bluuebunny/crossref_metadata_2025 huggingface dataset:
Root Cause Analysis of the Lack of Market Success of Micro Gas Turbine Systems
Authors: Tilocca Giuseppe , Sánchez D. , Torres García M.
Published: October 2022

Micro gas turbine systems were introduced to the market at the dawn of the twentieth century, with the selling arguments of small footprint, low gaseous (NOx) and acoustic emissions, low maintenance and versatility for high-grade Combined Heat and Power applications. Unfortunately, the technology has enjoyed very limited market success and, currently, its market share for decentralized applications is marginal. Fierce competition by reciprocating internal combustion engines (ICEs), an established technology, has always been identified as the main barrier hindering the market deployment of micro gas turbines.

In this landscape, this work presents a root cause analysis that aims to identify the causes of this weak market penetration of MGTs. It aims to solve a block of the logic tree that represents the end-user choice to adopt one or the other technology. A single Key Performance Indicator is used to combine technical, economic, emission, and operational factors. This KPI is a compound indicator based on several weighted penalty factors and represents an original approach enabling the identification of the potential markets for this technology. The indicator is computed for the range of electrical power outputs in which microturbines compete.

This work compares three different case studies all related to CHP applications. The new methodology confirms the lack of competitiveness of microturbines in market segments without specific heat or emission requirements.
Investigations of the Unsteady Aerodynamic Characteristics for Intakes at Crosswind
Authors: Piovesan Tommaso , Wenqiang Zhang , Vahdati Mehdi , Zachos Pavlos K.
Published: October 2022

The ground vortex generated in front of an intake operating near the ground and subjected to crosswind is investigated using CFD and compared to the experiments. The flow field of a scale-model intake is numerically simulated with both steady and unsteady approach, with the aim of predicting ground vortex effects and to characterize the vortex unsteady behaviour. The experimental results showed that for an intake near the ground under crosswind the ground vortex that forms under the intake and the in-duct separation, when present, exhibit unsteady behaviour that becomes stronger as the crosswind velocity is increased. The simulations indicate that a steady-state approach only partially reproduces the time-averaged ground vortex characteristics and in-duct distortion losses, while an unsteady approach shows a lower level of unsteadiness compared to the experimental observations. The consequences of the unsteady flow in the intake on the fan aerodynamic and aeroelastic stability are finally discussed to reinforce that these can result in significant non-synchronous vibration (NSV) and loss of stall margin which cannot be adequately assessed if no unsteady component of the inlet distortions is taken into account.
FGM Applied to Grid Plate Flame Stabilisers for NOx Prediction in Non-Premixed Gas Turbine Combustion
Authors: Quiñonez Arce José Ramón , Andrews Gordon E. , Phylaktou Herodotos
Published: October 2022

The present work investigates one of the lowest NOx design concepts using directly fueled grid plate flame stabilisers [10] termed Grid Mix (GM). The work uses CFD to predict experimental results for the GM low NOx flame stabilisers operated with propane. An additional study was undertaken to analyse their performance on hydrogen, a zero-carbon fuel at the heart of the UK zero-carbon power generation policy. Combustors are in production using similar technology to GM, and at least two manufacturers have low NOx hydrogen combustors using similar flame stabilisers [9, 18, 21–24]. Also, as the tests were at atmospheric pressure, the results are relevant to process burners, and the test condition for the CFD was a 140 kW thermal input process burner.

The Grid Mix technique for non-premixed combustion, with fuel injected into the airflow at the periphery of the air holes, allows rapid fuel and air mixing for lean non-premixed ultra-low NOx combustion. The technology has been investigated at high entry temperatures of modern industrial gas turbines with all the combustion air passing through the flame stabiliser at a typical reference Mach number for this condition of M = 0.047, at an overall pressure loss of ΔP/P = 2.4%, for a heat release of 28MW/m2. These conditions are well above most experimental and CFD publications on low NOx gas turbine emissions.

The combustion and NOx predictions for hydrogen show that Grid Mix flame stabilisers offer a viable solution to low NOx with hydrogen combustors. In addition, the advantage of adding fuel and air mixing passage downstream of the Grid Mix fuel injector is also demonstrated, as used by Yorke et al. [18].
Influence of Real Gas Properties on Loss in a Super Critical CO2 (sCO2) Centrifugal Compressor
Authors: Cai Ruikai , Yang Mingyang , Deng Kangyao , Zhuge Weilin , Yang Bijie , Martinez-Botas Ricardo , Chen Tao
Published: October 2022

The performance of the SCO2 centrifugal compressor is the key component influencing the efficiency and stability of the whole Close-Bryton cycle system. It is important to understand the loss mechanism inside the compressor to guide the design and performance optimization of the compressor. However, the physical properties of SCO2 are strongly nonlinear near the critical point, and the internal flow of the compressor is highly coupled with its properties, which inevitably profoundly influences the loss generation in the device. In this paper, the loss mechanism of SCO2 compressor is investigated comprehensively based on numerical method compared with experimental data. CO2 real gas model embodied in RANS model are used for the study. Firstly, grid independence and influence of the resolution of real gas properties tables are discussed. The numerical simulation results are in good agreement with the experimental data of Sandia SCO2 compressor. Secondly, the distribution of the loss of the compressor are evaluated by means of local entropy generation at different mass flow rates. In particular, a direction comparison between the cases with real gas properties and the constant properties is carried out for manifesting of the influence by real gas properties. The results manifest that the loss of the case with constant properties is profoundly higher than that of the real gas properties, especially at small flow rate. Detailed flow field is compared to understand the influence of the properties. It is shown that the tip leakage flow is evidently decreased with the real gas properties and results in a much more uniform flow distribution throughout the impeller. The decrease in static temperature and pressure due to the acceleration of SCO2 at the tip of the main blade causes an increase in fluid density, reducing the tip leakage and secondary flow. Moreover, the influence on the flow in the impeller results in smaller incidence angle near hub side for the case with real gas properties, thus the separation on the suction surface which happens in the case with constant properties is alleviated. Therefore, the loss in both the impeller and diffuser is significantly reduced by the real gas properties.
Numerical Investigation Into Maximum Pressure Capability of Intershaft Hydraulic Seals
Authors: Warusevitane Achinie , Johnson Kathy , Ambrose Stephen
Published: October 2022

Hydraulic seals are used as intershaft seals in aero-engines and consist of an oil filled trough on the higher speed shaft and a fin on the lower speed shaft that dips into the oil forming the seal. Rotation is imparted to the sealing fluid within the trough and, similar to a manometer in operation the liquid either side of the fin can be at different heights allowing the seal to withstand differential pressure. In normal operation hydraulic seals do not leak air but if the differential pressure becomes too high the seal will break down and leakage will occur.

There is limited published research relating to hydraulic seals and the accuracy and reliability of the existing design approaches based on analytical derivations is not fully known. This acknowledged need to improve the ability to develop accurate computational models of hydraulic seals provides context for the current study.

An approach to evaluate the maximum pressure capacity of a hydraulic seal is therefore introduced in this work. Building on previously published studies, this paper presents results of a 2D numerical study into the performance of a simplified hydraulic seal geometry. This paper reports a numerical CFD methodology based on an axisymmetric Volume-of-Fluid (VOF) method. In this study there is no oil feed into the trough.

Results are presented for a range of shaft speeds of 2000–8000 rpm for the high speed shaft and 1000–4000 rpm for the low speed shaft. Fin position within the trough was varied. A criteria for broken seal was developed. The CFD data shows that the seal can withstand higher pressure at higher shaft speed with the characteristic following the expected linear relationship between differential pressure and shaft speed squared. The seal could withstand a higher differential pressure if the fin was closer to the housing on the high pressure side with this being attributed to the secondary air flow in the cavity.

The average core velocity was compared to values obtained using different analytical approaches and it was found that one where core angular velocity is proportional to the area averaged rotational velocities of the housing and fin was the best match to CFD data.
A Detailed Modelling of Deposition on Superheater Tubes to Enhance Boiler Flexibility
Authors: Thanganadar Dhinesh , Simms Nigel , Patchigolla Kumar , Mori Stefano , Kulkarni Anand
Published: October 2022

Biomass cofiring in coal-fired power plants is a promising way to reduce CO2 emissions from existing coal plants. However, the changes in the fuel composition influence the ash deposition mechanisms on superheater tubes, therefore negatively impacting the boiler efficiency, as well as promoting corrosion which compromises the life of the boiler tubes. The continuous fluid flow combined with the ash particle trajectories has been simulated using a Eulerian-Lagrangian model. A novel alkali vapour condensation model has been added to the previous in-house powdery dry deposition model. This paper describes the modelling methodology applied and the in-house user-defined functions. This work analyses the deposition flux, and deposit profiles around the superheater tubes for the changes in four different boundary conditions namely 1) flue gas temperature, 2) tube metal surface temperature, 3) flue gas inlet velocity, and 4) alkali vapour concentration from the flue gas by performing a series of sensitivity studies., revealing that flue gas temperature variation primarily influences the mean ash deposition flux. The tube-tube interactions were analysed in detail by simulating three rows of tube banks containing a total of six tubes arranged in a staggered manner, and results show that row 2 encounters the highest ash deposition flux.
Unsteady Effects of Casing Treatment on Tip Flow Structures in a Subsonic Compressor Rotor
Authors: Chi Zhidong , Chu Wuli , Zhang Haoguang , Luo Bo
Published: October 2022

With the help of the dynamic mode decomposition (DMD) analysis, the unsteady effects of casing treatment on tip flow structures in a subsonic compressor rotor were numerically studied. Taking the change of casing treatment geometric parameters into account, the frequency characteristics and dynamic modes were compared and discussed, for further revealing the stability enhancement mechanism of casing treatment. At smooth casing, the mode analysis showed that the tip flow structures were dominated by high absolute mode values alternately emerging along passage streamwise, which is consistent with the evolution of tip leakage vortex (TLV), and the mode frequency is 0.42 BPF. After applying casing treatment, the unsteady characteristics of tip flow fields changed significantly. The mode analysis indicated that the tip flow structures were dominated by intermittent high-energy excitation, which was caused by suction and injection actions of casing treatment. As a result, the relative position of slot and rotor determined the flow features inside casing treatment slots, and an significant induced vortex structure varied in one mode period. By comparing the casing treatment configurations with different slot number, it could be found that the suction and injection effects of casing treatment were closely related to the dominant frequency brought by the slots. When the slot number was not adequate (less than 2 per passage), the excitation energy of suction and injection effects on tip flow field were limited. With the slot number increasing, the excitation energy raised gradually, so the stability enhancement brought by casing treatment was better. This paper demonstrated the effectiveness of DMD method on investigating the unsteady effects of slot-type casing treatment, giving a encouraging prospect for the application of DMD in the internal flow fields with passive control strategies.
Research on Particle Motion and Erosion Characteristics in the Blade Passage of Multistage Axial Compressors
Authors: Cai Liu-xi , He Yao , Hou Yan-fang , Li Yun , Wang Shun-sen , Mao Jing-ru
Published: October 2022

Aviation and ground compressors are susceptible to the erosion of hard particles in the sandy environment, leading to lower performance and shorter service life of the equipment. Although many studies have been performed on this topic, current literature mainly focused on the steady ideal operating conditions of compressors. In this paper, particle motion behavior and erosion characteristics in the blade passage of a 3.5-stage axial compressor under actual service environment are investigated with the RANS numerical simulation method systematically. By comparing the particle trajectories, erosion rate density and other indicators, effect of particle diameter, particle mass concentration, compressor speed and inlet conditions on erosion characteristics are explored in detail.

Results show that the value of erosion rate density on the blade pressure side is overall higher than the suction side. The erosion area and intensity of the rotors are generally more serious than stators, especially on the first rotor blade. With variation in particle size, particle diameter of 100 μm becomes the turning point to change the erosion trend of the blades. Moreover, the overall erosion rates increase linearly with increasing mass concentration of inhaled particles. However, its impact on the erosion position and morphology are not obvious.

When the compressor speed increases from 6050 rpm to 6650 rpm, the eroded mass of R1 increases by 10.7%, and the casing erosion rate increases about 11 times. Compared with the winter condition, the overall erosion rate in summer increases by 62%. The results of this paper will provide a technology basis for the prediction on particle erosion behavior and formulation of operation and maintenance programs for aero engines and ground gas turbines under the actual service environment.
MRI Investigations of Internal Blade Cooling Flow and CFD Optimization Through Data Matching
Authors: Wüstenhagen Carolin , Domnick Clemens , John Kristine , Bruschewski Martin , Grundmann Sven
Published: October 2022

The optimal turbulence model to be used in a CFD simulation varies depending on the application and the scientific question at hand. It is always a difficult task to predict which model best represents reality. This study focuses on the internal cooling system of a high-pressure turbine airfoil. It presents a CFD validation routine, which includes a data matching process with experimental data as well as global and local error metrics to quantify the differences between the experiment and CFD. The experimental data of the time-averaged three-dimensional velocity field is obtained with Magnetic Resonance Velocimetry (MRV). The airfoil in question is a second stage blade of a small industrial gas turbine, consisting of a three-pass internal cooling serpentine. The three-dimensional three-component MRV data is compared to CFD using the data matching process and the error metrics. The simulations are performed with the eddy-viscosity based turbulence model k-ω SST and the Reynolds-Stress SSG, and BSL-EARSM turbulence models. The results indicate local differences between the examined turbulence models and the MRV results. Referring to the global and local error quantities presented in the study, the BSL turbulence model is identified as the optimal turbulence model for this specific high-pressure turbine airfoil.
Experimental Investigation of an Aggressive S-Shaped Intermediate Compressor Duct
Authors: Kasper A. , Dygutsch T. , Grund S. , Beversdorff M. , Hakansson S. , Nicke E. , Lejon M.
Published: October 2022

Reducing the fuel consumption of airplanes is one of the main research topics of the aero industry. Due to this, the bypass ratio in modern aero engines is increasing and the radial offset between the low pressure compressor (LPC) and the high pressure compressor (HPC) is getting larger. Motivated by shortening the length of the duct between the LPC and HPC, called the intermediate compressor duct (ICD), a workgroup from DLR Institute of Propulsion Technology, MTU Aero Engines AG and GKN Aerospace set up a measurement series in the new DLR ring cascade wind tunnel, that simulates a shorter and therefore aero-dynamically more aggressive s-shaped ICD. The setup consists of a full annulus channel. It provides 60 swirler blades which simulate the last rotor of the LPC, 120 LPC outlet guide vanes (OGV), 10 struts and 30 HPC inlet guide vanes (IGV). The airfoil counts are generic counts proposed for validation. Behind the OGV, there is a bleed air outlet which can be varied between 3% and 35% of the mass flow. This paper describes the highly instrumented test rig and its measurement techniques. We are able to analyze the specific flow behavior as well as determine the main ICD-performance parameter. Seven different measurement planes are located between the mentioned blade rows. The total state and the velocity (absolute value and directions) are among others measured in the plane. For each task and measurement location the best suited measurement method is selected. These are mainly multi hole probes in the main measurements planes, L2F in narrow places. The tests are conducted at eight different operating points, varying in Mach number, Reynolds number, bleed rate, stagger angle of swirler and HPC IGV. The high number of measurements leads to a profound understanding of the behavior of the ICD. The resulting conclusion is that in spite of the reduced axial length the flow through the aggressive s-shape of the ICD no separation occurs and therefore the desired performance is achieved.
The Interaction of Main Stream Flow and Cavity Flows in Turbine Center Frames and Turbine Vane Frames
Authors: Merli Filippo , Hafizovic Asim , Krajnc Nicolas , Schien Malte , Peters Andreas , Heitmeir Franz , Göttlich Emil
Published: October 2022

This paper focuses on the interaction between the last high-pressure turbine (HPT) stage purge flows and the intermediate turbine duct (ITD) in modern turbofan engines. Two state-of-the-art ITD concepts are analyzed in this work: the Turbine Center Frame (TCF), which is supported by symmetric aerodynamic strut fairings and generally adopted in conventional dual-spool engines; the Turbine Vane Frame (TVF), which features turning struts and splitters and is typical of geared turbofan engines.

The measurement campaigns for both setups are carried out in the Transonic Test Turbine Facility (TTTF) at Graz University of Technology. The test vehicles consist of an HPT stage, the ITD (TCF or TVF) and the first LPT vane or blade row. The same HPT stage is used for both ducts, to enable consistent, engine-representative inlet conditions between the two solutions. All the HPT stator-rotor cavities are supplied with purge flows by a secondary air system, with independent mass flow and temperature control for each purge line. Five-hole probe data are acquired at the inlet and outlet sections of the ITDs, to characterize the aerodynamic flow field entering and leaving the duct. In addition to the pneumatic probe tests, seed gas concentration measurements are performed in the same planes, to track down the cavity air in the main stream and investigate its post-egress behavior. Finally, detailed post-test CFD results are presented to get additional insight into the flow phenomena developing through the strut passage.

The concentration effectiveness field at the inlet of the ducts shows the same characteristics in both configurations: the upstream purge flows are entrained in the HPT rotor secondary flows, leading to high-concentration spots that influence large portions of the channel. On the other side, the downstream purge air is confined into a thin concentration boundary layer in close proximity to the endwalls. The thickness of this boundary layer is affected by the circumferential pressure distribution from the HPT vanes and struts. At the TCF and TVF outlet, the upstream purge forms a circumferentially uninterrupted band, shaped by the secondary vortices evolving through the duct. The downstream purge interaction with such vortices leads to the formation of well-bounded lobes, whose size, count, and position are inherently related to the secondary structures and thus differ significantly between the two cases.
Unsupervised Feature Selection of Multi-Sensor SCADA Data in Horizontal Axis Wind Turbine Condition Monitoring
Authors: Miele Eric Stefan , Bonacina Fabrizio , Corsini Alessandro , Peruch Arianna , Cannarozzo Marco , Baldan Daniele , Pennisi Francesco
Published: October 2022

Wind power is one of the fastest-growing renewable energy sectors and is considered instrumental in the ongoing decarbonization process. However, wind turbines (WTs) present high operation and maintenance costs caused by inefficiencies and failures, leading to ever-increasing attention to effective Condition Monitoring (CM) strategies. Nowadays, modern WTs are integrated with sensor networks as part of the Supervisory Control and Data Acquisition (SCADA) system for supervision purposes. CM of wind farms through predictive models based on routinely collected SCADA data is envisaged as a viable mean of improving producibility by spotting operational inefficiencies. However, given the large number of variables monitored by SCADA systems, selecting those that contribute the most to the modelling of wind turbine health conditions is an open challenge. In this paper, we propose an unsupervised feature selection algorithm based on a novel multivariate Predictive Power Score (PPS). Unlike other approaches in literature that only consider relationships between pairs of variables, here we propose a Combined PPS (CPPS), where the information content of combinations of variables is considered for the prediction of one or more key parameters. The algorithm has been tested on 9 turbines belonging to the same wind farm located in the Italian territory. The results show that the proposed approach is more flexible and outperforms standard PPS.
Impact of Boundary Layer Ingestion on the Performance of Propeller Systems for Hybrid Electric Aircraft
Authors: Vouros Stavros , Hieb David , Kyprianidis Konstantinos
Published: October 2022

Boundary layer ingestion (BLI) has demonstrated potential for reduced thrust requirements, fuel consumption and environmental impact. An integrated approach is developed for evaluating the performance of propeller systems including BLI propulsors. A rotor model based on lifting-line theory is coupled with a high-order panel method and an integral boundary layer formulation. The impact of BLI on single propeller performance maps is quantified, with efficiencies up to 15% higher compared to uniform freestream conditions. A design space exploration framework is developed for the analysis of BLI effects at propeller system level, including the impact of weight differentiation, installation technology factors, thrust split between rotors and electrical transmission losses. A reference 19-passenger aircraft featuring two wing-mounter propellers is compared with a series of conceptual designs featuring an aft-fuselage BLI propeller and two wing-mounted propellers. A system-wide power saving coefficient is derived for the quantification of performance deltas between the conceptual and the reference system, including all propulsors. For systems with BLI aerodynamic benefits entirely negated by weight penalties, and electrical transmission losses of 10%, power savings of 1.5% are accrued. In a technologically advanced system with 2% reduced thrust requirements due to BLI and 3% transmission losses, power savings rise to 6.5%. This work reveals the anticipated performance potential and limitations of BLI propeller systems for the electrified future fleet.
Gas Turbine Combined Cycle Range Enhancer - Part 1: Cyber-Physical Setup
Authors: Reboli Tommaso , Ferrando Marco , Mantelli Luca , Gini Lorenzo , Sorce Alessandro , Garcia Jose , Guedez Rafael
Published: October 2022

Natural gas turbine combined cycles (GTCCs) are playing a fundamental role in the current energy transition phase towards sustainable power generation. The competitiveness of a GTCC in future electrical networks will thus be firmly related to its capability of successfully compensating the discontinuous power demands. This can be made possible by enhancing power generation flexibility and extending the operative range of the plant.

To achieve this goal, a test rig to investigate gas turbine inlet conditioning techniques was developed at the TPG laboratory of the University of Genoa, Italy. The plant is composed of three key hardware components: a micro gas turbine, a butane-based heat pump, and a phase-change material cold thermal energy storage system. The physical test-rig is virtually scaled up through a cyber-physical approach, to emulate a full scale integrated system.

The day-ahead schedule of the plant is determined by a high-level controller referring to the Italian energy market, considering fluctuations in power demands.

By using HP and TES, it is possible to control the mGT inlet air temperature and thus enhance the operational range of the plant optimizing the management of energy flows.

This article (Part 1) introduces the new experimental facility, the real-time bottoming cycle dynamic model, and the four-level control system that regulates the operation of the whole cyber-physical plant. The experimental campaign and the analysis of the system performance are presented in the Part 2.
Aerodynamic Assessment of Turbine Center Frames and Turbine Vane Frames Under the Influence of Purge Flows
Authors: Merli Filippo , Hafizovic Asim , Krajnc Nicolas , Schien Malte , Peters Andreas , Heitmeir Franz , Göttlich Emil
Published: October 2022

This paper investigates and compares the aerodynamics of two state-of-the-art configurations for the intermediate turbine duct (ITD) in a turbofan engine: the turbine center frame (TCF), which is typical of conventional dual-spool engines and features symmetric aerodynamic strut fairings, and the turbine vane frame (TVF), which integrates a set of turning struts and splitters directly in the duct, thus enabling length and weight benefits at engine system level.

The measurement data utilized for the analysis are a product of almost ten years of research at Graz University of Technology, involving multiple test campaigns with either TCF or TVF setups at consistent inlet conditions. The experimental tests are carried out in the Transonic Test Turbine Facility at the Institute of Thermal Turbomachinery and Machine Dynamics (Graz University of Technology). All test vehicles include not only the ITD (TCF or TVF), but also the last High-Pressure Turbine (HPT) stage and the first Low-Pressure Turbine (LPT) vane or blade row, in order to ensure engine-representative conditions at the duct inlet and outlet sections. For the same purpose, the test facility supplies all the stator-rotor cavities with purge air, with independent control of temperature and mass flows for each cavity.

The measurements are performed with pneumatic probes (five-hole probes, Kiel-head rakes) at the inlet and outlet of the ITDs, for three different HPT purge flow rates. The aerodynamic comparison between TCF and TVF setups is based on three key topics: duct inlet and outlet flow fields, duct total pressure losses and duct aerodynamic excitation on the LPT rotor blades. For each one of them, the sensitivity to HPT purge variation in both configurations is evaluated.

Due to the presence of turning struts and splitters inside the ITD, the TVF shows a more complex outlet flow field than the TCF, characterized by the interaction of HPT and TVF secondary phenomena. The TVF total pressure loss is less sensitive to purge variation compared to an advanced TCF design with high casing slope. While the weaker TVF loss derivative to HPT purge may provide off-design operating point benefits relative to a TCF-based engine, the increased level of flow nonuniformity at the TVF exit, distributed over a wider range of engine orders, represents a design challenge for the first-stage LPT rotor.
Aerodynamic Optimization of the SRV2 Radial Compressor Using an Adjoint-Based Optimization Method
Authors: Châtel Arnaud , Verstraete Tom
Published: October 2022

The design of radial compressors is typically a trade-off between peak performance at the design conditions and maintaining a good efficiency over a wide operating range. In the present paper, a gradient-based optimization of the well-known SRV2 radial compressor is presented. The optimization problem is formulated to increase the total-to-total efficiency of the compressor at peak efficiency while maintaining a wide operating range. To achieve an efficient optimization strategy, a gradient-based optimization method is used. Gradients of the RANS solver are obtained through the adjoint approach, leading to a computational cost that is almost independent of the degrees of freedom. A total of 44 design parameters are used to define a rich design space for the radial compressor impeller. A Sequential Quadratic Programming algorithm is used as optimizer and achieves an optimal design in less than 20 major iterations. The optimization process allows to significantly increase the efficiency of the SRV2 compressor at peak efficiency while maintaining the operating range of the baseline. Detailed analysis of the flow field in baseline and optimized compressors reveal the mechanisms which allow to improve the performance of the baseline compressor.
Development of Machine-Learnt Turbulence Closures for Wake Mixing Predictions in Low-Pressure Turbines
Authors: Frey Marioni Yuri , Adami Paolo , Vazquez Diaz Raul , Cassinelli Andrea , Sherwin Spencer , Montomoli Francesco
Published: October 2022

In this work, a DNS – Machine Learning (ML) framework is developed for low-pressure turbine (LPT) profiles to inform turbulence closures in Reynolds-Averaged Navier-Stokes (RANS) calculations. This is done by training the coeffcients of Explicit Algebraic Reynolds Stress Models (EARSM) with shallow artificial neural networks (ANN) as a function of input flow features. DNS data are generated with the incompressible Navier-Stokes solver in Nektar++ and validated against experiments. All calculations include moving bars upstream of the profile to capture the effect of incoming wakes. The resulting formulations are then implemented in the Rolls-Royce solver HYDRA and tested a posteriori. The aim is to improve mixing predictions in LPT wakes, compared to the baseline model, Wilcox’s k-ω SST, in terms of velocity profiles, turbulent kinetic energy (TKE) production and mixing losses. LPT calculations are run at Reynolds numbers spanning from ≈ 80k to ≈ 300k, to cover the range of aircraft engine applications. Models for the low and high Reynolds datasets are trained separately and a method is developed to merge the two together. The resulting model is tested on an intermediate Reynolds case. This process is followed for two computational domains: one starting downstream of the profile trailing edge and one including the last portion of the profile. Finally, the developed closures are tested on the entire profile, to confirm the validity of the improvements when the additional effect of transition is included in the simulation. This work explains the methodology used to develop ML-driven closures and shows how it is possible to combine models trained on different datasets.
The Application of the Arbitrary-Order Galerkin Reduction Method to the Dynamic Analysis of a Rotor With a Preloaded Single-Pad Foil-Air Bearing
Authors: Ghalayini Ibrahim , Bonello Philip
Published: October 2022

The compressible Reynolds Equation (RE) is typically integrated within a fully-coupled dynamical foil-air bearings (FABs)-rotor system via spatial discretisation transformation e.g. Finite Difference (FD), Finite Element (FE). An alternative way of integrating the RE is through Galerkin Reduction (GR). The motivation for using GR is the computational benefit coming from the drastic condensation of the problem due to the elimination of the two-dimensional grid used for the air film in FD or FE. This paper presents a novel application of arbitrary-order GR to both nonlinear and linearised analyses of rotor systems supported by single-pad FABs with variable radial clearance (preload). Simulations using FD gave close correlation with those using GR for all preloads, with discrepancies increasing as the preload approaches the nominal clearance (c). The simulations show that the preload has to exceed a certain level in order to delay the onset of instability speed (OIS), and significant delay in OIS and suppression of sub-synchronous vibration is possible when the preload is comparable to c. Experimental validation is provided.
Modeling of Flashback With Different Blends of CH4 and H2 by Using Finite Rate Chemistry With Large Eddy Simulation
Authors: Verma Ishan , Yadav Rakesh , Ansari Naseem , Orsino Stefano , Li Shaoping , Nakod Pravin
Published: October 2022

Due to its clean combustion characteristics, hydrogen fuel is gaining attention in power generation. New designs of engine systems and components are being explored to allow blending with the increasing amount of hydrogen in natural gas. Adding H2 increases the probability of flashback and often is one of the main constraints in using high H2 blends in premixed combustors. There are several mechanisms of flashback like boundary layer flashback, combustion induced vortex break down, turbulence in the flow, fluctuations in equivalence ratio, etc. Semi-empirical models, based on non-dimensional numbers and flame speed, have successfully predicted flashback propensity for a given operating condition. The semi-empirical models are computationally very efficient; however, they lack generality. A typical combustor can have multiple flashback mechanisms. The relative importance of each mechanism can change with a change in the combustor design or even with a difference in the operating conditions for the same combustor. Since prediction of flashback requires accurate modeling of highly transient chemistry phenomena and the impact of heat loss on chemistry, a viable detailed chemistry solution is preferred to model flashback.

This paper describes the use of a finite rate chemistry model to predict flashbacks in a turbulent premixed combustor in this work. The configuration used is a swirl stabilized combustor (SimVal) from National Energy Technology Laboratory. The current computations are done with Finite Rate Chemistry (FRC) and Large Eddy Simulations (LES). Simulations are carried out for a varied percentage of CH4/H2 blends, ranging from 0% H2 to 100% H2 at a fixed equivalence ratio and inlet mass flow. As the percentage of H2 is increased in the fuel, flame speed also increases. With this, the propensity for flashbacks also increases. A 28-species reduced mechanism for CH4/H2 blend flames is used to keep the simulations computationally tractable. The simulations with the reduced mechanism are performed by considering non-adiabatic effects from heat loss near the walls and multi-component property considerations. This improves the accuracy of the FRC-LES simulations to capture the onset of boundary layer flashback towards the inlet. The simulations from FRC-LES suggest a fine mesh in the boundary layer for an accurate prediction that makes the simulations expensive. Therefore, an Adaptive Mesh Refinement (AMR) approach has been used for different CH4/H2 blends to accurately model the flashback without any loss in generality as the AMR criteria used here are applicable for a wide range of conditions. The FRC-based solution strategy proposed in this work provides a framework to model flashback for different blends without any case-specific tuning.
Nonlinear Dynamic Analysis of the Pressure Signals on a Swirl-Stabilized Atmospheric LDI Burner Across Different Operating Conditions
Authors: Torregrosa Antonio , Broatch Jacobi Alberto , García-Tíscar Jorge , Rodríguez Pastor Marc
Published: October 2022

Lean Direct Injection (LDI) burners are a promising technology aimed at reducing NOx emissions in new generation aeroengines. However, one of the main drawbacks of this technology is the appearance of combustion instabilities at certain operating conditions. In order to investigate these issues, a confined, atmospheric, swirl-stabilized LDI burner has been set up at the Institute CMT-Motores Térmicos. In this configuration, air mass flow, temperature, and fuel mass flow rate, which is controlled by the injection pressure, can be independently modified to reach different combustion states. In this paper, a parametric study of the equivalence ratio (0.3 ≤ Φ ≤ 0.8), air temperature (50, 100, 150 °C) and fuel mass flow rate (200, 250, 300, 335, 370 mg/s) has been performed to assess their influence on the dynamics of the system through the evaluation of the pressure signals inside the chamber. These signals have been acquired with two piezoresistive sensors flush-mounted to the combustor wall at the same axial distance but in opposite sides of the chamber. Large-amplitude unsteady oscillations are detected for some combinations of the variables of interest. Equivalence ratio variations are shown to affect deeply the dynamic features of the pressure signal, obtaining more stable configurations either close to the lean limit (Φ = 0.3) or at the richest condition tested (Φ = 0.8). Mid-range equivalence ratio values (0.4 ≤ Φ ≤ 0.7) are shown to display the most unstable behavior, featuring large pressure oscillations that remain nearly constant over time (quasi-periodic states) or signals that experience sudden variations in their amplitude (intermittent states). Since turbulent swirl-stabilized spray flame combustors may experience complex flow-flame interactions that could lead to nonlinear behavior of these combustion regimes, several signal processing techniques such as three-dimensional phase space reconstruction or recurrence plots have been applied to the experimental data in order to obtain better insight into these highly dynamic features.
Analytical Methods for Transonic Compressor Rotor Blade Tip Clearance Measurements Using Capacitive Probes
Authors: Magno David , Gannon Anthony , Smith Walter , Hobson Garth
Published: October 2022

A method is presented to improve the capability of proximity sensing capacitive probes used in rotor blade tip clearance (BTC) measurements. This research presents the development and result of a post-processing method used to calibrate capacitive probe instrumentation that will be used to passively analyze BTC of a transonic axial fan under high-speed and high-transient loading. The method attempts to address limitations currently placed on BTC measurements due to poor a SNR. Each revolution’s raw capacitive probe signal is uniformly resampled to a synchronizing once-per-revolution signal, normalizing the data. This reduces timing inaccuracies in the sampling frequency inherent to the data acquisition system and transfers data into a spatial domain removing time dependence and rotational speed variance, which in turn improves the SNR. A Fast Fourier Transform (FFT) is used to identify acceptable lowpass filter passbands that are then adaptively applied to this resampled data based on tip clearance distance. This produces increased precision and dynamic range in capacitive probe calibration compared to existing BTC calibration methods. Use of the proposed method gives the potential ability to operate capacitive probes at larger ranges and in poor SNR environments and gives a possible application in monitoring rotor blade integrity, at a low, additional computation time cost.
An Integrated Creep Damage Analysis Method of Turbine Blades Based on the Service History
Authors: Shi Duoqi , Cheng Muwei , Yang Xiaoguang , Fan Yongsheng
Published: October 2022

The creep fracture life of turbine blades is a limitation of the whole engine life because of its high operating temperature. Thus, developing an analysis approach of creep damage based on complex service history is of significant importance for the safe operation and economic overhaul. Within this content, an integrated creep damage analysis method is constructed, which can be used to calculate the accumulation of creep damage in real time once obtaining the service history. This approach first gets some critical parameters such as rotor speed and turbine forward temperature of the turbine blades through thermodynamic performance model of the engine. Then the stress and temperature states of the turbine blade is obtained by the thermal-fluid-solid coupling analysis. Based on the numerical results, a train of surrogate models from engine operating state to the detail load states including temperature, thermal stress and centrifugal stress are established. The classical Rabotnov-Kachanov creep model is selected to calculate the creep damage accumulation. This integrated damage analysis method has been carried out by a turbofan engine’s turbine blades. The results show that this method works well and quickly when faced with a large number of flight record data with only once numerical simulation under the typical service state. The blades damage accumulation changes reasonably as flight profile. The proposed method decreases the time cost by the developed surrogate models when flight profile changes, which has the potential to be used to monitor individual engine life and to extend to study the other damage types of turbine blades under different flight loads.
Crossflow Effect on Heat Transfer and Flow Characteristics of Simplified Double Wall Cooling Structure
Authors: He Juan , Deng Qinghua , Xiao Kun , Feng Zhenping
Published: October 2022

Double wall cooling is regarded as one of the advanced cooling technologies of modern gas turbines, but its internal cooling is always confronted with crossflow effect. To reveal the conjugate heat transfer characteristics under different crossflow configurations, this paper utilized ANSYS CFX to numerically simulate a double wall cooling model with staggered impingement holes and film holes. CFX numerically solves steady three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations. Both the overall cooling and internal heat transfer performance of four different crossflow mass flow ratios (CMFR = 0, 0.25, 0.5, 0.75) under four impingement jet Reynolds numbers (Rej = 15,000, 25,000, 35,000, 45,000) are compared in detail. The calculated results show that the CMFR has significant influence on double wall cooling performance. The averaged blowing ratio increases with the increase of jet Reynolds number under the same crossflow configuration, and it decreases with the increase of CMFR under the same impingement jet Reynolds number. The area-averaged Nusselt number decreases with the increase of CMFR at the CMFR ranging from 0.25 to 0.75, but the area-averaged overall cooling effectiveness increases with the increase of CMFR since better film coverage plays a dominated role in the enhancement effect of double wall cooling. In addition, the influence of solid thermal conductivity is also taken into consideration. It is revealed that solid thermal conductivity has great influence on double wall cooling. Under all crossflow configurations, the overall cooling effectiveness increases with the increase of solid thermal conductivity, but the increase rate slows down with the increase of thermal conductivity.
Developing a Scalar Flux Model Solely Based on Mean Flow Quantities for the Film Cooling Jet Flow
Authors: Shi Bo , Li Xueying , Ren Jing
Published: October 2022

Previous studies showed that the Reynolds-averaged Navier Stokes simulation (RANS) which used gradient diffusion hypothesis (GDH) severely under-predicts the scalar diffusion downstream the film cooling jet flow. Scalar flux models of different types have been developed throughout the years. Of particular interest is the algebraic model, which is easy to implement and has a low computational cost. Well-known algebraic models include the generalized gradient diffusion hypothesis (GGDH) and the high-order generalized gradient diffusion hypothesis (HOGGDH). However, due to the dependence on the Reynolds stress, GGDH and HOGGDH may suffer from a lack of scalar prediction along with RANS, because the Boussinesq core of which will lead to a loss of anisotropy. In a previous study [1], we revealed the mechanism of turbulent scalar transport in the shear layers of the film cooling jet based on the analysis of the flow and scalar field predicted by the large eddy simulation (LES). Upon the mechanism revealed, this paper aims to develop a scalar model that only depend on mean flow quantities, including mean velocity, turbulent kinetic energy and turbulent viscosity. It is our hope that the model can be comparable or surpass the GGDH and HOGGDH concerning the ability of scalar prediction, while not be dependent on the Reynolds stress. Scalar transport equation was solved with the mean flow data provided by the previous LES. The prediction of an inclined cylindrical hole with VR = 0.46 using GGDH, HOGGDH and current model (namely SLR) were compared and analyzed.
Interaction Mechanism of Impeller and Diffuser Stall in a Centrifugal Compressor
Authors: Fujisawa Nobumichi , Naitou Momoko , Ohta Yutaka
Published: October 2022

The interaction mechanism of impeller and diffuser stall in a centrifugal compressor with a vaneless diffuser was investigated by experimental and computational analyses. This study focuses on the effect of impeller stall on the diffuser stall behavior. Impeller stall rotated at 58% of the impeller rotational speed was generated inside the impeller. Two-cell diffuser stalls (with each of the cells rotating at 25%–30% of the impeller rotational speed) were generated inside the diffuser. The diffuser stall fluctuations were observed at 180° from the cutoff. The magnitudes of the diffuser stall fluctuations gradually increased near the volute tongue. The diffuser stall fluctuations were generated near both the shroud and hub sides. Finally, the diffuser stall cell vanishes when it passes the cutoff because mass flow recovery occurs. The numerical results revealed that boundary layer separation occurred near the hub side at 45°–90° of the diffuser because of the circumferential adverse pressure gradient. Subsequently, the low-velocity region discharged from the impeller caused by impeller stall merged into the boundary layer separation, which was generated near the hub side at 45°–90°. Diffuser stall was initiated by the hub-side boundary layer separations, which were caused by the impeller stall. The diffuser stall cell was then further developed by the boundary layer separation accumulation and the induced low-velocity area. The boundary separation was further developed by merging the wake from the impeller stall passage.