Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session HP: Turbulence Simulations: LES II |
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Chair: Sanjiva Lele, Stanford University Room: Hilton Chicago Stevens 1 |
Monday, November 21, 2005 1:20PM - 1:33PM |
HP.00001: LES of Propeller Crashback Martin Vysohlid, Krishnan Mahesh Crashback is an operation where the direction of rotation of a propeller is suddenly reversed. Crashback is characterized by massive flow separation and unsteady propeller loads. LES of the flow around a marine propeller is performed. The simulations are performed in a rotating frame of reference on unstructured grids using the algorithm developed by Mahesh at al. (2004, J. Comput. Phys. 197). Good agreement is obtained with experiment for the thrust and torque coefficients. The flow-field shows the presence of an unsteady ring vortex. A model problem is studied, where the propeller is approximated by a disk with prescribed axial and swirl velocity. The model problem results show ring vortex and thrust fluctuation similar to the real propeller. The results of the model problem will be used to explain the fluctuating loads observed during crashback. [Preview Abstract] |
Monday, November 21, 2005 1:33PM - 1:46PM |
HP.00002: A comparative quadrant analysis of canopy turbulence based on LES and field-PIV data Wusi Yue, Weihong Zhu, Rene von Hout, Charles Meneveau, Marc Parlange, Joseph Katz Based on the conditional sampling technique of Lu and Willmarth (1973), a detailed quantitative quadrant-hole analysis is presented of canopy turbulence data, comparing computational and field data. The computational data are obtained from large-eddy simulation (LES) of a corn canopy that resolves coarse features of individual corn plants and uses the Lagrangian, scale-dependent dynamic subgrid model. The field data are obtained using PIV. The quadrant hole analysis shows that around the canopy top, ejections are the most frequently occurring events (longest duration) while sweeps are the biggest contributors (largest fraction) to the Reynolds shear stress. Sweeps also contribute the most to the turbulence kinetic energy (TKE), vorticity and dissipation rate around the canopy top. However, the magnitudes of the vorticity (at the LES/measurement resolution) and dissipation rate are the highest in the first quadrant (the outward interactions events). With few exceptions, there is excellent agreement between the quadrant-hole analysis results from the LES and the field data confirming the applicability of LES for fundamental studies of canopy turbulence. [Preview Abstract] |
Monday, November 21, 2005 1:46PM - 1:59PM |
HP.00003: Coarse Projective Integration of a One-Dimensional Turbulence Model Anne Staples, Alexander Smits, Yannis Kevrekidis Multiscale methods may be useful in turbulence if we choose the correct level of description of the problem. A typical turbulent velocity field has continua of length and time scales and hence is not amenable to Multiscale methods. The energy spectrum variables, however, exhibit a separation of time scales. Consider a box of fluid, shaken. The energy spectrum will immediately fill out, but the $k^{-\frac{5}{3}}$ character of the intermediate wave numbers and the rest of the overall shape of the spectrum will fill out slowly over time. In this work we apply a Multiscale method, Coarse Projective Integration (CPI), to the simulation of a one-dimensional turbulence model, the MMT equation. We find a significant saving in computational (wall clock) time using CPI, compared to using standard direct numerical (DNS) simulation procedures, $\frac{{\rm T}_{DNS}}{{\rm T}_{CPI}}=4.78$, where ${\rm T}_{DNS}$ is the wall clock time using DNS and ${\rm T}_{CPI}$ is the wall clock time using CPI. [Preview Abstract] |
Monday, November 21, 2005 1:59PM - 2:12PM |
HP.00004: A Predictive LES Wall Model using Optimal Control Techniques Jeremy Templeton, Meng Wang, Parviz Moin A wall model for large-eddy simulation (LES) based on optimal control theory has been developed. Reynolds-averaged Navier-Stokes equations, coupled to both the LES and control, is used near the wall to provide a target velocity profile which can be used to define a cost function. The control then minimizes this cost function by modifying the wall stresses, used as boundary conditions by the LES. This significantly generalizes the previous work of Nicoud \emph{et al.} (Phys. Fluids 13(10), 2001) in that no \emph{a priori} target profiles are needed, making the wall model truly predictive. In addition, the restriction to basing the control sensitivity to the near-wall region means that away from the wall, where the subgrid scale model is more accurate, the flow is allowed to evolve according to the LES equations. This wall model has been successfully tested in a plane channel flow on a coarse grid for Reynolds numbers up to $Re_{\tau}=20,000$. In the case of $Re_{\tau}=4,000$, the mean velocity and rms velocity fluctuations are found to be comparable to those of Nicoud \emph{et al.} [Preview Abstract] |
Monday, November 21, 2005 2:12PM - 2:25PM |
HP.00005: Large Eddy Simulation of Film-Cooling Jets Ioulia Iourokina, Sanjiva K. Lele Large Eddy Simulation of inclined jets issuing into a turbulent boundary layer crossflow has been performed. The simulation models film-cooling experiments of Pietrzyk et al. (J. of. Turb., 1989), consisting of a large plenum feeding an array of jets inclined at 35° to the flat surface with a pitch 3D and L/D=3.5. The blowing ratio is 0.5 with unity density ratio. The numerical method used is a hybrid combining external compressible solver with a low-Mach number code for the plenum and film holes. Vorticity dynamics pertinent to jet-in-crossflow interactions is analyzed and three-dimensional vortical structures are revealed. Turbulence statistics are compared to the experimental data. The turbulence production due to shearing in the crossflow is compared to that within the jet hole. The influence of three-dimensional coherent structures on the wall heat transfer is investigated and strategies to increase film- cooling performance are discussed. [Preview Abstract] |
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