bluuebunny/crossref_metadata_2025 huggingface dataset:
A Novel LES-Based Process for NOx Emission Assessment in a Premixed Swirl Stabilized Combustion System
Authors: Meloni R. , Andreini A. , Nassini P. C.
Published: September 2021

This paper presents a new CFD approach for the assessment of the NOx emission. The methodology is validated against the experimental data of a heavy-duty gas turbine annular combustor. Since the NOx formation involves time scales that are different from the fuel oxidation time, the present work defines the transport equation source terms for NOx on the basis of a dedicate NOx-Damköhler number. The latter parameter allows to properly distinguish the “in-flame” contribution from the “post-flame” one. While the former is a mix of several mechanisms (prompt, N2O-pathway thermal), the latter is dominated by the thermal contribution.

The validation phase is developed in a Large-Eddy Simulation (LES) framework where the Extended Turbulent Flame Speed model is implemented to consider the influence of both heat loss and strain rate on the progress variable source term. The accuracy of the model against the most important operability parameters of the combustor is verified. A strong focus on the fuel composition effect onto NOx is presented as well.

For any simulated operating condition, the present methodology is able to provide a limited percentage error if compared with the data, considering also different combustion regimes. Leveraging this alignment, the last portion of the paper is dedicated to a detailed post processing highlighting the role of some key factors on to NOx formation. In particular, the focus will be dedicated to the impact of the fuel gas composition and the pilot split.
Investigation on the Robustness of Rotor/Stator Contact Interactions With Respect to Small Mistuning
Authors: Nyssen Florence , Batailly Alain
Published: September 2021

In this work, the impact of small mistuning on rotor/stator contact interactions is investigated. First, a detailed study of a rotor/stator interaction between the first bending modes and the second engine order is presented in the tuned case. Then, a numerical investigation on the effect of mistuning on the studied rotor/stator contact interaction is carried out. In particular, a stochastic analysis is performed to evaluate the robustness of the interaction with respect to the mistuning level. Simulations are conducted using a reduced order model (ROM) of an industrial bladed disk that combines both physical degrees of freedom (along blades tip for contact treatment) and modal coordinates. Mistuning is introduced in the tuned ROM by means of a modified version of the component mode mistuning method that allows to keep physical degrees of freedom within the reduced basis. Nonlinear amplification factors, i.e. the amplification factors in the context of contact nonlinearities, are compared with their linear counterparts, the latter are computed using a linear forcing on each blade using a two nodal diameters traveling wave excitation on the mistuned and the tuned bladed disk. The comparison between the linear and nonlinear amplification factor for each sample highlights that no correlation exists between a mistuning pattern leading to high amplifications in a linear context or when contact nonlinearities are taken into account. Therefore, dedicated analyses on the effect of mistuning should be undertaken with contact nonlinearities considerations at the design stage especially if intentional mistuning is considered.
Numerical Study of Thermal Performance and NOx Emission for An Ammonia-Fuelled Micro-Combustor With Ring-Shaped Ribs in Lean Combustion
Authors: Ni Siliang , Zhao Dan
Published: September 2021

As a renewable energy source, ammonia is regarded as one of the ideal gases that can replace fossil fuels and has been extensively studied in large-scale combustion. However, studies on energy conversion efficiency and NOx emission in microscale are still inadequate. In this work, ammonia/oxygen premixed cylindrical micro-combustors with inner ribs under condition of lean combustion is numerically investigated. The key geometrical parameters of the ribs and the ammonia/oxygen equivalence ratio are evaluated based on thermal performance and NOx emission performance. Finally, the sensitivity analysis of NO and related reaction pathways are analyzed under different equivalence ratios. The results show that increasing the height of the rib and decreasing the distance between the first rib and the inlet can effectively inhibit the generation of NO. Among all cases, the combustor with U-shaped ribs is observed the minimum mole fraction of NO at the outlet under the same working condition, which is 16% less comparing to the rectangular-shaped one. Besides, the mean wall temperature shows a weak correlation with NO emission. Increasing the equivalence ratio can help gain higher mean wall temperature, but at the same time promotes NOx production. This study is helpful to the design and improvement of micro-combustors fuelled by ammonia.
Experimental and Numerical Investigation of Vaned Hub and Shroud Wall Contoured Diffusers Designed to Improve Flexibility and Efficiency of an Open Impeller Centrifugal Compressor Stage
Authors: Hermann Daniel , Wirsum Manfred , Robinson Douglas , Jenny Philipp
Published: September 2021

State-of-the-art centrifugal compressor stages are required to provide both a flexible and a highly efficient operation. To extend the stable operating range and to improve the design-point polytropic total-to-total efficiency of an open impeller centrifugal compressor stage, three vaned contoured diffusers characterized by geometric modifications of the hub and shroud wall in the vaneless space upstream the diffuser vanes and within the diffuser passages were designed. In this paper, a shroud wall, a hub wall and a hub and shroud wall contoured diffuser and a state-of-the-art baseline diffuser are experimentally examined. For the hub-contoured diffuser an operating range extension of 5.3% was measured at design stage Mach number. For the shroud-contoured diffuser an improvement of polytropic total-to-total efficiency by up to 0.3% is observed. The experimental data including normalized total-to-static pressure ratio and 5-hole-probe data is utilized to validate the numerical setup. By means of the CFD simulations the hub- and the shroud-contoured diffuser designs are analyzed and the hub-contoured diffuser’s effect on the local flow at diffuser vane leading edge is investigated. The results illustrate the local effect of the hub-contoured diffuser design on the flow field in the examined centrifugal compressor stage.
Steam Turbine Overspeed Scenarios: Comparison Between API Energy Method and Dynamic Simulation
Authors: Piras Fabrizio , Bucciarelli Federico , Checcacci Damaso , Ingrasciotta Filippo
Published: September 2021

In turbomachinery applications the possibility to reduce size and costs of main flow-path components, by increasing shaft rotating speed, has always been appealing. The technological challenge in increasing this power density capability is typically related to performance prediction, to operating stress in blades and shafts, as well as to the need for a more accurate rotor-dynamic analysis. Yet another aspect, often reduced to standard assessments in less demanding applications, is related to the analysis of overspeed scenarios where, following a sudden loss of load and/or driven inertia, the turbomachine shall maintain its mechanical integrity.

Especially in steam turbines applications, where the behavior of the machine is strongly affected by the plant conditions, valves intervention time and connected volumes, the reduction of the rotor inertia, against comparable power, may produce overspeed scenarios that can become a primary design constraint and, if overlooked, may have both availability and safety implications.

In this paper several approaches to the analysis of overspeed scenarios are discussed, with increasing level of detail. The energy-based overspeed analysis method, as required by API612, is first discussed against practical design cases. A more accurate dynamic model is then presented, and its results compared with those of the energy-based approach. Finally, the sensitivity analysis of the overspeed peak value with respect to critical design parameters is discussed. With respect to previous works, mostly based on load rejection scenarios, the main focus is on the scenario of sudden coupling loss.
Surface Heater Fabrication Using Micro-Lithography for Transpiration Cooling Heat Transfer Coefficient Measurements
Authors: Min Zheng , Parbat Sarwesh , Wang Qing-Ming , Chyu Minking K.
Published: September 2021

Transpiration cooling is able to provide more uniform coolant coverage than film cooling to effectively protect the component surface from contacting the hot gas. Due to numerous coolant ejection outlets within a small area at the target surface, the experimental thermo-fluid investigation on transpiration cooing becomes a significant challenge. Two classic methods to investigate film cooling, the steady-state foil heater method and the transient thermography technique, both fail for transpiration cooling because the foil heater would block numerous coolant outlets, and the semi-infinite solid conduction model no longer holds for porous plates. In this study, a micro-lithography method to fabricate a silver coil pattern on top of the additively manufactured polymer porous media as the surface heater was proposed. The circuit was deliberately designed to cover the solid surface in a combination of series connection and parallel connection to ensure the power in each unit cell area at the target surface was identical. With uniform heat flux generation, the steady-state tests were conducted to obtain distributions of a pair of parameters, adiabatic cooling effectiveness, and heat transfer coefficient (HTC). The results showed that the adiabatic cooling effectiveness could reach 0.65 with a blowing ratio lower than 0.5. Meanwhile, the heat transfer coefficient ratio (hf/h0) of transpiration cooling was close to 1 with a small blowing ratio at 0.125. A higher HTC ratio was observed for smaller pitch-to-diameter cases due to more turbulence intensity generated at the target surface.
Transient Analysis of Supercritical Carbon Dioxide Air Cooler With Using IDAES Model
Authors: Gentile Russell , Vesely Ladislav , Goyal Vipul , Kapat Jayanta S.
Published: September 2021

The supercritical CO2 (sCO2) power cycle is a promising system for meeting future electricity grid demands. Its main advantage over Brayton cycles with other working fluids is its high net efficiency. To maintain this efficiency, the compressor must operate close to the critical point of CO2 (7.32 MPa and 31 °C). Maintaining a near constant inlet temperature is crucial, posing a design and operations challenge. In this study, we simulate the air cooler in an sCO2 power plant using a dynamic model with a focus on transient analysis. This was done for a 100 MWe sCO2 power cycle molten salt application (solar and nuclear reactors). For transient analysis, step changes in ambient temperature were simulated. A parametric study was also conducted using the model in steady-state. The model was implemented using the Institute for the Design of Advanced Energy Systems (IDAES) Process Systems Engineering (PSE) framework, an open-source software package. A brief description of the software architecture is given. Model applications and its overall fit in the digital twin landscape are also discussed.
Assessment of Profile Transformation for Turbomachinery Large Eddy Simulations - From Academic to Industrial Applications
Authors: Gout Clovis , Papadogiannis Dimitrios , Dombard Jérôme , Duchaine Florent , Gicquel Laurent , Odier Nicolas
Published: September 2021

Large Eddy Simulation (LES) of turbomachinery stages has been recently brought to attention due to its potential increased prediction fidelity and its reduced dependency to modeling. Such simulations are however often very CPU intensive, with potentially long return times and only possible for reduced periodic sectors. For real applications, such limitations are prohibitive for a daily use in a design phase. Indeed, most industrial turbomachinery applications rely on designs where at least one of the blade rows has a prime number of blades. Full 360° simulations are in such a case required for appropriate flow dynamics predictions, which implies prohibitive computational costs although recent demonstrations prove these feasible. To make LES affordable in an industrial context, it is clearly necessary to find ways to reduce its cost and return time, one approach being the reduction of the computational domain size.

The Profile Transformation Approach (PTA) is one of such specific methods that allows to simulate down to a single blade passage per blade row, thus decreasing the domain size of the problem and its CPU cost. PTA has been devised and validated in a URANS context and its limits are well known in this specific context. In terms of development and implementation in a code, PTA essentially consists in re-scaling the flow field at the rotor/stator interface to comply with the geometrical constraints on both sides of the interface since these often have different angular extents. Thanks to this flow re-scaling, periodic flow conditions can be applied on the azimuthal limits of both domains while retaining only one passage per row. In the following, the method is assessed in the context of fully unsteady LES simulations in an attempt to identify generated approximations and errors. This LES approach is then used to address a set of cases of increasing complexity ranging from the academic problem focusing first on the convection of a vortex across an interface and finishing with simulations of industrial relevance.
Development of a Harmonic Balance Method-Based Numerical Strategy for Blade-Tip/Casing Interactions: Application to NASA Rotor 37
Authors: Colaïtis Yann , Batailly Alain
Published: September 2021

In this study, a frequency-domain approach based on the harmonic balance method coupled to a predictor-corrector continuation algorithm is implemented for the qualitative analysis of blade-tip/casing contacts in aircraft engines. Unilateral contact and dry friction are taken into account through a regularized penalty law. To enhance the robustness of the methodology, particular attention is paid to the mitigation of the Gibbs phenomenon. To this end, the employed Alternating Frequency/Time scheme features a Lanczos σ-approximation so that spurious oscillations of the computed nonlinear contact forces become negligible. This approach is applied in combination with a model reduction technique on an industrial compressor blade: NASA rotor 37. In order to assess the influence of both the contact law regularization and the Lanczos σ-approximation, obtained results are thoroughly compared to an existing time integration-based numerical strategy relying on a Lagrange multiplier-based approach for contact treatment and that was previously confronted to experimental results. Presented results underline the very good agreement between the proposed methodology and the reference time integration numerical strategy. The proposed developments thus complement existing results on blade-tip/casing contact adding a much needed qualitative understanding of the interaction and an accurate assessment of the contact stiffening phenomenon.
A Non-Compact Effective Impedance Model for Can-to-Can Acoustic Communication: Analysis and Optimization of Damping Mechanisms
Authors: von Saldern Jakob G. R. , Orchini Alessandro , Moeck Jonas P.
Published: September 2021

Can-annular combustors can feature azimuthal instabilities even if the acoustic coupling between the individual cans is weak. Recently, various studies have focused on modeling the acoustic communication between adjacent cans in can-annular systems. In this study, a coupling model is presented that, in contrast to previous models, includes the effect of density fluctuations, mean flow, and dissipative effects at the connection gaps. By assuming plane acoustic waves inside each can and exploiting the discrete rotational symmetry of the can-annular system, the acoustic can-to-can interaction can be represented by an effective Bloch-type impedance. A single can modeled with the effective impedance at the downstream end emulates the acoustic response of the entire can-annular arrangement. We then propose the idea of installing a liner just upstream of the first turbine stage to damp azimuthal instabilities. By using the proposed can-to-can coupling model, we discuss in detail the effect that the impedance of the liner has on the effective reflection coefficient for different Bloch wavenumbers. In the low-frequency limit, we derive an analytical condition for achieving maximum damping at a specific Bloch-number. We show that the damping of azimuthal modes depends on the porosity of the liner, mean flow parameters and the Bloch-structure of the mode. These results suggest the possibility of targeting the damping of modes of certain azimuthal order by geometric variations of the liner or of the connection gap. As an exemplary application of the theory, we set up a network model of a generic industrial 12-can combustor and investigate a cluster of acoustic and thermoacoustic eigenvalues for a varying liner porosity. The findings of this study provide a deeper understanding of the mechanisms that drive the can-to-can acoustic communication, and open the path for devising passive damping strategies aimed at stabilizing specific modes in can-annular combustors.
Determining Total Pressure Fields From Velocimetry Measurements in a Transonic Turbine Flowfield
Authors: Rusted Alexander , Lynch Stephen
Published: September 2021

This work describes a method for calculating pressure fields from temperature and velocity data in non-adiabatic compressible flows, such as the flow around a cooled turbine vane. Prior studies have demonstrated the ability to use particle image velocimetry methods to estimate the pressure gradient in the momentum equation, which is subsequently integrated to produce pressure fields. Due to changes in total temperature for non-adiabatic compressible flows, pressure fields cannot be computed from velocity measurements alone and temperature data must also be provided. In this work, a benchmarked steady 3D RANS simulation is used to generate velocity, temperature, and pressure fields in the transonic flow around a high-pressure turbine inlet guide vane. A procedure for solving the momentum equation and integrating for pressure is developed for non-adiabatic flows. Error is assessed by comparing calculated pressure to CFD predicted pressure, and the effects of PIV spatial resolution and measurement error are considered. The accuracy of the method on non-adiabatic flows is assessed using a vane with extensive film cooling. A clear benefit of incorporating temperature measurements in the pressure determination method is demonstrated, offering opportunities for deeper understanding of aerodynamic losses and entropy generation in cooled turbine flowfields.
A Dynamic Systems Based Approach to Estimate Cyclic and Creep Damage of a Power Turbine Blade Subjected to a Random Transient Operation
Authors: Dua Dipankar , Le Quang , Saladino Anthony , Thirumurthy Deepak , Singh Jaskirat
Published: September 2021

The Paper presents a novel computationally efficient physics based framework for continuous assessment of cyclic and time dependent damage consumption for Siemens Aeroderivative power turbine components based on actual engine operation.

The framework discussed in paper provides the capability for Siemens’ customers to move away from fixed overhaul schedule to a customized schedule which is based on a given gas turbines actual operation and inspection findings. This customized overhaul schedule enables the customers a flexibility to maximize the unit availability and minimize operating costs.

Semi-empirical framework discussed in this paper, utilizes dynamic systems theory-based approach to estimate the cyclic & creep damage as a response to transient engine operation; characterized by relevant installed engine instrumentation data from the Engine Health Monitoring system.

To estimate damage response through any given complex transient operating cycle, algorithm solves a set of ordinary differential equations (ODEs), that have been calibrated to the engine control and safety instrumentation parameters such as shaft speed, turbine temperatures, pressures etc. by pre-analyzed operating envelope cases.

The framework can be setup for predicting accumulated cyclic and creep damage for all type of turbine components (Aerofoils, disks, casings, diffusers etc.), transient stress state complexity (in-phase, out-of-phase, uniaxial, multiaxial stress profiles) and is capable to handle unit specific ramp rates, start-up times, restart/cooldown effects specific and random changes in load, history.

The framework for discussion in this paper has been demonstrated as applied to the stage-1 blade of an A-35 RT62 power turbine as an example.
Heat Transfer in a Rotating, Blade-Shaped, Two-Pass Cooling Channel With a Variable Aspect Ratio
Authors: Chen I-Lun , Sahin Izzet , Wright Lesley M. , Han Je-Chin , Krewinkel Robert
Published: September 2021

This study features a rotating, blade-shaped, two-pass cooling channel with a variable aspect ratio. Internal cooling passages of modern gas turbine blades closely follow the shape and contour of the airfoils. Therefore, the cross-section and the orientation with respect to rotation varies for each cooling channel. The effect of passage orientation on the heat transfer and pressure loss is investigated by comparing to a planar channel design with a similar geometry. Following the blade cross-section, the first pass of the serpentine channel is angled at 50° from the direction of rotation while the second pass has an orientation angle of 105°. The coolant flows radially outward in the first passage with an aspect ratio (AR) = 4:1. After a 180-degree tip turn, the coolant travels radially inward into the second passage with AR = 2:1. The copper plate method is applied to obtain the regionally-averaged heat transfer coefficients on all the interior walls of the cooling channel. In addition to the smooth surface case, 45° angled ribs with a profiled cross section are also placed on the leading and trailing surfaces in both the passages. The ribs are placed such that P/e = 10 and e/H = 0.16. The Reynolds number varies from 10,000 to 45,000 in the first passage and 16,000 to 73,000 in the second passage. The rotational speed ranges from 0 to 400 rpm, which corresponds to maximum rotation numbers of 0.38 and 0.15 in the first and second passes, respectively. The blade-shaped feature affects the heat transfer and pressure loss in the cooling channels. In the second passage, the heat transfer on the outer wall and trailing surface is higher than the inner wall and leading surface due to flow impingement and the swirling motion induced by the blade-shaped tip turn. The rotational effect on the heat transfer and pressure loss is lower in the blade-shaped design than the planar design due to the feature of angled rotation. The tip wall heat transfer is significantly enhanced by rotation in this study. The overall heat transfer and pressure loss in this study is higher than the planar geometry due to the blade-shaped feature. The heat transfer and pressure loss characteristics from this study provide important information for the gas turbine blade internal cooling designs.
Enhanced Film Cooling Effect Downstream of a Cylindrical Hole Using SDBD and DBD-VGs Plasma Actuations
Authors: Huang Yuefeng , Zhang Zihan , He Kun , Yan Xin
Published: September 2021

Effects of SDBD and DBD-VGs plasma actuations on film cooling performance of a plain wall were numerically investigated based on the RANS solutions and linearized body force model. With a user defined function (UDF), the plasma actuation forces were implemented into the momentum equations as the source terms in the commercial CFD solver ANSYS Fluent. With the experiment data and referenced numerical results, reliabilities of the linearized body force model and numerical methods were validated. At a range of dimensionless actuation strengths and frequencies, the film cooling effectiveness on the wall surface and flow structure development in the near-wall regions were analyzed and compared with the plasma-off case. The results show that both SDBD and DBD-VGs plasma actuations are beneficial for reducing the development of kidney vortex pair downstream of the cooling hole, thus significantly improving the film cooling effect on the wall surface. With SDBD plasma actuation, the streamwise velocity gradient in near-wall region is increased compared with the plasma-off case, resulting in delayed coolant flow lifting-off downstream of the cooling hole. However, with DBD-VGs plasma actuation, the development of anti-kidney vortex pair is intensified, which in turn weakens the development of kidney vortex pair and widens the coolant coverage on the wall surface along lateral direction. As the actuation strength and frequency increase, the film cooling effectiveness on the wall surface is enhanced along both streamwise and lateral directions. Compared with the plasma-off case, the area-averaged film cooling effectiveness for DBD-VGs plasma actuation case is increased by 331% at dimensionless actuation frequency of 2.5 and dimensionless actuation strength of 30, whereas for SDBD plasma actuation case the area-averaged film cooling effectiveness is only increased by 42.8% at dimensionless actuation frequency of 2.5 and dimensionless actuation strength of 60. With the same actuation parameters, compared against the SDBD case, a higher film cooling effectiveness is achieved on wall surface for the DBD-VGs plasma actuation case, and the coolant coverage along the lateral direction is significantly improved by DBD-VGs plasma actuation.
Evaluation of Different Turbulence Models Applied in Turbopump’s Hydraulic Turbine
Authors: Barbosa Daniel Ferreira Corrêa , Tonon Daniel da Silva , Whitacker Luiz Henrique Lindquist , Tomita Jesuino Takachi , Bringhenti Cleverson
Published: September 2021

The aim of this work is an evaluation of different turbulence models applied in Computational Fluid Dynamics (CFD) techniques in the turbomachinery area, in this case, in an axial turbine stage used in turbopump (TP) application. The tip clearance region was considered in this study because it has a high influence in turbomachinery performance. In this region, due to its geometry and the relative movement between the rotor row and casing, there are losses associated with vortices and secondary flow making the flowfield even more turbulent and complex. Moreover, the flow that leaks in the tip region does not participate in the energy transfer between the fluid and rotor blades, degradating the machine efficiency and performance. In this work, the usual flat tip rotor blade geometry was considered.

The modeling of turbulent flow based on Reynolds Averaged Navier-Stokes (RANS) equations predicts the variation of turbine operational characteristics that is sufficient for the present turbomachine and flow analysis. Therefore, the appropriate choice of the turbulence model for the study of a given flow is essential to obtain adequate results using numerical approximations. This comparison become important due to the fact that there is no general turbulence model for all engineering applications that has fluid and flow.

The turbomachine considered in the present work, is the first stage of the hydraulic axial turbine used in the Low Pressure Oxidizer Turbopump (LPOTP) of the Space Shuttle Main Engine (SSME), considering the 3.0% tip clearance configuration relative to rotor blade height. The turbulence models evaluated in this work were the SST (Shear Stress Transport), the k-ε Standard and the k-ε RNG. The computational domain was discretized in several control volumes based on unstructured mesh. All the simulations were performed using the commercial software developed by ANSYS, CFX v15.0 (ANSYS). All numerical settings and how the boundary conditions were imposed at different surfaces are explained in the work. The boundary conditions settings follow the same rule used in the test facility and needs some attention during the simulations to vary the Blade-Jet-Speed ratio parameter adequately.

The results from numerical simulations, were synthesized and compared with the experimental data published by National Aeronautics and Space Administration (NASA), in which the turbine efficiency and its jet velocity parameter are analyzed for each turbulence model result. The work fluid considered in this work was water, the same fluid used in the NASA test facility.
Influence of Alternative Fuels on the Liner Metal Temperatures in a V2500 Combustor
Authors: Schäflein Lukas , de Guillebon Ludovic , Konle Marco
Published: September 2021

To reach ambitious emission goals, the use of sustainable aviation fuels (SAFs) is a short-term option in current aero engines. The combustion of such fuels can, due to their low soot formation, have an impact on the thermal radiation inside the combustor. This in turn can affect the combustor liner temperatures, which are directly linked to the lifetime of the combustor. To study the impact of SAFs, the authors numerically simulated the flow inside a V2500 aero engine combustor using an OpenFOAM-based solver capable of capturing multi-physics phenomena such as combustion, conjugate heat transfer, thermal radiation and soot formation.

The complex cooling system of the V2500 combustor makes the evaluation of the wall temperatures extremely challenging. To achieve results with the resources available, the authors replaced the densely packed pins inside the cooling channel with a boundary condition. This boundary condition was derived from a highly detailed simulation of a section of the cooling system. With this model reduction, the wall temperatures could be evaluated at four operating points. Back-to-back comparisons of the predicted wall temperatures with pictures of deteriorated combustor hardware out of the field operation reveals the plausibility of the numerical results.

Finally, this numerical model was extended to include the effects of thermal radiation and soot formation. To predict the combustion of Jet-A, both models were used with settings derived from former validation simulations. The SAF combustion with extremely low sooting level was mimicked by deactivating the soot formation completely. The comparison of the radiation source term reveals — as expected — locally a higher radiation emission in areas where soot is formed in the combustor. As consequence, this leads to higher net radiative heat flux into the combustor liners. However, due to its minor importance in the overall energy balance, this change did not lead to significantly different liner temperatures.
A Reduced-Order Model for the Preliminary Design of Small-Scale Radial Inflow Turbines
Authors: Manfredi Marco , Alberio Marco , Astolfi Marco , Spinelli Andrea
Published: September 2021

Power production from waste heat recovery represents an attractive and viable solution to contribute to the reduction of pollutant emissions generated by industrial plants and automotive sector. For transport applications, a promising technology can be identified in bottoming mini-organic Rankine cycles (ORCs), devoted to heat recovery from internal combustion engines (ICE). While commercial ORCs exploiting turbo-expanders in the power range of hundreds kW to several MW are a mature technology, well-established design guidelines are not yet available for turbines targeting small power outputs (below 50 kW). The present work develops a reduced-order model for the preliminary design of mini-ORC radial inflow turbines (RITs) for high-pressure ratio applications, suitable to be integrated in a comprehensive cycle optimization. An exhaustive review of existing loss models, whose development pattern is retraced up to the original approaches, is proposed. This investigation is finalized in a loss models effectiveness analysis performed by testing several correlations over six existing geometries. These test case turbines, operating with different fluids and covering a wide range of target expansion ratio, size, and gross power output, are then employed to carry out the validation procedure, whose results prove the robustness and prediction capability of the proposed reduced-order model.
Start-Up Process of 50kW-Class Gas Turbine Firing Ammonia Gas
Authors: Kurata Osamu , Iki Norihiko , Fan Yong , Matsunuma Takayuki , Inoue Takahiro , Tsujimura Taku , Furutani Hirohide , Kawano Masato , Arai Keisuke , Okafor Ekenechukwu C. , Hayakawa Akihiro , Kobayashi Hideaki
Published: September 2021

Ammonia combustion gas turbines have drawn much attention for their potential to power hydrogen-carrier applications. In 2014, 21-kW of power generation was achieved with kerosene-ammonia co-combustion using a 50-kW-class micro gas turbine. In 2015, methane-ammonia co-combustion and 100% ammonia gas combustion were separately employed to generate 42-kW of power in both cases. However, this microgas turbine still requires kerosene to start. In gas turbines, the suitability of the air flow for ignition depends on the fuel. Low-NOx combustors were developed using the staged combustion concept to achieve rich-lean combustion. These combustors can burn kerosene at start-up but not at full load. We have also developed a micro gas turbine system that utilizes 100% ammonia gas in combustion during full-load operation. However, start-up with ammonia gas is difficult without hot air. The ignition of ammonia gas is so difficult that during the startup process, a more easily ignitable fuel is also used. In this study, we developed a new 50-kW-class micro gas turbine that can be started with gaseous fuel. Start-up with methane gas was achieved using a newly designed low-NOx combustor. In addition, because hydrogen can be easily obtained from ammonia decomposition, the addition of hydrogen gas to ammonia gas has garnered attention for ammonia gas turbine applications. The application of hydrogen to initiate combustion in a micro gas turbine was also investigated.
Unsteady Effects of Blade Row Interaction on Flow Field and Aerodynamic Performance of a Transonic Centrifugal Compressor Impeller
Authors: Yamada Kazutoyo , Kubo Kosuke , Iwakiri Kenichiro , Ishikawa Yoshihiro , Higashimori Hirotaka
Published: September 2021

This paper discusses the unsteady effects associated with the impeller/diffuser interaction on the internal flow field and aerodynamic performance of a centrifugal compressor. In centrifugal compressors with a vaned diffuser, the flow field is inherently unsteady due to the influence of interaction between the impeller and the diffuser, and the unsteadiness of the flow field can often have a great influence on the aerodynamic performance of the compressor. Especially in high-load compressors, it is considered that large unsteady effects are produced on the compressor performance with a strong flow unsteadiness. The unsteady effect on aerodynamic performance of the compressor has not been fully revealed yet, and sometimes the steady-state RANS simulation finds it difficult to predict the compressor performance.

In this study, numerical simulations have been conducted for a transonic centrifugal compressor with a vaned diffuser. The unsteady effects were clarified by comparing the numerical results between a single-passage steady-state RANS analysis and a full-annulus unsteady RANS analysis. The comparison of simulation results showed the difference in entropy generation in the impeller. The impingement of diffuser shock wave with the impeller pressure surface brought about a cyclic increase in the blade loading near the impeller trailing edge. Accordingly, with increasing tip leakage flow rate, a second tip leakage vortex was newly generated in the aft part of the impeller, which resulted in additional unsteady loss generation inside the impeller.
Optimization of a Tip Appendage for the Control of Tip Leakage Vortices in Axial Flow Fans
Authors: Meyer Thomas O. , van der Spuy Sybrand J. , Meyer Christiaan J. , Corsini Alessandro
Published: September 2021

This paper presents the numerical optimization of a tip appendage design for the passive control of tip leakage vortices in subsonic axial flow cooling fans. The studied class of fan was designed in the conventional manner without the consideration of tip clearance effects. As such, the objective of this investigation is the improvement of the aerodynamic performance characteristics of the datum fan through consideration of the blade tip geometry. Based on previous studies involving fan performance enhancement using various tip end-plate configurations, the most promising end-plate geometry which is found to best improve the fan’s performance characteristics is selected for further development through optimization. Before the optimization process can begin, initialization of the chosen end-plate’s design space using the Design of Experiments (DoE) technique is performed. Formulation of the response surface is based on a multi-objective multi-point objective function which considers the fan’s various performance metrics. Considering the optimization process, the Design and Analysis of Computer aided Experiments (DACE) method is used in the development of the Kriging based surrogate model’s (SM) database. The resulting database is coupled with an Efficient Global Optimization (EGO) algorithm which completes the workflow of the optimization routine. The Pareto-front of non-dominated solutions is used to guide the optimal design selection, on which the experimental evaluations are based. The experimental results of the optimized design indicate improved fan performance characteristics at greater than peak efficiency flow rates. This design is found to increase the datum fan’s design point performance characteristics by a value of 32.90 percent in total-to-static pressure rise and a 7.66 percentage point increase in total-to-static efficiency at the fan’s design speed of 722 rpm.
A Cradle to Gate Approach for Life-Cycle-Assessment of Blisk Manufacturing
Authors: Fricke Kilian , Gierlings Sascha , Ganser Philipp , Seimann Martin , Bergs Thomas
Published: September 2021

The aviation industry has been growing continuously over the past decades. Despite the current Covid-19 crisis, this trend is likely to resume in the near future. On an international level, initiatives like the Green Recovery Plan promoted by the European Union set the basis towards a more environmentally friendly future approach for the aero-industry. The increasing air traffic and the focus on a more sustainable industry as a whole lead to an extensive need for a more balanced assessment of a products life cycle especially on an ecological level.

Blisks (or IBRs) remain a central component of every current and very possible every future aero engine configuration. Their advantages during operation compared to conventional compressor rotors are met with a considerably complex manufacturing and production process. In the high-pressure compressor segment of an engine, the material selection is limited to Titanium alloys such as Ti6Al4V and heat-resistant Nickel-alloys such as Inconel718. The corresponding process chains consist of numerous different process steps starting with the initial raw material extraction and ending with the quality assurance (cradle to gate). Especially the central milling process requires a highly qualified process design to ensure a part of sufficient quality.

Life-Cycle-Assessments enable an investigation of a products overall environmental impact and ecological footprint throughout its distinct life-cycle. Formal LCAs are generally divided by international standards into four separate steps of analysis: the goal and scope definition, the acquisition of Life Cycle-Inventory, the Life-Cycle-Impact-Assessment and the interpretation. This content of this paper focuses on a general approach for Life-Cycle-Assessment for Blisk manufacturing.

• Firstly, the goal and scope is set by presenting three separate process chain scenarios for Blisk manufacturing, which mainly differ in terms of raw material selection and individual process selections for blade manufacturing.

• Secondly, the LCI data (Life-Cycle Inventory) acquisition is illustrated by defining all significant in- and outputs of each individual process step.

• Thirdly, the approach of a Life-Cycle-Impact-Assessment is presented by introducing the modelling approach in an LCA-software environment.

• Fourthly, an outlook and discussion on relevant impact-indicators for a subsequent interpretation of future results are conducted.
Establishing an Acceptance Criteria for Assessing Fatigue of Additive Repair Processes
Authors: Scott-Emuakpor Onome , Sheridan Luke , Beck Joseph , Runyon Brian , George Tommy
Published: September 2021

Criteria for assessing high cycle fatigue (HCF) capability is important for transitioning additive repair technologies to turbine engine applications. By studying the fatigue results of two laser directed energy deposition additive manufacturing repairs on airfoil representative Titanium 6Al-4V coupons, acceptable HCF results for repairs can be determined by observing the confidence in predicted values and the reliability of the empirical data compared to baseline results. The following document details the steps and philosophies behind fabricating coupons that capture the repair capability. Furthermore, regression analysis as well as investigations of dataset distribution, fractography, and microscopy are necessary for instilling confidence in the understanding of repair fatigue behavior. The findings in this work provide a decision gate with quantifiable metrics for advancing novel repair techniques.
Self-Excited High-Frequency Transverse Limit-Cycle Oscillations and Associated Flame Dynamics in a Gas Turbine Reheat Combustor Experiment
Authors: McClure Jonathan , Berger Frederik M. , Bertsch Michael , Schuermans Bruno , Sattelmayer Thomas
Published: September 2021

This paper presents the investigation of high-frequency thermoacoustic limit-cycle oscillations in a novel experimental gas turbine reheat combustor featuring both auto-ignition and propagation stabilised flame zones at atmospheric pressure. Dynamic pressure measurements at the faceplate of the reheat combustion chamber reveal high-amplitude periodic pressure pulsations at 3 kHz in the transverse direction of the rectangular cross-section combustion chamber. Further analysis of the acoustic signal shows that this is a thermoacoustically unstable condition undergoing limit-cycle oscillations. A sensitivity study is presented which indicates that these high-amplitude limit-cycle oscillations only occur under certain conditions: namely high power settings with propane addition to increase auto-ignition propensity. The spatially-resolved flame dynamics are then investigated using CH* chemiluminescence, phase-locked to the dynamic pressure, captured from all lateral sides of the reheat combustion chamber. This reveals strong heat release oscillations close to the chamber walls at the instability frequency, as well as axial movement of the flame tips in these regions and an overall transverse displacement of the flame. Both the heat release oscillations and the flame motion occur in phase with the acoustic mode. From these observations, likely thermoacoustic driving mechanisms which lead to the limit-cycle oscillations are inferred. In this case, the overall flame-acoustics interaction is assumed to be a superposition of several effects, with the observations suggesting strong influences from autoignition-pressure coupling as well as flame displacement and deformation due to the acoustic velocity field. These findings provide a foundation for the overall objective of developing predictive approaches to mitigate the impact of high-frequency thermoacoustic instabilities in future generations of gas turbines with sequential combustion systems.
On the Correlation Between Span-Wise Inducer Incidence and Impeller Diffusion for Ruled Surface and Barreled Sweep-Bow Impeller Design at IGV-Off-Design
Authors: Hildebrandt A. , Ceyrowsky T. , Klausmann J. , Metz K. A.
Published: September 2021

In the present paper, three centrifugal stages of high volume flow coefficient are compared to each-other regarding their aerodynamic performance in design point and off-design point conditions at different speed and IGV-setting angle: two stages with full-blade design (no splitter blades) have been numerically designed with different design geometry methodology. One geometry is based on a classical ruling surface design with a linear leading edge, the second geometry based on a fully-3d surface including a blade bow at the trailing edge and a barreled sweep at the leading edge. According to impeller test rig measurements and CFD-calculation, the classical ruling surface designed impeller outperforms the more sophisticated centrifugal stage with fully-3D-blade at fully axially guided IGV-flow. In the contrary, at closing IGV-off-design setting angles, towards surge operation, the fully-3D-blade-impeller performs with higher efficiency and steeper negative pressure slope. On the search of the geometrical causes for the different aerodynamic performance (especially at IGV-off-design conditions), focus is set on the analysis of IGV-flow-interaction with the inducer flow, and impeller diffusion. The one-dimensional -analysis of the span-wise flow at the impeller leading edge reveals that, compared with the ruling surface impeller, the fully 3D-blade performs with lower flow incidence losses in favor to IGV-off-design operation than at IGV-neutral position. The stream-wise flow analysis confirms the improved flow incidence characteristics of the 3D-blade impeller due to reduction of aerodynamic blockage and entropy production in the vicinity of the impeller leading edge. Based on CFD-calculations, a new correlation of secondary flow and flow incidence is proposed, to be used for one-dimensional modelling.
Aerodynamic Functional Diagnostics Based on Angular Momentum Transport Lines
Authors: Yang Xiang I. A. , Jariwala Vishal , Xu Haosen H. A. , Larosiliere Louis
Published: September 2021

In analogy with the classical concept of mass-flux-based streamlines, we define Angular Momentum Transport (AMT) lines as an aerodynamic functional diagnostic tool. The AMT lines are the ones whose tangents are given by the average angular momentum flux. The mathematical and physical properties of these AMT lines are exploited to study the generation, removal, and transport of angular momentum in turbomachinery components. We illustrate the concept by visualizing AMT lines in two relatively simple flows, namely, vaneless incompressible diffuser and von Karman flow (a model of centrifugal compressors). Next, we apply the proposed diagnostic tool to flow in a return channel. A return channel is a part of a multistage centrifugal compressor stage. Its principal function is to remove angular momentum. In this work, we apply the diagnostic tool of AMT lines to a Reynolds averaged Navier Stokes simulation (RANS) and a wall-modeled large eddy simulation (LES) of flow in the return channel. We show that AMT lines give us insights into the angular momentum transport process that are otherwise not available with conventional visualization tools.