作者：
Xin-Liang LiDe-Xun FuYan-Wen MaXian LiangLHD
Institute of MechanicsChinese Academy of Sciences 100190 BeijingChina LNM
Institute of MechanicsChinese Academy of Sciences 100190 BeijingChina
This paper reviews the authors＇ recent studies on compressible turbulence by using direct numerical simulation （DNS）,including DNS of isotropic（decaying） turbulence, turbulent mixing-layer,turbulent boundary-laye...
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This paper reviews the authors＇ recent studies on compressible turbulence by using direct numerical simulation （DNS）,including DNS of isotropic（decaying） turbulence, turbulent mixing-layer,turbulent boundary-layer and shock/boundary-layer *** statistics, compressibility effects,turbulent kinetic energy budget and coherent structures are studied based on the DNS *** mechanism of sound source in turbulent flows is also analyzed. It shows that DNS is a powerful tool for the mechanistic study of compressible turbulence.
direct numerical simulation(DNS)of shock wave/turbulent boundary layer interaction(SWTBLI)with pulsed arc discharge is carried out in this *** subject in the study is a Ma=2.9 compression flow over a 24-degree *** num...
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direct numerical simulation(DNS)of shock wave/turbulent boundary layer interaction(SWTBLI)with pulsed arc discharge is carried out in this *** subject in the study is a Ma=2.9 compression flow over a 24-degree *** numerical approaches were validated by the experimental results in the same flow *** heat source model was added to the Navier-Stokes equation to serve as the energy deposition of the pulsed arc *** streamwise locations are selected to apply energy *** effect of the pulsed arc discharge on the ramp-induced flow separation has been studied in *** DNS results demonstrate the incentive locations play a dominant role in suppressing the separated *** show that pulsed heating is characterized by a thermal blockage,which leads to streamwise *** incentive locations upstream the interaction zone of the base flow have a better control *** separation bubble shape shows as"spikes",and the downstream flow of the heated region is accelerated due to the momentum exchange between the upper boundary layer and the bottom boundary *** high-speed upper fluid is transferred to the bottom,and thus enhances its ability to resist the flow *** stripe vortex structures are also generated at the edge of the ***,the turbulent kinetic disturbance energy is increased in the flow *** disturbances that originate from the pulsed heating are capable of increasing the turbulent intensity and then diminishing the trend of flow separation.
This article presents the direct numerical simulation results of the turbulent flow in a straight square duct at a Reynolds number of 600, based on the duct width and the mean wall-shear velocity. The turbulence stati...
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This article presents the direct numerical simulation results of the turbulent flow in a straight square duct at a Reynolds number of 600, based on the duct width and the mean wall-shear velocity. The turbulence statistics along the wall bisector is examined with the turbulent flow field properties given by streamwise velocity and vorticity fields in the duct cross section. It was found that the solutions of the turbulent duct flow obtained in a spatial resolution with 1.2×10^6 grid points are satisfactory as compared to the existing numerical and experimental results. The results indicate that it is reasonable to neglect the sub-grid scale models in this spatial resolution level for the duct flow at the particular friction Reynolds number.
Supercritical water gasification is an efficient and clean way of energy conversion. The research on different scales, such as the system, reactor, and particle, has different temporal and spatial significance. A stud...
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Supercritical water gasification is an efficient and clean way of energy conversion. The research on different scales, such as the system, reactor, and particle, has different temporal and spatial significance. A study on particle-particle and particle- fluid-particle interaction on the particle scale has a fundamental guiding value for revealing gasification performance on the reactor scale. Reactive particles such as coal are pyrolyzed and gasified in a high-temperature and high-pressure reactor to form Stefan flow, which affects the mass, momentum, and energy transfer between particles and supercritical water. In this paper, a particle-resolved direct numerical simulation study of a reactive particle layer in supercritical water is carried out to investigate the effect of different particle layer solid holdups and Stefan flow intensities and distributions on the flow and heat transfer process between the particle layer and supercritical water. This work analyzes the pressure and friction drag coefficients to which the particles are subjected and specifies the flow, velocity, and temperature distribution inside and around the particle layer. The results show that the drag coefficient and Nusselt number of particles in the particle layer decrease gradually along the flow direction, and the presence of particle Stefan flow further reduces the drag force and Nusselt number of particles. With the increasing solid holdup of the particle layer, the particle-fluid-particle interaction becomes more intense, and the effect of Stefan flow cannot be negligible.
direct numerical simulation (DNS) of complex multiphase flows is rapidly gaining attention. In this paper we explain the role of direct numerical simulation (DNS) in the context of a multi-scale approach to model syst...
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direct numerical simulation (DNS) of complex multiphase flows is rapidly gaining attention. In this paper we explain the role of direct numerical simulation (DNS) in the context of a multi-scale approach to model systems involving mass, momentum and heat transfer in dense fluid-particle systems. Following a brief description of the theoretical framework and the associated computational methods we present several illustrative results highlighting the power of DNS to generate detailed closures for fluid-particle interaction. Finally, several future challenges are indicated.
This paper investigates the effects of turbulence on radiative heat transfer in premixed flame propagation using a combination of direct numerical simulation (DNS) and the discrete ordinates method (DOM). The DNS code...
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This paper investigates the effects of turbulence on radiative heat transfer in premixed flame propagation using a combination of direct numerical simulation (DNS) and the discrete ordinates method (DOM). The DNS code has been validated and established in previous research, and the newly written DOM code is validated by solving a sample radiative heat transfer problem. The DOM code is explicitly combined with the DNS code using the 3rd-order Runge-Kutta scheme. In the numerical experiments, an initially flat laminar premixed flame interacts with imposed turbulent fluctuations and evolves over time. A remarkable increase in the temperature self-correlation factor < T-4 > / < T >(4) is observed in the middle of the reaction. Higher u' conditions induced faster and more intensive flame wrinkle evolution. However, flow turbulence reduces the radiative heat loss in planar premixed flame due to the flame curvature effects. (C) 2016 Elsevier Ltd. All rights reserved.
This paper presents a direct numerical simulation database of high-speed zero-pressure-gradient turbulent boundary layers developing spatially over a flat plate with nominal freestream Mach number ranging from 2.5 to ...
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This paper presents a direct numerical simulation database of high-speed zero-pressure-gradient turbulent boundary layers developing spatially over a flat plate with nominal freestream Mach number ranging from 2.5 to 14 and wall-to-recovery temperature ranging from 0.18 to 1.0. The flow conditions of the DNS are representative of the operational conditions of the Purdue Mach 6 quiet tunnel, the Sandia Hypersonic Wind Tunnel at Mach 8, and the AEDC Hypervelocity Tunnel No. 9 at Mach 14. The DNS database is used to gauge the performance of compressibility transformations, including the classical Morkovin's scaling and strong Reynolds analogy as well as the newly proposed mean velocity and temperature scalings that explicitly account for wall heat flux. Several insights into the effect of direct compressibility are gained by inspecting the thermodynamic fluctuations and the Reynolds stress budget terms. Precomputed flow statistics, including Reynolds stresses and their budgets, will be available at the website of the NASA Langley Turbulence Modeling Resource, allowing other investigators to query any property of interest.
We investigate a Cartesian-mesh immersed-boundary formulation within an incompressible flow solver to simulate laminar and turbulent katabatic slope flows. As a proof-of-concept study, we consider four different immer...
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We investigate a Cartesian-mesh immersed-boundary formulation within an incompressible flow solver to simulate laminar and turbulent katabatic slope flows. As a proof-of-concept study, we consider four different immersed-boundary reconstruction schemes for imposing a Neumann-type boundary condition on the buoyancy field. Prandtl's laminar solution is used to demonstrate the second-order accuracy of the numerical solutions globally. direct numerical simulation of a turbulent katabatic flow is then performed to investigate the applicability of the proposed schemes in the turbulent regime by analyzing both first- and second-order statistics of turbulence. First-order statistics show that turbulent katabatic flow simulations are noticeably sensitive to the specifics of the immersed-boundary formulation. We find that reconstruction schemes that work well in the laminar regime may not perform as well when applied to a turbulent regime. Our proposed immersed-boundary reconstruction scheme agrees closely with the terrain-fitted reference solutions in both flow regimes.
The critical review discusses the most accurate methods for description of turbulent flows: the computationally very expensive direct numerical simulation (DNS) and slightly less accurate and slightly less expensive l...
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The critical review discusses the most accurate methods for description of turbulent flows: the computationally very expensive direct numerical simulation (DNS) and slightly less accurate and slightly less expensive large eddy simulation (LES) methods. Both methods have found their way into nuclear thermal hydraulics as tools for studies of the fundamental mechanisms of turbulence and turbulent heat transfer. In the first section of this critical review, both methods are briefly introduced in parallel with the basic properties of the turbulent flows. The focus is on the DNS method, the so-called quasi-DNS approach, and the coarsest turbulence modeling approach discussed in this work, which is still on the very small-scale, wall-resolved LES. Other, coarser turbulence modeling approaches (such as wall-modeled LES, Reynolds Averaged Navier-Stokes (RANS)/LES hybrids, or RANS) are beyond the scope of the present work. Section II answers the question: "How do the DNS and LES methods work?" A short discussion of the computational requirements, numerical approaches, and computational tools is included. Section III is about the interpretation of the DNS and LES results and statistical uncertainties. Sections IV and V give some examples of the DNS and wall-resolved LES results relevant for nuclear thermal hydraulics. The last section lists the conclusions and some of the challenges that might be tackled with the most accurate techniques like DNS and LES.
In this study, a systematic assessment of turbulent combustion submodels of conditional moment closure (CMC) has been conducted using DNS data of a three-dimensional spatially-developing supersonic lifted hydrogen fla...
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In this study, a systematic assessment of turbulent combustion submodels of conditional moment closure (CMC) has been conducted using DNS data of a three-dimensional spatially-developing supersonic lifted hydrogen flame with a Mach number of 1.2 at the jet injection. It has been found that Beta pdf of mixture fraction can well capture the mixing space of the high speed reacting flow. The linear model exhibits a good performance for the axial velocity predictions. Girimaji's model for scalar dissipation rate performs well at upstream, while the AMC model presents better further downstream. The first order closure for the conditional reaction rate deviates a lot from the DNS extracted results. Second-order corrections made to temperature only or to the two rate-limiting reaction steps induce improvement, still with much discrepancy. Second order closure considering fluctuations of all the reacting species and temperature can accurately reproduce the DNS results. (C) 2014 IAA. Published by Elsevier Ltd. All rights reserved.
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