ABSTRACT We performed large-eddy simulations of the flow over an aerofoil to understand the effects of leading-edge roughness designed to mimic ice accretion. The roughness elements protrude outside the boundary layer, which, near the leading edge, is very thin; thus, the configuration does not represent a classical rough-wall boundary layer, but rather the flow over macroscopic obstacles. A grid convergence

The wall-shear stress (WSS) fluctuations in the interaction of an oblique shock wave with a flat-plate turbulent boundary layer are investigated by means of direct numerical simulation (DNS) at Mach 2.25. The numerical results agree very well with previous experiments and DNS data in terms of turbulence statistics, wall pressure, and skin friction. The fluctuating WSS characteristics, including probability

The discrete element (roughness) method developed a few decades ago is revisited using the double-averaging technique applied to the Navier-Stokes equation. A k−ω-based DANS turbulence model is thus derived to be able to account for roughness effects. Several closure relations are proposed to model all terms induced by the use of the double averaging. The momentum and energy equations are considered

Direct numerical simulations of a turbulent channel with liquid infused surfaces made of longitudinal micro-ridges have been performed to study the effect of texture geometry and interface deformation. The flow conditions consider a viscosity ratio μ1/μ2=0.37, several values of the micro-ridge pitch and two different Weber numbers, We = 0 and We = 50. The performance is analyzed in terms of drag reduction

A reduced-order model (ROM) is proposed for efficient drag prediction on a streamlined body with surface imperfections that emulate leading-edge roughness or erosion-induced damage. Surface imperfections are idealised as forward-facing step(s) for which the chordwise position, spanwise length, and distribution of steps are varied. It is hypothesised that superposed a bilinear dependencies on the chordwise

ABSTRACT Monistic thermomechanics of eddy mater-space with metric stresses of Maxwellian type and inelastic metric waves can be developed for purely kinetic densities of the nonlocal mass-energy integral. Pseudo-Riemannian 4-geometry uses locally warped time to preserve the Euclidean sublight transport of nonlocally correlated densities with instantaneous metric connections and coherent conservation

Tomographic particle image velocimetry (Tomo-PIV) was performed to study the initial transition process formed in a free round jet between the laminar flow at the jet exit, and the fully turbulent flow region at Red = 6500. The evolution of the small-scale turbulence characteristics in this particular region has been assessed by means of the invariants of the velocity gradient tensor (VGT). These invariants

For complex flow systems like the one of the wind turbine wakes, which include a range of interacting turbulent scales, there is the potential to reduce the high dimensionality of the problem to low-rank approximations. Unsupervised cluster analysis based on the proper orthogonal decomposition is used here to identify the coherent structure and transition dynamics of wind turbine wake. Through the

This study was aimed at examining the influence of the system rotation as an external action on the development of vortical structures and combustion. Specifically, three-dimensional direct numerical simulations of compressible mixing layers with non-premixed H2/air combustion were performed using a detailed chemical reaction scheme. The relationship between the developing vortical structures and chemical

Direct numerical simulations of turbulent boundary layers with roughness elements on a wall were performed to investigate the spatial characteristics of rough-wall turbulence and establish a corresponding prediction method. When the roughness height was larger than the buffer layer, the rough-wall turbulence exhibited different spatial characteristics of the turbulence structures from those pertaining

The dynamical effects of roughness geometry on the response of a half-height turbulent channel flow to an impulse acceleration are investigated using direct numerical simulations. Two rough surfaces different in the surface height spectrum are compared between themselves and with a smooth-wall baseline case. Both rough cases develop from a transitionally rough state to a fully rough one. Results show

ABSTRACT The objective of this paper is to propose a new intermittency transport equation that is naturally capable of capturing the effects of free-stream turbulence and pressure gradient on bypass and natural transition without need for any extra parameters/terms to take into account the free-stream turbulence and the pressure gradient. This new intermittency transport equation is obtained by derivation

Spontaneous and stochastic reversal of large scale flow structure is an intriguing and crucial phenomenon in turbulent Rayleigh-Bénard type natural convection. This paper proposes a new control approach to eliminate the reversals through stabilising the corner flows using two small sidewall controllers. Based on a series of direct numerical simulations, it is shown that the control can successfully

ABSTRACT We present an experimental and numerical study of the flow downstream of honeycomb flow straighteners for a range of Reynolds numbers, covering both laminar and turbulent flow inside the honeycomb cells. We carried out experiments with planar particle image velocimetry (PIV) in a wind tunnel and performed numerical simulations to perform an in-depth investigation of the three-dimensional flow

ABSTRACT We present a systematic approach to extract the characteristic vortex region that contains the essential features of a complex flow field. The process involves the analysis of the complex eigenvalues of the velocity gradient tensor. In particular, we propose the analysis using the joint and marginal probability distributions of the complex eigenvalues of the velocity gradient tensor that preserves

In purely axisymmetric turbulence sustained by a linear forcing mechanism, a stable, entirely poloidal flow is observed when the toroidal component of the forcing is below a threshold. We investigate using numerical simulations whether this state persists when toroidal variations of the flow are continuously reintroduced and the forcing is purely poloidal. It is shown how the pressure–strain correlation

(2021). Special issue on rotating turbulence. Journal of Turbulence: Vol. 22, Rotating Turbulence, pp. 231-231.

Turbulence is characterised by non-linear transfer of energy and other invariants across an extended range of scales, from the injection scale to where dissipation is active. Many flow configurations in nature and in the laboratories deviate from the ideal homogeneous and isotropic turbulent cases (HIT) characterised by the presence of direct energy cascade only and strong small-scales universality

Coriolis-centrifugal convection ( C3) in a cylindrical domain constitutes an idealised model of tornadic storms, where the rotating cylinder represents the mesocyclone of a supercell thunderstorm. We present a suite of C3 direct numerical simulations, analysing the influence of centrifugal buoyancy on the formation of tornado-like vortices (TLVs). TLVs are self-consistently generated provided the flow

Non-premixed impinging jet flames with different coflow conditions are performed using PIV technology combined with numerical simulation to investigate flame instability in the vicinity of wall. Results indicate that the increase of coflow velocity results in a more chaotic flow field and higher fuel efficiency, and the increase of coflow temperature leads to ignition advance and the increase of NO

We investigate the enstrophy dynamics in relation to objective Eulerian coherent structures (OECSs) and their impact on the enstrophy and scalar transport near the turbulent/non-turbulent interface (TNTI) in flows with and without stable stratification. We confirm that vortex-stretching produces enstrophy inside the boundaries of the OECSs, while viscous diffusion transfers the enstrophy across the

In this study, a RANS model of turbulent conjugate heat transfer has been developed, which is applicable across a range of different combination of fluid and solid thermal properties. This is achieved by focusing on the transport equations for the temperature variance and its dissipation rate across the solid walls which bound the flow region. In this investigation we make use of a wider range of DNS

An experimental investigation of near-wall scale interactions in the presence of a deterministic forcing input is presented in this work. The external forcing input was generated by a wall-mounted piezoelectric (PZT) actuator, which directly introduces a dynamic perturbation into the near-wall cycle of turbulent boundary layer flow. The spectra of velocity fluctuations indicated that the fundamental

ABSTRACT This paper explores the use of a small-span direct numerical simulation for a transient, smooth-wall turbulent channel flow and then applies the small-span simulation to a transient channel flow with riblets. A flow configuration similar to that of S. He and M. Seddighi (J Fluid Mech. 2013;715:60–102) is used to study the impulse response of a half-height channel flow to an abrupt increase

ABSTRACT Hydrocyclones are widely used in industry and CFD has been used to compute them. Reynolds stress turbulence models (RSM), which are computationally costly and oftentimes hard to converge, are often recommended in these computations. The present work has selected a liquid-liquid separation hydrocyclone for which single-phase experimental tangential and axial velocity profiles are available

ABSTRACT The performance of ultra-high-lift (UHL) low-pressure turbine (LPT) is subject to complex flow phenomena (e.g. separation, transition and reattachment) which require advanced modelling for accurate numerical predictions. The feasibility and fidelity of three widely used transition-based turbulence models are evaluated in the Reynolds-Averaged Navier-Stokes (RANS) prediction of low-Reynolds

Rotating Rayleigh–Bénard convection is a simple model system used to study the interplay of buoyant forcing and rotation. Many recent studies have focused on the geostrophic regime of turbulent rotating convection where the principal balance of forces is between the Coriolis force and the pressure gradient. This regime is believed to be representative of conditions in geophysical and astrophysical

ABSTRACT The present numerical study aims to numerically investigate the dynamic and turbulent characteristics of a two-dimensional and turbulent offset jet. Three different parameters were investigated: The Reynolds numbers (Re) which was varied from 10000 to 30000, wall inclination angle (α) that was from −20° to +20° and finally the offset ratio (OR) which extends from 3.25–13. Ansys Fluent was

Hysteresis behaviour was reported in spanwise rotating plane Couette flow (RPCF) at Reynolds number R e w = U w h / ν = 1300 with varying rotation number R o = 2 Ω z h / U w in a recent work (Huang et al. Phys. Rev. Fluids 2019;4:052401(R)). Here, U w is half of the velocity difference between two walls, h is half of the channel width, ν is the kinematic viscosity and Ω z is the constant angular velocity

Hysteresis behaviour was reported in spanwise rotating plane Couette flow (RPCF) at Reynolds number R e w = U w h / ν = 1300 with varying rotation number R o = 2 Ω z h / U w in a recent work (Huang...

We report of a series of laboratory experiments and numerical simulations of freely decaying rotating turbulent flows confined in domains with variable height. We show that the vertical confinement...

The local flow field and wake region over a forward-facing obstacle were experimentally investigated, when the water surface above the obstacle was dipped compared to flow further upstream and furt...

Heated horizontal plane jets find wide applications in engineering appliances such as air curtains and discharge of industrial effluents. In the present study, experimental investigations are conducted on a heated horizontal plane jet with the Reynolds numbers in the transitional regime, using a hotwire anemometer. In the far to very far-field (20 < x/d < 100) centreline velocity decay and jet spread

Asymptotic methods have been used to study a turbulent flat mixing layer comprising a viscous compressible gas flow descending from the trailing edge of a body and a gas at rest having the same chemical composition but a different temperature. In contrast to the existing methods for analysing turbulent flows using the Reynolds-averaged Navier-Stokes (RANS) equations, with some closure hypotheses, this

Aero-optical reduction in flat-plate turbulent boundary layer has been widely concerned due to critical application for high-speed target-seeking vehicles. From the perspective of disciplinary intersection between aerodynamic and optical engineering, the turbulence-aberrated optical behaviour, in high-Reynolds-number supersonic freestream, is numerically investigated using the in-house code High-Order

There is a substantial need to better understand multi-physics interactions in realistic laboratory experiments, yet it is currently unfeasible to perform direct numerical simulations (DNS) of most such problems. As a result, reduced-order models such as those used to represent unclosed subgrid-scale stresses in large-eddy simulations (LES) and advanced numerical techniques, including adaptive mesh

This paper investigates the effects of co-flow jet on the aerodynamic performance of some symmetric blade sections of wind turbines. The Reynolds number of 1.3 × 105, angles of attack between 0° and 18° and momentum coefficients of 0.03, 0.05, and 0.08 are considered for four airfoils of NACA 0012, 0015, 0018, and 0021 as the blade sections. To numerically simulate the fluid flow, the Navier-Stokes

The magnetohydrodynamic (MHD) control has great potential in the applications of hypersonic vehicles. Typically, the MHD flowfield in these applications is low magnetic Reynolds (Rem ) compressible turbulent flow, which is different from that without magnetic field and within the high Rem range. This paper investigated the low Rem compressible MHD isotropic turbulence in different Taylor-scale Reynolds

(2020). Editorial. Journal of Turbulence: Vol. 21, The machine learning: Guest edited by Federico Toschi, pp. 483-483.

ABSTRACT Motivated by the needs of wall modelled Large Eddy Simulation (LES), we introduce fits to numerical solutions of the Reynolds Averaged Navier–Stokes equations in their simplest near-wall, boundary layer approximation including a mixing-length model. We formulate the problem such that independent dimensionless variables are those directly available in LES. We provide practical fits for the

A numerical solution of the Navier–Stokes equations describing the instability of a two-dimensional subsonic flow about a flat plate is presented. It is obtained with the 16th-order multioperators-based scheme without introducing artificial exciters. It shows how small numerical disturbances produced by the scheme generate downstream from the leading edge a succession of wave packets formed by the

Direct Numerical Simulations (DNSs) of high Reynolds number turbulent flows, encountered in engineering, earth sciences, and astrophysics, are not tractable because of the curse of dimensionality associated with the number of degrees of freedom required to resolve all the dynamically significant spatio-temporal scales. Designing efficient and accurate Machine Learning (ML)-based reduced models of fluid

We performed direct numerical simulations of a turbulent channel flow in viscoelastic fluids to assess various spatial scaling methods and to find a scaling method that can visualise the spatial features regardless of fluid properties. The Giesekus and Oldroyd-B models were used as constitutive equations to model the viscoelastic fluids alongside a Newtonian fluid. The initial scaling method that can

The effects of Reynolds number on flow and mixing characteristics of a merged single swinging jet induced by a V-shaped fluidic oscillator were studied experimentally. The jet Reynolds number was varied from 80 to 3000. A high-speed digital camera was used to capture the instantaneous flow evolution processes using the laser light-sheet-assisted flow visualisation method. Long-exposure images together

ABSTRACT The Discrete Element Method (DEM) for modelling of flow over rough walls is revised in the framework of the DANS (Double Averaged Navier-Stokes) equations, with a special focus on the drag term appearing in the mean momentum equation as a key to the robustness of the model. A set of 14 Direct Numerical Simulations (DNS) of channel flows with systematically varying roughness topographies is

The constant growth of computational resources allows performing Large-Eddy Simulation (LES) on realistic flow configurations. In this context, it is important to properly model boundary conditions and particularly inflow turbulence. This study addresses wind tunnel applications where the object under investigation is downstream of a turbulence grid. This grid aims at generating a highly turbulent

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

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

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

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

ABSTRACT 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

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

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

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

ABSTRACT 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

Abstract 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

ABSTRACT 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

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

ABSTRACT 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

ABSTRACT 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