Science & Military 1/2010 26 APPLICATIONS AND COMPUTATIONAL ASPECTS REGARDING THE COANDĂ EFFECT Mircea BOŞCOIANU, Vasile PRISECARIU, Ionică CÎRCIU Abstract: Coanda effect is the phenomena in which a jet flow attaches itself to a nearby surface and remains attached even when the surface curves away from the initial jet direction.In free surroundings, a jet of fluid entrains and mixes with its surroundings as it flows away from a nozzle. When a surface is brought close to the jet, this restricts the entrainment in that region. As flow accelerates to try balance the momentum transfer, a pressure difference across the jet results and the jet is deflected closer to the surface - eventually attaching to it. Key words: Slot, attached jet, static pressure, centrifugation zone, suction zone. 1 INTRODUCTION IN PHYSICAL ASPECTS REGARDING THE COANDA EFFECT The Coandă effect is a natural phenomenon with action on the flow attached to a divergent wall (volet or airfoil) characterized by a high assimmetry. It is posible to remark the following aspects (Figure 1): 1. The depressured zone determines: a) flow acceleration upstream in the slot, without increasing upstream pressure or temperature, b) the displacement of the local fluid. 2. Detaching and re-attaching is caracterized by histerezis (the reattaching is produced at smaller angles than the detaching). 3. The global flow that results from the mixing between the main flow and the displaced one is situated in the depressure zone and is characterized by lower temperature. Figure 1 Coandă flow (2D) 2 A GLOBAL ANALYSIS OF THE MIXING PROCESS IN COANDĂ EJECTION EVICE Let consider an ejection device that we are going to analyse from the point of view of the mixture between the primary flow , the active one, through which energy is introduced into the system, and the secondary flow. a) b) Figure 2 Coanda ejector with: a) non uniform speed distribution, b) uniform speed distribution In the inlet (Section 0-0), the primary flow is introduced by compression, acceleration or through absorbtion directly from the environment. The absorbtion section (h-h) through which the resulting inflow moves only and is characterized by the fact that the total enthalpy i* of the flow is the same with that of the environment i H *. The place around A is supposed to be the spot where the depressurization flow is maximal. Section B-B shows the end of the Coanda profile (line OAB). Section C-C is where the absorption section ends and the thickness of the