Large wood in rivers can lead to accumulations in the river channel, affecting local flow structures, aquatic habitats, and the river’s topography. This plays a crucial role in the ecological restoration of the river...Large wood in rivers can lead to accumulations in the river channel, affecting local flow structures, aquatic habitats, and the river’s topography. This plays a crucial role in the ecological restoration of the river. This paper presents flow field measurements downstream of six types of logjams at different flow velocities using acoustic Doppler velocimetry (ADV) for artificially designed engineered logjams. The results indicate that the presence of logjams reduces the flow velocity and increases the turbulent kinetic energy in the wake region, and as the distance downstream increases, the flow velocity and turbulence intensity in the wake region gradually return to the upstream level. The minimum values of normalized flow velocity under different conditions are located in the region of the bottommost logs. The differences in normalized flow velocity at various flow rates are not significant. Jets are less likely to be generated in logjams with larger and more concentrated projection areas, but the strength of the jet is influenced by the physical structure of the logjam (projection area, gap ratio). The flow distribution behind the logjam is primarily influenced by the proportion of the projected area in different regions. Changes in the vertical physical structure of the logjam have minimal effect on the lateral flow distribution. Flow velocity in the gap area (b0) at the bottom of different logjams is influenced by their physical structure. The larger the overall blockage area of the logjams, the larger the flow velocity in the bottom gap area will be. The flow velocity in the bottom gap area of a densely placed logjam is mainly influenced by the gap ratio. The velocity of flow in the gap area can impact the initiation and deposition of sediment near the logjam. However, the internal structure complexity of the logjam does not significantly affect river energy dissipation and flow attenuation. This study broadens the applicability of certain theoretical models and explores the impact of logjams on river eco展开更多
Instantaneous and precise velocity sensing is a critical part of research on detonation mechanism and flow evolution.This paper presents a novel multi-projection tunable diode laser absorption spectroscopy solution,to...Instantaneous and precise velocity sensing is a critical part of research on detonation mechanism and flow evolution.This paper presents a novel multi-projection tunable diode laser absorption spectroscopy solution,to provide a real-time and reliable measurement of velocity distribution in detonation exhaust flow with obvious nonuniformity.Relations are established between overlapped spectrums along probing beams and Gauss velocity distribution phantom according to the frequency shifts and tiny variations in components of light-of-sight absorbance profiles at low frequencies analyzed by the fast Fourier transform.With simulated optical measurement using H2O feature at 7185.6 cm-1 carried out on a phantom generated using a simulation of two-phase detonation by a two-fluid model,this method demonstrates a satisfying performance on recovery of velocity distribution profiles in supersonic flow even with a noise equivalent absorbance up to 2×10^(-3).This method is applied to the analysis of rapidly decreasing velocity during a complete working cycle in the external flow field of an air-gasoline detonation tube operating at 25 Hz,and results show the velocity in the core flow field would be much larger than the arithmetic average from traditional tunable diode laser doppler velocimetry.This proposed velocity distribution sensor would reconstruct nonuniform velocity distribution of high-speed flow in low cost and simple operations,which broadens the possibility for applications in research on the formation and propagation of external flow filed of detonation tube.展开更多
Laminar flow and heat transfer in different protruding-edged plate systems are modelled and analyzed in the present work. These include the Parallel Flow (PF) and the Counter Flow (CF) protruding-edgedplate exchangers...Laminar flow and heat transfer in different protruding-edged plate systems are modelled and analyzed in the present work. These include the Parallel Flow (PF) and the Counter Flow (CF) protruding-edgedplate exchangers as well as those systems being subjected to Constant Wall Temperature (CWT) and Uniform Heat Flux (UHF) conditions. These systems are subjected to normal free stream having both power-law velocity profile and same average velocity. The continuity, momentum and energy equations are transformed to either similarity or nonsimilar equations and then solved by using well validated finite difference methods. Accurate correlations for various flow and heat transfer parameters are obtained. It is found that there are specific power-law indices that maximize the heat transfer in both PF and CF systems. The maximum reported enhancement ratios are 1.075 and 1.109 for the PF and CF systems, respectively, at Pr = 100. These ratios are 1.076 and 1.023 for CWT and UHF conditions, respectively, at Pr = 128. Per same friction force, the CF system is preferable over the PF system only when the power-law indices are smaller than zero. Finally, this work demonstrates that by appropriately distributing the free stream velocity, the heat transfer from a plate can be increased up to 10% fold.展开更多
In this paper,a model is established with application of the spectral-wave guide method,which has higher accuracy and can serve as a rapid calculation tool for sound transmission calculations.Based on this calculation...In this paper,a model is established with application of the spectral-wave guide method,which has higher accuracy and can serve as a rapid calculation tool for sound transmission calculations.Based on this calculation model,some numerical results of circumferentially non-uniform lined annular/circular ducts are carried out,and some physical mechanisms can be discovered.The numerical results show that periodical impedance distributions along the circumferential direction will lead to discontinuous scattered modes with regular spacing;and mirror-symmetric structure liner will converge the energy of opposite modes.Relying on this mechanism,the potential of acoustic scattering can be further developed by suppressing lower or enhancing higher order modes with expressly designed segmented liner configurations.In particular,the intrinsic mechanism of mode redistribution brought about by the non-uniform liner can be subtly utilized to attenuate broadband noise.The present work indeed shows that circumferentially non-uniform liner is conducive to the reduction of the practical broadband sound source.Furthermore,the effects of nonuniform flow are considered in the model,then distinction of noise attenuation and scattered modes energy in different flows is shown.A possible mechanism is proposed that refraction effects in complex flows lead to the distinction.These works show that the current model has profound potential and availability for the research and designs of circumferentially non-uniform liner.展开更多
Numerical study of three-dimensional evolution of wake-type flow and vortex dislocations is performed by using a compact finite diffenence-Fourier spectral method to solve 3-D incompressible Navier-Stokes equations. A...Numerical study of three-dimensional evolution of wake-type flow and vortex dislocations is performed by using a compact finite diffenence-Fourier spectral method to solve 3-D incompressible Navier-Stokes equations. A local spanwise nonuniformity in momentum defect is imposed on the incoming wake-type flow. The present numerical results have shown that the flow instability leads to three-dimensional vortex streets, whose frequency, phase as well as the strength vary with the span caused by the local nonuniformity. The vortex dislocations are generated in the nonuniform region and the large-scale chain-like vortex linkage structures in the dislocations are shown. The generation and the characteristics of the vortex dislocations are described in detail.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.52179056),the Fundamental Research Funds for the Central Universities(Grant No.QNTD202303).
文摘Large wood in rivers can lead to accumulations in the river channel, affecting local flow structures, aquatic habitats, and the river’s topography. This plays a crucial role in the ecological restoration of the river. This paper presents flow field measurements downstream of six types of logjams at different flow velocities using acoustic Doppler velocimetry (ADV) for artificially designed engineered logjams. The results indicate that the presence of logjams reduces the flow velocity and increases the turbulent kinetic energy in the wake region, and as the distance downstream increases, the flow velocity and turbulence intensity in the wake region gradually return to the upstream level. The minimum values of normalized flow velocity under different conditions are located in the region of the bottommost logs. The differences in normalized flow velocity at various flow rates are not significant. Jets are less likely to be generated in logjams with larger and more concentrated projection areas, but the strength of the jet is influenced by the physical structure of the logjam (projection area, gap ratio). The flow distribution behind the logjam is primarily influenced by the proportion of the projected area in different regions. Changes in the vertical physical structure of the logjam have minimal effect on the lateral flow distribution. Flow velocity in the gap area (b0) at the bottom of different logjams is influenced by their physical structure. The larger the overall blockage area of the logjams, the larger the flow velocity in the bottom gap area will be. The flow velocity in the bottom gap area of a densely placed logjam is mainly influenced by the gap ratio. The velocity of flow in the gap area can impact the initiation and deposition of sediment near the logjam. However, the internal structure complexity of the logjam does not significantly affect river energy dissipation and flow attenuation. This study broadens the applicability of certain theoretical models and explores the impact of logjams on river eco
基金the China Scholarship Council(Grant No.201906845059)the Young Scientists Found of the Natural Science Foundation of Jiangsu Province,China(Grant No.BK20190439)the Fundamental Research Funds of National Key Laboratory of Transient Physics(Grant No.6142604200202)。
文摘Instantaneous and precise velocity sensing is a critical part of research on detonation mechanism and flow evolution.This paper presents a novel multi-projection tunable diode laser absorption spectroscopy solution,to provide a real-time and reliable measurement of velocity distribution in detonation exhaust flow with obvious nonuniformity.Relations are established between overlapped spectrums along probing beams and Gauss velocity distribution phantom according to the frequency shifts and tiny variations in components of light-of-sight absorbance profiles at low frequencies analyzed by the fast Fourier transform.With simulated optical measurement using H2O feature at 7185.6 cm-1 carried out on a phantom generated using a simulation of two-phase detonation by a two-fluid model,this method demonstrates a satisfying performance on recovery of velocity distribution profiles in supersonic flow even with a noise equivalent absorbance up to 2×10^(-3).This method is applied to the analysis of rapidly decreasing velocity during a complete working cycle in the external flow field of an air-gasoline detonation tube operating at 25 Hz,and results show the velocity in the core flow field would be much larger than the arithmetic average from traditional tunable diode laser doppler velocimetry.This proposed velocity distribution sensor would reconstruct nonuniform velocity distribution of high-speed flow in low cost and simple operations,which broadens the possibility for applications in research on the formation and propagation of external flow filed of detonation tube.
文摘Laminar flow and heat transfer in different protruding-edged plate systems are modelled and analyzed in the present work. These include the Parallel Flow (PF) and the Counter Flow (CF) protruding-edgedplate exchangers as well as those systems being subjected to Constant Wall Temperature (CWT) and Uniform Heat Flux (UHF) conditions. These systems are subjected to normal free stream having both power-law velocity profile and same average velocity. The continuity, momentum and energy equations are transformed to either similarity or nonsimilar equations and then solved by using well validated finite difference methods. Accurate correlations for various flow and heat transfer parameters are obtained. It is found that there are specific power-law indices that maximize the heat transfer in both PF and CF systems. The maximum reported enhancement ratios are 1.075 and 1.109 for the PF and CF systems, respectively, at Pr = 100. These ratios are 1.076 and 1.023 for CWT and UHF conditions, respectively, at Pr = 128. Per same friction force, the CF system is preferable over the PF system only when the power-law indices are smaller than zero. Finally, this work demonstrates that by appropriately distributing the free stream velocity, the heat transfer from a plate can be increased up to 10% fold.
基金supported by the National Natural Science Foundation of China(No.52106038)the Science Center for Gas Turbine Project of China(No.P2022-B-Π-013-001).
文摘In this paper,a model is established with application of the spectral-wave guide method,which has higher accuracy and can serve as a rapid calculation tool for sound transmission calculations.Based on this calculation model,some numerical results of circumferentially non-uniform lined annular/circular ducts are carried out,and some physical mechanisms can be discovered.The numerical results show that periodical impedance distributions along the circumferential direction will lead to discontinuous scattered modes with regular spacing;and mirror-symmetric structure liner will converge the energy of opposite modes.Relying on this mechanism,the potential of acoustic scattering can be further developed by suppressing lower or enhancing higher order modes with expressly designed segmented liner configurations.In particular,the intrinsic mechanism of mode redistribution brought about by the non-uniform liner can be subtly utilized to attenuate broadband noise.The present work indeed shows that circumferentially non-uniform liner is conducive to the reduction of the practical broadband sound source.Furthermore,the effects of nonuniform flow are considered in the model,then distinction of noise attenuation and scattered modes energy in different flows is shown.A possible mechanism is proposed that refraction effects in complex flows lead to the distinction.These works show that the current model has profound potential and availability for the research and designs of circumferentially non-uniform liner.
基金the Special Founds for Major State Basic Research Projects (G1999032801), and by the National Climbing A Pre-selected Projects and the National Natural Science Foundation of China. Computational resourceswere provided by NCFC computer center, CAS. The he
文摘Numerical study of three-dimensional evolution of wake-type flow and vortex dislocations is performed by using a compact finite diffenence-Fourier spectral method to solve 3-D incompressible Navier-Stokes equations. A local spanwise nonuniformity in momentum defect is imposed on the incoming wake-type flow. The present numerical results have shown that the flow instability leads to three-dimensional vortex streets, whose frequency, phase as well as the strength vary with the span caused by the local nonuniformity. The vortex dislocations are generated in the nonuniform region and the large-scale chain-like vortex linkage structures in the dislocations are shown. The generation and the characteristics of the vortex dislocations are described in detail.
