On the generation of high-amplitude wall-pressure peaks in turbulent boundary layers and spots

Abstract

The coupling between high-amplitude wall-pressure peaks and flow structures, especially in the near-wall region, was studied for a zero-pressure-gradient turbulent-boundary-layer flow and for the flow in the interior of artificially generated turbulent spots. By use of an ‘enhanced’ conditional averaging technique it was shown that buffer region shear-layer structures are to a high degree responsible for the generation of large positive wall-pressure peaks. The relation was proved to be bi-directional in that strong shear layers were shown to accompany positive pressure peaks and correspondingly that large pressure peaks were associated with shear-layer structures detected in the buffer region. This also indicates a link between the wall-pressure peaks and turbulence-producing mechanisms. The pressure-peak amplitude was found to scale linearly with the velocity amplitude of the generating flow structure, indicating that a dominating role here is played by the so-called turbulence – mean shear interaction. The large negative wall-pressure peaks were found to be associated primarily with sweep-type motions. All essential features of the relation between wall-pressure peaks and flow structures in artificially generated spots in a laminar boundary layer were found to be identical to those in the equilibrium turbulent boundary layer.

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

“…Bidirectional analysis was conducted and averages were obtained based on the detection of HAPPs and also flow events. The conditional averages demonstrated similar trends to those of Johansson et al (1987); however, Haritonidis et al (1988) emphasized more the association of both positive and negative HAPPs with the wall-normal motions (v component). (iii) Robinson (1991) in his review of coherent motions in the turbulent boundary layer introduced the strong vortices of the turbulent boundary layer as a source of pressure disturbance by virtue of their low-pressure source.…”

“…The discrepancies among the above investigations could be due to the phase jitter in the conditional averaging of Johansson et al (1987) and Haritonidis et al (1988) or because Kim et al (2002) limited their investigation of the conditional averaging to streamwise vorticity at an upstream location of the pressure peak. The contradictory results require further investigation in order to characterize the structure of the HAPPs in the turbulent boundary layer and this is the subject of the current investigation.…”

“…Turbulent structure of high-amplitude pressure peaks 385 (i) Johansson, Her & Haritonidis (1987) applied simultaneous wall-pressure and hot-wire velocity measurements to investigate the HAPPs. Their conditional averaging based on wall-pressure amplitude and also detection of shear layers from the velocity measurements using the variable-interval time-averaging (VITA) technique showed that the positive HAPPs are associated with the shear layers in the buffer layer.…”

“…These turbulent structures are also referred to as burst events (Kim, Kline & Reynolds 1971;Johansson & Alfredsson 1982) and exhibit a rapid increase of streamwise velocity fluctuation (u) from a negative value to a positive value along with variation of wall-normal velocity fluctuation (v) from positive to negative (an ejection followed by a sweep event). Johansson et al (1987) also carried out a similar analysis on the negative HAPPs and associated them with sweep-type motions (a peak in u). They suggested that the negative HAPPs occur during the deceleration phase (decreasing u and increasing v) of the sweep event.…”

“…However, no evidence was provided to support the association of the negative HAPPs with the vortical structures of the turbulent boundary layer. He also linked the shear layer structures to positive wall-pressure fluctuations based on the investigation of Johansson et al (1987). (iv) De Ojeda & Wark (1997) conducted simultaneous planar particle image velocimetry (PIV) and wall-pressure measurement using an array of microphones.…”