bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of the Map Width Improvement in a Radially Reduced Diffuser Design Concept for a Centrifugal Compressor
Authors: McLaughlin Laura , Spence Stephen , Rusch Daniel , Stuart Charles , Geron Marco , So Kwok Kai , Fischer Magnus
Published: October 2022

Often, an improvement in performance at one operating point in a compressor/turbine operating map will lead to a reduction in performance at another area. For example, improving the efficiency of a compressor at design point (DP) may result in a reduction of efficiency at other operating points or it may result in a reduced stable operating range.

In order to reduce the compressor cost and weight, a 15% radial reduction was applied to the diffuser passage length of a high pressure ratio centrifugal compressor. The diffuser endwall was diverged to achieve an appropriate area ratio from diffuser inlet to outlet. Two different vane shapes were considered with the radially reduced diffuser passage. The first diffuser vane was a scaled version of the baseline airfoil vane shape and this was used to develop an understanding of the impact of the passage length reduction and diverging endwall. The second vane geometry was parameterized using an unconventional method derived from published literature and optimized to improve performance at DP.

Increased losses were generated through the diffuser passages of the radially reduced designs, but this was compensated for by lower losses through the volute due to more desirable flow at volute inlet. As a result, the radially reduced designs not only matched the performance of the baseline configuration, but also succeeded in achieving a marginal efficiency improvement. Furthermore, despite not being one of the goals of the optimization procedure, an extension of the stable operating range of 36% and 20% at the highest speed condition was achieved for the scaled and optimized designs, respectively. The current study focuses on understanding the physical reasons that generated this significant enhancement to the compressor operating range.

In order to acquire the desired understanding, experimental data is presented to validate the Computational Fluid Dynamics (CFD) model and a detailed numerical investigation is presented to explain the changes in the flow field within the radially reduced designs. The study focuses on low flow rate operating points, necessitating the use of an Unsteady Reynolds Averaged Navier-Stokes (URANS) approach to analyse the flow. Detailed scrutiny of the flow field revealed a secondary flow feature in the diffuser passage which resulted in higher diffuser passage losses at DP but stabilised the flow as it developed for lower mass flow rate operating points.
100-Hour Test of an Inside-Out Ceramic Turbine Rotor at Operating Conditions
Authors: Dubois P. K. , Picard B. , Gauvin-Verville A. , Méthot P. , Landry-Blais A. , Jean L.-P. , Richard S. , Plante J.-S. , Picard M.
Published: October 2022

Converting sub-MW turbine rotor blades to ceramics is not a trivial endeavour, but the promise of a substantial increase in turbine inlet temperature (TIT), and therefore cycle efficiency and power density, could mean wide use in upcoming, distributed power, turboelectric aircraft. The inside-out ceramic turbine (ICT) rotor configuration attempts to address this by loading ceramic blades in compression, as centrifugal force pushes them against a rotating structural composite shroud. This paper reports significant experimental progress in the development of ICT rotor technology, aimed at the development of a high-efficiency, turboelectric powerpack.

A 20-kW scale, single spool, recuperated ICT was operated with monolithic silicon nitride blades, for a total of 113 h above 1100 °C, including 13 h at the design tip speed of 400 m/s and a cumulative 100 h at 360 m/s, with no critical failure. ICT rotors sustained short excursions with TIT up to 1200 °C and tip speeds up to 430 m/s in hot conditions, and 500 m/s in ambient conditions. An ICT rotor was successfully integrated within a complete recuperated turbogenerator with a nested high speed electric motor. Results suggest that further work on an ICT turbogenerator should enable it to reach a TIT of 1275 °C, a target to achieve 45 % cycle efficiency in the sub-MW range.
Application of the Harmonic Balance Method for Large Spread Multiple Frequency Scales
Authors: Biesinger Thomas , Kölzer Maximilian , Schukmann Alexander , Roclawski Harald , Kainz Marc , Godin Philippe , Morales Juan Carlos , Zori Laith
Published: October 2022

This paper presents the application of the harmonic balance method to periodic turbomachinery flow problems containing multiple fundamental frequencies. It is well known that the solution convergence of a transient turbomachinery flow using classical integration methods is computationally intensive and requires the integration for multiple periods to achieve a converged periodic solution. The computational effort is even higher when multiple fundamental frequencies (vastly different time scales) are modeled since the time stepping required is limited by the higher frequency in the flow. Unlike the classical time integration methods, the multifrequency harmonic balance method is very well suited for these applications since it allows for much faster calculations than the standard time marching algorithms. In addition, to resolve all the fundamental frequencies and higher harmonics, the current implementation of the harmonic balance method allows for solutions on unequal time interval distributions of the time planes. Given a user-defined list of frequencies that govern the flow problem, this method utilizes an optimization strategy to compute the time planes. There are two simulation cases of interest: aerodynamic performance and forced response analyses, both with different accuracy requirements. The number of required frequencies is dependent on the goal of the simulation. For aerodynamic performance analysis, global quantities such efficiency, pressure ratio, etc. can be predicted with fewer fundamental frequencies than forced response analysis where accurate local flow details demand a higher number of fundamental frequencies.

The advantages of the multifrequency harmonic balance are illustrated by modeling two radial turbine configurations subjected to an inlet pulse from a reciprocating engine. Not only the expected trends such as higher-modes modeling granularity and time transient accuracy are shown, but also the calculations agree well with experimental data. The computational effort can be up to tenfold lower than the standard time-marching simulations. Machine aerodynamic performance predictions from the harmonic balance method are compared to accurate time-marching solutions and experimental data measurements. The efficiency of the computation is also discussed. The second example will compare the predicted surface excitation from the harmonic balance method vs. the time-marching solution.
History of Steam Expansion Machines Seen as Polytropic Efficiency Achievements
Authors: Wettstein Hans E.
Published: October 2022

Among the heat to power cycles the historically first successful technologies used cycles with steam expansion machines in its core. In the first phase as of the eighteenth century, reciprocating steam engines dominated. As of 1890 steam turbines were developed, which replaced the reciprocating steam engines until around 1930 with the exception of steam locomotives and some other niche applications. Up to now in steam cycle technology mostly the isentropic efficiency definition for expansion is used. Such numbers depend both on the dissipation and on the pressure ratio.

In history the overall pressure ratio of steam cycles has developed from low single digit values to over 3000. Thus it is interesting to consider the achievements of this technology especially for different pressure ratios with an efficiency definition, which is completely independent of the pressure ratio. Such a definition is well established in the form of the polytropic efficiency. This is the most used isentropic efficiency minus the heat recovery effect. The latter depends on the dissipated heat within the pressure drop and it grows with increasing pressure drop. The polytropic efficiency definition assumes a constant dissipation rate along the expansion change of state in contrast to the isentropic efficiency.
Predicting and Validating Spatial Distributions of Particulate Deposition in Gas Turbine Components
Authors: Gaskell Jack G. , Vadgama Nikul , Villain Florian Y. A. , Beal Simon , McGilvray Matthew , Gillespie David R. H. , Littley Benjamin
Published: October 2022

Cooling passages and the secondary air system of gas turbine components are prone to blockage from sand, dust and ash. The ability to model deposition accurately using CFD would allow the prediction of in-service performance degradation and the design of deposition-tolerant hardware. Predictions of deposition require accurate modelling of particle transport and wall interactions. Bounce stick models predict whether a particle will bounce, stick, or shatter upon impact and calculate rebound trajectories. Turbulent transport models allow the interaction of particles with near-wall turbulent structures to be predicted in RANS CFD solutions. This paper implements a Continuous Random Walk (CRW) transport model with a Discrete Elements Methods (DEM) based bounce stick model to predict deposition in commercial CFD software. The resulting spatial trends of deposition are compared with experimental data of particle deposition in an S-bend. The case considered is representative of the flow and metal conditions, particle size and loading distribution, and passage geometry seen in high pressure turbine blade cooling passages. Numerical predictions of deposition distribution show good qualitative agreement with experimental data. This validates the combined CRW/DEM approach for modelling the location of particulate deposition in gas turbine components. The approach is therefore suitable to assess and compare the susceptibility of components to particulate damage in industry. To the author’s knowledge, this is the first example in the open literature of experimentally-validated deposition trends in CFD. It was found that a deposit evolution and erosion model is essential to predict deposit height numerically. Particle tracking simulations without turbophoresis modelling showed significant differences in particle impact velocities and locations, justifying the use of the CRW model. The inclusion of the Magnus force produced considerable differences in quantitative and qualitative measures of deposition throughout the domain, demonstrating the importance of modelling collision-induced rotation in particle tracking. The performance of the DEM bounce stick model was favourable compared to energy-based alternatives which showed reduced accuracy in inertia-dominated regimes where multiple bounces occurred per particle. On average, eleven impacts were observed for each injected particle, reinforcing the dual importance of accurate bounce stick and turbulent transport models.
Numerical Prediction of Thermomechanical Sensitivity of the First Stage Nozzle Guide Vane With Film Cooling
Authors: Khumhaeng Siwanart , Suksa Thitapa , Laohalertchai Nutcha , Chaiprasit Benyapa , Chotroongruang Thanapat , Prapamonthon Prasert
Published: October 2022

Practically, a gas-turbine engine’s first-stage nozzle guide vane (NGV) must operate under extreme conditions induced by high temperatures from burned gases, causing severe damage to the vane, such as cracks or fatigue failures. As a result, the first stage NGV’s lifespan is shortened. In other words, the first stage NGV’s lifespan is determined by the vane material’s durability. Therefore, effective cooling systems and thermal barrier coating (TBC) are provided. This paper presents a numerical prediction of the thermomechanical sensitivity of the first stage NGV with film cooling under aerothermal conditions and TBC using a 3D CFD/CHT approach with a static structure model for a steady temperature analysis. Turbine inlet temperature (TIT), coolant inlet temperature (CIT), blowing ratio (BR), and TBC thickness, which are key factors for gas turbines’ performance improvement, are used as independent variables. An examination of vane cooling performance is presented in the first part, followed by a prediction of the thermomechanical sensitivity of the vane under the four variables in terms of von Mises equivalent stress and strain in the second part. The findings obtained from both parts show that the relationship between cooling performance and thermomechanical characteristics is sensitive to the influences of turbine inlet temperature (TIT), coolant inlet temperature, and TBC thickness. In addition, the findings indicate the role of the blowing ratio in thermal and mechanical sensitivity for the film-cooled vane.
Measured Leakage and Rotordynamic Force Coefficients for Two Liquid Annular Seal Configurations: Smooth-Rotor/Grooved-Stator Versus Grooved-Rotor/Smooth-Stator
Authors: Childs Dara W. , Yang Jing , San Andrés Luis , Torres Rueda Jose M. , Moreland J. Alex
Published: October 2022

This paper reports and compares the experimental results of leakage and dynamic force coefficients for two liquid annular pressure seals, one having a smooth-rotor/circumferentially-grooved stator (SR/GS), the other one with a circumferentially-grooved rotor/smooth-stator (GR/SS). Differing only in the grooves’ location, the GR/SS seal’s geometry and operating conditions are representative of those in electrical submersible pumps (ESPs) used for oil recovery. Supplied with an ISO VG2 oil at 46 °C, both seals have the same diameter D = 102 mm, length-to-diameter ratio L/D = 0.5, and nominal land clearance Cr = 0.203 mm. The seals have 15 circumferential grooves with groove and land lengths equal to 1.52 mm. Test variable ranges include: (a) shaft speeds (ω) ranging from 2 to 8 krpm (shaft surface speed ∼ 43 m/s), and (b) pressure differences (ΔP) from 2 to 8 bar. Upstream of the test seals, three separate pre-rotation rings generate a range of inlet circumferential velocities (entrance swirl). Under all conditions, the GR/SS seal leaks about 10% less than the SR/GS seal. For both seals, the direct stiffnesses (KXX, KYY) have low magnitudes that drop with increasing ω; in some cases, they turn negative at 6 krpm. The GR/SS seal produces cross-coupled stiffnesses (KXY, KYX) that are ∼1.5 times larger than those for the SR/GS seal. Under the same conditions, the SR/GS seal is more stabilizing as its direct damping and added mass coefficients are ∼ 20% larger than those for the GR/SS seal. Instability issues are likely to arise with either seal geometry because negative KXX and KYY drop a pump critical speed, aggravating the well-known destabilizing coefficients KXY and KYX. The whirl frequency ratio (WFR) combines the effects of the cross-coupled stiffness, direct damping and cross-coupled mass terms, thus providing a good basis for comparing two seals’ stability characteristics. Overall, the WFR magnitudes for the GR/SS seal are about three times higher than those for the SR/GS seal. Note that, irrespective of the inlet swirl condition, the GR/SS approaches a WFR ∼ 0.50 for operating shaft speeds greater than 4 krpm. At the lowest shaft speed (2 krpm), the WFR << 0.5 for the low inlet pre-swirl ring, whereas WFR > 0.8 for the medium and high pre-swirl rings. For the SR/GS seal, the WFR ∼ 0.2 at the highest shaft speed of 6 krpm, and not affected by the inlet pre-swirl condition. On the other hand, at the lowest shaft speed, the WFR ranges from 0.5 to 0.75 for the SR/GS seal with medium and high pre-swirl rings. At this speed, the WFR = 0 with the low inlet pre-swirl ring. Hence, to enhance the operational stability, an effective swirl brake that could drop the inlet pre-swirl ratio upstream of a seal is helpful for the GR/SS seal out to 4 krpm and for the SR/GS seal out to 6 krpm.
Experimental and Numerical Investigations of the Non-Equilibrium Condensation on the Performance and the Flow Pattern in Steam Turbine
Authors: Tabata Soichiro , Segawa Kiyoshi , Takahashi Tadashi , Aoyagi Jin
Published: October 2022

In this paper we present the test results of measurements in a scaled model steam turbine test operated at Mitsubishi Heavy Industries, Ltd. In order to understand the aerodynamic behavior of the low-pressure steam turbine, numerical and experimental results obtained on a five-stage scaled steam turbine module are presented.

In order to investigate the effect of non-equilibrium condensation on the performance of the low-pressure steam turbine, inlet temperature change tests were conducted, and wetness loss change was evaluated experimentally. Besides, the overall performance and the flow pattern were evaluated numerically by the commercial CFD code ANSYS CFX. The wetness loss and flow pattern change due to the non-equilibrium process was numerically evaluated by ANSYS CFX. Besides, the pressure ratio and loading distributions in low pressure turbine stage were evaluated numerically by ANSYS CFX. In a turbine stage in which the non-equilibrium condensation occurs, the pressure ratio is decreased, while the pressure ratio of the adjacent stage is increased. The flow pattern obtained by the non-equilibrium condensation modeling CFD was good agreement with that of tests data.

In order to more accurately capture the flow pattern characteristics by CFD analysis, it is necessary to consider non-equilibrium condensation modeling. Therefore, it was found that CFD is useful for understanding the flow pattern of a low-pressure steam turbine.
Impact of Central Piloting on the Static and Dynamic Stability of Swirl-Stabilized Flames
Authors: Doleiden Daniel , Karmarkar Ashwini , O’Connor Jacqueline , Blust James
Published: October 2022

One of the key challenges of lean, low-emissions combustor operation is flame stabilization, including both static and dynamic stabilization. Static flame stability encompasses a range of issues like flame holding, flashback, and blow-off. Dynamic flame stability refers to thermoacoustic combustion oscillations, which are driven by a coupling between combustor acoustics and flame heat release rate oscillations. Pilot flames are used as a passive means of achieving both static and dynamic stability in a number of gas turbine combustor technologies, likely by acting as a source of heat and radical species at the base of the main flame. Previous work used high-speed CH* chemiluminescence imaging to characterize the effect of a central pilot flame on the macrostructure and dynamic stability of a swirled lean-premixed natural gas-air main flame. In this study, the static and dynamic stability of the main flame are controlled by modifying the equivalence ratios of the main and pilot flames to better understand the mechanisms by which pilot flames enhance both static and dynamic stability. High-speed OH planar laser-induced fluorescence (OH-PLIF) is used to capture local instantaneous dynamics of the main and pilot flames across a range of operating conditions and stability outcomes, building upon the line-of-sight chemiluminescence analysis of the previous work. We find that the presence of the pilot flame controls anchoring of a relatively lean main flame. When the pilot flame is added to an unpiloted main flame, the main flame can rapidly change stabilization location, anchoring to the centerbody of the fuel injector. When a piloted main flame has the pilot removed, the flame lingers on the centerbody for a longer duration, likely due to the high-temperature boundary condition at the centerbody anchoring point. Further, the pilot flame mitigates combustion instability for a relatively broad range of operating conditions. Analysis of high-speed OH-PLIF shows that the main and pilot flames do not directly interact, and therefore the stabilizing mechanism of the pilot flame is indirect, as previously suggested.
Prediction of Rotating Instabilities in Low Pressure Steam Turbines Operating at Low Load
Authors: Pütz Oliver
Published: October 2022

Due to the increasing need for operational flexibility nowadays, the low-pressure (LP) steam turbine might face widely variable operation conditions up to extreme low volume flow situations. Hereby, rotating instabilities (RIS), well known from compressor aerodynamics, can initiate non-synchronous blade excitations which can lead to increased vibrations of the last stage moving blade (L-0R). This paper describes a numerical method able to be used in an applicable way for blade designing.

To judge the onset and the shape of RIS, a numerical approach based on a transient 3D URANS flow computation of the single passage L-1 stage, a full row L-0 stage, and an axis-symmetric diffuser was established. Mesh size, solver settings and other parameters were optimized to reduce the computational effort without losing prediction accuracy.

The dominant harmonic compound of a spatial Fourier transform of all monitored L-0R blade forces over the blade row’s circumference reveals the stall cell count and excitation amplitude for each timestep. The transient change of the corresponding phase lag provides the stall cell speed; and multiplied with the stall cell count the excitation frequency. Their distribution over decreasing flow rates finally displays the likely onset of RIS.

The approach is capable to run the analyses of several load conditions within a couple of days and was successfully validated using measured blade tip deflections and unsteady pressure probes in multistage test turbines. Furthermore, it is shown that the approach can be used to find LP blade designs where the effects of RIS can be significantly suppressed.
Optimal Strategy of the Energy Management Within the Microgrid Using the Hydrogen Fueled Gas Turbine
Authors: Ancona Maria Alessandra , Bianchi Michele , Branchini Lisa , Catena Francesco , De Pascale Andrea , Melino Francesco , Ottaviano Saverio , Peretto Antonio
Published: October 2022

The hydrogen production by means of renewable energy exploitation has the potential to address issues that arise when an increasing share of power is generated from sources that have a highly variable output. Although these systems have been widely studied, one of the key aspects to be considered is the choice of the energy management strategy.

The aim of this paper is to define and present an optimal strategy for the energy flow management of a pilot plant consisting of a turbine gas facility making use of power produced during turbine tests — along with solar — for hydrogen production integrated with batteries storage.

Key results from the analyses are: i) increasing the hydrogen production target, the hydrogen production ratio increases up to a maximum value equal to about 100%; ii) optimizing the management strategy, the system is always able to meet the demand of hydrogen; iii) with a larger hydrogen storage capacity, the microgrid is able to exploit a higher amount of renewable production, achieving the total renewable energy exploitation.
A Probabilistic Method for Predicting Particle-Blade Impact Kinematics in Turbomachinery
Authors: Klaoudatos D. , Bojdo N. , Filippone A. , Covey-Crump S. , Jones M. , Pawley A.
Published: October 2022

The trajectories of dust particles ingested into gas turbine engines are dictated by their inertial properties, which influence the likelihood of collision with solid surfaces along the gas path, including compressor blades and casing. If a particle impacts a surface, it will either bounce, stick, or shatter. The fate is dependent on the kinematics of the interaction, which vary widely across the blade span and chord, and across the range of particle size and composition that a gas engine may typically ingest. This makes the prediction of compressor fouling or erosion using traditional deterministic methods computationally expensive. In this contribution, a new reduced-order model is proposed that can rapidly predict the probability of particle interaction with the blade and casing, and the probability of particle escape from the rotor outlet as a function of a dimensionless parameter, the generalized centrifugal Stokes number. Numerical simulations of particle-laden flow through a single-stage axial compressor rotor, the NASA Rotor 37, are performed to generate a dataset of particle-surface interaction kinematics for three minerals, each with a wide size distribution (0.3–135 μm), at three different blade rotation speeds. We also introduce a new dimensionless parameter, the particle kinetic energy ratio, to enable a non-dimensional particle impact kinematic analysis. Our results show that particle impact kinetic energy may be estimated on the basis of Stokes number alone.
Spray Characterization of a Preheated Bio-Oil Surrogate at Elevated Pressures
Authors: Broumand Mohsen , Thomson Murray J. , Yun Sean , Hong Zekai
Published: October 2022

Atomization plays an important role in the gasification or combustion of bio-oils, where the atomizer parameters need to be properly controlled to efficiently atomize a highly viscous liquid at elevated pressures with imparting the least amount of kinetic energy to the discharged droplets because of evaporation and chemical reaction constraints. With a focus on bio-oil deployments in micro gas turbines (MGTs), an aqueous surrogate of a preheated bio-oil, injected from an original equipment manufacturer (OEM) twin-fluid atomizer, is used in the present study for spray size and velocity measurements at elevated pressures. The experiments were conducted in High Pressure Spray Facility of the National Research Council of Canada (NRC) using various optical diagnostics including laser sheet imaging (LSI), phase Doppler anemometry (PDA), and laser diffraction (LD). A scaling strategy was adopted to conserve the ranges of gas-to-liquid momentum flux ratio, M, at different working pressures, P. Over the range of conditions studied, it is found out that the cone angle of sprays is insensitive to P, but they decrease with increasing M. For a constant value of M, droplet mean diameters increase and their corresponding velocities decrease with increasing P, attributed to the effect of gas-to-liquid density ratio on the primary breakup of a liquid jet in a coaxial gas stream. Therefore, to predict the Sauter mean diameter of spray droplets, D32, a correlation previously reported in the literature is modified by including the effect of system air density at elevated pressures, and a novel correlation is proposed based on four dimensionless groups, namely gas Weber number and gas-to-liquid momentum flux ratio, density ratio, and viscosity ratio. The detailed results obtained in the present study could be used to define the optimal parameters required for twin-fluid atomization of high viscosity liquids with various atomization gases under realistic operating conditions and to enhance the capabilities of their numerical simulations.
Performance Assessment of a Recuperated Turboshaft Engine: A Multifuel Case
Authors: Anfossi Jody , Al-Zaili Jafar , El Samad Tala , Sayma Abdulnaser
Published: October 2022

The low cycle efficiency of simple cycle micro gas turbines is typically raised by the use of recuperators. The recuperated cycle allows for improved efficiency at low power-to-weight ratio, mainly due to the weight of the added heat exchanger. As weight is considered to be a key parameter for aeroengines, an analysis that addresses benefits and drawbacks of a more efficient, but heavier propulsion system design is required to be carried out. This paper assesses propulsion systems based on simple and recuperated cycle small gas turbine configurations, unusual in aviation, running with conventional jet fuel or hydrogen. An analytical model capable of modelling a turboshaft engine steady state design and off-design operation is developed. The specific fuel consumption of different engine arrangements is therefore calculated to evaluate the performance trade-off between the improved power plant fuel economy and its larger weight under a generic reference mission for a light helicopter. To enable a consistent mission analysis study of the hydrogen fueled rotorcraft, the weight of the tanks for liquid hydrogen storage is estimated according to a preliminary design model. The results obtained suggest that a hydrogen-fueled recuperated powerplant can shorten the flight time to reach the breakeven point, compared to a recuperated jet fuel powerplant of the same power rating.
Modeling and Cycle Parameter Matching of a High-Speed Variable Cycle Turbofan-Ramjet Engine
Authors: Yao Yao , Zhang Xiaobo , Zhang Mingyang , Wang Zhanxue
Published: October 2022

Variable cycle turbofan-ramjet (VCTR) engine is a promising propulsion system candidate for future Mach 4+ vehicles. Compared with conventional turbine engines, the VCTR engine has a higher thrust-to-weight ratio, a smaller diameter and a more compact structure. A component-based simulation model is developed to explore the operating characteristics of a high-speed VCTR concept. Modeling methods of variable-geometry components are characterized in this paper, and then the way to build the VCTR model solver is described. The VCTR engine simulation model is validated by the numerical and experimental results of double bypass variable cycle engines from NASA technical reports. Performance and control law of the VCTR engine along the flight trajectory with flight Mach number varying from 0.5 to 4.0 are obtained to maximize net thrust and compared with that of a conventional two-spool afterburning mixed-flow turbofan (MFTF). Results show that the VCTR’s performance is highly dependent on the fan characteristics and limited by various operating constraints, such as fan surge margin, turbine inlet temperature, and compressor discharge temperature. In addition, the thrust level of the MFTF with the variable-area low-pressure turbine is close to the VCTR engine.
Acoustic Optimization Approach for Annular Diffusers in Turbomachinery Applications Using Plane Wave Modelling
Authors: Fischer Felix , Seume Jörg
Published: October 2022

The experimental investigation of unsteady aerodynamic effects in turbomachinery test rigs requires the establishment of anechoic boundary conditions in order to acquire data unaffected by acoustic reflections outside the test section. In this manner, controlled measurement environments can be achieved that allow for the acquisition of high-quality aeroacoustic and -elastic measurement data in turbomachinery test rigs. In the case of the initial design of the Aeroacoustic Wind Tunnel (AWT) at the Institute of Turbomachinery and Fluid Dynamics, acoustic reflections were observed in the diffuser section of the test rig, which interfered with the sound transmission measurements of low-pressure turbine airfoils.

The present paper describes a one-dimensional semi-analytical modelling and optimization approach of sound propagation in the AWTs diffuser section for plane waves based on Webster’s horn equation. With this approach, a new hub diffuser was designed for defined geometric and aerodynamic boundary conditions, which compared to the original geometry, reduce acoustic reflections due to continuous impedance matching. The design of a new supporting strut configuration further reduces reflections due to scattering from installations in the flow path. Validation of the modelling and solution approaches are carried out based on a comparison with experimental data of the initial (reference) design, as well as numerical simulations of both designs. According to analytical and numerical models the optimized design reduces acoustic reflections by up to 21.2 dB compared to the initial design.
Analysis of Turbulent Effects in a Low-Pressure Model Steam Turbine Operating Under Various Operating Conditions Using Detached Eddy Simulation
Authors: Ercan Ilgit , Vogt Damian M.
Published: October 2022

Steam turbines are sometimes operated at extreme part-load conditions, specifically if the energy balance in power grids featuring a high share of fluctuating energy sources necessitates such operation. At such extreme operating conditions, the last stages of the low-pressure turbine are subject to highly unsteady flow. As the flow is heavily separated, Rotating Instabilities (RI) may establish, among other turbulent effects. These highly unsteady flow structures result in fluctuations of the flow field over a wide range of low frequencies.

The simulation of the flow at such extreme operating conditions using CFD is challenging due to its highly turbulent and separated nature. On one hand, the employed flow model must be able to handle turbulent structures with varying size in a computationally efficient manner. On the other hand, the extent of the computational domain must be relevant with respect to the unsteady flow phenomena. The analyzed domain in this study consists of a three-stage low-pressure model steam turbine. To capture the asymmetry, the model spans the full annulus and comprises the non-axisymmetric inlet section, all three stages, the axial-radial diffuser as well as the exhaust hood.

Based on the findings of a previous study in which the Improved Delayed Detached Eddy Simulation (iDDES) has been applied to low-volume flow operating conditions [1], the focus of this paper is drawn towards the turbulent structures that establish at extreme flow conditions, and whether they can also be found at increased volume flows. Time-averaged and FFT results of the unsteady pressure signals at different span heights measured during experimental and numerical radial probe traverses indicate a higher unsteadiness during the lowest volume flow condition when compared to higher volume flows. Various turbulent structures have been identified at the hub region, the midspan section and the tip region of the last stage rotor blade that could be linked to the higher flow unsteadiness.

Furthermore, the possibility of using URANS simulations for the prediction of such extreme flows has been investigated, leading to the finding that the choice of flow model has an impact on the results. Additionally, it was investigated if the extent of the computational domain could be reduced to save computational costs. It was found that a reduced domain did not yield the low frequencies that are of relevance at such operating conditions.
Large Eddy Simulation of an Open Rotor Fan Blade
Authors: Priebe Stephan , Wood Trevor , Yi Junsok , Mousavi Arash
Published: October 2022

Open rotor fan blades, when exercised across a range of operating conditions and design options, present a variety of complex flow physics including leading-edge flow separation, wake evolution and interaction effects, and laminar-to-turbulent transition. In this paper, we present a large-eddy-simulation (LES) study of a three-dimensional open rotor fan blade at realistic conditions. Specifically, we focus in this paper on takeoff conditions, run at a Reynolds number representative of a subscale rig typically used for aeroacoustic technology maturation testing, to explore the flow behavior and its effects on takeoff aerodynamic performance and aeroacoustics that contribute to community noise. The simulations were performed using GENESIS, a high-order unstructured LES solver. The convergence of the solution is assessed by varying the polynomial order of the solution from low to high order. The analysis presented in the paper focuses on the evolution of the flow near the blade surface and the subsequent mixing downstream in the wake for a realistic blade design that exhibits the full three-dimensionality of these flow physics. A detailed understanding of these flow features is most useful for the aerodynamic and acoustic design of open rotor propulsors and the related implications of the LES results relative to conventional RANS-based CFD/CAA predictions is discussed.
A Novel 100% Hydrogen Gas Turbine Combustor Development for Industrial Use
Authors: Cho Eun-Seong , Jeong Hanjin , Hwang Jeongjae , Kim Minkuk
Published: October 2022

Doosan is developing a 5 MW 100% hydrogen gas turbine combustor based on the existing NG (natural gas) firing combustor through a national project. This engine consists of 8 (eight) cans of the combustor and our plan is to develop a hydrogen burner to replace the existing NG burner, if possible, without any change of other combustor components such as liner & transition piece, etc. We developed various concept nozzles for 100% hydrogen combustion without flash back during the operating condition and low NOx emission using dry low NOx premixed combustion methods. Among the various concept nozzles several candidates conducted experiment test in ambient pressure condition which they showed low NOx emission and larger operating conditions through lean blow off and flame holding flash back test. The best nozzle will be selected and tested at ambient & high pressure can test for evaluating 100% hydrogen combustor development targets.
Innovative Cycles for Industrial Combined Heat and Power Generation With Carbon Capture and Storage
Authors: Kapoor Riddhi R. , Klein Sikke
Published: October 2022

Industry is a major contributor to the rise in global CO2 emissions, constituting one fifth of the global energy consumption, of which a significant amount is provided by fossil fuel combustion. Following the Paris agreement, emphasis has been made on the decarbonization of the industrial sector. This study focuses on industrial decarbonization by employing Carbon Capture and Storage for Combined Heat and Power (CHP) gas turbine plants. The scope of this study includes conceptual modelling and thermodynamic analysis of potential decarbonization options for zero carbon CHP plants. The studied options include post-combustion capture, exhaust gas recirculation, pre-combustion capture and oxyfuel combustion. As conventional air Brayton cycles are not applicable for oxy-fuel combustion in gas turbines, different working fluids and cycle configurations are proposed and thermodynamic performance is evaluated. Selected cycles were then compared based on thermodynamics, economics and off-design performance at a typical constant power to heat ratio of 0.78. It was observed that oxyfuel CHP cycle with CO2 working fluid is a promising solution for zero carbon CHP with relatively low costs and 100% CO2 capture. However, this solution requires new turbomachinery design.
Experimental Investigation of Interactions Between Two Closely Spaced Azimuthal Modes in a Multi-Nozzle Can Combustor
Authors: Kim Jeong-Won , John Tony , Adhikari Subodh , Wu David , Emerson Benjamin , Acharya Vishal , Lieuwen Timothy , Isono Mitsunori , Saito Toshihiko
Published: October 2022

Thermoacoustic instabilities in annular or circular combustors are often coupled with azimuthal modes. These modes can be characterized by a spin ratio, which quantifies the dominant mode between two counter-rotating waves, and a phase difference between them, which is directly related to the orientation of the anti-nodal line. This study investigates the instability amplitudes, spin ratio, and phase difference of two closely spaced (3% frequency difference), yet distinct azimuthal modes; one is the first azimuthal (1A) mode, and the other is a combination of first azimuthal and first longitudinal (1A1L) mode. Each mode itself consists of two peaks that are spaced even more closely in frequency (0.8% difference). Furthermore, distinct harmonics at 2X and 3X of these frequencies, presumably associated with nonlinearities, are also evident in the spectra. Each mode is band-pass filtered in spectrum to analyze them separately. For the 1A mode, the spin ratio and phase difference exhibit a variety of behaviors — including quasi-periodic standing waves, spinning waves, and intermittency — depending on operating conditions such as thermal power and azimuthal fuel staging. Similar trends are observed for the 1A1L mode. Moreover, there is clear coupling between the 1A and 1A1L modes, as their spin ratios are almost synchronized during the quasi-periodic standing wave. This synchronization is observed in phase differences as well, but not in the instability amplitude. For spinning dominant wave conditions, the spin ratio and phase difference of the two modes fluctuate in a seemingly random fashion, but the instability amplitudes are correlated, with modulation of the 1A mode leading that of the 1A1L mode. These results clearly indicate that complex coupling occurs across closely spaced and harmonically space frequencies under instability conditions, coupling that must be understood in order to capture limit cycle dynamics.
Micro-Gas Turbine Cycle Configurations for Biomass Combined Heat and Power Plants
Authors: Bollas Konstantinos D. , Efstathiadis Theofilos G. , Mertzis Dimitrios P. , Kalfas Anestis I.
Published: October 2022

The potential of integrating micro-gas turbine systems into biomass micro-Combined Heat and Power (CHP) units is investigated, following a thermodynamic analysis. Various cycle configurations are elaborated, utilising the producer gas of an existing biomass gasification CHP unit, with a capacity of 30 kWe. The reference CHP unit consists of a fluidised bed gasifier coupled with a gas treatment unit, a gas cooler and an Internal Combustion Engine (ICE). The gas cooler operation is entailed with environmental issues, concerning tar condensation and removal. In this paper, alternative approaches of direct fuel combustion, at elevated temperatures, through micro-gas turbine systems are investigated. Five configurations, based on the internally-fired (simple and recuperative μ-GT) or the externally-fired gas turbine (μ-EFGT), as well an additional reheated micro-gas turbine (μ-RHGT) are considered. The μ-EFGT is investigated for two cases: unfiltered (UF) and filtered (F) producer gas fuel. Each configuration is optimised, using in-house solvers, while the components are modelled using turbomachinery and heat exchanger detailed designs. The recuperative μ-rGT and the unfiltered μ-EFGT/UF show a similar electrical efficiency of around 31.5%, while the overall efficiencies are 63% and 74.8% respectively, which is improved by 5%, compared to the ICE. Challenges related to fuel compression, mainly due to the high rotational speed, are expected in the μ-rGT case, while fouling is expected to be a serious challenge in the μ-EFGT/UF case. Both challenges can be addressed by the filtered μ-EFGT, however, this results in lower electrical efficiency, around 26.5%, which is −12% compared to the ICE.
Advanced Thermal Profiling of Turbocharger Compressor Wheels Using Phosphorescence Thermal History Coatings
Authors: Karagiannopoulos Solon , Rode Martin , Peral David , Castillo Daniel , Araguas-Rodríguez Silvia , Rai Kieron , Inomata Ryosuke , Iosifidis Georgios , Feist Jörg
Published: October 2022

Compliance towards future emissions legislation requires internal combustion engines (ICE) to utilize highly efficient combustion concepts (e.g. Miller cycle), which, are often associated with increased boost pressure requirements, leading to increased mechanical stress on turbocharger components. This is especially the case for compressor wheels due to the increased speed and temperature loading. To offer cost competitive products, IHI seeks to further exploit the limits of conventional state-of-the-art materials used in automotive turbochargers and refine their component development processes. While knowledge of the exact boundary conditions under which turbocharger components are operating is essential, the actual material temperature components experience under real operating conditions is a significant source of uncertainty.

Temperature measurements are usually conducted during turbomachinery durability tests to validate thermodynamic models and assess component lifetime. Temperature measurement techniques typically include thermocouples, optical sensors and thermal paints. However, the former methods are limited mostly to stationary components and can only provide point measurements, while the latter only offers low resolution data for short durations and involves highly toxic materials. Thermal History Paint & Coating technology developed by Sensor Coating Systems (SCS) offers a unique solution for thermal mapping in harsh environments. The technology is based on a phosphor material which is applied as a paint or coating on the surface of the components to be measured. The luminescent properties of the coating material are permanently changing depending on the maximum exposure temperature during the test. The THP/C luminescent properties are measured in multiple locations using a laser-based instrumentation system and a robotic arm. High-resolution thermal maps directly on the 3D CAD models of the component are generated.

For this application, the THP material has been applied for the first time on the surface of three turbocharger compressor wheels tested under different cooling conditions. The THP material exhibited excellent durability during testing at high circumferential speeds above 580 m/s. More than 2,000 temperature measurements were obtained on pre-selected locations on the surface of the wheels. The test demonstrates that THP can be used on components with complex geometries such as turbocharger compressor wheels. Additionally, temperatures as low as 120 °C have been resolved for the first time.
Quasi-Two-Dimensional Numerical Model for Shock Wave Reformers
Authors: Madiot Ghislain , Mahmoodi-Jezeh S. V. , Tüchler Stefan , Davidson Mark , Akbari Pejman , Copeland Colin D.
Published: October 2022

The article details a numerical investigation of methane pyrolysis inside a shock wave reformer using a quasi-2-dimensional (Q2D) Reynolds-Averaged Navier-Stokes (RANS) CFD model. This work is in support of the New Wave Hydrogen, Inc. (NWH2) proprietary technology development. To take account of the characteristics of the flow in the presence of shock waves, a simplified approach is proposed that captures the gas dynamics during partial opening with a lower computational cost suitable for the wave reformer design. The model is based on the three-dimensional, compressible, and unsteady Navier-Stokes equation coupled with k-ω - SST turbulence closure. Boundary conditions are implemented through a cell-centered approach with fictitious cells outside of the domain boundaries. The numerical results are compared with solutions from a quasi-one-dimensional (Q1D) unsteady model reported in literature. The simulations show a good agreement between the two different modelling approaches in terms of spatial distribution of the pressure gradient for one complete cycle. It is observed from the Q2D results that the entrance for each passage, especially upon opening of the high-pressure driver gas port, is a location of particular interest in the formation of the shock. The resulting acute pressure gradients induce loss inside the channel, decreasing the maximum temperature during a complete wave cycle by 15%, and consequently, reducing the methane pyrolysis process.