Experimental Studies of Airfoil Cascades with High Velocity Vector Circulation around the Airfoil

Abstract—

The results from experimental studies of flat turbine airfoil cascades carried out at a steam setup are presented. Cascades having the same airfoil featuring an increased velocity vector circulation rate around the airfoil and also ones with modified initial airfoil versions were considered. The steam flow inlet and outlet angles for the airfoil cascades are approximately 50°/14°; the blade length is 100 mm, and the airfoil chord is 40.64 mm. The cascade blowing experiments were carried out at Re > 4 × 10⁵. The cascades of S-13GM airfoils were studied in a wide airfoil relative pitch variation range of 0.55‒0.98 and Mach number variation range M ≈ 0.5‒1.1. The initial blade airfoil had a configuration close to the well-known S-5515A airfoil developed at the Moscow Power Engineering Institute (MPEI). The optimal values of the airfoil relative pitch in the cascade versus the Mach number have been determined. It has been found that there are two energy loss minimums depending on the relative pitch of such airfoils in the cascade. Some technical solutions are suggested for reducing the total energy losses in the cascade of airfoils through adjusting the steam flow by design measures. The effect of incidence angles on the energy losses in the cascade of airfoils with and without a vortex chamber on the airfoil is studied. The effect the change in some geometrical and flowrate parameters in airfoil cascades has on the steam energy losses during the flow in the interblade channel is shown. A profiled slot at blade tips and also a two-row cascade increase the energy losses. A vortex chamber made on the airfoil convex part decreases the total energy losses in the cascade by approximately 0.5‒1.0% with М = 0.8‒0.9 and by 3% with М = 1.0; the decrease of total energy losses in the cascade with short blades may reach approximately 4%. Based on the geometrical similarity to the dolphin body outlines and profile smoothing methods, turbine blade airfoils have been fabricated and tested, which have shown high gas dynamic properties. The cascades assembled of airfoils of such type such show efficient performance, especially in operating on wet steam.