Influence of Surface Curvature on Coanda Effect for Vertical Jet Impacting Horizontal Cylinder

Abstract

The Coanda effect is a tendency of flowing fluid to follow the solid surface rather than to separate under the inertial effect. This paper presents the effects of surface curvature on the Coanda angle and jet deflection for a vertical jet impacting a horizontal cylinder (of diameter D) with Froude numbers Fr = 4.74 and 6.33. The penetration depth h of the cylinder in the jet is varied from h/D = 0.01-0.4 while the jet-to-cylinder diameter ratio d/D is varied from 0.11 to 2.0. For Fr = 4.74, the round jet impacting the cylinder evolves into a planar jet for d/D £ 0.40 where the jet deflection is positive, dictated by the Coanda effect. The deflection of the jet is negative for d/D = 0.60 and 0.83 where the bouncing (inertial) effect overwhelms the Coanda effect. Fr = 4.74, the jet deflects in the positive direction, regardless of d/D. With increasing h/D or decreasing d/D, both deflection and Coanda angles monotonically increase. An intermittent switch of the jet from one side of the cylinder to the other is observed for certain curvature of the cylinder, ascribed to the competition between bouncing and Coanda effects.

Keywords

• coanda effect
• jet
• cylinder
• bouncing effect
• curvature