An experimental study of the separated flow field about slender delta wings of triangular cross section

Abstract

The separated flow about slender delta wings of shallow triangular cross section is investigated. The Brown and Michael theory is extended for this cross section and the solution is indicated. The limitations of this theory are pointed out. Computation becomes very complex and other methods such as electrostatic analog procedures appear preferable. Wind-tunnel tests were carried out on four delta wings with apex angle of 30? and triangular spanwise cross sections with flat base surfaces and included angles at the leading edges of 0, 10, 20, 30?, respectively. These tests were done in the 10-ft. GALCIT low-speed wind tunnel. Pressure measurements were taken at speeds up to 160 ft./sec. and Reynolds numbers up to 4 x 10 [superscript 6] based on the maximum chord of 4 ft. Experimental spanwise pressure distributions are compared to theoretical results for a delta wing of zero thickness (due to Brown and Michael). Experimental results show secondary vortices near the leading edges. These are not taken into account in the theory and so the theoretical and experimental pressure distributions differ markedly. However, the experimental spanwise local lift coefficient, which is obtained by integrating the spanwise pressure distribution, does agree very well with theoretical results. A simple geometrical definition for a corrected angle of attack makes it possible to plot local lift coefficients for the four wings on one curve. It is shown that the drag of the wings with triangular cross section including base drag is higher than that for wings of zero thickness. The results are applied to a brief analysis of the possibility of reducing lift-dependent drag of slender delta wings. It is shown that this drag reduction can be substantial (more than 10% ) for certain special cross sectional shapes.