Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session Q15: Turbulence: Wallbounded Flows II 
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Chair: Sheldon Green, University of British Columbia Room: 310 
Tuesday, November 26, 2019 7:45AM  7:58AM 
Q15.00001: Statistical State Dynamics Based Study of the Role of Nonlinearity in the Maintenance of Turbulence in Couette Flow Brian Farrell, Petros Ioannou, MariosAndreas Nikolaidis While linear nonnormality underlies the mechanism of energy transfer from the externally driven flow to the perturbation field, nonlinearity is also known to play an essential role in sustaining turbulence. We report a study based on the statistical state dynamics of Couette flow turbulence with the goal of better understanding the role of nonlinearity in sustaining turbulence. The statistical state dynamics implementation used is a closure at second order in a cumulant expansion of the NavierStokes equations in which the averaging operator is the streamwise mean. Two fundamentally nonnormal mechanisms potentially contributing to maintaining the second cumulant are identified. These are parametric perturbation growth arising from interaction of the perturbations with the fluctuating mean flow and transient growth of perturbations arising from nonlinear interaction between components of the perturbation field. By the method of selectively including these mechanisms in a DNS parametric growth is found to maintain the perturbation field in the turbulent state while the mechanism of transient growth of perturbations arising from scattering by nonlinear interactions suppresses perturbation variance. [Preview Abstract] 
Tuesday, November 26, 2019 7:58AM  8:11AM 
Q15.00002: The MoninObukhov length in turbulent TaylorCouette flow Pieter Berghout, Roberto Verzicco, Richard Stevens, Detlef Lohse, Daniel Chung Turbulent TaylorCouette (TC) flow is the shear driven flow inbetween two concentric independently rotating cylinders. In recent years, direct numerical simulations and experiments (employing particle imaging velocimetry) revealed the shape of the mean streamwise and angular velocity profiles up to very high Reynolds numbers. However, so far no theory has been able to capture the Reynolds number effects of the mean streamwise velocity profile, and the classical vonKarman logarithmic law only fits in a minimal spatial region. In this talk, we show the application of the MoninObukhov length to turbulent TC flow. This length scale delineates the flow regions where the production of turbulent kinetic energy is governed either by shear or by the curvature of streamlines (centrifugal effects). We then derive an equation for the mean streamwise and angular velocity profiles that convincingly collapses the profiles for varying Reynolds numbers. Finally, we extend the analysis to varying radius ratios and find an equally convincing collapse. [Preview Abstract] 
Tuesday, November 26, 2019 8:11AM  8:24AM 
Q15.00003: The balance of Reynolds stresses equations in spanwise rotating plane Couette flows at dual states Zhenhua Xia In this work, the terms in the transport equations of the Reynolds stresses are analysed in spanwise rotating plane Couette flows at two different states. Our results show that they are generally of the same shape at two different states, but the state with more roll cells has a larger value. The energy transfer between the secondary and the residual fields shows that the secondary flows are more energetic at the state with more roll cells while the residual field is more energetic in the other state. Furthermore, a local inverse energy cascade is observed in the near wall region at the latter state with less roll cells where the energy is transferred from the residual field to the secondary flow field. Our results support the conjecture that the largescale secondary flows play a very important role in the dual states of spanwise rotating plane Couette flows. [Preview Abstract] 
Tuesday, November 26, 2019 8:24AM  8:37AM 
Q15.00004: The moving wall effects on structures in turbulent CouettePoiseuille flows Jun Hyuk Hwang, Jae Hwa Lee Direct numerical simulation of a turbulent CouettePoiseuille flow (hereafter, CPflow) is performed to investigate spatial development of turbulent structures in the asymmetric flows between two parallel planes. The asymmetric CPflows are generated by imposing the constant moving wall velocity condition on the top wall in the opposite direction to the main flow, and the velocity is varied systematically. As the moving wall velocity increases, the friction Reynolds number on the moving wall increases largely, although it is increased slightly on the stationary wall. Innerscaled mean velocity profiles show that the logarithmic layer is established clearly on the moving wall, whereas it is shortened on the stationary wall compared to that from turbulent pure Poiseuille flow at similar Reynolds number. Profiles of the turbulent intensities show that the turbulent activity increases/decreases near the moving/stationary wall with an increase of the moving wall velocity The asymmetric features of the CPflow are mainly attributed to significant growth of nearwall motions on the top wall throughout the elongated shear layer. [Preview Abstract] 
Tuesday, November 26, 2019 8:37AM  8:50AM 
Q15.00005: Largeeddy simulation of TaylorCouette flow at relatively large Reynolds number Wan Cheng, Dale Pullin, Ravi Samtaney We present largeeddy simulations (LES) of the incompressible NavierStokes equations for TaylorCouette flow at relatively high Reynolds numbers. The ratio of the two coaxial cylinder diameters is fixed as $\eta = R_i/R_o = 0.909$ with $R_i,R_o$ the inner and outer cylinder radii respectively. The outer cylinder is stationary while the inner cylinder rotates with constant angular velocity $\Omega_i$, leading to the driving Reynolds number $Re_i= (R_oR_i)\,R_i \Omega_i /\nu$ with $\nu$ the kinematic viscosity of the Newtonian fluid. Wallresolved LES is implemented using the stretchedvortex, subgrid scale model with $Re_i$ in the range $10^5  3 \times 10^6$. We develop an empirical flow model for the $Re_{\tau_i} = F(\eta,Re_i)$ relationship where $Re_{\tau_i} = u_{\tau_i}\,(R_o R_i)/(2\nu)$ is the innercylinder friction Reynolds number. Comparison of the model behavior with experimental data [van Gils \textit{et al.}, \textit{PRL}, 106, (2011), van Gils \textit{et al.}, \textit{J. Fluid Mech.},706, (2012), Merbold \textit{et al.}, \textit{Phys. Rev. E},87, (2013) ], direct numerical simulation [Ostilla M\'onico \textit{et al.}, \textit{J. Fluid Mech.}, 788, (2016)] and the present LES will be discussed. [Preview Abstract] 
(Author Not Attending)

Q15.00006: Direct numerical simulations of a swirling flow in a conical diffuser Ankit Awasthi, Ugo Piomelli We have performed Direct Numerical Simulations of a swirling flow in a conical diffuser using Nek5000, a spectralelement code. This configuration is a model of the draft tube of a hydroelectric power plant, which is used to increase the flow pressure downstream of the turbine. Separation may adversely impact the performance of the diffuser and should be avoided. A conical diffuser with an opening angle of 20 degrees is chosen. Previous experimental and numerical studies can be used for validation [Clausen et al., \textit{Exp.\ Therm.\ Fluid Sci.}, 6(1):3948, 1993]. The experiment uses a very short inlet section so that at the beginning of the diffuser the flow is not fully developed. The flow is extremely sensitive to the inlet boundary conditions. When the inlet boundary condition for axial and circumferential velocities at the beginning of the diffuser are taken from the experimental study, good agreement is achieved downstream. The use of fully developed pipe flow, on the other hand, results in a very different flow field. The effects of synthetic perturbation and forcing techniques to generate inflow conditions will be described. Future work will include the effect of rough walls on the separation characteristics and pressure recovery. [Preview Abstract] 
Tuesday, November 26, 2019 9:03AM  9:16AM 
Q15.00007: Is secondary flow of Prandtl's second kind due to intense Reynoldsstress events? Atzori Marco, Ricardo Vinuesa, Adri\'an LozanoDur\'an, Philipp Schlatter We investigate intense Reynoldsstress structures in the turbulent flow through ducts square and rectangular crosssections, with the aim of clarifying their relation with the secondary flow of Prandtl’s second kind. The intense Reynoldsstress structures are defined as connected regions of the domain that fulfil the condition $uv>H u' v'$, where $u$ and $v$ are the fluctuations of the streamwise and vertical component of the velocity, respectively, $u'$ and $v'$ are their rootmeansquare, and $H$ is a scalar threshold. In particular, we focus on the fractional contribution of these events to the mean vertical velocity, $V$. The comparison between duct and channel flows unveils that: 1) in the core of the duct, the fractional contribution is in very good agreement with that in the channel, despite the presence of the secondary flow in the duct; 2) in the corner of the duct, the fractional contribution is in good agreement with the channel only in a small region below the corner bisector. Both in the core and in corner of the duct, the behaviour of the fractional contribution as a function of the wall distance is significantly different from that of $V$. According to our results, the secondary flow of Prandtl’s second kind is not due to intense Reynoldsstress events. [Preview Abstract] 
Tuesday, November 26, 2019 9:16AM  9:29AM 
Q15.00008: Quantitative contribution of laminar, turbulence and secondary flow to velocity and temperature in rhombic ducts Naoya Fukushima In this study, Direct Numerical Simulation of turbulent flow in rhombic ducts have been carried out to investigate effects of the corner angle on the velocity and temperature distribution in the ducts. Due to anisotropy and inhomogeneity of the Reynolds stresses, secondary flow of the second kind, which goes from the center to the corner of ducts, are induced. The secondary flow affects the velocity and temperature distribution in the ducts and is supposed to enhance momentum and heat transfer. Even around the obtuse corner whose angle is 150$^{\mathrm{o}}$, the secondary flow with about 1.5 {\%} of bulk mean velocity is still induced. The origin of the secondary flow has not been clarified yet. Fukagata, Iwamoto and Kasagi (2002) have theoretically driven the FIKidentity to evaluate quantitative contributions of laminar and turbulence to the friction in turbulent channel. In this study, the FIKidentity has been numerically applied to DNS data in the rhombic ducts to evaluate quantitative contributions of laminar, turbulence and secondary flow to the velocity and temperature distribution. From the results, the effects of the corner angle on these contributions are investigated. Finally, one possible origin of the secondary flow will be suggested. [Preview Abstract] 
Tuesday, November 26, 2019 9:29AM  9:42AM 
Q15.00009: Analysis of Thermal BoundaryLayer Structure and ScaleDependence in Transcritical Flows at Turbulent Conditions Jack Guo, Xiang Yang, Matthias Ihme Previous literature has shown inadequacies of commonly employed scaling transformations to collapse the mean temperature profile for flows with large property gradients. This is particularly relevant for flows with large density gradients that are encountered in transcritical wallbounded flows. Here, we examine the breakdown of the temperature law of the wall as a function of compressibility via direct numerical simulation (DNS) of transcritical channel flows at turbulent conditions. We propose scaling corrections and suggestions towards the development of more accurate temperature profiles, representing an important step towards reliable predictions of highly compressible turbulent flows. We also analyze and discuss turbulent statistics and budgets related to the temperature transport and heat transfer and provide estimates under which conditions commonly employed transformations remain valid at transcritical flow regimes. [Preview Abstract] 
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