The Experts below are selected from a list of 13674 Experts worldwide ranked by ideXlab platform

Nilanjan Chakraborty - One of the best experts on this subject based on the ideXlab platform.

  • Effects of Equivalence Ratio and Turbulent Velocity Fluctuation on Early Stages of Pulverized Coal Combustion Following Localized Ignition: A Direct Numerical Simulation Analysis
    2014
    Co-Authors: Tamir Brosh, Nilanjan Chakraborty
    Abstract:

    This study utilized three-dimensional direct numerical simulations (DNS) in order to analyze the effects of turbulent Velocity Fluctuation, equivalence ratio based on volatile primary fuel in the p...

  • effects of lewis number on conditional fluid Velocity statistics in low damkohler number turbulent premixed combustion a direct numerical simulation analysis
    2013
    Co-Authors: Nilanjan Chakraborty, Andrei Lipatnikov
    Abstract:

    The effects of global Lewis number Le on the statistics of fluid Velocity components conditional in unburned reactants and fully burned products in the context of Reynolds Averaged Navier Stokes simulations have been analysed using a Direct Numerical Simulations (DNS) database of statistically planar turbulent premixed flames with a low Damkohler number and Lewis number ranging from 0.34 to 1.2. The conditional Velocity statistics extracted from DNS data have been analysed with respect to the well-known Bray-Moss-Libby (BML) expressions which were derived based on bi-modal probability density function of reaction progress variable for high Damkohler number flames. It has been shown that the Lewis number substantially affects the mean Velocity and the Velocity Fluctuation correlation conditional in products, with the effect being particularly pronounced for low Le. As far as the mean Velocity and the Velocity Fluctuation correlation conditional in reactants are concerned, the BML expressions agree reasonably well with the DNS data reported in the present work. Based on a priori analysis of present and previously reported DNS data, the BML expressions have been empirically modified here in order to account for Lewis number effects, and the non-bimodal distribution of reaction progress variable. Moreover, it has been demonstrated for the first time that surface averaged Velocity components and Reynolds stresses conditional in unburned reactants can be modelled without invoking expressions involving the Lewis number, as these surface averaged conditional quantities remain approximately equal to their conditionally averaged counterparts in the unburned mixture.

Tohru Fukano - One of the best experts on this subject based on the ideXlab platform.

  • experimental analysis on tip leakage and wake flow in an axial flow fan according to flow rates
    2005
    Co-Authors: Choonma Jang, D Sato, Tohru Fukano
    Abstract:

    The flow characteristics in the blade passage and in the wake region of a low-speed axial flow fan have been investigated by experimental analysis using a rotating hot-wire sensor and a five-hole probe for design and off-design operating conditions. The results show that the tip leakage vortex is moved upstream when the flow rate is decreased, thus disturbing the formation of wake flow near the rotor tip. That is, the tip leakage vortex interfaces with the blade suction surface and results in high Velocity Fluctuation near the blade suction surface. From axial Velocity distributions downstream of the fan rotor, large axial Velocity decay near the rotor tip is observed at near-stall condition, which results in a large blockage compared to that at the design condition. Finally, the wake flow downstream of the rotor blade is clearly measured at the design and off-design conditions. However, the trough of the high Velocity Fluctuation due to Karmann vortex street in the wake flow is observed at a higher flow condition than the design flow rate.

  • tip clearance noise of axial flow fans operating at design and off design condition
    2004
    Co-Authors: Tohru Fukano, Choonman Jang
    Abstract:

    The noise due to tip clearance (TC) flow in axial flow fans operating at a design and off-design conditions is analyzed by an experimental measurement using two hot-wire probes rotating with the fan blades. The unsteady nature of the spectra of the real-time velocities measured by two hot-wire sensors in a vortical flow region is investigated by using cross-correlation coefficient and retarded time of the two fluctuating velocities. The results show that the noise due to TC flow consists of a discrete frequency noise due to periodic Velocity Fluctuation and a broadband noise due to Velocity Fluctuation in the blade passage. The peak frequencies in a vortical flow are mainly observed below at four harmonic blade passing frequency. The discrete frequency component of Velocity Fluctuation at the off-design operating conditions is generated in vortical flow region as well as in reverse flow region. The peak frequency can be an important noise source when the fans are rotated with a high rotational speed. The authors propose a spiral pattern of Velocity Fluctuation in the vortical flow to describe the generation mechanism of the peak frequency in the vortical flow. In addition, noise increase due to TC flow at low flow rate condition is analyzed with relation to the distribution of Velocity Fluctuation due to the interference between the tip leakage vortex and the adjacent pressure surface of the blade.

  • frequency characteristics of fluctuating Velocity according to flow rates in a tip leakage vortex and a wake flow in an axial flow fan
    2004
    Co-Authors: Choonman Jang, Kwangyong Kim, Tohru Fukano
    Abstract:

    The frequency characteristics in an axial flow fan operating at a design and three off-design operating conditions have been investigated by measuring the Velocity Fluctuation of a tip leakage vortex and a wake flow. Two hot-wire probe sensors rotating with the fan rotor. a fixed and a moving ones, were introduced to obtain a cross-correlation coefficient between two sensors as well as the fluctuating Velocity. The results show that the spectral peaks due to the fluctuating Velocity near the rotor tip are mainly observed in the reverse flow region of higher flow rates than those in the peak pressure operating condition. However, no peak frequency presents near the rotor tip for near stall condition. Detailed wake flow just downstream of the rotor blade was also measured by the rotating hot-wire sensor. The peak frequency of a high Velocity Fluctuation due to Karman vortex shedding in the wake region is mainly observed at the higher flow rate condition than that in the design point.

  • effects of the tip clearance on vortical flow and its relation to noise in an axial flow fan
    2003
    Co-Authors: Choonman Jang, Tohru Fukano, Masato Furukawa
    Abstract:

    Three-dimensional vortical flow structures and Velocity Fluctuation near the rotor tip in an axial flow fan having two different tip clearances have been investigated by experimental analysis using a rotating hot wire probe and a numerical simulation. It is found that a tip leakage vortex is observed in the blade passage, which has a major role near the rotor tip. The tip leakage vortex formed close to the leading edge of the blade tip on suction side grows in the streamwise direction, and forms a local recirculation region resulting from a vortex breakdown inside the blade passage. The recirculation region is enlarged by increasing the tip clearance. The larger recirculation region induces the acceleration of the through flow, thus resulting in the increase of the broadband noise. High Velocity Fluctuation is observed at the interference region between the tip leakage vortex and the through flow in the flow field where the tip leakage vortex is tightly rolled up without its breakdown. Near the casing wall, a discrete frequency is formed between tip leakage vortex core and rotor trailing edge.

  • periodic Velocity Fluctuations in the near wake of a rotating flat plate blade and their role in the generation of broadband noise
    1995
    Co-Authors: Tohru Fukano, H Saruwatari, Hidechito Hayashi, H Isobe, M Fukuhara
    Abstract:

    Abstract The effect of the shape near the trailing edge of a rotating flat-plate blade on the periodic Velocity Fluctuation of the wake of the blade has been experimentally investigated. The results show that the characteristics of the near wake in the rotating flow field are similar to those in the uniform flow field; i.e., periodic Velocity Fluctuation does not occur when the suction surface of the blade is beveled near the trailing edge, but occurs if the pressure surface is beveled. In the latter case, two types of trailing edge separation generally occur: that is, the flow always adheres up to the trailing edge of the suction-side-beveled blade. On the other hand, the flow separation alternately and randomly occurs at two different locations, either the starting point of the beveling of the blade or a certain fixed point on the beveled surface in the case of a pressure side beveled blade. The important role of the periodic Velocity Fluctuation in the generation of broadband noise from a rotating flat-plate blade is also verified.

Xinnian Wang - One of the best experts on this subject based on the ideXlab platform.

  • effects of initial flow Velocity Fluctuation in event by event 3 1 d hydrodynamics
    2012
    Co-Authors: Longgang Pang, Qun Wang, Xinnian Wang
    Abstract:

    Hadron spectra and elliptic flow in high-energy heavy-ion collisions are studied within a (3+1)D ideal hydrodynamic model with fluctuating initial conditions given by the AMPT Monte Carlo model. Results from event-by-event simulations are compared with experimental data at both RHIC and LHC energies. Fluctuations in the initial energy density come from not only the number of coherent soft interactions of overlapping nucleons but also incoherent semi-hard parton scatterings in each binary nucleon collision. Mini-jets from semi-hard parton scatterings are assumed to be locally thermalized through a Gaussian smearing and give rise to non-vanishing initial local flow velocities. Fluctuations in the initial flow velocities lead to harder transverse momentum spectra of final hadrons due to non-vanishing initial radial flow velocities. Initial Fluctuations in rapidity distributions lead to expanding hot spots in the longitudinal direction and are shown to cause a sizable reduction of final hadron elliptic flow at large transverse momenta.

  • effects of initial flow Velocity Fluctuation in event by event 3 1 d hydrodynamics
    2012
    Co-Authors: Longgang Pang, Qun Wang, Xinnian Wang
    Abstract:

    Hadron spectra and elliptic flow in high-energy heavy-ion collisions are studied within a (3+1)D ideal hydrodynamic model with fluctuating initial conditions given by the AMPT Monte Carlo model. Results from event-by-event simulations are compared with experimental data at both Relativistic Heavy Ion Collider and Large Hadron Collider energies. Fluctuations in the initial energy density come from not only the number of coherent soft interactions of overlapping nucleons but also incoherent semi-hard parton scatterings in each binary nucleon collision. Mini-jets from semi-hard parton scatterings are assumed to be locally thermalized through a Gaussian smearing and give rise to nonvanishing initial local flow velocities. Fluctuations in the initial flow velocities lead to harder transverse momentum spectra of final hadrons due to nonvanishing initial radial flow velocities. Initial Fluctuations in rapidity distributions lead to expanding hot spots in the longitudinal direction and are shown to cause a sizable reduction of final hadron elliptic flow at large transverse momenta.

K R Sreenivasan - One of the best experts on this subject based on the ideXlab platform.

  • reynolds number scaling of the peak turbulence intensity in wall flows
    2021
    Co-Authors: Xi Chen, K R Sreenivasan
    Abstract:

    The celebrated wall-scaling works for many statistical averages in turbulent flows near smooth walls, but the streamwise Velocity Fluctuation, owing to the natural constraint of boundedness on the dissipation rate at the wall. This new formula agrees well with the existing data and, in contrast to the logarithmic growth, supports the classical wall-scaling for turbulent intensity at asymptotically high Reynolds numbers.

Zhongke Shi - One of the best experts on this subject based on the ideXlab platform.

  • an improved car following model with multiple preceding cars Velocity Fluctuation feedback
    2017
    Co-Authors: Lantian Guo, Xiangmo Zhao, Zhongke Shi
    Abstract:

    Abstract In order to explore and evaluate the effects of Velocity variation trend of multiple preceding cars used in the Cooperative Adaptive Cruise Control (CACC) strategy on the dynamic characteristic, fuel economy and emission of the corresponding traffic flow, we conduct a study as follows: firstly, with the real-time car-following (CF) data, the close relationship between multiple preceding cars’ Velocity Fluctuation feedback and the host car’s behaviors is explored, the evaluation results clearly show that multiple preceding cars’ Velocity Fluctuation with different time window-width are highly correlated to the host car’s acceleration/deceleration. Then, a microscopic traffic flow model is proposed to evaluate the effects of multiple preceding cars’ Velocity Fluctuation feedback in the CACC strategy on the traffic flow evolution process. Finally, numerical simulations on fuel economy and exhaust emission of the traffic flow are also implemented by utilizing VT-micro model. Simulation results prove that considering multiple preceding cars’ Velocity Fluctuation feedback in the control strategy of the CACC system can improve roadway traffic mobility, fuel economy and exhaust emission performance.

  • an improved car following model considering relative Velocity Fluctuation
    2016
    Co-Authors: Zhongke Shi
    Abstract:

    Abstract To explore and evaluate the impacts of relative Velocity Fluctuation on the dynamic characteristics and fuel consumptions of traffic flow, we present an improved car-following model considering relative Velocity Fluctuation based on the full Velocity difference model, then we carry out several numerical simulations to determine the optimal time window length and to explore how relative Velocity Fluctuation affects cars’ Velocity and its Fluctuation as well as fuel consumptions. It can be found that the improved car-following model can describe the phase transition of traffic flow and estimate the evolution of traffic congestion, and that taking relative Velocity Fluctuation into account in designing the advanced adaptive cruise control strategy can improve the traffic flow stability and reduce fuel consumptions.

  • an improved car following model considering Velocity Fluctuation of the immediately ahead car
    2016
    Co-Authors: Mengxing Huang, Jia Ren, Zhongke Shi
    Abstract:

    Abstract To better describe car-following behaviors in the adaptive cruise control strategy and further increase roadway traffic mobility and reduce fuel consumptions, the linkage between Velocity Fluctuation of the immediately ahead car and the following car’s acceleration or deceleration is explored with respect to the measured car-following data by employing the gray correlation analysis theory and then an improved car-following model considering Velocity Fluctuation of the immediately ahead car on basis of the full Velocity difference model is proposed. Numerical simulations are carried out and the effects of Velocity Fluctuation of the immediately ahead car on each car’s Velocity, acceleration, vehicular gap, fuel consumptions and the total fuel consumptions of the whole car-following system with different time window lengths are investigated in detail. The results show that Velocity Fluctuation of the immediately ahead car has significant effects on car-following behaviors and fuel consumptions, and that considering Velocity Fluctuation of the immediately ahead car in designing the adaptive cruise control system can improve traffic flow stability and reduce fuel consumptions.