INTERACTIVE AIRFOIL CALCULATIONS WITH HIGHER-ORDER VISCOUS-FLOW EQUATIONS

A critical examination of the use of higher-order viscous-now equations in the computation or airfoil flowfields with a viscid-inviscid interaction scheme is presented. Comparisons are made between experimental data and interactive solutions obtained using the boundary-layer equations, the second-order boundary-layer equations, and the Navier-Stokes equations, with corresponding approximations (o the viscid-inviscid matching conditions, for flows about symmetric and aft-loaded airfoils. In all cases, the viscous solution is coupled with a potential-flow solution. The results are restricted to attached, incompressible flow. An important feature of the comparisons is that the numerical algorithm, computational grid, and turbulence model are the same for all of the computations. Consequently, the effects of the higher-order terms can be studied separately from the influence or these factors. Detailed comparisons of computed and experimental results show that normal pressure gradients can be significant in the shear layers near the airfoil trailing edge and that the boundary-layer equations underestimate the boundary-layer growth in this region. The higher-order terms in the viscous-flow equations do not affect the lift and moment predictions but lead to significantly higher predictions of drag.