bluuebunny/crossref_metadata_2025 huggingface dataset:
The Pore Size Dependence of the Radiative Scattering Coefficient in Yttria-Stabilized Zirconia Films
Authors: Wang Yao , Hsu Pei-feng , McCay Mary Helen
Published: October 2022

The yttria-stabilized zirconia (YSZ) top coat provides a thermal resistance function in the thermal barrier coatings used in gas turbines and Diesel engines. Besides the thermal conductivity, the thermal radiative properties, especially their dependence on the coating microstructure, under the high temperature combustion temperature are critically needed to the design and operation of the thermal barrier coating (TBC) systems. In this study ceramic oxide films made of thermally sprayed YSZ powder are prepared with three average porosities 5.9%, 14.5%, and 23.3% at film thickness from 283 to 955 μm. These films are fabricated with the air plasma spray (APS) deposition on the aluminum surface. The porosity changes are accomplished by varying the spraying parameters or ceramic oxide powder particle size. The room-temperature, spectral directional-hemispherical transmittance and reflectance are measured over the wavelength range from 1.35 to 2.5 μm. The radiative properties of absorption and scattering coefficients are reduced by using a hybrid method of the discrete ordinate method and the Kubelka-Munk four-flux method, depending on the film’s optical thickness. The films are then mounted, sectioned, and polished for SEM imaging. Using the image processing tools developed in-house, the porosity and pore size distribution (PSD) are obtained for each film. A numerical algorithm is used to convert the two-dimensional PSD into a three-dimensional PSD assuming all pores are spheriod. The absorption and scattering coefficients can be computed directly by the Mie theory based on the electromagnetic wave scattering from a distribution of sphere sizes. The new approach provides a predictive model of radiative properties based on the pore size distribution and pore number density, which are dependent on the APS spraying parameters, powder size and morphology. Comparison of radiative properties obtain by direct Mie theory computation and those obtained by reduction from spectral measurement is made and discrepancy is discussed.
An Experimental Study of Supercritical Methane Injection Characteristics in a CO2 Environment
Authors: Ghorpade Ritesh , Kim Gihun , Manikantachari (Raghu) K. R. V. , Weiner Joshua , Banuti Daniel T. , Vasu Subith
Published: October 2022

Clean energy generation is gaining significant attention from industries, academia, and governments across the globe. The Allam cycle is one such technology that has been under focus due to its efficiency, environmental friendliness, and economics. This is a direct-fired cycle operating at supercritical conditions using carbon dioxide as a working fluid. Fuel or oxidizer jet mixing with CO2 is a vital phenomenon that governs combustion efficiency, and it is not well understood for the Allam cycle conditions. This paper experimentally and computationally investigated the jet characteristics of a methane jet injected into a subcritical to supercritical carbon dioxide environment. A wide range of injection pressures and temperatures were targeted between subcritical to supercritical conditions. Unlike previous studies, the current work focused on injecting lower-density (methane) jets into higher-density (carbon dioxide) environments. Schlieren imaging and methane absorption measurements were simultaneously performed with a CMOS high-speed camera and a 3.39 μm infrared laser. Specifically, we looked at the classical injection parameter of jet spreading angle, which was classically established to be mainly a density ratio function. Here, the jet cone angle was obtained from the post-processed schlieren videos. The jet cone angle is a critical characteristic parameter that describes the entrainment rate in a jet; thus, it is a crucial parameter in understanding the nature of the jet. The laser measurements were only used as an additional check to confirm the entry time of methane into the chamber filled with carbon dioxide. Notably, this paper makes a detailed comparison between the jet cone angles of jets with a density ratio. The result showed that the classical correlations, such as Abramovich’s theory applied to submerged turbulent gas jets developed for low-density ratio jets, were unsuitable for higher-density ratio jets. It was also observed that the divergence angles were dependent not only on density ratio but also on other parameters such as pressure ratios and reduced pressures.
CAD Integrated Gradient-Based Aero Optimization of the NASA Rotor 37
Authors: Tran Thanh-Son , De Bruyn Tom , Verstraete Tom
Published: October 2022

The present paper aims to optimize one of the highly loaded, compact, axial compressors investigated by NASA, using modern RANS-based optimization techniques. The NASA rotor 37 blade is used as a starting point and has been approximated by a CAD-based parametrization. Predictions by the RANS solver are compared with experimental and numerical data to validate the models. A gradient-based aero-optimization is performed to improve the performance on a single operating point while maintaining the same mass flow. The gradients are obtained through an adjoint approach where the cost is nearly independent of the number design variables. Particular attention is given to the quality of the computed sensitivities to reach a better convergence. A total of 53 design variables from the blade, hub, and shroud geometry are used to define the design space of the compressor. A 5.5% relative improvement in total-to-total efficiency is achieved by a Sequential Quadratic Programming optimization algorithm. While the efficiency is improved at a single operating point, the full operating map shows a narrow efficiency peak with a wider operating range toward the stall condition. Nonetheless, the overall performance of the optimized design is significantly improved compared to the baseline performance, with a limited computational effort.
Effect of the Axial Compressor Tip Clearance Size: Performance and Transition to Rotating Stall
Authors: Rannou Clémence , Dazin Antoine , Marty Julien , Tanguy Geoffrey , Castillon Lionel , Moubogha Joseph
Published: October 2022

The leakage flow that is developed between the rotor and the casing of an axial compressor is usually associated with losses and can promote the arising of rotating stall. During its life, an axial compressor can be subject to a variation of the tip clearance due to the aging of the machine, which can modify the leakage flow and affect its performance. The prediction of the tip leakage flow and of its evolution with gap size is thus essential to estimate correctly the performance and operability of a compressor stage. The support of this study is a single stage compressor for which three different gap size ratios R=τc=3.4%, defined by the tip gap size τ over the axial chord c) are considered (R = 0.6 %, 1.2 %, 2.4 %). Reynolds Averaged Navier-Stokes (RANS) simulations are performed on the three configurations. The analysis is performed with two types of computational domains (a single blade-channel and one tenth of the full annulus geometry). The aim is to identify the configuration which provides reliable results at the most reasonable computational cost. Then, a numerical study on the effect of the tip gap size on the performance and flow topology of the compressor is conducted, especially at near stall operating conditions.
Mission Severity Assessment Based on 1Hz Engine Data
Authors: Scarso Stefano , Staudacher Stephan , Keller Christian , Mathes Jürgen
Published: October 2022

The severity of a flight mission depends on a wide range of operating conditions caused by aircraft, pilot and engine control system interaction. However, today’s availability of continuously sampled data offers the chance to relate the severity of a mission to the details of operation. In this work, 1 Hz measurements are taken from the DASHlink dataset of NASA. Other measurements not directly available in the dataset are synthesized through an engine model. Those are then used to calculate a severity parameter and a set of non-dimensional groups which are averaged for each flight. Based on those, a severity classification is performed on a sample of flight missions. The severity classification algorithm consists of a principal component analysis and a support-vector machine model. The accuracy and the robustness of the severity classification algorithm are evaluated for several flight missions. The contribution of each flight segment to the severity of the entire flight mission is discussed. The mean flight mission severity for the engine of highest and lowest operating time on a particular aircraft are compared and results are discussed. Finally, the ability to identify more than two severity groups is discussed.
Large Eddy Simulation of Energy Transport in Highly Compressible Transverse Jets
Authors: Guo Hao , Jiang Peixue , Zhu Yinhai
Published: October 2022

Large eddy simulation is performed to study the thermal energy transport and mixing process of a round laminar jet in a fully-turbulent high-Mach-number crossflow. In this study, the energy equation of highly compressible fluid is systematically analyzed and the contributions of each term in the equation are compared quantitatively. Turbulent enthalpy transport is found to be in the same order of magnitude as the advection term associated with mean motion and thus is not negligible when considering the convective heat transfer problem of film cooling, which differs from the conclusion drawn from the incompressible-jets-in-crossflow studies. The inaccuracy of RANS turbulent modeling caused by counter-gradient transport of enthalpy is explained in detail and a more reasonable three-dimensional analysis method is proposed for in-depth mechanism analysis and turbulent model improvement. The numerical results also show that the contribution of mean motion to the overall kinetic energy dissipation in thermal energy transport is dominant in the near-field region where jets and crossflow interact and mix intensively while the turbulent kinetic energy dissipation term predominates in most other regions. Moreover, the irreversible increase in entropy caused by dissipation and heat transfer in the flow field is compared. The results show that the entropy production due to the latter one cannot be ignored when dealing with large temperature difference film cooling which is common in high-pressure turbines.
Large Eddy Simulation of a Pistonless Constant Volume Combustor: A New Concept of Pressure Gain Combustion
Authors: Detomaso Nicola , Laera Davide , Pouech Paul , Duchaine Florent , Poinsot Thierry
Published: October 2022

Classical gas turbine thermodynamic cycle has undergone no change over the last decades. The most important efficiency improvements have been obtained reducing thermal losses and raising the overall pressure ratio and peak temperature. Pressure Gain Combustion (PGC) represents an increasingly interesting solution to break out current technological limits. Indeed cycle models show that a pressure raise across the combustion process would reduce the fuel consumption, increasing the efficiency. Providing an efficiency close to the corresponding detonative technological concepts, Constant Volume Combustion (CVC) represents a viable solution that still needs to be studied. In the current work, the CV2 (Constant-Volume Combustion Vessel) installed at the Pprime laboratory (France) is numerically investigated using the high-fidelity compressible Large Eddy Simulation (LES) solver AVBP. All the successive phases of the CVC cycle, i.e. air intake, fuel injection, spark-ignited combustion and exhaust, are considered in the LES. Intake and exhaust valves are properly represented by novel boundary conditions able to mimic the valves impact on the flow without the need to directly consider their presence and dynamics during the simulation, reducing the computational costs. The spark ignition is modeled as an energy deposition term added to the energy equation. The combustion phase is treated by the dynamic version of the Thickened Flame model (DTFLES) extended to deal with non-constant pressure combustion. Time-resolved Particle Imaging Velocimetry (PIV) and pressure measurement inside the chamber reveal that cold and reactive turbulent flow are well captured in all the phases, showing the reliability of the approach and the models used.
The Importance of Airfoil Selection in the Design of UAS Propellers
Authors: Van Treuren Kenneth , Wisniewski Charles
Published: October 2022

With the development of unmanned aircraft systems (UASs), interest in the design of propellers is growing. UASs are being used in the military for a variety of applications to include intelligence, surveillance, and reconnaissance (ISR) as well as resupply. Larger scale Urban Air Mobility (UAM) and eVTOL (electric vertical take-off and landing) vehicles are also receiving attention. Many of these systems use electric motors with a fixed pitch propeller. More efficient, quiet propellers are needed if these systems are to operate near populated areas. Selection of an appropriate airfoil is critical to satisfy these requirements.

This study proposes seven guidelines to evaluate airfoils: 1) sufficient thickness, 2) high lift coefficient, 3) high maximum lift to drag ratio, 4) broad peak at the maximum lift-to-drag ratio, 5) linear lift curve slope over propeller’s airfoil operating angle-of-attack (AOA) range, 6) low drag over the operating AOA range, and 7) selecting the appropriate Reynolds number for airfoil design aerodynamic data.

The Clark Y, GM15, GOE 225, GOE 358 and S1223 airfoils were analyzed using the selection guidelines. Propellers were designed for each airfoil using Blade Element Momentum Theory and tested in a low-speed wind tunnel. The aerodynamic performance of each propeller is reported as well as the noise generated in the near field. The GM15 required the lowest mechanical power to meet the on-design conditions of T = 2.5 lbf at a freestream velocity of 44 ft/s. This propeller also had the lowest measured peak Sound Pressure Level. While no airfoil satisfies all the selection guidelines perfectly, having an awareness of these guidelines will help with the selection of a suitable propeller airfoil for the mission and design point.
Flow Scaling Considerations for Internal Coolant Warming
Authors: Wiese Connor J. , Bryant Carol E. , Rutledge James L.
Published: October 2022

An increasingly common experimental technique allows measurement of overall effectiveness by matching the Biot number between experimental and engine conditions. The measured overall effectiveness distribution correlates to the actual turbine component temperature distribution. In addition to matching the Biot number, the theory also suggests that the coolant warming factor χ, must be matched. While it is clear from prior work what conditions must be met to match the Biot number of an experimental campaign to that of the engine conditions, it is often taken for granted that the coolant warming factor will also be matched. In this paper we develop the theoretical requirements necessary to match χ and test their validity through experiments performed on a conducting model of a leading edge using a variety of coolant gases to test the scaling theory with a wide range of coolant fluid properties.
Real Time mGT Performance Assessment Tool: Comprehensive Transient Behaviour Prediction With Computationally Effective Techniques
Authors: Gaitanis Aggelos , Contino Francesco , De Paepe Ward
Published: October 2022

Conventional centralized power generation is increasingly transforming into a more distributed structure due to the transition towards more renewable energy sources. The periodic power production that is created by the renewable production unit generate the need for small-scale heat and power units. One of the promising technologies which can assist a flexible and renewable power grid is micro Gas Turbines (mGTs). Such engines are generally considered to have an electrical power output less than 500kWe and are competent candidates for small-scale Combined Heat and Power (CHP). mGTs, as compensators for the demand fluctuations, are required to work on transient and part-load conditions. Therefore, the connection of such unit to a non-dispatchable energy system creates new research challenges.

A complete characterization of their dynamic behaviour through a real-time simulation tool is necessary to establish effective and suitable control systems. This model should predict all the crucial parameters of the engine, such as the surge margin and combustion stability, which assist in the effective performance diagnosis. Moreover, the energy transition requires the conversion of conventional mGTs to more sophisticated high-efficient cycles with the addition of extra components (saturation unit, aftercooler, etc). Consequently, a modular and computationally fast real-time tool offers an asset in the development of future advanced cycles based on the mGT concept.

This paper presents the complete development of a numerical in-house tool implemented in the Python open-source programming language for the behaviour prediction of the mGT. The fundamental target of our work is to achieve high fidelity of the simulated dynamic responses by adopting modern coding techniques that decrease the computational time. The model is validated with experimental results from the VUB Turbec T100 test rig and with additional data published in the literature. The component modeling methods are also compared to other techniques to confirm the practicality of the current code. Key benefits of this tool are the low complexity highly efficient component modules. This code reproduces the experimental results well during transient operation as the important cycle parameters present a deviation from the measurements within the range of 1.5%.
Experimental Investigation of Combustion Dynamics in a High-Pressure Liquid-Fueled Swirl Combustor
Authors: Chandh A. , Adhikari S. , Wu D. , McKinney R. , Emerson B. , Zhang Q. , Joshi D. , Sen B. , Davis D.
Published: October 2022

In this paper, we present combustor acoustics in a high-pressure liquid-fueled Rich burn - Quick quench - Lean burn (RQL) styled swirl combustor with two separate fuel circuits. The fuel circuits are the primary fuel (which has a pressure atomizer nozzle) and secondary fuel (which has an air blast type nozzle) circuits. The data were acquired during two dynamical regimes — combustion noise, where there is an absence of large amplitude oscillations during the unsteady combustion process, and intermittency, where there are intermittent bursts of high amplitude oscillations that appear in a near-random fashion amidst regions of aperiodic low amplitude fluctuations. This dynamic transition from combustion noise to combustion intermittency is investigated experimentally by systematically varying the fuel equivalence ratio and primary-secondary fuel splits. Typical measures such as the amplitude of oscillations cannot serve as a measure of change in the dynamics from combustion noise to intermittency due to the highly turbulent nature. Hence, recurrence plots and complex networks are used to understand the differences in the combustor acoustics and velocity data during the two different regimes. We observe that the combustor transitions from stable operation to intermittency when the equivalence ratio is increased for a given primary fuel flow rate and conversely, when the percentage secondary fuel flow rate is increased for a given equivalence ratio. The contribution of this work is to demonstrate methodologies to detect combustion instability boundaries when approaching them from the stable side in highly turbulent, noisy combustors.
Study on the Emissions Performance of a CMC Combustor With Weakly Coupled Stratified Swirl Flames at Engine-Relevant Conditions
Authors: Wei Wei , Xu Quanhong , Xue Xin , Yang Yue , Liu Cheng
Published: October 2022

Experimental and theoretical studies were conducted to investigate the overall emissions of CO, NOx, and UHC in a centrally staged lean premixed prevaporized (LPP) combustor featuring weakly coupled stratified swirl flames. The combustor consisting of a ceramic matrix composites (CMC) plate was run at aero engine-relevant conditions, with inlet temperatures and pressures up to 810 K and 2.2 MPa. The combustor adopted the concept of impinging cooling thanks to the heat-resistant property of CMC. The cooling air entering from the dome subsequently participated in combustion. The design of the test matrix was based on the typical operating conditions of practical LPP combustor. Without downstream cooling holes on the liner, the injector equivalence ratio was equal to global equivalence ratio of the entire combustor. The overall emissions data including EICO, EINOx, and EIUHC were obtained using a gas analyzing system under 15 different operating conditions. With a low fuel-air ratio (FAR), EINOx reached its lowest value when the pilot-to-total fuel split ratio (SR) was close to 0.13. With the increase in FAR, the main stage and pilot stage started to collectively dominate the emissions performance, eventually making the EINOx-versus-SR curve level off at a high FAR. Since the trend of CO emissions is normally contrary to that of combustion efficiency, EICO consistently remained at a low level in this combustor under the currently investigated conditions. EIUHC varied significantly with SR, where the pilot stage contributed more to emissions at low SfR while the main stage played a more important role with the increment of SR. Moreover, a new empirical correlation for NOx emissions in LPP staged CMC combustor was proposed.
Select Trade-Offs in Parallel Hybrid Turboprop Cycle Design
Authors: Sielemann Michael , Kavvalos Mavroudis D. , Selvan Nithish , Claesson Jim , Kyprianidis Konstantinos
Published: October 2022

Parallel hybrid turboprop engines propose a means to reduce fuel consumption of regional aircraft due to lower flight velocities. They feature an electric drive, typically on the free power turbine, and require a design trade-off between the gas turbine and electric power sub-system characteristics. Degrees of freedom include the nozzle expansion, the propeller power loading, the gear ratio, and the selection of shaft speeds. The latter for instance requires a trade-off between propeller and free power turbine efficiency. For a parallel hybrid, the electric machine efficiency becomes a third factor to consider. The objective of this paper is to expose some key aspects of these trade-offs in terms of efficiency and weight. The paper applies sophisticated methodology in both the gas turbine and electrical power domains. For the gas turbine, multi-point design is used. Here, an extension of established synthesis matching schemes is used, which covers the design and operation rules also for the electric components of the hybrid. For the electrical machine, fully analytical sizing is used, which also captures the impact of cooling. For all main gas turbine components and the electric machine, the geometry is estimated based on the sizing methodology, and used as input for the weight estimation. Results are presented for parallel hybrid electric 2.5-spool geared turboprop architectures fulfilling requirements of a notional 19 passenger regional aircraft. Uninstalled fuel consumption can be lower for the hybrid than the conventional baseline, and the key relations to typical cycle parameters such as overall pressure ratio and shaft speed selection are exposed. Overall, the benefit of hybridization is low however with the concept of operations inspired by hybrid turbofans. This is related to differences in contradicting cycle design requirements.
Study on the Influence of Fuel Supply and Distribution on the Performance of Concentric Staged High Temperature Rise Combustor
Authors: Sun Bolun , Song Wenyan , Li Jie
Published: October 2022

Based on the increasing demand for high thrust-to-weight ratio and high temperature rise of military aero-engines, a design scheme of combustor with concentric staged combustion organization is proposed. The main combustion stage of the swirler is a combination of swirling and non-swirling air intake. The verified one-dimensional calculation method is used to calculate and evaluate the performance of the combustion chamber. Based on the verification of three-dimensional numerical method and grid independence, the effects of fuel supply and distribution on combustor performance are studied. The studies show that the combustion efficiency and outlet temperature distribution could be improved when the axial position of the pilot nozzle is located at the outlet of vane channel. However, it will cause the problem that the high temperature flame is too close to the outlet of swirler. With the increase of the main nozzle angle, the combustion efficiency increases, and the overall temperature distribution factor (OTDF) decreases gradually. The fuel distribution ratio of main stage has a great impact on the field of temperature. The increase of fuel distribution ratio is contributed to improve the combustion efficiency and reduce the OTDF, while the total pressure loss coefficient increases slightly within a certain range. However, when the fuel distribution ratio exceeds 80%, the temperature near the baffle plate of dome is overheated, and the improvement effect of combustion efficiency is no longer obvious.
Sensitivity Analysis of Impeller Blade Parameters to Compressor Performance and Aerodynamic Noise
Authors: Yipeng Cao , Zequn Ma , Chen Liu
Published: October 2022

The effects of a series of impeller blade parameters on compressor performance and aerodynamic noise are numerical analyzed in this paper. The inversed impeller blade model of a turbocharger compressor was first constructed by the reverse engineering method. Then, the performance and aerodynamic noise of the inversed impeller blade model was validated using a numerical approach, which combines computational fluid dynamics (CFD) and computational aerodynamic acoustics (CAA). A parameterization of blade starts from the inversed impeller and then morphs it with a number of design parameters, which including tip clearance, the curvature of cut-off trailing edge, exit lean angle, inlet blade angle on shroud and inlet blade angle on hub. The influence of different structural parameters on compressor performance and noise was studied, and the sensitivity analysis of different structural parameters was carried out based on the Morris’s method. The results indicate that the tip clearance, the outlet lean angle of blade and the inlet blade angle at shroud have a significant effect on compressor aerodynamic performance, while the curvature of cut-off trailing edge and the inlet blade angle on hub have less impact. The overall sound pressure level (OASPL) of the aerodynamic noise radiated at compressor inlet shows that the inlet blade angle on shroud and the inlet blade angle on hub have a significant effect on compressor aerodynamic noise. The results of sensitivity analysis further indicate that the tip clearance and the inlet blade angle on shroud are the main parameters that affect compressor aerodynamic performance and noise.
Digital Shadow and Robust Optimization of in Service Squealer Tip Turbine Blades
Authors: Virdis Irene , Ghisu Tiziano , Shahpar Shahrokh , de la Puerta Iñaki , Li Haidong
Published: October 2022

The term uncertainty quantification (UQ) refers to a set of techniques which are used to measure the statistical variability of several input parameters. In recent years, UQ has become increasingly relevant due to its applications in robust design and optimization (RDO). The present work focuses on the RDO of aero engine components. 200 in-serviced high pressure turbine rotors with a squealer tip design were digitized using a GOM 3D scanning technique and analyzed using high-fidelity numerical flow simulations. All the blades considered display some geometrical deviations from the nominal shape and strong erosion along the rim of the squealer tip. A digital shadow with parametrized geometric deviation from nominal is built for each 3D scanned blade. Reynolds-Averaged-Naiver-Stokes simulations are run on each digital shadow with an in-house CFD solver, to quantify the impact of the shape deviation on the performance of the rotor, and to identify the parameters with the largest impact on its adiabatic efficiency. Following this, a robust aerodynamic optimization of the rotor has been performed using gradient based approaches. The resulting geometries and flow-fields are compared in detail, with particular attention to the robustness of the geometries with respect to the parameters defining the uncertainty in blade shape, and to the ones used to characterize the tip erosion.
Asynchronous Communication Pattern for Reducing Simulation Time in Engine Performance Models
Authors: Krouse Charles , Connolly Brian , Gordon Emilio
Published: October 2022

Demand is constantly increasing for high-fidelity models that execute quickly. To increase the fidelity of aircraft engine simulations, low-fidelity thermodynamic models are often interfaced with high-fidelity models used for capturing 2D and 3D effects. Unfortunately, interfaces and high-fidelity models are typically slow compared to rapid lower-fidelity thermodynamic models.

This paper presents an approach for managing the interface between a low-fidelity model and high-fidelity model that, under certain circumstances, significantly reduces simulation time. The typical solver in a thermodynamic engine simulation sequentially iterates through each component in the system until a converged solution is reached. This type of communication pattern is also known as synchronous communication. Alternatively, an asynchronous communication pattern partitions the model into independent groups of components. Each partition contains its own solver, and each partition converges independently of the others. By partitioning a high-fidelity subsystem model, which was developed in an external tool, along with its associated interface, the solver variables associated with the subsystem model can be separated from the main solver. This implementation can reduce the number of calls to the high-fidelity subsystem and reduce overall simulation time.

To demonstrate the asynchronous communication pattern, and to explore the approach’s impact on simulation time, a turbine-based combined cycle (TBCC) engine performance model was developed using the Numerical Propulsion System Simulation (NPSS) software. The NPSS model was interfaced with a high-fidelity afterburner model that was developed in an external tool. Using an asynchronous communication pattern, the engine performance model converged roughly 2.2x faster than using the conventional synchronous communication pattern for the same model. However, it was also shown that the asynchronous communication pattern is not beneficial in all scenarios, because it requires more total solver iterations. In this paper, the authors discuss the implementation and application of the asynchronous communication pattern, results, and conclusions.
Circulation Budget Analysis of the Leading-Edge Vortex in a Wells Turbine Under Steady Inflow Conditions
Authors: Geng Kaihe , Yang Ce , He Xinyu , Hu Chenxing , Zhang Hanzhi , Shi Xin
Published: October 2022

Due to the narrow operating range with the high efficiency of Wells turbines, the performance of Oscillating Water Column (OWC) systems is extremely limited by the stall issue. In this study, a detailed investigation on the flow physics at three typical flow rates corresponding to the design, stall inception, and deep stall conditions is performed, aiming to explore the mechanisms governing the evolution of the leading-edge vortex in terms of the circulation budget analysis. For this purpose, 3D unsteady Reynolds-averaged Navier-Stokes equations with the shear-stress-transport turbulence model are solved for a monoplane Wells turbine with high solidity under the steady-state inflow conditions. The numerical results show encouraging agreement with the available experimental data. The transient flow behaviors of stall inception and deep stall mode are captured by the Proper Orthogonal Decomposition (POD) method. Furthermore, the contributions of the spanwise convection of the vorticity gradient, vorticity tilting term, and the shear layer flux to the circulation of the leading-edge vortex are quantitatively determined within the spanwise control surface. The results indicate that, for stall inception condition, the high turbulent kinetic energy regions are attached to the leading edge of the suction surface with a disturbance of 0.33 times of the rotor frequency. The leading-edge vortex appears after the turbine stall, and its stable development time is less than 1/4 of the rotor period. Although leading-edge vortex occurs periodically after the first shedding with a significant decrease of circulation, it is almost not reattached to the blade surface, which speeds up the shedding and vorticity dissipation. The first shedding of the leading-edge vortex is related to the increase of radial vorticity gradient, but not directly related to the radial velocity. Furthermore, the spatiotemporal distribution of the circulation is similar to the spanwise convection, but there is a phase difference. In addition, the tilting term changes greatly in the evolution of the leading-edge vortex, indicating that the tangential and axial vorticity are tilted, which is verified by the spatial streamlines.
Experimental Investigation of CH4-Humid Air Flame Characteristic of a Novel Micromix Concept Model Burner
Authors: Liu Ce , Shao Weiwei , Zhang Zhedian
Published: October 2022

The temperature and humidity of the combustion chamber inlet air under the humid air turbine cycle (HAT) vary dramatically, with the highest air temperature of approximately 900 K and high humidity of about 0.3 kg/kg. Compared with conventional lean premixed combustion, which may cause risks such as flashback and autoignition under high-temperature conditions, micromix combustion has the characteristics of small mixing scale, compact flame, flashback resistance, and low emissions, and has been implemented in HAT cycle combustion chambers. In this work, a 9-nozzle micromix model burner with a 3 × 3 array arrangement was designed based on the flow field organization of multiple micromix round jets. The effects of heat load (30∼55 kW), air temperature (300∼630 K), and steam ratio (0∼0.143 kg/kg) variation on the combustion and pollutant emission characteristics of methane-humid air micromix flame at atmospheric pressure conditions were experimentally investigated. Intensified Charge-Coupled Device (ICCD) is adopted to detect OH* chemiluminescence distribution thus investigating the turbulence-reaction interactions and the characteristics of the reaction field. And the effect of humidity on NOx emission was qualitatively analyzed by combining it with a reactor network model. Results indicated that compact flames were achieved for different cases with flame heights of about 85∼185 mm. The steam ratio has a significant influence on the flame structure and NOx emission. Compared with the dry air condition, the flame length increased by nearly 50% while the steam ratio reached 0.143 kg/kg, and the NOx emission was kept at a relatively low level of about 5 ppm (@15% O2) under the designed operating condition. The in-depth understanding of humid air micromix combustion technology is a significant step toward the design of future stability combustors for the HAT cycle.
Simultaneous Ultra-Small-Angle X-Ray Scattering and X-Ray Transmission Measurements of a Liquid Jet in Crossflow With Film Atomization
Authors: Sforzo Brandon A. , Ilavsky Jan , Powell Christopher F.
Published: October 2022

Aircraft atomizers generally rely on multiple physical phenomena to introduce, distribute, and mix liquid fuel with the continuous air flow. Many such devices use plain jets for high liquid flow rates and film shear atomization to encourage droplet formation. To further characterize the near-field of processes, experiments were conducted to examine multiphase development of a liquid jet issuing into a subsonic crossflow. The jet impinged on a wall and the liquid subsequently filmed and convected downstream until reaching the end of the splitter plate, where it broke up by shear forces. X-ray diagnostics were used to interrogate different regions of the flow at the Advance Photon Source at Argonne National Laboratory 9-ID beamline. The projected liquid mass distribution was measured through x-ray absorption correlations using the collimated beam. The light was conditioned for Ultra-Small-Angle-X-ray-Scattering measurements, which were collected simultaneously with the transmission signal. These transmission and scattering signals were used to compute the projected mass and path-specific surface area of the spray, which were combined to calculate Satuer mean diameter. Though the transmission is typically collected using focused beam with a finer spatial resolution during a separate experimental campaign, the near-simultaneous acquisition allowed for more accurate registration between the signals and control of the operating condition. The transmission mapping confirmed the liquid path length of the unbroken liquid jet issuing into the domain and the interaction point with the wall. The spreading and flowing of the liquid down the plate and shedding from the trailing edge of the plate revealed an order of magnitude greater liquid path length, indicating the spreading of the film. X-ray scattering results indicate surface wave formation on the liquid jet and the initial stripping of droplets from the column. Furthermore, the scattering was enhanced for droplets rebounding due to splashing from the plate. The combined signals were used to calculate the droplet diameters in the shear breakup region trailing the splitter plate. These combined measurements provide detailed breakup information to inform inputs required to initialize Lagrangian spray calculations, as well as validate high-fidelity atomization simulations.
The Effect of Gas and Surface Temperature on Cold-Side and Hot-Side Turbine Deposition
Authors: Bons Jeffrey P. , Lo Chihsiu , Nied Eric , Han Jiaxuan
Published: October 2022

Deposition studies were conducted using two impingement jet facilities: a 60m/s cold jet (830–950K) impinging on a heated Hastelloy-X surface (1033–1255K) and a 215m/s hot jet (1450–1625K) impinging on an uncooled ceramic target or a cooled thermal barrier coated (TBC) surface (1090–1400K). These can be considered analogs for an internal impingement cooling jet flow and an external nozzle guide vane leading edge flow respectively. Airflows were seeded with 0–10μm Arizona Road Dust and deposition accumulated over a period of 5–10 minutes. Select tests were completed with other size distributions. Studies were conducted by varying flow temperature at constant surface temperature, and vice-versa. For both the hot and cold impingement jets, the sensitivity of capture efficiency to fluid (and thus particle) temperature was found to be roughly double the sensitivity to surface temperature. Hot jet tests with three different size distributions of dust (0–5, 0–10, and 5–10μm) allowed particle size sensitivity to be evaluated. For both target types (ceramic and cooled TBC), the 0–10μm test dust produced the highest deposition rate of the three size distributions. Possible explanations for the observed behavior are proposed. Companion CFD studies modeling both impinging jets with particle deposition demonstrate that temperature induced variations in particle trajectories alone are not sufficient to explain observed deposition trends with temperature. Implications for the development of a universal sticking model relevant for gas turbine deposition are discussed.
Heat Transfer in a Rotating, Blade-Shaped, Two-Pass Cooling Channel With Various 45 Deg Rib Turbulators and a Tip Turning Vane
Authors: Chen I-Lun , Wright Lesley M. , Han Je-Chin , Krewinkel Robert
Published: October 2022

This work experimentally studied a rotating, blade-shaped, two-pass cooling channel with various 45 deg rib turbulators and a tip turning vane. The first passage of the cooling channel has an aspect ratio (AR) = 4:1 with the coolant moving radially outward. After a 180 deg blade-shaped tip turn, the coolant flows radially inward into the second passage with an AR = 2:1. The first and second passages are oriented at 50 deg and 105 deg from the rotation direction, respectively. In the tip turn portion, a tip turning vane with an oval cross section connects the mid-lines of the two passes. Two orientations of 45 deg angled ribs were considered in this work: unusual, and criss-cross. The ribs have a profiled cross section and were placed in-line (P/e = 10, e/H = 0.16) on the leading and trailing surfaces of the channel. Five inlet Reynolds numbers (10,000 to 45,000) and five rotational speeds (0–400 rpm) were considered in this study, with a maximum rotation number of Ro = 0.38 achieved in the first pass. The results showed that the reduction from the turning vane on heat transfer and pressure loss for the 45 deg unusual rib case was the lowest. The overall heat transfer for the criss-cross rib case was slightly increased by the turning vane. For pressure loss, the turning vane provided approximately 8% reduction in the 45 deg criss-cross rib case, which was the highest in the rib cases. The 45 deg criss-cross ribs presented the highest thermal performance with the turning vane.
Comparing Different Schemes in a Combined Technique of Kalman Filter, Artificial Neural Network and Fuzzy Logic for Gas Turbines Online Diagnostics
Authors: Togni Simone , Nikolaidis Theoklis , Sampath Suresh
Published: October 2022

The paper presents research on the online performance-based diagnostics by implementing a novel methodology, which is based on the combination of Kalman Filter, Artificial Neural Network, Neuro-Fuzzy Logic and Fuzzy Logic. These methods are proposed to improve the success rate, increase the flexibility, and allow the detection of single and multiple failures. The methodology is applied to a 2-shaft industrial gas turbine engine for the automated early detection of single and multiple failures with the presence of measurement noise.

The methodology offers performance prediction and the possibility of utilizing multiple schemes for the online diagnostics. The architecture leads to three possible schemes. The first scheme includes the base methodology and enables Kalman Filter for data filtering, Artificial Neural Network for the component efficiency prediction, the Neuro-Fuzzy logic for the failure quantification and the Fuzzy Logic for the failure classification. For this scheme, a performance simulation tool (Turbomatch) is used to calculate the thermodynamic baseline. The second scheme replaces Turbomatch with the Artificial Neural Network, that is used to calculate the deteriorated efficiencies and the reference efficiencies. The third scheme is identical to the first one but excludes the shaft power measurements, which are not available in aero engines or might not be usable for some power plant configurations.

The paper compares the performance of the three methodologies, with the presence of measurement noise (0.4% reference noise and 2.0% reference noise), and 24 types of random single and multiple failures, with variable magnitude. The first methodology has been already presented by Togni et al. [10], whereas the other two methodologies and results are part of the PhD thesis presented by Togni [18] and they extend the applicability of the method. The success rate, targeting the correct detection of the of the failure magnitude ranges between 92% and 100% without measurement noise and ranges between 66% and 83% with measurement noise. Instead, the success rate of the classification, targeting the correct detection of the type of failure ranges between 93% and 100% without measurement noise and between 85% and 100% with measurement noise.
A Numerical Study on Conjugate Heat Transfer of Supercritical Carbon Dioxide Cooling in a Staggered Pin Fin Structure
Authors: Wardell Ryan J. , Otto Marcel , Smith Matthew , Fernandez Erik , Kapat Jayanta
Published: October 2022

Focused research and development of pin fin geometry in the trailing edge as turbulators in turbine blades has been a subject thoroughly researched for the past several decades. Highly efficient turbomachinery requires higher inlet temperatures, introducing the need for these internal cooling channel features to increase the heat removal of the blades and prevent material failure. Turbomachinery commonly uses air cycles to operate, but recently there has been a shift towards supercritical carbon dioxide (sCO2) power cycles. Promising higher cycle efficiency and smaller footprints, sCO2 has become an attractive alternative to the well-established turbomachinery cycles used presently. This alternative introduces the need to re-visit the local heat transfer of these internal cooling solutions with the incorporation of sCO2 as the cooling fluid. The first objective of this paper is to study the conjugate heat transfer characteristics of sCO2 as the secondary internal cooling fluid, operating at temperature and pressure conditions significantly above the critical point. A new heat transfer correlation is proposed for sCO2 in a staggered pin fin array. Secondly, the resulting sCO2 cases are compared to air cases in a matching staggered pin fin array to investigate the differences and similarities between both working fluids. The steady RANS conjugate heat transfer study was carried out with the commercial computational software STARCCM+ for the sCO2 and air cases. Finally, this study will validate a future experimental rig with matching geometry.
Digital Service Twin to Assess Engine Deterioration and Remaining Part Life
Authors: Klein Markus , Staudacher Stephan , Abu-Taa Kimon , Schwengler Jonas
Published: October 2022

During its complete service life, a turbo jet engine undergoes a continuous change of condition due to environmentally caused deterioration. The description of this change for an individual engine or even a fleet of engines results in a computational challenge requiring tailor-made parallelization. A digital service twin model is presented, which is capable to predict the engine condition on part level at any time of its life cycle. Deterioration is expressed on the level of relevant engine parts, whereby the interaction of multiple damage phenomena can be considered. Changes in component efficiency and capacity are deduced from part deterioration, allowing to map the gradual deterioration depending on its operational conditions. Flights based on Engine Health Monitoring data, ADS-B - data or synthetically created flights are used to run the model. Deviations, which arise due to these different data bases, are discussed. Besides the validation of the digital service twin, a sensitivity analysis is presented for input parameters which are not prescribed by commonly used data bases. This embraces the effects of time resolution, model quality and selected assumptions of unknown input parameters. Finally, the outcome of the digital service twin is presented for a reference deterioration phenomenon.