An experimental study of oblique transition in plane Poiseuille flow

Abstract

Interactions of oblique waves have recently been investigated theoretically and numerically and found to give rise to rapid transition in flows subcritical to linear wave disturbances. The transition scenario consists of the formation and transient growth of streamwise streaks of high and low velocity and later a rapid growth of high-frequency disturbances leading to breakdown. The present study is the first extensive experimental investigation of oblique transition. The experiments were carried out in a plane Poiseuille flow air channel in which the oblique waves were generated, one at each wall, by vibrating ribbons and the development of the flow was mapped with hot-wire anemometry. The experiments consist both of low- and high-amplitude wave disturbances; in both cases streaky structures are created. For the low-amplitude case these structures decay, whereas for the high amplitude the flow goes towards breakdown. This study has confirmed and extended previous theoretical and numerical results showing that oblique transition may be an important transition scenario.

Silent inflow condition for turbulent boundary layers

“…The scenario thus pertains to the class of subharmonic transition. The details of the transition process from the location where -shaped structures emerge is reminiscent of the observations made for the oblique transition in numerical [64] or experimental [77] studies. The presence of an inflexion point in the velocity profile thus considerably shortens the distance required in the primary phase, and the transition follows thereafter boundary-layer physics.…”

“…The combination of one strongly coupled and one weakly coupled high-frequency mode is able to induce a complete transition process. As discussed in detail by Yaglom [76], modal interaction is also a key ingredient in the oblique transition scenario (O-type) [64,77] and the triad scenario (C-type) of Craik [78]. In the compressible regime, oblique TS waves are often present, and streamwise streaks are also at work in FST transition [79].…”

“…(8) shows that the contribution of streamwise velocity perturbations overwhelms the other components, and that the contribution of internal energy is negligible for the subsonic speed under consideration. The study ofûû * at the height where it is a maximum, which is notably used in experiments [77], yields the same modal evolutions as the integrated modal energy (only the levels are different due to the summation). Consequently, we show only the evolution of the modal energy in Fig.…”

Componentwise energy amplification in channel flows

“…Oblique wave transition scenario was introduced by Schmid & Henningson (1992). This transition scenario was studied experimentally by Elofsson & Alfredsson (1998) in Poiseuille flow, and both experimentally and numerically by Berlin, Wiegel & Henningson (1999) in boundary layers. The transition thresholds in oblique plane channel flow transition were examined by Reddy et al (1998), and recently by Chapman (2002).…”

Three-dimensional plasma actuation for faster transition to turbulence

“…The lambda shaped vortices interact with the structures downstream as well as upstream to create a staggered set of harmonic and subharmonic lambda vortices similar to an oblique wave transition. These have been experimentally and numerically tested using speakers and ribbons [58,59] and with a pair of oblique waves [60,61]. Although the frequency of actuation is kept at St = 0.584, the transition 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 occurs through the subharmonic mode which involves a fundamental mode and a subharmonic mode with a frequency half of the fundamental mode.…”