Numerical Investigation of Separated Flows in Low Pressure Turbines PDF Download
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Author: Nagabhushana Rao Vadlamani
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Languages : en
Pages :
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Author: Nagabhushana Rao Vadlamani
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Languages : en
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Author: Daniel J. Dorney
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Category :
Languages : en
Pages : 20
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Author: Ashwin V. Bhansali
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Category : Navier-Stokes equations
Languages : en
Pages : 176
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Author: Ki-Hyeon Sohn
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Category : Boundary layers
Languages : en
Pages : 16
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Author: Sergio Romero Martinez
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Category : Reynolds number
Languages : en
Pages : 188
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The fluid flow across a Low-Pressure Turbine passage has been simulated numerically for a chord-based low Reynolds number of Re = 5,000 and an inlet Mach number of 0.1. Although the practical Reynolds number regime in turbomachinery is considerably larger than 5,000, similarities of the flow topology between the 5,000 and Re = 100,000 flow were attained through boundary layer suction. The present results are for the L2F Low-Pressure Turbine (LPT) profile. This geometry has been developed by the Air Force Research Laboratory (AFRL) for investigating the flow physics of highly loaded LPT blades at low Reynolds numbers. The L2F profile has a front-loaded pressure distribution which attenuates the adverse pressure gradient on the suction surface, thus delaying or preventing separation. Without boundary layer suction the flow separates laminar from the suction surface. With boundary layer suction this separation is almost completely suppressed. Special attention is drawn to the secondary flow effects near the turbine end-wall or hub which are responsible for a large part of the pressure losses in axial jet engines. The two dominant features of the resulting flow topology are the corner flow separation and the passage vortex. Both features are loss mechanisms. Active flow control via harmonic wall-normal blowing or zero-net mass flux control is employed and its effect on the total pressure loss is investigated. The flow control strategies were characterized in terms of the momentum coefficient, c[mu], and the reduced frequency, F+. Remarkable total pressure gains were achieved with zero-net mass flux blowing and suction. The active flow control strategies as discussed here have the potential to increase the efficiency of real LPT stages which operate at higher Reynolds numbers. Any increase in LPT stage performance will result in almost equal overall engine performance gains and thus improve the economics of air travel.
Author: Lucian Hanimann
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ISBN: 9783844087239
Category :
Languages : en
Pages : 0
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Category :
Languages : en
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Low-pressure turbines (LPT) experience large changes in chord Reynolds number as the turbine engine operates from take-off to cruise conditions. Due to prevailing conditions at high altitude cruise, the Reynolds number reduces drastically. At low Reynolds numbers, the flow is largely laminar and tends to separate easily on the suction surface of the blade, and this laminar separation in particular leads to significant degradation of engine performance due to large re-circulation zones. Therefore, a better understanding of low-Reynolds number flow transition and separation is very critical for an effective design of LPT blade, and in exploring various possibilities for implementing flow control techniques, passive or active, to prevent or delay the flow separation in the low-pressure turbine. The objective of the present study is to understand the three-dimensional flow separation that occurs inside an LPT cascade at very low Reynolds numbers, and a high-order accurate numerical solution procedure is used to attain the same. A multi-block, periodic, structured grid generated by the grid generation software, GRIDPRO, is used to represent the flow domain. A MPI-based higher-order, parallel, chimera version of the FDL3DI flow solver, developed by the Air Force Research Laboratory at Wright Patterson Air Force Base, is extended for the present turbomachinery application. A sixth-order accurate compact-difference scheme is used for the spatial discretization, along with second-order accurate temporal discretization. Up to tenth-order filtering has been applied to minimize the numerical oscillations, and maintain numerical stability. Simulations have been performed for Reynolds numbers (based on inlet velocity and axial chord) 10,000 and 25,000. The effect of these low-Reynolds numbers on the flow physics for a low-pressure turbine cascade has been studied in detail. At Re = 10,000, the flow undergoes more separation than at Re = 25,000 as expected and the separation remains significant over the entire blade for both the Reynolds number. The location of the onset of separation matches with an available LES simulation and with the available experimental data. In addition to the above simulations, another study was carried out to understand the effect of two different sets of inflow/outflow boundary conditions on the flow solution. The two sets of boundary conditions include static inflow with extrapolated outflow (BC1), and dynamic inflow (BC2) that accounts for upstream influence in the subsonic flow. The computed Cp distribution for the LPT flow shows good agreement with the available experimental data. Application of BC2 boundary condition predicted a bounded region of separation, while BC1 boundary condition predicted significant separation over the entire blade of an LPT.
Author: S. W. Kim
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ISBN:
Category : Turbulence
Languages : en
Pages : 44
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Author: Aditi Sengupta
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Category :
Languages : en
Pages :
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Author: Frank Eulitz
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Category :
Languages : en
Pages :
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