bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterizing Flow Instabilities During Transient Events in the Turbine Rim Seal Cavity
Authors: Rozman Maria , DeShong Eric T. , Berdanier Reid A. , Thole Karen A. , Robak Christopher
Published: October 2022

Gas turbine engine design requires considerations not only for long-term steady operation, but also for critical transient events. Aircraft engines undergo significant stress during takeoff and landing while power generation turbines must be flexible for hot restarts as renewable energy sources come on and offline. During these transient cycles, engines sustain wear and degradation that can lead to a reduction in the lifespan of their components and more frequent, costly maintenance. Cooling flows are often used to mitigate these effects, but can lead to complex and problematic flow interactions. This study uses high frequency response pressure probes and heat flux gauges in the rim seal cavity of a one-stage research turbine to characterize the properties of large-scale flow structures during transient operation. A continuous-duration turbine testing facility provides the ability to assess the importance of these transients by first reaching steady state operation prior to imposing transient behaviors. Although previous studies have conducted similar measurements for steady purge flows and wheel speeds, varying these parameters to simulate transient effects revealed several unique phenomena not identifiable with discrete steady measurements. The measurement approach connects the varied transient parameter to the behavior of the flow structures to enable a better understanding of the type of instability observed and the root cause of its formation. In particular, a relationship between instability cell formation and rim sealing effectiveness was identified using experimental data and was supported through computational simulations.
Mean-Line Design and Optimization of Axial-Flow Turbines Based on Mixed Integer Nonlinear Programming
Authors: Dipierro Vincenzo , Martinelli Matteo , Persico Giacomo , Martelli Emanuele
Published: October 2022

This work proposes a novel equation-oriented approach for the mean-line design optimization of axial-flow turbines, in which turbine constitutive equations and design specifications are included as constraints of the optimization problem. The problem is formulated as a MINLP (Mixed Integer Nonlinear Programming), including either Soderberg or Traupel loss models. This model formulation allows the use of the gradient/Hessian information of both constraints and objective function, speeding-up the optimization process. Moreover, it allows using “Spatial Branch-and-Bound” optimization algorithms (e.g., BARON) which have guaranteed global optimality. After an exhaustive validation, the model is applied to the optimization of two case studies (air and sCO2 as working fluids), resulting in certified optimal solutions and computational time lower than the black-box approach.
Using Engineering Enhanced AI to Forecast Combined Cycle Power Plant Performance in the Presence of Uncertain Weather Conditions
Authors: Perullo Christopher A. , Boche Lea , Redling Alex , Lim Jamie , Choi Woosung , Lieuwen Timothy C. , Noble David
Published: October 2022

Characterizing the performance of gas fired combined cycle power plants is critical to economic dispatch decisions. Dispatch models rely on an accurate prediction of Gas Turbine and combined cycle power output and heat rate. Approaches for generating performance characteristics range from correction curves to detailed thermodynamic performance models. Unfortunately, most techniques are either too simplified, require significant expertise, or are manually labor intensive. Furthermore, these performance estimation techniques do not intrinsically capture uncertainty due to the inherent variability of the weather and state of the asset. This paper proposes a physics-enhanced Artificial Intelligence technique for automatically characterizing power plant performance including uncertainty due to weather effects. The model uses a layered sub-model approach to rapidly learn power plant performance without the need for extensive data preparation. The proposed technique is used to evaluate for accuracy, ease of use, and level of automation. The new technique is accurate to within 1% and provides a power and efficiency forecast one week out. The technique is also applicable to other power generation assets and scaling techniques, and challenges will be discussed. An overview of the automation framework is provided including discussion on modeling approaches, AI approaches used, modeling techniques, and use cases.
Formaldehyde Emissions from Dry Low Emissions Industrial Gas Turbines
Authors: Carlos Ivan , Witherspoon Leslie , Cowell Luke , Saxena Priyank
Published: October 2022

Formaldehyde is listed as a Hazardous Air Pollutant (HAP) by various regulatory agencies around the world because of its role as a carcinogen. To address this impact, several countries have regulated formaldehyde emissions from land-based gas turbines. In the United States (U.S.), the federal regulatory level is 91 ppb and state level formaldehyde requirements vary significantly. In Germany, the formaldehyde limit is 5 mg/Nm3 (∼3.7 ppm) from 70–100% load. Formaldehyde emissions from gas turbines are formed due to incomplete combustion of natural gas and predictably track with carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions trends. This paper presents results from a formaldehyde measurement campaign completed in test cells at Solar Turbines on Dry Low Emissions (DLE) turbine products including the Mars® 100, Titan™ 130 and Titan™ 250 operating on pipeline natural gas. Theoretical modeling of formaldehyde formation using a Chemical Reactor Network (CRN) model are also presented. Measurements have been taken in the engine test cells over a range of operating conditions from full load* to idle. The latest Fourier Transform Infrared (FTIR) technology has been used to meet the challenges of accurately measuring formaldehyde down to the 10-ppb detection level. Formaldehyde emissions were found to range from near the detection limit to 50 ppb at full load with a small increase as load is decreased within the typical DLE operating range and a sharper increase outside of DLE mode to idle. The variation is attributed to differences between gas turbine models based on pressure ratio and combustion system design. CRN modeling predictions were compared with the test data, and the modeling results were used to gain insight into the formaldehyde emissions formation mechanisms.
Design and Validation of an Improved Lower Emission Additively Manufactured Combustor Pilot Nozzle for F Class Industrial Gas Turbine
Authors: Kalb Bryan , Yaquinto Matthew , Vogel Gregory , Keshava Bhattu Ramesh
Published: October 2022

Emerging additive manufacturing technology offers many opportunities for improved design in gas turbine components by enabling optimization of parts that are not manufacturable with conventional methods. The combustion components, for example, require complex fuel and air circuits to achieve best possible mixing and oxidation process for the lowest emissions possible. Thanks to the additive manufacturing, new combustor parts are making a break thru for improved capabilities in fuel flexibility and operating conditions. Also, quick turn around and modularity makes additive manufacturing a key enabler for fast validation of design concepts.

This paper describes the application of additive manufacturing technology in an F class industrial gas turbine including design, development and validation steps of a combustor pilot nozzle. A systematic design approach was undertaken to examine all aspects of combustion operation and testing, down-selecting the appropriate design, material and to productionize. Experience gained from other additive manufactured production parts as well as testing coupons were leveraged to ensure a robust production process. Combustion atmospheric rig testing was conducted to validate emissions performance. Detailed thermal and structural analyses were performed and validated with testing experience.

The new design demonstrated a benefit of approximately 50% in start-up emissions as well as improved combustion stability. In addition to the operability benefits, a 50% reduction in cost of the production assembly was realized. A main cost advantage gained with the utilization of additive manufacturing was the reduction in part quantity from 7 individual components down to 1. Constraints typical of conventional manufacturing methods were avoided with the implementation of innovative geometries only achievable by additive manufacturing. In addition to combustor component reduction, the additive process was also leveraged to reduce the total number of fuel circuits in the combustion system, making the installation and control logic more straightforward.

Several sets were successfully installed in customer’s engines, benefiting from an improved combustor pilot nozzle. Detail of the design and development steps as well as the results of combustion tests are presented and discussed in this paper. It shows that with proper considerations of the additive manufacturing technology, very quick turn-around and implementation of improved combustions solutions can be achieved: less than a year from development to production.
The Cooling Effect of Combustor Exit Louver Scheme on a Transonic Nozzle Guide Vane Endwall
Authors: Mao Shuo , Van Hout Daniel , Zhang Kaiyuan , Ng Wing F. , Xu Hongzhou , Fox Michael
Published: October 2022

The ever-increasing combustor exit temperature in modern turbine engine designs raises challenges for the nozzle guide vane cooling. Due to the challenges of NGV cooling design, the cooling effect from the combustor cooling features can prove valuable. This study investigates, experimentally and numerically, the cooling effect of a louver cooling scheme near the combustor exit on the NGV endwall. The wind tunnel testing and CFD simulation are carried out with engine-representative conditions of Maexit = 0.85, Reexit = 1.5 × 106, Tu = 16%, and DR = 2.1. Various coolant mass flow rates from 1% to 4% are tested to demonstrate the effect of the coolant rate.

For the geometry studied, the results found a critical MFR between 1%∼2%. By exceeding this value, the coolant forms a uniform film which provides good coverage upstream of the NGV passage inlet. As for the cooling of the NGV passage, the MFR of the range investigated is not sufficient for desirable cooling performance. The pressure side endwall proves most difficult for the coolant to reach. In addition, the fishmouth cavity at the combustor-NGV passage causes a three-dimensional cavity vortex that transports the coolant in the pitch-wise direction. The coolant transport pattern is dependent on the coolant MFR. Based on the results, it is proposed to combine this louver scheme with the upstream jump cooling scheme for a desirable NGV cooling system.
Numerical Investigations on the Rotating Stall in an Axial Compressor and Its Control by Flow Injection at Casing
Authors: Marty Julien , Castillon Lionel , Joseph Pierric
Published: October 2022

The operating range of a compressor is limited by surge or rotating stall line, among others. Numerical simulations must accurately predict these phenomena. This study is based on the experimental compressor CME2, which is a low-subsonic axial compressor. This compressor is tip-critical as the rotor tip is responsible for the rotating stall. This paper shows that the rotating stall onset flow rate is well captured by CFD, compared to experiments. After ten revolutions, all cells are merged and only one cell remains, as in experiments.

Active flow control improves compressor performance and extends the stable operating range. In the present configuration, flow injection is performed at the casing. In the simulation, the insertion of the actuators is carried out through hybrid meshes: structured mesh for blade passages and unstructured mesh for each actuator. For the some stalled operating points of baseline configuration, there is no rotating cells in the controlled configuration. Thus, the rotating stall is delayed at lower flow rate, as expected by the use of active flow control and is in agreement with the experiments.
Measurement of Inertial and Acoustic Waves in a Turbine Chute Rim Seal Cavity
Authors: Bru Revert Anna , Beard Paul F. , Chew John W.
Published: October 2022

A chute rim seal cavity has been instrumented with time resolved and time-averaged pressure transducers as well as a gas concentration measurement system at the Oxford Rotor Facility. The unsteady pressure transducers were unevenly distributed along the circumference generating 15 combinations of angular spacing to conduct a phase analysis. The test operating conditions were modified through different configurations of mainstream flow, a range of rotational speeds and purge flows to obtain test data in the regimes of rotationally-driven, pressure-driven and combined ingestion. The rotating unsteady flow structures within the rim seal cavity were studied through a combination of phase analysis of dynamic pressure signals and inspection of the frequency domain. The introduction of mainstream flow (axial and swirled) increased the overall unsteadiness exciting an additional band of lower frequencies. The phase analysis revealed these were associated with acoustic waves, providing the first experimental evidence of the presence and coexistence of inertial and acoustic waves in the rim seal cavity. The interaction of the inertial and acoustic waves strongly depends on the operating conditions, and may be linked to changes in sealing effectiveness.
Establishment of a Baseline Integrated Energy System to Decarbonise Geographical Islands
Authors: Mansouri Mohammad , Madi Hossein , Breuhaus Peter
Published: October 2022

Achieving strict decarbonisation targets, while providing a safe, reliable, and affordable supply of energy on geographical islands is more complex than in mainland locations. Contrary to the mainland, where grid support and energy exchange with other regions are possible because of integration into large energy grids, the situation for geographical islands is different. Islands often have either no or limited connection to neighbouring ones or to the mainland resulting in a relatively costly energy supply and less opportunities for services such as balancing or backup to overcome the challenges that fluctuating renewables can cause. This can be tackled by development of highly flexible energy systems integrating various available renewable energy sources, multiple prime movers, and necessary energy storage and transportation infrastructure.

A currently ongoing ROBINSON project aims at contributing to decarbonise geographical islands by developing and installing a demonstrator of an integrated energy system on the island of Eigerøy in the southwest coast of Norway. As part of the ROBINSON project, this paper presents a brief overview of the project and its objectives, the baseline configuration of the integrated energy system and its energy fluxes that will be demonstrated on the island of Eigerøy in Norway. Even though the project is still in an early stage of implementation, this paper describes possible challenges and resulting requirements of different sub-systems including a gas turbine based combined heat and power unit within a highly integrated energy system.
Numerical Study of High-Altitude Relight for an Aviation Gas-Turbine Engine
Authors: Litrico Giuliana , Shrivastava Sourabh , Meeks Ellen , Nakod Pravin , Xu Fang , T. Dhanya , Muthuraj Sivaprakasam
Published: October 2022

The altitude relight capability of an aero-engine is a critical requirement that defines the operational flight envelope of the engine. Regulatory requirements from the Federal Aviation Administration (FAA) and European Union Aviation Safety Agency (EASA) ask to establish the altitude and airspeed envelope for in-flight engine restarting and adherence to engine performance. Further, engine manufacturers are changing combustor designs to meet aggressive goals that limit the emission of nitrogen oxides (NOx). While these design changes help reduce the NOx formation, they can be problematic for restart capabilities at high altitudes. Therefore, the engine design process becomes a complex optimization problem with conflicting goals. Test-rig data can provide insights into the performance; however, using testing to explore the entire design space is challenging, expensive, and sometimes infeasible. In this scenario, high fidelity computational fluid dynamics (CFD) simulations can bridge this gap and are, therefore, widely evaluated by designers and simulation engineers. Such simulations need to resolve flow structures, spray distribution, and ignition processes to predict the high-altitude relight accurately. Moreover, no, or limited parameter adjustments should be required for correctly predicting the relight outcome across different operating conditions.

In this work, numerical simulations are performed to predict an aviation gas-turbine combustor’s relight performance, operating under different conditions, including sea level and 40000 ft operation. The CFD simulations are performed using the unsteady RANS approach for turbulence, solution-adaptive meshing, and finite-rate kinetics for the combustion modeling that tracks the flame propagation during and after the spark event. The results are encouraging and predict accurate behavior of lighting and not lighting operating conditions consistent with the light/no-light outcomes from the experimental tests. The simulation methodology, best practices, and obtained results are discussed in this paper.
Impact of Compressor and Turbine Operating Range Extension on the Performance of an Electric Turbocharger for Fuel Cell Applications
Authors: Lück Sebastian , Schödel Markus , Menze Marco , Göing Jan , Seume Jörg R. , Friedrichs Jens
Published: October 2022

In this study, an electric turbocharger for fuel cell applications is investigated with regards to the extension of both compressor and turbine operating range by means of geometric changes to the turbomachinery components, namely variable nozzle and diffuser vane angles. Therefore, the interaction of the electric turbocharger subsystem with the fuel cell stack is investigated over the full operating range to judge the overall efficiency, system dynamics and stability. Initially, selected options for extending the performance maps of both compressor and turbine are presented and discussed. The numerical methods used for predicting the performance maps are then described. Subsequently, the entire machine is simulated under both steady-state and transient operating conditions using the in-house tool ASTOR (AircraftEngine for Transient Operation Research). Based on the wider operating ranges of compressor and turbine, promising setups are identified and investigated in further detail to select the best choice for the operation of the electric turbocharger. The impact of isolated component modifications is shown initially and substantial improvements of the operating range are shown. The modification of the compressor diffuser leading edge angles in a fixed-geometry diffuser increases the range of covered operating points from 4 to 7 while at the same time improving the compressor surge margin during steady state operation above the required safety margin of 20%. Additionally, the system efficiency can be increased by 0.2%. The application of a positive angle variable nozzle turbine significantly shifts the operating line towards higher mass flows, thus increasing the surge margin especially in the high speed range where the transient effects during deceleration of the machine are the greatest. By applying combined modified compressor with pivoting vanes and and variable nozzle turbine geometry, the operating range can be extended even further. The surge margin can be kept above 20% during the initial critical part of a transient deceleration manoeuvre. Nevertheless, a decrease of 0.5% in overall system efficiency has to be accepted due to the measures.
Part-Load Behaviour and Control Philosophy of a Recuperated Supercritical CO2 Cycle
Authors: Gini Lorenzo , Maccarini Simone , Traverso Alberto , Pesatori Emanuel , Milani Alberto , Bisio Valentina , Valente Roberto , Barberis Stefano , Guedez Rafael
Published: October 2022

High efficiency, flexibility and competitive capital costs make supercritical CO2 (sCO2) systems a promising technology for renewable power generation in a low carbon energy scenario. Recently, innovative supercritical systems have been studied in the literature and proposed by DOE-NETL (STEP project) and a few projects in the EU Horizon 2020 program aiming to demonstrate supercritical CO2 Brayton power plants, promising superior techno-economic features than steam cycles particularly at high temperatures.

The H2020 SOLARSCO2OL project1, which started in 2020, is building the first European MW-scale sCO2 demonstration plant and has been specifically tailored for Concentrating Solar Power (CSP) applications. This paper presents the first off-design analysis of such a demonstrator, which is based on a simply recuperated sCO2 cycle. The part-load analysis ranged from 50% of nominal up to a 105% peak load, discussing the impact on compressor and turbine operating conditions. The whole system dynamic model has been developed in TRANSEO MATLAB® environment. Full operational envelop has been determined considering cycle main constraints, such as maximum turbine inlet temperature and minimum pressure at compressor inlet.

The off-design performance analysis highlights the most relevant relationships among the main part-load regulating parameters, namely mass flow rate, total mass in the loop, and available heat source. The results show specific features of different control approaches, discussing the pros and cons of each solution, considering also its upscale towards commercial applications. In particular, the analysis shows that at 51% of load an efficiency decrease of 20% is expected.
Development of a Large-Scale High-Speed Linear Cascade Rig for Turbine Blade Tip Heat Transfer Study
Authors: Jiang Hongmei , Peng Xu , Xie Wenbo , Lu Shaopeng , Gu Yongmin , Zhang Qiang
Published: October 2022

The high-speed Over-Tip-Leakage (OTL) flow has significant impact on aerodynamic performance of the High-Pressure turbine (HPT) passage and generates high thermal load for the blade tip. Different tip sealing and cooling design strategies are applied to reduce the OTL loss and help turbine survive in high temperature environment. High-speed linear cascade experimental rigs play an important role in understanding the flow physics and evaluating their performance. Multiple blades and passages are often required to maintain a reasonable flow periodicity. To match the engine representative Reynolds number and Mach number, a high-speed multi-passage cascade design inevitably demands more compressed air supply. A very large amount of heating power is also required if the engine condition wall-to-gas temperature ratio needs to be matched. In this study, a simplified two-passage linear cascade rig for high-speed tip heat transfer research was developed. Both the design method and the rig performance are presented. Different from existing design method to match two-dimensional blade loading, this study shows there are other design flexibilities, such as assist blade tip gap, tailboard adjustment and profiling, adjustment, to match the periodic three-dimensional OTL flow structures. The design method was validated by experimental effort. High resolution tip heat transfer coefficient distribution at stationary and rotating conditions (Rotating Mach = 0.35) are reported. The enlarged test model can offer much more improved resolution of optical measurement near the tip region.
Method of the Vaneless Diffuser Rotating Stall Cell Size Assessment Based on the PIV Measurements
Authors: Grapow Filip , Liśkiewicz Grzegorz , Kryłłowicz Władysław
Published: October 2022

This paper presents the universal method of assessing the Vaneless Diffuser Rotating Stall (VDRS) cells’ size with the use of the Particle Image Velocimetry (PIV) technique. Two different cell dimensions’ definitions were introduced: Radial Cell Size (RCS) and Circumferential Cell Size (CCS). The step-by-step instructions for the calculation of both cell sizes are provided. Also, potential issues that readers may encounter while calculating the VDRS cell’s size are presented followed by examples of their solutions. The presented method for cell size assessment is universal and can be used not only with PIV measurements but with any technique allowing flow field reconstruction inside the diffuser or in numerical research. Such an analysis provides information regarding the most crucial zones inside the diffuser for anti-VDRS systems. Based on the results it is possible to increase the efficiency and applicability of the already developed and future VDRS prevention systems. Additionally, this method allows further understanding of the VDRS development by means of the cell growth study. Results of such an analysis may be used to improve compressor design resulting in better performance and wider operation range.
A Numerical Investigation on the Influence of Wall Roughness on the Performance of Volutes of Centrifugal Compressors
Authors: Wolbert D. , Schmitt M. , Koenig S. , Wannek M. , Hartmann J.
Published: October 2022

This paper presents the results of a numerical investigation on the influence of wall roughness on the performance of centrifugal compressor volutes. The main objective of the presented work was to gain further knowledge on the highly three-dimensional flow inside the volute with regard to wall roughness and operating point (surge, best efficiency point and choke). The numerical investigation was carried out with steady state simulations and SST with enabled Reattachment Modification as turbulence model for two centrifugal compressor stages with different outward wound volutes. By means of the equivalent sand-grain roughness ks, the wall roughness was systematically varied and its influence on the volute was evaluated by a thorough performance and flow analysis. The expected drop in efficiency and polytropic head with increasing wall roughness was observed, which was more distinct at choke conditions, mainly due to the increasing skin friction losses at the volute walls. The flow analysis also showed influences of the wall roughness on the secondary vortex flows structures at the smaller volute cross sections near the volute tongue area, with distinct changes compared to the smooth wall case in terms of location and form. An influence of wall roughness on a possible shift of the best efficiency point was not observed.
Transition of a Laminar Separated Boundary Layer Under Varying Adverse Pressure Gradient
Authors: Kumar Ravi , Singh Pradeep , Sarkar S.
Published: October 2022

This paper describes the effects of pressure gradients on the transition of a laminar separation bubble (LSB) formed over the flat plate. The measurements were performed using electronically scanned pressure (ESP) and hot-wire anemometer. The different adverse pressure gradients (APG) are achieved by changing the opening angle (α) of the upper boundary of the domain. The experiments were performed for α = 7°, 9.5° and 11.5° at a Re of 2 × 105 (based on the inlet freestream velocity and plate length) and freestream turbulence intensity (fst) of 1.02%. The onset of separation and transition occurs at x / L = 0.39, 0.449 respectively with reattachment at 0.491 for α = 7°. As APG increases, the separation, transition and reattachment shift upstream with respect to α = 7° leading to the reduction in bubble length. The decrease in the length of LSB is attributed to the earlier transition. Moreover, the growth rate of fluctuations increases with increasing APG. The power spectra of streamwise fluctuations illustrate that the transition occurs via K-H instability for all APG and the predominant shedding frequency increases with increasing pressure gradient. Moreover, the self-similarity of normalized urms profiles in the second half of the bubble show the presence of viscous instability.
Microtomography of Soil and Soot Deposits: Analysis Of Three-Dimensional Structures and Surface Morphology
Authors: Suman Alessio , Vulpio Alessandro , Pinelli Michele , D’Amico Lorenzo
Published: October 2022

The detrimental effects generated by the gas turbine fouling phenomenon are well known. Due to soil and soot particles ingestion, gas turbines experience performance drops related to greater fuel consumption and even lower efficiency. These effects are related to the modification of the shape and surface roughness of relevant surfaces (compressor and turbine blades and vanes, especially) due to the presence of a thin layer generated by micro/nano-sized particle adhesion. Such contaminants are swallowed by the unit and, as a function of the operating conditions, adhere to the surface, causing a sort of dangerous coating to the surface.

In this work, a microtomography analysis of the deposited layer is reported. The deposited layer has been generated using micro-sized soil and soot powders under specific impact conditions and substrate surface roughness similar to those in the cold section of a gas turbine compressor. The microtomography analysis has been carried out using the beamline at the ELETTRA Sincrotrone research center. Thanks to the resolution of the beamline, the detection of the three-dimensional internal structure of the soil and soot layers has revealed that within the layer, the structure is characterized by discontinuities. Soot and soil particles, even characterized by similar diameter distributions and test conditions, generate layer structures that differ by the magnitude, orientation, location of the internal discontinuities, and surface morphology (i.e., roughness). The comprehension of the packing process allows to understand the adhesion process and define general guidelines to predict the fouling phenomenon.
Performance Simulation of Micro Gas Turbines for Hydrogen Application
Authors: Esmaelpour Arias , Nikpey Somehsaraei Homam , Breuhaus Peter
Published: October 2022

The intermittency of renewable energy resources like solar and wind provides unstable outputs and may not comply with the energy demands at all time frames, and the network faces periodic surplus and shortage of energy. Dispatchable energy generation technologies that can be ramped up and down could be combined with intermittent renewables in hybrid systems to match the demand and to address the variability in generation.

Currently, the commonly used dispatchable energy generation technologies are operating with fossil fuels that contribute to CO2 emissions. On the other hand, carbon capture technologies are costly, energy consuming and cannot be applied for small scales. Hence, a dispatchable energy generation technology that can utilize clean and renewable based alternative fuels such as hydrogen to maintain the grid flexibility and stability becomes attractive. In this context, micro gas turbines (MGTs) with high operation flexibility and the ability for operating with various fuels and flue mixtures can potentially represent a lucrative solution for reliable and efficient energy supply, contributing to realize a sustainable future.

Therefore, this study investigates the performance of MGTs in hydrogen application, which is in line with ongoing hydrogen activities at UiS. To this end, this study focuses on the development of a physical model based on an existing Turbec T100 test rig. The modelling is carried out using UniSim software which is a commercial process simulation tool. The model is validated against steady-state experimental data obtained from the test rig operated by natural gas while the dynamic validation of model is a part of future work due to the lack of adequate transitional experimental data. Assuming necessary modifications to the engine, the effects of utilization of mixtures of hydrogen and natural gas from zero hydrogen to 100% hydrogen on the engine performance are analyzed at various operational conditions and compared with the standard natural gas fired engine.
High Accuracy Numerical Investigation of Trailing Edge Noise at Vortex Shedding Critical Angle of Attack
Authors: Zheng Huabin , Chen Jinqiang , Yu Peixiang , Ouyang Hua
Published: October 2022

In this paper, the trailing edge noise generated by a 2D airfoil around the critical angle of attack for vortex shedding is numerically investigated using an in-house code with high accuracy and efficiency. In the present method, a fourth-order upwind compact finite-difference scheme with dispersion relation preserving (DRP) property is applied for the convection terms, and a fourth-order Runge-Kutta scheme is used for temporal discretization. The reflection of sound on the boundary is suppressed with Navier-Stokes characteristics boundary condition (NSCBC). To improve computational efficiency, a novel parallel computing strategy for the high-order compact schemes is employed. Thus, direct numerical simulation (DNS) can be realized for the flows of low Reynolds number (Re), while implicit large eddy simulation (ILES) would be carried for the flows of high Reynolds number. The present numerical method is validated by comparing the lift coefficient, drag coefficient and Strouhal number (St) to the previous publications. Based on the high accuracy and high-fidelity method, the flow field and sound field of a two-dimensional NACA0012 airfoil around critical angle of attack (AoA) at Re = 1000 are simultaneously solved. The results indicate that sound source is dipole centered at the surface of the airfoil at vortex shedding frequency, and is dipole, quadrupole or more complex sources located at the wake close to the trailing edge at higher order frequencies. These findings will help to improve understanding about the generation and propagation mechanisms of trailing edge noises at low Reynolds number.
A Self-Sufficient Oil Cooling Mechanism for Fluid-Film Bearing Applications in Remote Operations
Authors: Gokaltun Seckin , Fabijonas Bruce R. , Krajewski Louis S. , Rodzwic Richard C.
Published: October 2022

The Kingsbury CH Bearing System is a self-contained bearing solution that utilizes a viscosity pump to supply lubrication to individual bearings. The system consists of a CH unit that houses a journal bearing and a double thrust bearing assembly as well as an oil reservoir and internal oil channels and a C unit which houses a second journal bearing. The names ‘CH’ and ‘C’ are historical. An external piping loop connecting the CH and C units lubricates the C journal bearing. Another external piping loop connects the oil reservoir in the CH unit to an external cooling system which cools the hot oil leaving the CH thrust bearings. The system traditionally employs a heat exchanger using cold water provided by a pumping station. Due to the self-contained nature of the CH system as described above, field applications can involve remote locations where utility access could be limited; therefore, it is desirable to avoid the dependence of the cooling system on a reliable water supply. This is especially critical for applications where there is additional difficulty in maintenance of the units due to reduced crew access. In this work, we present a solution for removing the reliance on a water-based cooling system for the CH Bearing System. Instead, the traditional shell-and-tube heat exchanger is replaced with a radiator/fan combination. The fan is mounted to the end of the shaft which extends through the CH housing on the non-drive end of the machine. This mounting method marries the cooling rate with the operating speed of the shaft and ensures that oil is being cooled as long as the shaft is rotating. Experiments with a CH test unit using this new cooling set up show that the required oil temperature in the oil reservoir can be achieved using the air-based system while not adversely affecting pressure drops and flowrates in the lubrication lines.
Modal Identification for Integrally Bladed Rotors Under Traveling Wave Excitation
Authors: Beck Joseph A. , Brown Jeffrey M. , Gillaugh Daniel L. , Kaszynski Alex A.
Published: October 2022

The safety of a fielded Integrally Bladed Rotor (IBR) is often assessed through vibration testing. Responses due to various types of excitation are measured and processed and can be inputs to follow-on analyses, such as mistuning identification. One such excitation technique is the Traveling Wave Excitation (TWE) where all blades are simultaneously excited at phase differences that attempt to replicate naturally occurring mode shapes and certain operating conditions. This test relies on non-contact exciters, e.g. magnets and speakers, that are often not directly measured. As a result, formulating the Frequency Response Function (FRF) is difficult and the extraction of system modal data using FRF fitting techniques in the absence of FRFs is not possible. This paper presents an approach to use measured responses from TWE tests. It is shown that the Fast Fourier Transform (FFT) of the TWE inputs are mostly independent over the prescribed frequency range. Consequently, the output spectral density matrix can be formulated in an Operational Modal Analysis (OMA) sense, where direct measurement of the inputs is not needed. A full spectral density matrix is then formulated from a single measurement on each blade obtained during a single test, thus reducing the number of measurement locations and testing excitation conditions. This matrix is fit by a Polyreference-Least Squares Complex Frequency-domain (P-LSCF) system identification technique tailored for OMA-type measurements. The methodology is tested using simulated TWE data for an IBR model using different damping levels. Comparisons between identified modal data and those used to create the model are made and show the methodology accurately predicts underlying system information even for closely-spaced modes that are common to IBRs. Finally, the method is used on experimental TWE data of an industrial IBR.
Off-Design of a Small-Scale Liquefaction Plant Operating With Biomethane
Authors: Baccioli Andrea , Pasini Gianluca , Barbieri Gregorio , Ferrari Lorenzo
Published: October 2022

Liquefied natural gas is recently playing an important role in the heavy-duty vehicle and marine fuel market due to the low ambient impact, easy onboard storage, and low commercial prices. Biomethane from biogas upgrading can integrate the LNG market by providing the added value of an almost zero carbon footprint fuel.

The production rate of biomethane is distributed in various anaerobic digestion plants, and daily amounts are limited to a few tons per day, with a substantial variability depending on digester feed. For this reason, small-scale liquefaction systems are requested to convert biomethane into bio-LNG. The Joule-Brayton reverse cycle is a promising solution for small-scale plants due to its simplicity and ease of regulation.

The control strategy of this plant is important since small-scale installations are characterized by relatively high specific consumption that might increase when the system is operated in part-load or off-design conditions. For this reason, the comparison between two control strategies is proposed in this study: variable rotating speed control strategy and inventory control are compared and assessed. A steady-state off-design model of the plant was implemented in Aspen Hysys by considering the behavior of all the main system components, including compressors, turbine, intercoolers and aftercoolers, turbine, and cold-box. Typical analytical relations for heat exchanger off-design were considered as well as typical characteristic maps for the fluidmachinery. The two control systems were introduced in the model by implementing the control equations at the steady-state. Results showed that inventory control allows the system to achieve better performance and results to be more flexible. Variable rotating speed control strategy led to surge issues at low small biomethane production and low ambient temperature. By considering a plausible biomethane production profile, inventory control allows the specific consumption to be reduced by 4.3 %, and liquefied biomethane production increases by about 131 t with respect to variable speed control.
Use of Multiple Tracer Gases to Quantify Vane Trailing Edge Flow Into Turbine Rim Seals
Authors: Monge-Concepción Iván , Barringer Michael D. , Berdanier Reid A. , Thole Karen A. , Robak Christopher
Published: October 2022

Overlapping features are commonly used as rim seals between stationary and rotating components in a turbine stage. These rim seals are used to prevent main gas path ingestion to the wheelspace cavity, which reduces the lifespan of critical engine components such as the turbine disk. In addition to the overlapping features, purge flow, diverted from the compressor, is injected into the rim cavity to act as an airflow sealing mechanism. Previous research identified that in addition to the purge flow in the rim cavity, cooling flow from the vane trailing edge (VTE) is ingested into the rim seal cavity carrying the potential to cool components in the wheelspace. These previous findings, however, were not able to distinctly separate purge from VTE cooling flows, which is the contribution of this paper based on uniquely using two different tracer gases. A one-stage test turbine operating at engine-relevant conditions and consisting of real engine hardware was used to validate and quantify the ingestion of the VTE flow by independently seeding the purge and VTE flows with two different tracer gases. Experimental results show the presence of VTE flow in the rim seal throughout all purge flowrates evaluated. Circumferential variation of VTE flow was also studied both experimentally and computationally using a computational fluid dynamics model. Results showed that ingested VTE flow can reduce the detrimental effect of hot gas ingestion particularly at higher purge flowrates.
Thermodynamic Assessment of Exhaust Gas Recirculation in High-Volume Hydrogen Gas Turbines in Combined Cycle Mode
Authors: Ravelli Silvia
Published: October 2022

To achieve a net-zero approach, while ensuring grid reliability and resiliency, gas turbine (GT) technology has a place for years to come thanks to high efficiency, low turndown, quick starts and fast ramp rates. However, shifting to low-carbon fuels, such as hydrogen, is the key to maintain positive returns in combined cycle (CC) power plants.

By recirculating a fraction of the exhaust gas exiting the heat recovery steam generator (HRSG) back to the inlet of a natural gas (NG) and hydrogen co-fired GT, the gas flow passing through the compressor and entering the combustor has a reduced oxygen concentration thus lowering flame temperature and hence NOx formation. Hydrogen reactivity is then turned into a benefit since the exhaust gas recirculation (EGR) rate can be higher than that with conventional fuels, without facing flame stability issues. In light of this, a thermodynamic assessment of EGR effects on a 2 × 1 large-scale CC is presented considering GT with hydrogen capability up to 65%. The impact of partially replacing NG with hydrogen on GT behavior and overall CC performance was firstly evaluated at both full and part load, with no EGR. Then EGR was simulated for a rate up to 0.5 for different fuel mixtures, under the assumptions of GT inlet flow at low (ISO) and high (up to 47°C) temperature. The analysis was again carried out at full and part load. In the latter case, EGR was exploited to improve CC efficiency at very low loads. For each scenario, CO2 emission intensity was computed thus highlighting the environmental benefits of hydrogen-natural gas blends.
Update of the sCO2-Test Rig at Cranfield University
Authors: Anselmi Eduardo , Belleoud Pierre , Roumeliotis Ioannis , Pachidis Vassilios
Published: October 2022

Since 2018, there is an experimental supercritical carbon dioxide (sCO2) facility operating at Cranfield University. The purpose of this rig is to enable the exploration of supercritical carbon dioxide as a working fluid for future bottoming power cycle applications and, more recently, for thermal management applications. The core of the rig is a transcritical closed loop, which has recently been upgraded. The upgrades include an increase in the number of measurement stations, changes to the types of measurements taken, as well as the addition of a new, dedicated data acquisition system. A summary of some of the lessons learned from different test campaigns conducted from 2018 to 2021 is provided, along with a discussion on the measurement upgrades performed. The experience obtained with this rig, as recounted in this paper, could be relevant to similar test rigs or future power cycles applications.
ICME Modeling of Erosion in Gas-Turbine Grade CMC and HVOF Test
Authors: Abdi Frank , Eftekharian Amirhossein , Huang Dade , Choi Sung , Morscher Gregory N. , Panakarajupally Ragavendra P.
Published: October 2022

Erosion of gas turbine grade ceramic matrix composites (CMC) has recently attracted attention because it limits performance and component life in hot engines. This study developed physics of erosion failure evolution including delamination, cavity formation, and fiber loss using an integrated computational material engineering (ICME) approach. The erosion behavior of two CMC systems at two elevated temperatures (ET) under two high velocities is tested utilizing a high velocity oxygen fuel (HVOF). Two CMC erodent systems were selected, and experiments showed that erodent type and size affect erosion degradation which shows sensitivity to retained strength test after erosion. A computational Multi-Scale Progressive Failure Analysis (MS-PFA) predicted the erosion and post-erosion behavior of CMC’s. Prediction of material degradation, micro-crack formation, interfacial degradation, and retained strength closely matched test observations.

Method: A Multiphysics-based ICME methodology, and virtual design of experiment (DOE) software method includes: 1) Thermo-physics modeling of galvanic ash particles of layered ceramics predicting the mass transfer, 2) Micro-Mechanical Material model including layered CMC interphase and microcrack density, predicting progressive erosion evaluation and delamination, fracture toughness and hardness, and 3) Finite element explicit software predicting: a) Erosion rate as a function of impact angle under ambient temperature conditions; b) Effect of erodent concentration on erosion rate; c) Erosion rate as a function of velocity at 815°C and 1200°C under normal impact conditions; d) Variation of erosion rate with impingement angle and particle size, and velocity range; and e) Erosion rate as a function of erodent concentration, particle size, temperature and velocity under normal impact conditions.