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Int. J. Turbomach. Propuls. Power, Volume 2, Issue 1 (March 2017) – 3 articles

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1467 KiB  
Article
CFD-Based Investigation of Turbine Tonal Noise Induced by Steady Hot Streaks †
by Axel Holewa, Sergey Lesnik, Graham Ashcroft and Sébastien Guérin
Int. J. Turbomach. Propuls. Power 2017, 2(1), 3; https://doi.org/10.3390/ijtpp2010003 - 21 Mar 2017
Cited by 6 | Viewed by 3458
Abstract
The interaction of steady hot streaks from an annular ring of combustion chambers with turbine rotating blades can potentially generate tonal noise. The relevance of this source mechanism in aeroengine noise is controversially discussed in the literature. In the present paper, the streak–turbine [...] Read more.
The interaction of steady hot streaks from an annular ring of combustion chambers with turbine rotating blades can potentially generate tonal noise. The relevance of this source mechanism in aeroengine noise is controversially discussed in the literature. In the present paper, the streak–turbine interaction is investigated using the computational fluid dynamics (CFD) method called harmonic balance (HB)—a truncated non-linear frequency domain approach with a high potential of reducing the computational effort. The investigated high-pressure turbine is composed of a single stator–rotor stage. The first part of the present paper compares the results obtained with the HB method to those obtained with the more established time-accurate unsteady Reynolds-averaged Navier–Stokes (URANS) approach and investigates their sensitivity with respect to the computational mesh density. Thereby, no streaks are simulated, and only the turbine alone tones are considered. Convincing results are obtained on aerodynamics and acoustics. The second part of the paper deals with a parametric study on the acoustical impact of steady hot streaks. The streaks are prescribed at the inlet of the stage using a boundary condition as an attempt to simulate a ring of combustor nozzles. No vorticity is coupled into the computational domain, as the objective is to measure the effect of temperature inhomogeneity only. Overall, the turbine appears to be slightly quieter with hot streaks. The streak-to-stator-vane ratio of 1-to-2 explains the generation of new acoustic modes with distinct azimuthal orders. The acoustic power amplitude of those additional modes scales roughly with the square of the temperature difference, the fourth-power of the diameter, and the square of the entropy difference. This last result agrees well with the 1D theory of Marble and Candel. The acoustic contribution of the unsteady force on the rotor blades due to the overspeed measured in the wakes of the streaks—resulting from the flow acceleration through the stator—remains an open question. Full article
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9232 KiB  
Article
3D Numerical Modeling of Zeotropic Mixtures and Pure Working Fluids in an ORC Turbo-Expander
by Ibrahim Gad-el-Hak, Ahmed E. Hussin, Ashraf M. Hamed and Nabil A. Mahmoud
Int. J. Turbomach. Propuls. Power 2017, 2(1), 2; https://doi.org/10.3390/ijtpp2010002 - 21 Mar 2017
Cited by 10 | Viewed by 6088
Abstract
The present paper provides a numerical study that leads to the proper selection of a working fluid for use in low-temperature organic Rankine cycle (ORC) applications. This selection is not only based on the provision of best efficiency but also to comply with [...] Read more.
The present paper provides a numerical study that leads to the proper selection of a working fluid for use in low-temperature organic Rankine cycle (ORC) applications. This selection is not only based on the provision of best efficiency but also to comply with global warming potential (GWP) regulations. For that purpose, different pure organic working fluids, including R245fa, R236fa, R123, R600a, R134a, and R1234yf as well as zeotropic mixture R245fa/R600a, are selected. The investigation is conducted on a single stage radial inflow turbo-expander, which was originally used in the Sundstrand Power Systems T-100 Multipurpose Small Power Unit. The commercial package ANSYS-CFX (version 16.0) was used to perform the numerical study using 3D Reynolds-Averaged Navier–Stokes (RANS) simulations. Peng–Robinson equation of state is adopted in the finite-volume solver ANSYS-CFX to determine the real-gas properties. The obtained results show that, while the use of R134a and R1234yf provides the best efficiency of all the working fluids under investigation, the latter is best selected for its comparatively low global warming effects. Full article
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5183 KiB  
Article
Advanced Endwall Contouring for Loss Reduction and Outflow Homogenization for an Optimized Compressor Cascade
by Oliver Reutter, Magdalena Rozanski, Alexander Hergt and Eberhard Nicke
Int. J. Turbomach. Propuls. Power 2017, 2(1), 1; https://doi.org/10.3390/ijtpp2010001 - 16 Mar 2017
Cited by 9 | Viewed by 5270
Abstract
The following paper deals with the development of an optimized non-axisymmetric endwall contour for reducing the total pressure loss and for homogenizing the outflow of a highly-loaded compressor cascade. In contrast to former studies using a NACA-65 K48 cascade airfoil this study starts [...] Read more.
The following paper deals with the development of an optimized non-axisymmetric endwall contour for reducing the total pressure loss and for homogenizing the outflow of a highly-loaded compressor cascade. In contrast to former studies using a NACA-65 K48 cascade airfoil this study starts with the design of a new high-performance airfoil which is based on the aerodynamic boundary conditions of the NACA-65 K48 cascade. This new airfoil is then used as a basis. Optimizations of the airfoil and of the endwall contour are performed using the German Aerospace Center (DLR) in-house tool AutoOpti and the RANS (Reynolds-averaged Navier-Stokes)-solver TRACE (Turbomachinery Research Aerodynamic Computational Environment). Three operating points at an inflow Mach number of 0.67 with different inflow angles are used to secure a wide operating range. The optimized endwall contour changes the secondary flow in such a way that the corner stall is reduced which, in turn, significantly reduces the total pressure loss. The endwall contour in the outflow region leads to a considerable homogenization of the outflow in the near wall region. Using non-axisymmetric endwall shaping demonstrates a valuable measure to further improve highly-efficient compressor blading on the vane level. Full article
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