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 D21: Turbulence: Simulations II - DNS and LES I |
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Chair: Krishnan Mahesh, University of Minnesota Room: 316 |
Sunday, November 24, 2013 2:15PM - 2:28PM |
D21.00001: Towards Feature-Resolved Simulations of Superhydrophobic Surfaces Yixuan Li, Karim Alame, Krishnan Mahesh Superhydrophobic surfaces have potential for viscous friction reduction, anti-corrosive protective coatings and self-cleaning techniques. Most previous studies focused on large scale grooves or pillars in the laminar regime. In this study, two fully covered microtextured superhydrophobic surfaces and two unit microtextured surfaces with different geometries (grooves and posts) are tested in both laminar and turbulent flows using DNS. Slip length and discharge are computed in the laminar regime and compared with theoretical estimate and experiment. The turbulent simulations are performed for both ``unit cells'' as well as the entire textured surfaces. Fully wetted simulations reveal the effect that geometry alone exerts. A volume of fluid methodology is being developed towards allowing for air/water interfaces inside the grooves, and will be discussed. [Preview Abstract] |
Sunday, November 24, 2013 2:28PM - 2:41PM |
D21.00002: Direct numerical simulation from laminar to fully-developed turbulence in spatially evolving pipe flow and flat plate boundary layer Xiaohua Wu, Parviz Moin, Ronald J. Adrian, Jon R. Baltzer, Jean-Pierre Hickey Direct numerical simulations of spatially evolving pipe flow and boundary layer have been performed. The pipe is 250R long, the flow Reynolds number is 6000 and 8000, and the calculation used up to 1.7 billion grid points. Pipe inlet disturbance is from a very-thin wire ring placed at different radial locations. It is found that energy norm in the flow downstream of such disturbance can grow exponentially with axial distance. The boundary layer's momentum thickness Reynolds number develops from 80 to 3000 with a free-stream turbulence intensity decaying from 3 percent to 0.8 percent. Its mesh has 4 billion grid points. Good quantitative agreement with experimental data is obtained. In both the pipe flow and the boundary layer, under these inlet disturbances, Lambda vortex, hairpin packet, infant turbulent spot, mature turbulent spot, and hairpin forest occur naturally and sequentially. Passive scalar was also introduced in the simulation in a manner analogous to the color band experiment of Osborne Reynolds. [Preview Abstract] |
Sunday, November 24, 2013 2:41PM - 2:54PM |
D21.00003: Application of the High Gradient hydrodynamics code to simulations of a two-dimensional zero-pressure-gradient turbulent boundary layer over a flat plate Bryan E. Kaiser, Svetlana V. Poroseva, Jesse M. Canfield, Jeremy A. Sauer, Rodman R. Linn The High Gradient hydrodynamics (HIGRAD) code is an atmospheric computational fluid dynamics code created by Los Alamos National Laboratory to accurately represent flows characterized by sharp gradients in velocity, concentration, and temperature. HIGRAD uses a fully compressible finite-volume formulation for explicit Large Eddy Simulation (LES) and features an advection scheme that is second-order accurate in time and space. In the current study, boundary conditions implemented in HIGRAD are varied to find those that better reproduce the reduced physics of a flat plate boundary layer to compare with complex physics of the atmospheric boundary layer. Numerical predictions are compared with available DNS, experimental, and LES data obtained by other researchers. High-order turbulence statistics are collected. The Reynolds number based on the free-stream velocity and the momentum thickness is 120 at the inflow and the Mach number for the flow is 0.2. Results are compared at Reynolds numbers of 670 and 1410. [Preview Abstract] |
Sunday, November 24, 2013 2:54PM - 3:07PM |
D21.00004: Estimating the Effective Reynolds Number in Implicit Large Eddy Simulation Fernando Grinstein, Ye Zhou, Adam Wachtor, Brian Haines In implicit large-eddy simulation (ILES) energy-containing large scales are resolved, and physics capturing numerics are used to spatially filter-out unresolved scales and implicitly model subgrid scale effects. From an applied perspective, it is highly desirable to estimate a characteristic Reynolds number (Re) -- and therefore a relevant effective viscosity, so that the impact of resolution on predicted flow quantities and their macroscopic convergence can be usefully characterized. We argue in favor of obtaining robust Re estimates away from the smallest scales of the simulated flow -- where numerically controlled dissipation takes place, and propose theoretical basis and framework to determine such measures. ILES examples include forced turbulence as a steady flow case, the Taylor-Green vortex to address transition and decaying turbulence, and simulations of a laser-driven reshock experiment illustrating a fairly complex turbulence problem of current practical interest. [Preview Abstract] |
Sunday, November 24, 2013 3:07PM - 3:20PM |
D21.00005: Large-Eddy Simulation of Propeller Crashback Praveen Kumar, Krishnan Mahesh Crashback is an operating condition to quickly stop a propelled vehicle, where the propeller is rotated in the reverse direction to yield negative thrust. The crashback condition is dominated by the interaction of free stream flow with strong reverse flow. Crashback causes highly unsteady loads and flow separation on blade surface. This study uses Large-Eddy Simulation to predict the highly unsteady flow field in propeller crashback. Results are shown for a stand-alone open propeller, hull-attached open propeller and a ducted propeller. The simulations are compared to experiment, and used to discuss the essential physics behind the unsteady loads. [Preview Abstract] |
Sunday, November 24, 2013 3:20PM - 3:33PM |
D21.00006: Large Eddy Simulation of Entropy Generation in a Turbulent Mixing Layer Reza H. Sheikhi, Mehdi Safari, Fatemeh Hadi Entropy transport equation is considered in large eddy simulation (LES) of turbulent flows. The irreversible entropy generation in this equation provides a more general description of subgrid scale (SGS) dissipation due to heat conduction, mass diffusion and viscosity effects. A new methodology is developed, termed the entropy filtered density function (En-FDF), to account for all individual entropy generation effects in turbulent flows. The En-FDF represents the joint probability density function of entropy, frequency, velocity and scalar fields within the SGS. An exact transport equation is developed for the En-FDF, which is modeled by a system of stochastic differential equations, incorporating the second law of thermodynamics. The modeled En-FDF transport equation is solved by a Lagrangian Monte Carlo method. The methodology is employed to simulate a turbulent mixing layer involving transport of passive scalars and entropy. Various modes of entropy generation are obtained from the En-FDF and analyzed. Predictions are assessed against data generated by direct numerical simulation (DNS). The En-FDF predictions are in good agreements with the DNS data. [Preview Abstract] |
Sunday, November 24, 2013 3:33PM - 3:46PM |
D21.00007: Large-eddy simulations of a fully appended submarine model Antonio Posa, Elias Balaras In the present study we report large-eddy simulations (LES) the flow around an idealized submarine geometry (DARPA SUBOFF) at a Reynolds number -based on the model length and free stream velocity- equal to 1.2 million. A finite-difference formulation on a cylindrical coordinate grid of 2.8 billion nodes is utilized, and boundary conditions on the submarine model are imposed using an immersed-boundary technique. The boundary layers are ``tripped'' near the leading edge to mimic the conditions in experiments reported in the literature. Our computations resolve the detailed dynamics of the turbulent boundary layers on the suboff body as well as their interaction with the large scale vortices generated at the sail and fin junctions. The time-averaged velocity profiles in the intermediate wake reach self-similarity, except for the region affected by the wake of the sail. The comparison with the exponential law from the experimental study in the literature is satisfactory. It is also confirmed that the flow coming from the fins causes a deviation from the self-similar profile, which is more evident than in the experiments. Details on the turbulent boundary layer on the surface of the body will be provided, showing a good qualitative agreement with the results in the literature. [Preview Abstract] |
Sunday, November 24, 2013 3:46PM - 3:59PM |
D21.00008: Direct numerical simulations of curvature effects on shear layer transition over airfoils Wei Zhang, Wan Cheng, Adnan Qamar, Wei Gao, Ravi Samtaney Shear layer transition and subsequent turbulent flow development over the leeward section of airfoils are affected by the surface curvature in terms of its associated effects, such as laminar flow separation, adverse pressure gradient, and the interactions between separated flow and wake vortices, etc. We present direct numerical simulations (DNS) of shear layer transitions over two airfoils, NACA 4412 and NACA 0012-64, at 10 deg. angle of attack, and \textit{Re}$_{c}=$10$^{4}$ based on uniform inflow velocity and chord length. The two airfoils chosen are geometrically almost the same with identical maximum thickness along with chordwise position but different cambers and hence different curvature. The curvature effects on the flow are presented by the unsteady evolution patterns of laminar flow separation; shear layer detachment, breakdown to turbulence, turbulent boundary layer reattachment and vortex shedding, and quantitative results on the development of turbulent boundary layer are emphasized. This DNS database is generated with an energy conservative fourth-order incompressible Navier-Stokes code with $O$(10$^{9})$ mesh points. [Preview Abstract] |
Sunday, November 24, 2013 3:59PM - 4:12PM |
D21.00009: Direct Numerical Simulation of a Transient Cumulus Flow Prasanth Prabhakaran, Suresh Deshpande, Roddam Narasimha Clouds play a major role in climate change, and the ability to simulate moist convection patterns is crictical for prediction of tropical weather and climate. Recent laboratory experiments (Narasimha et al. (2011) PNAS 108.39 (2011): 16164-16169) have successfully reproduced a variety of naturally occuring cloud types and shapes, and throw light on the mechanisms responsible for entrainment and detrainment in cloud flows. Based on this work it was proposed that a 'transient diabatic plume' subjected to off-source diabatic heating is an appropriate model for cumulus flow. In the present work we report the first direct numerical simulation of such a transient diabatic plume, by solving the 3D Navier-Stokes-Boussinesq equations. Visualisation of the cloud flow is carried out using a coarse grid of around 4 million grid points. The final simulation was performed using 128 million grid points at a Reynolds number of 2000. We present the evolution of different flow variables for the transient flow and compare it with a stationary state non-diabatic plume. In particluar, we present results on the dramatic effect of off-source heat addition on the vortical structures in the flow field and on the entraining velocity field. [Preview Abstract] |
Sunday, November 24, 2013 4:12PM - 4:25PM |
D21.00010: Reynolds number effects on drag reduction of turbulent boundary layers subject to wall oscillation Maneesh Mishra, Martin Skote Drag reduction (DR) of external flows were studied using direct numerical simulations of spatially growing turbulent boundary layers with temporal wall oscillations. Three simulations with similar oscillation parameters were performed at different streamwise positions to explore the effects of Reynolds number ($Re$) on DR. One of the simulation cases replicates an experiment and results are in excellent agreement for both mean quantities and turbulence statistics. Downstream development of skin friction, velocity profiles and turbulence statistics have been studied. Spatial transients for the peak values of turbulence statistics have been found to show a non-monotonic behaviour before reaching a stable steady value. To check the feasibility of DR at high $Re$, a predictive relation has been modelled based on current and previous experimental and simulation data. In light of these results, feasibility of this technique for real world applications is discussed. [Preview Abstract] |
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