Horseshoe vortex formation around a cylinder

A turbulent boundary layer approaching a local obstruction, such as when annulus wall boundary layers encounter airfoils and support struts, creates a critical problem in gas turbine engines. The slower portion of the approaching boundary layer cannot negotiate the adverse pressure gradient generated by the obstruction and consequently separates from the endwall. The resulting flow field includes a horseshoe vortex that is swept downstream around the body. The separation affects both the local heat transfer coefficients and aerodynamic losses in the endwall region. This investigation evaluated the detailed flow processes that lead to the symmetric horseshoe vortex formation around a large-diameter cylinder. Test conditions included a freestream velocity of 30.5 m/sec, a Reynolds number based on cylinder diameter of 5.5 x 10 to the 5th power, and a boundary-layer thickness equal to 13 percent of the cylinder diameter. The final report presents endwall and cylinder surface flow visualizations, endwall and cylinder static pressure distributions, and five-hole probe measurements in the separation region.