bluuebunny/crossref_metadata_2025 huggingface dataset:
Flametube Evaluation of a Lean-Lean Combustor Concept Developed for Supersonic Cruise Aircraft
Authors: Tacina Kathleen M. , Podboy Derek P. , Guzman Francisco
Published: October 2022

Gaseous emissions were measured in single-cup flametube tests of an advanced low-NOx combustor concept at simulated supersonic cruise conditions. The combustor concept is a low technology readiness level (TRL), lean front-end design developed under the NASA Fundamental Aeronautics/Supersonics project to minimize NOx emissions at supersonic cruise. The flametube conditions matched or approached combustor conditions at supersonic cruise, with combustor inlet temperatures up to 920 K, inlet pressures up to 19 bar, and combusted gas temperatures up to 2,120 K. Whether these conditions met or just approached supersonic cruise conditions depended on the type of engine the combustor would be installed in. Two types of engines were considered here: a “derivative” engine based on a current technology and an “advanced” engine with a higher operating pressure ratio and higher temperature limits. For the “derivative” engine, the combustor is expected to be at least close to meeting the NASA NOx emissions goal of 10 g-NOx/kg-fuel at supersonic cruise. However, with the higher combustor inlet and flame temperatures of the advanced engine, NOx emissions are expected to be well above the goal.
Feasibility of Achieving 62% Combined Cycle Efficiency With a 200 MW Gas Turbine
Authors: Gulen S. Can (John) , Zachary Justin
Published: October 2022

The current thermal performance of advanced gas turbines (J class) leads to combined cycle efficiencies exceeding 62%. Such results were achieved by making the gas turbines bigger, i.e., above 350 MW (larger air flow), and by increasing the firing temperature. However, a very significant part of the power generation market, particularly in support of solar or wind renewable power production, requires smaller gas turbines, producing in a 1 × 1 × 1 combined cycle configuration nominally rated at 300 MW. The paper investigates options to implement improvements realized by current J class gas turbines to a smaller gas turbine producing around 200 MW. It describes the challenges for such an endeavor. Taking each of the gas turbine components from the intake, compressor, combustor, turbine and exhaust, the paper examines the viability of technical solutions implemented in larger gas turbines (increased air flow, larger physical dimensions, more fuel flow etc.) to a lesser output gas turbine. It also discusses the impact of a smaller gas turbine on the bottoming cycle major equipment (HRSG, steam turbine and balance of plant). Finally, the study attempts to predict the feasibility of combined cycle efficiencies exceeding 61% combined cycles based on a gas turbine with a 200 MW output.
The Influence of Shrouded Stator Cavity Boundary Conditions on Performance of a 1.5-Stage Low-Speed Research Compressor
Authors: Shao Runzhu , Zhu Mingmin , Teng Jinfang , Qiang Xiaoqing
Published: October 2022

In axial compressor, the leakage flow from labyrinth cavity has a non-negligible influence on the aerodynamic performance and flow fields of shrouded stators due to its interaction with the main stream. A number of numerical researches have been carried out to predict and understand the cavity flow. However, details about the boundary conditions between cavity and mainstream are scarce in opening literature. Comparisons between numerical and experimental results are seldom reported to verify the rationality of the connecting method. Therefore, a four-stage low-speed research compressor (LSRC) with shrouded stators in Shanghai Jiao Tong University was investigated numerically in this paper, aiming at studying the influence of different cavity boundary conditions. A steady numerical research on the front 1.5-stage (IGV-rotor-stator) of LSRC was performed using NUMECA with four connecting methods for the interface between the cavity and mainstream. The investigation reveals that different boundary conditions make great impact on the aerodynamic performance and flow fields of the compressor. Validated by the experimental data, when using the full non-matching connections between cavity and mainstream while cavity domain rotating at the nominal speed, the steady three-dimensional RANS simulation of the 1.5-stage compressor can well predict the distributions of total pressure loss and flow angle near the hub at the stator outlet. The flow mechanisms of different connecting methods are elucidated by investigating the detailed flow fields inside the cavity and near the stator hub. The full-non matching cases with different rotational speeds of cavity domain from 0 to 900 RPM are also compared to demonstrate the influence of rotational speeds on performance and flow fields.
Effect of Surface Corrugations on Laminar and Transitional Flows
Authors: Jain Ishita , Sarkar S.
Published: October 2022

The effect of surface roughness on spatially developing transitional flow field is discussed in the present study by carrying out highly resolved Large Eddy Simulations (LES). The surface modification considered here is the two-dimensional rectangular ribs embedded in the flat plate, resulting into the formation of transverse spanwise cavities with pitch as λ = 3k, where k is the roughness height. The results are simulated for the three imposed inlet conditions, while the Reynolds number based on momentum thickness is 150, 300, and 500. The instantaneous and time-averaged flow features have been resolved. The mean flow characteristics revealed the appearance of the primary vortex within the cavity, which led the primary flow to slip over the cavities, attributing to reduction in the drag. The distributions of skin friction coefficient (Cf) are compared with the flat plate correlations, which illustrate significant percentage reduction within the cavities in the transitional regime. Further, the existence of elongated streaks with significant influence on laminar-to-turbulent transition and their interaction with the roughness is explained.
Performance and Economic Assessment of Mechanically Integrated Parallel Hybrid Aircraft
Authors: Carpentier Thibault , Zhang Jinning , van Heerden Albert S. J. , Roumeliotis Ioannis
Published: October 2022

In this study, a selection of environmental and economic considerations of mechanically integrated parallel hybrid (MIPH) electric propulsion systems for single-aisle civil transport aircraft are assessed. The environmental assessment focuses on the carbon dioxide and nitrogen oxide emissions with different power management strategies and levels of battery technology. In the economic study, the potential subsidies and tax incentives required to make these aircraft financially viable are determined. To capture the performance results, models of the propulsion systems and airframe were constructed using the Siemens Simcenter Amesim systems modelling software. The operating cost was then computed using adapted direct operating cost estimation methods. Battery replacement was incorporated by using a battery cycle aging model. The results showed that using a battery energy density of 300 Wh/kg will not provide any meaningful benefits. For 600 Wh/kg, fuel savings of up to 3% for missions below 650 nm could be obtained for a PMS where the electrical powertrain operates during takeoff, climb, and cruise. However, the NOx emissions were lowest for the takeoff and climb only PMS, implying a trade-off when selecting a PMS. Based on the cost results, it is determined that taxation on carbon emissions would have to increase at least 50-fold from its current levels for the most optimistic scenarios. Alternatively, considerable subsidies, representing large percentages of the purchase price of the aircraft, will be needed.
Model Setup for the Investigation of Flow Phenomena in a 1.5-Stage Gas Turbine Regarding Hot Gas Ingestion
Authors: Pehle Lukas , Schwertner Sven , Wirsum Manfred
Published: October 2022

This paper presents different modeling approaches on rim seal flow in a 1.5-stage test turbine resulting in the analysis of numerical data in comparison to existing test data. The analysis focuses on a very simple axial sealing gap and a reference operation point which shows significant hot gas ingestion in the experiments. The presented model will be used to gather more information on flow phenomena and their effect on the ingestion and hence contributes to a deeper understanding. In combination with broader research this understanding will help manufacturers to reduce their secondary air mass flow rate and increase gas turbine’s efficiency.

Experiments on the hot gas ingestion phenomenon have already been carried out at many international test facilities. As part of a recommissioning of a test rig for investigating hot gas ingestion into the wheel side cavities of axial-flow gas turbines at the RWTH Aachen University, this publication presents the numerical model set up in parallel. In particular, the aim is to investigate the sensitivity of the modeled flow field in the wheel side cavity for changes in the modeling and boundary conditions. In addition to the investigation of the sensitivity, the results are compared with existing measurements in order to be able to classify and evaluate the sensitivities in a specific manner.

The investigation starts with a mesh study followed by the analysis of different turbulence models including different inlet turbulence intensities. After analyzing different time steps in transient and steady state simulations, calculations are shown concerning different operation points. For all chosen combinations of settings and boundary conditions the main flow is modeled reasonably well compared to experimental data. Also the operation point dependency of the pressure field is modeled well with simple approaches.

For low purge air mass flow rates the flow field in the wheel side chamber, consisting of pressure and sealing gas concentration, is only represented with strong deviations in the one-segment model. These deviations are due to large structures forming in the cavity, which can not be reproduced using one or two pitches of the turbine. Above a certain dimensionless purge air mass flow rate, a transition in the flow field can be observed analyzing the experimental data. Above this flow rate the large structures break down and the sealing effectiveness increases. At these operation points the selected numerical model shows good agreement with experimental data regarding pressure and hot gas concentration. To improve predictions at low purge air flow rate multiple segment models will be used in the future.
Direct Numerical Simulations of Aerodynamic Performance of Wind Turbine Airfoil by Considering Flap-Wise Blade Oscillations
Authors: Erfanian Nakhchi Toosi Mahdi , Rahmati Mohammad
Published: October 2022

Aeroelasticity of modern wind turbines is a critical issue which can significantly affect the structural integrity and lifetime of the wind turbine blades. However, previous aeroelastic or aerodynamic studies were mostly concentrated on low-fidelity numerical methods, and the details of flow separation and vortex generation over wind turbine airfoils cannot be detected with these methods. In this study, a high-fidelity direct numerical model is used to investigate the details of flow separations and laminar separation bubbles (LSB) over a NACA-0012 wind turbine airfoil under oscillation. The simulations are conducted at Reynolds number of Re = 1.3 × 105 and the blade has harmonic pitch-wise oscillations at Mach number of Ma∞ = 0.4. Strong fluctuations are observed in the wake region of the vibrating wind turbine blade. The results show that the blade vibrations have a significant influence on vortex generation and separation point over wind turbine blades. details of flow structure over wind turbine blades compared to previously proposed models.
Fan Stability Enhancement With Partial Casing Treatments
Authors: Oldfield Matthew K. , Castillo Pardo Alejandro , Hall Cesare A.
Published: October 2022

Casing treatments are used to extend the stability margin of fans or compressors. These typically have an axisymmetric arrangement, but for a fan exposed to non-axisymmetric distortion, a casing treatment applied to a fraction of the annulus is of interest to target a particular distortion feature. In this paper, a partial casing treatment has been designed with axial-skewed slots and an experimental investigation has been carried out to determine the effects of the treatment extent and position.

Three inlet conditions were tested for each extent of casing treatment; clean, radial tip-low distortion and half-annulus tip-low distortion. For axisymmetric inlet conditions, the stall margin and efficiency penalty increased approximately linearly with casing treatment extent. However, for half-annulus tip-low distortion, there was a strong dependence between the position of the casing treatment relative to the distorted sector and the stall margin improvement. If the casing treatment is positioned where the rotor enters the distorted sector, unsteady disturbances in the rotor tip flow are minimized. However, if the rotor meets the casing treatment later in the distorted sector, the disturbances are able to grow, leading to earlier stall inception. Overall, this shows that partial casing treatments can target a distorted flow to give a disproportionately positive impact compared a full annulus casing treatment. For example, it was found that a 72° casing treatment extent could be positioned to achieve over 50% of the full annulus casing treatment stall margin improvement with only 20% of the efficiency penalty.
Low Wind Speed Characteristics of an Optimized Diffuser Augmented Wind Turbine
Authors: Abdelrahman Hazem H. , Elbaz Ahmed M. R. , Elkholy Ahmed M.
Published: October 2022

Towards a final aim of enhancing the feasibility of low-speed sites for wind energy generation, the current study introduces the diffuser augmentation as a method of enhancing the performance of wind turbines designed for poor wind conditions. The study uses a methodology that combines the MOGAII Genetic Algorithm (GA) and Computational Fluid Dynamics (CFD) to generate a novel optimized diffuser profile out of nearly 200 geometric shapes. A case for each of the bare turbine and the diffuser-augmented turbine were modeled using 3-dimensional Reynolds Averaged Navier Stokes equations (RANS) using k-ω SST model and FLUENT solver. The performance comparison indicated an overall average rise of 28.83% in power coefficient in favor of the diffuser-augmented case. The most significant performance rise of 47.19% was found at the low-speed region corresponding to Tip Speed Ratios between 8 and 12. Through investigating the starting torque at extremely low speeds above 1 m/s, it was evaluated that the starting torque increases significantly with an average rise of 60.64% in favor of the diffuser-augmented case, the enhanced starting torque widened the operational range of the wind turbine in the low wind speed region, and reduced the lowest required speed to induce a positive moment coefficient. This significant rise in performance particularly for low wind speeds which are dominantly more frequent in the annual wind conditions, combined with the enhanced starting capabilities, resulted in an annual generated energy increase of 23.18% compared to the bare turbine.
Specific Speed Considerations for Inward Flow Radial Supercritical CO2 Turbines
Authors: Hoque Syed J. , Kumar Pramod , Gopi Pramod Chandra
Published: October 2022

Inward flow radial supercritical CO2 turbines require higher operating speeds than steam or gas turbines making only low specific speed designs practically realizable. A theoretical model is presented to estimate the low specific speed design regime. The model incorporates boundary conditions across the turbine and engineering limitations such as blade height, Mach number, and flow angle at the rotor inlet to predict the minimum allowable rotational speed. A CFD study is subsequently performed to review the applicability of gas turbine design principles on sCO2 turbines for low specific speed designs. The effect of specific speed and velocity ratio on turbine efficiency and flow physics is studied for power output ranging from 100 kW to 5 MW. The results show a significant deviation in the optimal specific speed, velocity ratio, and incidence angle values than traditional gas turbine designs. It is found that viscous losses dominate low specific speeds, while Coriolis effects dominate the high specific speed designs. High specific speed designs require higher negative incidence angles ∼ −50° to −55° to overcome the flow stagnation at blade pressure surface arising from the Coriolis effect. Maximum turbine efficiencies (∼ 83%) are achieved at lower specific speeds of ∼ 0.4 than gas turbines’ optimal specific speed of ∼ 0.55 to 0.65. Variations of stator, rotor, and exit kinetic energy losses with specific speeds are also presented. Finally, the results are superposed on Balje’s Ns-Ds diagram and compared with gas turbine designs.
Research on Aerodynamic Axial Force in Single Rotor-Stator Cavity of a Gas Turbine
Authors: Jia Xingyun , Hou Qiyang , Zhang Le
Published: October 2022

To reveal the mechanism of the effect of rotor-stator cavity on the aerodynamic axial thrust of gas turbine rotor, a test rig for aerodynamic axial thrust of the rotor-stator cavity and the corresponding numerical model are proposed in this research. The geometric parameters and boundary conditions of the rotor-stator cavity numerical model and test rotor-stator cavity are modeled by the thermodynamic parameters and operational conditions of the real marine gas turbine. In this research, the aerodynamic induced axial force of one rotor-stator cavity can be visualized, measured, and directly collected dynamically for the first time. Flow characteristics, pressure distributions in rotor-stator cavity are analyzed, and the reliability of the test method is verified.
Influence of Casing Groove on Rotating Instabilities in a Low-Speed Axial Compressor
Authors: Chen Xiangyi , Koppe Björn , Lange Martin , Chu Wuli , Mailach Ronald
Published: October 2022

Rotating instability (RI) can be regarded as a pre-stall signal because such phenomena are usually detected when a compressor operates at a near stall point. Since RI is closely relevant to aerodynamic, acoustic, and structural issues, its mechanism has attracted industrial concerns and in-depth analysis. In this paper, a low-speed axial single compressor rotor row is selected as the baseline research object. A circumferential casing groove is mounted over the shroud. The solid casing and the casing treated configurations were simulated using the zonal large eddy simulation model, and the simulations present remarkable predictions in capturing the averaged and the dynamic characteristics of the investigated compressor. By implementing a data-driven method called dynamic mode decomposition, the mode with the highest amplitude is proved to be correlated to the dominant RI frequency. The spatial and temporal property of the RI is visualized. The results show that the casing groove has limited influence on the averaged flow field but manipulates the dynamic features. The groove allows the RIs to shift from around 0.5 blade passing frequency to higher frequencies in the upstream region and effectively suppresses the unsteadiness in the zones under and downstream of the groove. The RIs are triggered by the flow interaction of the tip leakage flow at the front part of the blade. It can be depicted as pressure waves staggering with the rotor blade and propagating over the blade tip region at around half of the blade speed. With the existence of the casing groove, the dominant wavelength changes, and the fluctuation is damped under the groove, which finally modifies the properties of RIs.
High-Fidelity Simulations of the Flow Around T106C Cascade at Low Reynolds Number: The Effects of Freestream Turbulence and Stagger Angle
Authors: Dufau Antoine , Marty Julien , Man Daniel , Piot Estelle
Published: October 2022

Flows in low-pressure turbines are highly dependent on the laminar-turbulent transition of the boundary layer and the separation of the laminar boundary layer. This study focuses on the flow around the T106C low-pressure turbine cascade blade for a low Reynolds number 100,000 and a moderately low turbulence intensity 0.8%. For this paper, three direct numerical simulations (DNS) are carried out to understand the discrepancies observed between the simulations and the experimental data. To that end, the effect of freestream turbulence intensity and blade stagger angle are investigated. A first simulation is performed without freestream turbulence, then a second one is performed with a modified stagger angle, and finally a third one is performed with an injection of synthetic turbulence at the inlet plane based on the synthetic eddy method (SEM). The results are compared to experimental data and RANS simulations. These comparisons show that there are still discrepancies between the flow predicted by the DNS and the experimental measurements. A comparison between DNS and RANS simulations highlights some leads to better understand these discrepancies.
An Euler-Based Throughflow Approach for Centrifugal Compressors – Part B: Experimental Investigations and Validation
Authors: Doerr Tobias , Yildiz Attilla , Dolle Bastian , Brillert Dieter
Published: October 2022

For turbomachinery design, manufacturers today need fast tools to predict the performance of an aerodynamic design with good accuracy. However, CFD tools are often cumbersome in terms of computation time and licensing costs for commercial solvers.

In this context, a quasi-three-dimensional solver, called tFlow, for centrifugal compressors is presented in Part A of this paper. To validate and calibrate the model, an experimental test rig is developed and presented in this paper. The setup consists of a single-stage centrifugal compressor with a shrouded impeller providing a pressure ratio up to 1.85. On the pressure side, the diffuser is followed by a volute and a throttle to capture the whole speed characteristic between surge and choke. Thermodynamic data, such as pressure and temperature upstream and downstream of the compressor, are recorded as well as torque and rotational speed at the shaft coupling. In addition, the test rig can also be used to investigate the effects of wet compression. For this purpose, a spray nozzle can be installed in front of the impeller’s bell mouth. In order to investigate the influence of temperatures on evaporation rates, a preheater in front of the compressor section is installed to heat the air up to temperatures of 80 °C.

In this paper, dry results are shown for inlet temperatures of 22, 30, 40 and 50 °C. To compare the characteristics at different preheated conditions, reduced rotational speed and air mass flow rate are kept constant. These resulting performance maps are in good agreement between each case. The numerical results of Part A are validated by the experimental data herein.
Machine-Learning Clustering Methods Applied to Detection of Noise Sources in Low-Speed Axial Fan
Authors: Tieghi Lorenzo , Becker Stefan , Corsini Alessandro , Delibra Giovanni , Schoder Stefan , Czwielong Felix
Published: October 2022

The integration of rotating machineries in human-populated environments requires to limit noise emissions, with multiple aspects impacting on control of amplitude and frequency of the acoustic signature. This is a key issue to address and when combined with compliance of minimum efficiency grades, further complicates the design of axial fans. The aim of this research is to assess the capability of unsupervised learning techniques in unveiling the mechanisms that concur to the sound generation process in axial fans starting from high-fidelity simulations. To this aim, a numerical dataset was generated by means of LES simulation of a low-speed axial fan. The data set is enriched with sound source computed solving a-posteriori the perturbed convective wave equation (PCWE). First, the instantaneous flow features are associated to the sound sources through correlation matrices and then projected on latent basis to highlight the features with the highest importance. This analysis in also carried out on a reduced dataset, derived by considering two surfaces at 50% and 95% of the blade span. The sampled features on the surfaces are then exploited to train three cluster algorithms based on partitional, density and Gaussian criteria. The cluster algorithms are optimized and their results are compared, with the Gaussian Mixture one demonstrating the highest similarity (> 80%). The derived clusters are analyzed, and the role of statistical distribution of velocity and pressure gradients is underlined. This suggests that design choices that affect these aspects may be beneficial to control the generation of noise sources.
Experimental Flow Investigation Inside an Axial Compressor With Active Flow Control
Authors: Moubogha Joseph Moubogha , Joseph Pierric , Roussette Olivier , Dazin Antoine
Published: October 2022

This paper describes the experimental study of the flow behavior in a rotor blade channel of an axial compressor equipped with an Active Flow Control (AFC) system using Particle Image Velocimetry. The AFC system consists of 40 actuators connected to an auxiliary supply pressure system. It is used to extend the stable operating range and to improve the performance of the compressor. The system is able to generate high speed jets blowing just at the tip of the rotor blades. PIV data are obtained at three radial positions (at 18%, 51% and 79% of the blade height) in the inter-blade channel region. The PIV results are discussed to analyze the effect of the control system on the compressor internal flows.
Numerical Prediction of Heat Transfer Coefficient and Adiabatic Effectiveness on a Nozzle Guide Vane With Representative Combustor Outflow
Authors: Tomasello Stella Grazia , Andreini Antonio , Bacci Tommaso , Facchini Bruno , Cubeda Simone , Andrei Luca
Published: October 2022

The employment of lean-premix combustors in modern gas turbines allows to reduce NOx emissions by controlling the flame temperature at the expense of highly unsteady and strongly non-uniform flow fields which are necessary to stabilize the flame. This highly complex swirled flow field characterized by evident temperature distortions alters the aerodynamics and heat transfer in the first high pressure turbine stator with potential detrimental consequences on engine life and efficiency. From a numerical point of view, the mutual combustor-turbine interaction has been studied by using standard turbulence modeling approaches, as commonly employed during the design phase, even if more advanced scale-resolving methods have been proven more reliable and benchmarked against various experimental findings.

From the experimental perspective, film-cooling adiabatic effectiveness and heat transfer coefficient (HTC) measurements on the external surface of the nozzle guide vanes, in the presence of representative combustor outflow characteristics, are not common since the relevant temperature distortions that are present make such kind of measurements really challenging to perform. For this reason, very limited assessment of such approaches regarding this aspect is available in literature.

In this study, an experimental test case with a combustor simulator and a nozzle cascade, where both adiabatic effectiveness and HTC measurements have been carried out, is investigated by carrying out a systematic computational study, through RANS calculations of the combustor-cascade integrated domain. The film cooling system performance has been predicted by meshing the whole vane internal cooling system, while the heat transfer coefficient is calculated using the conventional two-point method, normally adopted for heat transfer calculations in gas turbines.

The comparison between numerical predictions and experimental results was exploited to assess the capability of traditional modeling approaches in the characterization of both adiabatic effectiveness and heat transfer coefficient. This evaluation represents an effective means to assess if conventional/industrial approaches can be reliably used, when representative and highly unsteady combustor outflows are considered, or advanced and more time-consuming methods shall be adopted.
Additively Manufactured Guide Vane With Integral Measurement System for Validation on Engine
Authors: Naryzhnyy Oleg , Lindbaeck Martin , Laletin Petr , Rotar Alexander
Published: October 2022

Thermal validation of gas turbine components is one of the key activities performed for engine characteristics evaluation and verification of a newly developed product. There are several standard thermal validation methods: thermal paint, thermal crystals and thermocouples (TC). However, measurement results from all the above-mentioned techniques are affected by the design of the component or limited by the technological conditions of the application.

This article is related to the specific part design applied by additive manufacturing (AM) for the first-stage gas turbine vane. Validation is performed by thermocouple measurement technique. Thermocouple gauges are instrumented inside the additively manufactured turbine vane without any negative impacts on the part cooling system or key interfaces, such as hot gas surfaces, and as a result without impact on the operation of the entire turbine component.

Moreover, since guide vanes were covered with thermal barrier coating (TBC), and the metal temperature was recorded throughout the entire period of operation, it became possible to capture and analyze the effect of aging of the TBC. It is well known that the properties of TBC change over time and bring uncertainty into the component thermal state. This is due to the fact that the TBC conductivity value depends on the exposure time and the exposure temperature.

Thermal validation work shown in this paper was performed in frame of new AM product development and supports all stages of product development process in Siemens Energy.
Mixing Mechanism of Multi-Scale Flow in Tip Region of Turbine Rotor
Authors: Huang Lin , Zou Zhengping
Published: October 2022

The tip leakage loss of freestanding turbine rotor with transonic flow conditions is one of the important sources of the internal loss of high-pressure turbine. It mainly includes the internal loss of the tip and the mixing loss of the leakage flow and the main flow. The latter is the main contributor of the tip leakage loss. The mixing between the leakage flow and mainstream flow is a complex physical process, which contains abundant multi-scale flow structures. Therefore, it is of great significance to understand the mixing mechanism of multi-scale flow in order to accurately evaluate the tip leakage loss and improve the aerodynamic performance of the turbine. In the present, the high-precision flow field in the tip region is obtained by Detached Eddy Simulation, and the multi-scale flow are decomposed by Kolmogorov Spectrum Consistent Optimization (KoSCO). Furthermore, the mixing coefficient is defined by combining Lagrange and Euler method. The contribution and physical mechanism of the local multi-scale flow to the mixing is studied carefully. Finally, the mixing coefficient is associated with the velocity field. The results show that the KoSCO method in this paper can effectively induce the multi-scale flow structure in the tip region of turbine rotor. The mixing coefficient defined in this paper can effectively evaluate the difference of the contribution of different scale flows to mixing. The contribution of different scale flows to mixing is scale dependent. The mixing coefficient decreases with the decrease of flow scale. However, when the flow scale is smaller than a specific value, the mixing coefficient is almost the same. The physical mechanism of flow mixing of different scale flow is quite different. The transport and diffusion dominate mixing process in large-scale flow and small-scale flow, respectively. Specially, both transport and diffusion impact the mixing process. The relationship between the mixing coefficient and the velocity gradient is found, and the correlation formula between the mixing coefficient and the velocity field gradient is established to evaluate the mixing strength.
Methanol Production by a Chemical Looping Cycle Using Blast Furnace Gases
Authors: Palone Orlando , Hoxha Arian , Gagliardi Gabriele Guglielmo , Di Gruttola Francesca , Borello Domenico
Published: October 2022

Steel mills are responsible for high direct CO2 emissions. To mitigate climate changes, carbon capture and utilization strategies (CCU) aiming at neutralizing such emissions should be employed. Currently, the most widespread technologies for carbon capture (CC) are represented by chemical/physical absorption, adsorption, membrane separation, calcium looping cycles (CaL). One promising pathway for carbon capture and utilization (CCU) is represented by the coupling of chemical looping cycles with liquid fuel synthesis processes, such as methanol synthesis. Methanol is an interesting low-cost fuel for gas turbines engines, due to its potential reduction of NOx and particulate emissions along with the absence of SO2 emissions. Furthermore, being one promising solution to store excess power production from renewables, its availability is expected to increase significantly with the years. In this work, methanol production from the syngas generated by a three-reactors chemical looping process (TRCL) is investigated by mass and energy balances. The TRCL cycle is composed by a reducer reactor, where Fe2O3 is reduced to FeO by an endothermic reaction occurring at high temperatures and promoted by biogenic carbon; an oxidizer reactor, where FeO reacts exothermically with a gas stream composed of CO2 and H2O in order to produce a syngas (CO + H2); a fuel reactor, where the non-reacted FeO is oxidized to Fe3O4 and subsequently the whole amount of Fe3O4 is regenerated to Fe2O3 by the interaction with ambient air. The produced syngas is then sent to a methanol synthesis plant modelled with the Aspen Plus software. Several syngas compositions, deriving from different oxidizer’s inlet CO2/H2O molar fractions, are investigated and the resulting methanol production rates are compared. A WGS unit is located at the plant inlet in order to increase the H2 molar fraction in the feed stream. Results indicate that methanol production is almost equal in all investigated configuration and amounts to about 0.35 ton/h. From an energy standpoint, global heating/cooling duty is almost equal in all cases, while the electric power required is greater for higher hydrogen contents in the syngas. However, the case with high H2 content (0.75 in molar fraction) is characterized by the greatest methanol yield (12.6%), carbon efficiency (23%) and a limited feed over recirculation ratio, thus representing the most indicated configuration among the investigated ones.
Numerical Investigation of a Coupled Blow-Off/Flashback Process in a High-Pressure Lean-Burn Combustor
Authors: Soli Alessandro , Langella Ivan
Published: October 2022

Large eddy simulation is used to investigate the flashback mechanism caused by the combustion-induced vortex breakdown (CIVB) in a high-pressure lean-burn annular combustor with lean direct injection of kerosene. A single sector of the geometry, including a central pilot flame surrounded by a main flame, is simulated at take-off conditions. A previously-developed flamelet-based approach is used to model turbulence-combustion interactions due to its relatively low cost, allowing to simulate a sufficiently long time window. In stable operations, the flame stabilises in an M-shape configuration and a periodic movement of the pilot jet, with the corresponding formation of a small recirculation bubble, is observed. Flashback is then observed, with the flame accelerating upstream towards the injector as already described in other studies. This LES, however, reveals a precursor partial blow-out of the main flame induced by a cluster of vortices appearing in the outer recirculation region. The combined effect of vortices and sudden quenching alters the mixing level close to the injector, causing first the main, then the pilot flame, to accelerate upstream and initiate the CIVB cycle before the quenched region can re-ignite. Main and pilot flames partly extinguish as they cross their respective fuel injection point, and re-ignition follows due to the remnants of the reaction in the pilot stream. The process is investigated in detail, discussing the causes of CIVB-driven flashback in realistic lean-burn systems.
High-Fidelity CFD Analysis of In-Serviced Shrouded High-Pressure Turbine Rotor Blades
Authors: Carta Mario , Ghisu Tiziano , Shahpar Shahrokh
Published: October 2022

In-service deterioration can lead to undesired shape variations on high-pressure turbine rotor blades. This can have a significant impact on efficiency, power generation and component life. Loss of power production from the high-pressure turbine rotor causes engine over-throttling to compensate for the lower performance. This will in turn worsen the operating conditions and ultimately reduce the life of the component. The aim of this study is to provide a high-fidelity flow simulation of in-serviced shrou ded High-Pressure Turbine (HPT) blades of a modern Jet Engine. Shape variations effects on the aerodynamic performance of several shrouded HPT blades with different number of in-service hours have been investigated. In order to establish a digital model of the shape variation, a novel reverse engineering procedure is carried out, to come up with a parametrized definition of each blade’s variations from nominal including any observable damage. The investigation is conducted by means of an in-house, full 3D steady-state RANS simulation of the flow around a series of damaged rotor blade geometries, which are obtained through high-resolution GOM scans. The analysis shows that the aerodynamic performance of the HPT rotor blades under investigation is primarily sensitive to shroud damage, which is found to account for efficiency losses often greater than 3%, and for more than 80% of the total performance loss. A secondary role on efficiency is found to be played by the blade shape deviation. A highly linear correlation is found between HPT stage efficiency and a combination of shroud damage parameters.
Computational Investigation of Using Emulsified Fuels in Heavy Duty Gas Turbines
Authors: Suleiman Baha , Selim Hatem , Dawood Alaaeldin , Khalidi Abdurrahman , K. Vasudevarao , Goldmeer Jeffrey , Al-Ahmadi Kamal , Al-Ghamdi Ibrahim , Badr Eid , Al-Gahatani Mohammed
Published: October 2022

Gas turbines operating on liquid fuels may produce higher NOx and soot emissions and may suffer from reduced combustion part durability, as compared to gas turbines operating on gaseous fuels. With some fuels, like diesel (aka light distillate), the NOx emissions increase is related to the liquid fuel spray atomization process, which plays a vital role in the combustion process.

A promising technology for enhancing fuel atomization in a combustor is water-fuel emulsion technology. Injecting a water-fuel emulsion into a gas turbine combustor may lead to favorable effects. Since fuel atomization should be enhanced, combustion should occur at lower local equivalence ratio values, thus reducing the creation of NOx and soot emissions. Moreover, the presence of water in the combustion mixture decreases the average temperature of the combusting mixture due to the high latent heat of vaporization of water, which in turn should reduce NOx.

In this study, a numerical investigation is conducted to quantify the impact of the water-fuel emulsion technology on gas turbine combustors operating on diesel fuel. The objective is to determine if NOx and soot emissions are improved, and if flame structure changes when the emulsion technology is utilized at different water to fuel ratios.
The Heat Transfer and Coherent Structures of the Tangential Impingement Jets in the Annular Chamber Studied With Extended Proper Orthogonal Decomposition
Authors: Shi Lei , Zhu Xiaocheng , Du Zhaohui
Published: October 2022

The tangential impingement of turbulent circular jets on the cylindrical surface in an annular chamber is numerically investigated based on the SAS-SST model. The main purpose is to understand the role of the coherent structures on the temperature field inside the chamber and the heat transfer coefficient field on the hub surface. Based on the jet diameter and inlet velocity, the jet Reynolds numbers are given as 285000, 332000, and 392000, respectively. The accuracy of the numerical simulation is verified by the experimental data. The spectrum information of the velocity magnitude at the monitor point is obtained by the fast Fourier transform (FFT) method. An improvement of the proper orthogonal decomposition (POD) method is known as the extended POD (EPOD) method, which is mainly suitable for analyzing the correlation between the flow field and the synchronized scalar or vector fields, such as the correlation between the velocity and the heat transfer coefficient fields. In present study, both the POD method and the EPOD method are applied and compared. The POD method allows to visualize the main modes in terms of velocity, temperature, and heat transfer coefficient fluctuations. With the help of the EPOD method, the contribution of velocity fluctuations to temperature fluctuations in the chamber and heat transfer fluctuations on the hub surface are further analyzed. For Rej = 392000, the first two velocity POD modes and the velocity EPOD modes that contribute the most to the temperature fluctuations are very similar, reflecting the same large-scale coherent structures. The first two velocity EPOD modes that contribute the most to the heat transfer coefficient fluctuations have a high proportion of energy in the flow field, corresponding to the deflection motion of the jet.
Correlated Pressure-Velocity Instability in a Transonic High-Pressure Turbine Blade
Authors: Dellacasagrande Matteo , Lengani Davide , Bertolini Ettore , Sanz Wolfgang
Published: October 2022

The present work describes the coupled pressure-velocity instability in the suction side boundary layer of a transonic high-pressure turbine blade. The application case is the VKI LS89 turbine blade MUR237. Modal decomposition techniques such as the Proper Orthogonal Decomposition (POD) and the Dynamic Mode Decomposition (DMD) are applied to data obtained by large eddy simulations (LES) to inspect the existing correlation between pressure fluctuations induced by travelling pressure waves and the velocity disturbances growing into the boundary layer. To this end, POD and DMD were applied to both velocity and pressure fields from the leading edge up to the end of the blade surface. DMD was computed on a 2D slice oriented parallel to the blade surface inside the boundary layer. Data were ordered along the curvilinear abscissas, so that the most spatially amplified waves were obtained. Interestingly, unstable velocity modes were detected in the front blade suction side where pressure waves dominate. The unstable velocity modes computed upstream of the peak suction highlighted the occurrence of elongated streaky structures showing spanwise fluctuations which are typical of their instability. The comparison of pressure and velocity modes highlighted the occurrence of pressure-related fluctuations in the velocity field at the same time instants at which streak instability is observed. The analysis carried out in this work suggests that pressure waves can provoke localized instability of boundary layer streaks, which then break up further downstream causing transition.
Flow Modal Decomposition of a Vertical-Axis Wind Turbine With the Moving Boundaries of Rotating Blades
Authors: Tian Tian , Sun Chong , Zhu Xiaocheng , Du Zhaohui
Published: October 2022

Aiming at analyzing the wake evolution features of a 3-blade vertical axis wind turbine (VAWT), dynamic mode decomposition (DMD) is used to evaluate statistics of the flow field based on unsteady flow field computations. Considering the limitation that DMD can only be applied to problems with stationary boundaries, the technology to deal with the moving boundaries of rotating blades is investigated. First, the flow fields of VAWT are calculated using CFD, and computations are compared with the experimental results to verify the numeral calculations. Then the spectral analysis is performed on the VAWT wake at a tip speed ratio of 2.35, and different frequency characteristics are observed in the near wake, the transition region of the wake, and the far wake, respectively. Next, DMD is employed to investigate the dynamic stall and the wake evolution of the VAWT in the absolute frame and the relative frame, respectively. Details of different possessing methods are presented. Finally, depending on the corresponding frequencies obtained before, the dominant modes are extracted from the CFD results by DMD. The extracted modes corresponding to specific frequencies can capture the coherent structures with different scales, which reflecting the characteristics of the propagation of shedding vortices from blades and the bluff-body oscillation in the wake of the VAWT.
Aeroacoustic Interactions of Blade Skew and Leading Edge Serrations Applied to Low-Pressure Axial Fans
Authors: Biedermann Till M. , Hintzen Nils , Kameier Frank
Published: October 2022

Leading edge serrations are well known for their ability to reduce turbulence-induced noise of single aerofoils while also providing aerodynamic advantages under certain operating conditions. Continuatively, applying leading edge serrations to rotating machinery such as axial fans proved the validity to generally transfer the obtained aeroacoustic benefits of single aerofoils. However, for the rotating applications, besides the discrete and broadband characteristics of the investigated machines, the noise reduction potential highly depends on the point of operation. The current work aims at assessing the aeroacoustic effects of serrated leading edges under the increased geometrical complexity of the fan blades through blade skew, a combination of blade sweep and blade dihedral. Therefore, the question is whether combining two potentially effective noise-reducing treatments through blade skew and leading edge serrations results in leveraging or obstructing effects. By varying the skew angle from 0 deg to 38 deg, four different prototypes of the fan impeller are designed, manufactured and tested experimentally in a test rig according to ISO 5136 and ISO 5801, allowing for simultaneous assessment of the aerodynamic and acoustic performance of the machines. All configurations are tested with original blades of straight leading edges plus five sets of serrations each, parameterised by the serration amplitude and the serrations wavelength. The intensity of the incoming turbulence ranges from 2.6% to 12.1%. The results obtained show the skewed blades to improve both the aerodynamic performance and the noise radiation after exceeding an initial skew angle, complemented by a significant onset of stall. Moreover, no contraindication between blade skew and serrated leading edges is encountered, showing the potential to further extend the noise reduction capabilities by combining effects of blade skew and leading edge treatment.