TURBULENT EXPANSION FLOW OF LOW-MOLECULAR-WEIGHT SHEAR-THINNING SOLUTIONS

• Type: Article in International Scientific Journal
• Date: 1995

Authors

CASTRO, OS (Author) Other; F. T. Pinho (Author) FEUP

Journal

Title: Experiments in Fluids

Vol. 20

Pages: 42-55

ISSN: 0723-4864

Publisher: Springer Nature

Indexing

ISI Web of Knowledge - 16 Citations

Scopus - 18 Citations

Other information

Authenticus ID: P-001-G24

DOI: 10.1007/bf00190597

Abstract (EN): A Laser-Doppler anemometer and a pressure transducer were used to carry out detailed measurements of the mean and root mean square of the velocity and wall- pressure in an axisymmetric sudden expansion flow, with 0.4 and 0.5% by weight shear-thinning aqueous solutions of a low molecular weight polymer (6,000), after appropriate theological characterisation. In spite of their very low molecular weight, these solutions still exhibited elongational elastic effects through drag reduction of up to 35% relative to Newtonian turbulent pipe flow, as shown by Pereira and Pinho (1994). The results showed small variations of the recirculation bubble length with polymer concentration and Reynolds number and reductions of the normal Reynolds stresses of up to 30%, especially in the tangential and radial directions. The reduction in normal Reynolds stresses within the shear layer is an elongational elastic effect, but this elasticity needs to be considerably more intense, such as with high molecular weight polymers, in order to strongly affect the mean flow characteristics. The observed mean flow patterns with these low molecular weight polymer solutions were indeed similar to those exhibited by Newtonian and inelastic fluids.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 14