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 M38: Turbulence Theory II 
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Chair: Toshiyuki Gotoh, Nagoya Institute of Technology, Japan Room: Georgia World Congress Center Ballroom 1/2 
Tuesday, November 20, 2018 8:00AM  8:13AM 
M38.00001: State estimation in transitional and turbulent cylindricalCouette flow Mengze Wang, Tamer A. Zaki Transitional and turbulent cylindricalCouette flows are very sensitive to initial conditions and the startup process. As a result, in numerical simulations, it is difficult to prescribe appropriate initial conditions that achieve target flow states, and comparisons to experiments become challenging. This problem is addressed using an adjointvariational stateestimation algorithm. By combining simulations with limited measurements, we predict the appropriate initial conditions that track the correct flow states. We first consider estimation of a superposition of saturated wavy vortices from wall measurements. The computed initial condition contains all the relevant modes, and accurately reproduces the true energy spectra, meanflow distortion and flow structures within the time intervals where measurements are available. We subsequently investigate the more challenging turbulent case with coarsegrained velocity data. The velocity field is reconstructed on a much finer simulation grid. The estimation error is 70% lower than spacetime interpolation, with a better prediction of largescale structures and vorticity. 
Tuesday, November 20, 2018 8:13AM  8:26AM 
M38.00002: Fundamental limitations in initialstate estimation using surface measurements in wall turbulence Qi Wang, Tamer A. Zaki Estimating the initial state of turbulent channel flow from surface measurements is formulated as an adjoint variational minimization. The cost function is the difference between the true measurements and their prediction from the reconstructed state. The accuracy of the state reconstruction and the fundamental limitations in its prediction from wall measurement are examined in detail. The analysis relies on evaluation of the Hessian matrix of the cost function, in the vicinity of the true solution, and analysis of the Hessian eigenspectra. The leading eigenmodes correspond to the highest sensitivity of measurements to the flow; these modes are concentrated in the nearwall region upstream of the sensor location. Their structure explains the fundamental difficulty of estimating the flow state from wall measurements. 
Tuesday, November 20, 2018 8:26AM  8:39AM 
M38.00003: Extracting the Spectrum by Spatial Filtering Mahmoud Sadek, Hussein Aluie The spectrum of a flow quantifies the energy content of spatial scales and can yield valuable information about the cascade ranges, dissipation, and turbulence intensity. It is often calculated using Fourier series, which are formally justified only in periodic domains, and are inherently global in space, incapable of characterizing the flow locally. We will show that the spectrum of a flow field can be extracted within any local region by straightforward filtering in physical space. This can be as simple as unweighted averaging of adjacent gridcells. We derive the conditions under which such a "filtering spectrum" is meaningful, and discuss its close connections and important differences with the wavelet spectrum. We demonstrate the approach using synthetic fields, 2D turbulence from a Direct Numerical Simulation, and 3D turbulence from the JHU Database.

Tuesday, November 20, 2018 8:39AM  8:52AM 
M38.00004: Inputoutput based analysis of convective velocity in turbulent channels Chang Liu, Dennice F Gayme This work employs an inputoutput based approach to computing convective velocities in turbulent channel flows based on stochastically forced NavierStokes equations linearized about a turbulent mean velocity profile. We use this model to examine both the mean convective velocity for fluctuating quantities as a function of wallnormal location, and the convective velocity associated with individual streamwisespanwise wavelength pairs at each wallnormal location. We focus on the streamwise velocity and demonstrate the model's ability to reproduce the shape of the convective velocity profile, particularly its tendency toward a constant value in the nearwall region. The model predicted convective velocities also shows the Reynolds number invariance observed in computations using DNS data. We then isolate the contributions of each scale as well as each linear term in the momentum equation to examine their contribution to the convective velocity and their role in the known deviation from Taylor's hypothesis in the nearwall region. 
Tuesday, November 20, 2018 8:52AM  9:05AM 
M38.00005: A selfsustaining process theory for uniform momentum zones and internal layers in wall turbulence Brandon Montemuro, Gregory Chini, Joseph Charles Klewicki, Chris White 
Tuesday, November 20, 2018 9:05AM  9:18AM 
M38.00006: Abstract Withdrawn Vortexwave interaction theory gives a formal asymptotic framework to describe exact coherent structures in many shear flows. Here the theory is used to describe a possible nonlinear exact coherent structure consistent with the law of the wall of turbulent flows. The structure is made up of a stack of cells in the vertical direction with the local rollstreak structure locally periodically sustained by a small amplitude wave. The higher order equation for the slow dynamics yields an equation governing the mean flow and cell sizes. The structure described fails at two vertical locations leading to new structures corresponding to the wake and buffer layers of a turbulent shear flows. The approach gives an exact closure of the mean flow equation used in turbulence models and predicts results remarkably consistent with experimental and numerical results. The results for parts of the flow recover the exact vertical scalings predicted by the Townsend attached eddy hypothesis. 
Tuesday, November 20, 2018 9:18AM  9:31AM 
M38.00007: Scale interactions and spectral energy transfer in turbulent channel flow Minjeong Cho, Yongyun Hwang, Haecheon Choi Spectral turbulent energy transport is studied in the form of triadic wave interaction by focussing on the logarithmic layer. At the integral length scales, the main kinetic energy balance is formed between turbulence production and nonlinear turbulence transport, the latter of which plays the key role in the energy cascade. Visualisation of triadic wave interactions further revealed that there exist two new types of scale interaction processes highly active in the nearall and the lower logarithmic regions. First type of the scales interactions is associated with the energy cascade of relatively small energycontaining motions located in the region close to the wall, and considerable part of their energy transfer mechanisms from the integral to the adjacent small length scale in the energy cascade is found to be provided by the interactions between larger energycontaining motions. Second type of the scale interactions is the existence of a nonnegligible amount of energy transfer from small to large integral scales. This scale interaction is predominant only for the streamwise and spanwise velocity components, and it plays a central role in the formation of the wallreaching inactive part of large energycontaining motions which locally scales in inner units. 
Tuesday, November 20, 2018 9:31AM  9:44AM 
M38.00008: Transitions between largescale flow states in turbulent 3D Kolmogorov flow Cristian C Lalescu, Michael Wilczek For most turbulent flows in nature, the idealization of statistical homogeneity and isotropy only applies to the small scales. The large scales are typically nonuniversal with pronounced inhomogeneities resulting from walls, largescale driving etc. This motivates the investigation of the largescale structure, turbulent fluctuations as well as their interaction in a canonical flow. Here we present results on a generalized turbulent Kolmogorov flow in threedimensional periodic domains with aspect ratios larger than one. The flow is forced on a single Fourier mode and is subject to largescale friction. The flow develops largescale vortex patterns similar to twodimensional Kolmogorov flow, even in the presence of intense threedimensional smallscale fluctuations. We characterize transitions between different largescale flow states as the largescale friction is modified, including a regime reminiscent of noisesuppressed hysteresis. In addition to the largescale flow features, we address the question of smallscale isotropy in the presence of largescale anisotropies in this flow. Our results help to clarify the role of fluctuations for transitions in fully developed turbulence. 
Tuesday, November 20, 2018 9:44AM  9:57AM 
M38.00009: The OkuboWeiss Type Criteria in TwoDimensional Hydrodynamic and Magnetohydrodynamic Flows Bhimsen Shivamoggi, Gert Jan Van Heijst, Leon Kamp The OkuboWeiss type criteria for 2D quasigeostrophic (QG) flows (via the potential divorticity framework) and 2D magnetohydrodynamic (MHD) flows are formulated, and are interpreted in terms of the intrinsic metric properties of the underlying appropriate vorticity manifold. The OkuboWeiss parameter is shown to remain robust under the betaplane approximation to the Coriolis parameter, while the OkuboWeiss type parameter is shown to provide a useful diagnostic tool to parametrize the magnetic field topology in 2D MHD flows. The ability of the OkuboWeiss type criteria to separate the flowfield into coherent elliptic structures and hyperbolic flow configurations is validated via numerical simulations of quasistationary vortices in QG flows and 2D MHD flows in the decaying turbulence regime (in the presence of viscosity). 
Tuesday, November 20, 2018 9:57AM  10:10AM 
M38.00010: Interaction between cloud droplets and turbulence Toshiyuki Gotoh, Izumi Saito, Takeshi Watanabe, Tatsuya Yasuda We investigate the mechanism for the modification of turbulence spectra due to turbulencecloud droplet interactions reported in the previous DNS study (Saito and Gotoh, 2018, New J. Phys, 20, 023001), where it was found that spectra of scalar variances (temperature and vapor mixing ratio) tend to be k^{1/3} unlike the classical ObukhovCorrsin spectrum k^{5/3}. In order to explore the physical mechanism, we explore the mechanism of the spectral modification by using the cloud microphysics simulator under the conditions simpler than for the previous study. It is found that the particle inertia plays an essential role in the spectra modification. The classical 5/3 spectrum for the scalar variance at low wavenumers changes to the shallower spectrum at moderate wavenumbers, which resembles the characteristics reported in previous observational and DNS studies. We examined the dependence of the transition in the spectra on various parameters, such as gravity, Stokes numbers, Reynolds numbers, and so on. 
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