Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session D22: Turbulence Modeling: LES Wall Models |
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Chair: Dale Pullin, California Institute of Technology Room: 30C |
Sunday, November 18, 2012 2:15PM - 2:28PM |
D22.00001: LES of a turbulent channel flow with a predictive wall model Michio Inoue, Dale Pullin, Ivan Marusic, Romain Mathis Large-eddy simulations (LES) of turbulent channel flow are presented. These LES combine the stretched-vortex, subgrid-scale (SGS) model with a near-wall model (Chung \& Pullin {\it JFM} 2009) that here provides a plane-averaged, wall-shear stress together with a plane-averaged slip velocity at a raised or ``virtual'' wall. Instantaneous stream-wise fluctuations are then added to this slip velocity using an empirical inner-outer wall model (Mathis {\it et al}, {\it JFM} 2011) driven by a velocity time-series obtained from within the log-layer of the outer flow. This spatially fluctuating slip velocity is used as a boundary condition for the outer LES. Results using several variations of this wall model are described for turbulent channel flow at Reynolds numbers $Re_\tau$ up to $2.2 \times 10^4$. [Preview Abstract] |
Sunday, November 18, 2012 2:28PM - 2:41PM |
D22.00002: Turbulent boundary layer, wall shear-stress statistics using a predictive wall-model combined with LES Dale Pullin, Michio Inoue, Romain Mathis, Ivan Marusic Time-wise velocity signals obtained from large-eddy simulation (LES) within the near-wall, logarithmic region of the zero-pressure gradient, flat-plate turbulent boundary layer are used as input to a calibrated, empirical wall model (Mathis {\it et al}, 2011) to calculate the statistics of the fluctuating, wall shear stress $\tau_w$. These are compared with DNS (Schaltter \& \"Orl\"u, 2011; Komminaho \& Skote, 2002) at lower Reynolds number and with statistics obtained using the empirical wall model applied to experimentally generated time-series. The DNS, experimentally-based and LES-based predictions are consistent with a log-like increase of $\overline{(\tau_w'^+)^2}$ with $Re_\tau$. It is argued that the LES is thus able to capture large-scale motions within the log-region that are generating this increased wall activity, up to $Re_\tau = 2\times 10^5$. [Preview Abstract] |
Sunday, November 18, 2012 2:41PM - 2:54PM |
D22.00003: Total shear stress boundary condition at upper boundary of RANS in wall-modeled large eddy simulation Changwoo Sung, Jungil Lee, Haecheon Choi In wall-modeled large eddy simulation, how to exchange the flow field information between the solutions from RANS and LES through the boundary condition is one of the important issues. In general, the wall boundary condition of LES is given as a form of the instantaneous wall shear stresses from the solution of RANS, whereas the upper boundary condition of RANS is provided as the instantaneous velocity from the solution of LES. However, in this approach, the total shear stress at the upper boundary is not continuous and thus momentum transfer from LES to RANS is not strictly conserved. In our study, we provide the instantaneous total shear stresses at the upper boundary of RANS with mixing-length model and conduct simulations of turbulent channel flow at high Reynolds numbers. The results show excellent predictions of turbulence statistics. [Preview Abstract] |
Sunday, November 18, 2012 2:54PM - 3:07PM |
D22.00004: A nested-LES wall-modelling approach for high Reynolds number wall-bounded turbulence Yifeng Tang, Rayhaneh Akhavan A new wall-modelling approach for LES of high Reynolds number wall-bounded turbulence is proposed. The method couples coarse-grained LES in a full-size channel with nested fine-grained LES in a minimal channel. At each iteration, the fluctuating velocity field in both channels is rescaled to match the TKE components to that of the minimal channel in the near-wall region ($z^+<100$), to that of the full-size channel in the core ($z^+>300$), and to a weighted average of the two in between. Results were insensitive to the details and width of the weighting function. Simulations were performed for $1000\le Re_\tau \le 10,000$ in full channels of size $2 \pi h \times \pi h \times 2h$ and minimal channels of size $3000 \times 1500 \times 2Re_\tau$ wall units in the streamwise, spanwise and wall-normal directions, respectively. At all $Re_\tau$, resolutions of $64\times64\times65$ in the full-size channel and $32\times64\times65$ in the minimal channel were employed, rendering the cost of computations independent of $Re_\tau$. The Dynamic Smagorinsky model was used as the SGS model. The results show that the nested-LES approach can predict a friction coefficient within $5\%$ of Dean's correlation, and one-point statistics in good agreement with available DNS and experimental data. [Preview Abstract] |
Sunday, November 18, 2012 3:07PM - 3:20PM |
D22.00005: Mean wall shear stress boundary condition for large eddy simulation with coarse mesh near the wall Jungil Lee, Minjeong Cho, Haecheon Choi Mean wall shear stress is proposed for the wall boundary condition for large eddy simulation without resolving near-wall region. The motivation of using this wall boundary condition instead of no-slip boundary condition is that with very coarse resolution near the wall providing an accurate mean wall shear stress is most important in the momentum transport near the wall. As test problems, we consider two canonical wall-bounded flows at high Reynolds number: turbulent channel and boundary layer flows. First, the mean wall shear stress is obtained from the momentum balance for channel flow or from an empirical correlation of skin friction for boundary layer flow. The present boundary condition provides excellent predictions of the mean flow statistics, even if the first off-wall grid locates far away from the wall, $y^+ = O(10^1 \sim 10^3)$, where $y$ is the wall-normal distance from the wall. Next, a dynamic approach based on the log-law is developed to obtain mean wall shear stress during computation and is applied to both flows, showing also excellent results. [Preview Abstract] |
Sunday, November 18, 2012 3:20PM - 3:33PM |
D22.00006: Computing transitional flows using wall-modeled large eddy simulation Julien Bodart, Johan Larsson To be applicable to complex aerodynamic flows at realistic Reynolds numbers, large eddy simulation (LES) must be combined with a model for the inner part of the boundary layer. Aerodynamic flows are, in general, sensitive to the location of boundary layer transition. While traditional LES can predict the transition location and process accurately, existing wall-modeled LES approaches can not. In the present work, the behavior of the wall-model is locally adapted using a sensor in the LES-resolved part of boundary layer. This sensor estimates whether the boundary layer is turbulent or not, in a way that does not rely on any homogeneous direction. The proposed method is validated on controlled transition scenarios on a flat plat boundary layer, and finally applied to the flow around a multi-element airfoil at realistic Reynolds number. [Preview Abstract] |
Sunday, November 18, 2012 3:33PM - 3:46PM |
D22.00007: Dynamic wall-modeling for LES of shock/boundary-layer interacting separated flow at high Reynolds number Soshi Kawai, Johan Larsson We present a new dynamic procedure for non-equilibrium wall-modeling in large-eddy simulation (LES) at arbitrarily high Reynolds numbers. The proposed dynamic non-equilibrium wall-model is based on the methods that model the wall shear stress directly, and solves the full RANS equations in the wall-model layer. We first show how the existing non-equilibrium wall-model becomes inaccurate at high Reynolds number and then propose an improved method which solves this issue. The improvement stems directly from reasoning about how the turbulence length scale changes with wall distance in the inertial sublayer and the resolution-characteristics of numerical methods. The proposed method is shown to accurately predict both equilibrium boundary layers and non-equilibrium shock-induced separated boundary layer at very high Reynolds number, with both realistic instantaneous turbulent structures and accurate statistics (skin friction and turbulence quantities) without the use of ad hoc corrections, something that existing non-equilibrium wall-models fail to do robustly. [Preview Abstract] |
Sunday, November 18, 2012 3:46PM - 3:59PM |
D22.00008: Near-Wall Modeling for Large Eddy Simulation of Convective Heat Transfer in Turbulent Boundary Layers Hyun Wook Park, Kiyoung Moon, Ezgi Oztekin, Randall McDermott, Changhoon Lee, Jung-il Choi Necessity of the near-wall treatments for the large eddy simulation (LES) without resolving viscous layer is well known for providing a smooth transition from molecular to turbulent transport near wall region. We propose a simple but efficient approach based on modeling of wall shear stress and heat flux that enable accurate predictions of Nusselt number correlations for equilibrium boundary layers. The wall shear stress is directly modeled with Werner and Wengle (1991)'s power law model and wall heat flux is modeled with analogous wall laws between velocity and temperature with Kader (1981)'s empirical correlation. We perform the wall-modeled LES of turbulent convective heat transfer in a channel for various Prandtl numbers. The results show good agreement with the available experimental and numerical data. [Preview Abstract] |
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