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 Q13: Boundary Layers: Turbulent II |
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Chair: Hassan Nagib, Illinois Institute of Technology Room: 140 |
Monday, November 21, 2022 1:25PM - 1:38PM |
Q13.00001: Probing the outer-layer-inner-layer dynamics of a turbulent boundary layer using synthetic jets Randy K Belanger, Philippe Lavoie, David W Zingg The fraction of the turbulent kinetic energy associated with large-scale velocity structures in the logarithmic region of the boundary layer has been shown to increase with increasing Reynolds number, highlighting their importance for flows of engineering interest. This increase in energy is associated with an increase in the interaction with smaller-scale turbulence nearer to the wall through amplitude and frequency modulation. In this combined experimental/simulation study, we use synthetic jets to interact predominantly with large-scale structures in a turbulent boundary layer. Spectral analysis and conditional averaging is performed to ascertain the impact of the synthetic jets on these structures. The indirect influence on smaller-scale structures is determined by measurements of the wall shear stress. The results show that, in most cases, the synthetic jets reduce the energy of the large-scale structures and their coherence with the wall, with a corresponding increase in local wall shear stress. For a small range of forcing conditions, coherence is actually increased with the wall, with a corresponding decrease in local wall shear stress. This suggests that the larger-scale structures work to suppress the drag-increasing aspect of the inner layer. |
Monday, November 21, 2022 1:38PM - 1:51PM |
Q13.00002: Towards energy-efficient drag reduction through manipulation of inter-scale phase relationships Rahul Deshpande, DILEEP CHANDRAN, Alexander J Smits, Ivan Marusic This study investigates the mechanism of a new turbulent drag reduction strategy for high-Reynolds number wall-bounded flows that was reported by Marusic et al.1The strategy imposes streamwise traveling waves of spanwise velocity at the wall that targets the low-frequency, outer scales. This strategy has proven to be more energy-efficient than the conventional method of actuating the inner scales. Both pathways achieve drag reduction with an accompanying broadband attenuation of the wall-shear stress spectrum and modified inter-scale phase relationships. Statistics such as the amplitude modulation coefficient and skewness of the streamwise velocity, representing the average measures of phase between triadically consistent scales, reveal that higher drag reduction is associated with enhanced coupling between the inner and outer scales. This enhancement is due to a reduction of the inter-scale phase. The energy-efficient pathway to achieve drag reduction, thus, involves actuating the outer-scales with the corresponding low-frequency surface oscillations, and consequently, also leading to a substantial attenuation of the major drag contributing inner-scales. |
Monday, November 21, 2022 1:51PM - 2:04PM |
Q13.00003: Model-based spectral coherence analysis for high-Reynolds number turbulent shear flows Seyedalireza Abootorabi, Armin Zare We evaluate the predictive capability of the eddy-viscosity enhanced and data-enhanced variants of the stochastically forced linearized Navier-Stokes equations in capturing the geometric self-similarity of turbulent flow structures in high-Reynolds number channel flows. To this end, we use the linear coherence spectrum to quantify the wall-normal coherence of turbulent eddies, which is computed as the cross-correlation of the velocity field between two wall-normal locations normalized by the respective one-point correlations. The coherence spectrum can be used to construct spectral filters that decompose the energy spectrum of the inertial layer into contributions from wall-attached motions that are either self-similar or non-self-similar. We examine the ability of our model-based spectral filters in decomposing the energy spectrum and uncovering the inner-scaling of wall-attached self-similar motions at various Reynolds numbers. We also build on the wall-distance scaling of such spectral filters to propose analytical representations for their spectral parameterization. We demonstrate the Reynolds number independence of such parametric representations that can be leveraged for predicting coherent motions in higher Reynolds number flows. |
Monday, November 21, 2022 2:04PM - 2:17PM |
Q13.00004: Scale interactions in the atmospheric surface layer Michele Guala, Giacomo Valerio Iungo, Jiarong Hong, Nathaniel Bristow, Matteo Puccioni, Peter W Hartford, Jiaqi Li, Roozbeh Ehsani, Moss Coleman Near wall turbulence in the logarithmic and roughness sublayer has been observed to be influenced by large and very-large scale motions since early studies on inner-outer interactions and amplitude modulation. Here we present experimental results at the scale of the atmospheric surface layer, where the turbulent flow field has been captured by Super Large Particle Image Velocimetry (SLPIV) sampled at 120 Hz up to 10m height, synchronized and co-located with a fixed-scan LiDAR operating at 2Hz up to 120m height. This dataset was acquired at the EOLOS Research Field in Minnesota (winter 2022), as part of the Grand-scale Atmospheric Imaging Apparatus (GAIA) collaboration. Preliminary results include i) a brief discussion on scale-dependent, height dependent convection velocities for the spatio-temporal conversion of the LiDAR data, ii) conditional averages of small-scale turbulent quantities, e.g. turbulent kinetic energy dissipation rate, vorticity, swirling strength, based on the large-scale velocity signal from the LiDAR. Results are presented in the framework of rough wall zero pressure gradient turbulent boundary layers at high Reynolds number, and extended to near surface processes in the atmospheric surface layer. |
Monday, November 21, 2022 2:17PM - 2:30PM |
Q13.00005: GrAnd-scale Imaging Apparatus (GAIA) and wind LiDAR multi-scale turbulence measurements in the atmospheric surface layer Giacomo Valerio Iungo, Michele Guala, Jiarong Hong, Nathaniel Bristow, Matteo Puccioni, Peter W Hartford, Roozbeh Ehsani, Jiaqi Li, Coleman F Moss Understanding the organization and dynamics of turbulence structures in the atmospheric surface layer (ASL) is important for many scientific and technical research thrust areas, including particle transport, natural hazards, agriculture, meteorology, and wind energy. A better understanding of ASL flows is important to improve wall models for large-eddy simulations, numerical weather prediction and snow settling models, all of which must take into account the spatio-temporal heterogeneity and the multi-scale nature of ASL flows. To tackle the foregoing challenges, a grand-scale atmospheric imaging apparatus (GAIA) has been developed to perform particle image velocimetry (PIV) in the lowest part of the ASL with a high spatio-temporal resolution, which is coupled with two scanning Doppler wind LiDARs to achieve unprecedented coverage of spatial flow scales from 10-1 m up to 103 m. The field campaign and preliminary results are presented focusing on observations of complex flow scenarios, such as the modulation induced by larger flow structures, which are probed through the wind LiDARs, on the morphology, dynamics, and energy content of small-scale turbulence closer to the ground measured through the GAIA PIV. |
Monday, November 21, 2022 2:30PM - 2:43PM |
Q13.00006: Reynolds Number Required to Accurately Discriminate Between Proposed Trends of Peak Normal Stress in Wall Turbulence Hassan M Nagib, Peter Monkewitz, Katepalli R Sreenivasan In Nagib, Chauhan and Monkewitz (Phil Trans R. Soc. A, 2007) we concluded that nearly all available Cf relations are in remarkable agreement over the entire range Reτ < O(108), provided one coefficient is adjusted in each relation by anchoring it with accurate measurements. Regarding the peak of the streamwise turbulence intensity <uu>+P, we conclude here that accurate measurements in flows with Reτ > O(106) are required to discriminate between recently proposed trends of <uu>+P. We also find remarkable agreement between the three analyses of Monkewitz (JFM 2022), Chen and Sreenivasan (JFM 2021) and Monkewitz and Nagib (JFM 2015), with some coefficients slightly modified, by underpinning them with the same accurate measurements of <uu>+P from reliable channel and boundary layer data. All the three analyses conclude that the inner peak of <uu>+ remains finite in the limit of infinite Reynolds number, which is at variance with the unlimited growth of <uu>+P as ln(Reτ) predicted by the attached eddy model (Marusic & Monty, Annu. Rev. Fluid Mech., 2019). Accurate measurements of high-order moments and the guidance of consistent asymptotic expansions may help clarify the issue at lower Reτ values. |
Monday, November 21, 2022 2:43PM - 2:56PM |
Q13.00007: Analytical model for the streamwise-velocity linear coherence spectrum inspired from Townsend's attached eddy hypothesis: Assessment against wind LiDAR measurements of the near-neutral atmospheric surface layer Matteo Puccioni, Giacomo Valerio Iungo, Marc Calaf, Eric R Pardyjak, Sebastian Hoch, Travis J. Morrison, Alexei Perelet The inertial layer of high Reynolds-number wall-bounded flows is populated by eddies of different typologies inducing streamwise velocity fluctuations characterized by wavelengths either constrained by the boundary layer height (ΔE), or much larger than ΔE, which are denoted as Very-Large-Scale Motions (VLSMs). For the former, and specifically for velocity fluctuations associated with wall-attached eddies, Townsend provided a theoretical framework to predict their organization and turbulence statistics. Inspired by that theory, an analytical model is proposed for the Linear Coherence Spectrum (LCS) of the streamwise velocity to identify the spectral footprint and turbulence intensity associated with wall-attached eddies and VLSMs. The proposed LCS model is based on three parameters: the eddy aspect ratio (AR), the isolated-eddy contribution to the LCS (C1), and an offset parameter (C3) introduced to account for the presence of VLSMs. The model is assessed against streamwise velocity measurements performed with a scanning pulsed Doppler LiDAR in the near-neutral atmospheric surface layer (ASL). The results show that the maximum height attained by wall-coherent structures is equal to 0.31ΔE and the low-wavelength boundary of the VLSMs spectral region corresponds to roughly 4.5ΔE. |
Monday, November 21, 2022 2:56PM - 3:09PM |
Q13.00008: Asymptotic scaling laws for the skin friction of zero pressure gradient boundary layers Fabio A Ramos, Daniel A Cruz, Hamidreza Anbarlooei We propose a phenomenological description of the asymptotic near-wall momentum exchange mechanism of flat plate zero-pressure gradient turbulent boundary layer flows |
Monday, November 21, 2022 3:09PM - 3:22PM |
Q13.00009: Outer-layer universality of the mean velocity profile in turbulent wall-bounded flows Alexander J Smits, Sergio Pirozzoli We derive optimal objective criteria to discern universality of the outer-layer mean velocity profile in wall-bounded flows, which yield a novel set of outer velocity and length scales. The new scaling generalizes the Rotta-Clauser scaling and includes the Zagarola-Smits scaling as a special case for internal flows and supports the friction velocity as the most plausible velocity scale in the asymptotic high-Reynolds-number regime. Composite logarithmic/parabolic formulations are proposed for the mean velocity profile using the classical wall scaling and the new scaling, which yield accurate approximations for boundary layers, pipes and channels. |
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