The Experts below are selected from a list of 368103 Experts worldwide ranked by ideXlab platform
Cengiz Camci - One of the best experts on this subject based on the ideXlab platform.
-
factors influencing computational predictability of aerodynamic losses in a turbine nozzle guide vane flow
Journal of Fluids Engineering-transactions of The Asme, 2016Co-Authors: Ozhan H Turgut, Cengiz CamciAbstract:This paper deals with the computational predictability of aerodynamic losses in a turbine nozzle guide vane (NGV) flow. The paper shows that three-dimensional (3D) computations of Reynolds-Averaged Navier Stokes (RANS) equations have the ability to adequately represent viscous losses in the presence of laminar flows, Transitional regions, and fully turbulent flow areas in the NGV of an high pressure (HP) turbine stage. The Axial Flow Turbine Research Facility (AFTRF) used for the present experimental results has an annular NGV assembly and a 29-bladed HP turbine rotor spinning at 1330 rpm. The NGV inlet and exit Reynolds numbers based on midspan axial chord are around 300,000 and 900,000, respectively. A general purpose finite-volume 3D flow solver with a shear stress transport (SST) k–ω turbulence model is employed. The current computational study benefits from these carefully executed aerodynamic experiments in the NGV of the AFTRF. The grid independence study is performed with static pressure coefficient distribution at the midspan of the vane and the total pressure coefficient at the NGV exit. The Effect of grid structure on aerodynamic loss generation is emphasized. The flow Transition Effect and the influence of corner fillets at the vane–endwall junction are also studied. The velocity distributions and the total pressure coefficient at the NGV exit plane are in very good agreement with the experimental data. This validation study shows that the Effect of future geometrical modifications on the turbine endwall surfaces will be predicted reasonably accurately. The current study also indicates that an accurately defined turbine stage geometry, a properly prepared block-structured/body-fitted grid, a state-of-the-art Transitional flow implementation, inclusion of fillets, and realistic boundary conditions coming from high-resolution turbine experiments are all essential ingredients of a successful turbine NGV aerodynamic loss quantification via computations. This validation study forms the basis for the successful future generation of nonaxisymmetric endwall surface modifications in AFTRF research efforts.
-
a computational validation of turbine nozzle guide vane aerodynamic experiments in an hp turbine stage
Volume 1: Advances in Aerospace Technology; Energy Water Nexus; Globalization of Engineering; Posters, 2011Co-Authors: Zhan O H Turgut, Cengiz CamciAbstract:A computational validation study related to aerodynamic loss generation mechanisms is performed in an axial flow turbine nozzle guide vane (NGV). The 91.66 cm diameter axial flow turbine research facility has a stationary nozzle guide vane assembly and a 29 bladed HP turbine rotor. The NGV inlet and exit Reynolds numbers based on midspan axial chord are around 300000 and 900000, respectively. The Effect of grid structure on aerodynamic loss generation is investigated. GAMBIT and TGRID combination is used for unstructured grid, whereas GRIDPRO is the structured grid generator. For both cases, y+ values are kept below unity. The finite-volume flow solver ANSYS CFX with SST k–ω turbulence model is employed. Experimental flow conditions are imposed at the boundaries. The flow Transition Effect and the influence of corner fillets at the vane-endwall junction are also studied in this paper. Grid independence study is performed with static pressure coefficient distribution at the mid-span of the vane and the total pressure coefficient at the NGV exit. The velocity distributions and the total pressure coefficient at the NGV exit plane are in very good agreement with the experimental data. This validation study shows that the Effect of future geometrical modifications on the endwalls and the vane will be predicted reasonably accurately. The current study shows that an accurately measured turbine stage geometry, a properly prepared block structured/body fitted grid, a state of the art Transitional flow implementation, and realistic boundary conditions coming from high resolution turbine experiments are all essential ingredients of a successful NGV aerodynamic loss quantification via computations.Copyright © 2011 by ASME
F Jomni - One of the best experts on this subject based on the ideXlab platform.
-
dielectric and conduction mechanisms of parylene n at high temperature phase Transition Effect
Journal of Physical Chemistry A, 2015Co-Authors: Achraf Kachroudi, Abdelkader Kahouli, J Legrand, F JomniAbstract:Dielectric and electrical properties correlated with the structure analysis have been studied on 27% semicrystalline parylene-N (−H2C–C6H4–CH2−)n thin films. Transition-phase, AC- and DC-conduction mechanisms, and the MW-interfacial polarization were identified in parylene N at high temperature by experimental and theoretical investigations. The dielectric analysis based on the dc conductivity highlights a temperature of 230 °C as a Transition temperature from the α-form to the β1-form. This structure Transition is accompanied by a modification on the DC-conduction mechanisms from ionic to electronic conduction in the α-form and the β1-form, respectively. The AC conduction mechanism is governed by the small polaron tunneling mechanism (SPTM) with WH,α = 0.23 eV and a tunneling distance of 7.71 A in the α-form, while it becomes a correlated barrier-hopping (CBH) mechanism with a WM,β 1 = 0.52 eV in the β1-form. The imaginary part of the electrical modulus formalism obeys the Kohlrausch–Williams–Watt (KWW) ...
Polyanskiy Yury - One of the best experts on this subject based on the ideXlab platform.
-
Energy efficient coded random access for the wireless uplink
'Institute of Electrical and Electronics Engineers (IEEE)', 2021Co-Authors: Kowshik, Suhas S, Andreev Kirill, Frolov Alexey, Polyanskiy YuryAbstract:© 1972-2012 IEEE. We discuss the problem of designing channel access architectures for enabling fast, low-latency, grant-free, and uncoordinated uplink for densely packed wireless nodes. Specifically, we study random-access codes, previously introduced for the AWGN MAC, in the practically more relevant case of Rayleigh fading, when channel gains are unknown to the decoder. We propose a random coding achievability bound, which we analyze both non-asymptotically and asymptotically. As a candidate practical solution, we propose an explicit iterative coding scheme. The performance of such a solution is surprisingly close to the finite blocklength bounds. Our main findings are twofold. First, just like in the AWGN MAC, we see that jointly decoding a large number of users leads to a surprising phase Transition Effect, where, at spectral efficiencies below a critical threshold, a perfect multi-user interference cancellation is possible. Second, while the presence of Rayleigh fading significantly increases the minimal required energy-per-bit, the inherent randomization introduced by the channel makes it much easier to attain the optimal performance via iterative schemes. We hope that a principled definition of the random-access model, together with their information-theoretic analysis, will open the road towards unified benchmarking and performance comparison of various random-access solutions for the 5G/6G
-
Energy efficient coded random access for the wireless uplink
2019Co-Authors: Kowshik, Suhas S, Andreev Kirill, Frolov Alexey, Polyanskiy YuryAbstract:We discuss the problem of designing channel access architectures for enabling fast, low-latency, grant-free and uncoordinated uplink for densely packed wireless nodes. Specifically, we study random-access codes, previously introduced for the AWGN multiple-access channel (MAC) by Polyanskiy'2017, in the practically more relevant case of users subject to Rayleigh fading, when channel gains are unknown to the decoder. We propose a random coding achievability bound, which we analyze both non-asymptotically (at finite blocklength) and asymptotically. As a candidate practical solution, we propose an explicit sparse-graph based coding scheme together with an alternating belief-propagation decoder. The latter's performance is found to be surprisingly close to the finite-blocklength bounds. Our main findings are twofold. First, just like in the AWGN MAC we see that jointly decoding large number of users leads to a surprising phase Transition Effect, where at spectral efficiencies below a critical threshold (5-15 bps/Hz depending on reliability) a perfect multi-user interference cancellation is possible. Second, while the presence of Rayleigh fading significantly increases the minimal required energy-per-bit $E_b/N_0$ (from about 0-2 dB to about 8-11 dB), the inherent randomization introduced by the channel makes it much easier to attain the optimal performance via iterative schemes. In all, it is hoped that a principled definition of the random-access model together with our information-theoretic analysis will open the road towards unified benchmarking and comparison performance of various random-access solutions, such as the currently discussed candidates (MUSA, SCMA, RSMA) for the 5G/6G.Comment: 26 page
Vanav A Kumar - One of the best experts on this subject based on the ideXlab platform.
-
Transition of mhd boundary layer flow past a stretching sheet
Communications in Nonlinear Science and Numerical Simulation, 2010Co-Authors: V Kumaran, Vanav A KumarAbstract:In this paper a study is carried out to understand the Transition Effect of boundary layer flow: (1) due to a suddenly imposed magnetic field over a viscous flow past a stretching sheet and (2) due to sudden withdrawal of magnetic field over a viscous flow past a stretching sheet under a magnetic field. In both the cases the sheet stretches linearly along the direction of the fluid flow. Governing equations have been non-dimensionalised and the non-dimensionalised equations have been solved using the implicit finite difference method of Crank–Nicholson type. Comparison between the steady state exact solutions and the steady state computed solutions has been carried out. Graphical representation of the dimensionless horizontal velocity, vertical velocity and local skin friction profiles of the steady state and unsteady state has been presented. Computation has been carried out for various values of the magnetic parameter M. The obtained results has been interpreted and discussed.
Samuel Ranti Oke - One of the best experts on this subject based on the ideXlab platform.
-
processing alloy composition and phase Transition Effect on the mechanical and corrosion properties of high entropy alloys a review
Journal of materials research and technology, 2016Co-Authors: Kenneth Kanayo Alaneme, Michael Oluwatosin Bodunrin, Samuel Ranti OkeAbstract:Abstract This paper reviews from the corpus of literatures on high-entropy alloys (HEAs), their mechanical and corrosion behavior as affected by metallurgical factors such as processing technique, composition, phase formation and Transition. HEAs are a promising class of alloys which are designed based on the use of multiple component alloying elements in equimolar or near equimolar ratio. There has been surging interest in this class of alloys on account of their unique property range. Their unique metallurgical characteristics, structures, mechanical and corrosion properties, current and potential areas of applications, and suggestions for future research are discussed in this paper.