Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session R42: Turbulence: Wall-Bounded IV |
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Chair: Myoungkyu Lee, University of Houston Room: 207A |
Monday, November 20, 2023 1:50PM - 2:03PM |
R42.00001: Impact of the resolution on DNS results in pipe and channel flows. Sergio Hoyas, Victor Baxerres, Ricardo Vinuesa, Hassan M Nagib Recent results about the overlap region in wall-bounded flows suggest that a combination of log and linear functions is a better representation than the classic log law and covers a wider region of the profile. Utilizing these results requires a very exact representation of the indicator function Ξ ≡ y^{+}dU^{+}/dy^{+}=Y dU/dY. Unfortunately, the convergence and resolution of direct numerical simulations (DNSs) have not received adequate attention for most of the computations of wall-bounded turbulence. For the case of pipe flow, after decades of experience, we recognize that the fully-developed pipe is the ideal flow for comparing computations and experiments, following the experiments of Princeton and Bologna. Regarding channel flows, these have been the most extensively studied in turbulent flows for many years and provide good test cases. Numerically, we have utilized the OpenPipeFlow code for a large pipe of length 10πR. Simulations have been run for friction Reynolds numbers of 500 and 1000 using different meshes. These meshes are comparable to or better than many other DNS and they have been run for up to 100 eddy-turnover times, which exceeds most of the earlier computations. The simulations show a strong dependence on the mesh in the radial direction, needing a grid of around one wall unit. |
Monday, November 20, 2023 2:03PM - 2:16PM |
R42.00002: Direct numerical simulation of turbulent pipe flow at Re_tau=10,000 Philipp Schlatter, Jie Yao, Daniele Massaro, Saleh Rezaeiravesh, Fazle Hussain A new DNS of a (smooth-wall) turbulent pipe flow has been performed for a friction Reynolds number of 10,000 -- larger than previous simulations available in the literature. Given the excessive computational resources necessary, we limited the pipe length to 2 pi R, where R is the pipe radius. This length similar as in comparable recent channel simulations at high Reynolds numbers. The discretization is based on accurate high-order spectral/finite-difference approximations where special care has be put onto resolving the near-wall region. Various low and high-order turbulence statistics are compared with other DNS and experimental data in pipes as well as channels and other canonical flows, as available. Of particular interest is the log-law indicator function, which is shown to be nearly indistinguishable between the pipe and channel up to y+=250. Farther away from the wall, it develops a plateau, with a kappa=0.384, similar to other canonical turbulent wall-bounded cases. Given the new data for the mean flow, we will assess different composite profiles, asymptotic expansions and data-fitting approaches, and discuss some of the commonly employed corrections. Using the fluctuation field, we will also look at spectra to understand the energy distribution as compared to channels. Finally, we will also quantify the uncertainty in the data using an auto-regressive approximation. |
Monday, November 20, 2023 2:16PM - 2:29PM |
R42.00003: Self-similar, spatially localized structures in turbulent pipe flow from a data-driven wavelet decomposition Alex Guo, Daniel Floryan, Michael D Graham Within the chaotic flow field of wall-bounded turbulence, there exist structures that are coherent in space and time. Gaining a mechanistic understanding of wall-bounded turbulence necessitates characterizing these coherent structures. According to Townsend’s attached eddy hypothesis (AEH), these coherent structures are self-similar in the log layer. Subsequent models, such as the attached eddy model, propose these structures are also spatially localized. |
Monday, November 20, 2023 2:29PM - 2:42PM |
R42.00004: On the turbulence characteristics of axisymmetric pipe flow across varying cross section: An experimental Investigation Gal friedmann, dvir feld, Jibu T Jose, OMRI RAM Development of flow along axisymmetric pipes, encountering contractions and expansions are of great engineering significance. Sudden changes in cross sectional area of pipe flow can cause pressure losses, as well as sedimentation in the case of particle laden flows. In the current study, a refractive index matched facility with concentrated aqueous solution of Sodium Iodide is used to study the turbulent nature of the flow near the vicinity of the varying cross-sectional area. Time resolved Tomographic Particle Image Velocimetry (PIV) and 2D high resolution PIV are performed for five different geometries (±90^{o}, ±45^{o},0^{o}). Refractive index matching facilitates unobstructed optical access through the curved walls of the axisymmetric acrylic test section. The area ratios studied are 2.56 for contraction and 0.391 for expansion. The 2D PIV data along the center axial plane is used to measure the boundary layer profile as well as estimate turbulence statistics for various Reynolds numbers (1.8x10^{4}– 1.1x10^{5}). The results are compared for various cross section, including the forward-facing step (-90^{o}) and backward facing step (90^{o}) cases, and the growth and development of the recirculation region is analyzed. The 3D instantaneous flow structures are studied to understand the dominant features in the central flow as well as the near-wall region. |
Monday, November 20, 2023 2:42PM - 2:55PM |
R42.00005: Turbulent Hele-Shaw flow: a paradigm for large-scale model extraction Paolo Luchini Most direct numerical simulations of wall-bounded turbulence (DNS) take place in a doubly infinite plane channel, approximated as a rectangular periodic box. But a plane channel also has significant dynamics in its two homogeneous directions, on a scale typically larger than the channel's thickness, which is often overlooked. In the laminar flow this is evident in the noted Hele-Shaw cell with its governing 2D diffusion equation. It makes sense then to ask what dynamics does a turbulent plane channel, seen as a Hele-Shaw cell, exhibit; or in other words what kind of differential, local (or perhaps integral, nonlocal) equation asymptotically describes it. This question only involves the flow's behaviour in two statistically homogeneous directions, and is therefore in some sense easier to answer in an objective way than other fundamental questions concerning turbulence, yet it does not appear to have received attention. In its simpler form it can be answered theoretically, but to a much deeper extent it can be answered by extracting a large-scale linear response, or transfer function, from the DNS itself. |
Monday, November 20, 2023 2:55PM - 3:08PM |
R42.00006: Helicity and rate of turbulent kinetic energy dissipation in a Lagrangian framework. Oanh L Pham, Dimitrios Papavassiliou The relation between the helicity and the dissipation of turbulent kinetic energy in turbulent flows has been a matter of debate. In this study, Direct Numerical Simulations (DNS) of turbulent Poiseuille and Couette flow were used in combination with Lagrangian Scalar Tracking (LST) at Schmidt numbers of 0.7, 6 and infinite (i.e., fluid particles) to probe the correlation between helicity of the fluctuating velocity field and the dissipation. The scalar markers were released at different locations within the flow field, including the viscous wall sublayer, the transition layer, the logarithmic region and the outer flow. The autocorrelation coefficients, the cross-correlation coefficients and the joint probability density function were employed to investigate the relation between helicity and dissipation along the trajectories of the Lagrangian scalar markers. There was anticorrelation between helicity and dissipation in the near wall region, which was less obvious in the logarithmic region. Helicity was found to characterize flow structures that contribute to the dispersion of scalar markers. |
Monday, November 20, 2023 3:08PM - 3:21PM |
R42.00007: Non-linear temporal dynamics of large-scale structures and turbulence dissipation in turbulent channel flow Le Yin, Yongyun Hwang, John Christos Vassilicos The non-linear dynamics emanating from large-scale structures are explored in channel flow based on DNS datasets up to Reτ≈2000 using minimal computational box for large-scale structures (following Hwang & Cossu, Phys. Rev. Lett., 2010). Volume-averaged temporal correlations between TKE and turbulence dissipation show a well-defined average time lag similar to observations in homogeneous isotropic turbulence by Goto & Vassilicos (Phys. Lett. A, 2015). In channel flow, the TKE produced at large scales is strongly correlated with the large-scale streaks which break down with a downstream meandering motion. The correlation analysis suggests that the TKE in the intermediate layer is transported towards both the core and near-wall regions and dissipated there with a time-lag that is combined with a wall-distance lag. In the path towards the core region the wall-distance lag is equal to the time lag multiplied by the skin friction velocity, particularly if we condition on ejection events, and represents a non-linear interspace/interscale transfer process. The time lag found in the volume averaged picture ensues from both this time-space lag to the core but also from the time-space lag to the wall. The dissipation through the near-wall region has a wider spread of space-time lags and involves a non-trivial energisation of turbulence production in the near-wall and log regions. |
Monday, November 20, 2023 3:21PM - 3:34PM |
R42.00008: Unbounded wall turbulence induced by inverse cascade Pengyu Duan, Xi Chen, Jianchao He While seeking the ultimate statistical invariance of turbulence, classical boundary layer theory is unable to distinguish between the averaged states of wall flows with two- (2D) and three-dimensional (3D) fluctuations. Here we demonstrate glaring differences between 2D and 3D Poiseuille channel flows and present theoretical explanations for the differences in their Reynolds numbers ($Re_ au$) asymptotic behaviors. In particular, due to the peculiar inverse cascade, large-scale wavy structures (LSWS) are developed in 2D flows which inject high energy flux toward the wall and cause extreme wall dissipation. The latter follows a distinct $Re^{1/3}_ au$ scaling in our direct numerical simulation domain ($130<Re_ au<8100$), the trend observed also for the root mean square of the pressure and velocity fluctuations (as well as for the bulk velocity). Rationale for the scaling is further given through an LSWS-induced dissipative time scale (provided with the 2D friction law), which is unlike the viscous time scale in 3D flows due to the absence of LSWS. As a counterpart to the classical boundary layer of bounded 3D fluctuations (Chen & Sreenivasan J. Fluid Mech. 908, 2021; 933 2022), the results here reveal an unprecedented asymptotic state of wall flows in which the inverse cascade induces unbounded 2D fluctuations. |
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