Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session L35: Turbulence: LES Simulations |
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Chair: Onkar Sahni, MANE, RPI Room: Oregon Ballroom 204 |
Monday, November 21, 2016 4:30PM - 4:43PM |
L35.00001: Effect of stationary and dynamic transverse squared bars over the turbulent behavior in a channel flow Jesus Ramirez Pastran, Carlos Duque-Daza, Omar D Lopez Turbulent flows over rough surfaces are present in different industrial scenarios. Generally, roughness is used to modify the boundary layer behavior, in order to improve heat transfer rates and mixing processes, which is usually accompanied by an increase of skin-friction drag. In the present work two different techniques for modification of the turbulent boundary layer were explored: first, the use of an arrangement of transverse squared bars (synthetic roughness); second, the use of an oscillating movement of the squared bars. In both cases the goal was to assess the increase or decrease of the skin-friction drag and the changes in the turbulent behavior of the flow. Large Eddy Simulations were carried out in order to study a fully developed turbulent channel flow with a smooth upper wall and a synthetically roughed lower wall with a friction Reynolds number around 180. Channel flow over walls with stationary bars and with one of the bars oscillating in the spanwise direction were also considered. Consistency between skin-friction coefficient modification and evolution of Q-structures was observed. Finally, a comparison of changes on some of the TKE terms between smooth surfaces and synthetically rough surfaces allowed to identify the effect of the squared bars for each case. [Preview Abstract] |
Monday, November 21, 2016 4:43PM - 4:56PM |
L35.00002: Wall-pressure fluctuations beneath a spatially evolving turbulent boundary layer Krishnan Mahesh, Praveen Kumar Wall-pressure fluctuations beneath a turbulent boundary layer are important in applications dealing with structural deformation and acoustics. Simulations are performed for flat plate and axisymmetric, spatially evolving zero-pressure-gradient turbulent boundary layers at inflow Reynolds number of 1400 and 2200 based on momentum thickness. The simulations generate their own inflow using the recycle-rescale method (\textit{Lund et al., J. of Comput. Phys., 1998, 140 (2): 233-258}). The results for mean velocity and second-order statistics show excellent agreement with the data available in literature. The spectral characteristics of wall-pressure fluctuations and their relation to flow structure will be discussed. [Preview Abstract] |
Monday, November 21, 2016 4:56PM - 5:09PM |
L35.00003: Application of BCM-LES model to flow and pressure fields over urban roughness Tetsuro Tamura, Hidenori Kawai, Rahul Bale, Keiji Onishi, Makoto Tsubokura BCM (Building Cube Method) enables high-resolution CFD (Computational Fluid Dynamics) simulation by high parallelization performance. This study discusses the applicability of LES (Large Eddy Simulation) based on BCM to prediction of wind velocity and pressure around various building blocks in urban area. First, we validate the computed results of flows past 3D square cylinder in turbulent boundary layer. Fundamental accuracy of the surface pressure distribution on square cylinder is investigated by high-resolution BCM simulation with IBM (Immersed Boundary Method). Next, the BCM is applied to flow simulation of real urban area (Domain size: 25x12km). As a result of this simulation, the development process of urban boundary layer from coastal area to Tokyo central area is examined. Accordingly we show the present numerical model based on BCM-LES can represent sufficiently spatially fine structures and temporally unsteady fluctuations of turbulent flows with good accuracy. It is clarified that the complex pressure distributions acting on the buildings have been also reproduced from the sense of wind-resistance design of buildings in cities [Preview Abstract] |
Monday, November 21, 2016 5:09PM - 5:22PM |
L35.00004: The flow past a circular patch of vegetation with a low submergence depth and low solid volume fractions Gokhan Kirkil The effect of the Solid Volume Fraction (SVF) on the flow structure within and past a circular array of surface-mounted cylinders that extends over 75{\%} of the water depth, h is investigated using Detached Eddy Simulation (DES). This set up mimics the case of a submerged patch of rigid vegetation in a channel. The diameter of the cylinders in the array is d $=$ 0.02D, where D is the diameter of the circular array. The channel Reynolds number is close to 20,000 and the Reynolds number defined with D is around 24,000. DES is conducted for SVF $=$ 10{\%} and 25{\%}. It is found that as the SVF increases, fairly strong horseshoe vortex system forms around the upstream face of the vegetation patch, the strength of the separated shear layers on the sides of the vegetation patch increases and the length of the recirculation region behind the patch decreases. While an increase of the SVF results in a large increase of the turbulent kinetic energy in the wake, the opposite is observed within the porous vegetation patch. [Preview Abstract] |
Monday, November 21, 2016 5:22PM - 5:35PM |
L35.00005: Fluid-structure interaction of turbulent boundary layer over a compliant surface Sreevatsa Anantharamu, Krishnan Mahesh Turbulent flows induce unsteady loads on surfaces in contact with them, which affect material stresses, surface vibrations and far-field acoustics. We are developing a numerical methodology to study the coupled interaction of a turbulent boundary layer with the underlying surface. The surface is modeled as a linear elastic solid, while the fluid follows the spatially filtered incompressible Navier-Stokes equations. An incompressible Large Eddy Simulation finite volume flow approach based on the algorithm of Mahesh et al. (\textit{JCP 197.1 (2004): 215-240}) is used in the fluid domain. The discrete kinetic energy conserving property of the method ensures robustness at high Reynolds number. The linear elastic model in the solid domain is integrated in space using finite element method and in time using the Newmark time integration method. The fluid and solid domain solvers are coupled using both weak and strong coupling methods. Details of the algorithm, validation, and relevant results will be presented. [Preview Abstract] |
Monday, November 21, 2016 5:35PM - 5:48PM |
L35.00006: Large Eddy Simulation for Oscillating Airfoils with Large Pitching and Surging Motions Onkar Sahni, Reed Cumming, Steven Tran, Alexander Kocher Many applications of interest involve unsteady aerodynamics due to time varying flow conditions (e.g. in the case of flapping wings, rotorcrafts and wind turbines). In this study, we formulate and apply large eddy simulation (LES) to investigate flow over airfoils at a moderate mean angle of attack with large pitching and surging motions. Current LES methodology entails three features: i) a combined subgrid scale model in the context of stabilized finite element methods, ii) local variational Germano identity (VGI) along with Lagrangian averaging, and iii) arbitrary Lagrangian-Eulerian (ALE) description over deforming unstructured meshes. Several cases are considered with different types of motions including surge only, pitch only and a combination of the two. The flow structures from these cases are analyzed and the numerical results are compared to experimental data when available. [Preview Abstract] |
Monday, November 21, 2016 5:48PM - 6:01PM |
L35.00007: Large eddy simulation of tip-leakage flow in an axial flow fan Keuntae Park, Haecheon Choi, Seokho Choi, Yongcheol Sa, Oh-Kyoung Kwon An axial flow fan with a shroud generates a complicated tip-leakage flow by the interaction of the axial flow with the fan blades and shroud near the blade tips. In this study, large eddy simulation is performed for tip-leakage flow in a forward-swept axial flow fan inside an outdoor unit of an air-conditioner, operating at the design condition of the Reynolds number of 547,000 based on the radius of blade tip and the tip velocity. A dynamic global model (Lee \textit{et al.}, 2010, PoF) is used for a subgrid-scale model, and an immersed boundary method in a non-inertial reference frame (Kim \& Choi, 2006, JCP) is adopted. The present simulation clearly reveals the generation and evolution of tip-leakage vortex near the blade tip by the leakage flow. At the inception of the leakage vortex near the leading edge of the suction-side of the blade tip, the leakage vortex is composed of unsteady multiple vortices containing high-frequency fluctuations. As the leakage vortex develops downstream along a slant line toward the following blade, large and meandering movements of the leakage vortex are observed. Thus low-frequency broad peaks of velocity and pressure occur near the pressure surface. [Preview Abstract] |
Monday, November 21, 2016 6:01PM - 6:14PM |
L35.00008: Comparative Study of Reynolds Averaged and Embedded Large Eddy Simulations of a High Pressure Turbine Stage Sam Jones, Aleksandar Jemcov, Thomas Corke An Embedded Large Eddy Simulation (ELES) approach is used to simulate the flow path through a high pressure turbine stage that includes the entry duct, stationary inlet and exit guide vanes, and a rotor. The flowfield around the rotor is simulated using LES. A Reynolds Averaged Simulation (RAS) is used for the rest of the flow domain. The interface between RAS and LES domains uses the RAS turbulence quantities as a means of obtaining length scales that are used in computing the vorticity required to trigger a proper energy cascade within the LES part of the flow field. The objective is to resolve the unsteady vortical motions that eminate from the gap between the rotor tip and duct walls that are presumably under-resolved in a RAS approach. A comparative analysis between RAS and ELES approaches for this turbomachinery problem is then presented. [Preview Abstract] |
Monday, November 21, 2016 6:14PM - 6:27PM |
L35.00009: Large-eddy simulation of propeller wake at design operating conditions Praveen Kumar, Krishnan Mahesh Understanding the propeller wake is crucial for efficient design and optimized performance. The dynamics of the propeller wake are also central to physical phenomena such as cavitation and acoustics. Large-eddy simulation is used to study the evolution of the wake of a five-bladed marine propeller from near to far field at design operating condition. The computed mean loads and phase-averaged flow field show good agreement with experiments. The propeller wake consisting of tip and hub vortices undergoes streamtube contraction, which is followed by the onset of instabilities as evident from the oscillations of the tip vortices. Simulation results reveal a mutual induction mechanism of instability where instead of the tip vortices interacting among themselves, they interact with the smaller vortices generated by the roll-up of the blade trailing edge wake in the near wake. Phase-averaged and ensemble-averaged flow fields are analyzed to explain the flow physics. [Preview Abstract] |
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