Nature of turbulence inside a cubical lid-driven cavity: Effect of Reynolds number

https://doi.org/10.1016/j.ijheatfluidflow.2019.108498Get rights and content

Highlights

  • Large eddy simulation of cubic lid-driven cavity flow has been performed at Reynolds number varying from 1000 to 15000.

  • Flow is laminar but unsteady at Re = 3200; with increase in Re, flow becomes turbulent and crosscorrelation value decreases.

  • Fourier spectra of auto-correlation shows a slope of 5/3 in the sub-inertial range irrespective of the Reynolds number.

  • The turbulence is non-homogeneous even at low Re (= 3200) and inhomogeneity increases with Reynolds number.

  • AIM shows that turbulence is anisotropic, specially at near wall and corner regions.

Abstract

Large eddy simulation of incompressible flow inside a cubic lid driven cavity for a range of Reynolds number (Re=1000,3200,5000,10000,15000) is carried out using dynamic Smagorinsky model (DSM). Centerline average velocity profiles are compared with the existing experimental and numerical results. Except for Re = 1000, the boundary layer slope at wall remains almost same up to the point of inflexion on the mid-bottom wall and on the mid-upstream wall. With increase in Re, the point of inflexion adjusts in such a way so as to make larger and larger volume of fluid a sluggishly-rotating central core. The turbulent quantities such as turbulent kinetic energy and turbulent dissipation are found to be increasing with increase in Re. The auto and cross-correlation coefficient of velocity components are studied and it is found that low Re (= 3200) flow shows periodic nature and as Re increases it becomes aperiodic and turbulent. The cross-correlation decreases with increase in Re. The Fourier spectra of auto-correlation coefficient follows Kolmogorov’s 53 slope in the inertial subrange irrespective of the Re, but the length of inertial subrange increases as Re increases. Kolmogorov length scale (η) and Taylor micro scale (λ) are calculated and it is found that both decrease towards the wall as dissipation is high at the walls. Anisotropic invariant map (AIM) has been plotted; nature of turbulence is found to be non-homogeneous and anisotropic even at low Re (= 3200) and non-homogeneity increases as Re increases. With increasing Re, the turbulence at the core region of the cavity shifts closer to isotropic.

Introduction

In a rectangular three-dimensional cavity, tangential movement of a plane wall with constant velocity representing Dirichlet boundary condition evokes interesting fluid flow physics. Despite simple in geometry, the flow inside the cavity is very much involved, specially at high Reynolds number (Re). Evolution and sustenance of turbulence inside the cavity makes it very difficult to analyze with the presence of complex phenomena like flow separation and reattachment, vortex formation (demonstration of Prandtl-Batchelor theorem), vortex stretching, recirculation, flow bifurcation, transition from laminar to turbulent flow etc. Even though a large number of researcher studied the lid-driven-cavity (LDC) before, it is difficult to analyze all the aspects of the flow. Any change in the flow conditions like Reynolds number or geometrical conditions like aspect ratio, orientation of the cavity, shape of the cavity makes the flow to behave differently. A schematic of an LDC is shown in Fig. 1.

The central main vortex as presented on the plane of symmetry (y=W2) is called the primary vortex (PV). Three other secondary vortices viz. downstream secondary vortex (DSV), upstream secondary vortex (USV) and upper upstream secondary vortex (UUSV) are formed at the corners of the symmetry plane. In addition to these symmetry-plane vortices, Taylor-Görtler like (TGL) vortices are also present in the cavity on the transverse plane.

Koseff and Street (1984c) have conducted experiments in a cavity of L × H × W of 150 mm × 150 mm × 450 mm i.e. 1:1:3 cavity. Their focus was directed towards the presence of turbulence, three-dimensionality of flow, effect on DSV and the start-up flow for TGL vortices. The Reynolds number was varied from 1000 to 10000. They reported that the turbulent features appear at Re in the range of 6000–8000. The symmetry-plane velocity distribution and the DSV size were found to be smaller when compared with the two-dimensional (2D) numerical solutions of Ghia et al. (1982). The decrease was manifested due to the presence of the end-walls. The initial 30 s showed the formation of TGL for all the Reynolds number considered. Koseff and Street (1984b) also investigated the effect of the end-walls and found the DSV to decrease in size for span-wise aspect ratio (SAR) 1:1:1 and 1:1:2 whereas the size increased for 1:1:3 when Re is increased up to 10000. They attributed this phenomenon to the interaction of the DSV with the corner vortices. The time-mean averaged velocity measurements were provided by Koseff and Street (1984a) along with the turbulence measurements. They contend that the flow is concave in the DSV which produces maximum turbulence; end walls in a 3D flow play a significant role, which completely change the flow physics within the cavity. Freitas et al. (1985) made one of the pioneering 3D numerical study to predict the presence of TGL vortices. However, their work was limited to Re = 3200. A most comprehensive experimental study was conducted by Prasad and Koseff (1989). They carried out experiment on lid-driven cavity flow at a wide range of Reynolds number (3200 ≤ Re ≤ 10000) with varying span-wise aspect ratios (SAR = 0.25:1, 0.5:1, 0.75:1 and 1:1). They found that SAR has a dominant effect on flow field and this effect is different at higher and at lower Re. Reduced SAR causes drop in average and root mean square (rms) velocities and the Taylor-Görtler like (TGL) vortices are mostly responsible for velocity fluctuation at lower Re. Iwatsu et al. (1989) have examined the three-dimensional flow structure in detail over a wide range of Reynolds number Re up to 4000 and reported that the flow becomes unsteady at higher values when Re exceeds approximately 2000. Zang et al. (1993) have numerically simulated the LDC for Re = 3200 at 1:1:1 aspect ratio (i.e. cubic) and for Re = 7500 and 10000 at 1:1:0.5 span-wise aspect ratio. They reported that flow becomes unstable near the DSV at Re higher than 6000. Depth-wise aspect ratio (DAR) study along with cubic cavity study was numerically carried out by Cortes and Miller (1994) for Re up to 5000. However, a laminar flow formulation was used. In another numerical study, Chiang, Hwang, Sheu, 1996, Chiang, Sheu, Hwang, 1997, Chiang, Sheu, Hwang, 1998 have considered Re up to 3200 and focused on the transition from steady to unsteady flow. For example, transition occurs at much lower Re in 3D flows. Deshpande and Milton (1998) performed DNS on lid-driven cavity flow where they covered all the flow regime, starting from Stokes flow (Re = 0.1) to turbulent flow at Re = 10000. They noticed that instantaneous dissipation or total dissipation is very high near the moving lid and has high amplitude. The dissipation becomes lower towards the primary vortex core due to high Kolmogorov length scale (η). They also found that the dissipation due to fluctuation or turbulent kinetic energy (TKE) dissipation contributes more to the total dissipation as compared to the dissipation due to mean velocity except for the near wall region. Shankar and Deshpande (2000) in a review article have presented that there exists a considerable difference between a 2D flow and a 3D flow. They have discussed in details about turbulence and their length scales in a cubic cavity.

Leriche and Gavrilakis (2000) carried out DNS in a cubic lid-driven cavity at Re = 12000. Even at this Re, they found that at most part of the cavity, flow is laminar but unsteady and more than 70% of the total energy dissipation in the flow occurs in a thin region close to the moving lid. The flow is not span-wise homogeneous on the symmetrical mid plane which divides the flow into two statistically symmetrical halves. Bouffanais et al. (2007) repeated the work of Leriche and Gavrilakis (2000) but using large eddy simulation (LES) with dynamic Smagorinsky model (DSM) and dynamic mixed model (DMM). They found that the maximum turbulent production occurs at the DSV region just above the bottom plate and the turbulent energy dissipation is significant in the impingement region of the wall jets. Liberzon et al. (2011) conducted experiment on cubic LDC using particle image velocimetry to validate the numerical prediction of steady-oscillatory transition at lower Re. Their study showed that a stable steady state occurs for Re  ≤  1700. The steady-unsteady transition occurs in the range 1700  <  Re  <  1970 and for Re  >  1970, flow becomes oscillatory. The coherent structure passing through the maximum turbulent production zone have been discussed by Patel, Das, Roy, 2013, Patel, Das, Roy, 2014. In this study, λ2 criterion is used to identify the shearing and the swirling structures on the statistically symmetric plane. Using LES, Samantaray and Das (2018) have computed the LDC for aspect ratio (AR) 1:1:0.5 and 1:1:1.5, 1:1:1 and DAR 1:0.5:1 and 1:2:1 where equivalent Re (Rem) =10030. Their computed results are very close to the experimental results of Prasad and Koseff (1989). They concluded that DSV size increases with increase in SAR. Turbulent kinetic energy and turbulent production increases with lower DAR. The anisotropy in turbulence and type of anisotropy are also discussed at length.

By carrying out a detailed literature survey, it is observed that all the previous studies are classified under following broad categories: (a) mean flow distribution for laminar and turbulent regimes, (b) laminar to turbulent transition, (c) turbulence statistics at high Re, viz. at 10000. However, the effect of gradual increase of Re on the passage from laminar flow (i.e. absence of turbulence) to appearance of turbulence to change in the turbulent length scales, anisotropic nature of turbulence was not studied in details. The present work is a large eddy simulation of incompressible fluid flow in a cubic lid-driven cavity at a wide range of Reynolds number (1000 ≤ Re ≤ 15000) using dynamic Smagorinsky model. Though Leriche (2006) conducted a DNS study at Re as high as 18000 and 22000, limited information such as mean and rms velocities were given in that paper. The present study includes a detailed review of all the mean, rms and Reynolds shear stresses for Re 1000, 3200, 5000, 10000 and 15000. Other turbulent characteristics such as turbulent kinetic energy dissipation, auto- and cross-correlation are covered. The anisotropic nature of turbulence has been analyzed with the help of anisotropic invariant map (AIM). The study covers all the way from laminar to turbulent flow at high Re with in-depth description of the physics of the flow.

Section snippets

Governing Equation and Mathematical Formulation

The filtering process is carried out by averaging over a volume △x × △y × △z  and is given by the expression below.f¯(x,y,z,t)=1xyzDf(x,y,z,t)dxdydzHere f¯ is the filtered variable, Davidson (2011).

The non-dimensionalized continuity and Navier-Stokes equation for incompressible flow filtered by a filtering process (Davidson, 2011) as shown in Eq. (1) are given in Eqs. (2) and (3) respectively. Here, position, time, velocity and pressure are normalized by the scales L, LU0, U0 and ρU02

Discretization and Numerical procedure

By substituting Eqs. (4) and (5) in Eq. (3) and rearranging, we getu¯it=Hip¯xi whereHi=xj[(1Re+νsgs)u¯ixj]+xj(νsgsu¯jxi)xj(u¯iu¯j)Second order central difference scheme is used for the spatial derivatives of Eq. (11). They are discretized on a staggered grid arrangement. The velocity field for the first time step is obtained from one-step Euler method (Eq. (13)) and the subsequent steps are obtained from a second order time accurate Adams-Bashforth method (Eq. (14))u¯i*u¯inδt=Hi

Computational domain and boundary condition

The computational domain is cubic space and the flow inside the cavity is assumed to be Newtonian and incompressible with uniform temperature. The numerical simulation is carried out using a structured grid with a grid distribution of hyperbolic tangent transformation (Eq. (17)), which gives almost uniform grid structure in the middle and denser grid size near the walls.xi+1=l2(1+tanh[ζ(2iN11)]tanh[ζ])for0iN1

In Eq. (17), ζ is the stretching function and has the value of 1.0; l and N are

Results and discussion

The non-dimensional integration times are 1250, 1350, 1250, 1045 and 875 for Re =1000, 3200, 5000, 10000 and 15000 respectively. The time increment, δt is taken as 0.0025 in case of Re = 1000, 3200, 5000 and 0.002 in case of Re = 10000 and 15000. These time increment values are well below maximum δt that is calculated using the CFL condition (Eq. (15)) to ensure the numerical stability. Samples are collected at every 0.5 non-dimensional time and the samples that are collected after the

Conclusion

The large eddy simulation of a cubic lid-driven cavity flow for a range of Re (Re = 1000, 3200, 5000, 10000, 15000) has been performed. It is seen that the dynamic Smagorinsky model (DSM) is good at resolving the subgrid-scale stress tensor in the LES. The mean and the fluctuating flow fields have been validated by comparing center line velocities with the experimental results of Prasad and Koseff (1989) (for Re = 3200 and 5000) and Kato and Tanahashi (1992) (for Re = 5000). Conducting discrete

Declaration of Competing Interest

None.

Acknowledgment

The helpful comments and suggestions of the reviewers are gratefully acknowledged by the authors.

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