Bulletin of the American Physical Society
73rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 65, Number 13
Sunday–Tuesday, November 22–24, 2020; Virtual, CT (Chicago time)
Session X09: Turbulence: DNS Simulations (10:45am - 11:30am CST)Interactive On Demand
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X09.00001: Exploring Fluctuation-Induced Forces in Homogeneous Isotropic Turbulence Daniel Putt, Vamsi Spandan, Alpha A. Lee, Rodolfo Ostilla Monico Understanding force generation in nonequilibrium systems is a notable challenge in statistical physics. We uncover a fluctuation-induced force between two plates immersed in homogeneous isotropic turbulence using direct numerical simulations. The force is a nonmonotonic function of plate separation. The mechanism of force generation reveals an intriguing analogy with fluctuation-induced forces: In a fluid, energy and vorticity are localized in regions of defined length scales. When varying the distance between the plates, we exclude energy structures modifying the overall pressure on the plates. At intermediate plate distances, the intense vorticity structures (worms) are forced to interact in close vicinity between the plates. This interaction affects the pressure and forces between the plates. The combination of these two effects causes a nonmonotonic attractive force with a complex Reynolds number dependence. We show that this force remains present when using various plate shapes and sizes with slightly modified characteristics. Our study sheds light on how length scale–dependent distributions of energy and high-intensity vortex structures determine Casimir forces. [Preview Abstract] |
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X09.00002: Reaching high resolution for studies of intermittency in energy and scalar dissipation rates K. Ravikumar, P.K Yeung, K.R. Sreenivasan Passive scalar fields in high Reynolds number turbulence are often observed to be highly intermittent in both the inertial-convective (via the extreme anomaly of structure function exponents) and viscous-diffusive ranges (via intense fluctuations of the scalar dissipation rate, $\chi$), with the Schmidt number, $Sc$, acting as an additional parameter. High-resolution direct numerical simulations are clearly crucial, and reliable conclusions on the $Sc$-effects require that resolution be adequate for all scalars involved. Such calculations are computationally very expensive. However, it is possible (Yeung \& Ravikumar, to appear in Phys. Rev. Fluids, 2020) to replace long simulations of stationary isotropic turbulence at high resolution by multiple short segments evolved from lower-resolution data, at much lower cost. It is also useful to perform ensemble averaging over the statistics of scalars with the same $Sc$ but subjected to uniform mean gradients in different directions. Fluctuations of $\chi$ for a scalar with $Sc=1$ are more intermittent than those of the energy dissipation rate ($\epsilon$). Numerical results including moments of local averages of $\chi$ and conditional moments of $\chi$ given $\epsilon$ at resolution up to $6144^3$ will be presented. [Preview Abstract] |
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X09.00003: Effect of inlet spatial resolution on the direct numerical simulation of turbulent channel flow Ezhilsabareesh Kannadasan, Callum Atkinson, Adrian Lozano-Duran, Peter Schmid, Javier Jimenez, Julio Soria Direct numerical simulation (DNS) of turbulent flows requires a large computational domain and a long simulation time to capture and evolve the large-scale structures and attain a statistically stationary state. In contrast, experimental measurements can relatively easily capture the large-scale structures, but struggle to resolve the dissipative flow scales. This study investigates the spatial extent required for the DNS of a turbulent channel flow to recover turbulent fluctuations and energy when using experimental inlet data which is typically unable to capture fluctuations down to the viscous sub-layer or the smallest viscous scales (i.e. Kolmogorov scales). Synthetic experimental fields from streamwise periodic channel flow at Re$_{\mathrm{\tau \thinspace }}=$ 180 and 550 are used as an inlet for a channel flow DNS with inlet-outlet boundary conditions. The effect of limited spatial resolution on DNS is examined by filtering the small scales at the inlet. The influence of limited inlet spatial resolution on the convergence of mean and streamwise fluctuating velocity profiles are less significant. However, the spanwise fluctuations are slightly weakened. [Preview Abstract] |
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X09.00004: Scaling of rough-wall turbulence by the roughness height and steepness Guozhen Ma, Chunxiao Xu, Hyung Jin Sung, Weixi Huang A roughness scaling behavior is tested by performing the direct numerical simulation (DNS) of a turbulent channel flow over three-dimensional sinusoidal rough walls. The effects of roughness height (k$^{\mathrm{+}})$ and roughness steepness (S) on the turbulent instantaneous field and statistics are examined. The results show that the mean velocity and Reynolds stresses are highly dependent on both k$^{\mathrm{+\thinspace }}$and S, and a good scaling behavior is obtained on the roughness function and the peak of the streamwise turbulent intensity by using a coupling scale k$^{\mathrm{+}}$S. Then we define a rough-wall drag increasing ratio based on the roughness function. Accordingly, the wall resistance can be estimated directly from the coupling scale k$^{\mathrm{+}}$S for a given rough surface. [Preview Abstract] |
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