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Int. J. Turbomach. Propuls. Power, Volume 5, Issue 3 (September 2020) – 8 articles

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Open AccessArticle
Real Gas Models in Coupled Algorithms Numerical Recipes and Thermophysical Relations
Int. J. Turbomach. Propuls. Power 2020, 5(3), 20; https://doi.org/10.3390/ijtpp5030020 - 03 Aug 2020
Viewed by 142
Abstract
In the majority of compressible flow CFD simulations, the standard ideal gas state equation is accurate enough. However, there is a range of applications where the deviations from the ideal gas behaviour is significant enough that performance predictions are no longer valid and [...] Read more.
In the majority of compressible flow CFD simulations, the standard ideal gas state equation is accurate enough. However, there is a range of applications where the deviations from the ideal gas behaviour is significant enough that performance predictions are no longer valid and more accurate models are needed. While a considerable amount of the literature has been written about the application of real gas state equations in CFD simulations, there is much less information on the numerical issues involved in the actual implementation of such models. The aim of this article is to present a robust implementation of real gas flow physics in an in-house, coupled, pressure-based solver, and highlight the main difference that arises as compared to standard ideal gas model. The consistency of the developed iterative procedures is demonstrated by first comparing against results obtained with a framework using perfect gas simplifications. The generality of the developed framework is tested by using the parameters from two different real gas state equations, namely the IAPWS-97 and the cubic state equations state equations. The highly polynomial IAPWS-97 formulation for water is applied to a transonic nozzle case where steam is expanded at transonic conditions until phase transition occurs. The cubic state equations are applied to a two stage radial compressor setup. Results are compared in terms of accuracy with a commercial code and measurement data. Results are also compared against simulations using the ideal gas model, highlighting the limitations of the later model. Finally, the effects of the real gas formulations on computational time are compared with results obtained using the ideal gas model. Full article
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Open AccessArticle
Optimal Design of a Ljungström Turbine for ORC Power Plants: From a 2D model to a 3D CFD Validation
Int. J. Turbomach. Propuls. Power 2020, 5(3), 19; https://doi.org/10.3390/ijtpp5030019 - 20 Jul 2020
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Abstract
In the last few years, waste-energy recovery systems based on the Organic Rankine Cycle (ORC) have gained increased attention in the global energy market as a versatile and sustainable technology for thermo-electric energy conversion from low-to-medium temperature sources, up to 350 °C. For [...] Read more.
In the last few years, waste-energy recovery systems based on the Organic Rankine Cycle (ORC) have gained increased attention in the global energy market as a versatile and sustainable technology for thermo-electric energy conversion from low-to-medium temperature sources, up to 350 °C. For a long time, water has been the only working fluid commercially adopted in powerplants: axial and, for smaller machines, radial inflow turbines have been the preferred expanders since their gulp capacity matches the ρ-T curve of water steam. The density of most organic compounds displays extremely large variations during the expansion (and the volume flow rate correspondingly increases along the machine channels), so that Radial Outflow Turbines (ROTs) have been recently considered instead of traditional solutions. This work proposes a two-dimensional inviscid model for the stage optimization of a counter-rotating ROT, known as the Ljungström turbine. The study starts by considering five different working fluids that satisfy both the gulp requirements of the turbine and the hot source characteristics. On the basis of a limited number of geometric assumptions and for a fixed set of operating conditions, different kinematic parameters are optimized to obtain the most efficient cascade configuration. Moreover, as shown in the conclusions, the most efficient blade profile leads to higher friction losses, making further investigation regarding the best configuration necessary. Full article
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Open AccessArticle
Analysis of Nodal Diameter Zero Blade Vibrations of a Radial Turbine
Int. J. Turbomach. Propuls. Power 2020, 5(3), 18; https://doi.org/10.3390/ijtpp5030018 - 09 Jul 2020
Viewed by 199
Abstract
This paper presents results of strain gauge measurements, which have been carried out on a full-scale turbocharger test rig. Rotational speed of the turbocharger was ramped up and down through four preliminary anticipated rotor-blade resonances, with a known combination of main order of [...] Read more.
This paper presents results of strain gauge measurements, which have been carried out on a full-scale turbocharger test rig. Rotational speed of the turbocharger was ramped up and down through four preliminary anticipated rotor-blade resonances, with a known combination of main order of excitation and corresponding nodal diameter. An analysis of the transient data is presented. An investigation of spectra with high frequency resolutions, centered on individual blade resonance points in time, is presented. In contrast to former research, all blades resonate at the same point in time and thus at the same resonance frequency, if the excitation corresponds to a nodal diameter of zero. Strain data from the shaft is used to support findings, which, in other publications, often solely rely on strain data from individual blades. Full article
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Open AccessArticle
Heat Transfer Enhancement of Impingement Cooling by Adopting Circular-Ribs or Vortex Generators in the Wall Jet Region of A Round Impingement Jet
Int. J. Turbomach. Propuls. Power 2020, 5(3), 17; https://doi.org/10.3390/ijtpp5030017 - 07 Jul 2020
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Abstract
In the near future, when designing and using Double Wall Airfoils, which will be manufactured by 3D printers, the positional relationship between the impingement cooling nozzle and the heat transfer enhancement ribs on the target plate naturally becomes more accurate. Taking these circumstances [...] Read more.
In the near future, when designing and using Double Wall Airfoils, which will be manufactured by 3D printers, the positional relationship between the impingement cooling nozzle and the heat transfer enhancement ribs on the target plate naturally becomes more accurate. Taking these circumstances into account, an experimental study was conducted to enhance the heat transfer of the wall jet region of a round impingement jet cooling system. This was done by installing circular ribs or vortex generators (VGs) in the impingement cooling wall jet region. The local heat transfer coefficient was measured using the naphthalene sublimation method, which utilizes the analogy between heat and mass transfer. As a result, it was clarified that, within the ranges of geometries and Reynolds numbers at which the experiments were conducted, it is possible to improve the averaged Nusselt number Nu up to 21% for circular ribs and up to 51% for VGs. Full article
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Open AccessArticle
Comparison and Sensibility Analysis of Warning Parameters for Rotating Stall Detection in an Axial Compressor
Int. J. Turbomach. Propuls. Power 2020, 5(3), 16; https://doi.org/10.3390/ijtpp5030016 - 07 Jul 2020
Viewed by 278
Abstract
The present paper aims at evaluating the surveillance parameters used for early stall warning in axial compressors, and is based on unsteady pressure measurements at the casing of a single stage axial compressor. Two parameters—Correlation and Root Mean Square (RMS)—are first compared and [...] Read more.
The present paper aims at evaluating the surveillance parameters used for early stall warning in axial compressors, and is based on unsteady pressure measurements at the casing of a single stage axial compressor. Two parameters—Correlation and Root Mean Square (RMS)—are first compared and their relative performances discussed. The influence of sensor locations (in both radial and axial directions) is then considered, and the role of the compressor’s geometrical irregularities in the behavior of the indicators is clearly highlighted. The influence of the throttling process is also carefully analyzed. This aspect of the experiment’s process appears to have a non-negligible impact on the stall warning parameters, despite being poorly documented in the literature. This last part of this research work allow us to get a different vision of the alert parameters compared to what is classically done in the literature, as the level of irregularity that is reflected by the magnitude of the parameters appears to be an image of a given flow rate value, and not a clear indicator of the stall inception. Full article
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Open AccessArticle
Combined Optic-Acoustic Monitoring of Combustion in a Gas Turbine
Int. J. Turbomach. Propuls. Power 2020, 5(3), 15; https://doi.org/10.3390/ijtpp5030015 - 06 Jul 2020
Viewed by 342
Abstract
The need for better combustion monitoring in gas turbines has become more acute with the latest technical requirements, standards, and policies in terms of safety, environment, efficiency, operation flexibility, and operation costs. Combustion Bay One e.U. and FH JOANNEUM GmbH initiated in 2015 [...] Read more.
The need for better combustion monitoring in gas turbines has become more acute with the latest technical requirements, standards, and policies in terms of safety, environment, efficiency, operation flexibility, and operation costs. Combustion Bay One e.U. and FH JOANNEUM GmbH initiated in 2015 an experimental research program about the feasibility and first assessments of placing optical systems near the combustor. The project’s acronym “emootion” stands for “Engine health MOnitOring and refined combusTION control based on optical diagnostic techniques embedded in the combustor”. The motivation of the project is twofold. On one side, one wants to exploit the radiative feature of the flame and to transform it into a piece of reliable information about the combustion status. On the other side, this information can be useful in terms of data interpretation or data reconciliation with other information coming from other sensors such as temperature probes, fast pressure probes, or accelerometers. The focus is put on several aspects of combustor operations: on detection of the flame, on monitoring of the ignition process, on a quality assessment of combustion based on its spectral contents (including soot formation), and on the detection of possible combustion instabilities. Promising results were obtained using photodiodes that offer an adequate trade-off between narrow-band sensitivity and signal time response. It is shown that it is convenient to combine a fast-pressure sensor with an optical sensor in a compact form; this combination has led to the so-called Rayleigh Criterion Probe (RCP). The split in red, green, and blue (RGB) light components and their further analysis allows for mapping the different types of operation. Regarding the probe packaging aspect, it is discussed that the level of light collection needed to keep an acceptable signal-to-noise ratio has been so far a restraint for the use of optical fibres. Solutions are proposed to bring the optical sensor as close as possible to the optical interface and to make it operational and reliable in prevailing heat. This contribution closes with a description of the pressure tests in a new combustion facility built for this purpose. A compact and portable combustion monitoring system including at least 3 RCPs can become an instrumentation standard within the next decade. Full article
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Open AccessArticle
Gradient-Free and Gradient-Based Optimization of a Radial Turbine
Int. J. Turbomach. Propuls. Power 2020, 5(3), 14; https://doi.org/10.3390/ijtpp5030014 - 06 Jul 2020
Viewed by 208
Abstract
A turbocharger’s radial turbine has a strong impact on the fuel consumption and transient response of internal combustion engines. This paper summarizes the efforts to design a new radial turbine aiming at high efficiency and low inertia by applying two different optimization techniques [...] Read more.
A turbocharger’s radial turbine has a strong impact on the fuel consumption and transient response of internal combustion engines. This paper summarizes the efforts to design a new radial turbine aiming at high efficiency and low inertia by applying two different optimization techniques to a parametrized CAD model. The first workflow wraps 3D fluid and solid simulations within a meta-model assisted genetic algorithm to find an efficient turbine subjected to several constraints. In the next step, the chosen turbine is re-parametrized and fed into the second workflow which makes use of a gradient projection algorithm to further fine-tune the design. This requires the computation of gradients with respect to the CAD parametrization, which is done by calculating and combining surface sensitivities and design velocities. Both methods are applied successfully, i.e., the first delivers a well-performing turbine, which, by the second method, is further improved by 0.34% in efficiency. Full article
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Open AccessArticle
Experimental and Numerical Analysis of Deformation in a Rotating RC Helicopter Blade
Int. J. Turbomach. Propuls. Power 2020, 5(3), 13; https://doi.org/10.3390/ijtpp5030013 - 02 Jul 2020
Viewed by 229
Abstract
Rotating structures are important and commonly used in the transportation and energy generation fields, where a better understanding of the deformations these structures endure is essential for both the design and maintenance phases. This work presents a novel image sensing methodology for measuring [...] Read more.
Rotating structures are important and commonly used in the transportation and energy generation fields, where a better understanding of the deformations these structures endure is essential for both the design and maintenance phases. This work presents a novel image sensing methodology for measuring the displacements of rotating parts in operation due to dynamic loading. This methodology employs 3D digital image correlation combined with a custom stroboscopic lighting solution to achieve apparent stillness of the target while it rotates and then processes the acquired data to remove small imprecisions and align it to the rotor’s intrinsic coordinate system. It was applied to an RC helicopter, whose blade deformation was measured and compared with a computational model, using fluid–structure interaction between computational fluid dynamics (CFD) and finite element analysis (FEA). Using live measurement techniques, it was possible to obtain the actual behaviour of the blades, which can be used to validate and tune computational models. The proposed methodology complements the methods available in the literature, which were centred around relative out-of-plane displacements, by enabling the comparison of absolute out-of-plane and in-plane ones. Full article
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