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 E26: General Boundary LayersBoundary Layers
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Chair: Oscar Flores, Universidad Carlos III de Madrid Room: 707 |
Sunday, November 19, 2017 4:55PM - 5:08PM |
E26.00001: Compressibility effect on thermal coherent structures in spatially-developing turbulent boundary layers via DNS Guillermo Araya, Kenneth Jansen DNS of compressible spatially-developing turbulent boundary layers is performed at a Mach number of 2.5 over an isothermal flat plate. Turbulent inflow information is generated by following the concept of the rescaling-recycling approach introduced by Lund et al. (J. Comp. Phys. 140, 233-258, 1998); although, the proposed methodology is extended to compressible flows. Furthermore, a dynamic approach is employed to connect the friction velocities at the inlet and recycle stations (i.e., there is no need of an empirical correlation as in Lund et al.). Additionally, the Morkovin’s Strong Reynolds Analogy (SRA) is used in the rescaling process of the thermal fluctuations from the recycle plane. Low/high order flow statistics is compared with direct simulations of an incompressible isothermal ZPG boundary layer at similar Reynolds numbers and temperature regarded as a passive scalar. Focus is given to the effect assessment of flow compressibility on the dynamics of thermal coherent structures. [Preview Abstract] |
Sunday, November 19, 2017 5:08PM - 5:21PM |
E26.00002: Inception of Klebanoff streaks and large-scale motions in transitional and fully turbulent boundary layers Jin Lee, Tamer Zaki Transitional boundary layers feature long coherent motions of streamwise velocity fluctuation, $u'$, in both the laminar and turbulent regions. In the former, Klebanoff streaks amplify and become seats for breakdown to turbulence. In the fully turbulent region, large-scale motions contribute appreciably to the turbulence energy and shear stresses. Direct numerical simulation (DNS) of boundary-layer bypass transition over a flat plate with a leading edge is performed. Instantaneous realizations of spatially and temporally resolved fields are stored in a database. Structure identification techniques are used to identify these coherent flow structures [Lee, Sung {\&} Zaki, \textit{J. Fluid Mech}. \textbf{819}, 165-187 (2017)]. The inception rate, lifetime and amplification rate of Klebanoff streaks are evaluated in the laminar region, and conditional averaging is used to examine the early stages of streak formation. Structure identification and tracking is also used to study the inception of large-scale coherent motion in the nascent turbulent spots and fully turbulent boundary layer downstream. [Preview Abstract] |
Sunday, November 19, 2017 5:21PM - 5:34PM |
E26.00003: Direct numerical simulations of turbulent boundary layers beneath free-stream vortical forcing Jiho You, Tamer Zaki Direct numerical simulations (DNS) are performed to study the modifications to turbulent boundary layers when they are exposed to free-stream vortical perturbations. The inflow boundary layer is computed in a precursor simulation [see e.g. Lee, Sung {\&} Zaki, J. Fluid Mech. , 165-187 (2017)], and the free-stream disturbances are obtained from DNS of homogeneous isotropic turbulence. Additionally, a level-set approach is adopted to distinguish the free-stream and boundary-layer fluids and their contributions to the turbulence statistics. When the free stream is turbulent, the skin friction increases relative to the unforced flow. The enhanced wall friction can be attributed to an increase in turbulence kinetic energy production inside the boundary layer. Even though the free-stream perturbations are themselves void of Reynolds shear stresses, conditional statistics demonstrate that they enhance the shear stress within the boundary layer and, as a result, turbulence production and drag. In addition, the free-stream forcing alters both the spectral content and turbulence structures inside the boundary layer. [Preview Abstract] |
Sunday, November 19, 2017 5:34PM - 5:47PM |
E26.00004: Identifying vertical velocity eddies from wall-pressure Oscar Flores, Carlos Sanmiguel Vila During the last decades, a number of reduced order models based on coherent structures have been proposed to describe wall-bounded turbulence. Many of these models emphasize the importance of coherent vertical velocity eddies (v-eddies), which are the cause for the very long streamwise velocity structures observed in the logarithmic and outer region. In order to use these models to improve our ability to control wall-bounded turbulence in realistic applications, these v-eddies need to be identified from the wall in a non-intrusive way. In this talk, we will explore the possibility to use the pressure at the wall for this task. We will start by analyzing the correlation between the vertical velocity and the pressure at the wall, $R_{vp}(\mathbf{x}, t)$, where $\mathbf{x}$ is the separation between the points where wall-pressure and vertical velocity are measured, and $t$ is the time lag. This correlation is computed from time resolved DNS of turbulent channels, at moderate Reynolds numbers ($Re_\tau \sim 10^3$). We will also present this correlation for the filtered (in time and/or in space) wall-pressure, showing how the selection of the characteristic length and time scales of the filters allows us to discriminate v-eddies centered at different distances to the wall. [Preview Abstract] |
Sunday, November 19, 2017 5:47PM - 6:00PM |
E26.00005: Direct numerical simulation of a turbulent boundary layer with separation and reattachment at $Re_\theta=1500$ Hiroyuki Abe Direct numerical simulation (DNS) has been performed in a flat-plate turbulent boundary layer with large adverse and favorable pressure gradients, thus involving separation and reattachment. This work extends a series of our DNSs at lower Reynolds numbers (Abe et al. 2012; 2015), where suction and blowing are imposed at the upper boundary for providing pressure gradients. Particular attention is given to the $Re$ dependence. The present inlet Reynolds number is equal to $Re_\theta=1500$, which is by a factor of five larger than that for seminal DNSs (Spalart \& Coleman 1997; Na \& Moin 1998). Number of grid points used are 13 billion ($N_x \times N_y \times N_z = 4096 \times 1536 \times 2048$ in the streamwise ($x$), wall-normal ($y$) and spanwise ($z$) directions, respectively) to resolve the essential motions. At the inlet, spatial resolution normalized by wall units is set to $\Delta x^+ = 8$, $\Delta y^+ = 0.1 \sim 10$, $\Delta z^+ = 5$. Significant $Re$ effect is observed for skin friction outside the bubble, while it is small for mean quantities inside the bubble. In the separated region, large-scale structures of streamwise velocity fluctuations and pressure rollers become more prominent with increasing $Re_\theta$, which impinge significantly on the wall at reattachment. [Preview Abstract] |
Sunday, November 19, 2017 6:00PM - 6:13PM |
E26.00006: Analysis Of Direct Numerical Simulation Results Of Adverse Pressure Gradient Boundary Layer Through Anisotropy Invariant Mapping And Comparison With The Rans Simulations Ayse Gul Gungor, Ozan Ekin Nural, Ozgur Ertunc Purpose of this study is to analyze the direct numerical simulation data of a turbulent boundary layer subjected to strong adverse pressure gradient through anisotropy invariant mapping. RANS simulation using the “Elliptic Blending Model” of Manceau and Hanjolic (2002) is also conducted for the same flow case with commercial software Star-CCM+ and comparison of the results with DNS data is done. RANS simulation captures the general trends in the velocity field but, significant deviations are found when skin friction coefficients are compared. Anisotropy invariant map of Lumley and Newman (1977) and barycentric map of Banerjee et al. (2007) are used for the analysis. Invariant mapping of the DNS data has yielded that at locations away from the wall, flow is close to one component turbulence state. In the vicinity of the wall, turbulence is at two component limit which is one border of the barycentric map and as the flow evolves along the streamwise direction, it approaches to two component turbulence state. Additionally, at the locations away from the wall, turbulence approaches to two component limit. Furthermore, analysis of the invariants of the RANS simulations shows dissimilar results. In RANS simulations invariants do not approach to any of the limit states unlike the DNS. [Preview Abstract] |
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