Interaction of a Cylindrical Roughness Element and a Two-Dimensional TS-Wave

Plogmann, Benjamin; Würz, W.; Krämer, Ewald

doi:10.1007/978-3-319-03158-3_17

Cited by 3 publications

(4 citation statements)

References 8 publications

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“…Then, the disturbance growth is, however, most pronounced in the centreline region for s/d r < 4 with minima developing at z/d r = ±0.5. A comparison with the mean flow evolution (figure 7) shows these disturbance minima to coincide with the position of the high-speed streaks (compare also Plogmann et al 2014). Hence, the high-speed streaks result in a local decrease of the disturbance mode amplitude.…”

Section: Controlled Disturbance Excitation Upstream Of Medium Roughnementioning

confidence: 79%

“…Here, u ze is the mean flow velocity at the undisturbed spanwise edge of the measurement domain. Moreover, weakly distinct low-speed streaks are present at the outer edges of the high-speed streaks (compare also Plogmann, Würz & Krämer 2014). The formation of these high-and low-speed streaks hints at the presence of two counter-rotating vortex pairs as indicated in figure 6(a).…”

Section: Boundary Layer Roughness Interaction Without Controlled Distmentioning

confidence: 90%

“…In compliance previous findings by Wang (2004) suggest a disturbance maximum near y/δ 1,ref ≈ 1 in the evolution of a fundamental mode downstream of a cylindrical roughness element. Moreover, a comparison with measurements in wall-normal-spanwise (y-z) planes, which addressed the evolution of a single TS wave mode downstream of the roughness, show that the dominant features of both the mean flow and the disturbance evolution in the near-and far roughness wake can be well captured by spanwise scans at a constant wall-normal location of y/δ 1,ref ≈ 0.9-1 (see Plogmann et al 2014). However, this implies that the mean flow velocity at the measurement height is slightly decreasing in the streamwise evolution.…”

Section: Controlled Disturbance Excitation Upstream Of Medium Roughnementioning

confidence: 95%

“…In the present experiments this region is restricted to the near-wall region (y/δ 1,ref < 0.2) and can, therefore, not be investigated with the hot-wire measurement technique. Additional information on the mean flow field downstream of the medium height roughness element can also be found in Plogmann et al (2014).…”

Section: Boundary Layer Roughness Interaction Without Controlled Distmentioning

confidence: 99%

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On the disturbance evolution downstream of a cylindrical roughness element

2014

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Roughness-induced transition is one of the main parameters contributing to performance loss of airfoils. Within this paper, the disturbance evolution downstream of a single, cylindrical roughness element, which is placed in a laminar boundary layer in an airfoil leading edge region, is investigated. The experiments focus on medium height roughness elements with respect to the local boundary layer displacement thickness. Hence, transition is not directly tripped at the roughness element. The roughness diameter is comparable to the streamwise wavelength of the most amplified (linear) disturbance eigenmodes. The vortical structures observed downstream of the roughness are in agreement with previous findings in the literature. In the near roughness wake, a distinct growth of high-frequency (fundamental) modes, that is modes with a high n-factor at the roughness location, is observed. In the far roughness wake, these fundamental modes recover linear stability characteristics due to a possible relaxation of the mean flow. However, an interaction of particularly two-dimensional fundamental modes and by the roughness interference excited oblique fundamental modes results in an excitation of subharmonic type, low-frequency combination modes, which are associated with a phase-locked interaction mechanism. Depending on the initial growth of the fundamental modes in the near wake, the low-frequency modes can experience a nonlinear growth in the far roughness wake and, thereby, trip turbulence. The fundamental mode growth rate in the near wake in turn is a weak function of the disturbance frequency and of the pressure gradient, whereas it is decisively increasing with the roughness height, that is with the mean flow distortion caused by the roughness.

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Section: Controlled Disturbance Excitation Upstream Of Medium Roughnementioning

confidence: 79%

Section: Boundary Layer Roughness Interaction Without Controlled Distmentioning

confidence: 90%

Section: Controlled Disturbance Excitation Upstream Of Medium Roughnementioning

confidence: 95%

Section: Boundary Layer Roughness Interaction Without Controlled Distmentioning

confidence: 99%

See 2 more Smart Citations