The Performance of Aerofoil Cascades Using Circulation Control

Abstract

The performance of a cascade of two-dimensional, bluff aerofoils employing circulation control by a tangential blowing jet is investigated. Expressions for the lift and drag of such a cascade are derived to eliminate the direct effect of the blowing jet on the measured performance. The cascade characteristics for three cascade geometries over a range of incidences are presented as graphs of lift and drag coefficients and stream deflection plotted as functions of jet blowing momentum coefficient. All cascade tests were performed at a Mach number of 0.3. The cascade performance is found to be influenced strongly by vortex shedding at low jet blowing rates. A complete numerical solution procedure for calculating the performance of circulation controlled aerofoils, either isolated or in cascade, is presented. The procedure involves the calculation of a blade surface pressure distribution using a potential flow model with a representation of the separated region by the use of a source distribution. Aerofoil surface boundary layer developments are calculated by a finite-difference solution of the parabolic boundary layer momentum equation. The blowing jet development is calculated by the same finite-difference procedure applied to an angular momentum equation, using an intermittency representation of the eddy viscosity distribution. Results of the solution procedure are compared with experimental results obtained by other workers for an isolated aerofoil and for a cascade. The agreement is satisfactory and encouraging. The solution procedure is applied to two of the cascade configurations tested in the present investigation. The agreement between theory and experiment is excellent in one case, while the poorer agreement in the second comparison is attributed to the experimentally observed changes in wake flow characteristics with cascade geometry.