bluuebunny/crossref_metadata_2025 huggingface dataset:
Mistuning and Damping of a Radial Turbine Wheel. Part 2: Implementation and Validation of Intentional Mistuning
Authors: Nakos Alex , Beirow Bernd , Zobel Arthur
Published: October 2022

A radial turbine impeller of an exhaust turbocharger is analyzed in view of both free vibration and forced response. Due to random blade mistuning resulting from unavoidable inaccuracies in manufacture or material inhomogeneities, localized modes of vibration may arise, which involve the risk of severely magnified blade displacements and inadmissibly high stress levels compared to the tuned counterpart. Contrary, the use of intentional mistuning (IM) has proved to be an efficient measure to mitigate the forced response.

In part 1 of this three-part paper fundamental analyses have been carried out to find a suitable intentional mistuning pattern featuring only two different blade designs [1]. This part is focused on the implementation and validation of the intentional mistuning pattern and discusses the detailed geometric adaption of the turbine wheel hardware. The final design of the geometric adaption is developed in terms of manufacturability and efficiency so that a reliable and robust solution is presented. Its machined adaption is validated by both vibration testing at rest and optical measurements so that manufacturing deviations are detected and their impacts discussed and evaluated. Reduced order models are built up for checking the effect of the implemented intentional mistuning pattern on the forced response by using the subset of nominal system modes (SNM) approach introduced by Yang and Griffin [2], which conveniently allows for accounting both the design intention of the mistuning pattern and the actually machined implementation due to manufacturing deviations.
Assessment of RANS Turbulence Models on Simplified Geometries Representative of Turbine Blade Tip Shroud Flow
Authors: Uncu Fatih , François Benjamin , Buffaz Nicolas , Le Guyader Sébastien
Published: October 2022

RANS turbulence models are assessed here in simulations of simplified configurations representative of geometries and flows found in tip shrouds of low-pressure turbines rotor blades. The complex flow inside a tip shroud is highly turbulent, its boundary layer separates at the sharp angled tangential fins and reattaches in the inter-fin cavity after a recirculation. The flow in the tip seal of the rotor blade, and the jet mixing flow at the exit of the shroud cause pressure losses and influence substantially the aerodynamic performance of the turbine. Such flows are quite challenging for the RANS models. The main aim of this paper is to assess the capability of the used turbulence models to predict tip shroud representative physics of detached, reattached and jet mixing flows. The simplified geometries consist of a backward facing step, a rib roughened channel and a jet in cross-flow. The Reynolds numbers of these configurations are close to those estimated in real tip shrouds. Experimental data are available in each case to evaluate the accuracy of the simulations and understand the behavior of the models. The evaluated turbulence models include several widely used eddy-viscosity models based on Boussinesq’s hypothesis and a differential Reynolds stress model. Comparisons with measured components of the Reynolds stress tensor, turbulent kinetic energy and velocity profiles are presented. The velocity profiles are in good agreement with the measurements except in the recirculation regions, and eddy-viscosity models overpredict the level of experimental turbulent kinetic energy. Analysis of the strengths and weaknesses of the models for each flow are discussed.
Numerical Simulations of a Lifted Hydrogen Jet Flame Using Flamelet Generated Manifold Approach
Authors: Xia Yu , Verma Ishan , Nakod Pravin , Yadav Rakesh , Orsino Stefano , Li Shaoping
Published: October 2022

A turbulent lifted H2/N2 jet flame in a vitiating co-flow environment is numerically investigated, using the Flamelet Generated Manifold (FGM) combustion model with Large Eddy Simulations (LES). Due to the hot vitiated H2/air co-flow, the primary stabilization mechanism is the autoignition followed by a premixed flame. In addition to using H2 as a fuel, this flame poses two other modeling challenges: (i) the autoignition, which is a transient chemistry-driven phenomenon; (ii) the existence of multiple combustion regimes, e.g., diffusion at autoignition location but premixed in the post flame. A series of LES/FGM simulations are completed in this work by reducing the co-flow temperature from 1045 K to 1000 K. The FGM model can predict the characteristics of the flame by showing a lifted flame. It also accurately predicts the trend in the flame lift-off distance with a change in the co-flow temperature. The current results are compared for mixture fraction, temperature, and OH mass fraction at multiple locations, which have also been correctly captured. It is noted that for a high co-flow temperature (and hence a low lift-off distance), the flame’s lift-off is highly sensitive to the inlet boundary conditions and the mesh resolution near the jet entry. A relatively coarse mesh is used for all the simulations, which is generated using a careful strategy that not only resolves the jet instabilities near the fuel inlet, but also keeps the overall mesh count low and allows for a large computational time step. A systematic sensitivity analysis on the computational speed is also performed. This work provides some useful guidelines in simulating the H2 diluted flames using the FGM model, which may be valuable to the gas turbine industry.
Numerical Investigation on the Effect of Fuel Injection Location in a Multi-Swirl Lean Direct Injection Burner
Authors: Sarath Perikathra , Aditya Raparti Jogesh , Muruganandam T. M.
Published: October 2022

The lean direct injection (LDI) concept can potentially replace the existing combustion systems for future aircraft engines because of its low NOx emissions without compromising other parameters. A novel multi-swirl LDI burner1 with distributed fuel injection surrounded by airflow through multiple hexagonal swirlers of vane angle 45° was developed. The flow dynamics and combustion characteristics of three different fuel injection LDI configurations were compared using a three-dimensional (3D) computational fluid dynamic (CFD) study. Realizable k-ε turbulence model with a scalable wall function was adopted to get the flow features, distribution of velocity, pressure, and turbulent kinetic energy in the swirl burner, and combustion was parameterized by using non-premixed steady diffusion flamelet model with a PDF approach. Results obtained in the numerical model for temperatures and mole fractions of CO2, O2, and mass fraction of NOx show a behavior similar to that of the experimental model. Four types of flow structures were present in the flow field, and interaction of these structures plays an essential role in rapid mixing and flame stabilization. The numerical results showed that the LDI-2A burner achieved better mixing and had a lower flame temperature than the other two burners, which would improve flame stability and reduce the NOx emission.
Hysteresis and Bi-Stability in Transversely Excited Swirling Flows
Authors: Gupta Ravi , Gohiya Rajat , Vempati Chandan , Hemchandra Santosh , Panda Pratikash
Published: October 2022

In this work, we investigate the effect of transverse acoustic excitation on non-reacting swirling jets. The work is motivated by the azimuthal instabilities in annular gas turbine combustors which are one of the major challenges in aero-engines. Annular combustion chambers have a longer circumferential length in comparison to their length or height. As a result, thermoacoustic instabilities are driven by azimuthal acoustic modes. We have designed and fabricated a multi-nozzle (up to three nozzles) linear array combustor to simulate the flow conditions of an annular combustor. The nozzle features a dual co-rotating radial swirler, with a flow split of 44% and 56% between the primary and secondary swirlers. Two compression drivers (power 400 W each) placed on either side of the combustion chamber are used to generate acoustic fields in the direction transverse to the flow. Simultaneous 2D PIV and high-frequency pressure measurements are conducted to measure the time-averaged velocity field and the chamber acoustics, respectively. The time-averaged flow field of the quiescent swirling jet shows a typical low swirl number flow-field that features a narrow recirculation zone surrounded by a high-velocity annular jet. It is observed that once the swirling jet is excited with a transverse acoustic forcing, it instantaneously transitions to a conical type of vortex breakdown (CVB). However, this phenomenon is observed only above a threshold value of perturbation amplitude. In this condition, the flow moves radially outward and remains attached to the walls on either side of the nozzle, and is characterized by a recirculation zone with strong a negative axial velocity. It is a known phenomenon that swirling jets transition to a CVB upon transverse acoustic excitation. However, to the best of our knowledge, this is the first instance where it is shown that transverse acoustic excitation can lead to a bistable state in swirling flows. We investigated the acoustic response to low-amplitude forcing on the combustion chamber by performing a forced acoustic response analysis using COMSOL. It is observed that acoustic forcing leads to a peak response of the radial and azimuthal velocities at the flare of the swirler, which could induce an axisymmetric deflection of the jet shear layer pushing it into a CVB state. In the case of a multi nozzle array of three identical swirlers, we observed that the external acoustic forcing changes the time averaged base flow of the central nozzle.
Extension of Fuel Flexibility for Siemens Energy SGT-300-2S Dry Low Emission Combustion System
Authors: Hubbard Phill , Beita Jadeed , Liu Kexin , Sadasivuni Suresh , Bulat Ghenadie
Published: October 2022

This paper reports the results of high-pressure combustion rig testing carried out to assess the fuel flexibility of the standard Siemens Energy SGT-300-2S dry low emission (DLE) combustion system operated at engine conditions across a wide range of engine loads and ambient conditions. Variations of the fuel heating value, with Wobbe Index (WI) of 23 MJ/Sm3, 25 MJ/Sm3, 27.5 MJ/Sm3, 30 MJ/Sm3 and 45 MJ/Sm3 (UK natural gas) at standard conditions1, were achieved in a mixing plant by blending natural gas with CO2 as diluent. Emissions, fuel pressure, combustion dynamics, and flashback monitoring via measurement of burner and combustor can metal temperatures were the main parameters used to assess the effect of fuel flexibility on combustor performance. Test results show that NOx emissions decrease as the fuel heating value is reduced due to lower adiabatic flame temperatures for the MCV (Medium Calorific Value) fuels. CO emissions performance was found to be unaffected. However, decreasing fuel heating value leads to a requirement to increase the fuel supply pressure as a consequence of higher volumetric fuel flow rate to achieve the heat input requirements of the gas turbine. Combustion dynamics characteristics were found to be similar for the different fuel compositions. The impact of fuel heating value change on turbine nozzle guide vanes and blades was also investigated by measuring the combustion hot gas temperature profile at the exit of transition duct. The results show that there is no significant change in turbine entry temperature profile in terms of maximum temperature and pattern factors.

The successful development program has expanded the capability of the SGT-300-2S standard production DLE combustor to operate with a range of fuels covering a WI range of 25 MJ/Sm3 to 49 MJ/Sm3. The test results obtained on the SGT-300-2S combustion system provide significant experience for industrial gas turbine burner design for fuel flexibility.
Investigation of the Interaction Between Tip Leakage and Main Annulus Flow in the Large Scale Turbine Rig: Comparison of Different Rotor Tip Geometries
Authors: Ade Dominik , Eitenmüller Johannes , Leichtfuß Sebastian , Schiffer Heinz-Peter , Lyko Christoph , Schmid Gregor
Published: October 2022

Shroudless rotor blades are state of the art in modern high pressure turbines. Tip leakage flow has a crucial impact on turbine efficiency. Specific blade tip designs are a key factor to handle tip leakage losses by controlling tip leakage flow and its re-entry into the rotor passage.

Comparative measurements of a cavity squealer type tip and a notch type tip have been conducted at the Large Scale Turbine Rig at TU Darmstadt. The test rig has been operated at the blade tips design point. Experimental data has been acquired at rotor inlet and outlet as well as within the rotor passage.

For cavity squealer tips a tip leakage vortex develops at the suction side as the tip leakage flow is rolled-up and further mixed with main annulus flow. The tip leakage vortex determines the blockage of main annulus flow at the blade tip. The design of the suction side of the notch tip benefits a jet-like re-entry of tip leakage flow into the passage. Results are a vortex system with smaller scaled vortices and a more homogeneous mass flow redistribution in the outer annulus of the rotor. The zone of affected main annulus flow at the blade tip increases through the dominant tip leakage jet.
Flow Through a Steam Turbine Cascade With a Single Damaged Blade: Effect of Blade Height on Loss and Outflow Angle Distribution
Authors: Schmalacker Michael , Cakievski Leon , aus der Wiesche Stefan , Schatz Markus
Published: October 2022

Flow measurements were made in a steam turbine cascade with a single blade of reduced height modeling a blade damage. In the experiments, the height of the single blade varied from full span (i.e., no tip clearance) up to totally removing the blade. The experimental investigation was supported by computational fluid dynamics (CFD) simulations which enabled further insight into local flow phenomena and mechanisms. It was found that the additional loss due to a gap increased strongly for the usual clearance level of a few percent of the blade chord but reached a relatively stable high loss plateau for higher clearances or rudimentary blades in the cascade flow channel. The tip-leakage vortex remained to be the dominant downstream flow feature and contains a high amount of loss, but for rudimentary blades, it transforms to the vortex pattern also observed for finite wings. Regarding the impact on the outflow angle distribution, the local downstream flow field can be interpreted by using the relations for cascades with high and low solidity.
Pollutant Emissions Reporting and Performance Considerations for Hydrogen-Hydrocarbon Fuels in Gas Turbines
Authors: Douglas Christopher M. , Shaw Stephanie L. , Martz Thomas D. , Steele Robert C. , Noble David R. , Emerson Benjamin L. , Lieuwen Timothy C.
Published: October 2022

Hydrogen (H2) fuel for gas turbines is a promising approach for long duration storage and dispatchable utilization of intermittent renewable power. A major global discussion point, however, is the potential air quality impact of hydrogen combustion associated with nitrogen oxide (NOx) emissions. Indeed, several studies in the combustion literature have reported elevated NOx concentrations in terms of dry ppmv NOx at 15% oxygen (O2) as a fuel’s H2 fraction is increased. Yet, as emphasized in this work, this practice of directly comparing emissions on the basis of dry ppmv at a reference O2 concentration (ppmvdr) is inappropriate across hydrogen and hydrocarbon fuel blends due to differing concentration changes induced by drying and referencing the corresponding exhaust gasses. This paper addresses three distinct approaches for comparing emissions consistently across fuel blends. Furthermore, it presents examples that quantify the differences in the apparent pollutant emissions between each approach and the usual ppmvdr reporting practice across the full range of hydrogen-methane mixture ratios. In the first approach, ppmvdr emissions values are related to their actual volume concentration. Here, our calculations demonstrate that hydrogen and methane flames producing the same true pollutant concentration exhibit a 40% relative difference in ppmvdr values, resulting in a significant potential exaggeration of NOx emissions for high %H2 fuels. However, this concentration-based approach does not account for changes in the volumetric flow rate of exhaust gasses or the slightly different amounts of heat release required to achieve the same flame temperature across fuels. These effects are captured naturally in the second approach, where the emissions are quantified in terms of the emitted mass per unit of heat release. With this cycle-independent approach, our comparative calculations at equal mass-per-heat emission rates reveal 36% higher ppmvdr values for hydrogen flames than methane flames. Finally, the third approach accounts not only for the thermodynamic properties of the mixture, but also for the system’s overall cycle efficiency, which is shown to depend weakly upon the fuel composition. This method quantifies emissions in terms of the emitted mass per unit of useful shaft work output, a metric also used by environmental regulators. Illustrative results within a simulated F-class gas turbine cycle are presented, indicating 39% higher ppmvdr values for hydrogen flames at equal mass-per-work emission rates. Hence, in all of the considered approaches, ppmvdr emissions values are inflated for H2 fuel blends relative to hydrocarbon fuels, making them unsuitable for direct comparisons of emissions among conventional and alternative fuels.
Numerical Investigation of a Turbine Vane Frame for Co- and Counter-Rotating Configuration
Authors: Krajnc Nicolas , Merli Filippo , Hafizovic Asim , Peters Andreas , Göttlich Emil
Published: October 2022

This paper presents the numerical comparison of a turbine vane frame (TVF) for future high-bypass turbofan engines for architectures with a co-rotating setup between the high-pressure turbine (HPT) and the low-pressure turbine (LPT) and with a counter-rotating setup. The flow field in the TVF is impacted by the decision of a co- or counter-rotating architecture which is driven not only by aerodynamics but also by the dynamic and mechanical design constraints in an engine.

As boundary conditions for the steady RANS simulation, measurements are used which were carried out in the engine-representative two-spool rig at the Institute for Thermal Turbomachinery and Machine Dynamics at the Graz University of Technology. The test vehicle in this rig consists of an HPT with nearly axial exit flow and a counter-rotating LPT connected via the TVF with aft-loaded struts and splitters. To reproduce a realistic HPT flow field, purge air is provided by a secondary air system (SAS). The inlet and outlet boundary conditions are defined based on the five-hole probe (5HP) measurement set up- and downstream of the TVF, acquired for three different purge conditions (0%, 100% = nominal, and 200%).

To simulate a co-rotating configuration, the measured inlet flow field has been mirrored. The focus of this paper is to gain additional insights into the general flow behavior of a TVF in a co- and counter-rotating configuration, respectively. A special focus is placed on the differences between the development of strut secondary flows on their way through the TVF depending on the inlet flow field. Additionally, a duct loss comparison of the two configurations and its sensitivity to different purge flow levels is presented.
An Investigation of Non-Linear Surge Characteristic in a High-Speed Centrifugal Compressor
Authors: Hayashi Yoshihiro , Cao Teng
Published: October 2022

In centrifugal compressors, it is common to observe a rapid reduction in surge margin towards high rotational speed, which shows a non-linear surge characteristic against the change of rotational speed. This paper presents a comprehensive experimental and numerical study to understand the flow mechanisms leading to the non-linear surge behavior in a highspeed centrifugal compressor. It shows that for the studied compressor there are two critical flow coefficients (ϕ = 0.255 and 0.136) where the stability of the compressor stage is significantly weakened. At a higher speed, the impeller rotating stall happens at the first critical point where the diffuser instability is also enhanced. This is caused by the increase of the flow non-uniformity at impeller exit as well as increased diffuser inflow angle due to the impeller compressibility effect. Therefore, both the impeller and diffuser’s instability are matched and trigger the surge at a high flow coefficient. In contrast, at a lower speed, the diffuser instability is not enhanced by impeller rotating stall, this mismatch of the two component’s instability allows the compressor to pass through the first critical point and extend the surge limit to the second critical point where the diffuser reaches the stability limit and causes the rotating stall spontaneously. By these different behaviors in each speed, the non-linearity of surge characteristic is established.
A New Approach to Estimate Particulate Matter Emissions From Ground Certification Data: The nvPM Mission Emissions Estimation Methodology (MEEM)
Authors: Ahrens Denise , Méry Yoann , Guénard Adrien , Miake-Lye Richard C.
Published: October 2022

Estimating non-volatile Particulate Matter (nvPM) — or black carbon — emissions during an aircraft mission is extremely challenging because of the lack of reliable data in flight. For this reason, a detailed study has been undertaken to estimate in-flight emissions from data measured on the ground during engine certification. Aircraft engine emissions certification is based on the “Landing and Take-Off” (LTO) cycle developed by the Committee on Aviation Environmental Protection (CAEP) of the International Civil Aviation Organization (ICAO). It represents operations below 3000ft. The aim of this regulation is to control and reduce pollutant emissions in the vicinity of the airport. Carbon monoxide (CO), unburnt hydrocarbon (UHC), and Nitrogen oxides (NOx) have been regulated using the LTO cycle by different international standards for four decades. New certification standards on nvPM have been introduced recently. The first one, put in place in CAEP10, regulates the peak nvPM mass concentration. It has been in effect since 2020. The second set established in CAEP11 regulates the nvPM mass and number emissions on the LTO cycle and it becomes effective in 2023. With these regulations, manufacturers are now reporting nvPM emissions data publicly. All emissions data of in-production engines, and some legacy engines, are available in the engine emissions data bank (EEDB), downloadable from the European Union Aviation Safety Agency (EASA) website [1]. Methodologies have been proposed to estimate emissions at altitude and calculate total mission emissions for NOx, i.e. the “Boeing Fuel Flow Method” [2] or the “DLR Döpelheuer and Lecht” [3–5] methodology, which are only relying on these publicly available data from the EEDB. In the following, a new methodology for estimating nvPM emissions at altitude is proposed. The methodology was developed and validated in the framework of the CAEP technical working groups. It comprises four dedicated steps. In the present article, the different steps are explained and validation data is provided as applicable. Examples of in-production engines are analyzed, discussed, and compared against the full methodology using proprietary engine performance and emissions certification data. Following the proposed methodology, total nvPM mass and number mission emissions can be estimated and used for emissions inventories and evaluation of climate impacts.
Investigation of the Impact of Realistic Inlet Distortions on a 1.5-Stage Transonic Compressor
Authors: Werner Jan , Karl Maximilian , Mütschard Silas , Schiffer Heinz-Peter , Biela Christoph , Robens Sebastian
Published: October 2022

In this study the aerodynamic impacts of inlet distortions caused by a gas turbine inlet manifold are analyzed experimentally. The investigation is performed at the new transonic compressor test rig at Technical University of Darmstadt, that features high modularity and extensive instrumentation. The existing axial air inlet system of the test rig is replaced by a scaled inlet manifold. Analog to the design of a real gas turbine intake, bearing support struts are integrated in the experimental setup to investigate their interaction with the inlet distortions.

For the detailed analysis of compressor performance, the measurement systems were extended to resolve the flow over the whole circumference at three different axial positions. At the stage inlet a traversable rake with radially distributed five hole probes allows the quantification of the inflow conditions. To determine global compressor characteristics and analyze the propagation of inlet distortions through the compressor, a fully traversable instrumentation at the stage exit is installed. Additionally, a 360°-traversable rotor casing ring, instrumented with unsteady measurement systems, enables the analysis of the effects of non-uniform inflow conditions on the unsteady flow field of the rotor.
Study on the Non-Reacting Flowfield Characteristics of Lean Premixed Injector Modules With the Convergent Outlet
Authors: Sun Fujun , Suo Jianqin , Guo Luhua
Published: October 2022

To form lifting flame and prevent auto-ignition and flashback, this paper proposed an original lean premixed injector with a convergent outlet. The influence of key structures (swirler-vanes angles, swirler-vanes profiles and premixing section lengths) on flowfield characteristics of lean premixed injector was investigated by the combination of laser diagnostic experiments and numerical simulations. The results show that there is a stable and sizeable detached central recirculation zone (CTRZ) downstream of the all six injectors and the detached distance from the convergent outlet decreases with the increase of the swirl number (SN) of the injector. With the increase of the swirler-vanes angle or the premixing section length, the SN of the injector increases, resulting in the CTRZ closer to the convergent outlet. Compared with the straight swirler-vanes, the SN of the curved swirler-vanes with the same angle is smaller, and the size of the its CTRZ is smaller and more backward. In addition, The peak value of the reflux ratio, which is also an important parameter to measure the flowfield characteristics, increases with the increase of the SN of the injectors.
Assessment of Two Harmonic Balance Method-Based Numerical Strategies for Blade-Tip/Casing Interactions: Application to NASA Rotor67
Authors: Vadcard Thibaut , Colaïtis Yann , Batailly Alain , Thouverez Fabrice
Published: October 2022

The study presented in this paper focuses on the analysis of rubbing interactions — including unilateral contact and dry friction — between a rotating fan blade and a rigid casing by frequency domain methods. Two previously published Harmonic Balance Method-based methodologies are assessed: 1) an approach relying on augmented lagrangians and 2) a second method using a regularized penalty law combined with a Lanczos σ-approximation filter. Asa reference point for this comparison, a time-domain numerical strategy relying on a Lagrange multiplier-based contact treatment is considered. All computations are run with the NASA rotor 67 fan blade, an open industrial blade geometry. As it undergoes structural contacts, this blade features an intricate dynamics response, thus making it a challenging case study for nonlinear iterative solvers. The contact scenario is chosen to be an ovalization of the casing with no external forcing. This scenario induces highly nonlinear reponses of the blade and complex phenomena such as isolated frequency response curves. The results presented underline a very good agreement of the different strategies with the reference time marching approach. An in-depth comparison is made with an emphasis on nonlinear frequency response curves and time signals. In order to investigate further onto the frequency domain strategies, a comparative analysis is carried out on isolated nonlinear frequency response curves, referred to as isolas. Finally, a physical analysis of these isolas is presented through an in-depth investigation of the main modal contributions for each computed solution. In the end, this paper provides new qualitative elements allowing for a better understanding of rubbing interactions that may not be efficiently obtained with time marching procedures.
Symmetry Breaking in an Experimental Annular Combustor Model With Deterministic Electroacoustic Feedback and Stochastic Forcing
Authors: Humbert Sylvain C. , Orchini Alessandro , Paschereit Christian Oliver , Noiray Nicolas
Published: October 2022

In this study, we use an annular combustor experimental model with electroacoustic feedback to investigate systematically the effect of stochastic forcing and of non-uniform flame response distribution on azimuthal thermoacoustic modes. We break the symmetry of a nominally degenerate mode of azimuthal order m by imposing a non-zero 2m Fourier component of the flame gain, b2m, and of the time-delay, ε2m. Various orientations between the gain and the time-delay staging patterns are considered. In addition, stochastic forcing is introduced. First, all experiments are performed without noise, as well as at the maximum noise intensity. We observe that the mode nature that dominates in the presence of an intense noise may be far from the one observed in noise-free conditions. To better understand the effect of noise in the presence of asymmetries, we repeat some of the experiments at various noise intensities. Although our results confirm that for the axisymmetric configuration and for some asymmetric configurations pure spinning modes are never reached, we also observe some radically different behaviors. For a noise-free experiment leading to a purely standing mode, the introduction of a sufficient amount of noise can lead to beating. We also observe that, for a mode that is nearly standing in the absence of noise, an increase in the noise intensity leads to the predominance of mixed modes with a clearly favored spinning direction. We explain our experimental results with the aid of low order models.
Acoustic Localisation of High-Pressure Burst in a Confined Space
Authors: Bacci David , Ireland Peter , Hussain Zahid
Published: October 2022

Current turbofan systems are designed to be robust to high-pressure pipe rupture, inside their structure. Such failure event is typically detected through slow-response thermocouples Nevertheless, this approach has several limitations and typically requires sensing equipment to be placed close to harsh environmental areas.

An alternative route is represented by the introduction of an acoustic sensor, capable to detect the associated blast generated by the sudden breach of air through the fissure.

The aim of the study is to explore the feasibility of the concept of locating a sudden pressure rise (representing pressurised pipe rupture) in a closed environment, representative of the typical volume between the engine core and nacelle. A new system to locate the position of a burst, based on the analysis of an acoustic footprint, is presented and its performance is analysed.
Acoustic Flame Transfer Function Measurements in a Liquid Fueled High Pressure Aero-Engine Combustor
Authors: Venkatesan Krishna , Cross Arin , Han Fei
Published: October 2022

This paper describes an experimental approach and study of thermo-acoustic flame transfer functions in a high-pressure liquid-fueled rich burn combustor. The presence of high background flame luminosity in high-pressure sooty flame combustors precludes the application of any direct optical flame transfer function method. Instead, an acoustic method based on multiple microphones was employed to characterize the combustor acoustic pressure and velocity responses to acoustic forcing. A high-pressure siren device was employed to acoustically excite the combustor air flow over a broad range of frequencies from 150–1000Hz and modulate the combustor inlet dynamic pressure amplitudes. The acoustic pressures measured from the microphones located upstream and downstream of the flame were processed to obtain swirler impedances and flame transfer functions. Nonlinear behavior of the liquid fuel flame transfer function was studied by systematically varying the siren excitation pressure amplitudes. A parametric study of varying inlet air pressure, inlet air temperature, and thermal power was performed to study the impact of operating conditions on the measured liquid flame transfer function.
Development of an Acoustic Excitation Test Bench to Support the Validation of Bladed Disks
Authors: Ligot Jérôme , Denis Sophie , Hoffait Sébastien , de Cazenove Jean , Golinval Jean-Claude
Published: October 2022

This paper proposes a mixed hardware and software solution to impose different controlled dynamic load patterns to a bladed disk using non-intrusive acoustic excitation. The test bench is coupled to an autonomous measurement system consisting of an infrared Laser Doppler Vibrometer (LDV) placed on a robotic arm.

The development of the test bench is described from the definition of the requirements up to the calibration of the different components (acoustic excitation devices, power amplifiers, LDV positioning, etc.). The relation between the supplied voltage and the resulting pressure acting on the blade is also assessed.

The main application of the developed test bench consists in the imposition of Standing or Traveling Waves Excitation in order to appropriate a given nodal diameter content and experimentally study the response to typical excitation pattern encountered when integrated on motor.

Another application consists in the experimental mistuning measurement through modal analysis and the use of the Inverse Component Mode Mistuning method.
Experimental Investigation on the Accuracy of Blade Tip Timing Spectral Analysis Methods
Authors: Xiao Zhicheng , Meng Yiming , Ouyang Hua
Published: October 2022

The amplitude of spectral analysis of the tip timing data from individual blade observations is significant to turbomachinery health monitoring and aeroelastic researches. The accuracy of non-uniform discrete Fourier transform (NUDFT), extended discrete Fourier transform (EDFT), and compressed sensing (CS) is studied systematically. The benchmark data is obtained on a novel test bench where blade tip displacement can be acquired by laser displacement sensor directly. In the experiment, all three methods can successfully recognize the dominant 1F vibration but fail to discover the underlying 1T component. The accuracy of NUDFT to estimate the transient amplitude is approximately 69%. For EDFT and CS, the values are 30% and 84%, respectively. The number of cycles included in an analysis batch is found to influence the results. The robustness of the methods is discussed. The three methods are applied to a single-rotor rig and NSV is discovered in a field test. All of them could capture the frequency feature. It is determined that the blade is vibrating in the first flex mode. The difference between the measured frequency and the simulation is only 2.7%. Regarding the amplitude, CS yields the most convincing estimations.
Large Eddy Simulations of Wind Turbine Flows
Authors: Dabas Jérôme , Gicquel Laurent , Odier Nicolas , Duchaine Florent
Published: October 2022

The development of the wind energy sector has to come with an increase in wind turbine and wind farm efficiency. This increase can be achieved through the use of CFD tools that allow to accurately predict, at a reasonable cost, the efficiency of new wind turbine designs, wind farm layouts and control strategies. In this context, high order CFD tools such as the ones based on the LES approach are required to develop and calibrate lower order models that can be used for industry purposes. The aim of the present study is to assess the ability of CERFACS’ LES solver developed for turbo-machinery applications — AVBP — to perform high fidelity simulations of wind turbine flows.

To this end, a wall-modelled approach was chosen to describe the boundary layer on the blades. In addition, A static mesh adaptation method was developed to optimise the mesh size while accurately resolving the turbine wake. Finally, a Pressure Gradient Scaling method [1] was applied to artificially relax the compressible flow CFL condition to a low-mach one and increase the time step.

The aforementioned framework was assessed on reduced wind turbine configurations developed and experimentally investigated by NTNU. Although the Reynolds number of these configurations is one to two orders of magnitude inferior to real wind turbine one, the controlled boundary conditions and the available experimental data make these configurations particularly interesting for code validation. Two configurations have been simulated.

The results show the ability of the numerical approach to capture the transition between near and far wake and the interaction between inflow turbulence and the wake. The comparison with experimental measurements shows that simulations accurately predict the velocity deficit and recover the right amount of turbulent kinetic energy at the beginning of the far wake. As a conclusion, the framework developed in this study is adapted to reduced turbine computation yet it has to be further validated on real scale wind turbines.
Impact of Operating Conditions on Rotor/Stator Interaction of a High-Pressure Ratio Centrifugal Compressor
Authors: Lottini Fabrizio , Agnolucci Andrea , Pinelli Lorenzo , Pacciani Roberto , Toni Lorenzo , Guglielmo Alberto , Grimaldi Angelo
Published: October 2022

The current design trend of centrifugal compressors is aimed at obtaining compact machines with high pressure ratios and performance. This leads to high circumferential speeds and lighter components, thus increasing static stresses and dynamic forcing due to rotor/stator interactions. Therefore, the aerome-chanical characterization of these machines is a fundamental step of the design chain. This paper presents an in-depth aerome-chanical study of a high-pressure ratio centrifugal compressor using CFD. Firstly, the computational setup is validated against the experimental data; then, the same numerical setup is used to characterize the aeromechanical interactions between the impeller and the upstream and downstream static components. The URANS simulations are carried out at three different operating points (near stall, design, near choke), and the unsteady flow field is time and space decomposed showing higher forcing functions at near stall and near choke conditions with respect to the design point, as confirmed by the experimental acquisitions. The presented results highlight the importance of extending the aeromechanical evaluations to different operating points in order to avoid unexpected vibration responses when operating at off-design conditions. Finally, by virtue of an acoustic post-processing techniques, the unsteady pressure coupling in the inter-row region is analyzed to discern the main sources of the overall unsteady interaction.
Stabilization of Low-NOx Hydrogen Flames on a Dual-Swirl Coaxial Injector
Authors: Leroy Maxime , Mirat Clément , Renaud Antoine , Vicquelin Ronan
Published: October 2022

Hydrogen-fuelled carbon-free energy is a growing prospect for the future of several industries, among them the aeronautical and energy generation sectors. However, the transition to hydrogen comes with several challenges: flame stabilization due to the unique combustion properties of hydrogen compared to conventional fuels and control of nitrogen oxides (NOx) production due to the higher combustion temperature. In addition, the high flammability of hydrogen poses an increased risk of flashback in premixed configurations commonly used to generate low-NOx flames. As a consequence, research into strategies for low-NOx hydrogen combustion is developing, and several technologies are being considered for industrial use. Among these technologies, we consider here a dual swirl coaxial injector operated in non-premixed conditions. This setup enables the stabilization of multiple types of flame structures that are parametrically investigated for their NOx emissions. The flame structure is observed using OH* chemiluminescence images collected using an intensified CCD camera equipped with a band-pass filter. Exhaust gas species mole fractions of NO, NO2 and O2 are measured using NDIR gas detectors and a paramagnetic sensor. This investigation reveals that stabilization of hydrogen-air flames on the double swirl injector is possible and that varying the flow parameters induces changes in structure that affect NOx emissions, independently of swirl level, residence time and temperature that also play a role. The study is carried out at atmospheric pressure.
Flow Visualization Study From a Flat Plate With Multiple Impinging Jets for Different Cross-Flow Schemes
Authors: Dhanasegaran Radheesh , Pugazhendhi Ssheshan
Published: October 2022

A flow visualization study has been carried out computationally on a flat plate with a 5 × 5 array of impinging jets for different cross-flow schemes. The k-ω SST turbulence model is used for carrying out the RANS simulations. The parameters investigated are (i) cross-flow schemes (minimum, medium & maximum), (ii) jet-to-plate spacing (H/D = 1, 2, 3 & 5) and (iii) turbulent jet Reynolds numbers (15000, 25000 & 35000). The topology and three-dimensional separation phenomena are used to explain the flow and heat transfer characteristics. The skin friction lines on the interaction surface are explained with the help of nodal points of attachment and separation, saddle point, separation, and attachment lines. It is observed that the skin friction lines change their pattern with H/D and cross-flow. Peaks in the heat transfer are observed corresponding to the impingement point and wall jet interaction points. At lower H/D values, the effect of cross-flow is more prominent. However, these effects are marginal for higher H/D values. For lower H/D, the localized heat transfer rates are high but the uniformity in heat flux is obtained with an increase in H/D. In maximum and medium cross-flow cases, the heat transfer pattern changes with the distance from the center of the plate. It is found that the flow structure on the surface is independent of the jet Reynolds number.
Dynamic Seal Test Rig: O-Ring Leakage and Sliding Friction Measurements
Authors: Kerr Thomas , Nielson Jordan
Published: October 2022

Sliding seals play a critical role in the dynamic sealing of a wide-variety of machinery applications. There are many type of sliding seals, such as segmented carbon ring, O-ring, or bellows; and are used as sealing elements in hydraulic rod and piston seals, as well as secondary sealing elements in mechanical and dry-gas seals. Motion between the dynamic and static parts of the machine is most often lubricated by the process fluid, and therefore has leakage. This paper presents a new test rig capable of measuring leakage and friction force of annular sliding seals for a range of sealing pressures (0–24.8 MPa), temperatures (20–700 C), gasses, and motion. The rig is capable of large linear motions and high frequency dynamic motion. The large linear motion replicates piston movement or shaft thermal growth and the dynamic excitation matches the typical vibration response from a spinning shaft. Currently, there is little available information in the literature on the leakage performance of dynamic O-rings at high pressures, especially for gas sealing. The paper presents experimental results from two different material, 150 mm diameter, O-rings at sealing pressures up to 70 bar (1,000 psi) in CO2. The rings were tested for large ranges of motion, up to 4 mm. Two different durometer FKM O-rings (70 and 90) were compared to a 70 durometer BUNA O-ring. The softer rings exhibited superior leakage performance, and similar friction forces. The BUNA O-ring performed slightly better at sealing (10–20%) then the similar hardness Viton ring.
Tip Vortex Effects on Air-Cooled Condenser Axial Flow Fan Performance
Authors: Pretorius Johannes P. , Van Der Spuy Sybrand J. , Strümpfer Martin
Published: October 2022

Air-cooled Condensers (ACCs) are often used as main cooling system in modern power generation applications. These systems employ a multitude of large diameter axial flow fans, which draw power and reduce the net power produced by the power station. The improvement of fan operational efficiencies could therefore have a considerable positive influence to reduce these parasitic loads. This study aims to reduce the effect of blade tip vortices in order to improve fan performance. This is achieved through the addition of endplates at the blade tips. Previous work only drew preliminary conclusions, due to constraints in testing at a representative large tip clearance and the necessity to test at reduced speeds to avoid contact between the tip appendages and the fan casing. Through the introduction of a new fan hub design, experimental investigations are repeated on the same ACC scale fan to evaluate the effect of two tip endplate designs on fan performance. Results from testing confirm previous preliminary findings — increased fan static pressure rise and fan static efficiency are found when incorporating blade tip endplates, compared to the unmodified fan.
The Development of Turboexpander-Generators for Gas Pressure Letdown Part 3: Design Validation
Authors: Najeeb Ovais Ahmed Bin , Khatri Rasish , Zheng Liping , Liu Jeremy
Published: October 2022

This paper is a follow-up to GT2021-60125 (“Design and Analysis”) and GT2021-60317 (“Economic Analysis”), which collectively covered the design, analysis, and economics of innovative Turboexpander Generators (TEG) used in pressure letdown (PLD) applications. This paper describes the testing data of a family of TEGs, 280 kW and 125 kW, for natural gas pressure letdown applications. The TEGs are supported by active magnetic bearings (AMB). Machine design for the two TEGs is very similar for ease of manufacturing and control system design, with wheel design being the primary difference. A comprehensive controls analysis and AMB closed-loop dynamics study were presented earlier. This paper compares predicted and measured transfer functions along with the pre and post brush seals installation data. Drop testing results on the touchdown bearing are shown along with the full-speed touch-down events. Active front-end variable speed drive (VSD) design is presented along with the power generation results. Finally, measured force vs deflection data is presented for a tolerance ring, used as the resilient element for the touchdown bearings.