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 M32: DNS, LES and Hybrid RANS Applications |
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Chair: Reetesh Ranjan, Georgia Institute of Technology Room: Georgia World Congress Center B404 |
Tuesday, November 20, 2018 8:00AM - 8:13AM |
M32.00001: Direct numerical simulation of a separated turbulent boundary layer over a bump Riccardo Balin, Eric L Peters, John A Evans, Philippe R Spalart, Kenneth E Jansen The separated turbulent boundary layer over a Gaussian bump is computed by direct numerical simulation (DNS) of the incompressible Navier-Stokes equations. The smooth, two-dimensional bump causes a rapid succession of strong favorable-to-adverse pressure gradients, resulting in a separation bubble on the downstream side. At the start of the bump, the Reynolds number based on the momentum thickness is 3,200, and the boundary layer thickness is of the order of the bump height. Results from preliminary DNS simulations are discussed, assessing the effects of the inflow, outflow and far-field boundary conditions. Future data from this study will be used for the purposes of data driven turbulence modeling. |
Tuesday, November 20, 2018 8:13AM - 8:26AM |
M32.00002: Direct Numerical Simulation of Additively and Conventionally Manufactured Internal Turbine Cooling Passages David R Hanson, Stephen T McClain, Robert F Kunz, Michael Kinzel, Edward W Reutzel, Karen Anne Thole, Leslie Wright Metal additive manufacturing technology based on Powder Bed Fusion (PBF) is revolutionizing engineering practice and system performance in many venues including gas turbine systems. In order for the community to fully harness the opportunity that PBF offers in this context, we need to mature flow/thermal design tools to accommodate the very complex “roughness field” that invariably characterizes these engineered flow passages. Our team is executing a combined CFD+EFD program that includes Direct Numerical Simulation (DNS) of the turbulent flow in these passages to calibrate reduced order Reynolds Averaged Navier-Stokes (RANS) CFD based on Distributed Element Roughness Modeling (DERM). Here we will present our DNS results for PBF manufactured rectangular channels. These geometries have been obtained and meshed for DNS directly from CT scan and Optical Profilometry observations. Also they have been/are being tested at engine scale and large scale for flow and heat transfer performance. We compare the PBF channel DNS results with these measurements, and with smooth channel DNS and measurements. |
Tuesday, November 20, 2018 8:26AM - 8:39AM |
M32.00003: Direct Numerical Simulation of Electrorheological Fluids Shriram Pillapakkam, Suchandra Das, Ian S Fischer, Pushpendra Singh An electrorheological (ER) fluid is mixture of dielectric particles suspended in a dielectric fluid. When subjected to an electric field, the particles of ER fluids become polarized and interact with each other to form chains and columns. We analyze the behavior of suspended dielectric particles subject to an electric field using direct numerical simulations. Our simulation results show that the particle chains attract each other only when they are staggered in the field direction and the distance between the chains is less than 2.48 times the particle radius. Otherwise, they repel. This causes overall structure to fragment into chains and columns. To diminish this fragmentation of particle distribution in an electric field, we consider ER fluids consisting of particle mixtures. The numerical simulations are corroborated with experimental data. |
Tuesday, November 20, 2018 8:39AM - 8:52AM |
M32.00004: Analysis of the Wake Features of a Submarine Propeller via Large-Eddy Simulation Antonio Posa, Riccardo Broglia, Mario Felli, Massimo Falchi, Elias Balaras Large-Eddy Simulation, with an Immersed-Boundary method, is adopted to analyze the wake of a notional submarine propeller, using a cylindrical grid composed of about 840 million nodes. The accuracy of the overall approach is validated by comparisons with available measurements. Three different load conditions are investigated, allowing an assessment of the sensitivity to the rotational speed. Results demonstrate that tip and hub vortices are the main coherent structures. However, several additional vortices are produced across the span of the propeller blades. The evolution of turbulent kinetic energy in the propeller wake is substantially affected by coherent structures. The highest values occur at the axis and at outer radii, due to the hub and the tip vortices, respectively. In addition, downstream evolution of turbulence associated to the tip vortices is not monotonic. In contrast, fluctuations at the wake axis, originating mainly from instability of the hub vortex, keep decreasing starting from the near wake. |
Tuesday, November 20, 2018 8:52AM - 9:05AM |
M32.00005: DDES Investigation of Aerodynamic Flow Control Efficiency over A Vertical Tail/Rudder Assembly Jun Fang, Riccardo Balin, Michel Rasquin, Ramesh Balakrishnana, Kenneth E Jansen The simulations presented here are aimed at matching the experimental conditions where a 1/9th scale vertical tail/rudder assembly was tested at Reynolds number of 0.7 M. The numerical simulations adopt a delayed detached eddy simulation (DDES) turbulence model, which is particularly well suited for this application where flow separation occurs near the junction between the stabilizer and the rudder. Specifically, the DDES model applies the RANS model on the stabilizer where the flow is fully attached. Meanwhile, the LES model is automatically triggered in the plume of jets and above most of the rudder, downstream of the hinge line where flow separation occurs due to the rudder deflection. With the access to state-of-the-art HPC, the intended study will provide the much-needed insight to understand and exploit the underlying physical mechanisms related to active flow control. |
Tuesday, November 20, 2018 9:05AM - 9:18AM |
M32.00006: Large-Eddy Simulation of Propeller Flows Using an Unstructured Overset Grid Method Thomas Kroll, Wyatt Horne, Krishnan Mahesh We discuss the application of a novel unstructured overset grid methodology to compute the flow around a marine propeller. The numerical algorithm is based on that developed by Mahesh et al. [J. Compt. Phys (2004) 197:215-240], and addresses two significant challenges posed by the overset methodology - discrete conservation and scaling. The simulations consider both forward and crashback modes of operation. The results are compared to available experimental data and previous LES studies. Details of the flow field are discussed. |
Tuesday, November 20, 2018 9:18AM - 9:31AM |
M32.00007: Large-eddy simulation study of charged inertial particles in high Reynolds number turbulent channel flow Mustafa Rahman, Wan Cheng, Ravi Samtaney We present results from large-eddy simulations (LES) of turbulent channel flow at high Reynolds number of order O($10^9$) with suspended charged particles. The overarching goal of this work is to develop an LES framework for the simulations of sandstorms as charged particle-laden flow. The present investigation relies on simulating multi-physical two-phase (fluid and charged particles) turbulent flows in which the fluid flow is governed by the Navier-Stokes equationsin a LES setting employing the stretched spiral vortex subgrid-scale model and a virtual wall model, while sand particles are modeled using an Eulerian approach via a simplified version of the Direct Quadrature Method of Moments. The electrostatic approximation is used to model the interaction of charged solid particles. Preliminary results show fluctuations of the electrical field in the flow in reasonable agreement with some field observations in sandstorms. The effects of different sand particle distributions, and turbulent intensities on the root-mean-square of the generated electric fields will be examined. |
Tuesday, November 20, 2018 9:31AM - 9:44AM |
M32.00008: Large-Eddy Simulation of Turbulent Flow in a Channel with Streamwise Periodic Constrictions Wei Gao, Ravi Samtaney We present results from wall-resolved and wall-modeled large-eddy simulations of turbulent flows in a channel with streamwise periodic constrictions on the bottom. Two cases: (1) $Re_h=10600$, ERCOFTAC test case 81 and (2) $Re_h=33000$, periodic hill experiment reported by Kahler et al. (J. of Fluid Mech., 2016) are utilized to validate our wall-resolved and wall-modeled LES results. The stretched spiral vortex sub-grid scale (SGS) model is used to compute the SGS term, and the ``virtual'' wall model, originally developed by Chung & Pullin (J. of Fluid Mech., 2009), is extended to generalized curvilinear coordinates. The wall model dynamically couples the SGS stress from the outer region and offers boundary conditions at a raised ``virtual'' wall for the LES region. The numerical results show that the wall model is able to accurately predict mean flow characteristics, including the location of the separation bubbles. Moreover, the skin friction and near-wall streamlines are presented to quantify the separation and reattachment in the near-wall region. The anisotropy of the Reynolds stress tensor are also evaluated, potentially providing some guidance to the RANS modeling community. |
Tuesday, November 20, 2018 9:44AM - 9:57AM |
M32.00009: Investigation of subfilter models and scalar-scalar covariances for supercritical mixing Umesh Unnikrishnan, Xingjian Wang, Joseph Charles Oefelein, Vigor Yang The applicability of the conventional large eddy simulation (LES) simplifications and subfilter models for simulation of supercritical mixing and combustion has been uncertain and questioned in recent studies. The majority of modeling efforts are typically focused on the unclosed velocity-velocity and velocity-scalar covariance terms in the conservation equations for momentum and energy. There has been a lack of studies examining the relevance of other subfilter terms, for example, in the equation of state. This is especially important in the context of turbulent flows at supercritical conditions, where thermodynamic nonidealities play a dominant role. In this work, a three-dimensional direct numerical simulation of a binary species, supercritical spatial mixing layer at high Reynolds number is performed. The database is used to perform a priori analyses of the underlying LES assumptions and the subfilter models used for the unclosed velocity-velocity and velocity-scalar covariance terms. We then investigate the relevance of subfilter scalar-scalar covariance terms associated with the filtered equation of state and internal energy and an approximate deconvolution model is developed to accurately model these terms. |
Tuesday, November 20, 2018 9:57AM - 10:10AM |
M32.00010: LES of practical aeronautical flows at stall conditions George Ilhwan Park, Oriol Lehmkuhl, Sanjeeb Bose, Parviz Moin The present study aims to examine the performance wall-modeled LES in flows over realistic aircraft geometry using the state-of-the-art methodologies for low-dissipation LES and standard equilibrium wall model, particularly for prediction of massive flow separation encountered at high angles of attack. Simulations of two aircraft geometries at high angles of attack are considered: a high lift JAXA standard model (Rec = 1.93M; AIAA Papers 2010-0684, 2008-0350 by Yokokawa et al.) and the NASA Common Research model (Rec = 11M; Boyet, CEAS Aero. J., 2018). Wall-modeled LES calculations are conducted using equilibrium wall models and the static-coefficient subgrid-scale eddy-viscosity model of Vreman. Predictions of global forces and surface pressure distributions by two low-dissipation LES codes are shown to be in reasonable agreement with experimental measurements. All calculations presented were performed in less than 120 hours using < 3K Intel CPU cores, demonstrating that wall modeled LES for external aerodynamics is becoming increasingly affordable. |
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