Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session G38: Direct Numerical Simulations 
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Chair: Gillaume Blanquart, California Institute of Technology Room: Georgia World Congress Center Ballroom 1/2 
Monday, November 19, 2018 10:35AM  10:48AM 
G38.00001: Roughness effect in turbulent CouettePoiseuille flow over a rodroughened wall Jeong Hyun Kim, Young Mo Lee, Jae Hwa Lee Direct numerical simulations of fully developed turbulent CouettePoiseuille flow over a rodroughened wall is performed to investigate the effects of twodimensional surface roughness elements at Re=7200, based on the centerline laminar velocity and channel halfheight (h). The roughness elements are periodically arranged on the bottom wall with a streamwise pitch of p=8k and the roughness height is k/h=0.12, where k is roughness height. The mean velocity profile shows that the logarithmic layer of a turbulent CouettePoiseuille flow is shortened by surface roughness, compared to that for the smooth wall. The Reynolds stresses for the CouettePoiseuille flow with rod roughness are decreased in the outer layer, contrary to the observation in the turbulent Poiseuille flow with rod roughness, revealed by the decomposition of the Reynolds stresses. The temporally averaged ustructures for the CouettePoiseuille flow show that the largescale roll mode dominates the whole domain region but with the significantly weakened roll mode for the flow with rod roughness. 
Monday, November 19, 2018 10:48AM  11:01AM 
G38.00002: MolecularGasDynamics Simulation of Turbulent
Minimal Couette Flow John R Torczynski, Michael A Gallis, Neal P Bitter, Timothy P Koehler, Steven J Plimpton, George Papadakis The Direct Simulation Monte Carlo (DSMC) method of molecular gas dynamics (MGD) is used to simulate turbulent Minimal Couette Flow (MCF) at Re=500. The initial flow field is the laminar velocity profile plus a perturbation. Subsequently, streamwise vortices continually form, interact, and decay. The DSMC average wall shear stress, average kinetic energy, and Law of the Wall agree closely with Direct Numerical Simulation (DNS). These results indicate that MGD methods such as DSMC that use molecular chaos to perform collisions can simulate sustained wallbounded turbulent shear flows with good accuracy. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DENA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government. 
Monday, November 19, 2018 11:01AM  11:14AM 
G38.00003: Numerical Investigation of Plane Couette Flow with Weak Spanwise Rotation Yuhan Huang, Zhenhua Xia, Yipeng Shi, Minping Wan, Shiyi Chen Direct numerical simulation of rotating plane Couette flow (RPCF) at Re=1300 and Ro=0.02 is performed under varying mesh resolutions and different aspect ratios. Our results showed that a grid of 256×71×256 is fine enough to simulate the problem at a computational box of 8πh×2h×4πh. The streamwise length L_{x} and spanwise length L_{z} of the computational box have different impacts on the flow statistics, where the statistics were converged if L_{x} is longer than 8πh, while no converged results were obtained for different L_{z}. More importantly, our results with very long simulation time showed that a state transition would happen if L_{x}≥8πh, from a state with four pairs of roll cells to a state with three pairs of roll cells with L_{z}=6πh. Each state could survive for more than 1500h/U_{w}, and the flow statistics were different. 
Monday, November 19, 2018 11:14AM  11:27AM 
G38.00004: Surface wave effects on energy transfer process in an openchannel turbulent flow Lihao Wang, Weixi Huang, Chunxiao Xu, Lian Shen The coupled direct numerical simulation and highorder spectral method are performed to study the influence of surface waves on the overlying turbulent flow. The initial wave field is prescribed by the JONSWAP spectrum. The effects of wave age and wave amplitude on the turbulent instantaneous field and statistics are examined. For a slow wave, the nearwall streaky structure is disrupted by surface waves, and the flow is modulated by harmonics as the wave amplitude increases. For a fast wave, the flow pattern in the buffer region is recovered to that of the plate turbulence. Through the spectral analysis on the budget terms of the transport equation of the twopoint velocity correlation, the turbulent energy transfer process among different positions and different scales in the presence of surface waves is disclosed. 
Monday, November 19, 2018 11:27AM  11:40AM 
G38.00005: Numerical investigation of skin friction drag due to marine biofouling by barnacle aggregations Sotirios Sarakinos, Angela Busse Skinfriction drag is the dominant component of drag for most seafaring vessels. With the accumulation of marine organisms on ship hulls, skinfriction drag increases dramatically, increasing fuel consumption and associated emissions such as CO_{2}, NO_{x} and SO_{x}. Barnacles are one of the most common type of marine organisms found on fouled ship hulls, and they are also considered one of the most difficult to deal with. In this work, the fluid dynamic properties of surfaces partially populated with representative barnacle colonies are investigated using direct numerical simulations at a range of friction Reynolds numbers. With this method integral quantities such as the Hama roughness function ΔU^{+} and the equivalent sand grain roughness k_{s} can be evaluated, while turbulence statistics sampled between and directly above the barnacles can provide insight about the effects this type of marine biofouling induces into the nearwall flow. 
Monday, November 19, 2018 11:40AM  11:53AM 
G38.00006: DNS investigation on anisotropy and inhomogeneity of Reynolds stress in rhombic ducts Naoya Fukushima In noncircular ducts, such as rhombic ducts, anisotropy and inhomogeneity of Reynolds stress induce secondary flow of the second kind. In the present study, Direct Numerical Simulation of turbulent flow in rhombic ducts have been carried out to investigate effects of the corner angle on anisotropy and inhomogeneity of the Reynolds stress. Near diagonal lines not only from acute corner, but also from obtuse corner, turbulent kinetic energy is suppressed. In order to clarify the suppression mechanisms of turbulent kinetic energy, the budgets of Reynoldsstress transport are evaluated. Suppression of turbulent kinetic energy near the diagonal line from the acute corners is attributed to small production term due to low mean velocity gradient. On the other hand, mean velocity gradient near the diagonal line from the obtuse corner is as high as that away from the corners. However, the production term is small near the obtuse corner bisector. The main reason is that redistribution to the turbulent energy component in the diagonal direction is strongly suppressed. It is found that redistribution to turbulent energy components in the cross section from that in the streamwise direction is suppressed near acute and obtuse bisectors. 
Monday, November 19, 2018 11:53AM  12:06PM 
G38.00007: Direct Numerical Simulation of Rotating Turbulent Pipe Flows at Moderate Reynolds Numbers Jefferson Davis, Sparsh Ganju, Sean C.C. Bailey, Christoph Brehm Rotating turbulent flows are important not only due to the complex flow physics that occur, but also due to their relevance to many engineering applications, such as combustion, cyclone separation, mixing, etc. In these flows, rotation strongly affects the characteristics and structure of turbulence. However, the underlying complex flow phenomena are currently not well understood. Axially rotating pipe flow is a wellsuited prototypical case for studying rotation effects in turbulence due to its geometric simplicity and because it can be reproduced experimentally in a controlled environment. By examining turbulent statistics the physical mechanisms for turbulence suppression and possibly even relaminarization are investigated. Direct numerical simulations are conducted at moderate Reynolds numbers (Re_{D}=5300, 11700, and 19000) at rotation numbers of N = 0, 1, and 3. Turbulent kinetic energy budgets and Reynolds stresses are computed for these flows to quantify the effects of rotation on the turbulent flow. It is found that rotation causes an increase in dissipation near the wall and an increase in turbulent production near the center of the pipe flow, while some dependence on the rotation number is noted. 
Monday, November 19, 2018 12:06PM  12:19PM 
G38.00008: Turbulent channel flow at Reτ=10000. Sergio Hoyas, Martin Oberlack, Stefanie Kraheberger, Francisco AlcantaraAvila A new simulation of a turbulent channel flow was conducted up to the limit of Re_\tau=10.000. The domain size is 2π×2h×π. This domain is thought to be large enough to accurately compute the one point statistics of the flow. The simulation is carried out on 2048 SuperMUC phase II cores, at a mesh of (6144, 2101, 6144)≈8×10e10 grid points. A database with approximately 75 TB has already been created, which will be analyzed further at a later stage. As it was expected, a long logarithmic layer exists with κ\approx 0.40 and extending from y+≈70 to y+≈2000. The first maximum of the indicator function is not growing anymore and remains constant. A first analysis of the intensities shows that the near wall peaks of u′, w' and p' are still growing with Reynolds number. The possible secondary maximum of u′ is barely present. New scaling laws of U and u' based on symmetry theory will be also shown.

Monday, November 19, 2018 12:19PM  12:32PM 
G38.00009: Reynolds number dependence of doubleaveraged stresses in a roughwalled turbulent channel flow Angela Busse, Thomas Jelly Direct numerical simulations (DNS) of incompressible turbulent channel flow with irregular, threedimensional rough walls have been performed at four friction Reynolds numbers, namely, Re=(180,240,360,540). An identical roughness topography was used for each simulation which was synthesised to have a nearGaussian height distribution, an isotropic exponential autocorrelation function and a fixed mean peaktovalley height. The principal interest here is to investigate the statistical response of the nearwall flow to systematic increases in the friction Reynolds number. We compare the relative magnitude of “forminduced” dispersive stresses and Reynolds stresses and show that the former tends to dominate the nearwall region as the friction Reynolds number is increased. On the other hand, the dispersive stresses become negligible in the outer flow and the turbulent stresses satisfy Townsend’s outerlayer similarity hypothesis in this region. In addition, we assess the validity of Boussinesq’s hypothesis by quantifying the alignment between the Reynolds stress and mean strain tensors using Schmitt’s Indicator Function (Schmitt, Comptes Rendus Mécanique 2007; 335:617–627). The alignment (or lack thereof) between the dispersive stress and mean strain tensors will also be discussed. 
Monday, November 19, 2018 12:32PM  12:45PM 
G38.00010: Direct numerical simulations of finitethickness cross sections of jets Chandru Dhandapani, Guillaume Blanquart Direct numerical simulations (DNS) of turbulence have been performed extensively using homogeneous isotropic turbulence in a triply periodic cubic domain. However, turbulent flows in practical applications involve shear flows like turbulent round jets, simulating which would be computationally expensive. Instead, a new framework for simulating turbulent jets is proposed, wherein a portion of the jet is emulated with a "disk" of finite thickness, that is periodic in the axial direction. The analysis uses the selfsimilarity of turbulence in jets, and implements corresponding normalizations for velocity components and spatial coordinates. Both nonreacting and reacting flows are considered, and the velocity fluctuations are calculated and compared with that of experimental turbulent jets. The turbulent kinetic energy budget is computed and compared with the budget from other simulations and experiments. For the reacting case, the flame structure is observed and the flame surface area and turbulent flame speed are calculated and compared with results from previous large eddy simulations and experimental results of turbulent reacting jets. 
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