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.
Bachelor of Aerospace Engineering, E.T.S. Ingenieros Aeronauticos (2010)
Master of Science in Engr, E.T.S. Ingenieros Aeronauticos (2012)
Doctor of Philosophy, E.T.S. Ingenieros Aeronauticos (2015)
Parviz Moin, Postdoctoral Faculty Sponsor
- The coherent structure of the kinetic energy transfer in shear turbulence JOURNAL OF FLUID MECHANICS 2020; 892
- Uncovering Townsend's wall-attached eddies in low-Reynolds-number wall turbulence JOURNAL OF FLUID MECHANICS 2020; 889
- Non-equilibrium three-dimensional boundary layers at moderate Reynolds numbers JOURNAL OF FLUID MECHANICS 2020; 883
- Resolvent-based estimation of space-time flow statistics JOURNAL OF FLUID MECHANICS 2020; 883
- Causality of energy-containing eddies in wall turbulence JOURNAL OF FLUID MECHANICS 2020; 882
- Error scaling of large-eddy simulation in the outer region of wall-bounded turbulence JOURNAL OF COMPUTATIONAL PHYSICS 2019; 392: 532–55
- Turbulent windprint on a liquid surface JOURNAL OF FLUID MECHANICS 2019; 873: 1020–54
- Identity of attached eddies in turbulent channel flows with bidimensional empirical mode decomposition JOURNAL OF FLUID MECHANICS 2019; 870: 1037–71
- Characteristic scales of Townsend's wall-attached eddies JOURNAL OF FLUID MECHANICS 2019; 868: 698–725
Dynamic slip wall model for large-eddy simulation.
Journal of fluid mechanics
2019; 859: 400–432
Wall modelling in large-eddy simulation (LES) is necessary to overcome the prohibitive near-wall resolution requirements in high-Reynolds-number turbulent flows. Most existing wall models rely on assumptions about the state of the boundary layer and require a priori prescription of tunable coefficients. They also impose the predicted wall stress by replacing the no-slip boundary condition at the wall with a Neumann boundary condition in the wall-parallel directions while maintaining the no-transpiration condition in the wall-normal direction. In the present study, we first motivate and analyse the Robin (slip) boundary condition with transpiration (non-zero wall-normal velocity) in the context of wall-modelled LES. The effect of the slip boundary condition on the one-point statistics of the flow is investigated in LES of turbulent channel flow and a flat-plate turbulent boundary layer. It is shown that the slip condition provides a framework to compensate for the deficit or excess of mean momentum at the wall. Moreover, the resulting non-zero stress at the wall alleviates the well-known problem of the wall-stress under-estimation by current subgrid-scale (SGS) models (Jiménez & Moser, AIAA J., vol. 38 (4), 2000, pp. 605-612). Second, we discuss the requirements for the slip condition to be used in conjunction with wall models and derive the equation that connects the slip boundary condition with the stress at the wall. Finally, a dynamic procedure for the slip coefficients is formulated, providing a dynamic slip wall model free of a priori specified coefficients. The performance of the proposed dynamic wall model is tested in a series of LES of turbulent channel flow at varying Reynolds numbers, non-equilibrium three-dimensional transient channel flow and a zero-pressure-gradient flat-plate turbulent boundary layer. The results show that the dynamic wall model is able to accurately predict one-point turbulence statistics for various flow configurations, Reynolds numbers and grid resolutions.
View details for DOI 10.1017/jfm.2018.838
View details for PubMedID 31631905
View details for PubMedCentralID PMC6800713
Error scaling of large-eddy simulation in the outer region of wall-bounded turbulence.
Journal of computational physics
2019; 392: 532–55
We study the error scaling properties of large-eddy simulation (LES) in the outer region of wall-bounded turbulence at moderately high Reynolds numbers. In order to avoid the additional complexity of wall-modeling, we perform LES of turbulent channel flows in which the no-slip condition at the wall is replaced by a Neumann condition supplying the exact mean wall-stress. The statistics investigated are the mean velocity profile, turbulence intensities, and kinetic energy spectra. The errors follow ( Δ / L ) α R e τ γ , where Δ is the characteristic grid resolution, Re τ is the friction Reynolds number, and L is the meaningful length-scale to normalize Δ in order to collapse the errors across the wall-normal distance. We show that Δ can be expressed as the L2-norm of the grid vector and that L is well represented by the ratio of the friction velocity and mean shear. The exponent α is estimated from theoretical arguments for each statistical quantity of interest and shown to roughly match the values computed by numerical simulations. For the mean profile and kinetic energy spectra, α ≈ 1, whereas the turbulence intensities converge at a slower rate α < 1. The exponent γ is approximately 0, i.e. the LES solution is independent of the Reynolds number. The expected behavior of the turbulence intensities at high Reynolds numbers is also derived and shown to agree with the classic log-layer profiles for grid resolutions lying within the inertial range. Further examination of the LES turbulence intensities and spectra reveals that both quantities resemble their filtered counterparts from direct numerical simulation (DNS) data, but that the mechanism responsible for this similarity is related to the balance between the input power and dissipation rather than to filtering.
View details for DOI 10.1016/j.jcp.2019.04.063
View details for PubMedID 31631902
View details for PubMedCentralID PMC6800710
Characteristic scales of Townsend's wall-attached eddies.
Journal of fluid mechanics
2019; 868: 698–725
Townsend (The Structure of Turbulent Shear Flow, 1976, Cambridge University Press) proposed a structural model for the logarithmic layer (log layer) of wall turbulence at high Reynolds numbers, where the dominant momentum-carrying motions are organised into a multiscale population of eddies attached to the wall. In the attached-eddy framework, the relevant length and velocity scales of the wall-attached eddies are the friction velocity and the distance to the wall. In the present work, we hypothesise that the momentum-carrying eddies are controlled by the mean momentum flux and mean shear with no explicit reference to the distance to the wall and propose new characteristic velocity, length and time scales consistent with this argument. Our hypothesis is supported by direct numerical simulation of turbulent channel flows driven by non-uniform body forces and modified mean velocity profiles, where the resulting outer-layer flow structures are substantially altered to accommodate the new mean momentum transfer. The proposed scaling is further corroborated by simulations where the no-slip wall is replaced by a Robin boundary condition for the three velocity components, allowing for substantial wall-normal transpiration at all length scales. We show that the outer-layer one-point statistics and spectra of this channel with transpiration agree quantitatively with those of its wall-bounded counterpart. The results reveal 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 at the wall.
View details for DOI 10.1017/jfm.2019.209
View details for PubMedID 31631906
View details for PubMedCentralID PMC6800708
Identity of attached eddies in turbulent channel flows with bidimensional empirical mode decomposition.
Journal of fluid mechanics
2019; 870: 1037–71
Bidimensional empirical mode decomposition (BEMD) is used to identify attached eddies in turbulent channel flows and quantify their relationship with the mean skin-friction drag generation. BEMD is an adaptive, non-intrusive, data-driven method for mode decomposition of multiscale signals especially suitable for non-stationary and nonlinear processes such as those encountered in turbulent flows. In the present study, we decompose the velocity fluctuations obtained by direct numerical simulation of channel flows into BEMD modes characterized by specific length scales. Unlike previous works (e.g. Flores & Jiménez, Phys. Fluids, vol. 22(7), 2010, 071704; Hwang, J. Fluid Mech., vol. 767, 2015, pp. 254-289), the current approach employs naturally evolving wall-bounded turbulence without modifications of the Navier-Stokes equations to maintain the inherent turbulent dynamics, and minimize artificial numerical enforcement or truncation. We show that modes identified by BEMD exhibit a self-similar behaviour, and that single attached eddies are mainly composed of streaky structures carrying intense streamwise velocity fluctuations and vortex packets permeating in all velocity components. Our findings are consistent with the existence of attached eddies in actual wall-bounded flows, and show that BEMD modes are tenable candidates to represent Townsend attached eddies. Finally, we evaluate the turbulent-drag generation from the perspective of attached eddies with the aid of the Fukagata-Iwamoto-Kasagi identity (Fukagata et al., Phys. Fluids, vol. 14(11), 2002, pp. L73-L76) by splitting the Reynolds shear stress into four different terms related to the length scale of the attached eddies.
View details for DOI 10.1017/jfm.2019.272
View details for PubMedID 31631907
View details for PubMedCentralID PMC6800706
- Dynamic slip wall model for large-eddy simulation JOURNAL OF FLUID MECHANICS 2018; 859: 400–432
- Mandala-inspired representation of the turbulent energy cascade AMER PHYSICAL SOC. 2018
- Modeling boundary-layer transition in direct and large-eddy simulations using parabolized stability equations PHYSICAL REVIEW FLUIDS 2018; 3 (2)
- Turbulence intensities in large-eddy simulation of wall-bounded flows PHYSICAL REVIEW FLUIDS 2018; 3 (1)
- Characterization of turbulent coherent structures in square duct flow IOP PUBLISHING LTD. 2018
- Mandala-inspired representation of the turbulent energy cascade. Physical review fluids 2018; 3 (10): 100505
- A multifractal model for the momentum transfer process in wall-bounded flows JOURNAL OF FLUID MECHANICS 2017; 824
Transitional-turbulent spots and turbulent-turbulent spots in boundary layers
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2017; 114 (27): E5292–E5299
Two observations drawn from a thoroughly validated direct numerical simulation of the canonical spatially developing, zero-pressure gradient, smooth, flat-plate boundary layer are presented here. The first is that, for bypass transition in the narrow sense defined herein, we found that the transitional-turbulent spot inception mechanism is analogous to the secondary instability of boundary-layer natural transition, namely a spanwise vortex filament becomes a [Formula: see text] vortex and then, a hairpin packet. Long streak meandering does occur but usually when a streak is infected by a nearby existing transitional-turbulent spot. Streak waviness and breakdown are, therefore, not the mechanisms for the inception of transitional-turbulent spots found here. Rather, they only facilitate the growth and spreading of existing transitional-turbulent spots. The second observation is the discovery, in the inner layer of the developed turbulent boundary layer, of what we call turbulent-turbulent spots. These turbulent-turbulent spots are dense concentrations of small-scale vortices with high swirling strength originating from hairpin packets. Although structurally quite similar to the transitional-turbulent spots, these turbulent-turbulent spots are generated locally in the fully turbulent environment, and they are persistent with a systematic variation of detection threshold level. They exert indentation, segmentation, and termination on the viscous sublayer streaks, and they coincide with local concentrations of high levels of Reynolds shear stress, enstrophy, and temperature fluctuations. The sublayer streaks seem to be passive and are often simply the rims of the indentation pockets arising from the turbulent-turbulent spots.
View details for PubMedID 28630304
- Coherent structures in statistically stationary homogeneous shear turbulence JOURNAL OF FLUID MECHANICS 2017; 816: 167-208
- A statistical state dynamics-based study of the structure and mechanism of large-scale motions in plane Poiseuille flow JOURNAL OF FLUID MECHANICS 2016; 809: 290-315
- Multiscale analysis of the topological invariants in the logarithmic region of turbulent channels at a friction Reynolds number of 932 JOURNAL OF FLUID MECHANICS 2016; 803: 356-394
- Algorithm 964: An Efficient Algorithm to Compute the Genus of Discrete Surfaces and Applications to Turbulent Flows ACM TRANSACTIONS ON MATHEMATICAL SOFTWARE 2016; 42 (4)
- Numerically accurate computation of the conditional trajectories of the topological invariants in turbulent flows JOURNAL OF COMPUTATIONAL PHYSICS 2015; 295: 805–14
- Taylor's hypothesis in turbulent channel flow considered using a transport equation analysis PHYSICS OF FLUIDS 2015; 27 (2)
- Effect of the computational domain on direct simulations of turbulent channels up to Re-tau=4200 PHYSICS OF FLUIDS 2014; 26 (1)
- Aspect ratio effects in turbulent duct flows studied through direct numerical simulation JOURNAL OF TURBULENCE 2014; 15 (10): 677–706
- Time-resolved evolution of coherent structures in turbulent channels: characterization of eddies and cascades JOURNAL OF FLUID MECHANICS 2014; 759
- The three-dimensional structure of momentum transfer in turbulent channels JOURNAL OF FLUID MECHANICS 2012; 694: 100-130