bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Drag and Mixing From Lobed Nozzles Under High Swirl Conditions From a Ducted Fan
Authors: Zawislak Maverick , Birk Michael 
Published: January 2021

Abstract
The availability of aerodynamic performance and vorticity production data from mixers under swirl was a challenge for future full-scale design and CFD validation. This paper presents an experimental comparison of drag and mixing performance of a circular trialing edge, lobed nozzle and scalloped nozzle under high swirl conditions as produced by a ducted fan in a subsonic wind tunnel. The design methodology is shared in detail allowing for geometry reproduction. Swirl angles produced by the fan naturally varied between 12° up to 45° according to a free-vortex profile. Performance is compared in terms of net thrust, uniformity factor and vorticity production as measured by 6-component loadcells and a seven-hole pressure probe traverse. The goal of this work was threefold: to study the axial and normal vorticity production from mixers produced by the design methodology, a preliminary investigation into lobed mixers potential in engine plume cooling and to provide a data set for RANS-CFD validation.
A better understanding of lobed mixer mixing mechanisms relative to performance is offered. It is shown that the change in minimum throttle to achieve forward thrust varied between devices as did the twist load due to angular forces. A 4% reduction in required fan power to achieve forward thrust was achieved with the lobed mixer. Furthermore, maximum net thrust increased up to 20% with the mixing nozzles compared to the standard round nozzle suggesting flow straightening can lead to thrust gain in high swirling jet flows to a level that counters increases in drag. Axial and normal vorticity were clearly identified. Co-rotating vortex pairs were produced by the mixers of physical size proportional to the lobe height and wavelength. Axial vorticity levels integrated up to 110% of the round nozzle and occupied 5 times the area. Similarly, integrated normal vorticity increased up to 80% over an area 120% larger. Uniformity factor was best for the scalloped mixer due to enhanced mass flow entrainment through the notch and not the vortex production itself.
LM9000 Free Power Turbine: Advanced Test Bench
Authors: Mazzola Manfredi , Bulleri Andrea , Pennacchi Paolo , Chatterton Steven 
Published: January 2021

Abstract
In Oil and Gas framework, the need of innovative turbomachineries in terms of efficiency, weight, and flexibility is quickly growing.
For these reasons, the new LM9000 is entirely designed with aviation design criteria. It is composed by a gas generator derived from the GE90-115B twin shaft turbofan, coupled to a free power turbine (FPT). Both the gas generator and the FPT use rolling element bearings that contribute to reduce the weight and the complexity of the engine and its auxiliary systems architecture. The free power turbine represents the new element.
Due to the FPT dimensions, weight and characteristics, it was necessary to realize a dedicated test bench that is in a class by itself in the Oil and Gas industry. To give an idea of the dimensions, the ball bearing installed has a bore diameter of 320mm with a ball diameter close to 60mm.
The test bench was crucial to validate the sump configuration for on-shore and off-shore applications and to define the inputs range in which the FPT will operate properly.
The first part of the paper aim at describing the solutions adopted to realize the test bench. The main results are reported in the second part of the paper.
Moreover, the test bench provides flexibility to perform complex tests for different configurations thanks to its 20 tons allowable payload, considerable volume for the test article installation and its modular design.
High Fidelity Transient Forced Response Analysis of Mistuned Bladed Disks Under Complex Excitation and Variable Rotation Speeds
Authors: Tong Jing , Zang Chaoping , Petrov Evgeny 
Published: January 2021

Abstract
An effective method is developed for the efficient calculation of the transient vibration response for mistuned bladed disks under complex excitation and varying rotation speeds. The method uses the large-scale finite element modelling of the bladed disks allowing the accurate description of the dynamic properties of the mistuned bladed disks. The realistic distributions of the excitation forces are considered, which resulted in the multiharmonic excitation loads. The transient response calculation is based on the analytically derived expressions for the transient forced response and the effective method used for the model reduction.
The effects of the varying rotation speed on the natural frequencies and mode shapes of the mistuned bladed disk and its effects on the amplitude and the spectral composition of the loading are allowed for. The different functions of the rotation speed variation can be analyzed.
Numerical studies of the transient forced response and the amplitude amplification in mistuned bladed disks are performed when the resonance regimes are passed during gas-turbine engine acceleration or deceleration. The effects of different types of excitation force and mistuning on transient amplitude amplification are illustrated by a large number of the computational results and comparative analysis. These results and analysis of transient forced response are shown on an example of a realistic mistuned bladed disk.
Effects of Axial Casing Grooves on the Structure of Turbulence in the Tip Region of an Axial Turbomachine Rotor
Authors: Chen Huang , Li Yuanchao , Shankha Koley Subhra , Katz Joseph 
Published: January 2021

Abstract
Challenges in predicting the turbulence in the tip region of turbomachines include anisotropy, inhomogeneity, and non-equilibrium conditions, resulting in poor correlations between the Reynold stresses and the corresponding mean strain rate components. The geometric complexity introduced by casing grooves exacerbates this problem. Taking advantage of a large database collected in the refractive index-matched liquid facility at JHU, this paper examines the evolution of turbulence in the tip region of an axial turbomachine with and without axial casing grooves, and for two flow rates. The semi-circular axial grooves are skewed by 45° in the positive circumferential direction, similar to that described in Müller et al. [1]. Comparison to results obtained for an untreated endwall includes differences in the distributions of turbulent kinetic energy (TKE), Reynolds stresses, anisotropy tensor, and dominant terms in the TKE production rate. The evolution of TKE at high flow rates for blade sections located downstream of the grooves is also investigated. Common features include: with or without casing grooves, the TKE is high near the tip leakage vortex (TLV) center, and in the shear layer connecting it to the blade suction side tip corner. The turbulence is highly anisotropic and inhomogeneous, with the anisotropy tensor demonstrating shifts from one dimensional (1D) to 2D and to 3D structures over small distances. Furthermore, the correlation between the mean strain rate and Reynolds stress tensor components is poor. With the grooves, the flow structure, hence the distribution of Reynolds stresses, becomes much more complex. Turbulence is also high in the corner vortex that develops at the entrance to the grooves and in the flow jetting out of the grooves into the passage. Consistent with trends of production rates of normal Reynolds stress components, the grooves increase the axial and reduce the radial velocity fluctuations compared to the untreated endwall. These findings introduce new insight that might assist the future development of Reynolds stress models suitable for tip flows.
A Design Tool for Supercritical CO2 Radial Compressors Based on the Two-Zone Model
Authors: El Hussein Ihab Abd , Hacks Alexander Johannes , Schuster Sebastian , Brillert Dieter 
Published: January 2021

Abstract
In supercritical Carbon Dioxide (sCO2) cycles, the compressor inlet conditions are selected near the critical point where compressibility factor reaches values as low as 0.2. Consequently, conventional compressor design approaches formulated for fluids obeying the ideal gas law are not verified. Therefore, this paper proposes a design approach for sCO2 radial compressors that consists of a performance prediction model in addition to a set of geometry parameters suitable for radial compressors. The compressor model is based on the two-zone modeling approach, in which the Span and Wagner equation of state for CO2 is integrated. At first, the compressor model is presented in addition to the required correlations. Afterwards, a sensitivity analysis is performed on the model main parameters. Thereafter, a plausibility check is performed against experimentally obtained data. Finally, an overall design approach is proposed and its capability to deliver new geometries is assessed by comparing the tool predictions against the results from a verified CFD code for several test cases. The Comparison shows a maximum deviation of less than 2 percent for the pressure ratio and less than 3.5 percentage points for the efficiency. The results indicate the ability of the proposed approach to predict the performance of sCO2 compressor from correlations that originate from experience with conventional fluids. Additionally, the adopted geometric relations proved its applicability to sCO2 compressors.
Variance in Compressor Turndown When Implementing Surge Control Fallback Strategies
Authors: Garceau Sean W. 
Published: January 2021

Abstract
A centrifugal compressor surge prevention system is used to protect a compressor from surging while in operation. When using an invariant coordinate system for the compressor performance map within the surge protection system, reduced head versus reduced flow, surge control fallback strategies can be implemented within the control system to maintain operation of the compressor when instrumentation fails without placing the unit into a surge event, increasing unit availability. This paper reviews the different fallback strategies that can be implemented based on the function of the instrumentation that faulted and determine the variance between the calculated and actual turndown when different fallback strategies are active. Depending on the fallback strategy implemented, additional turndown margin may be required to ensure compressor surge is prevented by the surge prevention control system. This paper also reviews how the specific gravity, compressor pressure ratio, and compressor flow impact the variance between actual and calculated turndown when a given fallback strategy is active.
Knowing the variance in the turndown allows the operator of the compressor to correctly select the desired fallback strategies and determine the needed control margin to safety operate the compressor without process disruptions. Several recommendations are outlined in the paper.
Time-Resolved Measurements of the Unsteady Boundary Layer in an Annular Low-Pressure Turbine Configuration With Perturbed Inlet
Authors: Sinkwitz Martin , Winhart Benjamin , Engelmann David , di Mare Francesca 
Published: January 2021

Abstract
In this study the unsteady behavior of the boundary layers developing on a LPT stator profile and their effect on secondary flow patterns in a 1.5-stage turbine configuration are investigated under the influence of periodic inflow perturbations. The experimental setup previously employed to analyze the unsteady secondary flow in the stator wake has been enhanced by hotfilm sensor arrays placed on the stator profiles at different blade height positions to provide time-resolved data from within the passage. The turbine inflow is perturbed by periodically passing circular bars and a modified T106-profile has been considered for the blading. The modified profile, labeled as T106RUB, was developed for matching the transition and separation characteristics of the original T106 profile at low flow speeds, thus facilitating measurements to be taken in a large-scale test rig with its improved accessibility. The transition phenomena occurring in the profile boundary layers are investigated under both unperturbed and periodically perturbed inflow by means of spectral analysis, the semi-quantitative characterization of the wall-stress system and an evaluation of the statistic quantities. In particular, the periodic changes of the suction side boundary layer flow region towards the trailing edge are studied in detail. Furthermore, time-resolved hot-film measurements at different blade height positions facilitate a detailed comparison of the quasi two-dimensional mid-span profile flow and the near end wall profile flow which is subject to influence of secondary flow structures. These information are employed to assess to which extent the additional turbulence originating from the wakes affects the blade boundary layers and thus the secondary flow structures. Furthermore, the role of the perturbation frequency on the coupled system of boundary layers and secondary flow structures is evaluated.
Pressure Gain Combustion by Using Shock Flame Interaction Pressure Rise
Authors: Gundogdu Birol , Rose Martin G. 
Published: January 2021

Abstract
Pressure loss across a combustor in a gas turbine reduces thermal efficiency and increases specific fuel consumption. Theoretically, any pressure gain across the combustor results in higher thermal efficiency and lower specific fuel consumption. This work aims to obtain ‘time-averaged pressure rise across the combustor by using shock-flame interaction’. Multiple shock flame interaction increases the chemical heat release rate by two orders of magnitude. In this study, an impulsive heat addition for 30 microseconds with different heat release rates (10,30 and 100) is applied to a spherical zone within the primary zone of the combustor after a quasi-steady URANS combustion and the results are evaluated. A further study, the experimental part, will be based on shock flame interaction with different strengths of shocks. Inlet and outlet total pressures will be measured via high-pressure and high-temperature pressure transducers. Any pressure gain combustion can save billions of USD as gas turbines consume 13.9% of the total energy consumption.
Modal Analysis of Turbine Blades by Means of Distributed Optical Fiber Sensors
Authors: Pennacchi Paolo , Cazzulani Gabriele , Silva Alejandro 
Published: January 2021

Abstract
This paper investigates the possibility of identifying and monitoring the modal shapes of a turbine blade by means of continuous optical fiber sensors based on Optical Backscatter Reflectometry (OBR). The advantage of this approach would be the possibility of embedding the sensors in future carbon fiber blades, in order to make this modal analysis approach available also for the blade operating conditions, since no modifications in the blade fluid-structure interaction occur. The paper describes the proposed method and provides some experimental results obtained on a 3D printed model of an existing steam turbine blade.
Aero Engine Concepts Beyond 2030: Part 2 — The Free-Piston Composite Cycle Engine
Authors: Kaiser Sascha , Schmitz Oliver , Klingels Hermann 
Published: January 2021

Abstract
Recognizing the attention currently devoted to the environmental impact of aviation, this three-part publication series introduces two new aircraft propulsion concepts for the timeframe beyond 2030. Part one focuses on the steam injecting and recovering aero engine concept. This second part presents the free-piston composite cycle engine concept. A third publication, building upon those two concepts, presents the project which aims for demonstrating the proof of concept with numerical simulation and test-bench experiments up to a technology readiness level of three.
The free-piston composite cycle engine concept is composed of a gas turbine topped with a free-piston system. The latter is a self-powered gas generator in which the internal combustion process drives an integrated air compressor. Here, several free-piston engines replace the high-pressure core of the gas turbine. Through the ability to work at much higher temperatures and pressures, the overall system efficiency can be increased significantly, and fuel burn as well as CO2 emissions reduce.
The proposed free-piston composite cycle engine design is described in detail, and the sources of thermodynamic benefits are stated. Concrete engineering solutions consider the implementation into an aircraft. The free-piston design enables lower weight and size compared to a crankshaft-bound piston engine, as no mechanical transmission and lubrication system is required. The absence of a crankshaft and connecting rods eliminates reactive forces, reduces mechanical losses, and allows higher mean piston velocities. Facilitated through air lubrication, higher cylinder temperatures are viable. The reduction of heat losses enables cooling of the piston-cylinder with core fluid. The use of a sequential combustion chamber can enhance operability and tailor the production of NOx in low-altitude operation. A discussion of emissions affecting the environment shows the potential to reduce the climate impact of aviation.
Blade Tip Clearance Measurement Systems for High Speed Turbomachinery Applications and the Potential for Blade Tip Timing Applications
Authors: Stubbs Jack David , Shahid Muhammad Arslan 
Published: January 2021

Abstract
As turbomachinery OEMs focus efforts to further increase reliability, power and efficiencies, the running clearance between blade tips and stator continue to be of the utmost importance.
This paper investigates the capability of capacitive tip clearance systems to perform individual blade tip clearance measurements on high speed rotors of up to 90,000rpm. A rotor was designed using finite element analysis; unique blade responses have been predicted.
The objective of this investigation was to consider two different approaches to the application of blade tip clearance measurements and the system requirements to accurately measure low levels of radial displacement of a target rotating between 1,000rpm and 90,000rpm. The first uses the standard approach with passive probes and the second, a new technique using active probes that have demonstrated bandwidths of 1.2MHz and increased measuring range with a lower level of measurement uncertainty. Both systems’ approaches are compared, and their capabilities are evaluated for high-speed applications.
The higher bandwidth capabilities of the latter system, combined with smaller sensor diameters, produces comparable signal rise times to the optical systems used in blade tip timing measurements. The difference in approach offers the potential of contamination resistant sensors for long term blade tip timing applications and measurement probes that do not require cooling systems to withstand higher temperature applications.
The use of different probe configurations, in a number of applications, has demonstrated a two-fold improvement in the measurement range whilst producing lower levels of noise and uncertainty when applied to blade targets made from composites, aluminium and nickel-alloy materials. The measurement data presented includes individual blade’s radial displacement, identified shaft axial displacement, effects of resonance in the test system and the identification of the main drivers of measurement uncertainty along with an achievable value. The capacitive measurement systems’ performance for blade tip clearance is analysed and reported.
The capability to perform other measurement techniques such as blade tip timing with a dual use measurement probe is also analysed and reported. This is done by correlating measurement results between the capacitive systems with that of a repeat measurement of the same target using an optical BTT system.
Soot Emission Simulations of a Single Sector Model Combustor Using Incompletely Stirred Reactor Network Modeling
Authors: Gkantonas Savvas , Foale Jenna M. , Giusti Andrea , Mastorakos Epaminondas 
Published: January 2021

Abstract
The simulation of soot evolution is a problem of relevance for the development of low-emission aero-engine combustors. Apart from detailed CFD approaches, it is important to also develop models with modest computational cost so a large number of geometries can be explored, especially in view of the need to predict engine-out soot particle size distributions (PSDs) to meet future regulations. This paper presents an approach based on Incompletely Stirred Reactor Network (ISRN) modeling that simplifies calculations, allowing for the use of very complex chemistry and soot models. The method relies on a network of Incompletely Stirred Reactors (ISRs), which are inhomogeneous in terms of mixture fraction but characterized by homogeneous conditional averages, with the conditioning performed on the mixture fraction. The ISRN approach is demonstrated here for a single sector lean-burn model combustor operating on Jet-A1 fuel in pilot-only mode, for which detailed CFD and experimental data are available. Results show that reasonable accuracy is obtained at a significantly reduced computational cost. Real fuel chemistry and a detailed physicochemical sectional soot model are consequently employed to investigate the sensitivity of ISRN predictions to the chemical mechanism chosen and to provide an estimate of the soot particle size distribution at the combustor exit.
The Effect of Hub Configuration on the Performance of an Air-Cooled Steam Condenser Fan
Authors: Meiring Z. , van der Spuy S. J. , Meyer C. J. 
Published: January 2021

Abstract
Axial flow fans used in air-cooled condensers are typically analysed with smooth rounded hubs as they offer superior performance when compared to other hub configurations. However, such a hub configuration is impractical and may increase the manufacturing and installation costs of air-cooled condensers. As such, it is desirable to use a simpler, yet effective, hub configuration in order to reduce the installation cost.
This paper assesses the impact that a simpler hub configuration may have on the performance of an axial flow fan. This is done through a comparison of three hub configurations: a cylindrical hub with a flat nose, a cylindrical hub with a hemispherical nose, and a disk hub, installed on the B2a-fan. Computational fluid dynamics modelling, utilising OpenFOAM, is used to simulate each hub configuration.
It is found that the impact on performance due to hub configuration is dependent on the volumetric flow rate through the fan. A thin disk hub exhibits superior performance at low flow rates, resulting in a 8.4% improvement in total-to-static pressure rise and a 5.7% point improvement in total-to-static efficiency. As volumetric flow rate increases, the effectiveness of the disk hub configuration reduces while the hemispherical and flat nosed cylindrical hub configurations result in similar performance metrics at the design point flow rate. At above design point flow rate, the flat nosed cylindrical hub configuration shows an improvement in performance over the hemispherical nose cylindrical hub configuration, with a 9.5% increase in total-to-static pressure rise and a 5.1% point improvement in total-to-static efficiency.