Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session T40: Turbulent Wall Bounded Flow II |
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Chair: Rishita Das, Indian Institute Of Science Room: 355 F |
Monday, November 25, 2024 4:45PM - 4:58PM |
T40.00001: On precisely locating the inertial sublayer in turbulent channel flow Joseph C Klewicki, Jimmy Philip The spatial inertial sublayer in wall-bounded turbulent flows, which also coincides with the logarithmic mean velocity profile, factors importantly in physical, conceptual and mathematically-based flow characterizations. In this regard, studies that seek to predict or describe wall-flow structure are often assessed via the estimation of statistical and/or structural properties on the inertial sublayer. In the interest of obtaining the highest fidelity estimates, it is thus advantageous to have well-justified and precise bounds of the inertial sublayer. Toward this aim, inertial sublayer inner and outer bounds are developed for turbulent channel flow. The Reynolds number dependent bounds are independently founded in the properties of the mean dynamical equation and are set prior to estimating the statistical quantity of interest. The outer bound is shown to depend on the Reynolds shear stress profile curvature, and thus data accuracy sensitivities are important to this bound. With increasing Reynolds number, the inner bound is shown to move to increasing y+ and the outer bound moves to decreasing y/δ, where y+ and y/δ are the inner and outer normalized wall-distances, respectively. Once established, mean flow properties are estimated and assessed on the inertial sublayer using DNS channel data across a friction Reynolds number range 2,000 < δ+ < 16,000. |
Monday, November 25, 2024 4:58PM - 5:11PM |
T40.00002: Abstract Withdrawn
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Monday, November 25, 2024 5:11PM - 5:24PM |
T40.00003: Exploring Surface Pressure Fluctuations in DNS of Turbulent Channel Flow Pedro Ivo Almeida, Mukesh Sharma, Siddhartha Verma The pressure distribution generated by a turbulent boundary layer over a flat wall exhibits extreme localized variations in both space and time. A physical interpretation of the relationship between such wall-pressure fluctuations and coherent velocity structures found in boundary layers is presented here, using direct numerical simulation (DNS) of a turbulent channel flow at Reτ = 300. A visual inspection suggests that the variations in wall pressure may be isotropic. However, a closer examination using spatial and temporal correlations reveals the existence of distinct "pressure structures" in both the streamwise and spanwise directions. It is reasonable to expect that these pressure structures are closely related to the dynamics of wall-bounded turbulent flows, including the well-documented bursting events in the near-wall region. The dominant spatial and temporal frequencies that describe the evolution of wall-pressure distribution and their link to coherent velocity structures are examined using a highly time-resolved DNS database. Understanding the underlying causal link can benefit various practical applications such as noise suppression, sensor array design, and improving fluid transport efficiency in pipes. |
Monday, November 25, 2024 5:24PM - 5:37PM |
T40.00004: Causal interactions between inner and outer layer flow motions in wall-bounded turbulence Alvaro Martinez-Sanchez, Adrian Lozano-Duran The interaction of turbulent motions of different sizes within the thin fluid layers immediately adjacent to solid boundaries poses a significant challenge for physical understanding and prediction of wall-bounded turbulent flows. This study investigates the flow of information between outer layer (far from the wall) and inner layer (close to the wall) motions in a turbulent channel flow. The data were obtained from a direct numerical simulation of a turbulent channel flow at a friction Reynolds number Reτ≈1000. We use time-resolved signals of the streamwise velocity at two wall-normal locations within the inner and outer layers as the main quantities of interest. Then, we employ a method based on information theory to measure the causal relationship between the signals. The method, referred to as SURD (Synergistic-Unique-Redundant decomposition), assesses causality by quantifying the increments of information obtained about future events based on combinations of past events. The causal interactions among these events are further decomposed into redundant, unique, and synergistic contributions according to their nature. Our findings indicate that causality flows predominantly from outer-layer large-scale motions to inner-layer small-scale motions. These results are compared with those obtained from other causal inference methods and demonstrate that SURD offers a more reliable quantification of causality. |
Monday, November 25, 2024 5:37PM - 5:50PM |
T40.00005: ABSTRACT WITHDRAWN
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Monday, November 25, 2024 5:50PM - 6:03PM |
T40.00006: Understanding the scaling exponents in transitional pipe flows VISHNU RAVINDRAN The subcritical nature of the transition to turbulence in pipe flows is manifested as a scaling of the minimal triggering amplitude with Reynolds number. Previous studies have shown the existence of a power law relating the minimal amplitude A to Reβ. The exponent β is reported to be in around a range between -1 to -1.5. However, an investigation into the details of the initial conditions that can give a specific exponent is still not clear. Through a series of direct numerical simulations, we implement different initial conditions of finite width to investigate the variation of this scaling exponent. |
Monday, November 25, 2024 6:03PM - 6:16PM |
T40.00007: Theoretical analysis and stochastic modeling of turbulent heat transfer in annular pipe flows Pei-Yun Tsai, Heiko Schmidt, Marten Klein Heat transfer in annular pipes is determined by the thermal and momentum boundary layer at the cylindrical inner and outer walls, respectively. The relative contributions are expressed by a local Nusselt number that depends on the radius ratio, the Prandtl number, and the Reynolds number. Direct numerical simulation (DNS) has been used previously to infer closure relations constrained to weakly turbulent flow due to numerical resource requirements. Here, stochastic one-dimensional turbulence (ODT) is utilized as a standalone tool as an alternative to DNS. ODT offers full-scale resolution along a representative radial domain, providing predictive capabilities relative to a calibrated reference case at a radically reduced cost. On average, ODT obeys radial balance equations compatible with the Navier-Stokes equations. Separating the boundary layer into a diffusion and a mixing-length dominated region in cylindrical geometry yields wall-curvature corrections at the inner wall. The proposed expressions can be used to enhance prescribed wall functions, for example, in Reynolds-averaged Navier-Stokes simulations. |
Monday, November 25, 2024 6:16PM - 6:29PM |
T40.00008: Self-similar motions for the logarithmic variation of spanwise turbulence intensity in turbulent pipe flow Jeonghoon Yoon, Jinyul Hwang According to Townsend’s attached eddy hypothesis, the streamwise and spanwise turbulence intensities exhibit a logarithmic variation at extremely high Reynolds numbers (Re). However, the spanwise component shows a logarithmic variation even at very low Re, absent in the streamwise component. We investigate this discrepancy by focusing on self-similar motions responsible for the logarithmic variation of the wall-parallel component. We examine the direct numerical simulation dataset of turbulent pipe flows at Reτ = 1000–6000. The two-dimensional (2D) energy spectra of the streamwise and spanwise velocities (Фuu and Фww) are decomposed using linear stochastic estimation based on the cross-spectrum across the near-wall and logarithmic regions. The 2D spectra are decomposed into two components: Фss and Фvl. Фvl represents the cumulative energy contribution from tall wall-attached motions. Фss, obtained by subtracting Фvl from Ф, scales well with the friction velocity and wall-normal distance, indicating self-similar motions. The energy in Фvl, associated with very-large-scale motions, can distort the self-similar scaling in the logarithmic region. For w, Фss aligns along the linear relationship between the wall-parallel wavelengths over a broad range, and the energy contained in Фvl is weak compared to the streamwise component. These differences in spectral contributions explain the presence of the logarithmic variation of the spanwise turbulence intensity at lower Re. |
Monday, November 25, 2024 6:29PM - 6:42PM |
T40.00009: Uniform momentum zones for the logarithmic layer in turbulent pipe flow Dongmin Kim, Jinyul Hwang Wall-bounded turbulent flows are composed of spatial regions with relatively uniform streamwise velocity, known as uniform momentum zones (UMZs). These UMZs vary in size, and multiple UMZs coexist along the wall-normal direction in instantaneous flow fields. Although UMZs are essential coherent structures for understanding the multiscale phenomena and momentum transport in wall turbulence, there remains a question about which UMZs contribute to the logarithmic layer of wall turbulence. In this study, we explore relatively thick UMZs that span from the near-wall region and cross the logarithmic layer using the direct numerical simulation dataset of turbulent pipe flows at Reτ = 550-6000. The thickness of these UMZs is linearly proportional to the wall-normal distance, and the velocity jump across the shear layer between different UMZs scales with the friction velocity. The mean streamwise velocity profile is reconstructed from these UMZs, and it shows the existence of the logarithmic layer, which is supported by a clear plateau in the indicator function even in low Reτ. Additionally, the wall-normal turbulence intensity and the Reynolds shear stress profiles exhibit a region with constant values over the logarithmic layer. These findings indicate that the identified wall-attached UMZs directly contribute to the logarithmic layer and are important instantaneous structures that can explain the asymptotic behaviors of turbulence statistics predicted by Townsend's attached eddy hypothesis. |
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