Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session L08: Boundary Layers: Turbulent I |
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Chair: Umberto Ciri, University of Puerto Rico - Mayagüez Room: 135 |
Monday, November 21, 2022 8:00AM - 8:13AM |
L08.00001: Comparison between pressure-driven and shear-driven oscillatory flows over ripples Umberto Ciri, Sylvia Rodriguez-Abudo, Stefano Leonardi The seabed in littoral zones is characterized by an oscillatory flow motion generated by sea surface waves through gravity. The so-called wave bottom boundary layer affects the whole seabed ecosystem, from remodeling the bed morphology to the transport of nutrients and substances dispersed in water. To date, a complete understanding of this flow is still lacking. Commonly, in numerical or experimental laboratory studies, the oscillations of the bottom boundary layer are induced through either shear-driven devices (such as an oscillating tray bed in a tank with still water) or pressure-driven mechanisms (using, for example, oscillating water tunnels) to approximate field conditions. There has been relatively limited attention to compare the two types of forcings. The objective of this work is a systematic comparison of shear-driven and pressure-driven oscillatory flow over a bed made of ripples, such as those that are typically encountered in littoral areas. The study will be conducted using direct numerical simulations, with the immersed boundary method to model the bed geometry. Two oscillatory-flow forcing mechanisms (pressure-driven and shear-driven) will be compared for the same conditions. Implications for the dynamics of the seabed will be analyzed and discussed. |
Monday, November 21, 2022 8:13AM - 8:26AM |
L08.00002: Dynamics and boundary conditions are key to the universal scaling of drag in wall turbulence Shivsai A Dixit, Abhishek Gupta, Harish Choudhary, Thara Prabhakaran Scaling of surface drag in turbulent flows past solid surfaces is of prime scientific and technological importance. Successful scaling descriptions are available for canonical flow types and Reynolds number ranges that enable predictions in a limited class of flows. However, a truly universal scaling of drag uniformly valid across all types of flows (canonical as well as non-canonical) and covering complete (to date) range of Reynolds numbers has remained elusive so far. Here, we present the universal scaling of drag that comes with remarkable predictive power as a by-product. Theoretical foundation for this universal scaling enables correct choice of length and velocity scales that must be consistent with the flow dynamics; the scales that are customarily used fail to qualify this criterion. The main scaling consists of two aspects: first, a dynamically-consistent definition of dimensionless drag and Reynolds number, and second, accounting for the distinguishing differences in boundary conditions amongst different flows. Several high-quality data sets from a variety of flows in the literature unequivocally confirm the validity and practical utility of the universal scaling of drag. |
Monday, November 21, 2022 8:26AM - 8:39AM |
L08.00003: Turbulent drag reduction for rough wall boundary layers by spanwise wall oscillations Ivan Marusic, Rahul Deshpande, Aman G. G Kidanemariam, DILEEP CHANDRAN, Alexander J Smits Spanwise surface/wall oscillation has proven to be a successful active flow control technique for reducing turbulent boundary layer drag. Marusic et al.^{1} recently demonstrated that this technique could yield drag reduction at high Reynolds numbers via two possible strategies: (i) the well-known inner-scale actuation strategy, targeting the viscosity dominated motions, and (ii) the novel outer-scale actuation strategy, targeting the inertia-dominated motions. However, these strategies have only been tested for smooth wall boundary layers. This study investigates the efficacy of both these strategies for transitionally and fully rough wall boundary layers. Emphasis is placed on comparing the performance of the inner-scale actuation strategy for smooth and fully rough wall boundary layers, considering the near-wall viscous cycle is severely disrupted in the latter. For this, we consider low-Reynolds-number direct numerical simulations, and high-Reynolds-number drag measurements over smooth and rough wall flows, imposed with spanwise surface oscillations at matched actuation parameters. |
Monday, November 21, 2022 8:39AM - 8:52AM |
L08.00004: Temporal and Spatial Evolution of a Turbulent Boundary Layer from a Drag-Reduced to a Canonical State Thomas C Corke, Andrew Myers, Flint O Thomas Experimental results are presented that are designed to shed light on the long-held questions regarding the causal direction and importance of interactions between outer and near-wall vortical motions in turbulent boundary layers that are associated with turbulence production. This makes use of our approach (Duong, et al, JFM, 2021) to produce up to 80% viscous drag reduction in turbulent boundary layers, with scaling covering a full decade range of Mach numbers. The drag-reduced boundary layers exhibit reduction in all Reynold stress components, turbulence production and the frequency of discrete turbulence producing events in proportion to the degree of drag reduction. The experiments document the temporal and spatial development of the turbulent boundary layer when the actuation that produces drag reduction is impulsively ceased, and the boundary layer evolves back to the canonical state. The measurements include all three velocity components in 3-D space, and 3-D spatial reconstructions of conditionally-averaged velocity components based on the detection of Reynolds stress-producing "burst-sweep" events. The ensemble-averaged velocity components are used to document the evolution of 3-D vortical structures associated with the turbulence production in the wall layer. |
Monday, November 21, 2022 8:52AM - 9:05AM |
L08.00005: Building-block-flow model for large-eddy simulation Adrian Lozano-Duran, Yuenong Ling, Gonzalo Arranz, Emily Williams A unified subgrid-scale+wall model for large-eddy simulation is proposed by devising the flow as a collection of building blocks flows. The information from the building blocks enables the prediction of the eddy viscosity. The building blocks are simple canonical flows based on the turbulent Poiseuille-Couette configuration at different flow regimes. The model is constructed to predict wall-attached turbulence, adverse pressure gradient effects, separation, statistically unsteady turbulence, and laminar flow. The approach is particularly designed for coarse grids by accounting for numerical errors. |
Monday, November 21, 2022 9:05AM - 9:18AM |
L08.00006: Building-block flow model for large-eddy simulation: Applications Gonzalo Arranz, Yuenong Ling, Emily Williams, Konrad Goc, Kevin P Griffin, Adrian Lozano-Duran A subgrid-scale (SGS) model for large-eddy simulation is proposed by devising the flow as a collection of building blocks, whose information enables the prediction of the eddy viscosity. The building blocks are simple canonical flows based on turbulent Poiseuille-Couette flow at different regimes. The model is implemented in the finite-volume compressible solver charLES and validated in a realistic aircraft geometry, the high-lift CRM, which is representative of external aerodynamic applications with trailing-edge separation. The accuracy of the model is compared against traditional SGS models such as Vreman model and Dynamic-Smagorinsky model. |
Monday, November 21, 2022 9:18AM - 9:31AM |
L08.00007: Direct numerical simulation of the Gaussian (Boeing) bump: pressure gradient and curvature effects Aviral Prakash, Riccardo Balin, John A Evans, Kenneth E Jansen Direct numerical simulation of a turbulent boundary layer over the Gaussian (Boeing) bump is performed at Re_{L} = 2 million. The flow exhibits a strong pressure gradient and curvature of streamlines leading to mild flow separation just past the bump peak. We plan to present fully converged statistics of the velocity, Reynolds stresses, and turbulent kinetic energy budget in the pre-separation region of the flow. In this region, we analyze the flow in a streamline-aligned coordinate system to discern the influence of momentum balance on the flow behavior. Scaling analysis showing the collapse of velocity and stress profiles in different regions of the flow will also be presented. These insights will allow for a better understanding of the physics of a turbulent boundary layer under the influence of pressure gradients and could pave the path for improved turbulence models. |
Monday, November 21, 2022 9:31AM - 9:44AM |
L08.00008: Direct numerical simulation of the Gaussian (Boeing) Bump: Separated flow region Kenneth E Jansen, Aviral Prakash, Riccardo Balin, John A Evans Direct Numerical Simulation of a turbulent boundary layer over the Gaussian (Boeing) bump is performed at ReL = 2 million (based on the tunnel width L which corresponds to Reh=170,000 based on the bump height). This simulation will be contrasted with prior published results at ReL=1 million case (same geometry at half the speed) where the flow did not separate due to re-laminarization and re-transition. At 2 million the flow remains turbulent and separates soon after the onset of a strong adverse pressure gradient just past the bump apex. Velocity, Reynolds stresses, spectra, and turbulent kinetic energy budgets from the post-separation region of the flow will be presented and discussed. In this region, we also analyze the flow in a streamline-aligned coordinate system to better understand its flow physics. |
Monday, November 21, 2022 9:44AM - 9:57AM |
L08.00009: On the logarithmic layer in open channel flow Sergio Pirozzoli We carry out DNS of open channel flow up to Re_{τ}=6000. Compared with the case of a full channel, the outer part of the flow exhibits organization on a larger scale, with wider scale separation between the inner and the outer energetic sites. This implies changes in the outer-layer velocity profile, which stays much closer to a genuine logarithmic distribution that in a full channel, for given Reynolds number. Velocity variances are also affected, being generally larger than in the full channel case. Our results seem to support the notion that deviations from the logarithmic behavior observed in previous channel and pipe flow DNS are likely due to limited Reynolds number, rather that to other physical effects |
Monday, November 21, 2022 9:57AM - 10:10AM |
L08.00010: Relations for the skin-friction coefficient of canonical flows Pierre Ricco, Martin Skote It is shown that the relation discovered by Fukagata et al. (2002) for the skin-friction coefficient of free-stream boundary layers simplifies to the von Kármán momentum integral equation when the upper integration bound along the wall-normal direction is taken asymptotically large. If the upper bound is finite, the weighted contributions of the terms of the streamwise momentum equation depend spuriously on the bound itself. The family of infinite identities obtained by successive integrations also reduces to the von Kármán equation. For channel flows, we prove that only the original identity found by Fukagata et al. (2002) possesses a physical meaning as we show that the infinite family degenerates to the definition of skin-friction coefficient as the number of integrations grows asymptotically. The dependence on the number of repeated integrations is therefore also non-physical. By a twofold integration, we find an identity, valid for channel and pipe flows, that links the skin-friction coefficient with the integrated Reynolds stresses and the centreline mean velocity. We further use the identity found by Renard & Deck (2016) to decompose the momentum thickness as the sum of an energy thickness, a thickness related to the mean-flow wall-normal convection and a thickness linked to the mean-flow streamwise inhomogeneity. This decomposition is useful to interpret the skin-friction decomposition physically and for quantifying the role of the different momentum-equation terms on the friction drag. |
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