bluuebunny/crossref_metadata_2025 huggingface dataset:
Parametric Design of Radial Guide Vanes for Power Augmentation of Darrieus-Type Vertical-Axis Wind Turbines
Authors: Melani Pier Francesco , Balduzzi Francesco , Ferrara Giovanni , Bianchini Alessandro , Bissanti Roberto , Bissanti Palmiro
Published: October 2022

Among proposed solutions for power augmentation of Darrieus turbines, one of the most promising is represented by Radial Guide Vanes (RGVs) which can potentially increase both the velocity magnitude and the swirl of the incoming flow, without losing omni-directionality like in the case of diffusers. The main drawback of this technology is the increase in the dimension of the wind energy converter, which however comes together with reasonable cost (only static parts are added) and additional benefits like a higher safety and lower noise.

The study presents an extensive parametric analysis aimed at investigating the impact of some key design parameters of a RGV cascade on the performance of a medium-size industrial Darrieus rotor. Focus is given to vanes angle and length. Simulations are carried out by means of the two-dimensional Actuator Line Model developed by some of the authors for the commercial ANSYS® FLUENT® 20.2 solver. The hybrid simulation approach has been validated against blade-resolved unsteady CFD RANS simulations of the machine in both open- and vaned-rotor configurations. The use of high-fidelity techniques comes indeed with a non-negligible calculation cost, but it can solely provide the needed accuracy in modeling the physics related to the interaction of the flow with both static and rotating blades. Different turbine operating points and inlet flow angles are considered, so that the effective omni-directionality of the RGV concept could be verified. Tested configurations are compared in terms of power coefficient and blade loading azimuthal profile. Overall, results prove that — if the correct design is chosen — RGVs can provide notable improvements in the performance of a Darrieus VAWT, opening interesting prospects for their future application in industrial installation.
Modification of Pump Turbine Characteristics With Fluid Injection in Pump Operating Mode
Authors: Deniz Sabri , In Albon Simon
Published: October 2022

The requirements of a stable and reliable pump turbine operation under continuously expanding operating ranges, challenges the design of pump turbines and demand new developments. This paper presents the results of experimental (model pump turbine at the test rig) and numerical (CFD) investigations of the instabilities of a low specific speed (nq = 25) pump turbine in pump operating mode.

During the operation at off-design conditions, not only performance penalties but also flow instabilities may occur, limiting the operating range of the pump turbines. Although unstable behavior can be observed during the part load operation in turbine mode (i.e., draft tube vortex rope) and during the turbine mode operation near runaway speed (speed no load conditions), the focus of this paper is on the pump operating mode, the so-called hump instability at part load operation, when the head vs. flow rate characteristics of the pump has a positive slope. The pump mode dimensionless head vs. flow rate characteristics are measured for different diffuser opening angles, DA. Using the data of the unsteady pressure measurements, flow instabilities in the low-specific speed model pump turbine are analyzed in pump operating mode.

Flow control with fluid injection in the vaneless space (between the runner and the diffuser) on a model pump turbine during pump mode operation was applied for different diffuser angles at HSLU (Lucerne University of Applied Sciences, Switzerland) in order to modify the pump mode, head vs. flow rate characteristics and to eliminate the regions with positive slopes in the characteristics. Water-injection is first applied using an external energy source (pump) with discrete nozzles that are circumferentially distributed in the vaneless space. Later water injection is also implemented without an external energy source using a bypass, which is connecting the discharge of the pump with the vaneless space. With fluid injection, the pump head vs. flow rate characteristics are modified so that there are no more positive slope regions, meaning an improvement in the stability behavior and extension of the operating range of the pump mode operation. After the implementation of flow control in the laboratory, CFD simulations were carried out to calculate the pump head vs. flow rate characteristics with and without fluid injection. CFD simulations with the BSL EARSM (Baseline Explicit Algebraic Reynolds Stress) turbulence model are able to predict the experimentally determined pump head vs. flow rate characteristics with- and without water injection.
Carbon Capture Performance Assessment Applied to Combined Cycle Gas Turbine Under Part-Load Operation
Authors: Verhaeghe Antoine , Dubois Lionel , Bricteux Laurent , Thomas Diane , Blondeau Julien , De Paepe Ward
Published: October 2022

The growing share of renewable energies in our electricity production, together with the still lacking storage capacity, strongly reinforces the need for more flexible electricity production units. In this context, Combined Cycle Gas Turbines (CCGTs) have a role to play, both in the current and future electricity production system due to their high efficiency, high load flexibility, and low CO2 emissions compared to other conventional thermal power plants. Nevertheless, bearing in mind our current challenges concerning climate change, the CO2 emissions of these CCGTs need to be reduced drastically. The amine-based absorption Carbon Capture (CC) process is currently the most mature and applicable CC technology. This process is known to require a considerable amount of thermal energy, degrading plant performance. However, to back-up renewable production, CCGTs will operate most of the time under part-load conditions. The impact of these part-load operations on the CC is still relatively unknown. Within this framework, this study aims to assess the performance of the CC process applied to a typical CCGT under part-load operation using specific simulation models. The CC plant model has been successfully validated against experimental data from a pilot-scale capture facility. Then, the CC plant has been scaled-up to the CCGT scale and the process has been optimized for each operating condition. The simulation results show that the specific reboiler duty increases for part-load operation, while the specific cooling requirements decrease. Moreover, the analysis of the yearly CCGT operation highlights a relative increase in CC energy penalty of 21% for an annual CCGT load factor of 0.5, impacting significantly plant performance. The next step will involve reducing this energy penalty.
CFD Analysis of the Forces on a Steam Turbine Balance Seal Packing Ring
Authors: Bianchini Cosimo , Da Soghe Riccardo , Bertini Davide , Mazzei Lorenzo , Arcangeli Lorenzo , Cosi Lorenzo
Published: October 2022

In high-pressure single flow Steam Turbines, sealing of the radial gap between rotating and stationary parts in the front end of the turbine is a known design challenge. A traditional solution to control and reduce the leakages between the stationary and rotating parts in that area is to implement spring-backed labyrinth packings. The operating position of such packings, which affects the effective clearance and in turn the leakage flow, is determined by the equilibrium of the forces exerted by the steam and the spring load applied on the back. In order to select the adequate spring and guarantee the desired clearance, it is hence of paramount importance to precisely predict the forces acting on the packing ring during the design stage.

This paper describes a computational analysis aimed at characterizing the forces on the packing ring. A full 3D model of a single packing ring, assuming periodic flow in the tangential direction, including both the labyrinth seal on the bottom side, the packing ring chamber on top and the gap between consecutive packing rings was developed. Different clearances between the packing ring and the surrounding casing as a result of manufacturing tolerances are considered both in the axial and tangential direction.

The analysis showed that the radial force varies quite significantly with such clearances. The analysis also permitted to highlight that 2D modelling of the labyrinth seals, being intrinsically insensitive to such clearances, is not capable to estimate with sufficient accuracy the radial force on the packing ring.
Acoustic Scattering Behaviour of an Aero Engine Injector: Numerical Investigation Using Compressible CFD and CAA
Authors: Alanyalıoğlu Çetin , Reinhardt Hanna , Fischer André , Lahiri Claus , Hasse Christian
Published: October 2022

During development of modern lean burn aero engine combustors, prediction and characterization of injector thermoacoustic response plays an important role. The SCARLET (SCaled Acoustic Rig for Low Emission Technologies) test rig fulfills this need by providing acoustically defined upstream and downstream conditions under realistic operating conditions to characterize the acoustic response of full-scale injectors in a single sector setup. This work presents results from the complementary numerical analysis campaign that aims to reproduce the acoustic scattering behaviour as measured in the SCARLET rig. As a first step, non-reacting flow simulations were performed using fully compressible CFD simulations and the CAA (computational aero acoustics) method to compute upstream and downstream acoustic fields. The results obtained are then post-processed based on a multi-microphone method to yield the acoustic scattering matrix, which follows the employed experimental post-processing strategy. Results obtained from both methods show satisfactory agreement with measurements. Geometrical simplifications and their implications on scattering behaviour are investigated to achieve a trade-off between accuracy and geometrical complexity. Both methods are compared in terms of their inherent advantages and disadvantages. Limitations associated with employed models and possible improvements are discussed.
Numerical Prediction of Surface Roughness Effect on the Performance of Internal Channels
Authors: Sandeep  , Manoharan Mahendran , Kuchana Vinayender , Liu Jong
Published: October 2022

Additive Manufacturing (AM) in turbine technology enables the manufacture of complex and detailed shapes such as optimized cooling channel designs. However, the AM components are usually produced with high surface roughness. The ability to predict the pressure loss and heat transfer during the AM components’ design phase gives the designer an extra edge to arrive at a better design. In this paper, numerical prediction for the effect of roughness on pressure loss (friction factor) and heat transfer (Nusselt number) for flow in the internal channel is discussed. Numerical simulations were performed using the commercial computational fluid dynamics (CFD) tool by ‘Siemens Star-CCM+’. Initially, the best practices for the CFD process were arrived at by comparing the CFD results with the theoretical correlations for a fully developed channel flow. Further, these best practices were invoked to validate the two test cases from the open literature. From the first test case, three test coupons with the lowest, intermediate, and the highest level of roughness were selected for the validation. From the second test case, in-line and stagger configurations were selected for validation. To reduce the simulation time, modeling the full channel domain as a single channel was explored. The single-channel results were found to be matching well with the full channel results at the two Reynold’s numbers simulated. For all the cases, the friction factor predictions are close to the theoretical and test data, whereas the Nusselt number predictions show a consistent trend with the theoretical data but over-predicts when compared to the test data.
DMD Analysis of Radial Turbomachinery
Authors: Ludewig Alexander , Brenner Gunther , Skinder Kathrin
Published: October 2022

In the design of turbomachinery, the avoidance of flow-induced vibrations offers optimisation potential with regard to noise reduction and the extension of the service life of a machine. To achieve this, damage-relevant should be analyzed in the development phase using methods such as forced response or flutter calculations. A forced response analysis requires the specification of flow-induced excitations in the spectral range, which can be obtained from a temporal numerical simulation using FFT. Since the FFT depends on the time span and therefore only reproduces discrete frequencies, only rotational frequencies and their integer harmonics can be determined from a single rotational period. To work around this, a Dynamic Mode Decomposition (DMD) is applied to analyse the flow field in a high performance centrifugal fan obtained from simulation and measurement data. DMD is a model order reduction method based on singular value decomposition. It extracts modes and eigenvalues of a nonlinear, dynamic system. DMD is considered an ideal combination of proper orthogonal decomposition in space and Fourier transform in time. The numerical data were generated with a CFD calculation based on the unsteady Reynolds-averaged Navier-Stokes equations together with the k-ω SST turbulence model. As a result of this study, it can be shown that the DMD agrees exactly with the analysis of the FFT based on transient local pressure sensors. For the two-dimensional pressure field, however, the DMD deviates significantly from the FFT in the amplitudes for higher-frequency excitations, partly showing better agreement with the measurements of the pressure sensors.
Inverse Design of a Centrifugal Fan for High Flow Rate Operating at Low Noise Level
Authors: Singh Vijender , Baraiya Nikhil A. , Banerjee Jyotirmay
Published: October 2022

Centrifugal blowers are commonly used for heating and ventilation applications. Centrifugal fan is a kind of fluid machinery for energy conversion used in industrial engineering with huge energy consumption. The impeller is the core component of a centrifugal fan, and the performance of the impeller determines the performance of the fan. High-pressure blowers present the problem of high noise with low efficiency coupled with large dimensions.

The centrifugal fan is designed to provide 600 cfm of outflow with a static pressure rise exceeding 2.5kPa at all times at design rpm of 30000 with noise level restrictions up to 80 dB levels operated by a 2kW power input. Inverse design approach has been followed to generate the dimensions and blade profiles. Variable area distribution volute with circular cross-section has been developed, providing pressure recovery and reducing the flow separation. This provides better stall characteristics and increases the overall total to total efficiency of the stage. High rpm operating range provides the opportunity for reducing the overall size with increased noise.
Representation of Components Characteristics Under Performance Degradation of Gas Turbine Engine
Authors: Jiang Zhen , Wang Xi , Yang Shubo , Liu Jiashuai , Chen Huairong
Published: October 2022

The current self-tuning performance model can only reflect the components degradation under operating state, while not non-operating states. Aiming at this disadvantage, this paper studies the representation of components characteristic drift for the purpose of obtaining one that suitable for full operating conditions. Firstly, the real component characteristics regarding the measurement data of engine are calculated by gas path analysis, and the drift of component characteristics is determined by analyzing how original characteristic maps are shifted. Secondly, the relationship between component characteristic drift and operating condition is established. In the relationship, the operating condition is represented by feature parameters, which describe the feature of operating condition. The number of dimension of feature parameters (n) are determined as 0, 1, and 2 respectively. Finally, with the assistance of the relationship generated, component deterioration models are constructed and employed in a self-tuning model framework. By applying the characteristic drift obtained from the component deterioration models to the original characteristic maps, the framework can mirror the degradation of engine’s performance. Comparing the output of framework with reference data, results show that the deviation in the test range is no more than 0.86% when n = 2, while the maximum deviation of n = 0 and n = 1 are 1.92% and 2.51%. It is illustrated that the difference of component characteristic drift within operating envelope can be represented by corrected rational speed and inlet pressure of fan, which will help to realize the performance modeling under the concept of “digital twin”.
Advancement of Electrical Resistance Towards Monitoring Crack Growth in SiC Based Composites at Elevated Temperatures
Authors: El Rassi Joseph , Morscher Gregory N.
Published: October 2022

Electrical resistance has been used to detect in situ changes to SiC based material as damage occurs. Damage in the composite, typically in the form of matrix cracking, increases the resistance due to the local constrain of current flow. Efforts have been ongoing to quantify the effects of increasing potential drop with crack growth in a pre-preg SiC-based composite. Two variations of the pre-preg SiC-based composite were studied: one with a single layer of SiC monofilaments with carbon core (1 fiber/mm) inserted in the center of the composite and extending through the length of the composite and the other possessed three layers of monofilaments, one layer in the center of the composite and the other two layers near both surfaces of the composite. It was found that the high conductive Si phase varied considerably for the different variations of composites and dominated the current flow rather than C. Tension-tension fatigue tests were conducted at 815 °C in a static furnace for both composite systems, electrical resistance was monitored during the test along with acoustic emission. A ply level electric circuit was constructed, and ply resistivity at temperature was obtained based on the Si content in each ply. The function of the electric circuit was to interpret the change in resistance obtained during the fatigue testing of the MI material with the morphology of transverse crack growth. Microscopy and energy dispersive spectroscopy were conducted to better understand the crack morphology.
A Study on Fundamental Combustion Properties of Trimethyl Orthoformate: Experiments and Modeling
Authors: Ngũgĩ John Mbũrũ , Richter Sandra , Braun-Unkhoff Marina , Naumann Clemens , Riedel Uwe
Published: October 2022

Trimethyl orthoformate (TMOF: HC(OCH3)3) has recently been examined as a viable biofuel. TMOF is a branched isomer of oxymethylene ether-2 (OME2) that, due to its high oxygen content and lack of direct carbon-carbon bonds, considerably reduces the formation of soot particles. To meet the challenges of a more flexible and sustainable power generation, a detailed understanding of its combustion properties is essential for its safe and efficient utilization, neat or in blends. In this work, two fundamental combustion properties of TMOF were studied: (i) Auto-ignition of TMOF / synthetic air mixtures (φ = 1.0; diluted 1:5 with N2) using the shock tube method at pressures of 1, 4, and 16 bar, and (ii) Laminar burning velocities of TMOF / air mixtures using the cone angle method at ambient and elevated pressures of 3 and 6 bar. Furthermore, the impact of TMOF addition to a gasoline surrogate (PRF90) on ignition delay times was studied using the shock tube method at φ = 1.0, 1:5 dilution with N2, T = 900–2000 K, and at 4 bar. The experimental data sets have been compared with predictions of the in-house chemical kinetic reaction mechanism (DLR Concise mechanism) developed for interpreting the high-temperature combustion of a broad spectrum of different hydrocarbon fuels as well as oxygenated fuels, including TMOF. The results demonstrate that the ignition delay times of TMOF and OME2 are nearly identical for all pressures studied in the moderate-to high-temperature region. The results obtained for the blend indicate that ignition delay times of the TMOF / PRF90 blend are shorter than those of the primary reference fuel 90 (PRF90) at 4 bar. In the lean-to stoichiometric region, the results obtained for laminar burning velocities of TMOF and OME2 are similar. However, in the fuel-rich domain (φ > 1.0), laminar burning velocities for TMOF are noticeably lower, indicating a decreased reactivity. The model predictions based on the in-house model reveal a good agreement compared to the measured data within the experimental uncertainty ranges. In addition, sensitivity analyses regarding ignition delay times and laminar flame speeds were performed to better understand TMOF oxidation.
Performance Improvement of Heat Exchangers Used in a Hybrid Electric Aircraft
Authors: Rasimarzabadi Faezeh , Crain Alexander , Canteenwalla Pervez , Zdunich Patrick , Gibney Evan
Published: October 2022

Thermal management system analysis of a kW scale hybrid electric aircraft developed at the National Research Council of Canada (NRC) has been provided with the aim of assessing the cooling capacity and improving the efficiency. For the electric propulsion system of the aircraft, a series cooling loop has been designed that comprises a heat exchanger (radiator) and two pumps. As coolant travels through the motor and controller, it accumulates heat, then the heat is dissipated from the coolant passing through the radiator. From the calculated parameters for different demonstration flight phases of the aircraft, it is concluded that the current radiator design is limited by the air side resistance. This air thermal resistance comprises over 76% of the total thermal resistance in all flight phases. Therefore, a large frontal area to meet cooling needs is required. The potential of different methods for cooling improvement of the radiator were investigated and a new concept was suggested for heat transfer enhancement which is a passive enhancing method by applying different micro-fin roughness on the fins or coolant tubes of a radiator.
Numerical Prediction of Long Term Droplet Erosion and Washing Efficiency of an Axial Compressors Through the Use of a Discrete Mesh Morphing Approach
Authors: Agati Giuliano , Borello Domenico , Di Gruttola Francesca , Simone Domenico , Rispoli Franco , Castorrini Alessio , Gabriele Serena , Venturini Paolo
Published: October 2022

Online water washing represents an operation strategy commonly used to reduce compressor performance deterioration due to blade fouling. Since this kind of washing is applied when the machine operates close to full load conditions, injected droplets are strongly accelerated and consequently impact the rotor blades at high velocity, thus inducing undesirable phenomena like erosion. Here we present a novel technique to study long-term water droplets erosion by also considering the geometry modification caused by droplets impacts. Two-phase unsteady numerical simulations were carried out, considering the injection of water droplets and their transport across the fluid flow in the first part of a real compressor, which is modelled in the region extending from the inlet to the rotor blades of the first stage. Simulations are performed on the whole machine to account for the asymmetric distribution of the spray injectors, the machine struts, IGV and rotor blades. The k-ε realizable turbulence model with standard wall functions was adopted and coupled with the discrete-phase model to track injected droplets motion. Droplets-wall interaction is modelled following the Stanton-Rutland approach aiming at detecting the effect of droplet impact (deposit, rebound, splashing), depending on the impact conditions. Moreover, a semi-empirical erosion model developed by the authors was implemented in ANSYS Fluent through a User Defined Function (UDF) to evaluate the erosion induced by the droplets injection. Material removal due to erosion is converted into nodal mesh displacement that is used by a secondary UDF to implement mesh morphing. The mesh modification is applied at discrete steps to reduce the computational load. This technique is adopted to account for the blade geometry modification due to water droplet erosion leading to performance losses. Moreover, an estimation of the compressor operating life before maintenance operations is given and the water washing efficiency during the whole life of the machine is evaluated by means of proper indices. At the end of the simulation workflow erosion phenomena are observed on all the compressor regions, especially in the rotor where erosion peaks are reached at the hub of the leading edge. The rotor blades wet surface was found to remain almost constant around the 50% during compressor operating life. Erosive phenomena were proved to evolve non linearly with time indicating the necessity to account for the mesh modification for an accurate prediction of the long-time process.
Experimental Study on Combustion of Methane / Ammonia Blends for Gas Turbine Application
Authors: Ditaranto Mario , Saanum Inge , Larfeldt Jenny
Published: October 2022

Hydrogen from renewables or reformed natural gas with CO2 Capture and Storage (CCS) can be used as fuel to achieve CO2 free power production. Because of the challenges related to transport and storage of H2, NH3 has been proposed as a hydrogen carrier as it can be stored in liquid form at moderate pressures and temperatures. NH3 can be used as a fuel directly, but the low reactivity and flame speed in air makes combustion stability challenging in conventional gas turbine combustors. As no solutions are commercially available today, a transitional approach is to only replace part of the fuel with NH3 to limit the change in the combustion properties, although this only partly decarbonizes the fuel. This study investigates combustion of CH4/NH3 blends with air in a downscaled Dry Low Emission (DLE) burner at pressures up to 6 bar and thermal power up to 100 kW. The effects of equivalence ratio and NH3/CH4 mixture ratio on the emissions of NOx, CO, CH4, HCN, N2O, and NH3 are studied at different pressures and power. Even small amounts of NH3 introduction in the fuel results in unacceptable high NOx emissions in a conventional combustor and the flame stability limits the maximum NH3 content in the fuel. However, by using a two-stage combustion strategy with a rich primary zone, NOx emissions down to ca. 100 ppm could be achieved with a NH3 content up to 100%, provided the thermal intensity of the combustor is severely reduced.
Turbulence Model Impact on Predicting Precursors to Surge Flow Instabilities in a Turbocharger Compressor
Authors: Trigell E. , Mihaescu M.
Published: October 2022

Turbocharger compressor simulations can improve the development of compressors with broad operating ranges and improved noise signatures. At low mass flow rates aerodynamic instabilities, known as rotating stall and surge, limit the operating range of the compressor. However, the triggering factors for these instabilities are currently unknown. High quality numerical methods are therefore needed to capture instabilities and to simulate reliable performance maps. The aim of this study is to improve the understanding of the chosen numerical approach going from design to off-design operating conditions. It is shown that flow structures are under-predicted using URANS k-ω SST and that a LES WALE method better captures the flow structures in the blade region. Further, the level of fluctuations in different parts of the compressor is presented. By increasing the predictive quality of the numerical simulations, the need for empirical calibration can be reduced and turbocharger matching can be improved.
Innovative Expanders for Supercritical Carbon Dioxide Cycles
Authors: Perri Alessandro , Renuke Avinash , Traverso Alberto
Published: October 2022

Supercritical carbon dioxide plants are attracting strong interest, particularly for distributed power generation, thanks to the high-power density, allowing high compactness and efficiencies due to the particular features of the fluid conditions near the critical point. In the present work, the feasibility of innovative turboexpanders is evaluated for the first European demonstrator of MW size, coupling small volumetric flows with technological simplicity, typical of these types of plants. In particular, the possibility of replacing conventional turbines with bladeless expanders is studied, proposing a design in line with those achievable by small radial and axial turbomachines. The bladeless expanders consist of flat parallel disks mounted on a shaft, separated by spacers to maintain small gaps between them. The laminar flow inside the rotor makes it highly efficient: however, rotor-stator interaction losses reduce the overall performance. Such bladeless expanders maintain high interest for their capability to tackle low volumetric flows, their relatively simple design and ease of manufacturability.

The design case presented in this paper is the feasibility study of a single modular bladeless expander using the existing conventional design (axial and radial stages) as the reference design. 3D numerical analysis is carried out using commercial computational fluid dynamic software. The results show ∼55% total static efficiency of the bladeless expander at 37000 rpm for approximately 1.25MW output power. The impact on performance at different nozzle throat cross-sections and rotor disks diameter has been discussed. The overall performance of the expander is presented by evaluating the losses and improvement strategies that are discussed.
Validation and Assessment of a Numerical Methodology for Turbulent Liquid Fuel Jets in High-Speed Crossflow
Authors: Zghal Malika , Sun Xiaoxiao , Gauthier Pierre , Sethi Vishal
Published: October 2022

For lean combustion technology, sufficient mixing between fuel and air helps to move away from stoichiometric combustion, the flame temperature of which enormously promotes the production of harmful pollutants. Good fuel-air mixing is also essential to avoid fuel-rich pockets, where unburnt hydrocarbon and soot are likely to be produced. For low emissions gas turbines using liquid fuels, such as diesel, jet in crossflow is one the approaches to achieve efficient liquid jet breakup and evaporation as well as superior mixing characteristics.

In order to develop low emissions fuel spray technologies that use transverse jets, it is important that the current numerical tools have the ability to accurately predict the jet breakup, both primary and secondary, evaporation mechanisms, to properly assess the performance of an injector design. However, because the numerical tools often use model constants that are calibrated with experimental data mostly only applicable to a specific range of operating conditions, a particular test fluid or injection method, it is very challenging to assess the accuracy of the predicted results without further experimental validation. To the author’s best knowledge, the breakup mechanism and the predictive capabilities of the breakup models used to guide the design of novel injectors for fuel transverse jets at elevated pressure and high-speed turbulent crossflow have not been reported in full detail.

Thus, the main focus of this study is to compare and assess the capabilities of the breakup models used in state-of-the-art CFD, including a stochastic approach that relies less on experimental model constants, to predict the spray characteristics of turbulent jets in crossflow at different pressures, gas Weber numbers and momentum flux ratios that are more representative of gas turbine applications. This study will be conducted by using Simcenter STAR-CCM+.

The simulated results will be compared to experimental data to validate and calibrate the breakup models through a parametric and sensitivity study.
Computational and Experimental Assessment of a MW-Scale Supercritical CO2 Compressor Operating in Multiple Near-Critical Conditions
Authors: Toni Lorenzo , Bellobuono Ernani Fulvio , Valente Roberto , Romei Alessandro , Gaetani Paolo , Persico Giacomo
Published: October 2022

The present work illustrates the results of a wide experimental campaign in the frame of the EU-funded project sCO2-Flex, focused on the investigation of a MW-scale sCO2 compressor operating in plant-representative conditions. The experimental tests are carried out for four temperature levels between 304.15K and 309.15K at a fixed pressure (79.79 bar), hence covering an extended thermodynamic region close to the critical point. The experimental results are thoroughly discussed with the support of steady computational fluid-dynamics simulations, assuming homogeneous flows and thermodynamic equilibrium for the two-phase flow description. Changing the upstream total state, two peculiar variabilities in the compressor pressure ratio and choked-flow rate are experimentally and computationally observed. While the former is mainly related to the single-phase flow thermodynamics, the latter originates from the onset of two-phase flows. As the simulations predict the experimental choking with a maximum error of 3%, the corresponding two-phase speed of sound is analyzed to infer the underlying equilibria between phases. It is found that, for the tested conditions, two-phase flows quickly achieve thermodynamic equilibrium, and non-equilibrium or meta-stable effects arguably play a marginal role in the process.
A Reduction Technique for the Calculation of the Forced Response of Bladed Disks in Presence of Contact Mistuning at Blade Root Joints
Authors: Pinto Valeria , Battiato Giuseppe , Firrone Christian M.
Published: October 2022

The effect of differences in nominally equal sectors of a bladed disk (mistuning) is a well-known problem for designers since the forced response may show localized amplification of the blade response with respect to a cyclically symmetric (tuned) configuration. In order to perform a large number of simulations in a reasonable amount of time to characterize the highest blade response, corresponding to the worst mistuning pattern, reduction techniques have been developed where the mistuning is introduced directly in compact, Reduced Order Model (ROM) obtained from very large finite element (FE) models. Typically, mistuning is introduced in the ROM in terms of natural frequency perturbations of the blade; nevertheless, a better insight is specifically required in order to correlate mistuning to a specific source (geometrical, material, contact mistuning).

In this paper, a reduction technique is presented to take into account mistuning due to the contact uncertainties at the blade root joint, which can be caused by design tolerances, manufacturing process, assembly procedures, wear. The technique takes its basis from the Craig-Bampton Component Mode Synthesis applied to the uncoupled blade and disk sector, which is typically included in most of the FE software for an easy implementation in standard industrial practice. The full set of master degrees of freedom at the random contacts are purposely reduced using an optimal local modal basis based on the Gram-Schmidt Interface technique developed by the authors.

Experimental evidence of actual uncertain contact obtained during joint pre-loading is used to find an appropriate base to represent typical contact patterns.
Performance of Additively Manufactured Internally Cooled Airfoils for Small Industrial Gas Turbines
Authors: Straub Doug , Ramesh Sridharan , Searle Matthew , Robey Edward , Floyd Tim , Roy Arnab , Ames Forrest E.
Published: October 2022

The purpose of this effort is to screen several internally cooled airfoil designs that could be fabricated when additive manufacturing becomes a viable alternative for industrial gas turbine applications. This effort is part of a larger effort to increase gas turbine performance for combined heat and power systems using additive manufacturing for advanced cooling designs. The baseline cooling configurations have been described previously and include a baseline vane and a baseline blade. The baseline vane is impingement cooled with pin-fins in the trailing edge. The baseline blade incorporates a combination of impingement, rib turbulators and pin-fin features. This paper will compare the one-dimensional cooling model described previously with experimental measurements in a conjugate intermediate temperature (650K) test facility at NETL. A double-wall internally cooled concept will also be described. A preliminary stress comparison for the double-wall concept relative to the baseline blade will be discussed. The one-dimensional cooling model predictions overpredict the experimentally measured overall cooling effectiveness. The differences between the model and the experiment, as well as comparisons between technology curves of the different cooling designs will be described.
Optimum Injector Parameters for Thermoacoustic Stability in a Multi-Nozzle Can Combustion System
Authors: Acharya Vishal
Published: October 2022

High-frequency transverse instabilities are an important concern in can combustor configurations. In these configurations which are typically operated with multiple injectors around a central injector, each injector is subjected to different parts of the acoustic mode shape and thus respond differently for the same instability mode. Recent work by the author has modeled the response of premixed flames to excitation by natural high-frequency transverse modes in a can combustor both in the center and outer nozzles. The stability of these acoustically non-compact flames was assessed using the Rayleigh criterion (Rayleigh Integral denoted as RI) and not the overall unsteady heat release as is the case for compact flames. Several key control parameters were studied, namely — flame angle, swirling strength, nozzle location. For non-axisymmetric modes such as the commonly occurring 1-T mode, both radial and azimuthal offsets of the nozzle location affected stability. The framework was applied to an optimization study to identify the optimal combination of parameters that minimizes RI for the different nozzles in the multi-nozzle system. In this study, a N-around-1 configuration was studied, and the results indicated that the different nozzles needed to be operated at different flame angles and swirl numbers to result in an overall minimum RI. However, the specific response of the different injectors was not considered. The helical mode distribution at each injector varies as we azimuthally go around the combustor’s injector distribution and thus the most amplified mode and the resulting flame response would be different. To minimize RI, it is important to determine the injector configurations that result in a hydrodynamic profile that minimizes the individual RI for each nozzle. The resulting relationship between the injector’s flow and local hydrodynamics can then be used in a hydrodynamics study of an individual injector so that the most optimal injector is chosen depending on its location in the combustor dump plane.
Use of Convolutional Neural Network Image Classification and High-Speed Ion Probe Data Towards Real-Time Detonation Characterization in a Water-Cooled Rotating Detonation Engine
Authors: Johnson Kristyn B. , Ferguson Donald H. , Nix Andrew C.
Published: October 2022

As rotating detonation engine (RDE) technologies progress in maturity, the importance of monitoring methods progressing towards development of active control becomes more critical. High-speed processing of experimental RDE data on a time scale approaching real-time diagnostics will likely only be accomplished through the use of machine learning. This study aims to develop and deploy a real-time monitoring technique which integrates flame image classification by a convolutional neural network (CNN) and ionization current signal analysis with the goal of determining detonation wave number, direction, frequency, and individual wave speeds throughout experimental RDE operational windows. Wave mode identification through single image CNN classification bypasses the need to evaluate sequential images and offers instantaneous identification of the wave mode present in the RDE annulus. The output of the existing CNN is utilized alongside a correlation of ion probe data to generate diagnostic outputs. The diagnostic acquires live data using a modified experimental setup as well as Pylon and PyDAQmx libraries within a Python data acquisition environment. Lab-deployed diagnostic results are presented across a variety of wave modes, operating conditions, and data quality, currently executed at 3–4 Hz with a variety of iteration speed optimization options to be considered as future work. These speeds exceed that of conventional techniques and offer a proven structure for real-time RDE monitoring, which will play a vital role in the development of active control, necessary for the extension of operational capabilities and RDE technology maturation toward industrial integration.
Evaluation of Adjoint Optimized Holes - Part I Baseline Performance
Authors: Gutierrez Daniel , Yoon Christopher , Furgeson Michael T. , Veley Emma M. , Bogard David G. , Thole Karen A.
Published: October 2022

With the advent of the use of additive manufacturing to build gas turbine components, the design space for new hole geometries is essentially unlimited. Recently, a computational adjoint based optimization method was used to design shaped film cooling holes fed by internal co-flow and cross-flow channels. The associated RANS computations predicted that the holes optimized for use with cross-flow (X-AOpt) and co-flow (Co-AOpt) would significantly increase adiabatic effectiveness. However, only the X-AOpt hole was tested experimentally in this previous study. Though the experimentally measured performance for this hole was much less than computationally predicted, it still had a 75% improved performance compared to the conventional 7-7-7 shaped hole. In the current study, the X-AOpt and Co-AOpt shaped holes were experimentally evaluated using measurements of adiabatic effectiveness and overall cooling effectiveness. Coolant was fed to the holes with an internal co-flow channel. For reference, experiments were also conducted with the baseline 7-7-7 shaped hole, and a 15-15-1 shaped hole (shown in a previous study to be the optimum expansion angles for a shaped hole). Furthermore, overall cooling effectiveness measurements were made with engine scale models to evaluate the performance of additively manufactured (AM) X-AOpt and Co-AOpt holes with a realistic metal build. Results from this study confirmed that the X-AOpt hole had a 75% increase in adiabatic effectiveness compared to the 7-7-7 shaped hole. However, the Co-AOpt hole had only a 30% increase in adiabatic effectiveness, substantially less than had been computationally predicted. Measurements of overall cooling effectiveness for the engine-scale models and the large-scale models followed similar trends.
Heat Load Parameter and Cooling Effectiveness On a Supercritical CO2 Stage One Vane With a Serpentine Internal Cooling Scheme
Authors: Olson Weston , Fernandez Erik , Vesely Ladislav , Khadse Akshay , Kapat Jayanta
Published: October 2022

Supercritical CO2 Brayton cycles are considered by some as the next evolution in power generation. The question of cooling effectiveness for hot gas path components arises for this topic. In this work, a stage one vane was designed with an internal cooling scheme which consisted of a turbulated three-pass serpentine which fed a trailing-edge pin fin bank with pressure-side cutback trailing-edge slot extraction. A conjugate heat transfer analysis, with practical supercritical CO2 boundary conditions, was performed on the design with Rene 80 as the metal. The conjugate heat transfer model had a thermal barrier coating which consisted of 0.1 mm of NiCrAlY bond coat and 0.3 mm of YSZ. The investigation consisted of a construction of a relationship between cooling effectiveness and heat load parameter, internal cooling turn losses, external airfoil temperature profiles and a thermal boundary layer analysis at areas of interest. A recommendation for internal turn inlet-apex-outlet area ratios is provided for minimizing the dynamic pressure loss associated with the turn. The study concluded that heat transfer not only depends on buffer zone temperature, but also viscous sublayer thickness.
Harmonic Method for Simulating Unsteady Multispool Interactions
Authors: Wang Feng , di Mare Luca
Published: October 2022

Modern civil jet engines arrange components on spools with different rotational speeds in order to improve compressor stall margin, overall engine performance, etc. The unsteady interactions among these components can be significant and should be considered at an early design stage if possible. URANS is a common approach to simulate these unsteady effects, but the disparity in time scales in a multispool simulation can lead to expensive URANS simulations. Harmonic methods are effective and efficient approaches to simulate unsteady interactions among turbomachinery components, but their applications to multispool simulations remains a challenge. The objective of this paper is to address this challenge. This paper extends the Favre-averaged non-linear harmonic method to simulate multispool turbomachinery components using a unified bladerow interface which transfer disturbances with arbitrary blade counts at any rotational speed. The regularization of non-reflective boundary condition is described for certain circumferential wave number of the zero-frequency mode. The capability of the proposed approach is demonstrated by simulating the transfer of hot streaks through full 3D high- and intermediate-pressure turbines in a three-shaft engine. The temperature distributions from the harmonic method show good agreement with direct unsteady simulation and the radial migration of the hot streaks towards the hub are captured very well by the proposed harmonic method. The Favre-averaged temperature field also shows good agreement with direct unsteady simulation. The required computational cost of the harmonic method can be roughly two orders of magnitude smaller than the direct unsteady simulations. This demonstrates the proposed method can be a promising design tool to trace hot streaks in multispool turbines at the early design stage.
Comparison of Stall Point Predictions in a Transonic Axial Compressor Rotor Using Single Passage and Three Passage CFD Geometries
Authors: Meinster Benjamin , Smith Walter C. , Hobson Garth V. , Gannon Anthony J.
Published: October 2022

An investigation is presented which compares the predicted stall points and underlying flow fields for single-passage and three-passage CFD geometries of a transonic axial compressor rotor. The two cases are run using the commercial CFD code ANSYS CFX and compared to experimental data. The two predicted stall points are found to differ from each other, and both under-predict the rotor’s performance compared to the experimental data. However, the steady-state flow fields are found to be identical for all operating points short of the stall point. A mechanism is then proposed to reconcile the difference in predicted stall points with the identical steady-state flow fields. By the mechanism proposed, the addition of multiple passages makes flow through the three-blade geometry less stable, which causes the rotor to stall earlier.