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 Q07: Boundary Layers: Turbulent Boundary Layers III 
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Chair: Martin Oberlack, TU Darmstadt Room: North 122 C 
Tuesday, November 23, 2021 8:00AM  8:13AM 
Q07.00001: Spectral and Coherence Analyses of windLiDAR measurements collected in the Atmospheric Surface Layer for detecting the k^{1} spectral region Matteo Puccioni, Travis J. Morrison, Alexei Perelet, Sebastian Hoch, Marc Calaf, Eric Pardyjak, Giacomo Valerio Iungo In the realm of wallbounded turbulence, the k^{1} law of the streamwisevelocity spectrum ( is the wavenumber) has been ascribed to the statistical presence of wallattached eddies. However, previous investigations have shown puzzling results for the identification of the spectral boundaries of the k^{1} region, and their flowbased definition is still elusive. Investigations of coherent turbulent structures present in turbulent boundarylayer flows require a large scaleseparation, and, thus, a highReynolds number flow, which makes the atmospheric surface layer (ASL) a unique environment to investigate windgenerated turbulence. In this work, windLiDAR measurements collected within the ASL are leveraged to estimate the spectral boundaries of the k^{1} region with two approaches: the first one is based on piecewise modeling of the streamwisevelocity spectrum, while the second one is based on the coherence analysis of the streamwise velocity. The findings of this work include a generalized modeling of the linear coherence of the streamwise velocity, the estimate of the maximum height where the k^{1} region is detectable, and the vertical profiles of attached and detachededdy contributions to the streamwise turbulence intensity. 
Tuesday, November 23, 2021 8:13AM  8:26AM 
Q07.00002: An Experimental Investigation of the Influence of Superhydrophobic Surfaces on Turbulent Boundary Layer Separation Daniel J Grieb, Simo A Makiharju We investigate the separation of a turbulent boundary layer (TBL) in an adverse pressure gradient over a convex backward facing ramp coated with a superhydrophobic surface (SHS). Past research has shown that the location of TBL separation can be modified by the increased skin friction over a rough surface. SHSs in specific cases have been shown to also be effective in modifying the skin friction in a TBL. In our experiment, we investigate the influence of an air infused SHSinduced reduction in skin friction on the location of TBL separation. A TBL develops over a flat plate in a water tunnel, reaching a Reynolds number based on fetch distance on the order of Re_{x} ≈ 10^{6}. The developed boundary layer then separates in an adverse pressure gradient as it flows over a diverging ramp with a constant radius of 127mm. The location of separation on the ramp is compared for the cases with and without an SHS coating, and the flow is characterized by particle image velocimetry (PIV). 
Tuesday, November 23, 2021 8:26AM  8:39AM 
Q07.00003: A novel mean shear stress model and its application in pressure gradient turbulent boundary layers Praveen Kumar, Krishnan Mahesh

Tuesday, November 23, 2021 8:39AM  8:52AM 
Q07.00004: Streamline coordinate analysis of the flow past an axisymmetric body computed by largeeddy simulation Nicholas Morse, Krishnan Mahesh Turbulent boundary layers with streamline curvature are ubiquitous in engineering applications, and the flow around axisymmetric bodies is further complicated by transverse curvature. We analyze results of wallresolved largeeddy simulation of an axisymmetric hull in an orthogonal coordinate system defined by streamlines and streamlinenormal lines. The numerical algorithm used in the present work is based on the unstructured overset method developed by Horne and Mahesh [J. Comput. Phys (2019) 397: 108790]. Equations in the streamline coordinate frame reduce to the Bernoulli equation and the Euler equation for curved streamlines away from the body and provide insight into the momentum balance within the boundary layer. 
Tuesday, November 23, 2021 8:52AM  9:05AM 
Q07.00005: Nonequilibrium turbulent boundary layer with adverse pressure gradient and convex wall curvature Saurabh Pargal, Hao Wu, Junlin Yuan, Stéphane Moreau

Tuesday, November 23, 2021 9:05AM  9:18AM 
Q07.00006: Spatiotemporal statistics of a turbulent boundary layer under unsteady adverse pressure gradients : data from TimeResolved Particle Image Velocimetry Aadhy S Parthasarathy, Theresa SaxtonFox An unsteady adverse pressure gradient turbulent boundary layer was created by rapidly deforming a 0.45 m long ceiling panel of a boundary layer wind tunnel to the shape of a convex bump. The spatial strength of pressure gradient and the rate of change of pressure gradient imposed were independently varied using an electropneumatic control mechanism for the ceiling panel. TimeResolved Particle Image Velocimetry (TRPIV) was used to capture the response of the boundary layer for a range of adverse pressure gradients. This talk will focus on the spatial and temporal evolution of single and multipoint turbulent statistics obtained from phaselocked ensemble averages of the TRPIV data for 3 rates of imposition of pressure gradients corresponding to nondimensional times, t^{*} (defined as the ratio of convective time scale to imposed unsteady time scale), of 4.38, 1.53, and 0.61. The friction Reynolds number of the incoming flow, Re_{τ}, was 940 and the boundary layer thickness, δ, was 42 mm. 
Tuesday, November 23, 2021 9:18AM  9:31AM 
Q07.00007: Wallmodeled largeeddy simulations of flow over a Gaussianshaped bump with a relaminarization sensor Naili Xu, Ivan BermejoMoreno Largeeddy simulations are conducted with an equilibrium shearstress wall model to investigate the flow over a Gaussianshaped bump geometry. Spanwise periodic simulation results are compared with Direct Numerical Simulations by Uzun & Malik (2020) and experimental data by Williams et al (2020). We consider configurations at two different Reynolds numbers Re_{L}=10^{6 }and 3.41x10^{6} with a freestream Mach number M=0.2. The flow presents mild separation downstream of the bump apex for both Reynolds numbers, and a region of flow relaminarization around the apex for the lower Reynolds number configuration. Direct application of the wall model in the relaminarization region leads to a significant overprediction of the skin friction. A relaminarization sensor is developed to locally condition the application of the wall model based on simulation flow quantities. The predictive capabilities and robustness of the relaminarization sensor are assessed for both Reynolds numbers, along with previously developed laminartoturbulent transition sensors by Bodart & Larsson (2012) and Mettu & Subbareddy (2018). The proposed sensor correctly distinguishes the relaminarization region in the low Re_{L} case, leading to improved flow predictions. 
Tuesday, November 23, 2021 9:31AM  9:44AM 
Q07.00008: LargeEddy Simulation of a Boundary Layer with Unsteady Pressure Gradient Francesco Ambrogi, Zvi hantsis, David E Rival, Ugo Piomelli LargeEddy Simulation is used to study a turbulent boundary layer subject to a space and timedependent freestream pressure gradient. Comparison is made with steady cases with fixed pressure gradients. The adverse pressure gradient is strong enough to cause flow separation. The pressure gradient is prescribed by an oscillating blowing and suction profile at the top boundary. Several cases have been investigated for a range of reduced frequencies k. For the highest k the separation bubble is not as thick as in an equivalent steady case, but its length remains comparable. The phaseaveraged field shows that the flow is synchronized with the forcing throughout the domain. However, hysteresis occurs in the near wall region. As the reduced frequency decreases, the extent of the separation bubble in the wallnormal direction increases, but its length is reduced compared with the corresponding steady case. The region of slowmoving fluid generated by the flow reversal is advected downstream, causing a decorrelation between the forcing and the velocity and pressure in this region. 
Tuesday, November 23, 2021 9:44AM  9:57AM 
Q07.00009: Spectral analysis of a highReynoldsnumber nearequilibrium adversepressuregradient turbulent boundary layer Ramon Pozuelo, Qiang Li, Philipp Schlatter, Ricardo Vinuesa The effects of adverse pressure gradients (APG) in highReynoldsnumbers turbulent boundary layers (TBLs) is thoroughly assessed using both one and twodimensional spectra of the Reynolds stresses. The employed database was recently obtained through wellresolved largeeddy simulation (LES) of a nearequilibrium APG TBL with a moderate RottaClauser pressuregradient parameter β≈1.4, where the momentumthicknessbased and friction Reynolds numbers reach Re_{θ}=8,700 and Re_{τ}=1,900, respectively. The effects of the APG will be assessed by comparing the data with a zeropressuregradient (ZPG) TBL at similar Re_{τ}. The increase of energy in the outer region of the TBLs is partly linked with the presence of larger turbulent scales, but there is additional energy due to the rising of energetic smaller scales from the inner region close to the wall, as well as a new peak of production of TKE in the outer region. The twodimensional spectra show longer spatial and temporal scales in the streamwise and spanwise Reynolds stresses near the wall and in the overlap region. 
Tuesday, November 23, 2021 9:57AM  10:10AM 
Q07.00010: Effect of wingtip vortices on aerodynamic quantities of a NACA0012 wing Siavash Toosi, Adam Peplinski, Philipp Schlatter, Ricardo Vinuesa The present work aims at investigating the formation of wingtip vortices in a finitespan wing, studying their effect on the flow and the turbulent boundary layers developing on both the suction and pressure sides, and understanding their effect on the aerodynamic quantities of the wing. This is done by performing highresolution largeeddy simulations of a NACA0012 profile at a chordbased Reynolds number of Re_{c}=200,000, where many of the relevant quantities are compared between an infinitespan wing (i.e., periodic in the spanwise direction) and a finitespan wing with rounded wingtip geometry. The simulations are performed using the highorder spectralelement code Nek5000 with adaptivemeshrefinement (AMR) capabilities to achieve a high accuracy at an affordable computational cost. Our analysis will compare turbulence statistics around the wing and in the wake of both wings, powerspectral densities, as well as an assessment of the characteristics of the wingtip vortices. 
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