New aspects of turbulent boundary-layer structure

Head, M. R.; Bandyopadhyay, Promode R.

doi:10.1017/s0022112081001791

Cited by 802 publications

(561 citation statements)

References 21 publications

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“…More generally, the calculations above provide supporting evidence for the belief that 14 hairpins play a major role in the mechanics of turbulence (as was suggested in [15,16,30], and as is already quite firmly known to be the case near walls [28]), and also provide supporting evidence for the usefulness of polymeric models.…”

Section: Conclusion and _speculationssupporting

confidence: 76%

Hairpin removal in vortex interactions

Chorin¹

1990

Journal of Computational Physics

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An algorithm is presented for removing tightly folded hairpins in an evolving collection of vortex filaments. According to the recently developed polymeric models of turbulence, such removal provides a model of the effect of the small scales of turbulence. It results in a dynamic smoothing of vortex interactions and in a great reduction in the amount of labor required to sum them. The self-consistency of the model is exhibited numerically.

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Section: Conclusion and _speculationssupporting

confidence: 76%

Hairpin removal in vortex interactions

Chorin¹

1990

Journal of Computational Physics

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“…It is also seen that the vortex heads convect with slightly different velocities, what will result in the interaction or merging of the vortices at a later stage. Furthermore, the vortices are of approximately the same size and do not appear to be aligned along a 12 • -20 • slope with the wall as in Head & Bandyopadhyay (1981) or in the logarithmic layer vortex packets observed in Adrian et al (2000). Near the top of the volume at y/δ = 0.45 the velocity direction and magnitude is very irregular, which may indicate the presence of (vortical) flow structures just above this packet.…”

Section: Instantaneous Flow Fieldmentioning

confidence: 89%

Three-dimensional vortex organization in a high-Reynolds-number supersonic turbulent boundary layer

et al. 2010

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Tomographic particle image velocimetry was used to quantitatively visualize the three-dimensional coherent structures in a supersonic (Mach 2) turbulent boundary layer in the region between y/δ = 0.15 and 0.89. The Reynolds number based on momentum thickness Re θ = 34 000. The instantaneous velocity fields give evidence of hairpin vortices aligned in the streamwise direction forming very long zones of lowspeed fluid, consistent with Tomkins & Adrian (J. Fluid Mech., vol. 490, 2003, p. 37). The observed hairpin structure is also a statistically relevant structure as is shown by the conditional average flow field associated to spanwise swirling motion. Spatial low-pass filtering of the velocity field reveals streamwise vortices and signatures of large-scale hairpins (height > 0.5δ), which are weaker than the smaller scale hairpins in the unfiltered velocity field. The large-scale hairpin structures in the instantaneous velocity fields are observed to be aligned in the streamwise direction and spanwise organized along diagonal lines. Additionally the autocorrelation function of the wallnormal swirling motion representing the large-scale hairpin structure returns positive correlation peaks in the streamwise direction (at 1.5δ distance from the DC peak) and along the 45 • diagonals, which also suggest a periodic arrangement in those directions. This is evidence for the existence of a spanwise-streamwise organization of the coherent structures in a fully turbulent boundary layer.

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“…For example the hairpin vortices are inclined at ∼45 • (Head & Bandyopadhyay 1981) and shear layers are reported to have angles less than 45 • inclination relative to the free stream (Liu et al 1991;Adrian, Meinhart & Tomkins 2000). The higher inclination angle of the average pressure field is associated with the non-local characteristic of the pressure field.…”

Section: Spatio-temporal Scales Of Happsmentioning

confidence: 99%

Turbulent structure of high-amplitude pressure peaks within the turbulent boundary layer

Ghaemi

Scarano

2013

J. Fluid Mech.

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The positive and negative high-amplitude pressure peaks (HAPP) are investigated in a turbulent boundary layer at Re θ = 1900 in order to identify their turbulent structure. The three-dimensional velocity field is measured within the inner layer of the turbulent boundary layer using tomographic particle image velocimetry (tomo-PIV). The measurements are performed at an acquisition frequency of 10 000 Hz and over a volume of 418 × 149 × 621 wall units in the streamwise, wall-normal and spanwise directions, respectively. The time-resolved velocity fields are applied to obtain the material derivative using the Lagrangian method followed by integration of the Poisson pressure equation to obtain the three-dimensional unsteady pressure field. The simultaneous volumetric velocity, acceleration, and pressure data are conditionally sampled based on local maxima and minima of wall pressure to analyse the threedimensional turbulent structure of the HAPPs. Analysis has associated the positive HAPPs to the shear layer structures formed by an upstream sweep of high-speed flow opposing a downstream ejection event. The sweep event is initiated in the outer layer while the ejection of near-wall fluid is formed by the hairpin category of vortices. The shear layers were observed to be asymmetric in the instantaneous visualizations of the velocity and acceleration fields. The asymmetric pattern originates from the spanwise component of temporal acceleration of the ejection event downstream of the shear layer. The analysis also demonstrated a significant contribution of the pressure transport term to the budget of the turbulent kinetic energy in the shear layers. Investigation of the conditional averages and the orientation of the vortices showed that the negative HAPPs are linked to both the spanwise and quasi-streamwise vortices of the turbulent boundary layer. The quasi-streamwise vortices can be associated with the hairpin category of vortices or the isolated quasi-streamwise vortices of the inner layer. A bi-directional analysis of the link between the HAPPs and the hairpin paradigm is also conducted by conditionally averaging the pressure field based on the detection of hairpin vortices using strong ejection events. The results demonstrated positive pressure in the shear layer region of the hairpin model and negative pressure overlapping with the vortex core.

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New aspects of turbulent boundary-layer structure

Cited by 802 publications

References 21 publications

Hairpin removal in vortex interactions

Hairpin removal in vortex interactions

Three-dimensional vortex organization in a high-Reynolds-number supersonic turbulent boundary layer

Turbulent structure of high-amplitude pressure peaks within the turbulent boundary layer

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