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Early turbulent evolution of the Blasius wall jet
KTH, School of Engineering Sciences (SCI), Mechanics.
KTH, School of Engineering Sciences (SCI), Mechanics.
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0001-7864-3071
2006 (English)In: Journal of turbulence, ISSN 1468-5248, Vol. 7, 1-17 p.Article in journal (Refereed) Published
Abstract [en]

The first direct numerical simulation that is sufficiently large to study the self-similar behaviour of a turbulent wall jet is performed. The investigation is an extension of the simulation performed by Levin et al. (2005, A study of the Blasius wall jet. Journal of Fluid Mechanics, 539, 313-347). The same numerical method is used, but a significantly larger computational domain enables us to follow the development of the flow throughout the transition into its early turbulent evolution. Two-dimensional waves and streamwise elongated streaks, matched to measured disturbances, are introduced in the flow to trigger a natural transition mechanism. The Reynolds number is 3090 based on the inlet velocity and the nozzle height. The simulation provides detailed visualisations of the flow structures and statistics of mean flow and turbulent stresses. A weak subharmonic behaviour in the transition region is revealed by animations of the flow. The averaged data are presented in both inner and outer scalings in order to identify self-similar behaviour. Despite the low Reynolds number and the short computational domain, the turbulent flow exhibits a reasonable self-similar behaviour, which is most pronounced with inner scaling in the near-wall region

Place, publisher, year, edition, pages
2006. Vol. 7, 1-17 p.
Keyword [en]
Direct numerical simulation, Streaks, Transition; Turbulence, Wall jet
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-8904DOI: 10.1080/14685240600854884ISI: 000242548700001Scopus ID: 2-s2.0-33845970201OAI: oai:DiVA.org:kth-8904DiVA: diva2:14385
Note
QC 20100830Available from: 2005-12-08 Created: 2005-12-08 Last updated: 2010-12-06Bibliographically approved
In thesis
1. Numerical studies of transtion in wall-bounded flows
Open this publication in new window or tab >>Numerical studies of transtion in wall-bounded flows
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Disturbances introduced in wall-bounded flows can grow and lead to transition from laminar to turbulent flow. In order to reduce losses or enhance mixing in energy systems, a fundamental understanding of the flow stability and transition mechanism is important. In the present thesis, the stability, transition mechanism and early turbulent evolution of wall-bounded flows are studied. The stability is investigated by means of linear stability equations and the transition mechanism and turbulence are studied using direct numerical simulations. Three base flows are considered, the Falkner-Skan boundary layer, boundary layers subjected to wall suction and the Blasius wall jet. The stability with respect to the exponential growth of waves and the algebraic growth of optimal streaks is studied for the Falkner-Skan boundary layer. For the algebraic growth, the optimal initial location, where the optimal disturbance is introduced in the boundary layer, is found to move downstream with decreased pressure gradient. A unified transition prediction method incorporating the influences of pressure gradient and free-stream turbulence is suggested. The algebraic growth of streaks in boundary layers subjected to wall suction is calculated. It is found that the spatial analysis gives larger optimal growth than temporal theory. Furthermore, it is found that the optimal growth is larger if the suction begins a distance downstream of the leading edge. Thresholds for transition of periodic and localized disturbances as well as the spreading of turbulent spots in the asymptotic suction boundary layer are investigated for Reynolds number Re=500, 800 and 1200 based on the displacement thickness and the free-stream velocity. It is found that the threshold amplitude scales like Re^-1.05 for transition initiated by streamwise vortices and random noise, like Re^-1.3 for oblique transition and like Re^-1.5 for the localized disturbance. The turbulent spot is found to take a bullet-shaped form that becomes more distinct and increases its spreading rate for higher Reynolds number. The Blasius wall jet is matched to the measured flow in an experimental wall-jet facility. Both the linear and nonlinear regime of introduced waves and streaks are investigated and compared to measurements. It is demonstrated that the streaks play an important role in the breakdown process where they suppress pairing and enhance breakdown to turbulence. Furthermore, statistics from the early turbulent regime are analyzed and reveal a reasonable self-similar behavior, which is most pronounced with inner scaling in the near-wall region.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. viii, 48 p.
Series
Trita-MEK, ISSN 0348-467X ; 2005:17
Keyword
boundary layer, suction, wall jet, streaks, waves, periodic disturbance, localized disturbance, turbulent spot, algebraic growth, exponential growth, stability, transition thresholds, transition prediction, PSE, DNS
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-546 (URN)
Public defence
2005-12-16, F3, F-huset, Lindstedsvägen 26, Stockholm, 10:15
Opponent
Supervisors
Note
QC 20101025Available from: 2005-12-08 Created: 2005-12-08 Last updated: 2010-10-25Bibliographically approved
2. Numerical Studies of Turbulent and Separeted Flows
Open this publication in new window or tab >>Numerical Studies of Turbulent and Separeted Flows
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Place, publisher, year, edition, pages
Stockholm: KTH, 2006. x, 36 p.
Series
Trita-MEK, ISSN 0348-467X ; 2006:12
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-4044 (URN)
Public defence
2006-06-16, Sal F3, Lindstedtsvägen 26, Stockholm, 10:15
Opponent
Supervisors
Note
QC 20100830Available from: 2006-06-08 Created: 2006-06-08 Last updated: 2010-08-30Bibliographically approved

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