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 C15: Interact: Boundary Layers: from Laminar to Turbulent |
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Chair: Beverley McKeon, Stanford University Room: 155 E |
Sunday, November 24, 2024 10:50AM - 11:20AM |
C15.00001: INTERACT FLASH TALKS: Boundary Layers: from Laminar to Turbulent Each Interact Flash Talk will last around 1 minute, followed by around 30 seconds of transition time. |
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C15.00002: Laminar heat-flux from a cooled plate moving at hypersonic speed Thomas Ward, James Miller Heat transfer to a fluid via a laminar compressible boundary-layer flow over a flat plate with sharp leading edge is studied in the hypersonic limit. The interaction between the shock wave and boundary-layer is characterized using the hypersonic interaction parameter χ = M3(C/Re)1/2 where M and Re are the free-stream Mach and Reynolds numbers, respectively, and C is the Chapman-Rubesin constant. To study the heat transfer we solved the Prandtl boundary-layer equations that represent the viscous-layer flow over a cooled wall. For the inviscid-layer we utilized a tangent-wedge approximation. Boundary-layer, wall pressure and shear stress profile were computed. The computational results are used to estimate a steady wall heat flux profile over the plate that is compared with recent results from experiments performed in a Mach 6 wind tunnel. |
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C15.00003: The nonlinear parabolized stability equations for accurate wall-modeled large-eddy simulations of transitional flows Carlos A Gonzalez, Shaun R Harris, Parviz Moin For the prediction of natural transition, which is ubiquitous in external aerodynamic applications, the nonlinear parabolized stability equations (NLPSE) are computationally efficient, high-fidelity, and physics-based alternative to direct numerical simulations. Gonzalez et al. (CTR Ann. Res. Brief, 2023) and Lozano-Duran et al. (PRF, 2018) have shown that the NLPSE can be coupled to wall-modeled large-eddy simulations (WMLES) to provide a framework that can accurately simulate an H-type transitional boundary layer at affordable resolutions. |
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C15.00004: A Restricted Nonlinear Study of Laminar-Turbulent Transition Benjamin A Minnick, Dennice F Gayme We apply the restricted nonlinear (RNL) model to investigate K-type transition. The RNL model equations comprise a streamwise averaged mean interacting with a limited number of streamwise varying perturbation modes which lead to a reduced representation of the dynamics. We take advantage of the model tractability by interrogating the transient energy growth of each mode in this reduced representation during transition. When compared to direct numerical simulations (DNS), the RNL model is shown to predict greater energy and transition earlier. However, the reduced dynamics of the RNL model follow a similar transition process to DNS and reproduces salient streak and roll flow features. In this framework we vary the streamwise wavenumber support of the RNL dynamics to isolate and assess the role of scale interactions during transition. |
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C15.00005: Effects of streamline curvature on a transitioning boundary layer Tejas Kadambi, Marc Plasseraud, Krishnan Mahesh Several practical flows undergo laminar to turbulent transition under the simultaneous presence of streamline curvature and pressure gradients. This influence of curved streamlines still raises some unanswered questions. This study aims to analyze the effects of curvature on a developing turbulent boundary layer using a high fidelity wall-resolved large-eddy simulation. An array of roughness elements trips laminar flow to induce transition to turbulence, whereafter the fluid elements experience curvature effects in the spanwise and wall-normal directions. A variety of turbulent kinetic energy and Reynolds stress properties are observed and analyzed in a coordinate system that matches the curvature of the streamlines. These results will be discussed. |
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C15.00006: Impact of riblets on the drag of finite-sized bodies with non-zero pressure gradients Shabnam Raayai Riblets are an effective method of passive drag reduction with between 8-10% reductions observed in laboratory and less than 3% reported in industrial applications. The majority of implementation in both spaces has focused on the case of asymptotic boundary layers, well suited for larger vehicles such as ships and planes. Less exploration is available on the impact of riblets on the flow field around finite-sized, smaller bodies where the development of the boundary layers deviates from the zero pressure gradient conditions and the dependence on the streamwise direction becomes more pronounced. In this talk, we will consider the case of riblet-covered, finite-sized bodies in flow and discuss how the limited size of the body and riblets interact with each other and affect the development of the boundary layer and the pressure distribution around the sample. We use riblet covered foils in a water tunnel and employ particle image velocimetry experiments to capture the velocity distribution and subsequently the pressure field around the bodies and connect the measurements to the drag experienced by the sample and the differences with that of a smooth reference. We will use the experimental evidence to explore the impact of the pressure distribution on the performance of the riblets in altering the frictional and pressure components of the drag and how this can translate into practical implementation of riblets for vehicles with smaller or bulkier silhouettes. |
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C15.00007: Direct numerical simulation of forced air convection with variable physical properties Davide Modesti, Sergio Pirozzoli We present a theoretical framework for predicting friction and heat transfer coefficients in variable-properties forced air convection. Drawing from concepts in high-speed wall turbulence, which also involves significant temperature, viscosity, and density variations, we utilize the mean momentum balance and mean thermal balance equations to develop integral transformations |
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C15.00008: 3D Particle Tracking Velocimetry to the Wall in a Zero Pressure Gradient Turbulent Boundary Layer with a Single Plenoptic Camera Mark Yamakaitis, Philippe M Bardet, Alexander M Pigeon, Jason Anderson, Colin M Parker, Robert Ehrmann Using a single plenoptic camera we demonstrate 3D Particle tracking velocimetry (PTV) with velocities resolved down to the wall of a zero pressure gradient (ZPG) turbulent boundary layer. The unique plenoptic architecture creates four non-overlapping images of a scene directly on the camera sensor. Each image is a different orthographic view of the same scene with a maximum angle between views of 24○. The four images can be separated then treated independently for calibration. This arrangement allows three dimensional triangulation and reconstruction of a volume up to 11×11×2.5 mm. The commercial software DaVis with the "Shake-the-Box" add-on was used to perform 3D PTV. This imager was used to take measurements in the viscous sublayer and buffer layer of the turbulent boundary layer at the bottom of a wind tunnel. The tunnel was designed with an adjustable ceiling that allows for the pressure gradient to be adjusted. For these measurements only a ZPG test case was looked at. Measurements were taken at one wind speed. Hot wire was used to estimate a Reynolds number based on momentum thickness of 6,100 and a viscous Reynolds number of 1,600. For validation the recovered velocities and turbulence statistics from the 3D PTV are compared with the hot wire data as well as test cases from the literature. |
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C15.00009: Deep learning based spatio-temporal wall-shear stress quantification from velocity measurements Esther Lagemann, Christian Lagemann, Steven L Brunton Wall-shear stress dynamics are of fundamental interest in basic and applied research ranging from biomedical applications to aircraft design and optimization. However, we still lack experimental methods that can simultaneously measure the temporal dynamics of the wall-shear stress with a sufficient spatial resolution and domain size. Neither do we have universal models which adequately mimic the instantaneous wall-shear stress dynamics in numerical simulations of multi-scale systems for which direct numerical simulations are too expensive to be conducted. Working towards filling those gaps, we developed a deep learning architecture that takes wall-parallel velocity fields from the logarithmic layer of turbulent wall-bounded flows as an input and outputs the corresponding 2D wall-shear stress fields. Trained in a supervised fashion using datasets from direct numerical simulations where the true wall-shear stress distributions are known, we demonstrate a zero-shot applicability to experimental data with similar flow conditions. The physical correctness of the wall-shear stress estimation from experimental Particle-Image Velocimetry based velocity fields is verified using wall-shear stress measurements with the Micro-Pillar Shear-Stress Sensor. |
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C15.00010: Invariant properties of the Reynolds shear stress probability distribution in turbulent wall-bounded flows Spencer J Zimmerman, Jimmy Philip, Yoshinobu Yamamoto, Yoshiyuki Tsuji, Joseph C Klewicki Understanding the relationship between high- and low-order statistical moments of the fluctuating velocity is at the heart of the turbulence closure problem. Here, we examine properties of the Reynolds shear stress (RSS) probability distribution through the lens of the joint moments of the streamwise and wall-normal velocities in turbulent wall flows. A scaling for the fluctuating RSS is proposed based on properties of the mean dynamical equation. We also present a corrected version of an existing model equation for the RSS probability distribution, and evaluate this model for its fidelity to DNS data via the Kullback-Leibler divergence. It is shown that the fourth-order joint cumulants that comprise most of the model coefficients are essentially invariant with Reynolds number in the log layer (once one is established), despite changes in the correlation coefficient between the two velocity components. The ramifications of this finding for both the shape of the probability distribution as well as the scaling relationships for the fluctuating RSS in the log layer are discussed. |
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C15.00011: Resolvent modes as the foundation for LES wall models Zvi hantsis, Miles J Chan, Beverley J McKeon, Ugo Piomelli
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C15.00012: Fluid-Sediment-Object Interaction Under Oscillatory Flow Sylvia Rodriguez-Abudo, Edwin R Aponte A series of laboratory experiments on fluid-sediment-object interaction were conducted to thoroughly study the combined effect of sediment angularity, fluid stresses, bed roughness, and relative specific gravity on the object’s mobility and burial. The experiments consisted of oscillating a sediment tray in an otherwise still fluid, with the object placed on the sediment bed and moving with the frame of reference. Comparisons between flat-bed cases showed that burial increases with the object’s mobility number (ratio of fluid stresses to the object’s weight) and its relative specific gravity (ratio of the object’s specific gravity to that of the sediment), with no clear dependency on sediment angularity. Mobility over flat beds also increases with the object’s mobility number and its relative specific gravity, yet decreases 12-40% in angular sediments. Over bed roughnesses with length scales similar to those of the object, objects placed at the top of the roughness elements showed more mobility due to the unstable nature of their location. Objects whose axes were oriented perpendicular to the flow also showed more mobility than those parallel to the flow. When located at the flank of the roughness elements, objects showed consistently less mobility in angular sediments. |
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C15.00013: On the nonlocality of the slip length operator for scalar and momentum transport on patterned superhydrophobic surfaces in turbulent flow Kimberly Liu, Ali Mani Superhydrophobic surfaces (SHS) reduce skin friction drag via formation of air films on textured surfaces, resulting in an effective slip velocity. In this study, we seek to understand the effects of SHS and the usage of the Navier slip boundary condition in the context of mean mass and momentum mixing. We use the Macroscopic Forcing Method to compute the generalized eddy viscosity and slip length operators of a turbulent channel over SHS, implemented as both pattern-resolved and homogenized slip boundary conditions, for multiple pattern sizes and geometries. We present key differences in the mixing behavior of these boundary conditions through quantification of their implications on the near-wall eddy viscosity. More importantly, analysis of transport in turbulent flows over patterned surfaces reveals substantial nonlocality in the measured homogenized slip length for both scalar and momentum mixing when the Reynolds and Peclet numbers based on pattern size are finite. We present several metrics to quantify this nonlocality and observe possible trends relating to Reynolds number, texture size, and pattern geometry. We demonstrate the importance of including the nonlocality of the slip length operator by examining the impact on solutions for the mean scalar and velocity fields. |
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C15.00014: Minimum requirements for outer layer similarity and roughness function in wall turbulence over obstructing surfaces Zishen Chen, Ricardo Garcia-Mayoral Turbulent flows over rough and complex surfaces are generally believed to be essentially smooth-wall-like sufficiently far above the surface, exhibiting outer-layer similarity. The only difference with smooth-wall flows is then a constant shift in the mean velocity profile, also known as the roughness function, △U+. However, experimental and numerical studies have reported the loss of outer-layer similarity over certain obstructing layouts, such as porous substrates and canopies, and values for the Karman constant, κ, different from the smooth-wall value by factors of up to one half. Motivated by this, we have conducted an extensive set of direct simulations for flows over surfaces with tall elongated obstructions (canopies), aiming to disrupt the overlying flow as much as possible, varying the element height and spacing, friction Reynolds number, Reτ, and ratio of boundary-layer to canopy height, δ/h. The objective is to delimit under which conditions outer-layer similarity can be meaningfully defined, and when not. We find that spurious values of κ can result easily from trying to match the velocity profile to a log, when not even a smooth-wall flow at the same Reτ follows a log exactly, or from trying to extend that match into the roughness sublayer or above the log layer. We also suggest that outer-layer similarity implies a match not only of the log layer, but also of the wake, to a corresponding smooth wall flow, and that this should be taken into account. When this is done, outer-layer similarity can be recovered provided there is a sufficient extension of flow above the roughness sublayer. For δ/h≥20, a sufficient depth of log layer can develop and canonical values of κ can be observed. For δ/h∽10, however, the log layer is partially disrupted, and small decreases of order 10-15% in κ can be observed, although not as large as previously reported. At those low δ/h values, outer-layer similarity is only partially recovered, but the flow thickness is nevertheless sufficient to estimate △U+ accurately. |
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C15.00015: Understanding and modeling the roughness sublayer in non-equilibrium turbulent flows Junlin Yuan, Giles J Brereton The roughness sublayer (RSL) is the near-wall region of a rough-walled turbulence that is dynamically important in non-canonical flows but not well-understood. This work first summarizes recent findings on the RSL flow in non-equilibrium flat-plate boundary layers subject to strong favorable or adverse streamwise pressure gradients based on large-eddy simulations. It is shown that several mean flow quantities in the RSL stay invariant despite the strong pressure gradients, when they are normalized with a set of sublayer velocity and length scales. These quantities include the constant RSL thickness, constant hydrodynamic drag, and self-similar mean velocity and dispersive stresses. However, the Reynolds stresses normalized this way are not self-similar in the RSL. But the weak equilibrium criterion is satisfied as the Reynolds-stress anisotropy is invariant. Some of these observations appear to apply to flow sections with high local roughness Reynolds number only. Incorporation of the scaling relation into turbulence closures for rough-walled flows will be discussed. |
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C15.00016: Wall model for large-eddy simulation of high-speed flows over rough surfaces Rong Ma, Yuan Yuan, Gonzalo Arranz, Yuenong Ling, Michael P Whitmore, Rahul Agrawal, Ahmed Elnahhas, Clark C Pederson, Adrian Lozano-Duran Computational fluid dynamics (CFD) for Entry, Descent, and Landing (EDL) vehicles face unique challenges due to the ubiquity of complex aero/thermo-physics. Current CFD models are incapable of accurately predicting multiple aero/thermo-dynamic phenomena, especially those involving roughness-enhanced heating and shearing levels. To address this challenge, we have developed a wall model for large-eddy simulation (LES) using machine learning (ML) techniques, which accounts for compressibility and roughness effects in high-speed regimes. A DNS database of compressible turbulent flow over rough walls has been constructed, encompassing various roughness topographies, different Mach numbers, and Reynolds numbers. This database serves as the foundation for training our ML-based wall model. Information-theoretic dimensionless learning, based on the Buckingham-π theorem, is used to determine the most relevant non-dimensional inputs and outputs for the wall model. The predictive capability of the wall model is assessed a-posteriori in compressible turbulent channel flows with both smooth and rough walls, a high-pressure turbine blade with roughness, a compression ramp with roughness, and an EDL-like vehicle with roughness. The results demonstrate that the new wall model can predict drag and heat flux for high-speed flows in hydraulically smooth, transitionally, and fully rough regimes with an accuracy of within 10%. |
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C15.00017: Secondary vortices in turbulent boundary layers over combined roughness and temperature patterns Abdelhalim Abdeldayem, Johan Meyers, Raúl Bayoán Cal Earth topography is rich and diverse, ranging from smooth to highly rough topologies. Effects of varied topography not only impact local flow and ecosystems, but also extend to the atmospheric boundary layer (ABL), provoking transfer of energy, heat, and pollutants. In mountain ranges with extended valleys, cylindrical vortices propagate far above the surface, spanning the full height of the ABL in some cases. Added thermal complexity of low temperature mountain peaks compared to heated valleys affects the secondary vortices in various ways and even creates its own set of vortices. This work focuses on these secondary motions imposed by duality of roughness and thermal heterogeneities. Wind tunnel experiments considered stable boundary layer flow across surfaces of varied elevation and temperature. For smooth surfaces, temperature heterogeneity creates and strengthens secondary vortices up to a certain limit, where further heating then weakens vortices by the act of thermal stability. In rough cases, temperature and roughness effects on the secondary motions are opposite if the elevated part is kept at a higher temperature. As complex topography is common in nature, this work informs environmental and industrial systems such as wind farms, solar farms, and urban design. |
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C15.00018: Large-Eddy Simulation of Turbulent Flow Response to Abrupt Changes in Roughness and Thermal Conditions Xiaowei Zhu, Raúl Bayoán Cal Abrupt transitions in surface roughness and thermal conditions are ubiquitous in both environmental science and engineering applications. However, little is known about the combined effects of these abrupt changes. This study employs Large-Eddy Simulation (LES) techniques to simulate turbulent flows over heterogeneous surfaces with both abrupt changes in surface roughness and thermal conditions. Initially, the development of the internal boundary layer and the variation in momentum flux are observed separately for surface roughness heterogeneity and thermal heterogeneity. Subsequently, the flow behaviors are analyzed when both heterogeneities are present simultaneously. Additionally, this analysis scrutinizes the suitability of the Monin-Obukhov similarity theory, which is developed under homogeneous assumptions, within these contexts. Insights derived from this investigation can facilitate more accurate modeling of turbulence with abrupt changes, improving predictions for both environmental and engineering applications. |
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C15.00019: Turbulence and Energy Exchange in a High Reynolds Number Boundary Layer over a Compliant Surface Yuhui Lu, Tianrui Xiang, Tamer A Zaki, Joseph Katz Simultaneous measurements of the 3D time-resolved velocity/pressure field and the wall deformation in a turbulent boundary layer over a compliant surface at Reτ=3300-8900 are performed by combining tomographic particle tracking velocimetry and Mach Zehnder Interferometry. A previous study has shown that turbulence is advected at the surface wave speed up to the ‘critical layer,’ where the mean velocity is equal to the deformation wave speed, and at the local velocity at higher elevations. The critical height increases with Reynolds number, from y+=63 to 193. Here, we examine the critical layer effect on the turbulence and kinetic energy budget. The Reynolds stress profiles scale with inner variables near the wall, and with mixed ones in the outer layer. The velocity and pressure fluctuations are decomposed into the wave-coherent and ‘stochastic’ turbulence using Hilbert projections. The coherent stresses and pressure are smaller than the stochastic counterparts by an order of magnitude, except near the wall. The turbulent kinetic energy (TKE) budget is decomposed into the ‘wave kinetic energy’ (WKE) and stochastic turbulence. Shear production rate of WKE is 6-10% of that of the TKE, and both peak near the wall, well below the critical height. Energy flows from WKE to the stochastic turbulence below the critical layer, but reverses sign at higher elevations. The coherent pressure diffusion is dominated by the p-v correlation, adding energy to WKE below the critical layer, but depleting it at higher elevations. |
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C15.00020: Upstream History Effects in High-Reynolds Number Adverse-Pressure Gradient Turbulent Boundary Layers Mitchell Lozier, Ahmad Zarei, Rahul Deshpande, Ivan Marusic Turbulent boundary layers (TBLs) exposed to adverse-pressure gradients (APGs) are encountered in a number of engineering applications such as flows around wings or inside diffusers. Previous studies have demonstrated that the primary parameters influencing the characteristics of these TBLs are the Reynolds number, APG strength, and upstream pressure gradient (PG) history. Furthermore, every experimental investigation of an APG TBL is associated with a unique PG history, resulting from the use of different ramp geometries for example, which can potentially bias conclusions about APG TBL scaling characteristics. As such, past studies have investigated these PG history specific effects, however they have generally been limited to low-Reynolds number TBLs. We now propose to experimentally investigate high-Reynolds number, moderate APG TBLs, developing with variable upstream PG histories imposed using a purpose modified experimental facility. Preliminary results reveal PG history related effects on APG TBL scaling which are comparable to those seen in previous studies at lower Reynolds numbers. These new results additionally allow for comment on the regions of the TBL, and range of turbulent scales, specific to high-Reynolds number TBLs, which are influenced by PG history. |
Sunday, November 24, 2024 11:20AM - 12:50PM |
C15.00021: INTERACT DISCUSSION SESSION WITH POSTERS: Boundary Layers: from Laminar to Turbulent After each Flash Talk has concluded, the Interact session will be followed by interactive poster or e-poster presentations, with plenty of time for one-on-one and small group discussions. |
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C15.00022: Abstract Withdrawn |
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