Streamwise evolution of drag reduced turbulent boundary layer with polymer solutions

Abstract

The effect of local polymer solution injection on the evolution of a flat-plate turbulent boundary layer has been investigated experimentally. Polyethylene oxide (PEO) solutions were injected through an inclined slot. The influence of polymer injection on boundary layer development downstream of the slot is assessed at three different concentrations (100 ppm, 500 ppm, and 1000 ppm) using planar velocity field and concentration measurements. A local drag reduction (DR) of up to 60% was obtained in the vicinity of the slot. A systematic change observed in the inverse of the von Kármán constant (k = 1/κ) with an increase in DR is used to define the sub-regimes of the high DR regime, and a linear relation between k and DR is shown to persist over a wide range of Reynolds numbers. The analysis of combined velocity and concentration measurements provides added insight into the associated changes in the boundary layer characteristics and the underlying flow physics.

Interfacial mechanism of hydrogel with controllable thickness for stable drag reduction

“…For marine vehicles, drag reduction not only increases their navigation speed, but also reduces energy consumption and pollution, which is an important factor affecting economic development and environmental protection [1,2]. Different drag reduction strategies have been proposed, such as polymer additives [3,4], surface microstructures [5][6][7], superhydrophobic surfaces [8][9][10][11], and slippery liquid-infused porous surfaces [12][13][14]. Among the existing drag reduction techniques, the regulation of solid-liquid frictional resistance by constructing surfaces with special wettability has been a hot research topic [15,16].…”

Experimental investigation on the unsteady surface pressure fluctuation patterns over an airfoil

“…The experimental studies were primarily conducted in wind tunnels with size limitations, where the transition from laminar flow regime to turbulent flow regime is unlikely to occur due to the size of the test models. In order to achieve a turbulent flow over the airfoil, or at least over the trailing edge, and to mimic the conditions at high Reynolds number flow that the actual wings experience, a tripping tape is utilized to force an early (forced) transition to the turbulent regime over the airfoils in experiments [36][37][38][39][40]. Despite its utilization in almost all experiments, the number of investigations addressing the effect on mean quantities is limited [41][42][43] and frequency dependent effect does not exist.…”