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 L40: Turbulence: Boundary Layers |
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Chair: Agastya Balantrapu, University of Utah Room: 355 F |
Monday, November 25, 2024 8:00AM - 8:13AM |
L40.00001: ABSTRACT WITHDRAWN
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Monday, November 25, 2024 8:13AM - 8:26AM |
L40.00002: Modeling roughness sublayer turbulence using resolvent analysis Miles J Chan, Ugo Piomelli, Beverley J McKeon Prediction of turbulent flow physics and mean quantities (e.g. drag) over general engineering-relevant rough surfaces remains an open research area. In previous work, resolvent analysis has been shown to predict flow features representative of the near-wall cycle in turbulent flows over smooth surfaces, and experimental measurements suggest agreement between resolvent mode representations and features in the temporally-averaged flow over sinusoidal roughness geometry (Caltech Thesis, Morgan 2019). In this study, local resolvent analysis is applied to the turbulent flow over a sand-grain geometry as a proxy for engineering-relevant roughness, and its efficacy for flow predictions is evaluated. The ability of local resolvent analysis to predict wake field and roughness sublayer turbulent motions is demonstrated through comparison with spectral proper orthogonal decomposition and temporally-averaged data from DNS of a turbulent channel flow with roughness resolved using an immersed boundary method. Low order resolvent mode representations reproduce the surface geometry and dispersive terms with sufficient fidelity to inform an iterative estimation method for the mean flow and hydrodynamic drag. |
Monday, November 25, 2024 8:26AM - 8:39AM |
L40.00003: Bounded asymptotics for high-order moments in wall turbulence Xi Chen, Katepalli R Sreenivasan Turbulent wall-flows are the most important means for understanding the effects of boundary conditions and fluid viscosity on turbulent fluctuations. There has been considerable recent research on mean-square fluctuations. Here, we present expressions for high-order moments of streamwise velocity fluctuation $u$, in the form $ \langle u^{+2q} \rangle^{1/q}=\alpha_q-\beta_q y^{\ast1/4}$; $q$ is an integer, $\alpha_q$ and $\beta_q$ are constants independent of the friction Reynolds number $Re_\tau$, and $y^{\ast} = y/\delta$ is the distance away from the wall, normalized by the flow thickness $\delta$; in particular, $\alpha_q =\mu+\sigma q$ according to the `linear q-norm Gaussian' process, where $\mu$ and $\sigma$ are flow-independent constants. Excellent agreement is found between these formulae and available data in pipes, channels and boundary layers for $1 \leq q \leq 5$. For fixed $y^+ = y^*Re_\tau$, the present formulation leads to the bounded state $\langle u^{+2q} \rangle^{1/q}=\alpha_q$ as $Re_\tau\rightarrow\infty$ while the attached eddy model predicts that the moments continually grow as log Reynolds number. |
Monday, November 25, 2024 8:39AM - 8:52AM |
L40.00004: Spectral analysis of inner-outer layer nonlinear interactions using minimal channel turbulence Haruki Itsui, Soshi Kawai In the streamwise velocity spectra of high Reynolds number turbulent boundary layers, it is well known that in addition to the inner spectral peak originating from the inner-layer streaks, the outer peak originating from the large-scale motions in the outer layer appears, where the inner-outer layer interactions occur. |
Monday, November 25, 2024 8:52AM - 9:05AM |
L40.00005: Spatial Heterogeneity Shapes Turbulence in Vegetated Canopy Flows Ryan Scott, Elizabeth Scott, Katie N Taylor, Marc Calaf, Mitchell B Cruzan, Raúl Bayoán B Cal Vegetated canopy flows are characterized by aggregate momentum absorption and the formation of spatially complex coherent features shaped by canopy structure. A series of wind tunnel experiments were performed at Portland State University to quantify the role of individual and patch scale heterogeneity on shaping vegetated canopy flows. Reduced scale canopy models were manufactured from high porosity reticulated foam and organized into homogeneous canopies with uniform structure and heterogeneous canopies modeled after old growth forest stands. Patch-scale heterogeneity was introduced with regular gaps between canopy sections as well as snag cases where the vegetated layer was removed. Instantaneous measurements of the flow through and above the canopies were obtained from vertical transects with two time-synchronized hot wire anemometers. Canopy structure is quantified through a lacunarity-based heterogeneity index and linked to dominant physical length scales in each canopy arrangement. Turbulent flow statistics reveal canopy spatial heterogeneity drives fluid dynamics across multiple scales. Velocity profiles are shaped by the particular arrangement of individual trees within a stand as well patch-scale gaps and snags. The effect of canopy structure on high-order turbulence statistics and the formation of canopy-specific flow structures will be detailed in presentation. |
Monday, November 25, 2024 9:05AM - 9:18AM |
L40.00006: Dense-gas effects on the similarity behavior of turbulent boundary layer flows Anjini Chandra, Hang Song, Sanjiva K Lele Supercritical carbon dioxide (sCO2) serves as an efficient working fluid in compact energy systems. However, real-gas effects on the turbulent boundary layers (TBLs) that form in such systems are still under investigation. In this study, direct numerical simulations (DNS) of several sCO2 zero-pressure-gradient TBLs with isothermal walls are performed. The DNS solves the compressible Navier-Stokes equations and utilizes real-gas equation-of-state and transport models, and the numerical framework is based on high-order compact finite-difference methods without solution filtering. In addition, the wall and freestream temperature conditions vary from subcritical to supercritical across cases. The results show large gradients in transport and thermodynamic properties, such as density, viscosity, and thermal conductivity, for correspondingly small changes in temperatures near the critical condition. The similarity behavior of wall-normal mean profiles and turbulence statistics under real-gas thermodynamic conditions is investigated. Nondimensional streamwise correlations of quantities, such as the skin-friction coefficient and Stanton number, are also studied. Variable-density and compressibility effects are compared with corresponding theories formulated for ideal gas TBLs. |
Monday, November 25, 2024 9:18AM - 9:31AM |
L40.00007: Conditional analysis of the wake of a cylinder immersed in a turbulent boundary layer Elizabeth Torres De Jesús, Theresa A Saxton-Fox The aim of this study was to explore interactions between large-scale coherent structures in a turbulent boundary layer and small-scale vortices shedding from a cylinder wake. Experimental 2D particle image velocimetry data for a cylinder immersed at six different wall-normal distances in a turbulent boundary layer (D/δ = 0.05, where D is the cylinder diameter and δ is the boundary layer at 99% of the freestream velocity) over a flat plate were studied. In this presentation, conditional averages of the streamwise, wall-normal, and shear Reynolds stresses based on the large-scale velocity at streamwise positions between x=δ and x=3δ are presented. At the different streamwise locations, the stresses show evidence of amplitude modulation-like behavior in the wake region. Additionally, it will be shown that the wall-normal location of the peak of the streamwise stresses associated with the cylinder's wake is dependent on the sign of the local large-scale structure. |
Monday, November 25, 2024 9:31AM - 9:44AM |
L40.00008: Near-wall turbulence in channel flow boundary layer with large thermophysical property fluctuations at supercritical pressure TENG WAN, Xingjian Wang Direct numerical simulations of turbulent channel flow boundary layers are conducted using CO2 as a working fluid at supercritical pressure (SCP). The channel upper and lower walls are treated as isothermally heated and cooled, respectively, ensuring the pseudo-boiling process occurs in the channel flow. The objective is to elucidate how the property variations affect the first- and second-order turbulence statistics, near-wall scaling laws, and turbulence anisotropy. The results demonstrate that large property fluctuations occur near the heated wall due to the proximity of the pseudo-boiling point. This real-fluid effect leads to the failure of conventional temperature scaling law and promotes turbulence anisotropy. A new scaling law based on enthalpy calibration utilizing energy conservation is proposed to exhibit substantial improvement. The budget analysis shows that drastic changes in thermophysical properties lead to the redistribution of turbulent kinetic energy among different components, resulting in turbulence anisotropy. Further insights are gained through turbulence statistical decomposition, quadrant analysis, and instantaneous flow snapshots. These results could enhance the understanding of the impact of drastic property changes on near-wall turbulence in SCP fluids and provide guidance for turbulence modeling of SCP fluids. |
Monday, November 25, 2024 9:44AM - 9:57AM |
L40.00009: DNS of an oscillating turbulent boundary layer with an enlarged Reynolds-number range Hiroyuki Abe, Philippe R Spalart DNS is used to examine oscillating turbulent boundary layers (TBLs) with doubly-periodic boundary conditions in which the mean pressure gradient varies sinusoidally in time (one cycle consists of the phase-angle φ= 0 to π). In the cycle, the adverse-pressure-gradient (APG) is first imposed (φ=0 to π/2), causing a reversal of the wall shear stress equivalent to separation. The favorable-pressure-gradient (FPG) is subsequently imposed (φ = π/2 to π) so that the flow which has reversed direction is attached and then momentarily exhibits a laminar-like velocity profile. As the FPG is reduced, the flow finally approaches the zero-pressure-gradient TBL (φ =0 and π). The seminal DNS study has been performed by Spalart and Baldwin (1989) at Reδs =600 to 1200, where Reδs denotes the Reynolds number based on the amplitude of the freestream velocity and the laminar boundary-layer thickness. Their Reynolds number includes the transitional Re range. In the current DNS, three values of the Reynolds number (Reδs =1000, 1800 and 2600) are used to compare with the measurements of Jensen et al. (1989). The latter two Reynolds numbers are free of low Re effects. At Reδs =1000, there appears a large peak in the wall-shear stress profile near φ =π. By contrast, the latter peak becomes insignificant for Reδs =1800 and 2600 where the profile varies slowly with Reδs. With increasing Re, the mean streamwise velocity exhibits a log law over a wider range of φ, while large-scale motions and their near-wall footprints become prominent with the APG. |
Monday, November 25, 2024 9:57AM - 10:10AM |
L40.00010: Wall-pressure–velocity couplings in turbulent boundary layers spanning three orders of magnitude in Reynolds number Vijaya Rama Reddy Gudla, Rahul Deshpande, Ivan Marusic, Joseph C Klewicki Turbulent boundary layer pressure fluctuations on an aircraft fuselage or ship hull play a significant role in their design since such pressure disturbances can affect the structural integrity and passenger comfort. These wall-pressure fluctuations originate from the coherent motions coexisting in the overlying turbulent boundary layers, and the correlation between the two has been studied only in the low friction Reynolds number regime (Reτ ~103). For instance, Gibeau & Ghaemi (2021, JFM) and Deshpande et al. (2024, arXiv:2406.15733) show that the mid-frequency range (0.0014< f+ <0.012) of the wall-pressure fluctuations strongly correlate with intermediate-scaled Reynolds shear stress carrying motions, while those of the low-frequency range (f<0.0014) correlate with the large-scale motions. The wall-pressure power spectrum of these low Reτ flows is, however, beset with limited scale separation and exhibits weak signatures at large scales; these large scales are well known to become statistically significant at very high Reτ, relevant to flows over aircraft and ships. The present study addresses this knowledge gap through simultaneous measurements of wall pressure and velocity fluctuations at Reτ~106, taken from the near-neutral atmospheric surface layer forming over the salt playa of Utah's west desert. These large Reτ results reveal that pressure-velocity correlations at low frequencies have significantly enhanced magnitudes relative to those at mid-frequencies. |
Monday, November 25, 2024 10:10AM - 10:23AM |
L40.00011: Oblique stripes and local energy flux vectors in wall turbulence model without walls Masanori Takaoka Globally subcritical flows that jump to nontrivial branches due to nonlinearities in finite amplitude perturbations become turbulent via spatially localized turbulent states such as puffs, spots, and stripes. Waleffe proposed a self-sustaining process and derived a reduced-order model of the process from the Navier-Stokes equations for sinusoidal forcing. This approach was extended by Manneville as a Swift-Hohenberg-like model. Chantry et al. developed a Waleffe model that retains only four Fourier modes in the shear direction and showed that this model has the potential to capture a range of spatially localized turbulent conditions. These results suggest that the driving mechanisms of spatially localized turbulent states may be investigated under periodic boundary conditions, i.e., without walls. Recently, we have revealed the anisotropic structure of cascades in wavenumber space by introducing local flux vectors for invariants. In this talk, we use the local flux vector in the wavenumber space to investigate the driving mechanisms of oblique stripes in the Waleffe flow model. The model also shows that the turbulence consists of anisotropic streamwise structures called streaks. The driving mechanisms of these will be discussed in terms of the local energy flux vectors in the wavenumber space too. |
Monday, November 25, 2024 10:23AM - 10:36AM |
L40.00012: Identification of wall attached and detached structures in turbulent channels using informative/non-informative decomposition (IND) Gonzalo Arranz, Adrian Lozano-Duran The IND is a method to decompose flow fields into two components with respect to a target variable: an informative field, which embeds all the information of the target, and a residual (non-informative) field, which contains no information of the target. We use the IND to introduce an information-based definition of wall-attached and wall-detached velocity fields as those that con- tain information of the wall and those that do not, respectively. The analysis is performed in turbulent channel flow with friction Reynolds numbers in the range Reτ ≈ 500 − 2000. Two different target fields are considered to define attached/detached eddies: the wall shear stress and the wall pressure. We analyze the topological differences between these structures for the two target variables considered. The IND also allows us to select whether the information about the target is referred to the present state or some time in the future, and the effect of this time interval on the resulting attached/detached eddies is also investigated. |
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