bluuebunny/crossref_metadata_2025 huggingface dataset:
Emissions Performance of Staged Premixed and Diffusion Combustor Concepts for an NH3/Air Flame With and Without Reactant Humidification
Authors: Pugh D. , Valera-Medina A. , Bowen P. , Giles A. , Goktepe B. , Runyon J. , Morris S. , Hewlett S. , Marsh R.
Published: January 2021

Renewably generated ammonia offers a form of carbon-free chemical energy storage to meet the differences between uncertain renewable supply and fluctuating demand, and has the potential to support future energy requirements as a power-to-X concept. The storage and transportation characteristics of NH3 are favorable compared with H2, however there are significant combustion research challenges to enhance fuel reactivity whilst reducing harmful emissions production.

The purpose of the presented work was to evaluate different fuel delivery concepts for a representative GT combustor. An experimental and numerical comparison was made between swirl-stabilized premixed and diffusion NH3-air flames at elevated inlet temperature (473 K). The exhaust NOx and unburned NH3 emissions generated from each concept were quantified to optimize operational combustor performance. High-speed OH* and NH2* chemiluminescence was employed to characterize the change in flame topology with variation in fuel-air equivalence ratio, and the resultant influence on measured emission concentrations. Chemiluminescence intensities were shown to elucidate changes in sampled exhaust emissions, enabling detailed analysis of intermediate chemistry. A comparison was made between experimental data and chemical kinetic simulations with a reactor network model, demonstrating the sensitivity of NOx emissions to premixed fuel-air equivalence ratio.

A comparison was also made between exclusive primary airflow, and the staged introduction of secondary air, to quantify the change in NOx production between each configuration and improve fuel burnout. Secondary air loadings were incrementally increased through the combustor, and the change in exhaust emissions mapped. In addition, reactant humidification was employed as a secondary process for NOx reduction, having shown favorable performance with NH3/H2 mixtures to limit thermochemical NO production. The efficacy of humidification was compared for both premixed and diffusion configurations.
Additively Manufactured Compliant Hybrid Gas Thrust Bearing for sCO2 Turbomachinery: Experimental Evaluation and Fluid-Structure Model Predictions
Authors: Ertas Bugra , Gary Keith , Delgado Adolfo
Published: January 2021

The following paper presents rotating test results and advances an analytical predictive fluid-structure model for a new type of gas lubricated thrust bearing fabricated using direct metal laser melting (DMLM). The bearing concept in the present study is a compliant hybrid gas thrust bearing that uses external pressurization to increase load carrying capacity, where the testing campaign in the present study was only focused on steady state static performance. The need for the bearing concept comes from enabling highly efficient supercritical carbon dioxide (sCO2) turbomachinery by replacing oil-lubricated bearings with process gas lubrication. Leveraging the process gas of the turbomachine for bearing lubrication results in lowered bearing power loss [1], simplified mechanical design, and allows for novel oil-free hermetic drivetrains resulting in an efficient emission-free system [2,3]. The new concept utilizes hydrostatic pressurization on individual tilting pads flexibly mounted with hermetic squeeze film dampers (HSFD). The paper focuses on rotating tests of a 173mm outer diameter gas thrust bearing in air up to 10krpm and hydrostatic inlet pressures to 365psi (2.52MPa). The influence of thrust runner speed and bearing inlet pressure on force deflection characteristics and load carrying capability of the gas film were experimentally evaluated. The present work also advances a predictive fluid-structure thrust bearing model using an isothermal ideal-gas based compressible Reynolds flow equation directly coupled to a lumped stiffness element possessing axial and rotational degrees of freedom. The rotating testing demonstrated load capability of 1,816 lbs (8.1KN), which equates to a thrust bearing unit load of 67psi (0.46 MPa). Gas film force-deflection curves reveal a nonlinear relationship between thrust load and film clearance. Comparison of film thickness values with the predictive model show good agreement under high load and inlet pressure, however deviate as load and pressure decrease. Load capability was shown to increase with increasing hydrostatic inlet pressure while the increase in thrust runner speed revealed a small decrease in load capacity.
Single and Multiple Circumferential Casing Groove for Stall Margin Improvement in a Transonic Axial Compressor
Authors: Mustaffa A. F. , Kanjirakkad V.
Published: January 2021

The stability limit of a tip-stalling axial compressor is sensitive to the magnitude of the near casing blockage. In transonic compressors, the presence of the passage shock could be a major cause for the blockage. Identification and elimination of this blockage could be key to improving the stability limit of the compressor. In this paper, using numerical simulation, the near casing blockage within the transonic rotor, NASA Rotor 37, is quantified using a blockage parameter. For a smooth casing, the blockage at conditions near stall has been found to be maximum at about 20% of the tip axial chord downstream of the tip leading edge. This maximum blockage location is found to be consistent with the location of the passage shock-tip leakage vortex interaction. A datum single casing groove design that minimises the peak blockage is found through an optimisation approach. The stall margin improvement of the datum casing groove is about 0.6% with negligible efficiency penalty. Furthermore, the location of the casing groove is varied upstream and downstream of the datum location. It is shown that the stability limit of the compressor is best improved when the blockage is reduced upstream of the peak blockage location. The paper also discusses the prospects of a multi-groove casing configuration.
Combined Hazard Analyses to Explore the Impact of Liquid Hydrogen Fuel on the Civil Aviation Industry
Authors: Benson C. M. , Holborn P. G. , Rolt A. M. , Ingram J. M. , Alexander E.
Published: January 2021

Interest in green technology in aviation is increasing. To address environmental issues, novel fuels such as cryogenic liquid hydrogen (LH2) are being explored, however there are safety concerns. This work combines safety studies to explore LH2 fuel safety for civil aviation. Preliminary hazard analyses (PHAs) (utilizing over 70 standards and guides) have been performed identifying possible LH2 hazards on-board aircraft. A PHA has also been produced, with industry stakeholder involvement, to understand the major concerns for LH2 use at airports.

Gaps in fundamental knowledge and LH2 technology have been identified, and two of these explored. Firstly, work has been started to understand the fundamental flammability of hydrogen in altitude conditions. Secondly, FLACS CFD modelling has been used to simulate large-scale LH2 pool releases to examine behavior and predict pool size, downwind flammable regions, and flammable mass clouds formed for different environmental conditions and release scenarios. This has identified significant effects of wind speed on buoyancy and flammable cloud travel which must be taken into account of any hydrogen fuel facility design.

This work (part of the EC funded ENABLEH2 project) is some of the first in over a decade to re-examine the safety of hydrogen propulsion in aircraft. This process has identified wide-ranging issues that must be addressed before hydrogen propulsion can be introduced in civil aviation.
Uncertainty Quantification of Spalart-Allmaras Turbulence Model Coefficients for Compressor Stall
Authors: He Xiao , Zhao Fanzhou , Vahdati Mehdi
Published: January 2021

The turbulence model in Reynolds-Averaged Navier-Stokes simulations is crucial in the prediction of the compressor stall margin. In this paper, parametric uncertainty of the Spalart-Allmaras turbulence model in predicting two-dimensional airfoil stall and three-dimensional compressor stall has been investigated using a metamodel-based Monte Carlo method. The model coefficients are represented by uniform distributions within physically acceptable ranges. The quantities of interest include characteristic curves, stall limit, blockage size and turbulence magnitude. Results show that the characteristics can be well predicted in the stable flow range, but the inaccuracy and the uncertainty increase when approaching stall. The stall point of the airfoil can be enveloped by the parametric uncertainty range, but that of the rotor cannot. Sensitivity analyses identified the crucial model coefficients to be source-related, where an increase in the predicted turbulence level will delay the onset of stall. Such results imply that implementing new turbulence production terms with respect to the rotor-specific flow features is likely to improve the model accuracy. The findings in this paper not only provide engineering rules of thumb for the model users, but also guide the future implementation of a data-driven turbulence model for the model developers.
Adiabatic Effectiveness and Thermal Field Measurements of a Shaped Hole in the Showerhead of a Model Turbine Blade
Authors: Moore Jacob D. , Horner Matthew J. , Bogard David G.
Published: January 2021

Few published studies incorporating shaped hole designs in the leading-edge region, or showerhead, of turbine airfoils have been performed; but among them is the indication that shaped holes may offer an improvement in coolant performance compared to cylindrical holes. A shaped hole was designed with the goal of high performance in the showerhead. The performance and physical behavior of this shaped hole design was studied in comparison to a traditional cylindrical hole design in a series of experiments. The geometries were built into the leading edge of a scaled-up turbine blade model for testing in a low-speed simulated linear cascade. To accomplish an engine-representative test environment, a nominally 5% approach turbulence level was used for this study. Adiabatic effectiveness as a function of coolant injection rate was measured for the two designs using infrared thermography. In addition, off-the-wall thermal field measurements were performed for each hole geometry in the leading-edge region. It was found that the shaped hole offered ∼20–100% higher performance in terms of adiabatic effectiveness depending on the coolant injection rate. The thermal field measurements suggested that this was due to the better attachment of the jets exiting the shaped holes, the momenta of which were effectively reduced by the diffusers.
Prediction of the Autoignition of a Fuel Jet in a Confined Turbulent Hot Coflow Using Machine Learning Methods
Authors: Li Suhui , Qian Wenkai , Liu Haoyang , Zhu Min , Markides Christos N.
Published: January 2021

For advanced lean premixed gas turbine combustors that have high inlet air temperatures, autoignition may occur during the fuel/air mixing process, which can cause flame-holing inside the premixing device and burn the hardware. An experimental study was performed using a setup that mimics the fuel/air mixing process of lean-premixed combustors. In the present experiment, the preheated air was injected into a quartz tube, and a fuel jet was injected concentrically into the hot turbulent air coflow. The quartz tube allows for direct observation of the autoignition behavior, which develops when the fuel and air mix as they flow inside the tube. This paper presents a study combining machine learning methods and physical analysis that is aimed at predicting autoignition in such flows. A model for the prediction of autoignition of a fuel jet in a flow configuration referred to as a ‘confined turbulent hot coflow’ (CTHC) is developed using machine learning techniques based on binary logistic regression and support vector machine. Key factors that impact the autoignition phenomenon are identified by analyzing the underlying physics and are used to form the feature vector of the model. The model is trained using data from experiments and is validated by an additional set of data, which are selected randomly. The results show that the model predicts the autoignition event with satisfactory accuracy and quick turnaround. The trained model parameters in turn provide insights into the quantitative contribution of different factors that impact the autoignition event. Thus, the machine-learning based method can form an alternative to CFD modeling in some cases.
Numerical and Experimental Flame Stabilization Analysis in the New Spinning Combustion Technology Framework
Authors: Walter Agostinelli Pasquale , Kwah Yi Hao , Richard Stephane , Exilard Gorka , Dawson James R. , Gicquel Laurent , Poinsot Thierry
Published: January 2021

Global warming, climate change and pollution are burning environmental issues. To reduce the carbon footprint of the aviation sector, aeronautical companies have been striving to lower engine emissions via the development of reliable lean combustors. In this context, effort has been devoted to the better understanding of various flame dynamics with emphasis on thermoacoustic instabilities, lean blow-off and extinctions. In line with this effort, Safran Helicopter Engines has recently developed and patented the revolutionary spinning combustion technology (SCT) for its next generation of combustors. This technology has indeed great flexibility when it comes to ignition and blow-off capabilities. To better understand the various physical mechanisms occurring in a SCT combustor, a joint numerical and experimental analysis of the flame stabilization in this spinning combustion technology framework has been devised. On the experimental side, the NTNU atmospheric annular combustor has been modified to introduce a relevant azimuthal component of velocity while operating under premixed fuel conditions, following the SCT concept. Note that to reduce temperature at the backplane of the chamber, film cooling is incorporated to avoid fuel injector damage. On the numerical side, high fidelity Large Eddy Simulations of the test bench have been carried out with the AVBP code developed at CERFACS, providing insights on the flame stabilization in this unique SCT geometry. In particular, it is noted that there is a strong interaction between the cooling film and the highly swirled flames exiting from the fuel injector bend. In that respect, changing the injector or global equivalence ratios while operating the SCT is shown to affect the combustion of this design.
Application of Artificial Neural Network Based Gas Path Diagnostics on Gas Pipeline Compressors
Authors: Suleiman Suleiman M. , Li Yi-Guang
Published: January 2021

This paper presents the development of an artificial neural network (ANN) Gas Path Diagnostics (GPD) technique applied to pipeline compression system for fault detection and quantification. The work detailed the various degradation mechanisms and the effect of such degradations on the performance of natural gas compressors. The data used in demonstrating the ANN diagnostics is so derived using an advanced thermodynamic performance simulation model of integrated pipeline and compressor systems, which has embedded empirical compressor map data and pipeline resistance model. Implantation of faults within the model is in such a way to account for faults degradations caused by fouling, erosion and corrosion, of various degrees of severities, to obtain wide range of corresponding simulated “true” measurements. In order to account for uncertainties normally encountered in field measurements, Gaussian noise distribution was combined with simulated true measurements, which depends on the instrument’s tolerances. Furthermore, since judicious measurements selection are crucial in ensuring flawless GPD predictions, a sensitivity and correlation analysis of the available measurements revealed that discharge temperature, rotational speed and torque are the most effective measurements for the diagnostics with acceptable degrees of accuracies. The measurements observability technique is a novel approach in pipeline compressor diagnostics. Analytical case studies of the developed method show that, a selected ANN architecture can detect and quantify faults related to degradation in efficiency and flow capacities in the presence of instrument error, varied operational and environmental conditions.
Measured Influence of Clearance and Eccentricity on Brush Seal Leakage Characteristics
Authors: Thorat Manish R. , Bauer Brian
Published: January 2021

Brush seals are used in turbomachinery for reduced leakage as compared to conventional seals such as labyrinth seals. Early applications tended to favor having a line-to-line to a slight interference fit of the bristles to the shaft, but more recent applications have favored the use of a slight initial clearance fit for the purpose of reducing bristle wear. In these brush seals with clearance, the phenomenon of bristle blow-down largely negates the leakage degradation due to clearance, with bristles bending to reduce the clearance gap. This paper presents experimental results for a 10.5 inch bore brush seal with 0.0028 inch bristle diameter. Bristle blow-down is characterized with measurements at three different clearances then compared to a calibrated brush seal leakage model.

Tolerances in brush installation may lead to a brush seal bore that is eccentric to the rotor. The influence of this seal eccentricity on measured leakage performance is also characterized in the paper. Seal eccentricities up to 55% of brush fence height are tested. Effective clearances for eccentric operation are estimated from the measurements.

Brush seals are described as unidirectional seals because the bristles have a lay angle in the direction of rotation. This paper also investigates the influence of rotation direction on measured leakage performance of brush seal. This influence is characterized by non-pressurized reverse rotation operation and measurement of leakage performance prior to and after reverse rotation operation.
Numerical Investigation Into Fully and Partially Wetted Disk Geometries With Relevance to Intershaft Hydraulic Seals
Authors: Warusevitane Achinie , Johnson Kathy , Ambrose Stephen , Walsh Mike , Young Colin
Published: January 2021

Civil aero-engines contain two or three shafts that are supported by bearings. Seals are required both between pairs of rotating shafts and between static elements and shafts. Seals located between two co/contra rotating shafts within the bearing chamber are known as intershaft seals and are typically classified as either hydraulic or oil backed. This paper focuses on research relevant to intershaft hydraulic seals.

A hydraulic seal is formed by a seal fin on the inner shaft immersed in an annulus of oil in the outer shaft where the oil in the annulus is centrifuged outwards by the radial pressure gradient. Once formed a hydraulic seal does not allow air to flow across the seal and any pressure difference across the seal creates different oil levels either side of the fin. Despite their reliable operation with zero leakage, the application of hydraulic seals is restricted due to temperature limitations, oil degradation and coking. Research and development of the next generation of hydraulic seals needs to focus on addressing these issues so that the seals can be utilized in hotter zones in future engines. Understanding of the detailed fluid dynamic behaviour during hydraulic seal operation is relatively limited with very little published data. There is an acknowledged need for improved knowledge and this is the context for the current study.

The ability to accurately computationally model hydraulic seals is highly desirable. Prior experimental and analytical investigations into fully and partially wetted rotating disks have been used to aid understanding of the performance and flow characteristics of hydraulic seals as there are many geometric and operational similarities. These fundamental experimental investigations in the literature provide validation data that allows the authors to establish a CFD modelling methodology.

This paper initially compares the flow characteristics of a fully wetted rotating disk against experimental results available in literature including the radial and tangential velocity components. This paper subsequently investigates the flow characteristics of a partially wetted disk by examining the effect on the angular velocity of the fluid core with varying engagement and spacing ratios for two flow regimes.
Characterising Mixing and Soot Production Using a Lagrangian Statistical Method
Authors: Kampanas Vasileios , Williams Maxwell , Garmory Andrew
Published: January 2021

An understanding of fuel-air mixing, along with the link between turbulent fluid flows and soot production is vital for the design of an efficient, low emissions gas turbine combustor. This paper uses a Lagrangian statistical method to investigate the time histories of mixing hence and soot development for massless parcels tracked within an LES calculation. This provides the advantage of investigating soot development using an inexpensive post-processing technique. The method comprises tracking massless parcels through the flow and recording the local temperature and composition at the parcel location, as well as the age of the parcel. This can be used to give statistical information about various aspects of mixing and soot production, such as distributions of mixture fraction or residence times. The history for each parcel can then be used in a postprocessing step to predict the soot development in time for that parcel path. This has been used to compare Large Eddy Simulations (LES) of reacting flows in both a laboratory aero-engine model combustor and a geometry representative of an annular sector from an aircraft engine combustor. It was found, that when normalized by a reference time scale based on combustor length and bulk velocity, the residence times for the annular sector were considerably shorter and mixture fraction distributions wider. This was due to a much higher chance of parcels being recirculated within the primary zone of the laboratory combustor. Further analysis of the annular combustor sector showed that very different mixing is found between the oxidation ports on the centre of the sector compared to those at the edge. The instantaneous mixing is seen to be less effective for those ports at the edge of the sector and this leads to higher soot levels in these regions.
Experimental Study on Heat Transfer Characteristics of Array Impingement With Initial Cross-Flow
Authors: Zhu Tian-liang , Xu Wei-jiang , Shi Xiao-yu , Su Bo , Lu Fei
Published: January 2021

In order to increase the thermal efficiency, combustion are designed to operate at higher temperature, which requires highly efficient cooling structures for combustion walls. Impingement is an effective structure to enhance the convective heat transfer in the combustion cooling. In the present study, two array impingement cooling structures with cross-flow are presented, and the heat transfer characteristics are obtained experimentally. The heat transfer performance of the impingement cooling structures are studied by using the transient liquid crystal thermography technique for turbulent flow in rectangular channels within the Reynolds number range from 75,000 to 125,000. The impingement hole diameters of the two test pieces were 12mm and 11mm, respectively. The impingement distances-to-hole diameter ratios (z/d) were 1.25 and 2, and the dimensionless hole spacing (x/d) was 2.5 and 2.727. It is found that crossflow shifts the jet downstream, resulting in asymmetric flow, the heat transfer coefficient upstream of the jet weakens, and the shape of stagnation area transitions from circular to hoof-shaped. The cross-flow disturbance accelerates the diffusion of the jet, which makes the distribution of the Nusselt number on the target more uniform, and the overall heat transfer on the target is enhanced. With the change of cross-flow intensity, there are differences in the influence of heat transfer on target under different impact geometries.
Effect of the Foam Metal Casing Treatment on a Low-Speed Axial Compressor
Authors: Li Jia , Sun Dakun , Xu Reize , Dong Xu , Sun Xiaofeng
Published: January 2021

Foam metal is a foam-like substance made out of metal and can be used in flow control, vibration damping and acoustic absorption mainly based on their special physical properties. A kind of foam metal casing treatment is proposed and tested in this study. The impact of the foam metal casing treatment on compressor stability and noise reduction are experimentally investigated. The foam metal selected in the experiments is constructed from ferronickel and its PPI (pores per inch) is 35. The foam metal casing treatment comprises annular support casing and foam metal ring. The effect of foam metal location on stability of the test compressor are investigated by placing shims in support casing. Both time-mean and high-response instrumentation are applied to capture the steady and unsteady compressor performances with the presence of the foam metal casing treatment. 20 microphones of G.R.A.S type are used to measure in-duct acoustic level of the compressor. It is found that the SMI (stall margin improvement) is 36.1% and the efficiency loss is 1.5% at location 7. When foam metal moves to rotor leading edge, the SMI as well as the efficiency loss are getting smaller. The optimal location in the experiments is location 4 where the SMI of compressor is 14.9% and the efficiency loss is 0.1%. The interaction of foam metal with flow in the blade tip region at these locations are investigated and presented in detail. The PSD (power spectrum density) analysis is carried out to show the unsteady signal development in stall inception. The noise attenuation varies in 0.18∼1.6 dB when foam metal is at different locations. Finally, the mechanism and application of the foam metal casing treatment are also discussed.
Numerical Investigation for Characteristics and Oil-Air Distributions of a Tilting-Pad Journal Bearing Under Different Loads
Authors: Ding Aoshuang , Li Xuesong
Published: January 2021

This paper analyses the flow characteristics and oil-air distributions of oil flows in a tilting-pad journal bearing under different bearing loads. This titling-pad journal bearing is working at 3000 rpm rotation speed and its minimum film thicknesses have been measured under different loads from 180 kN to 299 kN. Based on the previous researches of this bearing under 180 kN, the gaseous cavitation and low-turbulence flow exists in this bearing flow. A suitable gaseous cavitation model and the SST model with low-Re correction are used in the film flow simulations. With the rotor and pads assumed to be rigid, the dynamic mesh and motion equations are applied to simulate the motions of the rotor and the rotations of the pads. Based on the simulation results under different bearing loads, the simulated minimum film thicknesses agrees well with the measured data. It indicates that the simulation results can catch the film geometries and flows correctly. With the load increasing, the rotor moves closer to the loaded pads and the minimum film thickness decreases. Taking the effect of boundary layers into consideration, the turbulence has a negative relationship with the film thickness and decreases in the loaded area under higher bearing load. It can be verified by the simulated lower turbulent viscosity ratio distributions in the loaded pads. In the unloaded area, both the film thickness and turbulence viscosity ratio are positively related to the bearing loads. Thus, the higher bearing load may lead the flow to be more different in the loaded and unloaded area, and the turbulence in the loaded pads may transfer to laminar in the end. As for the oil-air distributions, in the unloaded pads, with the bearing load increasing, the simulated air volume fraction increases in the unloaded pads with lower pressure. It should be caused by the higher film thickness of the unloaded pads under higher loads. In sum, the flow turbulence and cavitation process changes with the bearing load. With a higher load, the cavitation becomes more in the unloaded pads and the flow changes sharper from the high-turbulence unloaded area to the low-turbulence loaded area. As the simulation results is in good accordance with the experimental data, the SST model with low-Re correction and the gaseous cavitation model are verified to be suitable for bearing film simulations under different loads.
Implementation of Wide Diffusion Angle V-Shaped Holes for Gas Turbine Cooling: Design Phase and Numerical Simulation
Authors: Odemondo V. , Abba L. , Abram R.
Published: January 2021

This paper describes the design process carried out to develop a new hole geometry. This geometry is able to increase the cooling coverage effect on a turbine blade, in order to have a higher efficiency compared to the standard holes. The first step of the activity described is a CFD analysis of the performances of different hole geometries on a flat plate. Starting from the cylindrical holes the performances of several geometries have been compared. This study allowed the determination of the geometrical parameters mostly responsible of the film effectiveness increase. In this way a criterion able to optimize the hole geometry has been found. Keeping as constraint the same inlet section for all the geometries, the shape of the outlet section was modified in order to maximize the film coverage performances. An optimized hole geometry had been determined. This solution, called V-Shaped hole is characterized by a wide lateral expansion angle and a negligible laidback angle and it is able to increase the cooling effectiveness compared to cylindrical and shaped holes with typical expansion angles (lateral and laidback about 10°). Finally, a comparison with an experimental campaign has been performed to confirm the main results of the CFD analysis.
Combined Numerical and Experimental Study on the Use of Gurney Flaps for the Performance Enhancement of NACA0021 Airfoil in Static and Dynamic Conditions
Authors: Balduzzi Francesco , Holst David , Melani Pier Francesco , Wegner Felix , Nayeri Christian Navid , Ferrara Giovanni , Paschereit Christian Oliver , Bianchini Alessandro
Published: January 2021

The use of power augmentation devices in wind energy applications has been receiving increasing interest from both the scientific and the industrial community. In particular, Gurney Flaps (GFs) showed a great potential thanks to the passive functioning, the simple construction and the possibility to add them as a retrofit to existing rotors. The possibility of having a high quality set of airfoil data for a wide range of both angle of attack (AoA) and Reynolds number is pivotal in the design phase of newly developed machines. Such data are usually available in the technical literature for smooth airfoils, while there is a lack of generalized results in case of airfoils with GFs. Within this context, the authors have performed an extended investigation on the lift increase capabilities of GFs for the well-known NACA 0021 airfoil, which has been used in several wind energy applications up to now. The present paper shows the results of a combined experimental and numerical analysis considering different geometrical configurations of the flaps under both static and dynamic conditions.

Experimental data were first obtained for the AoA range of 180 degrees at a low value of Reynolds number (i.e. Re = 180 k) to analyze the impact of three different geometrical configurations of the GF on the aerodynamic behavior for the full range of incidence angles. The geometrical configurations were defined by varying the length of the flap (i.e. 1.4% and 2.5% of the chord length) and its inclination angle with respect to the blade chord (i.e. 90 degrees and 45 degrees). The experimental investigation involved also dynamic sinusoidal pitching movements at multiple reduced frequencies to evaluate the stall hysteresis cycle. Subsequently, an unsteady CFD numerical model was first calibrated against wind tunnel data at low values of the Reynolds number. Then, the virtual model was exploited to extend the investigation to a wider range of Reynolds number for dynamic AoA rates of change typical for example of vertical-axis wind turbines, i.e. characterized by higher reduced frequencies with a non-sinusoidal motion law.
Heat Transfer Characteristics of Blade Internal Tip Surface by Arrays of Delta-Winglet Vortex Generator Pairs
Authors: Zhao Zhiqi , Luo Lei , Qiu Dandan , Zhou Xun , Wang Zhongqi
Published: January 2021

This paper numerically investigated the effect of the arrays of the delta-winglet vortex generators (DWVGs) pairs on the flow field and heat transfer characteristics of gas turbine blade tip internal surface. Six different arrangements including three inclinations (30°, 45°, 60°) and two aspect ratios of DWVGs are calculated at Reynolds numbers ranging from 6000 to 14,000. The internal cooling passage of gas turbines are simplified as two-pass U bend channel and the U bend channel without any tabulators are considered as Baseline. The detailed flow structure, the evolution of vortices and heat transfer performance over the tip internal surface are presented. The results show that the arrays of DWVGs placed on the tip internal surface have great influence on the tip flow and heat transfer. Small-scale vortices are induced by the DWVGs, which have negligible impact on the main flow. Due to the nature of 180-deg turn, the impingement-like flow contributes the highest heat transfer performance. But too many DWVGs placed on the attachment region will weaken the energy of main flow and therefore reduce the local heat transfer. Besides, the blocked DWVGs (BVG) will enhance the heat transfer at the center line, and the guided DWVGs (GVG) will extend the low-energy flow cluster and thus weakening the heat transfer intensity. The results of this study are useful for understanding the mechanism of heat transfer characteristics in a realistic gas turbine blade by using the arrays of DWVGs.
Experimental and Numerical Comparison of Non-Reacting Flow Formation From a 7-Point Lean Direct Injector Array
Authors: Capil Tyler , Guzman Francisco , Tacina Kathleen , Hicks Yolanda
Published: January 2021

An experimental and numerical comparison of cold-flow structures from two configurations of a 7-point lean direct injector array was completed for this study. The comparison seeks to have the computational model aid in understanding of the experimental flow fields and expand on the underlying physics involved. Qualitative data of mean axial velocity contours as well as quantitative data of mean axial profiles facilitated the comparison between experiment and numerical solutions. Experimental data was collected using particle image velocimetry (PIV) with water seeding through the center fuel nozzle. The numerical computation was carried out with NASA’s OpenNCC (Open National Combustion Code) using steady state Reynolds Averaged Navier-Stokes (RANS) simulation to calculate gas phase velocities. There were notable quantitative differences in the average axial velocity profiles, especially at locations closest to the dump plane. However, good qualitative agreement was consistent for each 7-point configuration.
Building Digital Twins to Simulate Manufacturing Variation
Authors: Shahpar Shahrokh
Published: January 2021

To improve the quality of a manufactured part in industry, a variety of techniques are used to scan a built geometry to bring it back to the physics based simulation world to assess its true performance. There are various laser and structured light measurement techniques (GOM), Computed Tomography (CT) scan as well as touch-point probes in the form of CMM cloud of data that can provide an estimate for the shape of an object. However, there are many challenges on how to construct the digital geometry from the scan in order not to lose any deviations and defects and yet being able to mesh a solid manifold for simulation purposes. In this paper, a novel method based on multi-layered Artificial Intelligence (AI) is presented to produce a meaningful engineering design space to perturb the design-intent geometry to match the manufactured data cloud. The inverse mapping techniques has been applied to a range of real turbomachinery components to demonstrate its flexibility and robustness, even when the original GOM is not perfect. A case study is presented based on a real modern jet engine bypass outlet guide vane (BOGV) to show how constructing and using its digital twin and high-fidelity simulation can save a significant cost for a fleet of engines/aircraft.
Feasibility of Innovative Solar-Thermo-Acoustic Power Conversion Cycles
Authors: Behar Omar , Saxena Saumitra , Roberts William L.
Published: January 2021

The techno-economic assessment of the concentrating solar power thermo-acoustic power conversion systems is carried out to identify the optimum conditions, under-which the solar thermo-acoustic might be competitive to the current commercial solar thermal power technologies.

The thermal and economic performance of a thermo-acoustic engine integrated to five different solar collectors including Compound Parabolic Collector, Linear Fresnel, Parabolic Trough, Central receiver, and Solar Dish is compared to the current commercial solar thermal power technologies as well as to their corresponding Carnot-cycle. To do so, a modular modeling approach is used to consider all the available commercial technologies, through combining a modular energy model with a simplified economic model.

Jeddah city (Saudi Arabia) has been chosen as a reference site for the present study. The results indicate that the integration of compound and dish solar collectors to a thermo-acoustic engine might offer competitive solutions. Compound collectors might be more suitable for integration with the thermo-acoustic engine than linear Fresnel collectors, if the exergy efficiency of the engine reaches 40%. Besides, dish-thermo-acoustic system becomes more competitive than current dish-mechanical Stirling engine, if the investment costs of the thermo-acoustic engine are reduced to 3500 $/kWe, but the operating temperature should be above 700°C. Improving the exergy efficiency of the thermos-acoustic engines, from 35% to 40%, could make the dish-thermo-acoustic system more competitive than current dish-mechanical Stirling engines at a working temperature of 500°C.

The study concludes that more efforts must be focused on reducing the costs of the TA devices rather than on improving efficiency.
A Toolbox of Hardware and Digital Solutions for Increased Flexibility
Authors: Demougeot Nicolas , Steinbrenner Alexander , Cires Alfredo , Paskin Marc
Published: January 2021

The power generation market has been changing rapidly with the injection of an ever increasing usage of renewable power sources. The cyclic and highly unpredictable nature of power generation output from renewable sources is forcing Gas Turbine (GT) operators to significantly increase the operational flexibility of their engines.

While the industry has been, for many years, developing and fielding solutions providing increased output at the high end of the operating range, the focus has shifted recently to solutions allowing for a safe decrease of the engines’ minimum operating load.

The AutoTune (AT) system was introduced at last year’s Turbo Expo conference [5], and the challenges of developing a safe Extended Turndown add-on are detailed herein. Other digital and hardware solutions presented include Part Load Performance, decreased start-up time for both simple and combined cycle units, disc cavity cooling modulation and Exhaust Bleed. Increased ramp rate is addressed with the associated significant difficulty of maintaining the mechanical integrity of the rotors and casings.

PSM has been working on a toolbox of both hardware and digital solutions to increase on GT operability both on the high and low ends of the load range and the technical issues faced are described in this paper.
Intelligent Fault Diagnosis of Planetary Wheel Bearing Using Constrained Independent Component Analysis and Stacked Sparse Autoencoder
Authors: Li Hongkun , Huang Gangjin , Ou Jiayu , Zhang Yuanliang
Published: January 2021

Industrial machinery is developing in the direction of large-scale, automation, and high precision, which brings novel troubles to mechanical equipment management and maintenance. Intelligent diagnosis of mechanical running state based on vibration signals is becoming increasingly important, and it is still a great challenge at pattern recognition. As one of the indispensable components in mechanical equipment, planetary gearboxes are widely used in wind power, aerospace, and heavy industry. However, the problem of automatically maximizing the accuracy of planetary gearbox under different working conditions has not been solved. Therefore, an intelligent diagnosis method for planetary wheel bearing based on constrained independent component analysis (CICA) and stacked sparse autoencoder (SSAE) is presented in this research. Firstly, the fault signal with obvious time-domain characteristics is extracted by constrained independent component analysis (CICA), and the fault signals and noise is separated. Then, calculating the correlation kurtosis value of the time domain signals at different iteration periods as the eigenvalue to obtain the training samples and the test samples. The parameters of the network layer, the number of hidden nodes and learning rate are determined to build the model of SSAE. In the end, the training samples are input into the model for training and the whole network is fine-tuned. The advantages and disadvantages of the model are verified by the test samples. The intelligent classification and diagnosis of the mechanical running state are completed. Experiments analysis with real datasets of planetary wheel bearing show that the proposed method can achieve higher accuracy and robustness for fault classification compared with other data-driven methods. The application of this method in other major machinery industry also has bright prospects.
Machine Learnt Synthetic Turbulence for LES Inflow Conditions
Authors: Corsini Alessandro , Delibra Giovanni , Giovannelli Marco , Traldi Stefania
Published: January 2021

LES computations have limited applications in turbomachinery predictions because of the formidable amount of resources they require. Due to the exponential increase of requirements with Reynolds number, LES is usually limited to elements with moderate flow velocities and to investigate flows characterized by multiple length and time scales that overlaps. It is the case of combustion, aeroacoustics, unstable range of operations such as stalled conditions.

In all these cases LES can provide unique insights on thermo-fluid-dynamics. The main drawback is that LES is not only very expensive, but also extremely sensitive to inflow conditions. A number of studies pointed out that slight differences in LES inflow conditions can result in a very different flow development and therefore different prediction of performance, noise and so on. It is so sensitive that comparison of computations with different inflow conditions and same arrangement for other parameters result in completely diverging results.

There are two major solutions to this problem. First, is to use a cyclic inflow channel to generate a fully turbulent profile to feed to the main simulation. Second, the use of a synthetic turbulence model to generate analytically an unsteady turbulent profile. The drawback of the first approach is the fact that a fully developed inflow can be un-realistic for most turbomachinery applications. On the other hand, the second approach was proved not to be able to correctly reproduce the statistics of turbulence and therefore the synthetic inflows do not provide a real solution to the problem. In this paper we discuss a novel method to generate LES inflow conditions, based on adversarial machine learning. In particular we trained a generative adversarial network (GAN) to reproduce the inflow conditions of a channel flow. In this way, the generator of the GAN is trained to correctly reproduce an unsteady turbulent profile, while the discriminator is used during the training phase as an adversarial agent for the generator. During the validation of the method both the discriminator and the generator will be used to validate the proposed methodology.
Using Feature-Based Mesh Adaptation to Improve the Adjoint Optimisation of Transonic Compressor Blades
Authors: John Alistair , Vivarelli Guglielmo , Qin Ning , Shahpar Shahrokh
Published: January 2021

The benefit of mesh adaptation to improve the optimisation process of turbomachinery components is here demonstrated for the first time. Mesh movement is used to automatically cluster and align the cells with significant flow features such as shocks, shock-induced separation and wakes for every geometry tested during a transonic compressor blade optimisation. Using mesh movement means that the same size grid is used while significantly improving the accuracy of the simulation and resulting adjoint gradients. A method is demonstrated to automatically carry out feature based mesh movement during every step of an adjoint optimisation process. Optimisations are carried out using the adaptation method and also using the starting mesh as a comparison. It is shown that (when tested on a very fine grid) the adaptation-optimisation process results in a better design, due to more accurate flow and gradient prediction throughout the optimisation process. A cost breakdown of the process is given to show that using adaptation during the optimisation process only increases the overall optimisation cost by a small amount, but results in greater efficiency of the final blade design.
A Machine-Learnt Wall Function for Rotating Diffusers
Authors: Tieghi Lorenzo , Corsini Alessandro , Delibra Giovanni , Tucci Francesco Aldo
Published: January 2021

Data-driven tools and techniques have proved their effectiveness in many engineering applications. Machine-learning has gradually become a paradigm to explore innovative designs in turbomachinery. However, industrial Computational Fluid Dynamics (CFD) experts are still reluctant to embed similar approaches in standard practice and very few solutions have been proposed so far. The aim of the work is to prove that standard wall treatments can obtain serious benefits from machine-learning modelling.

Turbomachinery flow modeling lives in a constant compromise between accuracy and the computational costs of numerical simulations. One of the key factors of process is defining a proper wall treatment. Many works point out how insufficient resolutions of boundary layers may lead to incorrect predictions of turbomachinery performances. Wall functions are universally exploited to replicate the physics of boundary layers where grid resolution does not suffice. Widespread wall functions were derived by the observation of a few canonical flows, further expressed as a simple polynomial of Reynolds number and turbulent kinetic energy. Despite their popularity, these functions are frequently applied in flows where the ground assumptions cease to be true, such as rotating passages or swirled flows. In these flows, the mathematical formulations of wall functions do not account for the distortion on the boundary layer due to the combined action of centrifugal and Coriolis forces.

Here we will derive a wall function for rotating passages, through means of machine-learning. The algorithm is directly implemented in the N-S equations solver. Cross-validation results show that the machine-learnt wall treatment is able to effectively correct the turbulent kinetic energy field near the solid walls, without impairing the accuracy of the RANS turbulence model in any way.