaume , Lartigue Ghislain , Hadjadj Abdellah
Published: October 2022

In the last decade, progresses in additive manufacturing (AM) have paved the way for optimized heat exchangers whose disruptive design will heavily rely on predictive numerical simulations. However, due to typical roughness induced by AM, current wall models used in steady and unsteady 3D Navier-Stokes simulations do not take into account such characteristics. For the development and assessment of novel wall models for AM, a high-fidelity roughness-resolved Large-Eddy Simulation (RRLES) database is built. This article describes the numerical setup and the methodology used for conducting RRLES, from surface generation to post-processing. In addition, three different cases representing two printing directions plus a streamwise and spanwise isotropic case are investigated. While the roughness distributions are the same in the three cases, the effective slope (ES) is very different and the impact of this parameter on turbulence and heat transfer is analyzed at different Reynolds numbers.
Design and Commissioning of the Constant Condition Dynamic Test Rig
Authors: Pearce Robert , Tombs Michael , Hussain Zahid
Published: October 2022

This paper presents details and data from a new facility designed, constructed and commissioned at the Oxford Thermofluids Institute. The constant condition dynamic test rig is designed primarily to test aero-engine butterfly valves under a wide range of representative conditions. A novel strategy of actively controlled downstream valves placed between the test section and vacuum tank is used to provide a tightly controlled constant pressure drop across the test section. This strategy effectively synthesises a much larger volume than the physical size of the available downstream tank, providing long test times under true steady state conditions. Full experimental test rig details are given in this paper with an overview of the control strategy and verification of the test conditions obtained in this novel rig configuration. Primary data outputs of discharge and torque coefficients for the test valve are presented for static points across the full range of valve opening with RANS CFD data included for verification of the experimental data. This initial commissioning data is presented at a low pressure ratio of approximately 1.05. Localized pressure data are presented for analysis of local flow fields around the valve and for further validation. Finally, a modified discharge coefficient formulation is presented to account for cross-sectional area changes in the test rig and to ensure the experimental data is directly transferable to practical engine cases.
Analysis of a Multi-Generation Renewable Energy System with Hydrogen-Fueled Gas Turbine
Authors: Bahlawan Hilal , Losi Enzo , Manservigi Lucrezia , Morini Mirko , Spina Pier Ruggero , Venturini Mauro
Published: October 2022

It is now universally established that the use of fossil fuels is responsible for environmental issues such as global warming. Among the different renewable energy sources, solar energy is considered one of the most affordable resources for meeting current energy demands and mitigating environmental problems. However, the exploitation of solar energy is challenging because of both diurnal and seasonal variations. Power-to-Hydrogen technologies can play a key role to counterbalance the variation of solar irradiance. Moreover, hydrogen-fueled gas turbines are considered promising technologies to decarbonize the electricity sector.

To tackle these concerns, this paper presents a multi-generation energy system operated in island mode in which a hydrogen-fueled gas turbine is coupled with a solar photovoltaic plant, an electrolyzer, an absorption chiller, electric and thermal energy storage, as well as a hydrogen storage. Therefore, the energy system is 100% based on renewable energy. The sizes of the components and the respective energy management strategy are optimized by maximizing the exploitation of renewable energy sources, while the supply of electricity from the national grid must be null. Moreover, the effect of ambient conditions on the optimal sizing is also investigated by considering the thermal, cooling and electrical energy demands of two case studies located in two different climatic zones. The paper demonstrates that the adoption of hydrogen-fueled gas turbines coupled with Power-to-Hydrogen technologies can effectively support the transition towards a clean energy supply. Moreover, this study provides a procedure for the optimal sizing of a multi-generation energy system fully based on solar energy, by also demonstrating that both PV panel area and hydrogen storage volume are feasible, if compared to the considered district layout.
Blade Health Monitoring System for Gas Turbines Subjected to Contaminated Air
Authors: Tayebi Kamel , Khalidi Abdurrahman , Dawood Alaaeldin
Published: October 2022

Air contamination continues to cause corrosion sometimes leading to catastrophic failures costing tens of millions of dollars in repair/replacement and revenue losses. In the case of heavy-duty gas turbines in the power industry, the problem starts with pitting due to corrosion and progresses to crack initiation, then crack extension due to cyclic load then to unstable crack propagation leading ultimately to blade liberation which in turn creates an extended trail of damage through the various stages of the compressor and the casing. This type of failure usually requires total rotor replacement. It is important to identify the early stages of crack formation and relate it to the level of air contamination and operational parameters of the turbine.

This paper addresses improved methods of commissioning and integrated monitoring of a blade health monitoring (BHM) system installed on a turbine that witnessed a previous compressor failure. We particularly show how BHM can be combined with engine operation information for a better understanding of the impact of operational changes on blade behavior. Such an understanding is necessary to detect potential changes in amplitude or frequency characteristics due to damage initiation and progression. It also enables the development and continuous update of site-specific and engine-specific knowledge bases that can be used in predictive analysis and effective decision making for optimal operational performance.
Secondary Air System: A Current Review and Future Investigations
Authors: Fuchs Fabian , Cordes Laura
Published: October 2022

Since every new scientific work starts with a comprehensive literature study about the state of the art, this paper should give an overview about previous, but still useful, and more recent publications to describe a secondary air system (SAS) for gas turbines. Nevertheless, in current times it is impossible to present a complete research, but the well-disposed reader will get a meaningful insight and may use the references as a start for their own detailed search. The first part will give a description of a typical set up of a SAS and the common flow elements that can be found along the flow path. It also includes an explanation of the elements operating behavior, especially regarding the pressure and temperature changes as well as the resulting air mass flow. In the second part the authors describe the plans at the German Aerospace Centers (DLR) Institute of Test and Simulation for Gas Turbines in the SAS’ field of research.
Heat Transfer Coefficient and Adiabatic Wall Temperature Measurements on a High-Pressure Turbine Nozzle Guide Vanes With Representative Inlet Swirl and Temperature Distortions
Authors: Bacci T. , Picchi A. , Babazzi G. , Facchini B. , Cubeda S.
Published: October 2022

Combustor-exit conditions in modern gas turbines are generally characterized by significant temperature distortions and swirl degree, which in turn is responsible for very high turbulence intensities. These distortions have become particularly important with the introduction of lean combustion, as a mean to control NOx pollutant emissions. For this reasons combustorturbine interaction studies have recently gained a lot of importance. Past studies have focused on the description of the effects of turbulence, swirl degree and temperature distortions on the behavior of the high pressure stages of the turbine, both considering them as separated aspects, and accounting for their combined impact. Aspects like pressure losses, hot streaks migration and film-cooling behavior have been widely investigated. Even if some studies have focused on the characterization of the heat transfer coefficient (HTC) on the nozzle guide vane external surface, none of them have addressed this aspect from a purely experimental point of view. Indeed, when inlet conditions are characterized by both swirl and temperature distortions they represent a severe challenge for the commonly adopted measurement techniques. The work presented in this paper was carried out on a non-reactive, annular, three-sector test rig made by a non-reactive combustor simulator and a nozzle guide vane cascade; it is able to create a representative combustor outflow, characterized by all the flow characteristics described before. A novel experimental approach, that was developed in a previous work, was exploited to experimentally retrieve the heat transfer coefficient and the adiabatic wall temperature distributions on a non-cooled nozzle guide vane. Temperature measurements on the cascade inlet and outlet planes were also used to provide boundary conditions and achieve a better understanding of the investigated phenomena. The results allowed to evidence the effect of the inlet swirl on the heat transfer coefficient distribution, as well as the evolution of the temperature distribution on the vane surface moving through the cascade, constituting the first attempt to evaluate these aspects from a purely experimental point of view.
Experimental Investigation of Local Heat Transfer in a Rotating Two-Pass Cooling Channel Using the Transient Thermochromic Liquid Crystal (TLC) Technique
Authors: Waidmann Christian , Poser Rico , Gutiérrez de Arcos David , Göhring Michael , von Wolfersdorf Jens , Semmler Klaus , Jäppelt Bernhard
Published: October 2022

A test rig for the investigation of rotating turbine blade internal cooling channel configurations is presented. Local heat transfer distributions are evaluated using the transient thermochromic liquid crystal (TLC) technique. The rig can be operated at rotational speeds of up to 900 rpm, mass flow rates between 3 g/s and 30 g/s, fluid temperatures between −100 °C and +80°C and fluid pressures of up to 10 bar. This allows for a broad range of possible test conditions.

The investigated cooling channel model is a two-pass leading edge configuration manufactured out of acrylic glass. It consists of a first pass with a trapezoidal cross-section and radially outward flow, a 180° bend, and a second pass with a rectangular cross-section and radially inward flow. The suction side and pressure side surfaces are equipped with angled ribs.

The evaluation method is based on the measurement of TLC indication times. A sudden fluid temperature change is applied to cool down the TLC-coated heat transfer surfaces. This induces a TLC color play which is captured using cameras that are co-rotating with the test model. Assuming 1D heat conduction inside a semi-infinite wall, heat transfer coefficients are then calculated from the TLC indication times and the fluid reference temperature measurements.

The data evaluation procedure and the results of a typical experiment are presented. Heat transfer data are shown in contour plots of the Nusselt number distribution. Furthermore, a method to directly compare the results of a rotating with a corresponding non-rotating experiment using normalized Nusselt number ratios is shown. Finally, data reduction methods are described that provide line-averaged values as well as histograms of normalized Nusselt number ratios.
Numerical Prediction of a Lean Blow-Out Event of a Lab-Scale, Swirl-Stabilized Spray Flame
Authors: Ruoff Stephan , Eckel Georg , Le Clercq Patrick , Aigner Manfred
Published: October 2022

Alternative jet fuels have a high potential to reduce emissions in aviation and to increase the independence from mineral oil. However, as a safe operation must be guaranteed, new fuels have to pass elaborate and expensive tests to be finally certified. To reduce the costs and time of the certification process, numerical simulations can be used to assess the impact of a new fuel on combustion. Further, the detailed simulations provide an insight into the fuel sensitive sub-processes. The lean blowout (LBO), i.e. the lower stability limit of a gas turbine combustor, is of primary concern for safe operation and the approval of alternative jet fuels. The paper at hand focuses on the formulation of a calculation protocol for the numerical representation of a lab-scale LBO experiment. The test case is a swirl-stabilized spray flame, which mimics several key features of aero-engine combustors. The LBO-limits are determined by a stepwise reduction of the fuel mass flow starting from a stable operation point above the measured blowout limit. Towards extinction, the heat release rate in the combustor drops. Furthermore, fuel is still evaporating, but less fuel is burned, leading to an accumulation of fuel in the combustion chamber. The blow-out is defined by a steep drop in heat release combined with a large increase of the gaseous fuel mass fraction in the computational domain. The semi-automated calculation protocol is able to successfully capture a blowout event at an equivalence ratio of ϕ = 0.32 and can thus be applied to evaluate alternative jet fuels in the future. In addition, a reignition event is observed for equivalence ratios slightly above ϕLBO.
An Approximate Time Domain Nonlinear Harmonic Method for Analyzing Unsteady Flows With Multiple Fundamental Modes
Authors: Wang Dingxi , Zhang Sen
Published: October 2022

In this paper, a new hybrid time and frequency domain method called the approximate time domain nonlinear harmonic method is proposed for a robust and efficient analysis of turbo-machinery unsteady flow with more than one fundamental modes. The proposed method combines the features of the nonlinear harmonic method and the time domain harmonic balance method. Unsteady flow components are grouped according to their fundamental frequencies and inter blade phase angles and separate unsteady flow governing equations are constructed for each mode group. These mode groups are connected using the least squares method based Fourier transform. The proposed method is expected to be exact for a linear problem, but approximate for a nonlinear problem. Three sets of analyses with increasing level of difficulties are presented to demonstrate the validity and effectiveness of the proposed method by comparing it with the time domain harmonic balance method based upon the almost periodic Fourier transform.
Effects of the Ribbed-Squealer Tip on the Blade Tip Aerothermal Performance in a High Pressure Gas Turbine Cascade
Authors: Du Kun , Li Huarong , Hui Na , Gao Yuanyuan , Liu Cunliang
Published: October 2022

In modern gas turbines, High-temperature gas gives rise to the heat load dramatically to the tip region, inducing the leakage flow through the blade tip gap by the lateral pressure difference. Squealer tip, as an efficient technique, has been widely utilized to reduce the tip leakage flow and the heat load. In order to enhance efficiency of squealer tip, the present research proposed kinds of ribbed-squealer tip. Ribs along the axial direction and the circumferential direction are inserted inside the conventional squealer tip. The effects of different squealer tips on the blade tip leakage flow and heat transfer characteristic were numerically investigated. Three-dimensional (3D) Reynolds-Averaged Navier-Stokes (RANS) equations and standard k-ω turbulence model were solved to conduct the simulations. The numerical results indicated that the ribs significantly alter the full development of various vortices inside the tip cavity, thus improving the aerothermal performance in the ribbed-squealer tip. In all simulated cases, the case with the staggered rib within 0–40% chord region obtains the smallest heat transfer coefficient, and achieve the best performance in minimizing the tip leakage mass flux within the 0–10% stream-wise region.
The Effect of Nitrogen Impurities on Oxy-Fuel Combustion Under Supercritical-CO2 Conditions
Authors: Gokulakrishnan Ponnuthurai , Shao Jiankun , Klassen Michael , Davidson David , Hanson Ronald
Published: October 2022

The direct-fired supercritical-CO2 (sCO2) cycle has demonstrated the ability to produce clean energy by burning hydrocarbon feed stocks under oxy-fuel conditions. High-pressure operation of the direct-fired cycle allows for more economic extraction of CO2 for carbon capture and storage. However, the presence of nitrogen impurities in the oxidizer (i.e., N2) and in fuel feed stocks (e.g., NH3) can generate NOx in the exhaust. The presence of NOx in the recycled-CO2 stream can impact the combustion process as well as the structural integrity of the system. Also, even trace amounts of nitrogen oxides (considered acid gases) can be detrimental for CO2 capture, transportation and storage at supercritical conditions.

Therefore, it is critical to understand and accurately model the effects of nitrogen impurities on NOx formation and the impact of NOx in the recycled CO2 on combustion kinetics under oxy-fuel sCO2 conditions. It is also important to understand the effects of pressure with a sCO2 medium as the direct-fired sCO2 cycle operates up to 300 atm pressure. In this work, experimental and modeling work were performed to study the effect of nitrogen species on emissions as well as effect of NOx on ignition of CH4 and syngas fuels at sCO2 conditions. A chemical reactor network simulation was used to investigate the effects of nitrogen impurities in fuel and oxidizer stream on emissions from a direct-fired combustor condition. Monte Carlo simulations were also carried out to study the impact of model input variables on the emission profile.

High-pressure shock tube ignition delay time experiments were performed to investigate the effect of NOx on ignition at conditions relevant to direct-fired oxy-fuel sCO2 combustion. The ignition delay time measurements were made for syngas and CH4 fuels with and without NO addition using CO2 as bulk diluent at nominal pressures around 100 atm. Experimental data showed that the presence of NO promotes the ignition at the oxyfuel sCO2 combustion conditions. Reaction sensitivity analyses and model uncertainty analyses were conducted to identify important reactions and their rate uncertainty on the model predictions, respectively.
Investigation of the Performance of Hydrogen-Fueled Wankel Rotary Engine Using 0-D Model
Authors: Du Yang , Yang Zhenghao , Geng Qi , Wang Rui , He Guangyu
Published: October 2022

This paper establishes a 0-D model based on the real gas properties and laminar flame propagation speed to predict the performance of a hydrogen-fueled Wankel rotary engine. The performance comparative analysis between hydrogen-fueled and gasoline-fueled Wankel rotary engines is conducted under the same fuel heat value input. Furthermore, the effects of rotational speed, ignition advance angle on the chamber temperature, pressure, heat release rate, engine effective fuel consumption, indicated thermal efficiency and effective power output are investigated. are evaluated. The results show that as the gasoline is replaced by hydrogen with the constant total input heat value, the effective power and indicated thermal efficiency are reduced by 16.93% and 5.97% at design condition, respectively. As the rotational speed increases from 4000rpm to 10000rpm, the effective powers of gasoline and hydrogen are increased by 204% and 238%, respectively. The peak pressure of hydrogenfueled engine appears is 28° ahead of gasoline-fueled engine. With the decreasing ignition advance angle, the effective power output and indicated thermal efficiency of gasoline-fueled engine firstly increase and then drop, while that of hydrogen-fueled increase. Meanwhile, the combustion duration angles of two fuels decrease with decreasing ignition advance angle. The maximum indicated thermal efficiencies of 31.7% and 35.4% for hydrogen-fueled and gasoline-fueled engines are obtained at ignition advance angles of 7°and 27° with nominal rotational speed of 7000rpm, respectively.
Improvement of the Primary Atomization Model for Jet Into Subsonic Crossflow
Authors: Ju Hongyu , Suo Jianqin , Li Yue , Zheng Longxi
Published: October 2022

An improved primary atomization model for the jet-in-crossflow (JICF) atomization has been suggested and incorporated into the solver SprayFoam of OpenFOAM. The assumption of replacing jets with blobs, the maximum growth rate of the Kelvin-Helmholtz (K-H) wave, and its corresponding wavelength in the WAVE model are inherited. The present model assumes that the blobs move uniformly in the jet direction and accelerate uniformly in the crossflow direction to simulate the jet trajectory. It considers the Rayleigh-Taylor (R-T) wave on the liquid surface and assumes that the growth rate determines the R-T wave and K-H wave competition. The frequency, position, and mass of liquid surface breakup, the velocity, and the size of stripping drops are given in detail. Results of the present model have been compared with the experimental data in other literature under varying momentum flux ratios, Mach number, and air Weber number. The agreement between calculated results and the measured value is generally good, and a quantitative assessment of the model performance has been conducted.
Highly Resolved Large-Eddy Simulations of a Transonic Compressor Stage Midspan Section Part I: Effect of Inflow Disturbances
Authors: Bode Christoph , Przytarski Pawel J. , Leggett John , Sandberg Richard D.
Published: October 2022

Flows in modern compressors are highly complex. They are subject to adverse pressure gradients, high levels of unsteadiness and often operate at transonic conditions. Such conditions often render low order methods such as URANS unreliable. This is due to the inherently unsteady nature of shock-boundary layer interaction as well as the interaction between deterministic and stochastic unsteadiness. These issues are further exacerbated by the current design trends towards more compact machines with higher work coefficients. It is therefore desirable to study the flow within a transonic compressor stage using highly-fidelity scale resolving simulation. To enable fully wall resolved stage calculations at a realistic rotor Reynolds number of 1 × 106, a quasi three-dimensional translational setup was carefully generated to feature similar midspan blade loadings to the three-dimensional rotational set up of the Transonic Compressor Darmstadt. Two cases were considered, one with a laminar inflow to the rotor and one with inflow turbulence. It is found that the inflow turbulence suppresses the rotor suction side separation bubble with implications on the shock-boundary layer interaction, mainly in terms of an upstream moved shock location and changes to the shock oscillations, and the shock-related passage losses. The changes to the early development of the rotor suction side boundary layers also affects the boundary layer losses. The stator suction side boundary layer on the other hand appears insensitive to the introduction of inflow disturbances. However, a larger passage loss is found for the laminar inflow case in the stator. Additional URANS calculations of the same setup show overall good comparison with the high-fidelity results for most integral values, but lack in predictive accuracy for some details, such as shock boundary layer interaction as well as wake and passage losses.
Design Optimization of a High-Speed Twin-Stage Compressor for Next-Gen Aircraft Environmental Control System
Authors: Giuffre’ Andrea , Colonna Piero , Pini Matteo
Published: October 2022

The environmental control system (ECS) is the largest auxiliary power consumer, i.e, around 75% of non-propulsive power, among the aircraft subsystems. The adoption of a novel ECS architecture, based on an electrically-driven vapor compression cycle system, can enable a twofold increase of coefficient of performance (COP), as compared to the conventional air cycle machine (ACM). The core of this technology is a high-speed, miniature centrifugal compressor, consisting of two impellers mounted in back-to-back configuration, and running on gas bearings operating with refrigerant. The fluid dynamic design optimization of the twin-stage compressor, to be installed in the vapor compression cycle test rig under realization at Delft University of Technology, is documented in this paper. First, the scaling analysis for centrifugal compressor is extended to provide guidelines for the design of twin-stage machines. Then, a multi-objective conceptual design optimization is performed by resorting to an in-house reduced-order model (ROM), coupled to a genetic algorithm. The fluid dynamic performance and the structural integrity of the optimal design are assessed by means of a hybrid framework, encompassing CFD and ROMs, and by FEA. The results show that it is possible to design a twin-stage compressor for the target application, featuring an average efficiency higher than 70%, a maximum compression ratio exceeding 9, and an operating range of 0.27 at the design rotational speed, despite the detrimental effects of motor cooling and miniature size.
Modal Identification of Bladed Disks by Time-Frequency Analysis of the Non-Synchronous Response
Authors: Carassale Luigi , Guida Roberto , Marrè-Brunenghi Michela
Published: October 2022

In some circumstances it is impossible to exploit resonance crossings to identify the modal properties of rotor disks. In these cases, the identification process must rely on nonsynchronous vibrations and becomes challenging for two reasons. First, the signals are weak (compared to the levels measured during resonance crossings) and random, thus an averaging procedure is necessary. Second, the dynamical system is time-variant due to the variation of the rotor speed. This paper presents a modal identification procedure formulated in the framework of the time-frequency analysis. A region of the time-frequency plane is stretched to map the system into a fictitious LTI system. Then, the PSD of the response is computed by an averaging procedure. Finally, the modal properties are estimated through an output-only modal identification algorithm. The procedure is applied to simulated and experimental data regarding a bladed disk of a steam turbine.
Performance Investigation of Airfoils for Axial Flow Fans in Low Solidity Cascades Operating at High Inlet Flow Angles
Authors: Cravero Carlo , Milanese Gabriele
Published: October 2022

Axial flow fans are usually characterized by blade sections with low solidity and high inlet flow angles.

Two main approaches are followed in the preliminary design phase, to take into account blade interaction effects: the use of available airfoil cascades data (or related correlations) and that of isolated airfoil data together with interference coefficients.

The working conditions of low solidity airfoil cascades with highly tangential inflow are not widely studied in literature, leaving the designer the possibility to rely on limited cascade data or often on the use of isolated airfoil data, with the assumption of negligible interference effects.

A systematic investigation of the above working conditions for airfoil cascades is performed with RANS simulations. Three different airfoils are used to evaluate the influence of the design lift coefficient and maximum blade thickness. The results provide a better insight into the aerodynamic behaviour of airfoil sections in such operating conditions, showing that interactions cannot be neglected.

The use of metamodeling coupled with CFD simulations is presented as a suitable tool for treating interference effects within the fan design process.

The main findings of the present work can be used as a support for design choices as well as for developing design strategies both for the fan blades and for the airfoil sections.
An Analytical-Empirical Approach to Model Liquid Fuel Combustion Dynamics
Authors: Magina Nicholas , Han Fei , Samarasinghe Janith , Venkatesan Krishna
Published: October 2022

Combustion dynamics is one of the most important factors to be understood and navigated in the design of modern gas turbine combustors. For liquid-fueled combustors this becomes especially challenging given the complexity of additional physics involved, which includes fuel atomization and transport, mixing, reactive kinetics, and acoustics. In this paper an analytical approach to model combustion dynamics is described for an industrially relevant liquid fuel nozzle. For determining the flame fluctuating heat release response to inflow perturbations, an analytical liquid-fuel model was leveraged, developed as an extension and augmentation of traditional diffusion flame models. The acoustic response of the combustor was calculated using 3D finite-element models, including acoustic damping effects of key geometric features. These individual responses were then utilized in a time-domain Green’s function based approach to calculate the response, including growth and saturation, of pressure oscillations. To gain modeling approach confidence and enhanced accuracy, some model parameters impacted by real effects were calibrated manually to achieve better general agreement with the breadth of experimental and computational data available. This included measured flame transfer functions and dynamics metrics, both frequencies and amplitudes, and computed mode shapes and flame shapes. The calibrated modeling approach was then applied to two different combustors, a single-cup and full-annular configurations. It was found that the results agreed well with test data, especially trend-wise, across a modest range of operating conditions. However, at conditions which extended too far beyond the bounds of the data used for model calibration, model inaccuracies became evident. Lastly, sources of model inaccuracies and areas for improvement were discussed.
Extending Highly Loaded Axial Fan Operability Range Through Novel Blade Design
Authors: Lopez Diego I. , Ghisu Tiziano , Kipouros Timoleon , Shahpar Shahrokh , Wilson Mark
Published: October 2022

The tip clearance size has historically been considered to be the main factor affecting stability range in axial fan and compressors. This paper reveals that the stall characteristics are defined by the axial momentum flux of the tip leakage flow and that tip clearance is primarily a strong driver for this metric. A bespoke methodology for carefully tailoing the axial momentum via three-dimensional design is presented, which enables a higher degree of control over the stability range for cases where the tip clearance responds to other considerations and cannot be defined for this purpose. The effect of the axial momentum on efficiency is also addressed and the trade-off between operability range and design point performance derived. The results show that that the conditions for optimal stability differ from those for optimal efficiency and that control over the axial momentum enables tuning the design for a desired exchange. Numerical simulations have been employed to drive the analysis through a high-fidelity computational model whose behavior is supported by rich set of experimental data. Contrary to current belief, results further indicate that an accurate characterization of stall, including onset mechanism, can be achieved through steady-state simulations, minimising the need for expensive time-accurate computations during the design phase.
Assessment of Computational Fluid Dynamic Modeling of Multi-Jet Impingement Cooling and Validation With the Experiments
Authors: Tabassum Sadiya , Hilfer Michael , Brakmann Robin G. , Morsbach Christian , Willert Christian , Matha Marcel , Schroll Michael
Published: October 2022

The current study involves numerical and experimental investigations of circular in-line jets impinging on a heated flat plate. The generic configuration is characterized by 9 jets, each with a diameter of D = 0.0152 m. The jets are influenced by a self-generating crossflow and are positioned at a nozzle-to-plate distance (H/D) of 5 and a jet pitch (p/D) of 5. The steady Reynolds-Averaged Navier-Stokes (RANS) simulations are performed for turbulent jet Reynolds numbers with the DLR in-house CFD code TRACE. The Menter k-ω SST model is applied for turbulence modeling and the turbulent scalar fluxes are modeled based on the Reynolds analogy for a constant turbulent Prandtl number. To gain a closer insight into the impingement jet physics, high-resolution near-wall velocity and thermal fields are obtained through Large Eddy Simulations (LES) and measurements from the Particle Image Velocimetry (PIV). Focus is laid on the comparison of RANS results with the LES data and the experimental data. The results exhibit a qualitative similarity between the simulations and the experiments. Furthermore, correlations of the Nusselt number from the literature are used to validate the simulation results.
Automatized Experimental Combustor Development Using Adaptive Surrogate Model-Based Optimization
Authors: Reumschüssel Johann Moritz , zur Nedden Philipp Maximilian , von Saldern Jakob G. R. , Reichel Thoralf G. , Ćosić Bernhard , Paschereit Christian Oliver
Published: October 2022

Lean premixed combustion is the state of the art technology to achieve ultra low NOx emissions in stationary gas turbines. However, lean premixed flames are susceptible to thermoacoustic instabilities, lean blowout and flashback. The design of such a combustion system is thus always related to the balancing between the levels of emissions and flame stability. Data-driven optimization methods and the adaptation of models through artificial intelligence have experienced a surge in development in the past years. The goal of this study is to show the potential of these methods for gas turbine burner development. A special pilot burner that features 61 different positions of fuel injection, manufactured by means of selective laser melting is used to modify the gas mixture close to the flame anchoring position. Each of the injector lines is equipped with an individual valve, such that the distribution of fuel-air mixture can be modified variously. Installed into an industrial MGT6000 swirl combustor, a data-driven optimization method is used to find an optimal subset of injection locations by automated experiments. The method uses a surrogate model that is based on Gaussian Processes Regression. It is adopted for experimental optimization, keeping measurement efforts to a minimum. The optimizer controls the fuel valves and uses live measurements to find a distribution that generates minimal NOx emissions, while ensuring flame stability. The solutions found by the optimization scheme are analyzed and advantages and limitations of the approach are discussed.
Parametric Studies and Simulations of a Hydrogen Micromix Combustor
Authors: French Ainslie , Mingione Giuseppe , Schettino Antonio , Roncioni Pietro , Vitagliano Pier Luigi , Minervino Mauro
Published: October 2022

The use of hydrogen as an alternative fuel in the combustion chamber of an aircraft turbine engine would offer a practical solution to reducing levels of emissions which contribute to atmospheric pollution. In recent years various designs of the basic system component of such an engine have been proposed being described as the hydrogen micromix combustor. This technology requires the design and development of a safe mechanism for hydrogen combustion which avoids auto-ignition and flashback and permits the initial balance and mixing of a hydrogen-air mixture to produce thrust from the combustion of hundreds of miniature low temperature diffusion flames which produce extremely low levels of NOx.

In this paper a potential geometry and typical operating conditions of such a micromix combustor has been selected for a critical examination of the numerical modelling with particular attention to the levels of NOx predicted. In particular the level of grid independence of the NOx modelling is assessed as well as the variations in NOx levels generated in the march towards steady state solutions for various numerical methods.

Additionally, a series of parametric studies associated with modifications of the basic micromix combustor design are explored to verify both the consistency in the numerical methods adopted as well as assessing the impact of such modifications on the overall micromix combustor performance.
Operating Characteristics of a Flameless Combustor Obtained By Experiments Informed Modelling
Authors: Sampat Rishikesh , Goselink Niek , Schrijer Ferry , Gangoli Rao Arvind
Published: October 2022

Flameless Combustion is an interesting low NOx combustion technology for gas turbine engines. In order to design systems for stringent performance standards, it is important to understand emission formation in this regime. To this end, the characteristics of a combustor capable of operating in the Flameless regime are studied. Particle Image Velocimetry and thermocouple measurements were performed to obtain the velocity field and gas temperatures respectively, in the combustor under reacting conditions. Results from experiments were used to generate an “informed” chemical reactor network (CRN) model from which, temperature and species distributions were obtained. As such, this paper presents measured data and a methodology to combine it with CRN modelling to obtain gas composition and temperature. The temperature, NOx, CO and O2 mole fractions obtained at three different operating conditions shall be validated with gas composition measurements in the future.
Methodology for the Pitch Controller Wind Prediction System in Small Wind Turbines
Authors: Lara-Mendoza Oscar , Jáuregui-Correa Juan Carlos , Chavero-Navarrete Ernesto , García-Martínez José R.
Published: October 2022

Nowadays, it is necessary to generate electrical energy using renewable natural resources even when the wind is limited. Small wind turbines are required to operate even with turbulence due to operation height. In this research, a fuzzy logic controller for the angular position of the blades in a wind turbine is proposed. The pitch system regulates the rotational speed of the generator to keep it at a nominal value. The mechanics of a blade pitch system usually act slower than an electrical control signal, which causes problems when the blades need fast positioning. The need for a quick blade positioning response arises when wind gusts occur. Wind gusts are undesirable in all regions of wind turbine operation, making efficient pitch control a problem. This work develops the experimental platform on a small wind turbine located in Mexico at the Autonomous University of Queretaro (UAQ). The wind speed conditions in a non-steady-state regime are presented at the experimental site. A weather station meters ahead of the wind turbine anticipates the position of the rotor blade before being impacted. Results of this methodology prove that the rotor blades reach in advance the ideal position to receive air gusts. This methodology will contribute to the efficient and safe utilization of wind turbines with turbulent wind speeds.