Vortex Flow Study on Non-Newtonian Fluids in Concentric Annulus withInner Cylinder Rotating

摘要

The present paper concerns the characteristics of transitional flow ofrnnon-Newtonian fluids in a concentric annulus with a diameter ratio ofrn0.52, whose outer cylinder is stationary and inner one rotating. Thernpressure drop and skin friction coefficients have been measured for thernfully developed flows of 0.2% aqueous solution of sodium carbomethylrncellulose (CMC) at inner cylinder rotational speeds of 0～600 rpm.rnThe pressure drop is increased in the laminar region as the rotationalrnspeed increases. The transitional flow has been examined by thernmeasurement of pressure drops and visualization of flow fields, tornreveal the relation between the Reynolds and Rossby numbers with thernskin friction coefficients and to understand the flow instabilityrnmechanism.rnThe effect of Reynolds number and rotation of the inner cylinder onrnthe skin friction coefficient is significantly dependent on the flowrnregime. Consequently, the critical bulk flow Reynolds number RernRecrndecreases as the rotational speed increases. Thus, the rotation increasernof the inner cylinder promotes the onset of transition due to thernexcitation of Taylor vortices.