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Int. J. Turbomach. Propuls. Power, Volume 6, Issue 4 (December 2021) – 7 articles

Cover Story (view full-size image): In many cases, fan or compressor stages have to face azimuthal flow distortion at inlet, which affects their performance and stability. These distortions can be caused by external events or by geometrical features. This work proposes a joined analysis of the flow behavior in a single axial compressor stage under flow distortion. Experimentally, the flow analysis is based on the measurements obtained by unsteady pressure sensors. The distortion is simulated by a drop of stagnation pressure ratio at the inlet boundary condition. This study focuses on the ability of a pressure drop, imposed as an inlet boundary condition in CFD, to accurately reproduce the effect of a flow distortion. Attention is then paid to the experimental level, to the arising of the rotating stall, from the onset of the instability up to completely developed stall cells. View this paper
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18 pages, 20785 KiB  
Article
Numerical Steady and Transient Evaluation of a Confined Swirl Stabilized Burner
by Federica Farisco, Luisa Castellanos, Jakob Woisetschläger and Wolfgang Sanz
Int. J. Turbomach. Propuls. Power 2021, 6(4), 46; https://doi.org/10.3390/ijtpp6040046 - 30 Nov 2021
Cited by 2 | Viewed by 3630
Abstract
Lean premixed combustion technology became state of the art in recent heavy-duty gas turbines and aeroengines. In combustion chambers operating under fuel-lean conditions, unsteady heat release can augment pressure amplitudes, resulting in component engine damages. In order to achieve deeper knowledge concerning combustion [...] Read more.
Lean premixed combustion technology became state of the art in recent heavy-duty gas turbines and aeroengines. In combustion chambers operating under fuel-lean conditions, unsteady heat release can augment pressure amplitudes, resulting in component engine damages. In order to achieve deeper knowledge concerning combustion instabilities, it is necessary to analyze in detail combustion processes. The current study supports this by conducting a numerical investigation of combustion in a premixed swirl-stabilized methane burner with operating conditions taken from experimental data that were recently published. It is a follow-up of a previous paper from Farisco et al., 2019 where a different combustion configuration was studied. The commercial code ANSYS Fluent has been used with the aim to perform steady and transient calculations via Large Eddy Simulation (LES) of the current confined methane combustor. A validation of the numerical data has been performed against the available experiments. In this study, the numerical temperature profiles have been compared with the measurements. The heat release parameter has been experimentally and numerically estimated in order to point out the position of the main reaction zone. Several turbulence and combustion models have been investigated with the aim to come into accord with the experiments. The outcome showed that the combustion model Flamelet Generated Manifold (FGM) with the k-ω turbulence model was able to correctly simulate flame lift-off. Full article
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15 pages, 17224 KiB  
Article
Transport of Swirling Entropy Waves through an Axial Turbine Stator
by Andrea Notaristefano and Paolo Gaetani
Int. J. Turbomach. Propuls. Power 2021, 6(4), 45; https://doi.org/10.3390/ijtpp6040045 - 26 Nov 2021
Cited by 5 | Viewed by 2973
Abstract
The transport of entropy waves and their impact on the stage aerodynamics are still open questions. This paper shows the results of an experimental campaign that focuses on the swirling entropy waves advection through an axial turbine stator. The research aims at quantifying [...] Read more.
The transport of entropy waves and their impact on the stage aerodynamics are still open questions. This paper shows the results of an experimental campaign that focuses on the swirling entropy waves advection through an axial turbine stator. The research aims at quantifying the aerodynamic impact of the swirling entropy waves on the first nozzle and characterizing their transport. The disturbance is generated by a novel entropy wave generator that ensures a wide set of different injection parameters. The device injects the disturbance axially, four different clocking positions are investigated. Measurements show a severe temperature attenuation of the swirling entropy wave at stator outlet. The high temperature location changes with the injection position as a result of the different interaction with the stator secondary flows. Depending on the injection position, the aerodynamic flow field is strongly perturbed by the injected swirl profile, instead the entropy wave effect is negligible. Full article
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17 pages, 10764 KiB  
Article
Data Driven Modal Decomposition of the Wake behind an NREL-5MW Wind Turbine
by Stefania Cherubini, Giovanni De Cillis, Onofrio Semeraro, Stefano Leonardi and Pietro De Palma
Int. J. Turbomach. Propuls. Power 2021, 6(4), 44; https://doi.org/10.3390/ijtpp6040044 - 25 Nov 2021
Cited by 2 | Viewed by 2980
Abstract
The wake produced by a utility-scale wind turbine invested by a laminar, uniform inflow is analyzed by means of two different modal decompositions, the proper orthogonal decomposition (POD) and the dynamic mode decomposition (DMD), in its sparsity-promoting variant. The turbine considered is the [...] Read more.
The wake produced by a utility-scale wind turbine invested by a laminar, uniform inflow is analyzed by means of two different modal decompositions, the proper orthogonal decomposition (POD) and the dynamic mode decomposition (DMD), in its sparsity-promoting variant. The turbine considered is the NREL-5MW at tip-speed ratio λ=7 and a diameter-based Reynolds number of the order 108. The flow is simulated through large eddy simulation, where the forces exerted by the blades are modeled using the actuator line method, whereas tower and nacelle are modeled employing the immersed boundary method. The main flow structures identified by both modal decompositions are compared and some differences emerge that can be of great importance for the formulation of a reduced-order model. In particular, a high-frequency mode directly related to the tip vortices is found using both methods, but it is ranked differently. The other dominant modes are composed by large-scale low-frequency structures, but with different frequency content and spatial structure. The most energetic 200 POD modes account for ≈20% only of the flow kinetic energy. While using the same number of DMD modes, it is possible to reconstruct the flow field to within 80% accuracy. Despite the similarities between the set of modes, the comparison between these modal-decomposition techniques points out that an energy-based criterion such as that used in the POD may not be suitable for formulating a reduced-order model of wind turbine wakes, while the sparsity-promoting DMD appears able to perform well in reconstructing the flow field with only a few modes. Full article
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12 pages, 5321 KiB  
Article
Experimental and Numerical Analysis of a Compressor Stage under Flow Distortion
by Alberto Baretter, Benjamin Godard, Pierric Joseph, Olivier Roussette, Francesco Romanò, Raphael Barrier and Antoine Dazin
Int. J. Turbomach. Propuls. Power 2021, 6(4), 43; https://doi.org/10.3390/ijtpp6040043 - 23 Nov 2021
Cited by 3 | Viewed by 3090
Abstract
On many occasions, fan or compressor stages have to face azimuthal flow distortion at inlet, which affects their performance and stability. These flow distortions can be caused by external events or by some particular geometrical features. The aim of this work is to [...] Read more.
On many occasions, fan or compressor stages have to face azimuthal flow distortion at inlet, which affects their performance and stability. These flow distortions can be caused by external events or by some particular geometrical features. The aim of this work is to propose a joined numerical and experimental analysis of the flow behavior in a single axial compressor stage under flow distortion. The distortions are generated by different grids that are placed upstream to the rotor. Experimentally, the flow analysis is based on the measurements obtained by a series of unsteady pressure sensors flush-mounted at the casing of the machine rotor. URANS computations are conducted using the elsA software. The flow distortion is simulated by a drop of stagnation pressure ratio at the inlet boundary condition. The study is focusing first on the ability of a pressure drop, imposed as an inlet boundary condition in CFD, to reproduce accurately the effect of a flow distortion. The analysis is conducted using singular value decomposition (SVD) and dynamic mode decomposition (DMD). A special attention is then paid, on the experimental level, to the arising of rotating stall, from the onset of the instability up to completely developed stall cells. Full article
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19 pages, 3366 KiB  
Article
Turbine Broadband Noise Predictions Using Linearised Frequency Domain Navier-Stokes Solvers
by Ricardo Blázquez-Navarro and Roque Corral
Int. J. Turbomach. Propuls. Power 2021, 6(4), 42; https://doi.org/10.3390/ijtpp6040042 - 12 Nov 2021
Cited by 3 | Viewed by 2970
Abstract
A linear frequency domain Navier-Stokes solver is used to retain the influence of turning, thickness, and main geometric parameters on turbine broadband noise. The methodology has been applied to predict the broadband interaction noise produced by a representative low-speed low-pressure turbine section. The [...] Read more.
A linear frequency domain Navier-Stokes solver is used to retain the influence of turning, thickness, and main geometric parameters on turbine broadband noise. The methodology has been applied to predict the broadband interaction noise produced by a representative low-speed low-pressure turbine section. The differences in the spectra with respect to those yielded by state-of-the-art flat plate based methodologies are up to 6 dB. The differences are caused by multiple effects that semi-analytical methodologies do not account for. The most important are blade thickness and turning, which have been studied separately to quantify their impact on the broadband noise footprint. The influence of changing the turbine operating conditions has been discussed as well. The outlet sound pressure level scales with the third and second power of the inlet and outlet Mach number, respectively, for constant turbulence intensity, within most of the frequency range considered. Full article
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15 pages, 11862 KiB  
Article
The High-Speed Cascade Wind Tunnel at the Bundeswehr University Munich after a Major Revision and Upgrade
by Reinhard Niehuis and Martin Bitter
Int. J. Turbomach. Propuls. Power 2021, 6(4), 41; https://doi.org/10.3390/ijtpp6040041 - 29 Oct 2021
Cited by 7 | Viewed by 3677
Abstract
Since its first operation in 1956 at DFL Braunschweig and after its movement to Munich, the High-Speed Cascade Wind Tunnel (HGK) at Bundeswehr University Munich is intensively used for fundamental and application-oriented research on aero-thermodynamics of turbomachinery bladings. Numerous systematic airfoil design studies [...] Read more.
Since its first operation in 1956 at DFL Braunschweig and after its movement to Munich, the High-Speed Cascade Wind Tunnel (HGK) at Bundeswehr University Munich is intensively used for fundamental and application-oriented research on aero-thermodynamics of turbomachinery bladings. Numerous systematic airfoil design studies were performed over the last decades. Thanks to the HGK facility, which enables thorough and detailed cascade testing at turbomachinery-relevant conditions, many of those airfoils for different purposes finally made it into turbomachinery applications. Nowadays, the HGK still provides very useful contributions to the understanding of the complicated flow in compressor and turbine bladings, and thereby extends the knowledge on relevant physical phenomena. As a consequence of the intense usage, this unique test facility was subject to a major revision and upgrade. The performed changes are presented within this paper including an overview on new capabilities in terms of the extended operating range, the data acquisition system, and the recently available measurement equipment. Full article
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17 pages, 4518 KiB  
Article
Experimental Study of the Leakage Flow in an Axial-Flow Fan at Variable Loading
by Edward Canepa, Andrea Cattanei, Mehrdad Moradi and Alessandro Nilberto
Int. J. Turbomach. Propuls. Power 2021, 6(4), 40; https://doi.org/10.3390/ijtpp6040040 - 20 Oct 2021
Cited by 6 | Viewed by 2955
Abstract
The present paper reports a 2D-PIV (particle image velocimetry) study of the effect of the operating point on the leakage flow in a low-speed ring fan. First, the flow pattern has been studied at 12 operating points covering the whole characteristic curve. At [...] Read more.
The present paper reports a 2D-PIV (particle image velocimetry) study of the effect of the operating point on the leakage flow in a low-speed ring fan. First, the flow pattern has been studied at 12 operating points covering the whole characteristic curve. At very low loading, the leakage flow streams along the rotor ring and is directly reingested; then, a separation bubble attached to the ring forms that, approaching the design point, modifies in a flow streaming radially outward. As the loading further increases, a separated flow region appears in the blade tip region that finally merges with the leakage flow. A further, more detailed study has been performed at eight operating points in the neighborhood of the design one. Very small loading variations may yield the leakage flow pattern modification, but no intermittence is present during the transition, as instantaneous flow patterns of any intermediate type continuously alternate. These results provide a consistent explanation for the ones of previous acoustic measurements. Full article
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