Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session D22: Turbulent Boundary Layers I 
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Chair: Ronald Panton Room: 210 
Sunday, November 22, 2015 2:10PM  2:23PM 
D22.00001: Vorticity Fluctuations Require a Twoterm Asymptotic Representtion Ronald Panton Channel flow DNS data produced by several authors is analyzed. In the inner region, the vorticity fluctuations, \textless $\omega $i$\omega $i\textgreater , require twoterm asymptotic expansions. The first terms are scaled by the mixed velocity (U0 u$\tau )$1/2. They are the viscous response to imposed potential fluctuations, decay exponetially, and therefore do not require matching terms in the outer region. The first term is zero for the normal component, \textless $\omega $y$\omega $y\textgreater. The second terms are scaled by u$\tau $ with a gauge function u$\tau +$(Re$\tau $ ). They are active in the turbulence. In the log region they have an overlap behavior $\sim$ Ci / y$+$ or Co / (y/$\delta$). This behavior demands a rescaling in the outer region where the proper vorticity scale is $\tau \eta = \nu $ / $\varepsilon $ $=$ ($\nu $h / u$\tau $3 )1/2. This is the Kolmogorov time scale appropriate for viscous dissipation. In the outer region all components scale nicely with Re$\tau $ and have similar magnitudes. [Preview Abstract] 
Sunday, November 22, 2015 2:23PM  2:36PM 
D22.00002: Generalized higher order twopoint moments in turbulent boundary layers. Xiang Yang, Ivan Marusic, Charles Meneveau Generalized higher order twopoint moments such as $\langle {u'_z}^{m}(x){u'_z}^{n} ( {x+r}\rangle ^{2/(m+n)}$ and $\langle {[ {{u'_z}^{2}(x){u'_z}^{2}( {x+r})}]^{n}}\rangle ^{1/n}$ (where $z$ is the distance from the wall, $r$ is the distance in the flow direction, and $m$ and $n$ are arbitrary integers) are examined using high Reynolds number experimental data in turbulent boundary layer flow. Logarithmic behaviors with respect to both $s$ and $z$ in such statistics are observed. Certain predictions for such generalized log laws can be made in the context of the attached eddy hypothesis. Particularly simple results can be obtained for the scaling if one considers the velocity fluctuations at some point x and height z being the outcome of a random additive process, e.g. ${u}'_{N} =\sum\nolimits_{i=1}^N {a_{i} } $, where $N $depends on the wall normal distance $z $as $N\sim \log ( {\delta /z} )$, and the $a_{i} $'s are identical independent random additives. Predictions can be made of the slopes in the generalized log laws and these can be compared to the experimental data. For instance, already for single point higherorder moments it was known that the model overpredicts some slopes, indicating a subGaussian behavior in the statistics. Gaussian behavior is rooted in the assumption of independency in $a_{i} $'s. We discuss some variants that introduce correlations, and provide evidence that the generalized higher order twopoint moments can help discriminate among various possible models. [Preview Abstract] 
Sunday, November 22, 2015 2:36PM  2:49PM 
D22.00003: A multilayer description of Reynolds stresses in canonical wall bounded flows Xi Chen, Fazle Hussain, ZhenSu She A complete description of the Reynolds stress tensor is obtained for all three canonical wall turbulence (channel, pipe and turbulent boundary layer  TBL). The result builds on a multilayer description of length (order) functions and their ratios, including viscous sublayer, buffer layer, mesolayer for the near wall (inner) region, and bulk flow or a central core (absent in TBL) for the outer region. It is shown that the streamwise mean kineticenergy profile is quantified with high accuracy over the entire flow domain. The model contains only three \textit{Re}dependent parameters for Reynolds number (\textit{Re}) covering nearly three decades. Furthermore, the inner peak location is predicted to be invariant at y$^{+}=$15, while its magnitude shows notable \textit{Re} and geometry effects, predicted to be .9.2 for high \textit{Re}'s pipe flows. A mechanism is proposed for the emergence of outer peak in pipes, whose magnitude is predicted to scale as .Re$_{\tau }^{0.05}$ beyond a critical Re$_{\tau }$ about 10$^{4}$(). The recently reported logarithmic dependence in the bulk is recovered, but with an alternative explanation. The result is successfully extended to TBL flows by a fractional total stress and an absence of core. Equally accurate descriptions of vertical and spanwise kineticenergy are also presented for the three flows. The result has been used to modify turbulent engineering models (i.e. k$\omega $ model) with significant improvement. [Preview Abstract] 
Sunday, November 22, 2015 2:49PM  3:02PM 
D22.00004: Interaction of freestream turbulence with a turbulent boundary layer R. Jason Hearst, Eda Dogan, Bharathram Ganapathisubramani The interaction of freestream turbulence with a turbulent boundary layer is investigated with planar particle image velocimetry. An active grid consisting of a series of wings mounted to stepper motoractuated rods is used to generate freestream turbulence in a wind tunnel. In this study, turbulence intensities between 7\% and 13\% are investigated. The boundary layer is formed over a plate mounted downstream of the grid. When the turbulent freestream case is compared to a canonical turbulent boundary layer with an approximately laminar freestream, the distinct angled structure of the velocity correlation maps becomes homogeneous much closer to the wall relative to the boundary layer thickness. However, when comparisons are made between the canonical turbulent boundary layer and a case with significant freestream turbulence for matched shear levels, their structures are approximately the same. It is also found that there is a distinct lack of uniform momentum zones in the turbulent boundary layer for high levels of freestream turbulence. This is particularly interesting given that the outer layer of the boundary layer still exhibits a single strong lowfrequency peak in the velocity spectrum. [Preview Abstract] 
Sunday, November 22, 2015 3:02PM  3:15PM 
D22.00005: The time signature of the turbulent/nonturbulent interface over a turbulent boundary layer Angeliki Laskari, R. Jason Hearst, Roeland de Kat, Bharathram Ganapathisubramani The turbulent/nonturbulent interface (TNTI) between a turbulent boundary layer and an approximately laminar freestream is investigated with timeresolved planar particle image velocimetry (PIV). The turbulent boundary layer ($Re_\tau \approx 4000$), was formed on the floor of a water channel and was captured by a PIV system composed of a Phantom v641 4 megapixel camera and a Litron LDY 304 Laser. Images were acquired at 800~Hz, which was sufficient to resolve the motions of the TNTI in time. The instantaneous TNTI can be located by thresholding the velocity field based on physical arguments. A threshold of $0.95U_\infty$ can be selected based on identifying the limits of a uniform momentum zone encompassing the freestream. The timeresolved data set allows for instantaneous tracking of the TNTI topology and detection of its convection velocity, and thus provides novel insight into the TNTI. Preliminary findings based on a sample of the data set suggest the interface is convected at a velocity between $0.6U_\infty$ and $0.7U_\infty$. The final study will include analysis of the full data set of over 400,000 timeresolved images and a more accurate estimate of the convection velocity of the interface. [Preview Abstract] 
Sunday, November 22, 2015 3:15PM  3:28PM 
D22.00006: Internal shear layers and interfaces in turbulent boundary layers Charitha de Silva, Jimmy Philip, Dougal Squire, Nicholas Hutchins, Ivan Marusic We examine regions of concentrated shear in turbulent boundary layers that are observed to demarcate patches of relatively uniform streamwise momentum. To this end, we employ particle image velocimetry databases that span over a decade of Reynolds numbers ($Re_\tau =$ $\mathcal{O}$($10^310^4$)) which are tailored to capture the larger spatial features in the order of the boundary layer thickness, but with adequate spatial resolution to resolve most structural features. These databases are also complimented by experiments with enhanced spatial resolution in the order of the Kolmogorov scale, albeit over a narrow spatial extent. Our analysis quantitatively characterises several recurrent structural features, together with their associated scaling arguments. The Reynolds number dependence of these features is also investigated. Preliminary comparisons are also drawn between the observed edges of uniform momentum zones to the turbulent/nonturbulent interface at the edge of the boundary layer. [Preview Abstract] 

D22.00007: ABSTRACT WITHDRAWN 
Sunday, November 22, 2015 3:41PM  3:54PM 
D22.00008: On the development of turbulent boundary layer with wall transpiration Marco Ferro, Robert S. Downs III, Bengt E. G. Fallenius, Jens H. M. Fransson An experimental study of the development of the transpired boundary layer in zero pressure gradient is carried out on a 6.4 m long hydrodynamically smooth and perforated plate. The relatively longer development length of the present perforated plate compared to the ones used in previous studies allows us to investigate whether an asymptotic suction boundary layer with constant thickness is achieved for the turbulent state, analogously to what happens in the laminar state. Velocity profiles are obtained via hotwire anemometry while the wall shear stress is measured at several streamwise locations with hotfilm and wallwire probes as well as with oilfilm interferometry. The threshold suction coefficient above which relaminarization starts to occur is examined. The scaling of the mean velocity and of higher order velocity moments is discussed in light of the measured wall shear stress data. [Preview Abstract] 
Sunday, November 22, 2015 3:54PM  4:07PM 
D22.00009: Restricted nonlinear largeeddy simulations of wallturbulence Dennice F. Gayme, Joel U. Bretheim, Charles Meneveau The prominence of streamwise elongated structures motivates the use of a restricted nonlinear (RNL) model for studying the dynamics of wallturbulence. This model is formed by partitioning the Navier Stokes equations into a streamwise constant mean flow interacting with a streamwise varying perturbation field in which the nonlinear perturbationperturbation interactions are neglected. RNL simulations have been shown to support selfsustaining turbulence with a mean profile and structural features consistent with DNS in a number of canonical flows. Recent results have shown that the accuracy of the statistical properties predicted by the RNL model at higher Reynolds numbers can be significantly improved by limiting the streamwise varying Fourier components in the perturbation dynamics; this ``bandlimiting'' procedure also opens the door for lowercost simulations. Here, we extend the RNL model to high Reynolds number boundary layer flows through the creation of a RNL largeeddy simulation (LES) framework. The results indicate that a bandlimited RNLLES approach captures key flow statistics with a drastically reduced number of degrees of freedom versus a standard LES. [Preview Abstract] 
Sunday, November 22, 2015 4:07PM  4:20PM 
D22.00010: Direct numerical simulation of the incompressible temporally developing turbulent boundary layer Melissa Kozul, Daniel Chung, Jason Monty We present a Direct Numerical Simulation of the incompressible temporally developing turbulent boundary layer. The approach is inspired by temporal simulations of flows which are generally thought of as developing in space, such as wakes and mixing layers, and has previously been applied to the study of compressible boundary layers. The flow is the turbulent counterpart to the laminar Stokes' first problem where a fluid at rest is set into motion by a wall moving at constant velocity. An initial profile that models the effect of a wallmounted trip wire is implemented allowing characterisation of initial conditions by a trip Reynolds number. Comparisons of various statistics demonstrate that the temporally developing boundary layer is a good model for the spatially developing boundary layer once initial conditions can be neglected. Analysis of similarity solutions point to their asymptotic collapse. We therefore propose its use as a tool with which to study further manipulations of the turbulent boundary layer. In this study, the development of the turbulent boundary layer under the condition of isotropic freestream turbulence is investigated. Our temporal tool allows rapid and simplified simulation for a parameter space beyond the reasonable scope of costly spatial simulations. [Preview Abstract] 
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