# CTR Seminars Archive 2018

**Multi-scale modeling of low-density carbon-phenolic ablators**

Date and Time: Friday, November 9, 2018 - 16:30

Location: CTR Conference Room 103

Event Sponsor: Parviz Moin, Director of Center for Turbulence Research

Speaker(s): Dr. Nagi N. Mansour, Chief Division Scientist at the NASA Advanced Supercomputing Division

Protecting a spacecraft during atmospheric entry is one of highest risk factors that needs to be mitigated during design of a space exploration mission. At entry speeds from space, air turns into high-temperature plasma, and spacecraft Thermal Protection Systems (TPS) are needed to protect the vehicle payload. Modern successful material architectures of spacecraft shields use a porous carbon fiber substrate impregnated with phenolic as an ablator material. In the lecture, efforts to build a Predictive Material Modeling framework for porous ablators from micro-scale to macro-scale will be presented. Several numerical methods and techniques will be summarized that use voxelized images to compute geometrical properties of the porous substrate. These computed properties include porosity, specific surface area and tortuosity that are otherwise indirectly measured through experimental techniques. Direct simulation Monte Carlo (DSMC), a particle based method for approximating the Boltzmann equation, is used to compute the permeability coefficient of the porous substrate based on its digitized representation. The method computes the flow within the microstructure, where the size of the pores may approach the mean-free-path of the flow. Finally, a high-fidelity model implemented in PATO (Porous-material Analysis Toolbox) is discussed, and some examples of ablative material response are presented including for the first time 3D simulations of the full tiled heat-shield for the Mars Science Laboratory (MSL) capsule.

Bio:

Dr. Mansour is currently Chief division Scientist at the NASA Advanced Supercomputing division. He received his Ph.D. in Mechanical Engineering at Stanford in 1978 where he carried out one of the earliest Large-Eddy simulations of a turbulent mixing layer. He also pioneered the use of direct numerical simulation for turbulence model development. He is the founding lead of the Heliophysics Modeling and Simulation (HMS) project at the NASA Advanced Supercomputing division. During his NASA career, Dr. Mansour has served in technical management positions including chief of the Reacting Flow Environments Branch, Chief of the Computational Physics Branch, and as deputy director of the Stanford Center for Turbulence Research, operated jointly with NASA. He is a fellow of the American Physical Society. Dr. Mansour’s current research interests include the development of high-fidelity models for Thermal Protection Systems used for spacecraft atmospheric entry, and development of realistic modeling of plasma with coupled radiative transfer and magneto-hydrodynamics effects on exascale computing systems; large eddy simulations of the solar convection zone, modeling sound propagation in plasma; and the development of emerging magnetic flux models. Dr. Mansour has published over 200 journal and conference articles in the fields of fluid mechanics, turbulence physics, solar physics, aerothermodynamics, magneto-hydrodynamics, and high-temperature material science.

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**Direct numerical simulation of turbulent flow and heat transfer in a spatially developing turbulent boundary layer laden with small solid particles**

Date and Time: Friday, October 19, 2018 - 16:30

Location: CTR Conference Room 103

Event Sponsor: Parviz Moin, Director of Center for Turbulence Research

Speaker(s): Dr. Dong Li

Turbulent flows laden with particles are widely encountered in a great number of natural physical processes and in a host of industrial and environmental applications. In these flows there exist complex interactions between inertial particles, flow turbulence and heat transfer, many of which have not yet been adequately investigated and still remain open questions. In this talk, we will present the results of direct numerical simulations of particle-laden spatially developing turbulent boundary layer flows, using a two-way coupled Eulerian-Lagrangian approach. The main focus of this work is to discuss the effects of inertial particles on turbulent flow, heat transfer and turbulent coherent structures, as well as the phenomenon of particle preferential concentration in the flat-plate turbulent boundary layer. The underlying physical mechanisms of turbulence modulation caused by particles will be analyzed from various aspects.

Bio:

Dr. Dong Li obtained his PhD degree in Power Engineering and Engineering Thermophysics from Zhejiang University in 2016. Before joining CTR, he was a Postdoctoral Researcher at Zhejiang University. His research interests include numerical studies of particle-laden flows, turbulent boundary layer and heat transfer.

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**Color of Turbulence: Low-complexity stochastic dynamical modeling of turbulent flows**

Date and Time: Friday, October 5, 2018 - 16:30

Location: CTR Conference Room 103

Event Sponsor: Parviz Moin, Director of Center for Turbulence Research

Speaker(s): Dr. Armin Zare

This talk describes how to account for second-order statistics of turbulent flows using low-complexity stochastic dynamical models based on the linearized Navier-Stokes (NS) equations. The complexity is quantified by the number of degrees of freedom in the linearized evolution model that are directly influenced by stochastic excitation sources. For the case where only a subset of correlations are known, we develop a framework to complete unavailable second-order statistics in a way that is consistent with linearization around turbulent mean velocity. In general, white-in-time stochastic forcing is not sufficient to explain turbulent flow statistics. We develop models for colored-in-time forcing using a maximum entropy formulation together with a regularization that serves as a proxy for rank minimization. We show that colored-in-time excitation of the NS equations can also be interpreted as a low-rank modification to the generator of the linearized dynamics. Our method provides a data-driven refinement of models that originate from first principles and it captures complex dynamics of turbulent flows in a way that is tractable for analysis, optimization, and control design.

Bio:

Dr. Armin Zare received his B.Sc. degree in Electrical Engineering from Sharif University of Technology, Tehran, Iran, in 2010, and his Ph.D. degree in Electrical Engineering from the University of Minnesota, Minneapolis, in 2016, under the supervision of Mihailo Jovanovic. Zare is currently a Postdoctoral Research Associate in the Ming Hsieh Department of Electrical Engineering at the University of Southern California, Los Angeles. He is broadly interested in the modeling and control of distributed systems in addition to large-scale and distributed optimization. His primary research interests are in the modeling and control of wall-bounded shear flows using tools from optimization and systems theory. Zare was the recipient of the Doctoral Dissertation Fellowship from the University of Minnesota in 2015 and a finalist for the Best Student Paper Award at the 2014 American Control Conference.

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**Shock-turbulence interactions at high turbulence intensities**

Date and Time: Friday, September 7, 2018 - 16:30

Location: CTR Conference Room 103

Event Sponsor: Parviz Moin, Director of Center for Turbulence Research

Speaker(s): Mr. Chang-Hsin Chen

The interaction of turbulence with shock waves, while very common in nature and engineering systems, is a very difficult problem from a theoretical, numerical and experimental perspective. A main challenge arise from the two-way coupling between the shock and turbulence which occurs at a wide range of scales in time and space. The focus of this work is on the fundamental understanding of these shock-turbulence interactions (STI) at high turbulence intensities with high-fidelity direct numerical simulations (DNS) that fully resolve the shock. The numerical study is guided by novel theoretical work that results in analytical expressions for thermodynamic jumps across the shock which depend on turbulence characteristics. Comparison with DNS data shows that these expressions can indeed predict quantitatively a number of statistical variables of interest. The theory presented here also predicts distinct shock amplification for the first time. Results on the shock structure are used to validate previous theoretical proposals and extend the analysis to much stronger interactions which leads to the observation of a new regime (vanished shocks) in which turbulence undergoes a classical spatial decay as it across the shock. Finally, the amplification of turbulence across the shock is discussed. Disagreements in the literature on Reynolds stresses are solved by recognizing a special kind of similarity scaling on two different parameters in two different limits.

Bio:

Mr. Chang-Hsin Chen is an PhD Candidate in the Department of Aerospace Engineering at Texas A&M University working under the supervision of Professor Donzis. He received both his BS and MS from National Chiao Tung University. For his PhD research, he is supported by AFOSR and NSF. Mr. Chen’s research interests are in the areas of compressible turbulence, supersonic/hypersonic flows, non-equilibrium flows and high-performance CFD.

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**Towards a priori models for differential diffusion in turbulent non-premixed flames**

Date and Time: Friday, June 8, 2018 - 16:30

Location: CTR Conference Room 103

Event Sponsor: Parviz Moin, Director of Center for Turbulence Research

Speaker(s): Mr. Nicholas Burali

The flamelet-based chemistry tabulation technique is a popular reduced-order model for non-premixed turbulent flames. In this approach, the one-dimensional flamelet equations are solved, and thermo-chemical quantities are tabulated with respect to the mixture fraction and either its scalar dissipation rate or a progress variable. In generating the individual flamelets to populate the chemical table, the correct choice of the species Lewis numbers plays an important role. Experimental observations have shown that, in turbulent non-premixed jet flames, the effect of turbulent transport on the flame structure becomes gradually dominant over molecular mixing with (*i*) increasing axial distance from the burner exit plane, and (*ii*) increasing jet Reynolds number. In the current work, this transition is characterized and a priori models for the effective species Lewis numbers in turbulent non-premixed flames are assessed.

First, a flamelet-based methodology is proposed to extract these effective Lewis numbers from data sets of turbulent non-premixed flames. This methodology is then applied to the Sandia flames B, C, D, and E. The effective Lewis numbers are found to transition from their laminar values, close to the burner exit plane, to unity further downstream. Previously-suggested models for the effective Lewis numbers, based on the local Reynolds and Karlovitz numbers, are then assessed. To overcome the limitations associated with the experimental data, a campaign of Direct Numerical Simulations (DNS) of Sandia flame B (Re_{jet}≈8200) is carried out. A baseline grid is carefully designed, and grid independence is assessed through simulations using refined grids in the axial, radial and azimuthal directions. Radiation and differential diffusion effects are systematically isolated by considering radiating and unity Lewis number cases, respectively. The DNS database is then validated using experimental data. Finally, effective Lewis numbers are extracted from the DNS data, and models based on the local Reynolds and Karlovitz numbers are tested.

Bio:

Mr. Nicholas Burali is a PhD Candidate in Mechanical Engineering at the California Institute of Technology. He received his BS (2010) and MS (2013), both cum laude, from Sapienza University of Rome, where he was a student of the Lamaro Pozzani University College, and an MS (2014) from Caltech. For his PhD thesis work, which received support from the NDSEG and Josephine de Karman fellowships, Nicholas investigated modeling of differential diffusion effects in turbulent non-premixed flames using experimental and numerical data.

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**Direct numerical simulation of grid-element turbulence and its effect on heat transfer**

Date and Time: Friday, May 18, 2018 - 16:30

Location: CTR Conference Room 103

Event Sponsor: Parviz Moin, Director of Center for Turbulence Research

Speaker(s): Dr. Immanuvel Paul

Fractal-grid-generated turbulence has gained considerable attention in the past decade owing to its novel unique characteristics including the nonequilibrium energy cascade present in the near field. This talk will present direct numerical simulation results of turbulence generated by a simplified fractal grid called a square grid-element.

This talk consists of three parts. The first part focuses on the small-scale dynamics of grid-element turbulence. Specifically, the generating mechanisms and the dynamics of velocity gradient tensor, in the downstream of the grid-element, are studied. An attempt is made to establish the relationship between the small-scale dynamics and the energy cascade by exploring the vortex stretching term in detail. In the second part, a passive scalar is continually injected into the wakes of the grid-element and the scalar small-scale dynamics are analyzed. A nonzero lateral scalar gradient skewness is observed along the far-downstream homogeneous region despite the absence of mean gradients. Through a conditional statistical analysis, the source and mechanism of scalar anisotropy in heated grid-element turbulence are revealed. In the final part, the effect of grid-element turbulence on heat transfer is studied by placing heated cylinders in the wake of an insulated grid-element. The turbulence in the near-field of the grid-element is found to have some unique characteristics that cause unusual stagnation-point heat transfer increase. The probable reasons for this increase along with heat transfer mechanisms are explored.

Bio:

Dr. Immanuvel Paul obtained his PhD from Imperial College London in May 2017. He has been working on fractal-grid-generated turbulence, fine-scale structure of fluid and scalar turbulence, numerical heat transfer, laminar and turbulent wakes, and immersed boundary methods. He is interested in studying the computational and physical aspects of particle-laden flows with heat transfer.

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**Exploring the ultimate of thermally driven turbulence**

Date and Time: Friday, May 4, 2018 - 16:30

Location: CTR Conference Room 103

Event Sponsor: Parviz Moin, Director of Center for Turbulence Research

Speaker(s): Dr. Xiaojue Zhu

In this talk, Dr. Zhu will present "the newest results" on fully developed Rayleigh-Bénard turbulence. For the first time in numerical simulations we find the transition to the ultimate regime, namely at Ra*= 10^13. We reveal how the emission of thermal plumes enhances the global heat transport, leading to a steeper increase of the Nusselt number than the classical Malkus scaling. Beyond the transition, the temperature profiles are only locally logarithmic, namely within the regions where plumes are emitted, and where the local Nusselt number has an effective scaling exponent of 0.38 with respect to Ra, corresponding to the effective scaling in the ultimate regime.

Furthermore, we analyse the local scaling properties of the lateral temperature structure functions in the boundary layers (BL), employing extended self-similarity (ESS) (i.e., plotting the structure functions against each other, rather than only against the scale) in the spirit of the attached eddy hypothesis. We find no ESS scaling below the transition and in the near wall region. However, beyond the transition and for large enough wall distance, we find clear ESS behaviour, as expected for a scalar in a turbulent boundary layer. In striking correspondence to the Nu scaling, the ESS scaling region is negligible at Ra = 10^11 and well developed at Ra = 10^14 , thus providing strong evidence that the observed transition in the global Nusselt number at Ra*= 10^13 indeed is the transition from a laminar type BL to a turbulent type BL.

Bio:

Dr. Xiaojue Zhu obtained his PhD in February 2018 from the Physics of Fluids Group at the University of Twente in the Netherlands. He is currently a postdoctoral researcher in the same group. His research interests include Turbulence, Fluid Structure Interaction, Surface Nanobubbles and Nanodroplets, and Computational Fluid Dynamics.

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**Wall-less wall-bounded turbulence**

Date and Time: Friday, April 27, 2018 - 16:30

Location: CTR Conference Room 103

Event Sponsor: Parviz Moin, Director of Center for Turbulence Research

Speaker(s): Dr. Adrian Lozano-Duran

At first sight, walls appear as the most relevant ingredient in turbulence confined or limited by solid surfaces, and it seems plausible to assume that they should be the origin and organizing agent of wall-bounded turbulence. Consequently, many efforts have been devoted to understand the structure of turbulence in the vicinity of walls. Particularly interesting is the region within the so-called log-layer, where most of the dissipation resides in the asymptotic limit of infinite Reynolds number.

In the present work, the role of the wall and mean momentum transfer on the outer layer of wall-bounded turbulence is investigated via direct numerical simulation (DNS) of turbulent channel flows where the no-slip wall is replaced by a Robin boundary condition for the three velocity components. The new set-up allows for non-zero streamwise, wall-normal and spanwise instantaneous velocities at the boundaries with intensities comparable to those in the bulk flow. We show that the outer-layer one-point statistics and spectra of this 'wall less' channel flow agree quantitatively with those of its wall-bounded counterpart. This suggests that the wall-parallel no-slip condition is not required to recover classic wall-bounded turbulence far from the wall and, more importantly, neither is the impermeability condition. The results are remarkable since no transpiration is assumed to be one of the most distinctive features of walls, and it is commonly understood as the mean by which the log-layer motions 'feel' the boundaries. Instead, we argue that the energy-containing eddies are controlled by the mean momentum flux rather than by the distance to the wall. The hypothesis is further supported by examination of channel flow simulations with modified mean pressure gradients and velocity profiles where the resulting outer-layer flow structures are substantially altered to accommodate the new momentum transfer. Finally, a scaling for the intensities and sizes of the momentum-carrying eddies is proposed based on the mean shear and momentum flux.

Bio:

Dr. Adrian Lozano-Duran received his PhD from the Technical University of Madrid in 2015 at the Computational Fluid Mechanics Lab. headed by Professor Jiménez. His main research has focused on Computational Fluid Mechanics and the fundamental physics of wall-bounded turbulence. Currently, he is a Postdoctoral Fellow at the Center for Turbulence Research at Stanford University working on large eddy simulation and wall-modeling.

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**On fractional derivative closures for turbulence: a critical evaluation**

Date and Time: Friday, April 6, 2018 - 16:30

Location: CTR Conference Room 103

Event Sponsor: Parviz Moin, Director of Center for Turbulence Research

Speaker(s): Dr. Perry Johnson

Turbulence modeling has traditionally relied heavily on the eddy viscosity concept relating turbulent fluxes to local gradients. Important deficiencies of the eddy viscosity concept include its inability to capture non-local and memory effects of turbulence. This has motivated recent interest in exploring how fractional derivatives (derivatives with non-integer order) may be helpful in generalizing the eddy viscosity concept to include non-local effects. Building on the speculative work of Chen (Chaos 16, 023126, 2006), a recent study by Epps & Cushman-Roisin has provided a systematic derivation for a fractional Laplacian model of the Reynolds stress. Meanwhile, unpublished work by Song & Karniadakis applies numerical optimization to determine the fractional order for a variable fractional RANS model in wall-bounded turbulence using DNS results, finding universal results across a range of Reynolds numbers. This talk will evaluate the general claims made in support of fractional turbulence modeling, the assumptions in the Epps & Cushman-Roisin derivation, as well as the relative success of results in these works, with an eye toward clarifying the promise and difficulties of such an approach to turbulence modeling.

Bio:

Dr. Perry Johnson earned his PhD in Mechanical Engineering at Johns Hopkins, and he was awarded the 2017 Corrsin-Kovasznay Outstanding Paper Award. He joined CTR as a postdoctoral scholar September 2017. His research interests include small-scale turbulence, multiphase flows, and near-wall dynamics.

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**Nonlinear stability analysis of plane shear flows and related flow control**

Date and Time: Friday, March 16, 2018 - 16:30

Location: CTR Conference Room 103

Event Sponsor: Parviz Moin, Director of Center for Turbulence Research

Speaker(s): Dr. Zhu Huang

The minimal seeds (the disturbance with the lowest energy which triggers turbulence) for plane shear flows have been captured by the variational method dealing with the nonlinear Navier-Stokes equations. The subcritical transition of plane Poiseuille flow and the fluid structures of minimal seed are explored in the Reynolds number range 1500 ≤ Re ≤ 5000, the energy threshold of minimal seed scales Re^{-3} with respect to Re which agrees well with the theoretical prediction and the direct numerical simulations. The minimal seeds and the generated coherent structures corresponding to edge stage of plane Couette flow and plane Poiseuille flow are compared. The effect of base velocity and mean shear on minimal seed and subcritical transition is discussed.

The physical processes of subcritical transition of plane shear flows can be explained by minimal seeds. The naive and interesting question follows: If the generation of turbulence could be avoided or delayed by some flow control techniques? For example, the more nonlinear stable flow could be obtained if the energy threshold of minimal seed is increased by certain technique. The more nonlinear stable plane Poiseuille flow is achieved by the oscillating streamwise pressure gradient with proper pulsating frequency.

Bio:

Dr. Zhu Huang is a Postdoctoral Fellow of the Center for Turbulence Research at Stanford University. He earned his Ph.D. degree in Power Engineering and Engineering Themophysics from Xi’an Jiaotong University in 2015. Before he joined CTR, he was a visiting student of AOSS (now CSSE) at the University of Michigan (2013.9-2015.7) and a visiting research associate of DAMTP at the University of Cambridge (2016.3-2018.2). His research interests include nonlinear stability analysis of channel flows and related flow control, spectral methods, and radial basis functions method.

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**Turbulence in a microchannel**

Date and Time: Friday, March 2, 2018 - 16:30

Location: CTR Conference Room 103

Event Sponsor: Parviz Moin, Director of Center for Turbulence Research

Speaker(s): Professor V. Kumaran

It is well known that the transition from a laminar to a turbulent flow takes place in a rigid tube takes place at a Reynolds number of about 2100, and in a rigid channel at a Reynolds number of about 1200. Experimental results are presented to show that the transition Reynolds number could be as low as low as 200 in micro-channels of height 100 microns with a soft wall, provided the elasticity modulus of the wall is sufficiently low. At the point of transition, motion is observed in the walls of the channel/tube, indicating that the instability is caused by a dynamical coupling between the fluid and the wall dynamics, which is qualitatively different from that in rigid tubes/channels.

Theoretical calculations show that the transition Reynolds number de- pends on a dimensionless parameter Σ = (*ρ**G**R*^{2}*/µ*^{2}), where, *ρ *and *µ* are the fluid density and viscosity, *G* is the elastic modulus of the wall material, *R* is the cross-stream length scale and *V* is the maximum velocity. A low Reynolds number analysis indicates that there could be a transition even at zero Reynolds number when the dimensionless parameter (*V**µ/GR*) exceeds a critical value (the transition Reynolds number is proportional to the parameter Σ). The mechanism of destabilisation is the transfer of energy from the mean flow to the fluctuations due to the shear work done at the fluid-solid interface. Two different types of instabilities are identified at high Reynolds number using asymptotic analysis the inviscid mode instability for which the critical Reynolds number sales as Σ^{1/2} , and the wall mode instability for which the critical Reynolds number scales as Σ^{3/4} . Numerical continuation is used to extend the results to the intermediate Reynolds number regime. The low Reynolds number analysis is found to be in quantitative agreement with experiments. However, the high Reynolds number analysis is in agreement only if the wall deformation and consequent flow modification due to the applied pressure gradient is incorporated in the analysis.

The transition to turbulence and the consequent large velocity fluctuations results in ultra-fast mixing the microchannel. Experiments show that across a width of 1.5*mm*, mixing occurs in 10 − 100 ms. This is in contrast to mixing in a laminar flow due to molecular diffusion, which requires approximately 10^{3}s. Thus, the transition to turbulence reduces the mixing time by up to five orders of magnitude.

Key words: Transition, Turbulence, Microchannel, Soft wall.

Bio:

Dr. Viswanathan Kumaran is the Senior Professor (HAG scale) & J. C. Bose National Chair, Department of Chemical Engineering, Indian Institute of Science, Bangalore since November 2010. His areas of research include: Flow in biological systems such as tubes with flexible walls, kinetic theories for rapid granular flows, statistical mechanics and rheology in complex fluids such as lyotropic liquid crystalline mesophases, polymer solutions and melts, high Mach number gas dynamics.

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**Eigenspace-based characterization of structural uncertainty in large-eddy simulation closure models**

Date and Time: Friday, February 23, 2018 - 16:30

Location: CTR Conference Room 103

Event Sponsor: Parviz Moin, Director of Center for Turbulence Research

Speaker(s): Dr. Lluis Jofre-Cruanyes

Large-eddy simulation (LES) has gained significant importance as a high-fidelity technique for the numerical resolution of complex turbulent flow. The low-pass filtering of the conservation equations significantly reduces the computational cost of solving turbulence, however, at the expense of modeling the subgrid-scale (SGS) physics. In consequence, the assumptions introduced in the closure formulations may result in potential sources of structural uncertainty that can affect the quantities of interest (QoI), especially in multi-physics phenomena, e.g., combustion processes and interfacial flow, where the small-scale dynamics are crucial to the development of the large scale flow. Therefore, in order to facilitate the analysis, the aim of this work is to characterize SGS model-form uncertainty and estimate the impact on the QoIs by means of eigenspace-based, controlled perturbations within plausible physical bounds [Jofre et al. Flow Turbulence Combust (2018) 100:341]. In the presentation, the strategy will be described in detail and investigations based on LES of canonical turbulent flows will be discussed.

Bio:

Dr. Lluis Jofre is a Postdoctoral Fellow at the Center for Turbulence Research (CTR) at Stanford University. He graduated from Polytechnic University of Catalonia (Spain) in conjunction with KTH - Royal Institute of Technology (Sweden), and obtained a PhD with honors in Mechanical Engineering from the same university. He is part of the Stanford's PSAAP II Exascale Center working on predictive simulations of particle-laden turbulence in a radiation environment. His main research interests are uncertainty quantification in turbulent flows, modeling of two-phase phenomena, and numerical methods for multi-physics applications.

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**A combined volume-of-fluid method and low-Mach-number approach for DNS of evaporating droplets in turbulence**

Date and Time: Friday, February 9, 2018 - 16:30

Location: CTR Conference Room 103

Event Sponsor: Parviz Moin, Director of Center for Turbulence Research

Speaker(s): Dr. Michael S. Dodd

A set of governing equations to describe gas-liquid flows with phase change in the low Mach number limit will be presented. The system of equations accommodates local volume change at the gas-liquid interface due to condensation and evaporation while the total volume of the gas-liquid mixture remains constant. The framework is useful for simulating flows in computational domains that only use combinations of periodic and wall boundary conditions (e.g., isotropic turbulence and turbulent channel flow). Also, compared to the fully compressible formulation, this approach has the advantage of removing acoustic effects from the problem. Using the volume-of-fluid approach, a numerical method to solve the system of equations is developed. The cases of an evaporating and condensing droplet in a closed vessel are solved numerically, and the results show that the algorithm conserves mass while capturing the motion of the interface. The robustness of the method is demonstrated by performing DNS of an evaporating droplet in forced isotropic turbulence.

Bio:

Dr. Michael Dodd is a Postdoctoral Fellow at the Center for Turbulence Research at Stanford University. Dodd received his Bachelor’s degree in Aerospace Engineering from the University of Michigan in 2009 and his Ph.D. in Aeronautics and Astronautics in 2017 from the University of Washington.

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**The high order TENO schemes: concepts, methods and performances**

Date and Time: Friday, January 26, 2018 - 16:30

Location: CTR Conference Room 103

Event Sponsor: Parviz Moin, Director of Center for Turbulence Research

Speaker(s): Dr.-Ing. Lin Fu

A family of high order TENO (targeted ENO) schemes has been proposed by Fu et al. [JCP 305 (2016): 333-359] [JCP 349 (2017): 97-121]. In this talk, the key concept of TENO schemes and the differences between TENO and WENO will be addressed, as well as the framework to construct arbitrarily high-order TENO reconstruction. Then, he will introduce the method to optimize and control numerical dispersion and dissipation separately. Thirdly, the TENO schemes capable of capturing shocks and resolving incompressible and compressible turbulence as an implicit LES model will be outlined. At last, he will summarize the wave-resolution property, shock-capturing capability, numerical robustness and the computational efficiency of TENO schemes.

Bio:

Dr.-Ing. Lin Fu is a postdoctoral fellow of CTR at Stanford University. Before he joined CTR, he did postdoctoral research with Professor N.A. Adams in Technical University of Munich. In the same institute, he obtained his Ph.D. degree with a grade of Summa Cum Laude. He develops new numerical methods including the high-order TENO schemes, the CVP and SPH based domain decomposition method, SPH method and mesh generation method. He is interested in multiphase flows, MHD flows and turbulence.

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**Attached eddies in turbulent channel flow: scale interactions and spectral energy transfer**

Date and Time: Friday, January 12, 2018 - 16:30

Location: CTR Conference Room 103

Event Sponsor: Parviz Moin, Director of Center for Turbulence Research

Speaker(s): Dr. Minjeong Cho

A large-eddy simulation of turbulent channel flow at Re_tau=1700 is conducted to clarify scale interactions and spectral energy transfer. The spectral turbulent kinetic energy equation is considered with emphasis on the visualization of triadic interactions in turbulent energy transport between the Fourier modes. The major role of the turbulent transport is turned out to be the energy cascade, as in many other turbulent shear flows. In addition to this, two new types of scale interaction processes have been discovered in the near-wall region. First, for relatively small energy-containing motions, part of the energy transfer mechanisms in the energy cascade is provided by interactions between larger energy-containing motions. Second, there exists an energy transfer from small to large scales, and this is particularly important for the streamwise and spanwise velocity components in the near-wall region. Finally, it is proposed that turbulence production and pressure-strain spectra support the existence of the self-sustaining process as the main turn-over dynamics of all the energy-containing motions