A novel method of flow injection and suction for lift enhancement

Abstract

This paper describes a novel method of injection and suction conducted on an airfoil in a manner analogous to Co-Flow Jet (CFJ) control. The objectives of this study are two-fold. First, in relation to the CFJ technique, to assess the effectiveness of a modified design in which the injection and suction slots conform to the surface of the original airfoil geometry. This is done with the aim of maintaining the baseline performance of the airfoil in the absence of any external fluid transfer. The second involves a comparison of two different fluid injection locations. The conformal surface of the modified airfoil is found to maintain its baseline performance and thus eliminates the need for continuous operation of the injection and suction processes required of the CFJ technique. The experimental results for counter-streamwise injection are less favorable than anticipated. Although the momentum coefficient observes a direct relationship with the indicative lift, the lowest value tested leads to a poorer performance than the baseline. Any lift augmentation seems to be largely confined to the immediate vicinity of the injection location and does not translate into an overall increase in suction. Streamwise injection however, produces notable increases in the pressure integral for relatively small momentum coefficients at all angles of attack. Flow separation is also effectively suppressed at high incidence angles of up to 20°. Based on the current experimental results, streamwise injection is clearly a more effective alternative compared to counter-streamwise injection. Copyright © 2008 by the authors.