bluuebunny/crossref_metadata_2025 huggingface dataset:
High-Frequency Instability Driving Potential of Premixed Jet Flames in a Tubular Combustor due to Dynamic Compression and Deflection
Authors: Mohammadzadeh Keleshtery Payam , Heilmann Gerrit , Hirsch Christoph , Panek Lukasz , Huth Michael , Sattelmayer Thomas
Published: January 2021

Constructive interference of acoustic oscillations and combustion heat release can result in high-frequency thermoacoustic instabilities in gas turbine combustion chambers with strong pressure pulsations. They may cause component wear and limit the safe operating range of the engine. During the development of stable combustors the influence of design variables on the driving mechanisms of these instabilities is of particular interest. This paper studies the influence of design parameters on the linear growth rates of high-frequency thermoacoustic transverse modes in a tubular combustor of hexagonal cross-section equipped with 12 turbulent premixed jet burners. Two flame dynamics models are used, i. e. the dynamic compression and the deflection mechanisms, which have in the past been validated for turbulent swirl burners. To demonstrate the applicability as well as the shortfalls of these flame dynamics models the impact of different geometrical and flow parameters on the driving potential of high-frequency thermoacoustic modes are considered. A parameter variation study of thermal power, air excess ratio, diameter of the combustor and the radial position of jet burners was performed.

The first transversal eigenmodes and eigenfrequencies were computed by solving the inhomogeneous Helmholtz equation with the flame driving source terms in the frequency domain using the finite element method. The required mean fields of temperature and heat release rate were obtained using a generic flame distribution scaled with respect to the experimental OH* chemiluminescence measurements. The resulting growth rates give a measure for the thermoacoustic driving potential.
Impact of Additive Manufacturing on Internal Cooling Channels With Varying Diameters and Build Directions
Authors: Wildgoose Alexander J. , Thole Karen A. , Sanders Paul , Wang Lieke
Published: January 2021

The use of additive manufacturing (AM) processes, such as direct metal laser sintering, provides the design freedom required to incorporate complex cooling schemes in gas turbine components. Additively manufactured turbine components have a range of cooling feature sizes and, because of the inherent three-dimensionality, a wide range of build angles. Previous studies have shown that AM build directions influence internal channel surface roughness that, in turn, augment heat transfer and pressure loss. This study investigates the impact of additive manufacturing on channel feature size and build direction relative to tolerance, surface roughness, pressure losses, and convective cooling. Multiple AM coupons were built from Inconel 718 consisting of channels with different diameters and a variety of build directions. An experimental rig was used to measure pressure drop to calculate friction factor and was used to impose a constant surface temperature boundary condition to collect Nusselt number over a range of Reynolds numbers. Significant variations in surface roughness and geometric deviations from the design intent were observed for distinct build directions and channel sizes. These differences led to notable impacts in friction factor and Nusselt number augmentations, which were a strong function of build angle.
Forced Response Variation of a Compressor Utilizing Blade Tip Timing, Strain Gages, and As-Manufactured Finite Element Models
Authors: Gillaugh Daniel L. , Janczewski Timothy J. , Kaszynski Alexander A. , Brown Jeffrey M. , Beck Joseph A. , Nessler Chase
Published: January 2021

The dynamic response of turbine engine components varies widely due to manufacturing deviations in the blades known as mistuning. This dynamic variation is investigated using a single stage compressor experimentally using both blade tip timing (BTT) and strain gage (SG) measurements and using as-manufactured finite element models (AMMs) on a 1st bend mode. Operational BTT and SG safety limits were generated using both averaged and AMM models via Goodman material properties. The predicted individual blade stress/deflection (S/D) ratios and strain gage ratios for this mode will be compared to the average finite element counterparts. Additionally, the correlation between BTT and SG’s will be presented. This correlation will be performed using two approaches: blade maximum stress comparisons and measured response compared to the sensors safety limits. It will be shown that accounting for geometry with AMMs produce more accurate strain gage to BTT correlation compared to average models. An experimental model updating procedure is developed to increase the strain gage to BTT correlation by optimizing the location the BTT optical spot probes measure on the blade chord. Implementing this procedure using as-manufactured models are able to improve strain gage to BTT correlation.
Transonic Relief in Fans and Compressors
Authors: Lefas Demetrios , Miller Robert J.
Published: January 2021

Every supersonic fan or compressor blade row has a streamtube, the ‘sonic streamtube’, which operates with a blade relative inlet Mach number of one. A key parameter in the design of the ‘sonic streamtube’ is the area ratio between the blade throat area and upstream passage area, Athroat/Ainlet. In this paper, it is shown that one unique value exists for this area ratio. If the area ratio differs, even slightly, from this unique value then the blade either chokes or has its suction surface boundary layer separated due to a strong shock. It is therefore surprising that in practice designers have relatively little problem designing blade sections with an inlet relative Mach number close to unity. This paper shows that this occurs due to a physical mechanism known as ‘transonic relief’. If a designer makes a mistake, and designs a blade with a ‘sonic streamtube’ which has the wrong area ratio, then ‘transonic relief’, will self-adjust the spanwise streamtube height automatically moving it towards the unique optimal area ratio, correcting for the designer’s error. Furthermore, as the blade incidence changes, the spanwise streamtube height self-adjusts, moving the area ratio towards its unique optimal value. Without ‘transonic relief’, supersonic and transonic fan and compressor design would be impossible. The paper develops a simple model which allows ‘transonic relief’ to be decoupled from other mechanisms, and to be systematically studied. The physical mechanism on which it is based is thus determined and its implications for blade design and manufacturing discussed.
Design Framework for Optimized Multifunctional Coatings
Authors: Moazami Nima , Abdi Frank , Morscher Gregory N. , Godines Cody , Zawada Larry , Jefferson George , Ahmed Jalees
Published: January 2021

An ICME (Integrated Computational Material Engineering) and lifing model/method is developed for optimizing multifunctional coatings Atmospheric Plasma Spray (APS) process of metallic TBC (Thermal Barrier Coating) system. Optimized TBC performance was achieved by minimizing thermal conductivity and residual stresses/strains during APS utilizing multiphysics-based multi-objective topology optimization methodology, and virtual design of experiment (DOE), surrogate meta modeling methodology. Thermal conductivity and residual strains were minimized 41% and 27%, respectively, for APS 8YSZ TBC with MCrAlY bond over Waspaloy substrate considering as variables yttria (mol.%), number of layers, total thickness, substrate initial temperature, and coating initial temperature.

Durability and Damage Tolerance (D&DT) analysis of Metallic bonded TBC dogbone specimen was performed using Multi-Scale Progressive Failure Analysis (MS-PFA). The objective was to determine the Remaining Useful Life (RUL) of Metal/TBC (8YSZ, Bond, Inconel-718) system under Low Cycle Fatigue (LCF) in-service loading at 900°C. The multi-scale multi-layer TBC modeling considered Thermal Growth Oxidation (TGO) in bond coat, and recession of top coat. Prediction was validated by Rig testing; TGO measurement Progressive damage analysis revealed that failure is due to tension and out of plane shear, delamination growth due to when recession penetrates bond. The results showed that predicted fatigue life compared well to experimental observations.
Simulation Driven Design Workflow for Aircraft Gearbox
Authors: Park Youn , Gasevski Dragi , Springer Marlow , Stanic Milos , Kulkarni Viraj , Marjadi Dhiren
Published: January 2021

The aerospace industry is driven more than ever to reduce time and cost of developing aircrafts while reducing weight without compromising performance. This challenge cascades down to design of aircraft engines, where manufacturers are striving to deliver engines with higher fuel efficiency and power per unit weight. The challenge cascades down further to aerospace systems such as gearboxes. The focus of this paper is to addresses this challenge through application of model-based systems engineering and a design workflow based on simulation and optimization.

A typical gearbox design starts with system level performance requirements such as power requirements, speed, torques and operating conditions. The goal is to design a minimum weight, manufacturable gearbox in the shortest possible time that meets the performance requirements. In this paper, authors present a design workflow developed for meeting this goal.

The efficiency of the workflow presented here comes from the use of advanced simulation technologies, seamless integration of the workflow tasks, and modern and intuitive user experience.

The proposed workflow focuses on design of housing and lubrication. This workflow is demonstrated on an aircraft engine accessories gearbox. Gear and bearing design are currently out of the scope of this paper and can be addressed in future work.

Demonstrating a fully detailed workflow on a real-life gearbox housing with all the physics covered here would require many man-months of work and is outside the scope of authors’ IRAD funding. Instead, authors have presented a proof of concept of the workflow while providing key statistics to support the value and feasibility of the workflow.
Experimental Study of Full Coverage Film Cooling Effectiveness for a Turbine Blade With Compound Shaped Holes
Authors: Zhang Shuai-qi , Liu Cun-liang , Guo Qi-ling , Liang Da-peng , Zhang Fan
Published: January 2021

The film coverage of a turbine blade surface is determined by all the film cooling structures. The direct study of full coverage film cooling is relatively rare, especially for related research on turbine blades. In this paper, the pressure-sensitive paint (PSP) measurement technique is used to carry out experiments under different turbulence intensities and mass flux ratios, and the distribution of the film cooling effectiveness on the entire surface is studied in detail. In this study, a basic turbine blade and an improved turbine blade are investigated. The film cooling hole position distribution on the improved blade is the same as that on the basic blade, but the film cooling hole shape on the suction surface and the pressure surface is changed from cylindrical holes to laid-back fan-shaped holes. Both blades have 5 rows of cylindrical holes at the leading edge and 4 rows of film cooling holes on the suction surface and the pressure surface. The leading edge, suction surface, and pressure surface have their own coolant inlet cavities. This kind of design is not only close to the actual working conditions in a flow distribution but also conveniently eliminates the mutual interference caused by the uneven flow distribution between the pressure surface and the suction surface to facilitate the independent analysis of the pressure surface and the suction surface.

In this paper, the film cooling effectiveness of two kinds of turbine blades under different turbulence intensities and mass flux ratios is studied. The results show that the average cooling effectiveness of the improved blade is much better than that of the basic blade. The laid-back fan-shaped hole rows improve the cooling effectiveness of the suction surface by 60% to 100% and 50% to 120% on the pressure surface. The increase in turbulence intensity will reduce the cooling effectiveness of the blade surface; however, the effect of the turbulence intensity becomes weaker with an increase in the mass flux ratio. Compared with the multiple rows of cylindrical holes, the cooling effectiveness of the laid-back fan-shaped holes is more affected by the turbulence intensity under the small mass flux ratio.
Effect of Matching Parameters Between Rotor and Diffuser on the Flow Loss Characteristic in an Axial Turbine
Authors: Wang Xing , Zhu Yangli , Li Wen , Zhang Xuehui , Chen Haisheng
Published: January 2021

Diffuser is a key component affecting the aerodynamic performance of an axial turbine significantly. However, there is little research on the matching parameters between a rotor and a diffuser. In present study, effect of matching parameters which are normalized axial clearance (ACLR‘) and normalized radial size deviation (RDev‘) between rotor and diffuser on the aerodynamic performance and flow loss characteristic of a typical diffuser is revealed. A validated Computational Fluid Dynamic (CFD) model which couples the cavity between the rotor and diffuser is also proposed. The results illustrate that the isentropic efficiency is decreased with the increase of ACLR‘ and RDev‘. The RDev‘ presents a larger influence on isentropic efficiency. When ACLR‘ is increased from 0.21 to 0.43, the isentropic efficiency is only decreased by 0.3%, while the isentropic efficiency reduction of 0.65% is achieved when RDev‘ is increased from 0.091 to 0.192. A “leakage flow”, which is a result of the egress and ingress of the fluid near diffuser-cavity interface, is formed. It presents limited effect on the main flow in the diffuser when ACLR’ is only included and the flow loss near the guide cone surface is increased slightly. However, obvious back flow caused by the “leakage flow” is observed near the diffuser-cavity interface, when RDev’ is included. A flow separation is thus formed downstream and the flow loss in the diffuser is thus increased. The efficiency reduction caused by actual matching parameters (ACLR‘ with 0.21 and RDev‘ with 0.091) is increased with the decrease of expansion ratio. It can be more than 1.26% when the expansion ratio is less than 2.0. An isentropic efficiency reduction of 0.65% is found when different tip clearance are further adopted, and the mixture loss between tip leakage flow and back cavity flow can be neglected. In summary, matching parameters, especially for radial deviation, should be minimized reasonably in further optimization.
Experimental Study on Internal Flow Field of a High-Speed Centrifugal Compressor at Different Altitudes
Authors: Yu Xinghang , Ma Hongwei , Shi Lei , Zhao Lianpeng
Published: January 2021

The alteration of altitude will affect the stability of centrifugal compressors. In this paper, the pressure field on the casing wall of a high-speed centrifugal compressor at two different altitudes (h = 0m and h = 4500m) was investigated by using 15 high-response pressure sensors. The operating condition of the centrifugal compressor ranged from choke condition to developed stall condition. The results show that the interaction of the shock wave and splitter-blade tip leakage flow occurs at 70% chord region near the choke condition, and the loss is more severe at the high altitudes. At the near-stall condition, the unstable disturbance at the low altitude is caused by the collapse of the horseshoe vortex, and the unstable disturbance at the high altitude is dominated by advanced breakdown of the main-blade tip leakage vortex. At the developed-stall condition, the stall mechanisms at the two altitudes are different, both of which are closely related to the main-blade tip leakage flow. With the decrease of flow rate, the unsteady disturbance caused by the volute tongue moves upstream from the diffuser to the impeller inlet. At the same time, the unsteady disturbance propagates along the opposite direction of the rotational direction in the partial impeller passage at the low altitude case. However, the circumferential propagation characteristics at the high altitudes case are not obvious.
Numerical Simulation of Reacting Flows Around a Bluff-Body Flame Stabilizer With Lattice Boltzmann Method
Authors: Zhang Zhihong , Li Zhiqiang , Wu Yunke
Published: January 2021

A 2-dimensional lattice Boltzmann model for combustion phenomena is presented. Mathematically, the model is composed of a standard lattice Boltzmann distribution function to recover the hydrodynamic model which describe the density and flow velocity and two distribution functions to recover the governing equation of temperature and chemical reaction process. The temperature could be described by solving an advection-diffusion equation with a simpler lattice. The actual combustion processes are very complicated. In this work, we consider the simple combustion processes with the assumption that the reaction process is irreversible and described by an empirical equation. The evolution of chemical process is described by another passive scalar convection-diffusion equation. The chemical energy released in the progress of combustion is dynamically coupled into the system by adding a chemical term to the temperature distribution function. The model is verified and validated via well-known benchmark tests. In this paper, the case of vortex street arising from the flow around the circular cylinder at Re = 100, 150 and 200, is taken to examine the validation of the numerical simulation. The Strouhal numbers achieved in the numerical simulation match well with the theoretical values. We also simulate a flame at constant pressure to validate the model, the temperature and concentration distributions is consistent with the laminar premixed combustion theory. The objective of the present work is to investigate the effect of Reynolds number on the stability of the flame behind the bluff-body. For the circular cylinder flame stabilizers, the effect of different inlet speeds on flame stability was investigated.
Averaging for High Fidelity Modelling: Towards Large Eddy Simulations in Multi-Passage Multi-Row Configurations
Authors: He L.
Published: January 2021

A major challenge in high-fidelity turbomachinery flow computations is the need for high resolution in a very large domain of multiple blade-passages and multiple blade-rows. Scale-resolving turbulent solutions are prohibitively costly. The question is, what will it take to get high-fidelity solutions if we are only after time-mean flows for aerothermal performance?

A novel two-scale approach is adopted to address the issue by coupling between a local fine-mesh domain in a singlepassage and a global coarse-mesh multi-passage domain. This is achieved by harnessing the extra product terms generated when averaging a nonlinear process in time, as well as in space. As such a space-time averaging is purposely utilized in either a direct mode or an inverse one in the two domains respectively. The source terms in a compact form (one scalar for one equation) can be conveniently obtained and used to enable the interaction between the single-passage fine-mesh and the multipassage coarse-mesh solutions. The converged solution for this two-scale coupled system should meet two seemingly conflicting requirements: an otherwise poorly conditioned local fine-mesh domain is now subject to a right environment/flow conditions, and an otherwise poorly resolved global coarse-mesh domain is now effectively subject to high resolution. In this paper, the concepts, the formulations of the framework methodology and the implementation methods will be described. The validity and feasibility of the approach for efficient scale-resolving high-fidelity turbomachinery flow simulations will be illustrated by several computational examples of practical interest.
Uncertainty Based Optimization Strategy for the Gappy-POD Multi-Fidelity Method
Authors: Poethke Bernhard , Völker Stefan , Vogeler Konrad
Published: January 2021

In the surrogate model-based optimization of turbine airfoils, often only the prediction values for objective and constraints are employed, without considering uncertainties in the prediction. This is also the case for multi-fidelity optimization strategies based on e.g. the Gappy-POD approach, in which results from analyses of different fidelities are incorporated. However, the consideration of uncertainties in global optimization has the advantage that a balanced coverage of the design space between unexplored regions and regions close to the current optimum takes place. This means that on the one hand regions are covered in which so far only a few sample points are present and thus a high degree of uncertainty exists (global exploration), and on the other hand regions with promising objective and constraint values are investigated (local exploitation).

The genuine new contribution in this work is the quantification of the uncertainty of the multi-fidelity Gappy-POD method and an adapted optimization strategy based on it. The uncertainty quantification is based on the error of linear fitting of low-fidelity values to the POD basis and subsequent forward propagation to the high-fidelity values. The uncertainty quantification is validated for random airfoil designs in a design of experiment.

Based on this, a global optimization strategy for constrained problems is presented, which is based on the well-known Efficient Global Optimization (EGO) strategy and the Feasible Expected Improvement criterion. This means that Kriging models are created for both the objective and the constraint values depending on the design variables that consider both the predictions and the uncertainties. This approach offers the advantage that existing and widely used programs or libraries can be used for multi-fidelity optimization that support the (single-fidelity) EGO algorithm.

Finally, the method is demonstrated for an industrial test case. A comparison between a single-fidelity optimization and a multi-fidelity optimization is made, each with the EGO strategy. A coupling of 2D/3D simulations is used for multi-fidelity analyses. The proposed method achieves faster feasible members in the optimization, resulting in faster turn-around compared to the single-fidelity strategy.
Experimental Investigation in Turbocharger Compressors During Surge Operation
Authors: Marelli Silvia , Misley Anna , Ferrando Marco
Published: January 2021

Flow instabilities in centrifugal compressors are one of the most limiting factors to the performance of the system where the compressor is installed (i.e., internal combustion engines, fuel cell, etc.). A better understanding of the surge phenomenon allows to properly set-up the operative region of the turbomachine in order to avoid a decrease in performance and to prevent the risk of damage. Actually, the instability phenomenon of surge can seriously damage the compressor for vibrations and temperature stress. To avoid damage to the compressor, the maximum boost pressure is generally limited with a by-pass system, reducing the mass flow rate provided by the machine.

The results of a broad experimental investigation performed at the turbocharger test bench of the University of Genoa are reported to deeply analyze the behavior of a small centrifugal compressor. A specific circuit adaptable in volume and length is used to study the effect of different configurations on steady compressor performance with special reference to the unstable operation. Measurements of instantaneous pressure and mass flow rate signals are performed in different sections located upstream and downstream the turbomachine. The difficulties related to measurement of instantaneous fluid-dynamics parameters in the turbocharging circuit and data post-processing are highlighted under unsteady flow conditions occurring in surge operation.

The effect of the compressor operating conditions (i.e., turbocharger rotational speed) and the circuit geometry is studied during the transition from steady to unsteady operation. In particular, the hysteresis loops surrounding the steady state map are reported highlighting filling and emptying and wave action phenomena, also in the region of zero mass flow and in the case of reverse flow condition. All measured quantities presented in this paper are the time synchronous averages of a large number of consecutive cycles in deep surge operation.

The aim of the paper is to extensively analyze the compressor behavior in unstable operating conditions in order to improve simulation models such as a physics-based compressor model previously developed by the Authors.
Vortex Structures Analysis and Loss Mechanisms in Axial Compressor Cascade With and Without Bleeding Slot Using Large Eddy Simulation
Authors: Gong Yun , Chen Shaowen , Zheng Haipeng , Wang Songtao
Published: January 2021

Tip leakage flow is one of the main sources of flow losses in an axial compressor, and the understanding of the tip leakage flow helps to explore better flow control methods and design more advanced compressors. Therefore, the vortex structures and loss mechanisms were analyzed in a compressor cascade with tip clearance in the present paper. Large eddy simulation was used to better resolve the vortices with more accurate numerical results. The iso-surface of Q criterion in the compressor cascade is captured for recognizing and analyzing the vortex structures. The horse shoe vortices, tip leakage vortex, induced vortex, tip separation vortex and passage vortex were well captured and their interactions were interpreted. Fast Fourier Transformation was also applied to analyze the frequency signal in the flow field. Afterwards, the case with an upstream bleeding slot was also calculated and compared with the original case without a bleeding slot. The bleeding rate is 2.8% of the mass flow rate at inlet. The removal of the inlet boundary layer resulting from the bleeding leads a 42.4% reduction of the total pressure loss coefficient compared with that of the case without the bleeding slot. In the case with the bleeding slot, the size of the passage vortex is greatly reduced, and the mixing between the tip leakage vortex and passage vortex is postponed. Better performance is achieved with the bleeding slot accordingly.
Injection of Kerosene Into a High-Temperature and High-Speed Air Crossflow
Authors: Yulan Wang , Yong Mu , Xiongjie Fan , Qianpeng Zhao , Gang Xu
Published: January 2021

The jet of kerosene into high-temperature and high-speed air crossflow was studied experimentally, to study the characteristics of penetration and evaporation in afterburner. A fuel injection bar with a 0.6 mm diameter plain orifice was used in the experiment. The angle between jet and air flow was 90°. The tests were conducted at atmospheric pressure. The air temperature was between 400 °C to 800 °C, and the air velocity increased from 100 m/s to 250 m/s, which was close to the working condition of the afterburner. The jet flow rate also increased from 5 kg/h to 40 kg/h. Fuel-PLIF was used to visualize the trajectory and structure of the jet trajectory. It was observed that the core region of the jet (the largest volume flow) was close to the windward side, and the leeward side of the jet had a relatively wide peripheral area due to the shear of the high-speed airflow. The jet trajectory is affected by viscosity force, inertia force and surface tension in different proportion under high-temperature and high-speed airflow. The jet penetration is related to the momentum ratio (q), air flow Weber number (We0), and aerodynamic Weber number (Wea). In experiment, q ranged from 2 to 236, We0 ranged from 72 to 735, and Wea ranged from 0.36–41. The relationship between penetration to these variables was established. The plume width and evaporation distance under different test conditions were compared. The results show that the plume width varied within a narrow range in high-temperature and high-speed air crossflow, and the fuel evaporation distance was much more affected by the fuel flow than the airflow condition, basically in a linear correlation with fuel flow. The results are of great significance to the size design and arrangement of the stabilizers in afterburners.
Nonlinear Response and Stability of an Experimental Overhung Compressor Mounted With a Squeeze Film Damper
Authors: Gooding William J. , Meier Matthew A. , Gunter Edgar J. , Key Nicole L.
Published: January 2021

This paper presents rotordynamic data obtained within a test facility studying the aerodynamics of a high-speed centrifugal compressor for aero-engine applications. The experimental overhung compressor is supported by two rolling element bearings. The compressor-end ball bearing is supported by an oil-fed squeeze film damper.

After some period of operation, the compressor began to exhibit a unique nonlinear increase in the rotordynamic response followed by an unexpected subsynchronous whirl instability as the speed continued to increase. Finally, as the rotor speed was increased further, the rotor re-stabilized.

A numerical model of the compressor system was created using a commercially available software suite. This model indicates the effective weight of the damper support has a significant effect on the frequency of the second critical speed. Increasing this weight causes the second critical speed, originally predicted at 35,200 RPM, to shift down to 15,650 RPM. This increase in the support weight is due to inertial interaction between the damper support and the surrounding static structure. The increased shaft deflection that occurs as the rotor passes through this shifted critical speed causes the damper to lockup, resulting in the increased response observed experimentally. At a slightly higher speed, Alford-type aerodynamic cross-coupling forces excite the two subsynchronous critical speeds. Finally, as the rotor departs from the second critical speed, the damper unlocks and is able to effectively suppress the Alford-type instabilities, allowing the rotor to return to stable operation.
The Effect of Reaction on Compressor Performance
Authors: Chana Krishan S. , Miller Robert J.
Published: January 2021

Reaction is the fundamental parameter by which the asymmetry of the velocity triangle of a stage is set. Little is understood about the effect that reaction has on either the efficiency or the operating range of a compressor. A particular difficulty in understanding the effect of reaction is that the rotor and stator have a natural asymmetry caused by the centrifugal effects in the rotor boundary layer being much larger than that in the stator boundary layer. In this paper a novel approach has been taken: McKenzie’s ‘linear repeating stage’ concept is used to remove the centrifugal effects. The centrifugal effects are then reintroduced as a body force. This allows the velocity triangle effect and centrifugal force effect to be decoupled. The paper shows the surprising result that, depending on how the solidity is set, a 50% reaction stage can either result in the maximum, or the minimum, profile loss. When the centrifugal effects are removed, 50% reaction is shown to minimise endwall loss, maximise stage efficiency and maximise operating range. When the centrifugal effects are reintroduced, the compressor with the maximum design efficiency is found to rise in reaction by 5% (from 50% reaction to 55% reaction) and the compressor with the maximum operating range is found to rise in reaction by 15% (from 50% reaction to 65% reaction).
LES of the Ignition of a Two-Phase Staged Swirling Burner: Influence of Ignition Location and Operating Conditions on the Flame Shape
Authors: Mesquita Léo C. C. , Vié Aymeric , Ducruix Sébastien
Published: January 2021

Staged multipoint injection has been developped as an interesting technology to control flow and flame dynamics in Lean Premixed Prevaporized (LPP) swirled gas turbine burners. The BIMER combustor, a two-staged swirling burner composed of a pilot stage and a multipoint stage, has been operated for many years to shed light on the complex phenomena related to such kinds of burners, as well as to build an experimental database for the validation of numerical developments. During the experimental campaigns, several flame archetypes have been encountered, flame shape transitions and a consequent hysteresis cycle were observed depending on the liquid fuel splitting between the stages. As each flame archetype presents different combustion characteristics and thermoacoustic behavior, it is highly relevant to understand how to stabilize such archetypes. In this optics, the objective of the present paper is to investigate ignition as a way to control the final flame archetype. By means of Large Eddy Simulations, we explore different operating conditions and have a direct insight into the flame propagation process. Two operating conditions are simulated: a low and a high flow rate condition. Two simulations are performed for each operating point, one where the ignition kernel is initiated in the Outer Recirculation Zone (ORZ) and the other one where it is initiated in the Central Recirculation Zone (CRZ). In all cases the fuel is injected only through the pilot injector, as in the ignition process during experiments. For the low power point, both ORZ and CRZ ignitions lead to the stabilization of a V-flame. When igniting on the high power operating point, the ORZ ignition results in a M-shaped flame, while the CRZ one results in a tulip shape. These different behavior are analyzed and discussed in the final part of the paper.
Prediction of Gas Turbine Performance Using Machine Learning Methods
Authors: Goyal Vipul , Xu Mengyu , Kapat Jayanta , Vesely Ladislav
Published: January 2021

The current study is based on multiple machine learning algorithms to predict the normal behavior of operational parameters including power generated and blade path temperature spread. The predictions can be used to identify anomalies and probable failures in the gas turbine performance. The data used in the study is taken from multiple heavy-duty gas turbine units of combined cycled utility power plants which are known to contain operational failures. The predictors include operational parameters such as fuel flow, various thermodynamic variables, etc.

In the first step, we cluster the observations into different working modes, because of the heterogeneous behavior of the gas turbine parameters under various modes. Then we consider predicting the operational parameters under each mode respectively, via algorithms including random forest, generalized additive model, and neural networks. The models are trained and parameters are selected based on the overall prediction performance on the validation set.

The comparative advantage based on prediction accuracy and applicability of the algorithms is discussed for real-time use and post processing. The advantage of our method is that they achieve high predictive power and provide insight into the behavior of specific gas turbine variables, e.g.- turbine blade path temperature spread, which are not explicitly known to have any correlation with other thermodynamic variables.
Film Cooling Superposition Theory for Multiple Rows of Cooling Holes With Multiple Coolant Temperatures
Authors: Fuqua Matthew N. , Rutledge James L.
Published: January 2021

The classical method of superposition has been used for several decades to provide an estimate of the adiabatic effectiveness for multiple sets of already well-characterized film cooling hole rows. In this way, design work is aided by classical superposition theory prior to higher fidelity experiments or simulations that would account for fluid dynamic interaction for which superposition cannot account. In the present work, we consider the additive effects of multiple rows of coolant holes, but now also with coolant issuing at different temperatures. There are a number of ways that coolant may issue from different cooling hole rows at different temperatures, one of which is simply the necessarily different internal channels through which the coolant must pass.

The film cooling effectiveness is investigated for double rows of cooling holes wherein the two rows have different coolant temperatures. A double row consisting of an upstream slot and a downstream row of 7-7-7 cooling holes were first evaluated with a single coolant temperature to demonstrate that classical superposition theory applies well to the present configuration. Superposition theory is then extended to the context of multiple coolant temperatures and a new non-dimensional parameter is identified, which governs cooling performance. The theory is experimentally evaluated by independently varying the coolant temperatures of the two rows. Circumstances are identified in which a second row of cooling holes may be detrimental to cooling performance.
Design and Optimization of Turbomachinery Components for Parabolic Dish Solar Hybrid Micro Gas Turbine
Authors: Arifin Maulana , Schatz Markus , Vogt Damian M.
Published: January 2021

The application of power plants based on renewable energy sources is attractive from an ecological viewpoint. Micro Gas Turbine (MGT) combined with solar energy is a highly promising technology for small-scale electric power generations in remote areas. In MGT state-of-the-art development, the necessity of the numerical optimization in turbomachinery components becomes increasingly important due to its direct impact on the MGT cycle performance.

The present paper provides the multidisciplinary design optimization (MDO) of a radial turbine and radial compressor for a 40 kW Solar Hybrid Micro Gas Turbine (SHGT) with a 15m diameter parabolic dish concentrator. The objectives of MDO are to maximize the stage efficiency, to minimize the maximum stress and the inertia, and to enhance the operational flexibility. Preliminary design and performance map prediction using one-dimensional (1D) analysis are performed for both turbine and compressor at various speed lines followed by full three-dimensional (3D) Computational Fluid Dynamics (CFD), Finite Element (FE) analyses and 3D parameterization in the MDO simulations. The purpose of 1D analysis is to set the primary parameters for initial geometry such as rotor dimensions, passage areas, diffuser and volute size.

The MDO has been performed using fully coupled multi-stream tube (MST), 3D CFD and FE simulations. MST is used for calculating the load on the blade and the flow distribution from hub to shroud and linearized blade-to-blade calculations based on quasi-three dimensional flow. Thereafter, 3D CFD simulations are performed to calculate efficiencies while the structural stresses are simulated by means of FE analyses. In the current studies, Numeca Fine/Turbo is used as a CFD solver and Ansys Mechanical as a FEA solver, together with Axcent™ as an interface to Fine/Design 3D for geometry parameterization.

Furthermore, the cycle analysis for SHGT has been performed to evaluate the effect of the new turbomachinery components from the MDO on the SHGT system performance. It is found that using the MST fully coupled with CFD and FE analysis can significantly reduce the computational cost and time on the design and development process.
Comparison of Blind Diagnostic Indicators for Condition Monitoring of Wind Turbine Gearbox Bearings
Authors: Qi Junyu , Mauricio Alexandre , Gryllias Konstantinos
Published: January 2021

Under the pressure of climate change, renewable energy gradually replaces fossil fuels and plays nowadays a significant role in energy production. Among different types of energy sources, wind power covered 14% of the EU’s electricity demand in 2018. The Operations and Maintenance (O&M) costs of wind turbines may easily reach up to 20–25% of the total leverised cost per kWh produced over the lifetime of the turbine for a new unit. According to Wood Mackenzie Power & Renewables (WMPR) onshore wind farm operators are expected to spend nearly $15 billion on O&M services in 2019. Manufacturers and operators try to reduce O&M on one hand by developing new turbine designs and on the other hand by adopting condition monitoring approaches. One of the most critical and rather complex assembly of wind turbines is the gearbox. Gearboxes are designed to last till the end of asset’s lifetime, according to the IEC 61400-4 standards. On the other hand, a recent study over approximately 350 offshore wind turbines indicated that gearboxes might have to be replaced as early as 6.5 years. Therefore a plethora of sensor types and signal processing methodologies have been proposed in order to accurately detect and diagnose the presence of a fault. Among others, Envelope Analysis is one of the most important methodologies, where an envelope of the vibration signal is estimated, usually after filtering around a selected frequency band excited by impacts due to the fault. Sometimes the gearbox is equipped with many acceleration sensors and its kinematics is clearly known. In these cases Cyclostationary Analysis and the corresponding methodologies, i.e. the Cyclic Spectral Correlation and the Cyclic Spectral Coherence, have been proposed as powerful tools. On the other hand often the gearbox is equipped with a limited number of sensors and a simple global diagnostic indicator is demanded, being capable to detect globally various faults of different components. The scope of this paper is the application and comparison of a number of blind global diagnostic indicators which are based on Entropy (Permutation entropy, Approximate entropy, Samples entropy, Fuzzy entropy, Conditional entropy and Wiener entropy), on Negentropy (Infogram), on Sparsity (Sparse-L2/L1, Sparse-L1/L0, Sparse-Gini index) and on Statistics (Mean, Standard deviation, Kurtosis, etc.). The performance of the indicators is evaluated and compared on a wind turbine data set, consisted of vibration data captured by one accelerometer mounted on six 2.5 MW wind turbines, located in a wind park in northern Sweden, where two different bearing faults have been filed, for one wind turbine, during a period of 46 months. Among the different diagnostic indicators Permutation entropy, Approximate entropy, Samples entropy, Fuzzy entropy, Conditional entropy and Wiener entropy achieve the best results detecting blindly the two failure events.
Influence of Labyrinth Clearance on the Flow of Rotating Orifices in a Parallel Labyrinth-Orifice System
Authors: Wang Jie , Ding Shuiting , Qiu Tian , Gao Ziqiang
Published: January 2021

Orifices, especially rotating orifices, are an important flow element of the secondary air system in a modern aero-engine, and their discharge coefficient depends on the geometry, the operating point and the surrounding environment. The influence of Reynolds number, pressure ratio, rotational speed, inlet chamfer, inclination angle, length-to-diameter ratio, etc. on the discharge coefficient of rotating orifices under the assumption of room temperature and adiabatic has been reported in many literatures. However, the rotating speed, the temperature of the gas in the front and rear chambers of rotating orifices and the temperature of the chamber wall change continuously during the actual operation of the engine, especially during the acceleration and deceleration of the engine, which will cause deformation of the chamber wall and the rotating components, resulting in a large change in the labyrinth seal clearance on the periphery of the rotating orifice disk. Although the change of the seal clearance can be evaluated by some methods, it still has a crucial influence on the fluid flow in the front cavity of rotating orifices, which may affect the discharge coefficient of rotating orifices, thereby affecting the amount of cooling air flowing through rotating holes. Therefore, the knowledge of the influence of labyrinth seal clearance should be considered into the discharge coefficient of rotating orifices, which is essential for a reasonable distribution of the cooling air in the second air system under various working conditions and ensures the safety and reliability of the aero-engine in all-inclusive line.

This paper presents the relationship between the discharge coefficient of rotating orifices and theoretical velocity ratio in the relative frame of reference (U/Wax) under different labyrinth seal clearance conditions, which is based on the study of the flow state in the front chamber of rotating orifices under different seal clearances, rotating speeds and pressure ratios. The results indicate that with the increase of the labyrinth seal clearance on the periphery of the rotating orifices disk, the discharge coefficient of rotating orifices decrease under the condition of small velocity ratio, while the discharge coefficient is almost unchanged under the large velocity ratio. Comparing the flow field structure and velocity field under the condition of different labyrinth seal clearances, the same pressure ratio and the same velocity ratio, the reasons for the influence of labyrinth seal clearance on the discharge coefficient of rotating orifices are analyzed.
Investigating Boundary Layer Flashback of a High Turbulence Intensity Jet Flame at Gas Turbine Conditions
Authors: Auwaijan Nicolas , McDonell Vincent
Published: January 2021

Hydrogen derived from non-fossil sources is an attractive candidate to replace carbon based fuels in gas turbines, as it is inherently carbon free. Yet the unusual combustion properties of hydrogen requires some care to successfully use it in gas turbines. To attain the lowest NOx emissions, uniformly low reaction temperatures must be assured thus the reactants must be well mixed. This is accomplished in low emission gas turbines by mixing the reactants within a pre-mixer section prior to entry into the combustor. With the addition of hydrogen into the fuel, certain issues arise such as higher flame speeds compared to carbon based fuels. Flashback is a phenomena that occurs when the flame no longer propagates beyond the exit of the premixer/injector but instead retracts and propagates upstream towards, and ultimately into the pre-mixer, causing significant damage due to such high temperatures. Flashback occurs when the flame speed exceeds either the local or bulk flow velocity. In practice, the question arises regarding the impact of turbulence levels. While an increase in turbulence intensity may help improve mixing, it also known to increase turbulent burning velocity. In the present work, the influence of bulk turbulence intensity of the flow on boundary layer flashback is investigated. Data are acquired for a different turbulence intensities at pressures from 3 to 8 bar with preheated reactants up to 750 deg. K. Various mixtures of hydrogen and methane are evaluated. The results show that even with significantly different bulk flow turbulence intensities (based on the ratio of flow centerline turbulence to centerline axial velocity) boundary layer flashback is not strongly affected. This is attributed to the role of the quenching distance in connection with damping within the boundary layer. It is noted that core flow flashback or other flashback mechanisms may be affected differently.