La organizacin de las grandes escalas en flujos

La organización de las grandes escalas en flujos de pared Master Universitario en Ingeniería Aeronáutica Autor Tutor Sergio Gandía Barberá Dr. Sergio Hoyas Calvo serganba@etsid. upv. es serhocal@mot. upv. es In collaboration with: M. Oberlack and S. Kraheberger TU DARMSTADT July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 1

Content § Motivation § Objectives § Summary of cases § Velocity fields and counter-rotating rolls § Vortex properties § Conclusions July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 2

Motivation § The behavior of the flow near a wall is a first-order challenge in Physics. § A detailed simulation (DNS) of the flow around a commercial jet is still an impossible problem, and will be in the next decades. § Thus to understand the physics of near-wall flows is a must to produce better models and further aircraft improvements. July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 3

Motivation § Three very simple geometries have been employed in the last 30 years to better understand the near-wall flow. Simple geometries allow the use of Direct Numerical Simulation (DNS), as extremely efficient spectral methods can be employed Pipe flow Flat-plate boundary layer Channel flow July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 4

Motivation § Couette and Poiseuille studies Pressure-driven Flow • Kim, Moin and Moser, 87. Re τ = 180 NASA Ames Research Center • Spalart and Moser, 91. Reτ = 550 NASA Ames Research Center • Del Álamo , Jimenez et al, 2005. Reτ = 950 UPM School of Aeronautics, Stanford University Turbulence • Sergio Hoyas and Jimenez, 2006. Reτ = 2003 UPM School of Aeronautics • Pirozzoli and Bernardini, 2014. Reτ = 5000 Università di Roma, Dipartamento di Meccanica e Aeronautica • Yamamoto and Tsuji, 2018. Reτ = 8000 Yamanashi University, Mechanical July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 5

Motivation § Couette and Poiseuille studies Shear-driven Flow • Jukka Komminaho, 95. Re = 750. KTH, Department of Mechanics • Pirozzoli and Bernardini, 2015. Reτ = 1000 Università di Roma, Dipartamento di Meccanica e Aeronautica • Avsarkisov and Hoyas, 2014. Reτ = 550 TU Darmstadt, Fluid Dynamics • Lee and Moser, 18. Reτ = 500 University of Texas, Department of Mechanical Engineering • Kraheberger and Hoyas, 2018. Reτ = 2000 TU Darmstadt, Fluid Dynamics July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 6

Motivation § In a paper published in 2014, Avsarkisov, Hoyas et al found numerical evidence of anomalous long turbulent structures present in fully turbulent Couette flows. July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 7

Objectives § What do we know abouth them? § These structures also appear experimentally (Kominnaho et al) § They get stronger with increasing Reynolds number (Lee & Moser) § They are not broken by transversal flows (Kraheberger et al) § What do we want to know? § How affects the Reynolds number on the length of the rolls? § Is there any quantity triggering the rolls? § How different is the dynamic of the eddies in both flows? July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 8

Very-large scale motions (VLSM) § VLSM are defined as regions of space where a turbulent quantity, as streamwise velocity, shows some coherence § For example, Poiseuille flow clearly DOES NOT present VLSM persisting in time z July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 9 x

Very-large scale motions (VLSM) § Couette flows, however, apparently present this kind of structures. Flow direction x z July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 10

Summary of cases § § Code: § Post-process: § LISO Matlab Routines created for this project July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 11

Streamwise- and time-averaged • Number of simulations: • Around 70 per case • Streamwise average • Results in Y-Z planes July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 12

Velocity fields: C to P transition Couette flow Streamwise velocity: u Counter-rotating rolls July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 13

Velocity fields: C to P transition P Streamwise velocity: u Spanwise velocity: w C-P C July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 14

Velocity fields: C to P transition P Streamwise velocity: u Reynolds stress: <uv> C-P C July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 15

Link with Reynolds stress § Counter-rotating rolls are only present if the Reynolds stress stays negative along the wall-normal direction (y/h). July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 16

Spectra July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 17

How long? July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 18

Vortex distribution Channel centre (CC) • Population of small vortices relevant in CC • Largest vortices in TC are one order of magnitude larger than in TP. July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 19

Conclusions § Very large coherent structures conforming counter-rotating rolls were found in pure TC and transition cases. § A link between the distribution of Reynolds stress and the presence of the rolls was confirmed. § The size of the rolls is presented for the first time at friction Reynolds 125. Their length increases with Reynolds number, but not their width. § The vortex clusters in the channel centre affected by the presence of the rolls. Bigger clusters develop due to their presence. July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 20

Conclusions § Part of these results have been published in the journal Physics of Fluids and presented in the ICOSAHOM meeting. § The second part of thesis will be published in the journal of Fluid Mechanics (hopefully). July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 21

Thank you for your attention! July 2018 | TFM | Universitat Politècnica de València | serganba@etsid. upv. es | 22