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David Thompson - One of the best experts on this subject based on the ideXlab platform.
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Effect of Cavity Flow control on high-speed train pantograph and roof aerodynamic noise
Railway Engineering Science, 2020Co-Authors: Zhiwei Hu, David ThompsonAbstract:The pantograph and its recess on the train roof are major aerodynamic noise sources on high-speed trains. Reducing this noise is particularly important because conventional noise barriers usually do not shield the pantograph. However, less attention has been paid to the pantograph recess compared with the pantograph. In this paper, the Flow features and noise contribution of two types of noise reduction treatments rounded and chamfered edges are studied for a simplified high-speed train pantograph recess, which is represented as a rectangular Cavity and numerically investigated at 1/10 scale. Improved delayed detached-eddy simulations are performed for the near-field turbulent Flow simulation, and the Ffowcs Williams and Hawkings aeroacoustic analogy is used for far-field noise prediction. The highly unsteady Flow over the Cavity is significantly reduced by the Cavity edge modifications, and consequently, the noise radiated from the Cavity is reduced. Furthermore, effects of the rounded Cavity edges on the Flow and noise of the pantographs (one raised and one folded) are investigated by comparing the Flow features and noise contributions from the cases with and without rounding of the Cavity edges. Different train running directions are also considered. Flow analysis shows that the highly unsteady Flow within the Cavity is reduced by rounding the Cavity edges and a slightly lower Flow speed occurs around the upper parts of the raised pantograph, whereas the Flow velocity in the Cavity is slightly increased by the rounding. Higher pressure fluctuations occur on the folded pantograph and the lower parts of the raised pantograph, whereas weaker fluctuations are found on the panhead of the raised pantograph. This study shows that by rounding the Cavity edges, a reduction in radiated noise at the side and the top receiver positions can be achieved. Noise reductions in the other directions can also be found.
Hendrik C Kuhlmann - One of the best experts on this subject based on the ideXlab platform.
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accurate three dimensional lid driven Cavity Flow
Journal of Computational Physics, 2005Co-Authors: Stefan Albensoeder, Hendrik C KuhlmannAbstract:A Chebyshev-collocation method in space is introduced, which allows an accurate calculation of three-dimensional lid-driven Cavity Flows. The time integration is carried out by an Adams-Bashforth backward-Euler scheme. The accuracy of the method relies on the representation of the solution as a superposition of stationary local asymptotic solutions and a residual Flow field. This way the most severe discontinuities in the boundary conditions, which arise along the lines where moving and stationary walls meet, are taken care of analytically and thus do not spoil the numerical part of the solution. Calculations are carried out for no-slip boundary conditions at the Cavity end-walls as well as for periodic end-wall conditions. In general, the spatial accuracy is better than fifth order. For rigid end-wall conditions, the accuracy is reduced near the end-walls to O(N^3^/^2), but recovers in the bulk. Tabulated data are provided for the most interesting Flow properties.
S Almeida - One of the best experts on this subject based on the ideXlab platform.
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effect of the hub endwall Cavity Flow on the Flow field of a transonic high pressure turbine
Journal of Turbomachinery-transactions of The Asme, 2004Co-Authors: Guillermo Paniagua, R Denos, S AlmeidaAbstract:In high-pressure turbines, a small amount of cold Flow is ejected at the hub from the Cavity that exists between the stator and the rotor disk. This prevents the ingestion of hot gases into the wheel-space Cavity, thus avoiding possible damage. This paper analyses the interaction between the hub-endwall Cavity Flow and the mainstream in a high-pressure transonic turbine stage. Several cooling Flow ratios are investigated under engine representative conditions. Both time-averaged and time-resolved data are presented. The experimental data is successfully compared with the results of a 3D steady Navier-Stokes computation. Despite the small amount of gas ejected, the hub-endwall Cavity Flow has a significant influence on the mainstream Flow. The Navier-Stokes predictions show how the ejected cold Flow is entrained by the rotor hub vortex. The time-resolved static pressure field around the rotor is greatly affected when traversing the non-uniform vane exit Flow field. When the Cavity Flow rate is increased, the unsteady forces on the rotor airfoil are reduced. This is linked to the decrease of vane exit Mach number caused by the blockage of the ejected Flow.Copyright © 2004 by ASME
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effect of the hub endwall Cavity Flow on the Flow field of a transonic high pressure turbine
Journal of Turbomachinery-transactions of The Asme, 2004Co-Authors: Guillermo Paniagua, R Denos, S AlmeidaAbstract:In high-pressure turbines, a small amount of cold Flow is ejected at the hub from the Cavity that exists between the stator and the rotor disk. This prevents the ingestion of hot gases into the wheel-space Cavity, thus avoiding possible damage. This paper analyzes the interaction between the hub-endwall Cavity Flow and the mainstream in a high-pressure transonic turbine stage. Several cooling Flow ratios are investigated under engine representative conditions. Both time-averaged and time-resolved data are presented. The experimental data is successfully compared with the results of a three-dimensional steady Navier-Stokes computation. Despite the small amount of gas ejected, the hub-endwall Cavity Flow has a significant influence on the mainstream Flow. The Navier-Stokes predictions show how the ejected cold Flow is entrained by the rotor hub vortex, The time-resolved static pressure field around the rotor is greatly affected when traversing the non-uniform vane exit Flow field. When the Cavity Flow rate is increased, the unsteady forces on the rotor airfoil are reduced. This is linked to the decrease of vane exit Mach number caused by the blockage of the ejected Flow.
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effect of the hub endwall Cavity Flow on the Flow field of a transonic high pressure turbine
ASME Turbo Expo 2004: Power for Land Sea and Air, 2004Co-Authors: Guillermo Paniagua, R Denos, S AlmeidaAbstract:In high-pressure turbines, a small amount of cold Flow is ejected at the hub from the Cavity that exists between the stator and the rotor disk. This prevents the ingestion of hot gases into the wheel-space Cavity, thus avoiding possible damage. This paper analyses the interaction between the hub-endwall Cavity Flow and the mainstream in a high-pressure transonic turbine stage. Several cooling Flow ratios are investigated under engine representative conditions. Both time-averaged and time-resolved data are presented. The experimental data is successfully compared with the results of a 3D steady Navier-Stokes computation. Despite the small amount of gas ejected, the hub-endwall Cavity Flow has a significant influence on the mainstream Flow. The Navier-Stokes predictions show how the ejected cold Flow is entrained by the rotor hub vortex. The time-resolved static pressure field around the rotor is greatly affected when traversing the non-uniform vane exit Flow field. When the Cavity Flow rate is increased, the unsteady forces on the rotor airfoil are reduced. This is linked to the decrease of vane exit Mach number caused by the blockage of the ejected Flow.Copyright © 2004 by ASME
Steven L Ceccio - One of the best experts on this subject based on the ideXlab platform.
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the dynamics of partial Cavity formation shedding and the influence of dissolved and injected non condensable gas
Journal of Fluid Mechanics, 2017Co-Authors: Simo A Makiharju, Harish Ganesh, Steven L CeccioAbstract:In the present study, the experimental set-up of Ganesh et al. (J. Fluid Mech., vol. 802, 2016, pp. 37–78) is used to examine the dynamics of a shedding Cavity by examining the vapour production rate of the natural Cavity and determining how minimal injection of non-condensable gas can substantially alter the vapour production rate, the resulting Cavity Flow and the Cavity shedding process. The influence of the dissolved gas content on the shedding natural Cavity Flow is also examined. High-speed visual imaging and cinemagraphic X-ray densitometry were used to observe the void fraction dynamics of the Cavity Flow. Non-condensable gas is injected across the span of the Cavity Flow at two locations: immediately downstream of the Cavity detachment location at the apex of the wedge or further downstream into mid-Cavity. The gas injected near the apex is found to increase the pressure near the suction peak, which resulted in the suppression of vapour formation. Hence, the injection of gas could result in a substantial net reduction in the overall Cavity void fraction. Injection at the mid-Cavity did less to suppress the vapour production and resulted in less significant modification of both the mean Cavity pressure and net volume fraction. Changes in the Cavity void fraction, in turn, altered the dynamics of the bubbly shock formation. Variation of the dissolved gas content alone (i.e. without injection) did not significantly change the Cavity dynamics.
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bubbly shock propagation as a mechanism for sheet to cloud transition of partial cavities
Journal of Fluid Mechanics, 2016Co-Authors: Harish Ganesh, Simo A Makiharju, Steven L CeccioAbstract:Author(s): Ganesh, H; Makiharju, SA; Ceccio, SL | Abstract: © 2016 Cambridge University Press. Partial cavitation in the separated region forming from the apex of a wedge is examined to reveal the Flow mechanism responsible for the transition from stable sheet Cavity to periodically shedding cloud cavitation. High-speed visualization and time-resolved X-ray densitometry measurements are used to examine the Cavity dynamics, including the time-resolved void-fraction fields within the Cavity. The experimentally observed time-averaged void-fraction profiles are compared to an analytical model employing free-streamline theory. From the instantaneous void-fraction Flow fields, two distinct shedding mechanisms are identified. The classically described re-entrant Flow in the Cavity closure is confirmed as a mechanism for vapour entrainment and detachment that leads to intermittent shedding of smaller-scale cavities. But, with a sufficient reduction in cavitation number, large-scale periodic cloud shedding is associated with the formation and propagation of a bubbly shock within the high void-fraction bubbly mixture in the separated Cavity Flow. When the shock front impinges on Flow at the wedge apex, a large cloud is pinched off. For periodic shedding, the speed of the front in the laboratory frame is of the order of half the free-stream speed. The features of the observed condensation shocks are related to the average and dynamic pressure and void fraction using classical one-dimensional jump conditions. The sound speed of the bubbly mixture is estimated to determine the Mach number of the Cavity Flow. The transition from intermittent to transitional to strongly periodic shedding occurs when the average Mach number of the Cavity Flow exceeds that required for the generation of strong shocks.
Zhiwei Hu - One of the best experts on this subject based on the ideXlab platform.
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Effect of Cavity Flow control on high-speed train pantograph and roof aerodynamic noise
Railway Engineering Science, 2020Co-Authors: Zhiwei Hu, David ThompsonAbstract:The pantograph and its recess on the train roof are major aerodynamic noise sources on high-speed trains. Reducing this noise is particularly important because conventional noise barriers usually do not shield the pantograph. However, less attention has been paid to the pantograph recess compared with the pantograph. In this paper, the Flow features and noise contribution of two types of noise reduction treatments rounded and chamfered edges are studied for a simplified high-speed train pantograph recess, which is represented as a rectangular Cavity and numerically investigated at 1/10 scale. Improved delayed detached-eddy simulations are performed for the near-field turbulent Flow simulation, and the Ffowcs Williams and Hawkings aeroacoustic analogy is used for far-field noise prediction. The highly unsteady Flow over the Cavity is significantly reduced by the Cavity edge modifications, and consequently, the noise radiated from the Cavity is reduced. Furthermore, effects of the rounded Cavity edges on the Flow and noise of the pantographs (one raised and one folded) are investigated by comparing the Flow features and noise contributions from the cases with and without rounding of the Cavity edges. Different train running directions are also considered. Flow analysis shows that the highly unsteady Flow within the Cavity is reduced by rounding the Cavity edges and a slightly lower Flow speed occurs around the upper parts of the raised pantograph, whereas the Flow velocity in the Cavity is slightly increased by the rounding. Higher pressure fluctuations occur on the folded pantograph and the lower parts of the raised pantograph, whereas weaker fluctuations are found on the panhead of the raised pantograph. This study shows that by rounding the Cavity edges, a reduction in radiated noise at the side and the top receiver positions can be achieved. Noise reductions in the other directions can also be found.