Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session E20: Boundary Layers IV: Flow through Pipes |
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Chair: Stephen B. Pope, Cornell University Room: 315 |
Sunday, November 24, 2013 4:45PM - 4:58PM |
E20.00001: Large-eddy simulation of turbulent pipe flow at large Reynolds number Namiko Saito, Dale Pullin, Hugh Blackburn We describe large-eddy simulations (LES), using a spectral-element method, of turbulent smooth- and rough-wall pipe flows. The spectral-element code SEMTEX was used (Blackburn and Sherwin {\it J. Comput. Phys.} 2004) in a mode where the axial direction is treated using Fourier modes, with a spectral-element representation within the cross-flow plane with Dirichlet boundary conditions on the circular pipe boundary. The stretched-vortex subgrid-stress model is utilized together with the wall-model of Chung and Pullin ({\it JFM, 2009}). For rough-wall flows, local subgrid roughness is incorporated by the addition of an empirical roughness function $u_\tau\,\Delta^+(k_s^+)$, where $k_s^+ = k_s\,u_\tau/\nu$ and $k_s$ is the equivalent sand roughness. This is used in both the inner-scaling ansatz for the unsteady term of the wall-normal integration of the stream-wise momentum equation, and also in the log-like profile used to give a boundary condition for the outer-flow LES. Results will be discussed that include variation of the skin-friction coefficient as a function of both Reynolds number and the ratio of $k_s$ to the pipe radius, and also mean velocity profiles and some turbulence statistics. [Preview Abstract] |
Sunday, November 24, 2013 4:58PM - 5:11PM |
E20.00002: Deconstructing the effectiveness of opposition control in turbulent pipe flow Mitul Luhar, Ati S. Sharma, Beverley J. McKeon We develop a simple model for opposition control based on the resolvent analysis of McKeon {\&} Sharma (2010, \textit{J Fluid Mech}). This model decomposes the velocity field for turbulent pipe flow into a series of highly-amplified response modes, identified via a gain analysis of the Fourier-transformed Navier-Stokes equations. Changing the boundary conditions to reflect control alters the structure and amplification of these velocity responses, such that a reduction in gain signifies a reduction in drag. With basic assumptions, this rank-1 model reproduces trends seen in previous DNS and LES. Further, a wavenumber-frequency breakdown helps explain the deterioration of opposition control performance with increasing sensor elevation and Reynolds number. We show that opposition control only suppresses attached modes localized near the wall; detached modes, which are more energetic at higher Reynolds number and active far from the wall, are further amplified. Such detached modes require a phase lag between sensor and actuator velocity for suppression. Thus, the efficacy of traditional opposition control is determined by a tradeoff between modes sensed, but it may be possible to prescribe an optimal scheme tailored to individual mode behavior. [Preview Abstract] |
Sunday, November 24, 2013 5:11PM - 5:24PM |
E20.00003: Mechanism for skin friction reduction in temporally accelerated turbulent pipe flow Jae Hwa Lee, Ronald J. Adrian Direct numerical simulations of temporally accelerating turbulent pipe flow are performed to examine the modification of the coherent structures due to acceleration and its relationship to the reduction of turbulent skin friction. Two types of simulations are performed: a) fully developed turbulent flow subjected to constant mean acceleration, and b) evolution of a single hairpin eddy subjected to the same acceleration. The initial eddies are extracted by conditional averaged flow fields associated with second-quadrant Reynolds shear stress events from DNS data of the fully developed turbulent pipe flow at the initial Reynolds number. In the case of fully turbulent initial flow, the temporal acceleration increases the Reynolds number from \textit{Re}$_{D}=$5,300 to 26,500, and the response of the turbulence is found to be delayed relative to the response of the mean flow, as also reported by previous studies. The delay causes the ratio of velocity induced by the hairpin to the mean velocity to decrease below the threshold value for nonlinear formation of new hairpin vortices from the initial hairpin. The autogeneration of new hairpin vortices is suppressed, resulting in reduction of turbulent transport and, consequently, reduction of skin friction. [Preview Abstract] |
Sunday, November 24, 2013 5:24PM - 5:37PM |
E20.00004: Distinct organisational states of large-scale motions in turbulent pipe flow Francesca M. Sogaro, David J.C. Dennis An experimental investigation focussing on the structural organisation of large scale motions (LSMs) in fully developed turbulent pipe flow has been conducted in the Very Large Scale Pipe Flow (VLSPF) facility at the University of Liverpool. Measurements using high-speed stereoscopic particle image velocimetry in the radial-azimuthal plane at a Reynolds number of 35000 (based on bulk velocity and pipe diameter) have been analysed, paying particular attention to the two-point spatial correlation of the streamwise velocity fluctuations. A method has been developed to select similar individual instances (in time) of the planar correlation to identify the presence of a set of distinct organisational states. The application of the selective correlation method demonstrates how the pairs of positive-negative correlation directly correspond to the presence of persistent positive and negative streamwise velocity fluctuations in the instantaneous velocity fields, often referred to as LSMs. The duration that the selective spatial correlation indicates the flow is in a certain state can be related to the length of the large scale motions in the flow and provides a method of identifying and quantifying the characteristics of LSMs in turbulent pipe flow. [Preview Abstract] |
Sunday, November 24, 2013 5:37PM - 5:50PM |
E20.00005: Statistics and large scales in turbulent pipe and channel flows Jin Lee, Jae Hwa Lee, Hyung Jin Sung Turbulent pipe and channel flows have been generally accepted as having a similar turbulent flow structure. However, turbulence statistics in the core region of pipe flow are different from that of channel flow owing to the difference in the averaged spanwise dimension of the low-speed structures. In particular, wall-normal and spanwise stresses of channel flow are smaller than those of pipe flow. In the present study, DNS dataset of turbulent channel and pipe flows with the friction Reynolds number Re$=$934 have been compared to elucidate the difference of statistics in terms of the populations of large and very-large scales in the low-speed region. To this end, large and very-large scales were extracted by a low-pass filtered streak detection algorithm. We found that the population density of large scales of pipe flow is more increased in the core region than that of channel flow. Although the density of very-large scales of pipe flow decreases, the area of low-speed region increases due to the large number of large scales. Further comparison of pipe and channel flows showed that the higher turbulence intensity of pipe flow is caused by the interference of large scales with the azimuthal distance. [Preview Abstract] |
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