An investigation of Venturi and coanda effects in blown film cooling

Numerical simulation of turbulent air flow tangentially impinging on a blow n film bubble has been carried out. The cooling air is assumed to originate from a dual orifice adjustable air-ring. The stream line pattern and heat flux are determined through a finite volume numerical technique using a ver sion of the so called k-epsilon modeling. It is shown that as the air flows through the air ring passage relatively large under-pressure is created (V enturi effect), which applies a suction to the bubble. Depending on the flo w rates and geometrical configurations the air jet may attach itself (Coand a effect) to either the air ring surface and/or to the bubble. The Coanda e ffect has a significant influence on local heat flux. The numerical results suggest that the Venturi and Coanda effects influence significantly proces s stability, production rate and final film properties.