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  • Controlling Rayleigh–Bénard convection via reinforcement learning
    J. Turbul. (IF 1.573) Pub Date : 2020-07-29
    Gerben Beintema; Alessandro Corbetta; Luca Biferale; Federico Toschi

    Thermal convection is ubiquitous in nature as well as in many industrial applications. The identification of effective control strategies to, e.g. suppress or enhance the convective heat exchange under fixed external thermal gradients is an outstanding fundamental and technological issue. In this work, we explore a novel approach, based on a state-of-the-art Reinforcement Learning (RL) algorithm, which

    更新日期:2020-07-29
  • Large eddy simulation of the periodic cavity evolution and the turbulence characteristics around a Delft Twist-11 hydrofoil
    J. Turbul. (IF 1.573) Pub Date : 2020-07-27
    An Yu; Xincheng Wang; Qinghong Tang; Daqing Zhou

    In the present investigation, the LES WALE method along with the Zwart cavitation model is utilised to predict the cavitating flow around a Delft Twist-11 hydrofoil and the numerical results show a reasonable agreement with the experimental data. A novel elucidation is provided to the formation of the U-type structure and the Lumley method is introduced into the numerical simulation which can offer

    更新日期:2020-07-27
  • Numerical study of passive forcing on the secondary instability of a laminar planar free shear layer
    J. Turbul. (IF 1.573) Pub Date : 2020-06-01
    H. Valtchanov; J. R. Brinkerhoff; M. I. Yaras

    Direct numerical simulations were performed of a free shear layer developing downstream from a no-slip splitter plate. The simulation results show that three-dimensional streaky perturbations developing in the boundary layer on the high-speed side of the splitter plate are convected downstream from the trailing edge and influence the development of three-dimensional perturbations in the planar free

    更新日期:2020-07-24
  • Transitional and turbulent flows in rectangular ducts: budgets and projection in principal mean strain axes
    J. Turbul. (IF 1.573) Pub Date : 2020-06-18
    Paolo Orlandi; Sergio Pirozzoli

    We carry out Direct Numerical Simulation (DNS) of flows in closed rectangular ducts with several aspect ratios. The Navier–Stokes equations are discretised through a second-order finite difference scheme, with non-uniform grids in two directions. The duct cross-sectional area is maintained constant as well as the flow rate, which allows to investigate which is the appropriate length scale in the Reynolds

    更新日期:2020-07-24
  • Comparison between temporal and spatial direct numerical simulations for bypass transition flows
    J. Turbul. (IF 1.573) Pub Date : 2020-07-13
    Satish Muthu; Shanti Bhushan

    Temporally developing direct numerical simulations (T-DNS) are performed for free-stream turbulence induced bypass transition flow over a flat-plate under zero-pressure gradient, and results are validated using experimental data and spatially developing DNS (S-DNS) results. The temporal simulations predict the growth of near-wall Klebanoff modes in the pre-transition regime and their subsequent breakdown

    更新日期:2020-07-24
  • Wall-shear stress fluctuations in a supersonic turbulent boundary layer over an expansion corner
    J. Turbul. (IF 1.573) Pub Date : 2020-07-23
    Fulin Tong; Jianqiang Chen; Dong Sun; Xinliang Li

    The effect of wall expansion on the structural and statistical characteristics of wall-shear stress (WSS) fluctuations was investigated by direct numerical simulations of a supersonic turbulent boundary layer over a sharp expansion corner with various deflection angles (β = 00, 20, 50 and 100). It is found that the two-dimensional fields of WSS are characterised as streamwise-elongated streaky structures

    更新日期:2020-07-23
  • Towards a self-consistent Boltzmann's kinetic model of fluid turbulence
    J. Turbul. (IF 1.573) Pub Date : 2020-07-22
    Sauro Succi

    A closure for the effective relaxation time of the Boltzmann–BGK kinetic equation for fluid turbulence is presented, based on a double-averaging procedure over both kinetic and turbulent fluctuations. The resulting effective relaxation time appears to agree with values obtained via a renormalisation group treatment of the Navier–Stokes equation only at low values of k/T, the ratio of turbulent kinetic

    更新日期:2020-07-22
  • A perspective on machine learning in turbulent flows
    J. Turbul. (IF 1.573) Pub Date : 2020-04-24
    Sandeep Pandey; Jörg Schumacher; Katepalli R. Sreenivasan

    The physical complexity and the large number of degrees of freedom that can be resolved today by direct numerical simulations of turbulent flows, and by the most sophisticated experimental techniques, require new strategies to reduce and analyse the data so generated, and to model the turbulent behaviour. We discuss a few concrete examples for which the turbulence data have been analysed by machine

    更新日期:2020-04-24
  • Length scales in turbulent free shear flows
    J. Turbul. (IF 1.573) Pub Date : 2020-04-15
    G. Cafiero; M. Obligado; J.C. Vassilicos

    We address the important point of the proportionality between the longitudinal integral lengthscale (L) and the characteristic mean flow width (δ) using experimental data of an axisymmetric wake and a turbulent planar jet. This is a fundamental hypothesis when deriving the self-similar scaling laws in free shear flow. We show that L/δ is indeed constant, at least in a range of streamwise distances

    更新日期:2020-04-21
  • Staircase scaling of short-time energy transfer in turbulence
    J. Turbul. (IF 1.573) Pub Date : 2020-04-21
    L. Fang; T. Wu; Wouter J.T. Bos

    It is illustrated that a sharply truncated initial kinetic energy spectrum evolves to a staircase-shaped spectrum at short times. This effect is directly associated with the triadic nature of the energy transfer. A rigorous analysis leads to predictions on the time-dependence of this effect, and these predictions are verified by both direct numerical simulations and eddy-damped quasi-normal Markovian

    更新日期:2020-04-21
  • Three-dimensional inert and reactive shock-interface interactions: statistical flow characterisations
    J. Turbul. (IF 1.573) Pub Date : 2020-04-21
    Dandan Wang; Gang Dong

    Three-dimensional inert and reactive shock-interface interactions are simulated by solving NS equation with ninth-order WENO scheme. An initial planar shock wave with Mach number 1.7 accelerates a single mode and finite thickness interface with initial wavelength 4 mm and amplitude 0.4 mm from the reactant composed of C2H4+3O2+4N2. Then the transmitting shock branch is reflected at the end boundary

    更新日期:2020-04-21
  • Direct numerical simulations of forced homogeneous isotropic turbulence in a dense gas
    J. Turbul. (IF 1.573) Pub Date : 2020-03-19
    A. Giauque; C. Corre; A. Vadrot

    Direct Numerical Simulations (DNS) of forced homogeneous isotropic turbulence in a dense gas (FC-70), accurately described by a complex EoS, are computed for a turbulent Mach number of 0.8. In a numerical experiment, results are compared to the ones obtained when considering the fluid as a perfect gas. It is found that the dense gas displays a deeply modified shocklets' structure. The amplitude of

    更新日期:2020-04-20
  • Effect of hemispherical turbulators in a double-pipe heat exchanger for heat transfer augmentation
    J. Turbul. (IF 1.573) Pub Date : 2020-03-19
    Shiva Kumar; P. Dinesha; Akshith Narayanan; Rahul Nanda

    In a double-pipe heat exchanger, heat transfer enhancement can be carried out by active or passive methods. In the present study, heat transfer characteristics are studied by the addition of hemispherical turbulators placed in the annulus region in a double-pipe heat exchanger. The turbulators are placed in the annulus region on the inner pipe separated at 90° to each other around the circumference

    更新日期:2020-04-20
  • Experimental investigation of turbulent boundary layers at high Reynolds number with uniform blowing, part I: statistics
    J. Turbul. (IF 1.573) Pub Date : 2020-03-17
    G. Hasanuzzaman; S. Merbold; C. Cuvier; V. Motuz; J.-M. Foucaut; Ch. Egbers

    Uniform blowing in wall bounded shear flows is well known for its drag reducing effects and has long been investigated ever since. However, many contemporary and former research on this topic has confirmed the drag reducing effect but very less is known regarding how blowing is effecting the Reynolds stresses at high Reynolds number. Therefore, effect of uniform blowing has been experimentally investigated

    更新日期:2020-04-20
  • Monte Carlo science
    J. Turbul. (IF 1.573) Pub Date : 2020-03-19
    Javier Jiménez

    This paper explores how far the scientific discovery process can be automated. Using the identification of causally significant flow structures in two-dimensional turbulence as an example, it probes how far the usual procedure of planning experiments to test hypotheses can be substituted by ‘blind’ randomised experiments and notes that the increased efficiency of computers is beginning to make such

    更新日期:2020-03-19
  • Neural network models for the anisotropic Reynolds stress tensor in turbulent channel flow
    J. Turbul. (IF 1.573) Pub Date : 2019-12-24
    Rui Fang; David Sondak; Pavlos Protopapas; Sauro Succi

    Reynolds-averaged Navier-Stokes (RANS) equations are presently one of the most popular models for simulating turbulence. Performing RANS simulation requires additional modelling for the anisotropic Reynolds stress tensor, but traditional Reynolds stress closure models lead to only partially reliable predictions. Recently, data-driven turbulence models for the Reynolds anisotropy tensor involving novel

    更新日期:2019-12-24
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