bluuebunny/crossref_metadata_2025 huggingface dataset:
System-Level Assessment of a Partially Distributed Hybrid Electric Propulsion System
Authors: Sahoo Smruti , Kavvalos Mavroudis D. , Diamantidou Dimitra Eirini , Kyprianidis Konstantinos G.
Published: October 2022

Hybrid electric propulsion system based aircraft designs are paving the path towards a future greener aviation sector and thus, have been the major focus of the aeronautical community. The fuel efficiency improvements of such propulsion system configurations are realized at the aircraft level. In order to assess such benefits, a radical shift in the sub-system modeling requirements and an integrated conceptual aircraft design environment is necessary. This work highlights performance model development work pertaining to different hybrid electric propulsion system components and development of a design platform which facilitates tighter integration of different novel propulsion system disciplines at aircraft level. Furthermore, a serial/parallel partially distributed hybrid electric propulsion system is chosen as the candidate configuration to assess the potential benefits and associated trade-offs by conducting multidisciplinary design space exploration studies. It is established that the distributed hybrid electric configurations pose the potential for aircraft structural weight reduction benefits. The study further illustrates the impacts from onboard charging during the low thrust requirement segments, quantitatively. It is highlighted that the amount of off-take power extraction for onboard charging of the battery is limited due to engine operability and higher specific fuel consumption issues. Though provisioning of onboard charging lowers the potential for block fuel savings, improvement in battery specific energy can make it more promising, which is also dependent on the hybridization power level. It is established that distributed propulsion system configurations particularly benefit from a high aspect ratio wing structure, which manifests for high hybridization power levels. A high voltage level transmission system with more efficient electrical components, enhances opportunities for achieving block fuel saving benefits.
Numerical Investigation of Potential Flow Induced Vibrations of Steam Turbine Last Stage Rotor at Low Load Operation - Part 2: Rotating Instabilities Detection
Authors: Diurno Tommaso , Andreini Antonio , Facchini Bruno , Maceli Nicola , Arcengeli Lorenzo
Published: October 2022

Steam turbines play an important role in global power generation since they are widely used, as thermal engines, in fossil-fueled, nuclear, and concentrated solar power plants. Therefore, recent trends in steam turbine design practices are closely related to the development of the energy market, which is especially focused on expansion of fast renewable energy. As a direct consequence, due to intrinsic variability of the green-energy resources, the steam turbines address the need to increase their flexibility to ensure the stable functioning of the power grid. Greater flexibility is linked to even increasing Low Volume Flow (LVF) operating conditions which could trigger dangerous non-synchronous aerodynamic excitations of the last stage bucket (LSB). In order to discover the source of such excitations, an extensive numerical study, presented in a two-part publication, has been carried out to investigate two different mechanisms potentially accountable for flow induced vibrations. In part one, the focus is on the flutter stability, while the present part deals with the detection of rotating instability phenomena that might arise in the last stage during LVF conditions. Such aerodynamic instabilities are investigated using CFD simulations by performing 3D, Unsteady Reynolds Averaged Navier Stokes (URANS) of the low pressure, last turbine stage coupled with an axial exhaust hood, with structural struts. The full annulus mesh of both the last stage and diffuser is considered with the transient stator-rotor interface to properly account for unsteady interaction effects.

The influence of the operating conditions on the fluid dynamic behavior is assessed by considering six different operating conditions, starting from the design condition and gradually decreasing the mass flow rate. The presence of rotating instabilities is demonstrated by monitoring the fluid dynamic variables during the simulation and by using advanced post-processing techniques, such as Proper Orthogonal Decomposition (POD).
Effects of Freestream Turbulence on Air-Mist Film Cooling: Two-Phase Flow Simulations
Authors: Dwivedi Anjali , Sarkar S.
Published: October 2022

Air-mist film cooling is a potential technique to protect the surface of turbine vanes operating at high temperatures for improved thermal efficiency. The variation in the performance of air-mist film coolant is evaluated here for a wide range of freestream turbulence (0.2 to 10%) like the operating condition of the gas turbine. The investigated domain consists of a flat plate with a series of discrete holes of 35° streamwise orientation and connected to a common delivery plenum chamber via a pipe of diameter D = 12.7mm. A two-phase mist consisting of finely dispersed water droplets of 10.0μm in an airstream at a mist concentration of 3.0% is introduced as a secondary flow. The blowing ratio and density ratio are 0.5 and 1.2, respectively, where the Reynolds number based on the diameter of the hole is 1.0 × 104. The Reynolds Averaged Navier Stokes equation in the Eulerian-Lagrangian frame is used to simulate the two-phase flow by ANSYS Fluent 15.0 with the k-ε realizable model. The simulation resolves the mean thermal-flow field and dynamics of droplets. The injected droplets in the crossflow behave like a small heat sink as they evaporate while advecting downstream and are expected to provide improved protection of the heated surface. High turbulence intensity enhances the mixing of droplets with the crossflow, thereby improving the spanwise diffusion of droplets. Reduction of the strength of the counter-rotating vortex pair is also evident. The area-averaged film cooling effectiveness increases by 21.5%, with an increase of turbulence intensity from 0.2 to 10%. However, the increase in aerodynamic losses is almost as high as 39%.
Research on Acoustic Resonance Characteristics of Flat Plate Cascades Based on Acoustic Analogy
Authors: Zhao Feng Tong , Cui Bo , Yang Mingsui , Sha Yun Dong
Published: October 2022

The model of flow around the flat plate cascades is a fundamental study for the flow-induced acoustic resonance phenomenon. Parker first conducted an experimental study on the acoustic issue with the vibration of the built-in plate in the rectangular pipe. It was found that the plate vibration amplitudes and the sound pressure level inside the pipe grow rapidly when the plate vortex frequency, the acoustic mode frequency and the natural frequency of the blade are the same, which is a new resonance mechanism. In this paper, a rectangular pipe built-in flat plate model is established on the basis of the Parker experimental model. A method combined the large eddy simulation used to process the flow field and the Lighthill acoustic analog used to capture the acoustic characteristics of the acoustic calculation model is proposed. The obtained sound pressure spectrum curves are highly consistent with the experimental data of Parker, which verifies the applicability and accuracy of the large eddy simulation and Lighthill acoustic analog calculation methods. The acoustic resonance problem of flat plate cascades is investigated using this method. The sound pressure spectrum curve at different flow velocities are obtained. The sudden jump of the sound pressure level when the acoustic resonance, the relationship between the characteristic frequency and the shedding vortex, and the anti-phase shedding mode of the shedding vortex at the trailing edge of the plate had been captured by taking the above methods for the flat plate cascades research. The flat plate cascades model established in this paper shows well the law of the plate shedding vortex motion and the sound pressure distribution characteristics under different incoming flow speeds. This paper may provides a model research method for the blade fracture problem caused by acoustic resonance of the aero-engine compressor.
Analytical Modeling of the Injector Response to High Frequency Modes in a Tubular Multi-Jet-Combustor
Authors: Rosenkranz Jan-Andre , Sattelmayer Thomas
Published: October 2022

Gas turbine combustors with multi-jet burners have been shown to provide better fuel flexibility compared to large swirl burners and can meet current low emissions standards at increasing turbine inlet temperatures. In case thermoacoustic combustion instabilities occur, the resonant feedback loop of the thermoacoustic mode in the chamber leads to injector coupling, which has not yet been investigated in same depth as in rocket engines in the past. The higher order mode inside the combustor initiates longitudinal modes in the upstream injector tubes leading to flame surface and location modulations as potential drivers of instability. Furthermore, fuel injection in the mixing tubes generate equivalence ratio fluctuations, which have an additional influence on flame dynamics. As these effects deteriorate emissions, flashback safety and lead to increased wear or even severe damage of the combustor, proper calculation of the acoustic injector response is an important aspect of combustor stability modelling. The paper at hand aims for an analytical model to describe the injector response to higher order modes as an alternative to the existing approaches, which are largely based on numerical computations. For this purpose, lumped parameter models are used to calculate the wave scattering at the injector tube-chamber interface. It is shown that the Rankine-Hugoniot conditions at the area jump can be applied to high frequency acoustics in a similar manner as to low frequency acoustics. Numerical simulations in COMSOL are used to verify the model for the first and second transversal and the first radial mode.
Experimental Verification of a Practical Engineering Design Method for Mixed-Flow Compressor Stages
Authors: Zhang Chenqing , Zhao Chenxi , Tang Yonghong , Xi Guang
Published: October 2022

The mixed-flow compressor has high efficiency and pressurization ability even at an extremely high flow rate. However, so far the design principle of the mixed-flow compressor has not well been established. In this paper, a novel and practical design method of mixed flow impellers is developed, in which the meridional construction needs few control parameters, and easily applied to engineering product design.

In order to verify the developed method, a mixed-flow impeller with flow rate coefficient of 0.2374 is designed and manufactured for the experimental study. The experimental results show that the peak efficiency of the compressor at the machine Mach number of 0.6 and 0.8 reach 85.17% and 85.20%, respectively, which are competitively well-performed at large flow coefficient in the published literature. The comparison between experimental and numerical results verifies the feasibility and effectiveness of this proposed method and also provides some valuable guidance for the choice of the exit inclination angle of the mixed-flow impellers.
Validation of an Analytical Model for the Acoustic Impedance Eduction of Multi-Cavity Resonant Liners by a High-Fidelity LES Approach
Authors: Giaccherini Simone , Pinelli Lorenzo , Marconcini Michele , Pacciani Roberto , Arnone Andrea
Published: October 2022

The massive growth of the air traffic during the last years is leading to stricter limitations on the noise emission levels radiated from aircraft engines. To face this issue, the installation of acoustic liners on the intake duct and the exhaust nozzles is a common strategy adopted to properly abate noise emissions coming from the fan, the compressor, the turbine, and the jet.

In this context, the aim of the present paper is to use high-fidelity LES simulations to validate a MDOF (multi-degree of freedom) extension of the single- and double-degree of freedom (SDOF and DDOF) analytical model provided by Hersh for impedance eduction of acoustic liners.

Firstly, the results of the original Hersh model are compared with LES calculations performed with the OpenFOAM suite on a single-orifice and single-cavity layout (SDOF). Then the extension of the Hersh model to multi-cavity (MDOF) geometries by using a recursive formulation is presented. Finally, high fidelity simulations are carried out for single-orifice and multi-cavity (MDOF) configurations to validate the method extension and to understand how resonant coupling and acoustic impedance are affected by multi-cavity resonant elements.

The excellent agreement between the high-fidelity results and the analytical predictions for the single-cavity pattern confirms that the Hersh model is a useful formulation for a preliminary design of a SDOF acoustic liner. The model extension to MDOF configurations enables the designers to broaden the design space, and thus a validated analytical method is strictly necessary to perform sensitivity studies to the multi-cavity geometrical parameters (i.e., face-sheet thickness, cavities depth, porosity). Basically, a multi-cavity configuration makes the liner element resonate at different frequencies leading to multiple absorption peaks in the audible range. In this way, the acoustic performance of the liner is extended to a wider frequency range, overcoming the limitations of a traditional SDOF configuration.
A Model and Experimental Validation for a Piston Rings - Squeeze Film Damper: A Step Toward Quantifying Air Ingestion
Authors: Koo Bonjin , San Andrés Luis
Published: October 2022

Rotor-bearing systems often rely on squeeze film dampers (SFDs) to increase the dynamic stability and reduce rotor motion amplitudes while traversing critical speeds. In aircraft engines, to increase the damping capacity within a limited physical space, piston rings (PRs) seal the axial ends of a squeeze film land. However, lubricant still leaks through the slit in the PR abutted ends, and air enters into the film to make a bubbly oil mixture with a much reduced damping capability. This paper presents a volume of fluid (VOF) model for a PR sealed ends SFD facing ambient air (not submerged in lubricant and prone to air entrainment) and delivers predictions benchmarked against experimental results obtained in a dedicated test rig. A lubricant feed pressure and flow large enough to prevent air ingestion vary with the damper geometry, the lubricant inlet and outlet conditions, and the kinematics of the journal. A parametric study for a typical SFD shows the period-averaged gas volume fraction (GVF) increases as the journal squeeze film velocity (vs) increases and as the film clearance decreases. Most importantly, the location of the PR slit relative to the feedhole affects the amount of air drawn into the film. When the PR slit faces a feedhole, the film land is mostly filled with a pure lubricant. The GVF increases as the arc distance from the PR slit to the feedhole increases. The physical model, anchored by the test data, effectively addresses a fundamental challenge in SFD design and operation; namely, to quantify the amount of air ingested and its effect on the damper forced performance.
Numerical Predictions of Mean Performance and Dynamic Behavior of a 10 MWe sCO2 Compressor with Test Data Validation
Authors: Hosangadi Ashvin , Weathers Tim , Liu Zisen , Pelton Robert , Wygant Karl , Wilkes Jason
Published: October 2022

High-fidelity aerodynamic analysis has been demonstrated for mean performance and unsteady dynamics in a sCO2 compressor designed by Hanwha Power Systems Americas for a 10 MWe Concentrating Solar Power plant. Simulations were performed with CRUNCH CFD® software tool that was matured to accurately model near critical real fluid effects in sCO2. Pre-test predictions for mean performance were validated with test data collected later. Performance predictions were accurate and captured sensitivity of the efficiency to inlet temperature of CO2 as well as steep drop-off at high flow rates due to condensation in the inlet throat. Detailed analysis was performed to understand the source of these performance losses at near critical conditions. Unsteady dynamic effects in the compressor at off-design conditions were also identified and quantified. In particular a system wide “condensation surge” condition was detected at high flow coefficients that results in large amplitude pulsations with accompanying mass flow fluctuations at low frequencies and has potential to cause damage in closed loop systems.
Stratified and Buoyancy-Induced Flow in Closed Compressor Rotors
Authors: Lock Gary D. , Jackson Richard W. , Pernak Mikolaj , Pountney Oliver J. , Sangan Carl M. , Owen J. Michael , Tang Hui , Scobie James A.
Published: October 2022

The radial growth of compressor discs is strongly influenced by conjugate heat transfer between conduction in the co-rotating discs and buoyancy-driven convection in the rotating fluid core between the discs. An accurate prediction of metal temperatures of these discs is an important issue in thermo-mechanical design, where blade-tip clearances must be controlled carefully to ensure safety and efficiency under all operating conditions. This paper presents an experimental study of the fluid dynamics and heat transfer in a closed rotating cavity, comparing results with theoretical models and introducing a new compressibility parameter χ. At large values of χ, where compressibility effects are significant, the air temperature approaches that of the shroud; such conditions suppress buoyancy effects and the flow in the rotating cavity becomes stratified, with convection replaced by conduction inside the fluid core. There are important practical consequences of stratification with significant differences in temperature distributions and stresses inside compressor discs.

The influence of χ is also shown on the radial temperature distributions for the discs and on the shroud heat transfer correlations, which are compared qualitatively with previously published data collected where the effects of compressibility are relatively small. The experiments reveal that there is a critical value of χ where the convective heat flux to the shroud is zero. The radial distribution of disc temperature was that expected from pure conduction in a cylinder. A new heat transfer correlation based on measured shroud heat flux and the theoretical core temperature is presented.

The unsteady flow characteristics in the cavity were also investigated, identifying coherent rotating structures across a range of experimental conditions. These cyclonic / anti-cyclonic vortex pairs generate the non-dimensional circumferential pressure difference necessary for the radial outflow (of cold fluid) and inflow (of hot fluid) through the rotating core. The experiments show the magnitude of these pressure variations can be correlated against Grashof number and that at high values of χ the structures do not exist. The combined experimental and theoretical results will be of practical interest to engine designers and for the validation of computational models.
Simulating Stall Inception in a High-Performance Fan With Clean and Distorted Inlets
Authors: Bedke Andrew M. , Adams Tyler , Gorrell Steve E.
Published: October 2022

The effect of distorted inflow on jet engine fan stability is an important consideration in both commercial and high performance aircraft applications. Novel commercial aircraft configurations offer significant reductions in fuel burn, but require engine fans to continuously operate with severe amounts of inlet distortion. Complex inlet ducts in high performance aircraft also result in distorted flow at the fan inlet. This paper investigates and compares the mechanisms of stall inception for cases of both clean and distorted inlet flow. Unsteady RANS simulations of stall inception in a high performance transonic fan were obtained for both cases. In both instances, the mechanism for stall inception is shown to be interactions between the detached bow shock and the tip clearance vortex, which causes the formation of two vortices within the blade passage. The location and strength of these vortices both affect the LE spillage into the adjacent blade rows. When inlet distortion is present, mass redistribution upstream of the fan results in variations in rotor incidence. An area of high incidence is located outside the circumferential extent of the applied distorted sector. In the high incidence region, the shock is detached 3.9%–8.1% chord more than the clean inlet case, making LE spillage more likely. The same mechanisms of stall inception are observed when distortion is present. However, the severity of the stalling phenomena is more pronounced within the high incidence region of the annulus. A rotating stall cell grows out of the stalled passages present at the near-stall operating point and ultimately extends 59% chord upstream of the LE and 18.7% span radially. Understanding the effect of distortion on the mechanisms of stall inception will allow appropriate steps to be taken to extend the stable operating range of modern commercial and high performance fans.
Oxygen Storage Incorporated Into Net Power and the Allam-Fetvedt Oxy-Fuel sCO2 Power Cycle – Technoeconomic Analysis
Authors: Moore J. Jeffrey , Pryor Owen , Cormier Ian , Fetvedt Jeremy
Published: October 2022

With the planned future reliance on variable renewable energy, the ability to store energy for prolonged time periods will be required to reduce the disruption of market fluctuations. This paper presents a method to analyze a hybrid liquid-oxygen (LOx) storage / direct-fired sCO2 power cycle and optimize the economic performance over a diverse range of scenarios. The system utilizes a modified version of the NET Power process to produce energy when energy demand exceeds the supply while displacing much of the cost of the ASU energy requirements through cryogenic storage of oxygen. The model uses marginal cost of energy data to determine the optimal times to charge and discharge the system over a given scenario. The model then applies ramp rates and other time-dependent factors to generate an economic model for the system without storage considerations. The size of the storage system is then applied to create a realistic model of the plant operation. From the real plant operation model, the amount of energy charged and discharged, the CAPEX of each system, energy costs and revenue and other parameters can be calculated. The economic parameters are then combined to calculate the net present value (NPV) of the system for the given scenario. The model was then run through the SMPSO genetic algorithm in Python for a variety of geographic regions and large-scale scenarios (high solar penetration) to maximize the NPV based on multiple parameters for each subsystem. The LOx storage requirements will also be discussed.
Design of Annular Thermoelectric Generators System to Recover Waste Heat From Aircraft Jet Engine
Authors: Aljaghtham Mutabe
Published: October 2022

Thermoelectric (TE) materials were investigated in several applications due to their capability to convert waste heat into electrical power. The possibility of implementing thermoelectric generators (TEGs) onto exhaust pipe of turbojet engine to recover waste heat energy is introduced in this study using 3D finite element method. The annular TE configuration can be mounted on the exhaust pipe utilizing the temperature difference between hot gas flow and cool air bypass flow. Geometrical parameters of annular TEGs structure such, TE leg angle, and gap distance angle are also optimized to quantify the total amount of TE modules on the outer surface area of the exhaust pipe. Due to higher values of thermomechanical properties, silicon germanium which also performs better at higher temperature range with higher values of figure of merit (ZT) is selected as TE materials. However, due to high temperature gradient, the cascade annular thermoelectric systems are also included in this study by inserting skutterudite as another TE material at lower stage which is suitable at intermediate temperature range. The comparison of using annular single stage (silicon germanium) and two stages (silicon germanium & skutterudite) TE systems is investigated.
Numerical Modeling of Lean Spray Lifted Flames in Inclined Multi-Burner Arrangements
Authors: Langone Leonardo , Amerighi Matteo , Andreini Antonio
Published: October 2022

Modern combustors operate with lean mixtures to prevent Nitrogen oxides (NOx) formation by limiting the peaks of the temperature inside the combustion chamber. One of the main drawbacks of these technologies is the higher risk of Lean Blow-Off (LBO) compared to the state-of-art Rich Quench Lean combustors. To limit this possibility, combustor designers introduced pioneering concepts for this component. In this fashion, the CHAiRLIFT (Compact Helical Arranged combustoRs with lean LIFTed flames) concept founds its advantages in the structure of the combustion chamber. It combines two concepts: the tilting of the burner’s axis relative to the engine axis with a low-swirl lifted spray flame. Here, the combustion can be stabilized at very low equivalence ratios thanks to the interaction between consecutive burners. A numerical analysis was carried out to support the experimental campaign aiming to investigate the performance of the burner under different tilting angles for the burners. Two-phase simulations of the CHAiRLIFT full rig burner were performed in the commercial CFD suite ANSYS Fluent and the results were compared with the available experimental data. Furthermore, a deeper sensitivity to the tilting angle was conducted through the introduction of specific performance parameters to assess the performance and to seek the best promising setup. The outcomes have shown that tilt angles between 20° and 30° could lead to an improvement of the exhaust recirculation, regarding the considered operating conditions.
Free-Stream Turbulence Induced Boundary-Layer Transition in Low-Pressure Turbines
Authors: De Vincentiis Luca , Ðurović Kristina , Lengani Davide , Simoni Daniele , Pralits Jan , Henningson Dan S. , Hanifi Ardeshir
Published: October 2022

In the present work the evolution of the boundary layer over a low-pressure turbine blade is studied by means of direct numerical simulations. The set-up of the simulations follows the experiments by [1], aiming to investigate the unsteady flow field induced by the rotor-stator interaction. The free-stream flow is characterized by high level of free-stream turbulence and periodically impinging wakes. As in the experiments, the wakes are shed by moving bars modeling the rotor blades and placed upstream of the turbine blades. To include the presence of the wake without employing an ad-hoc model, we simulate both the moving bars and the stationary blades in their respective frames of reference and the coupling of the two domains is done through appropriate boundary conditions. The presence of the wake mainly affects the development of the boundary layer on the suction side of the blade. In particular, the flow separation in the rear part of the blade is suppressed. Moreover, the presence of the wake introduces alternating regions in the streamwise direction of high- and low-velocity fluctuations inside the boundary layer. These fluctuations are responsible for significant variations of the shear stress. The analysis of the velocity fields allows the characterization of the streaky structures forced in the boundary layer by turbulence carried by upstream wakes. The breakdown events are observed once positive streamwise velocity fluctuations reach the end of the blade. Both the fluctuations induced by the migration of the wake in the blade passage and the presence of the streaks contribute to high values of the disturbance velocity inside the boundary layer with respect to a steady inflow case. The amplification of the boundary layer disturbances associated with different spanwise wavenumbers has been computed. It was found that the migration of the wake in the blade passage stands for the most part of the perturbations with zero spanwise wavenumber. The non-zero wavenumbers are found to be amplified in the rear part of the blade at the boundary between the low and high speed regions associated with the wakes.
Canned Sealless Pumps for Hazardous Applications?
Authors: Alsultan Abdulrahman , Alharbi Shuja
Published: October 2022

Oil and Gas industry has many applications considered as toxic or hazardous, where process fluid leakage is not permitted and leads to health, safety and environmental impacts. Caustic/Acidic applications, High Benzene Concentrations, Hydrogen sulfide rich oil/gas as well as liquids operating above their auto-ignition temperatures are examples of such liquids that pose as a risk to the industry operation, and for those, special arrangements are in place to allow for the safe operation environment.

Pumps in the industry requires special attention, specifically in the interface between the fluid and the environment, where potential of leakages are foreseen. Mechanical Seals are used to contain the fluid within the equipment, but the prices are ever increasing for such seals, along with maintenance, design and operating requirements. Several alternatives to seals are being employed nowadays, such as Sealless systems, which is hermitically sealed from atmosphere, and does not require sealing. This technology is considered relatively new, and requires more studies to understand the limitations and factors associated, from an owner and design perspective. Things like financial factors, maintenance factors and design limitation should be studies further, in order to have a mature and reliable technical solution available to end users.
Experimental Investigation of the Effects of Thermal Barrier Coating on Twisted Blade Full Film Cooling
Authors: Yan Hao-nan , Liu Cun-liang , Zhang Li , Guo Yu-hang
Published: October 2022

Film cooling and thermal barrier coating technologies are often used in thermal protection of aero-engine turbine blades. But the film-hole structure can be often affected by thermal barrier coatings (TBC) spraying, resulting in the variations of aerodynamic and thermal performances of film cooling. In this paper, adiabatic film cooling effectiveness distribution contours of twisted vanes with multi-row film cooling holes in fan-shaped cascade tunnel were obtained by PSP technology. The effects of TBC on twisted vanes film cooling effectiveness were studied, which was sprayed by electron beam physical vapor deposition (EB-PVD). Three typical density ratio (DR) of 1.0, 1.5 and 2.0 and three mass flow ratio (MFR) of 8.92%, 10.45% and 12.21% were test. The air was selected as the mainstream, nitrogen, carbon dioxide and 15% sulfur hexafluoride mixd with 85% argon were independently selected as secondary flow to produce three density ratios of 1.0, 1.5 and 2.0.

The results indicate that TBC improves film cooling effectiveness on suction surface by 6.2%–16.67%, and significantly reduces the film cooling effectiveness on the leading edge (37.7%–52.7%) and gill areas of the pressure surface (28.8%–32%). In these three regions, the difference between vanes with and without TBC is slightly affected by the change of MFR, and gradually decreased with the increase of density ratio. The film cooling effectiveness of the pressure surface near the trailing edge is less weakened by the TBC, where the maximum reduction is 8.92%. Compared with the cylindrical hole rows, TBC has less impacts on film cooling effectiveness at fan-shaped hole rows.
Numerical Study of Combustor-Turbine Interaction by Using Hybrid RANS-LES Approach
Authors: Tomasello Stella Grazia , Andreini Antonio , Meloni Roberto , Cubeda Simone , Andrei Luca , Michelassi Vittorio
Published: October 2022

The complex flow field of gas turbine lean combustors is meant to reduce NOx emissions and maintain a stable flame by controlling the local temperature and promoting high turbulent mixing. Still, this may produce large flow and temperature unsteady distortions capable of disrupting the aerodynamics and heat transfer of the first high-pressure-turbine cooled nozzle. Therefore, the interaction between the combustion chamber and the turbine nozzle is analyzed first with the help of scale-resolving simulations that notably also include a realistic turbine nozzle cooling system. To determine the nature and severity of the interaction, and the risks associated to performing decoupled simulation, the results of the coupled computer simulation are analyzed and compared with those of decoupled simulations. In this case, the combustor is computed by replacing the turbine nozzle with a discharge convergent with the same throat area, and the conditions at the interface plane are used as inlet boundary conditions for a conventional RANS of the nozzle. The analyses of the coupled and decoupled simulation reveal that the combustion chamber is weakly affected by the presence of the nozzle, whereas the two thermal fields of the nozzle surface differ considerably, as well as the disruption of the film cooling by the incoming flow distortions.
Turbine Endwall Contouring Through Advanced Optimization Techniques
Authors: Burigana Matteo , Verstraete Tom , Lavagnoli Sergio
Published: October 2022

Non-axisymmetric endwall profiling offers features to simultaneously mitigate aerodynamic losses and hot gas ingestion in axial turbines. The current paper presents an optimization methodology to generate a contoured surface integrated with real geometrical effects such as blade fillets and a rim seal channel with the aim of achieving higher efficiencies while reducing the hot gas ingestion.

The contoured rotor platform is constructed using a B-spline surface clamped in the axial direction. On the azimuthal direction the surface is unclamped to allow geometrical continuity across the periodic boundaries. The endwall parametrization is used to optimize a rotor hub platform of a high-pressure turbine stage.

A differential evolution optimizer is used to rank individuals in terms of efficiency. The single-objective optimization is set to maximize the aerodynamic efficiency and it is defined such that it accounts for the flow non-uniformity trough a mixed out averaging procedure. Engine representative conditions typical of a two-stage high pressure turbine are used as boundary conditions. Geometrical and aerodynamic constraints are set to guarantee a fair comparison among individuals and to meet engine requirements. Two surface parameterizations, which use a different number of design variables but share the same construction strategy, are presented to show the trade-off between the number of degrees of freedom and the aerodynamic improvement. Different purge flow conditions are considered to assess the robustness of the optimization results at off-design condition for relevant geometries.

The aim of the paper is to show the advanced shape flexibility of the implemented parametrization for contoured platforms featuring technological effects such as blade fillet and rim seal channel. The work provides design guidelines to set-up engine-realistic constraints for endwall contour optimization of turbine stages.
Influence of Geometric Parameters for a 100 kW Inward Flow Radial Supercritical CO2 Turbine
Authors: Hoque Syed J. , Kumar Pramod , Gopi Pramod Chandra
Published: October 2022

As an emerging technology, supercritical CO2 (sCO2) power generation systems currently focus on small-scale power generation. Inward flow radial (IFR) turbine is preferred for small-scale power generation due to its efficient and compact design. The influence of design parameters on sCO2 turbine performance can be different from gas turbines due to small size, high rotational speed, and low viscous losses. This paper presents a CFD study to find the optimal value of four geometric design parameters — axial length, outlet-to-inlet radius ratio, number of rotor blades, and velocity ratio for a 100 kW IFR turbine and their effect on the turbine’s performance. The results are compared against well-established gas turbine correlations in the 0.2 to 0.8 specific speed range to review their applicability on sCO2 turbines. The results show significant differences in the optimal value of design parameters compared to gas turbines. sCO2 turbines require fewer blades and a higher velocity ratio for optimal performance. The maximum turbine efficiencies (∼ 82%) are achieved at a lower specific speed of ∼0.4 than gas turbine results ∼ 0.55 to 0.65. Also, high incidence angles ∼ −50° to −55° are required at high specific speeds to counter the Coriolis effect in rotor passage. The results also show the variation of stator, rotor, and exit kinetic energy losses with specific speeds, which shows the cumulative losses are minimum at the specific speed of ∼ 0.4.
Experimental Investigation Into Oil Film Thickness and Behaviour Near an Aero-Engine Bearing
Authors: Sinha Avick , Hann David , Johnson Kathy , Walsh Michael
Published: October 2022

In an aero-engine transmission system, bearings are used for shaft location and load support. These bearings are housed in bearing chambers and oil is supplied to the chamber for lubrication and cooling. To achieve the targets of ACARE Flight-path 2050, improved engine design, including the transmission oil system, is required, necessitating a better understanding of oil flow behaviour and management in the bearing chambers.

The present work focuses on investigating oil flow behaviour on static surfaces near a bearing in a representative, purpose-built test rig, at four angular locations: 0°, 90°, 180° and 270° from top dead centre. The rig was run at shaft speeds up to a rotational Reynolds number of 1.7 × 106, for two oil flow rates and two axial load conditions. The investigation was conducted using high-speed imaging and subsequent detailed image analysis. These are the first experimental results obtained on this facility for film characteristics near the bearing slot at high shaft speeds. The current work has value both in terms of insights into the physics of the oil flow behaviour and also in generating high-quality data for comparison with CFD models.

Three different film regimes were identified based on the shape of the film interface and these have been descriptively characterised as long wave, short wave and uniform film. Median film thickness obtained from image analysis was found to be highest at the 180° location and lowest at the 90° location. At all speed/load conditions investigated, the surface waves were found to be capillary waves.
Carbon Capture: CO2 Compression Challenges and Design Options
Authors: Taher Matt
Published: October 2022

Carbon Capture and Storage are essential technologies to help achieve the ambition of net zero anthropogenic greenhouse gas emissions by 2050 [1]. Independent of the method used to capture the CO2, it remains central to compress carbon dioxide for liquefaction, transportation, and storage. The CO2 stream exiting almost any capture technology is in the gas phase, while it will be transported as a sub-cooled liquid for ship-based transportation or a dense-phase in pipeline-based transportation. The CO2 compression process that involves compressing low-pressure CO2 in gas phase to high-pressure supercritical phase is ‘transcritical’, i.e., with subcritical low-side and supercritical high-side pressure.

This paper is intended to provide a summary of the current CO2 compression technologies and design challenges. Different possible pathways to compress CO2 from subcritical to supercritical conditions are explained. Also, the anomalous behavior of supercritical CO2 and its effect on design and performance of the compression system is highlighted. Inline centrifugal compressors and integrally geared compressors are compared for transcritical CO2 compression applications. Also, the use of centrifugal pumps and reciprocating compressors are briefly addressed.
Method of Analysis for Impact of Input Uncertainty Error Propagation in a Highly Nonlinear System: Applied to Modern Aircraft Engine
Authors: Castaldo Timothy
Published: October 2022

Current methods for compressor vane control in a turbo-jet engine rely on measurements or estimates of compressor inlet temperatures and speed to determine the most favorable compressor stator vane angles over the course of an effectively infinite-horizon control decision process. During each instance of this process, the stator vane angles must be adjusted with a regular frequency to manage compressor efficiency and stability over the course of a flight. The optimality suffers from uncertainty in compressor inlet temperature, though the extent of deviation from optimality is unknown, as is the cost-benefit trade space for addressing this issue. This is an example of a more general problem in systems engineering, which is to estimate the cost of uncertainty in information with respect to its effect on deviations from optimality in infinite- and indefinite-horizon decision processes subject to a stochastic state machine that determines decision outcome. This thesis will develop a methodology for (A) estimating the cost of uncertain information in these kinds of sequential decision processes, (B) characterizing the trade space associated with addressing this problem, and (C) application to the jet engine design refinement problem.
Development of a Laser Igniter for Direct Fired sCO2 Combustor
Authors: Gupta Sreenath , Aithal Shashikant , Hosangadi Ashvin , Weathers Timothy , Fetvedt Jeremy
Published: October 2022

The combustor of a typical Allam-Fetvedt cycle has pressures ranging up to 300 bar and CO2 dilution levels up to 90% by volume, which present a rather challenging environment to ensure reliable ignition. Laser igniters offer improved performance under such adverse conditions, i.e., extend ignitability to a wider range of pressures, equivalence ratios and dilution levels. Additionally, unlike hypergolic igniters laser igniters can be used for ignition multiple times. Additionally, the capability of laser igniters to ignite at higher pressures reduces the relight operation in a power plant from several hours to less than a second. In this paper we report our efforts to design and develop a laser igniter for such combustors. First, high-fidelity CFD modeling was performed for a combustor geometry fueled by coal-derived syngas. Based on the predicted flow field, a laser igniter having a capability to place the ignition kernel at the optimal location was designed and developed. Finally, the performance of the laser igniter was evaluated using several bench-scale tests using premixed mixtures of coal-derived syngas and oxidizers. These bench-scale tests showed that laser ignition was possible over a wide range of equivalence ratios, ϕ = 0.7 to 1.6, and initial pressures up to 50 bar. These tests also showed that multiple ignition kernels form at the focal point along the laser line of sight. Both volumetric ignition and use of multiple ignition pulses (i.e., burst mode) significantly improve ignitability of the fuel-oxidizer mixtures.
Unsteady Gas Dynamics of Radial Turbine Volutes Under Pressure Pulsations
Authors: Yang Bijie , Xue Yingxian , Martinez-Botas Ricardo , Yang Mingyang
Published: October 2022

Turbocharging is the key technique to improve engine-specific power and reduce CO2 emissions of a piston-driven engine. Repeated actions of engine pistons and valves give rise to engine pulsations resulting in intensive unsteady flow in the turbines. Understanding the pulsation effects on a turbine that is steady-flow designed is crucially important for performance enhancement. The present work derives an equation that is capable of evaluating the pulsation effects on the volute-outlet flow angle. Based on the equation, a reduced order model (1-D) is proposed and applied to a single-entry mixed flow turbine. By comparing to 3-D unsteady computational fluid dynamics (CFD), the ability and accuracy of the 1-D model on predicting the unsteady volute-outlet flow angle is verified. The effects of the unsteady flow angle on the turbine performance are further investigated by comparing unsteady and quasi-steady flow field characteristics given by 3-D CFD. The present work unveils the volute unsteady behaviour and explains the unsteady coupling mechanism between the volute and the rotor. The findings can lead to improvement of turbine design methodology under pulsating flow conditions.
Evolution of Turbulence and Its Modification by Axial Casing Grooves in a Multi-Stage Axial Compressor
Authors: Koley Subhra Shankha , Saraswat Ayush , Katz Joseph
Published: October 2022

This paper examines the distribution of turbulent kinetic energy (TKE), normal Reynolds stresses, and production rates of stress components in the JHU refractive index-matched axial compressor at pre-stall and near the best efficiency (BEP) flow rates. Modifications to the turbulence caused by installing semicircular axial casing grooves (ACGs) are also investigated. The stereo-PIV measurements are performed in axial planes covering entire passages, from the hub to the tip, both between and within blade rows. The TKE is highly anisotropic and spatially inhomogeneous, with each of the normal stress components evolving differently. Most of the trends can be explained by examining the dominant production rate terms. Upstream of the rotor, at pre-stall flowrate, the TKE is high in the inlet guide vane (IGV) wakes, and in the tip region. The turbulence increases significantly upon entering the rotor with peak RMS values of axial velocity fluctuations reaching as high as 71% of the spatially averaged mean axial velocity. Near the rotor leading edge (LE), the TKE is elevated over the entire outer 30% of the span, expanding to 50% near the rotor trailing edge. Upon entering the stator, there is a rapid reduction in turbulence in the outer half of the passage aided by negative turbulence production due to axial extension. However, further downstream near the stator trailing edge, the turbulence increases along the lower suction side of the stator blade as the boundary layer separates intermittently. By stabilizing and homogenizing the flow, the ACGs reduce the turbulence production, hence the TKE, in the rotor and the stator. The only exception is an increase in turbulence at the interface between the outflow from the grooves at their upstream end and the passage flow. Near BEP of the untreated endwall, the TKE is much lower in all the investigated planes except for the region influenced by the groove outflow. The TKE downstream of the rotor and the stator for both smooth endwall and with the ACGs appears to be quite similar. Yet, the ACGs cause a reduction in the TKE peak but expand the area of elevated turbulence in the tip region. Distributions of measured eddy viscosity highlight the extreme non-equilibrium conditions over the entire machine, questioning the fundamental assumptions of local equilibrium in eddy viscosity-based Reynolds stress models.