Velocity profile statistics in a turbulent boundary layer with slot-injected polymer

Abstract

The modification of a flat-plate turbulent boundary layer resulting from the injection of drag-reducing polymer solutions through a narrow inclined slot into the near-wall region of the flow has been studied. Two-component coincident laser-Doppler velocity profile measurements were taken with a free-stream velocity of 4.5 m/s with polymer injection, water injection, and no injection. Polyethylene oxide solutions at concentrations of 500 and 1025 w.p.p.m. were injected. These data are complemented by polymer concentration profile measurements that were taken using a laser-induced-fluorescence technique. Also, integrated skin friction measurements were made with a drag balance for a range of polymer injection conditions and free-stream velocities. The immediate effects of polymer injection are a deceleration of the flow near the wall, a dramatic decrease of the vertical r.m.s. velocit}’ fluctuation levels and the Reynolds shear stress levels, and a mean velocity profile approaching Virk's asymptotic condition. These effects relax substantially with increasing stream wise distance from the injection slot and become similar to the effects observed for dilute homogeneous polymer flows.

Structure of near wall turbulence downstream of a wall mounted protrusion: an interesting Reynolds stress suppression phenomena

“…The profile at x + --58 suggests that the effective size of the sublayer and buffer region has increased, thus shifting the profiles in y+. This behavior in the u' profiles is similar to that reported by Fontaine et al (1992) for drag reduced turbulent boundary layers with polymers. The profiles show a continual axial recovery beyond 232 wall units, with a complex spanwise recovery.…”

“…The mean streamwise velocity profiles exhibit an upward shift of the log region when scaled with the reduced value of the Walker and Tiederman (1990) and Fontaine et al (1992) among others have shown a similar behavior in skin friction reduced profiles of flows with drag reducing polymers. The profiles at x + = 58 do not exhibit any noticeable distortions in their shape due to either the spike or the short separation zone behind the spike.…”

“…This closely parallels the present results with a near doubling of the time between bursts at a location with an approximate 38% local skin friction reduction. In drag reducing polymer laden flows, the increased extensional viscosity of the viscoelastic polymer retards strong wall normal motions, as illustrated by Fontaine et al (1992). This causes a significant suppression of both v' and uv.…”

Turbulent drag reduction of boundary layer flow with non-ionic surfactant injection

“…The flow rate of the injection Q i was set at 1.45 × 10 −2 l s −1 , which was comparable with the volume flow rate in the viscous sublayer and satisfies the limitation of Wu & Tulin (1972) as well as previous studies (e.g. Fontaine et al 1992;Hou et al 2008). We confirmed that turbulence statistics obtained by LDV measurements for turbulent boundary layer flow with the water injection were almost the same as those without the water injection (not shown in this paper).…”

“…Koskie & Tiederman (1991) investigated the drag reduction by the injection of polymer solutions for a turbulent boundary layer using LDV measurements. Fontaine, Petrie & Brungart (1992) performed the LDV and laser-induced fluorescence (LIF) measurements and found that the bursting process was suppressed by injection of polymer solutions into the near-wall region of a turbulent boundary layer. White, Somandepalli & Mungal (2004) and Hou, Somandepalli & Mungal (2008) clarified the effects of polymer additives on the turbulent boundary layer using PIV measurements.…”