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 A28: Turbulence: Wall-Bounded Flows IBoundary Layers Turbulence
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Chair: Anthony Leonard, California Institute of Technology Room: 207 |
Sunday, November 19, 2017 8:00AM - 8:13AM |
A28.00001: Well-resolved turbulence measurements in high Reynolds number turbulent boundary layer flows Milad Samie, Ivan Marusic, Nicholas Hutchins, Yuyang Fan, Matthew Fu, Marcus Hultmark, Alexander Smits Despite several decades of research in wall-bounded turbulence there is still controversy over the behavior of streamwise turbulence intensities near the wall, especially at high Reynolds numbers. Much of it stems from the uncertainty in measurement due to finite spatial resolution. Conventional hot-wire anemometry is limited for high Reynolds number measurements due to limited spatial resolution issues that cause attenuation in the streamwise turbulence intensity profile near the wall. To address this issue we use the NSTAP (nano-scale thermal anemometry probe) developed at Princeton University to conduct velocity measurements in the high Reynolds number boundary layer facility at the University of Melbourne. NSTAP is almost one order of magnitude shorter than conventional hot-wires. This enables us to acquire fully-resolved velocity measurements of turbulent boundary layers up to $Re_\tau=$ 20000. Results show that in the near-wall region, the viscous-scaled streamwise turbulence intensity increases with $Re_\tau$ in the Reynolds number range of the experiments. Moreover, the energy spectra in the near-wall region show excellent inner-scaling over the small to moderate wavelength range, followed by a large outer-scale influence that increases with Reynolds number. [Preview Abstract] |
Sunday, November 19, 2017 8:13AM - 8:26AM |
A28.00002: Targeting specific azimuthal modes using wall changes in turbulent pipe flow Tyler Van Buren, Leo Hellström, Ivan Marusic, Alexander Smits We experimentally study turbulent pipe flow at Re$=$3486 using stereoscopic particle image velocimetry. Using pipe inserts with non-circular geometry to perturb the flow upstream of the measurement location, we excite specific naturally occurring energetic modes. We consider inserts that directly manipulate the flow momentum (vortex generators), and/or induce secondary flows through Reynolds stresses (sinusoidally varying wall shape). These inserts substantially change the mean flow, and produce distinct regions of low and high momentum corresponding to the mode being excited. The inserts add energy in the targeted modes while simultaneously reducing the energy in the non-excited azimuthal modes. In addition, inserts designed to excite two modes simultaneously exhibit non-linear interactions. Supported under ONR Grant N00014-15-1-2402, Program Manager/Director Thomas Fu and the Australian Research Council. [Preview Abstract] |
Sunday, November 19, 2017 8:26AM - 8:39AM |
A28.00003: Turbulent flow in a partially filled pipe Henry Ng, Hope Cregan, Jonathan Dodds, Robert Poole, David Dennis Turbulent flow in a pressure driven pipe running partially full has been investigated using high-speed 2D-3C Stereoscopic Particle Imaging Velocimetry. With the field-of-view spanning the entire pipe cross section we are able to reconstruct the full three dimensional quasi-instantaneous flow field by invoking Taylor's hypothesis. The measurements were carried out over a range of flow depths at a constant Reynolds number based on hydraulic diameter and bulk velocity of $Re=32,000$. In agreement with previous studies, the ``velocity dip'' phenomenon, whereby the location of the maximum streamwise velocity occurs below the free surface was observed. A mean flow secondary current is observed near the free surface with each of the counter-rotating rollers filling the half-width of the pipe. Unlike fully turbulent flow in a rectangular open channel or pressurized square duct flow where the secondary flow cells appear in pairs about a corner bisector, the mean secondary motion observed here manifests only as a single pair of vortices mirrored about the pipe vertical centreline. [Preview Abstract] |
Sunday, November 19, 2017 8:39AM - 8:52AM |
A28.00004: Splitting of turbulent spot in transitional pipe flow. Xiaohua Wu, Parviz Moin, Ronald J. Adrian Recent study (Wu et al, PNAS, 1509451112, 2015) demonstrated the feasibility and accuracy of direct computation of the Osborne Reynolds' pipe transition problem without the unphysical, axially periodic boundary condition. Here we use this approach to study the splitting of turbulent spot in transitional pipe flow, a feature first discovered by E.R. Lindgren (Arkiv Fysik 15, 1959). It has been widely believed that spot splitting is a mysterious stochastic process that has general implications on the lifetime and sustainability of wall turbulence. We address the following two questions: (1) What is the dynamics of turbulent spot splitting in pipe transition? Specifically, we look into any possible connection between the instantaneous strain rate field and the spot splitting. (2) How does the passive scalar field behave during the process of pipe spot splitting. In this study, the turbulent spot is introduced at the inlet plane through a sixty degree wide numerical wedge within which fully-developed turbulent profiles are assigned over a short time interval; and the simulation Reynolds numbers are 2400 for a 500 radii long pipe, and 2300 for a 1000 radii long pipe, respectively. Numerical dye is tagged on the imposed turbulent spot at the inlet. Splitting of the imposed turbulent spot is detected very easily. Preliminary analysis of the DNS results seems to suggest that turbulent spot slitting can be easily understood based on instantaneous strain rate field, and such spot splitting may not be relevant in external flows such as the flat-plate boundary layer. [Preview Abstract] |
Sunday, November 19, 2017 8:52AM - 9:05AM |
A28.00005: Turbulent spots and scalar flashes in pipe transition Ronald Adrian, Xiaohua Wu, Parviz Moin ~ Recent study (Wu et al, PNAS, 1509451112, 2015) demonstrated the feasibility and accuracy of direct computation of the Osborne Reynolds' pipe transition experiment without the unphysical axially periodic boundary condition. Here we use this approach to address three questions: (1) What are the dynamics of turbulent spot generation in pipe transition? (2) How is the succession of scalar flashes, as observed and sketched by Osborne Reynolds, created? (3) What happens to the succession of flashes further downstream? In this study, the inlet disturbance is of radial-mode type imposed through a narrow, three-degree numerical wedge; and the simulation Reynolds number is 6500. Numerical dye is introduced at the inlet plane locally very close to the pipe axis, similar to the needle injection by O. Reynolds.~ Inception of infant turbulent spots occurs when normal, forward inclined hairpin packets form near the walls from the debris of the inlet perturbations. However, the young and mature turbulent spots consist almost exclusively of reverse, backward leaning hairpin vortices. Scalar flashes appear successively downstream and persist well into the fully-developed turbulent region. Their creation mechanism is addressed.~ [Preview Abstract] |
Sunday, November 19, 2017 9:05AM - 9:18AM |
A28.00006: Essential Development of Streamwise Vortical/Secondary Flows in All Ducts with Corners or Slope Discontinuities in Perimeter Hassan Nagib, Alvaro Vidal, Ricardo Vinuesa, Philipp Schlatter Direct numerical simulations of fully-developed turbulent flow through various straight ducts with sharp or rounded corners of various radii were performed to study influence of corner geometry on secondary flows. Unexpectedly, increased rounding of corners in rectangular ducts does not lead to monotonic trend towards pipe case. Instead, secondary vortices relocate close to regions of wall-curvature change. This behavior is connected to inhomogeneous interaction between near-wall bursting events, which are further characterized in this work with definition of their local preferential direction, and vorticity fluxes. Although these motions are relatively weak compared to streamwise velocity their effect on turbulence statistics and shear-stress distribution is very important and has not been sufficiently documented or fully understood. Flow through spanwise-periodic channels, with sinusoidal function to define the geometry of wall, $y_w$ = $\pm$ $h$ + $A$ $cos(\omega z)$, was also studied as model flow that is parametrically changed using $A$ and $\omega$, while taking advantage of many resulting symmetries. Consequences on experimental facilities and comparisons between experiments and various numerical and theoretical models are discussed revealing the uniqueness of pipe flow. [Preview Abstract] |
Sunday, November 19, 2017 9:18AM - 9:31AM |
A28.00007: Internal shear layers and uniform momentum zones in a turbulent pipe flow Melika Gul, Gerrit E. Elsinga, Jerry Westerweel Turbulent pipe flow has previously been shown to contain large-scale nearly uniform momentum, which are separated by layers of significant shear. These internal layers are of interest, because they are associated with fluid transport between uniform momentum zones, hence with the growth of these large energy-containing motions. In this study, we compare two methods to detect and analyse the internal shear layers; the triple decomposition method (TDM) and the streamwise velocity histogram method. The assessment is based on time-resolved PIV measurements in the cross-section of the pipe spanning a range of Reynolds numbers (Re$_{\mathrm{\tau }}=$700-1178). The strong jumps in the conditionally averaged flow statistics across the layers detected by TDM are smeared out with the histogram method. Using the TDM method, some scaling analyses are performed for the layer thickness, and the velocity jump over the layer. It is found that the layer thickness becomes almost constant after 0.4R, and the streamwise velocity jump decreases from the wall region to the core of the pipe. With the histogram method, on the other hand, one distinct shear layer is distinguished from the distribution of all local peak velocities, which is corresponding to the 95{\%} of the central velocity of the pipe. [Preview Abstract] |
Sunday, November 19, 2017 9:31AM - 9:44AM |
A28.00008: Study of Turbulence in Unsteady Flows using Particle Image Velocimetry (PIV) and Constant Temperature Anemometry (CTA) Benjamin Oluwadare, Akshat Mathur, Shuisheng He Experimental studies are carried out to investigate transition to turbulence of a transient turbulent flows, a concept proposed by He {\&} Seddighi (2013) based on DNS results. PIV is used in this study to measure instantaneous velocity of the unsteady flows. CTA is used to determine skin friction coefficient and wall shear stress. A pneumatically regulated valve is used to control the flowrate during the transient flows. The valve opening is controlled to produce pre-determined flow variations. Measurements of mean and turbulent statistics of the transient flows are obtained. Immediately after the flow excursion, skin friction coefficient increases sharply and reaches the maximum value. This reflects the creation of a thin boundary layer near the wall that results in an increase of velocity gradient and viscous force. As the boundary layer thickness increases, the viscous force decreases and the skin friction coefficient reduces. Later, the boundary layer becomes unstable resulting in a transition to turbulence. The minimum point of the friction coefficient marks the beginning of transition. The friction increases again during the transitional period. These observations conform the theories presented by Jacobs {\&} Durbin (2001) and He {\&} Seddighi (2015). [Preview Abstract] |
Sunday, November 19, 2017 9:44AM - 9:57AM |
A28.00009: Equilibrium Boundary Layer Analysis of Filtered Turbulent Flow Fields Pedram Tazraei, Sharath Girimaji Analysis of equilibrium turbulent boundary layer is of fundamental value as well of practical importance in developing closure models. To date, the analysis has been performed only in the context of mean and fluctuating flow field variables, leading to important implications for Reynolds Averaged Navier-Stokes (RANS) closure models. In this work, we extend the analysis to filtered flow fields. The degree of filtering is characterized in terms of the ratio of resolved-to-total kinetic energy (k) and dissipation (ε). Scaling relationships between different statistics of the filtered flow-field are developed as a function of the degree of filtering. Closure-modeling analysis is performed in the context of a generic scale-resolving simulation (SRS) method. In many SRS approaches, such as the Partially-averaged Navier-Stokes (PANS) approach, the filtered flow equations are supplemented with model equations for unresolved kinetic energy and dissipation. The filtered kinetic energy and dissipation equations are subject to equilibrium boundary layer scaling, leading to closure expressions for SRS turbulent transport models. PANS simulations are performed at various Reynolds numbers and degrees of resolutions to confirm the scaling relationships and validate the transport closure models. [Preview Abstract] |
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