Bulletin of the American Physical Society
74th Annual Meeting of the APS Division of Fluid Dynamics
Volume 66, Number 17
Sunday–Tuesday, November 21–23, 2021; Phoenix Convention Center, Phoenix, Arizona
Session A04: Turbulence: Wall-Bounded Flows I: Turbulence Structure |
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Chair: James Brasseur, University of Colorado, Boulder Room: North 121 B |
Sunday, November 21, 2021 8:00AM - 8:13AM |
A04.00001: Uniform momentum zone scaling arguments from direct numerical simulation of inertia-dominated channel turbulence William Anderson, Yiran Zheng, Scott T Salesky Inertia-dominated wall-sheared turbulence is composed of an inner and outer layer, the former occupied by the well-known autonomous inner cycle while the latter composed of coherent structures with spatial extent comparable to the flow depth. Outer-layer structures instantaneously manifest as regions of quasi-uniform momentum – relative excesses and deficits about the Reynolds average – termed uniform momentum zones (UMZs). Successive UMZs exhibit abrupt wall-normal gradients in streamwise momentum, which cannot be explained by the notion of attached eddies, for which the vertical gradient goes as (x3)-1 (x3 is wall-normal position). Using DNS data of channel turbulence across inertial regimes, we recover vertical profiles of Kolmogorov length a posteriori and show that η ~ (x3)1/4, thereby requiring that ambient wall-normal gradients in streamwise velocity scale as (x3)-1/2 . The data reveal that UMZ interfaces are responsible for these relatively larger wall-normal gradients. The DNS data afford a unique opportunity to interpret inner- and outer-layer structures simultaneously: UMZs – and associated outer-layer dynamics – can be explained as the product of inner-layer bluff-body-like interactions, wherein wakes of quasi-uniform momentum emanate from the inner layer. |
Sunday, November 21, 2021 8:13AM - 8:26AM |
A04.00002: Scalings of turbulence dissipation in space and time for turbulent channel flow Argyrios Apostolidis, John C Vassilicos, Jean-Philippe Laval We investigate the turbulence dissipation scaling in turbulent channel flow in connection with Kolmogorov's equilibrium dissipation scaling. We determine the scalings of three different integral length scales arising from the non-isotropy of the flow, each integral scale resulting in different scalings for the dissipation coefficient. We retrieve the classical Taylor-Kolmogorov dissipation scaling when integral scales based on the wall-normal velocity are used, but we also find a new non-homogeneous dissipation scaling when the dissipation coefficient is computed from the integral scale of the spanwise velocity in the spanwise direction. We also analyse the time dynamics of the dissipation coefficient and the Taylor length-based Reynolds number and find that the two signals are anti-correlated with absolute correlation values from 0.5 to 0.9 across the channel. This translates into an inverse average power-law scaling of the fluctuating dissipation coefficient as a function of Taylor Reynolds number, with exponent between -1 and -1.7 depending on wall-normal direction and choice of integral scale. This anti-correlation must reflect a non-stationary cascade and, in fact, persists when the signals are filtered using either low- or high-pass filters. |
Sunday, November 21, 2021 8:26AM - 8:39AM |
A04.00003: Numerical measurements of temporal and streamwise nonlocality in turbulent channel flow Jessie Liu, Danah Park, Ali Mani In contrast to the commonly used Boussinesq approximation, a purely local approximation, nonlocality refers to the dependence of Reynolds stresses at a given point on mean velocity gradients at all points in space and at previous times. Previous studies of nonlocality in turbulent channel flow (Park and Mani (2019), Hamba (2005)) have focused on quantifying nonlocality in the wall-normal direction. We present measurements of temporal nonlocality and nonlocality in the streamwise direction using direct numerical simulation (DNS) and the macroscopic forcing method (MFM) (Mani and Park (2021)). Our results demonstrate significant nonlocality in the streamwise direction as compared to the wall-normal direction, which may impact modeling of wall-bounded flows with strong mean velocity gradients in the streamwise direction such as separated boundary layers. |
Sunday, November 21, 2021 8:39AM - 8:52AM |
A04.00004: Role of pressure in Reynolds shear stress transport in high Re wall-bounded turbulence Robert D Moser, Myoungkyu Lee We investigate the role of pressure in the transport equation of the Reynolds shear stress (RSS), 〈u'v'〉, in high Re wall-bounded turbulent channel flows. The spectral analysis technique from Lee & Moser (J. Fluid Mech., vol 860, 886-938) is applied to channel flow DNS data at Reτ = 5200. The spectral density of the RSS is highly concentrated in streamwise-elongated modes with a negligible contribution from spanwise-elongated modes. However, there is a non-negligible production of RSS in the spanwise elongated modes, and the inter-scale transfer mechanism moves RSS from streamwise elongated to spanwise elongated modes. The pressure-strain correlation is the only term in the transport equation that is a sink of RSS in spanwise elongated modes. Decomposing the pressure into rapid, slow, and Stokes contributions shows that the rapid pressure-strain is responsible for removing about half of the RSS produced in the spanwise elongated modes. The slow pressure-strain removes the remainder, plus the RSS deposited in spanwise elongated modes via scale transfer. These observations can be interpreted as the consequence of the kinematic continuity constraint on the production and scale transfer processes. |
Sunday, November 21, 2021 8:52AM - 9:05AM |
A04.00005: Symmetry induced high-moment scaling laws of wall-bounded shear flows for arbitrary moments - validation using high Reτ DNS and experimental data Martin Oberlack, Sergio Hoyas, Stefanie V Kraheberger, Francisco Alcántara Ávila, Jonathan Laux, Dario S Klingenberg, Paul Hollmann, Margit Egerer, Marcus Hultmark, Gabriele Bellani, Alessandro Talamelli, Spencer J Zimmerman, Joseph C Klewicki Using symmetry-based turbulence theory, we derive turbulent scaling laws in wall-bounded shear flows for arbitrarily moments of U1. Beside scaling of space and time, we use statistical symmetries, which are not directly observed in Navier-Stokes equations. These symmetries are admitted by the infinite hierarchy of moment and provide a measure of intermittency and non-Gaussianity. In the near-wall region the theory predicts a log-law for the mean velocity (n=1) and an algebraic law with the exponent ω (n - 1) for moments n > 1. Hence, the exponent w of the 2nd moment determines the exponent of all higher moments. Moments here always refer to the instantaneous velocities U and not to the fluctuations u’. For the core regions of both plane and round Poiseuille flows we find an algebraic deficit law for arbitrary moments n with a scaling exponent n(σ2-σ1)+2σ1-σ2. Hence, the moments of order one and two with its scaling exponents σ1 and σ2 determine all higher exponents. All new results are validated by a new plane Poiseuille flow DNS at Reτ=104 and by pipe flow data from the CICLoPE and Superpipe flow experiments up to Reτ=3.8*104. We find that σ1 and σ2 are almost identical, so that the exponents of all moments are essentially constant, which corresponds to anomalous scaling. |
Sunday, November 21, 2021 9:05AM - 9:18AM |
A04.00006: A new length scale for DNS of wall-bounded turbulent flows. Svetlana V Poroseva Comparison of model and DNS profiles for fifth-order velocity moments in a turbulent channel flow under the strain and in a turbulent boundary layer over a flat plate revealed small discrepancies in the buffer zone of both flows. The discrepancies were found to be associated with the magnitude of velocity fluctuations in the streamwise direction, the turbulence production by the shear in the transport equations of odd (third- and fifth order) velocity moments, and with the balance errors in the DNS budgets of the odd velocity moments, all reaching their maximum in the flow buffer zone at close locations. Previous studies confirmed adequacy of convergency of the DNS data used in the study but pointed toward potential issues with the grid resolution near a wall (Poroseva et al. AIAA2016-3940). The standard practice in generating grids for DNS is the use of the Kolmogorov length scale as a guide. This criterion was also applied to obtain the DNS data used in the study. Yet, the theory of local isotropy, where this length scale comes from, is not applicable near the flow boundaries (Kolmogorov, 1941). A new length scale will be presented for the buffer zone to improve the quality of relevant statistics collected from DNS. |
Sunday, November 21, 2021 9:18AM - 9:31AM |
A04.00007: Complete and incomplete similarity for the mean velocity profile of turbulent pipe and channel flows at extreme Reynolds number FABIO A RAMOS, Daniel A Cruz, Hamidreza Anbarlooei, Gabriel Sanfins The recent availability of experimental data on turbulent pipe flows in the extreme Reynolds number range has shown strong evidence that when Re >> O(105), the flow exhibits a transition to new scaling laws for important physical quantities, such as the friction factor and the Reynolds stress. In this work, we discuss a transition concerning the scaling of the mean velocity profile (MVP) of turbulent pipe and channel flows. We will first show that for sufficiently large Re number, the MVP exhibits complete similarity asymptotics in bulk coordinates. Then, using a recent friction power-law formulation for extreme-Re flows, we show that this is equivalent to an incomplete similarity asymptotics. We then use the incomplete similarity asymptotics to relate the representation of the flow in bulk coordinates to the representation of the flow in inner coordinates, so that u+ can be approximated by a Reτ-dependent functional. We also propose a multiscale polynomial model of the MVP, which yields excellent approximations of available data in both bulk and inner coordinates. |
Sunday, November 21, 2021 9:31AM - 9:44AM |
A04.00008: Generalizing the Concept of the Surface Layer Samantha J Sheppard, James G Brasseur, John A Farnsworth, John C Vassilicos The classical description of a "surface layer" is a wall-adjacent region within a high Reynolds number turbulent boundary layer in which turbulence fluctuations are directly modified by surface impermeability and where turbulence integral scales scale with z, the distance from the surface. This description includes both modulation by surface blockage and production by mean shear. To generalize the concept of a "surface layer," we consider these effects separately. Canonical boundary layer PIV data from LMFL is compared to SPIV measurements of grid turbulence blown over an impermeable flat plate to characterize the direct influence of surface impermeability on turbulence structure. We identify a region for the grid turbulence case where integral length scales of fluctuating vertical velocity grow with z and where there exists a deficit in turbulent kinetic energy. The latter is not observed in the canonical turbulent boundary layer data but is consistent with theory developed by Hunt & Graham (1978) and experiments of Thomas & Hancock (1976). By isolating surface blockage effects on grid turbulence, we aim to isolate key surface layer elements associated with the creation of attached turbulence eddies in the absence of turbulence production. |
Sunday, November 21, 2021 9:44AM - 9:57AM |
A04.00009: An experimental study of interaction of Von Kármán vortices and coherent structures in a turbulent boundary layer Elizabeth Torres De Jesús, Theresa Saxton-Fox This experimental study looks into the interaction of vortex shedding and a turbulent boundary layer (TBL) over a flat plate. The aim of the study is to further the understanding of the organization and interaction between large and small coherent structures, with special attention to the outer region. In previous studies, a correlation between them through amplitude modulation and conditional averaging has been described (Mathis et al, 2009; Chung & McKeon, 2010) and structures such as hairpin vortices have been observed to organize in a certain manner in the outer region (Adrian et al, 2000 & 2007). In this study, the interaction between externally-generated small vortices and coherent structures in a TBL over a flate plate is analyzed in the 381mm × 381mm subsonic wind tunnel facility at University of Illinois, Urbana-Champaign, and compared to a canonical TBL over a flat plate in the same facility. The small vortices are generated through the formation of a Von Kármán vortex street in the wake of a cylindrical rod (d=1.905mm) at a fixed wall-normal position with the longitudinal axis pointing span-wise. Using 2D-2C Particle Image Velocimetry (PIV), measurements are taken immediately downstream of the cylinder. |
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