Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session L26: Boundary Layers: Turbulent Boundary LayersBoundary Layers Turbulence
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Chair: Tindaro Ioppolo, Southern Methodist University Room: 707 |
Monday, November 20, 2017 4:05PM - 4:18PM |
L26.00001: Experimental Investigation of Compliant Wall Surface Deformation in Turbulent Boundary Layer Jin Wang, Karuna Agarwal, Joseph Katz On-going research integrates Tomographic PIV (TPIV) with Mach-Zehnder Interferometry (MZI) to measure the correlations between deformation of a compliant wall and a turbulent channel flow or a boundary layer. Aiming to extend the scope to two-way coupling, in the present experiment the wall properties have been designed, based on a theoretical analysis, to increase the amplitude of deformation to several $\mu $m, achieving the same order of magnitude as the boundary layer wall unit (5-10 $\mu $m). It requires higher speeds and a softer surface that has a Young's modulus of 0.1MPa (vs. 1Mpa before), as well as proper thickness (5 mm) that maximize the wall response to excitation at scales that fall within the temporal and spatial resolution of the instruments. The experiments are performed in a water tunnel extension to the JHU refractive index matched facility. The transparent compliant surface is made of PDMS molded on the tunnel window, and measurements are performed at friction velocity Reynolds numbers in the 1000-7000 range. MZI measures the 2D surface deformation as several magnifications. The time-resolved 3D pressure distribution is determined by calculating to spatial distribution of material acceleration from the TPIV data and integrating it using a GPU-based, parallel-line, omni-directional integration method. [Preview Abstract] |
Monday, November 20, 2017 4:18PM - 4:31PM |
L26.00002: High-Fidelity PIV of a Naturally Grown High Reynolds Number Turbulent Boundary Layer Drummond Biles, Chris White, Joeseph Klewicki High-fidelity particle image velocimetry data acquired in the the Flow Physics Facility (FPF) at the University of New Hampshire is presented. Having a test section length of 72m, the FPF employs the ``big and slow'' approach to obtain well-resolved turbulent boundary layer measurements at high Reynolds number. We report on PIV measurements acquired in the streamwise---wall-normal plane at a downstream position 59m from the test-section inlet over the friction Reynolds number range $7000 < Re_\tau < 15000$. Local flow tracer seeding is employed through a wall-mounted slot fed by a large volume plenum located 13.4m upstream of the PIV measurement station. Both time-independent and time-dependent turbulent flow statistics are presented and compared to existing data. [Preview Abstract] |
Monday, November 20, 2017 4:31PM - 4:44PM |
L26.00003: Structure of Turbulent Boundary Layers Subjected to Wave Forcing Maius Wong, Owen Williams Surface waves are known to have a strong non-linear interaction with the turbulence of current-induced bottom boundary layers, making the prediction of mixing and nutrient transport in estuaries and rivers difficult to predict. To aid our understanding of this interaction, we examine the turbulent spatial structure of submerged boundary layers within the newly constructed Air-Sea Interaction facility at the University of Washington (WASIRF). Initial studies have indicated that surface waves disrupt the large-scale turbulence of the bottom boundary layer, altering structures of the size of the wavelength or larger. We build upon this result by observing the boundary layer response to a wider range of wave parameters. Changes to velocity statistics under the triple decomposition are compared with highly converged Partial Orthogonal Decomposition (POD) modes, linking the structure of productive motions to more conventional single-point statistics. [Preview Abstract] |
Monday, November 20, 2017 4:44PM - 4:57PM |
L26.00004: Spanwise vorticity and wall normal velocity structure in the inertial region of turbulent boundary layers Juan Carlos Cuevas Bautista, Caleb Morrill-Winter, Christopher White, Gregory Chini, Joseph Klewicki The Reynolds shear stress gradient is a leading order mechanism on the inertial domain of turbulent wall-flows. This quantity can be described relative to the sum of two velocity-vorticity correlations, $\overline{v\omega_z}$ and $\overline{w\omega_y}$. Recent studies suggest that the first of these correlates with the step-like structure of the instantaneous streamwise velocity profile on the inertial layer. This structure is comprised of large zones of uniform momentum segregated by slender regions of concentrated vorticity. In this talk we study the contributions of the $v$ and $\omega_z$ motions to the vorticity transport ($\overline{v\omega_z}$) mechanism through the use of experimental data at large friction Reynolds numbers, $\delta^+$. The primary contributions to $v$ and $\omega_z$ were estimated by identifying the peak wavelengths of their streamwise spectra. The magnitudes of these peaks are of the same order, and are shown to exhibit a weak $\delta^+$ dependence. The peak wavelengths of $v$, however, exhibit a strong wall-distance ($y$) dependence, while the peak wavelengths of $\omega_z$ show only a weak $y$ dependence, and remain almost $O(\sqrt{\delta^+})$ in size throughout the inertial domain. [Preview Abstract] |
Monday, November 20, 2017 4:57PM - 5:10PM |
L26.00005: Inner-outer interactions in a rough wall turbulent boundary layer over hemispherical roughness using PIV Gokul Pathikonda, Caitlyn Clark, Kenneth T Christensen Inner-outer interactions over rough-wall boundary layer were investigated using high frame-rate, PIV measurements in a Refractive index-matched (RIM) facility. Flows over canonical smooth-wall and hexagonally-packed hemispherical roughness under transitionally rough flow conditions (and with $Re_\tau \sim 1500$) were measured using a dual camera PIV system with different fields of view (FOVs) and operating simultaneously. The large FOV measures the large scales and boundary layer parameters, while the small FOV measures the small scales very close to the wall with high spatial ($\sim 7y^*$) and temporal ($\sim 2.5t^*$) resolutions. Conditional metrics were formulated to investigate these scale interactions in a spatio-temporal sense using the PIV data. It was found that the observations complement the interaction structure made via hotwire experiments and DNS in previous studies over both smooth and rough-wall flows, with a strong correlation between the large scales and small scale energies indicative of the amplitude modulation interactions. Additionally, frequency and scale modulations were also investigated with limited success. These experiments highlight the similarities and differences in these interactions between the smooth- and rough-wall flows. [Preview Abstract] |
Monday, November 20, 2017 5:10PM - 5:23PM |
L26.00006: Entrainment rates and quadrant events across the turbulent/non-turbulent interface over a turbulent boundary layer Angeliki Laskari, Roeland de Kat, R. Jason Hearst, Bharathram Ganapathisubramani Mass entrainment rates across the turbulent non/turbulent interface (TNTI) of a turbulent boundary layer ($Re_{\tau}=5300$) are estimated using time-resolved planar particle image velocimetry (PIV). The resulting entrainment velocities are found to be of the order of the friction velocity and are distributed around a positive net entrainment rate. The latter is in agreement with theoretical estimations of average mass entrainment rates, based on boundary layer growth. Effects of the interface geometry and wall-normal location on entrainment are also investigated and the average TNTI location is shown to have a moderate effect on the resulting mass flux rate. More specifically, larger positive entrainment values are found to be correlated with higher than average interface locations, a case that is also linked with a strong prominence of $Q2$ events at the vicinity of the TNTI. For lower TNTI locations, where larger detrainment values are observed, $Q4$ events are shown to dominate below the interface. This scenario is also linked with less convoluted interface shapes, although the total path length of the interface itself does not appear to directly influence the entrainment rate. [Preview Abstract] |
Monday, November 20, 2017 5:23PM - 5:36PM |
L26.00007: Large-scale Motions in a Separated Turbulent Boundary layer Suranga Dharmarathne, Humberto Bocanegra Evans, Ali Hamed, Burak Aksak, Leonardo Chamorro, Murat Tutkun, Luciano Castillo Proper orthogonal decomposition was used to decompose the velocity field measured using particle image velocimetry over a separated turbulent boundary layer for investigating the effect of large-scale motions (LSM) on Reynolds stresses. LSMs are defined here by the fluctuating velocity field that is responsible for $55\%$ turbulence kinetic energy. Results show that $\approx 90\%$ of the Reynolds shear stress, $\overline{uv}$, is due to the LSM. The same motions contribute about $70\%$ of the streamwise component of the Reynolds normal stress, $\overline{u^2}$. Surprisingly, both large-scale and small-scale motions equally contribute to the wall-normal component of the Reynolds normal stress, $\overline{v^2}$. Furthermore, the study reveals the characteristic length scales and frequencies of the LSMs that might be modulated to control the flow separation. [Preview Abstract] |
Monday, November 20, 2017 5:36PM - 5:49PM |
L26.00008: Convection of wall shear stress events in a turbulent boundary layer Rommel Pabon, David Mills, Lawrence Ukeiley, Mark Sheplak The fluctuating wall shear stress is measured in a zero pressure gradient turbulent boundary layer of $Re_\tau \approx 1700$ simultaneously with velocity measurements using either hot-wire anemometry or particle image velocimetry. These experiments elucidate the patterns of large scale structures in a single point measurement of the wall shear stress, as well as their convection velocity at the wall. The wall shear stress sensor is a CS-A05 one-dimensional capacitice floating element from Interdisciplinary Consulting Corp. It has a nominal bandwidth from DC to 5 kHz and a floating element size of 1 mm in the principal sensing direction (streamwise) and 0.2 mm in the cross direction (spanwise), allowing the large scales to be well resolved in the current experimental conditions. In addition, a two sensor array of CS-A05 aligned in the spanwise direction with streamwise separations $\mathcal{O}(\delta)$ is utilized to capture the convection velocity of specific scales of the shear stress through a bandpass filter and peaks in the correlation. Thus, an average wall normal position for the corresponding convecting event can be inferred at least as high as the equivalent local streamwise velocity. [Preview Abstract] |
Monday, November 20, 2017 5:49PM - 6:02PM |
L26.00009: Influence of scale interaction on the transport of a passive scalar in a turbulent boundary layer Theresa Saxton-Fox, Scott Dawson, Beverley McKeon A mildly heated turbulent boundary layer is experimentally studied using particle image velocimetry to measure the velocity field and a Malley probe (Malley et al., 1992; Gordeyev et al., 2014) to measure the passive scalar field. Strong gradients in the passive scalar field are observed to be correlated to the interaction of specific velocity scales, illuminating an effect of scale interaction on the passive scalar field. A resolvent analysis performed on the fluctuating velocity and passive scalar equations of motion is used to identify the most amplified velocity and scalar mode shapes at particular wavenumbers. The superposition of a small number of these modes is shown to reproduce the velocity scale interaction phenomenon observed experimentally, as well as the corresponding strong gradient in the scalar field. [Preview Abstract] |
Monday, November 20, 2017 6:02PM - 6:15PM |
L26.00010: The behavior of turbulent boundary layer flow over periodic flexible walls . Tindaro Ioppolo This study describes the interaction of a zero pressure gradient turbulent boundary layer with periodic circular flexible plates. The elastic plates are mounted on the floor of the test section of a subsonic wind tunnel and exposed to a free stream velocity between 20m/s and 70m/s. The ceiling of the test section of the wind tunnel is adjustable so that a nearly zero pressure gradient is obtained in the test section of the wind tunnel. Hot-wire anemometry was used to measure the velocity components. Velocity and turbulence quantities are measured for different plate's stiffness and geometries and are compared with the measurements obtained using a rigid plate. [Preview Abstract] |
Monday, November 20, 2017 6:15PM - 6:28PM |
L26.00011: Spatial and temporal properties of vorticity in high Reynolds number turbulent boundary layers Spencer Zimmerman, Joseph Klewicki The Reynolds number dependence of the mean dynamics of turbulent wall-bounded flow has been shown to be intimately related to the properties of the vorticity field. For example, in aggregate, the spatial distribution and strength of the spanwise vorticity underpins the eventual shape of the mean velocity profile. Additionally, decomposition of the Reynolds stress gradient in the mean momentum equation reveals the dependence of this term on the alignment between the velocity and vorticity fields. Toward investigating the evolution with Reynolds number of the role of vorticity in the transport of momentum, simultaneous temporally-resolved measurements of the velocity and vorticity vectors have been acquired across a wide range of Reynolds numbers. These measurements allow for inspection of the magnitudes and length scales at which the various components of vorticity congregate as functions of both wall-distance and Reynolds number. In this presentation, various spatial and temporal properties of the vorticity and velocity fields are presented and discussed in the context of the leading balance structure of the mean momentum equation. [Preview Abstract] |
Monday, November 20, 2017 6:28PM - 6:41PM |
L26.00012: Characterization of Rare Reverse Flow Events in Adverse Pressure Gradient Turbulent Boundary Layers Christian J. Kaehler, Matthew Bross, Thomas Fuchs Time-resolved tomographic flow fields measured in the viscous sublayer region of a turbulent boundary layer subjected to an adverse pressure gradient (APG) are examined with the aim to resolve and characterize reverse flow events at Re$_{\tau}$ = 5000. The fields were measured using a novel high resolution tomographic particle tracking technique. It is shown that this technique is able to fully resolve mean and time dependent features of the complex three-dimensional flow with high accuracy down to very near-wall distances ($\sim$10 $\mu$m). From time resolved Lagrangian particle trajectories, statistical information as well as instantaneous topological features of near-wall flow events are deduced. Similar to the zero pressure gradient case (ZPG), it was found that individual events with reverse flow components still occur relatively rarely under the action of the pressure gradient investigated here. However, reverse flow events comprised of many individual events, are shown to appear in relatively organized groupings in both spanwise and streamise directions. Furthermore, instantaneous measurements of reverse flow events show that these events are associated with the motion of low-momentum streaks in the near-wall region. [Preview Abstract] |
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